HomeMy WebLinkAboutPD 2023-0034; 7500 CADENCIA ST; REPORT GEOTECHNICAL INVESTIGATION GUINN RESIDENCE; 2018-06-05
GEOTECHNICAL
MATERIALS
SPECIAL INSPECTION DVBE SBE SDVOSB SLBE
4373 Viewridge Avenue, Suite B San Diego, CA 92123 P: 858.292.7575
usa-nova.com 16610 Aston Street Irvine, CA 92606 P: 949.388.7710
Mr. Rick Guinn September 30, 2024
7500 Cadencia Street NOVA Project No. 2022270
Carlsbad, CA 92009
Subject: Responses to City of Carlsbad Geotechnical Report
Review Comments (1st Review)
Guinn Residence Additions
7500 Cadencia Street, Carlsbad, California
References: City of Carlsbad (2024), Geotechnical Report Review, 7500 Cadencia Street (1st
Review), Project ID PD2023-0034, Grading Permit No. GR2023-0041, December 9.
NOVA Services, Inc. (NOVA) (2018), Preliminary Geotechnical Investigation, Guinn
Residence Additions, 7500 Cadencia Street, Carlsbad, Carlsbad, California, NOVA
Project No. 2018049, June 5.
Vanryn (undated), Grading Plans for 7500 Cadencia St, Carlsbad, CA, 92009, Project No. PD2023-0034, Drawing No. 545-9A, undated.
Dear Mr. Guinn:
NOVA Services, Inc. (NOVA) prepared this letter to respond to the referenced geotechnical report
review comments from the City of Carlsbad (2024) for the addition at 7500 Cadencia Street in Carlsbad
California. NOVA is retained by Mr. Rick Guinn as the geotechnical consultant of record for the project.
The review comments and our responses are provided below.
Comment 1: Please review the most current grading and foundation plans for the proposed project
and provide any additional geotechnical recommendations or modifications to the geotechnical report,
as necessary. As the submitted geotechnical report was prepared approximately 5-½ years ago and
references the 2016 California Building Code, please revisit and update sections of the geotechnical
report as necessary to address the currently adopted 2022 California Building Code and ASCE 7-16.
Response: NOVA reviewed the current grading plans (Vanryn, undated). NOVA’s review was limited
to the geotechnical aspects of the plans. Based on our review, it is NOVA’s opinion that the plans have
been prepared in accordance with the recommendations contained in the project’s geotechnical
reports (NOVA, 2018).
As requested, NOVA updated the site coefficients and maximum considered earthquake (MCER)
spectral response acceleration parameters in accordance with the 2022 California Building Code
(CBC) and ASCE 7-16 as presented in Table 1.
DRAFT Responses to City of Carlsbad Geotechnical Report Review Comments (1st Review) Guinn Residence Addition, 7500 Cadencia Street, Carlsbad, CA NOVA Project No. 2022270
September 30, 2024
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Table 1. 2022 CBC and ASCE 7-16 Seismic Design Parameters
Site Coordinates
Latitude: 32.08771° Longitude: -117.23807°
Site Coefficients and Spectral Response Acceleration Parameters Value
Site Class C
Site Amplification Factor at 0.2 Second, Fa 1.2
Site Amplification Factor at 1.0 Second, Fv 1.5
Spectral Response Acceleration at Short Period, SS 0.955g
Spectral Response Acceleration at 1-Second Period, S1 0.349g
Design Spectral Acceleration at Short Period, SDS 0.764g
Design Spectral Acceleration at 1-Second Period, SD1 0.349g
Peak Ground Acceleration, PGAM 0.5g
Comment 2: Please provide a statement addressing the potential impact of the proposed project on adjacent off-site properties from a geotechnical standpoint.
Response: In NOVA’s professional opinion, the proposed project will not have an impact on adjacent
off-site properties from a geotechnical standpoint, provided the recommendations in our geotechnical
report are followed.
Comment 3: Please provide a Geotechnical Map utilizing the most current revision of the grading plan
for the project as the base map and at a sufficiently large scale to clearly show (at a minimum) a) existing site topography and structures/improvements, b) proposed structures and improvements, c)
proposed finished grades, d) geologic units and structure, and e) the locations of subsurface exploration. Please note that the “Subsurface Investigation Map” included in the submitted report
consists essentially of an architectural site plan that only shows the residence and driveway (no
topography, proposed structure/improvements, etc.).
Response: The requested geotechnical map is attached to this response letter at Plate 1.
Comment 4: No geologic cross-sections are provided in the report. Please provide detailed geologic
cross-sections (at least one trending east-west through the proposed garage/ADU at the location of
the highest cut and one through the area of the proposed building addition and site retaining wall) based on the Geotechnical Map requested above in comment #3. Please ensure the requested cross-
sections show and label, at a minimum, a) existing site topography and structure/improvements, b) proposed finish grades, c) the limits of the d) the contacts between the various soil/geologic units and
geologic structure units and geologic structure underlying the site, e) temporary slopes necessary for
the remedial grading and/or for retaining wall construction, f) slope setback requirements, and g) the
locations of subsurface exploration.
Response: The requested cross-sections are attached to this response letter at Plate 2.
Comment 5: As the subsurface exploration only extended to a maximum depth of 3’ below existing
grade, please discuss how the geotechnical conditions and engineering properties of the bedrock were
DRAFT Responses to City of Carlsbad Geotechnical Report Review Comments (1st Review) Guinn Residence Addition, 7500 Cadencia Street, Carlsbad, CA NOVA Project No. 2022270
September 30, 2024
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determined with respect to the proposed project and relatively deep cuts necessary to establish
proposed site grades.
Response: Based on NOVA’s geotechnical investigation (NOVA, 2018) competent
metasedimentary/metavolcanic rock (Mzu) was encountered in the test pits and borings at the surface.
NOVA anticipates that massive metasedimentary/metavolcanic rock (Mzu) will be exposed at the
bottom of the excavations. Revised plans depict maximum cuts no greater than 6 feet.
Comment 6: Please provide a discussion addressing the geologic structure (direction/dip of any relic
bedding and/or fracturing) of the metasedimentary/metavolcanic rock and the relationship between the structural geology of the bedrock underlying the site as it relates to the stability of the site and proposed
up to approximate 12’ high cuts that will apparently be required to construct the building retaining walls
associated with the proposed garage/ADU structure and other proposed site retaining walls. Please provide the basis for the geologic structure reported for the site.
Response: NOVA’s geotechnical investigation (NOVA, 2018) exposed competent, massive
metasedimentary/metavolcanic rock (Mzu) at the surface. NOVA anticipates that massive
metasedimentary/metavolcanic rock (Mzu) will be exposed at the bottom of the excavations. Revised
plans depict maximum cuts no greater than 6 feet.
Comment 7: Strength (direct shear) testing of the on-site soils is not provided in the reviewed report. Please provide the appropriate laboratory testing to substantiate the values for bearing capacity,
passive earth pressure, coefficient of friction, and active/at-rest earth pressures that are presented in the report. If presumptive values from the code are being recommended by the consultant, please
indicate the soil class and use values consistent with the appropriate soil type (Class) in Tables 1806.2
and 1610.1 of the 2022 California Building Code. If soil parameters other than soil class 5 in Tables 1806.2 and 1610.1 are provided, please provide justification and explain the basis for the specified soil
class.
Response: Presumptive load-bearing values are used from Table 1806.2 based on soil class 2,
sedimentary and foliated rock. For footings supported on Mzu, an allowable bearing capacity of 4,000
psf can be used. Lateral loads will be resisted by friction between the bottoms of footings and passive
pressure on the faces of footings and other structural elements below grade. An allowable coefficient
of friction of 0.35 can be used. An allowable passive pressure of 400 psf per foot of depth below the
ground surface can be used for level ground conditions. The allowable passive pressure should be
reduced for sloping ground conditions. The passive pressure can be increased by ⅓ when considering
the total of all loads, including wind or seismic forces. The upper 1 foot of soil should not be relied on
for passive support unless the ground is covered with pavements or slabs.
Comment 8: Expansion Index testing presented in the report indicates an EI of 71 (Medium), and the
test of the report (pages 22 and 27) locally indicates soils used as fill should have an Expansion Index below 50 (“Low”). As soil with Expansion Index (EI) over 20 are considered expansive and require
mitigation in accordance with Section 1803.5.3 and 1808.6 of the 2022 CBC, please provide recommendations to satisfy the 2022 California Building Code. Please indicate the method of Section
1808.6 that is being recommended to satisfy the requirement for expansive soils, and provide the
Effective Plasticity Index and any other parameters for slab-on-ground design in accordance with
1808.6.2 and WRI/CRSI Design of Slab-on-Ground floors or a post-tensioned design in accordance
DRAFT Responses to City of Carlsbad Geotechnical Report Review Comments (1st Review) Guinn Residence Addition, 7500 Cadencia Street, Carlsbad, CA NOVA Project No. 2022270
September 30, 2024
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with PTI DC 10.5 and provide a statement that the foundation/slab system for the proposed residential
structures will meet the requirements of Section 1808.5 of the 2022 California Building Code.
Response: NOVA recommends the backfill behind the walls possess an expansion index EI of 20 or
less. It is expected import of Select Fill will be required for backfill behind the retaining walls. The
foundation recommendations will meet the requirements of Section 1808.6 of the 2022 California
Building Code (CBC).
Comment 9: Based on the location of the proposed garage/ADU structure, please provide justification
for the encroachment into the hillside as necessary to address Section 1808.7.1 of the 2022 California
Building Code.
Response: The planned garage was eliminated from the current updated plans. Revised plans depict
maximum cuts no greater than 6 feet. Based on NOVA’s geotechnical investigation (NOVA, 2018)
planned excavations into the hillside will expose competent, massive metasedimentary/metavolcanic
rock (Mzu).
Comment 10: Please confirm (see page 26 of the report) that the retaining wall recommendations and
parameters provided in the report are suitable for use for design of the up to the proposed approximate
12’ high retaining walls associated with the proposed garage/ADU structure; and provided additional
recommendations if necessary (see comment #7 above).
Response: Based on NOVA’s review of the current plans, the proposed garage/ADU structure was
eliminated and is no longer proposed. In addition, NOVA recommendations for retaining walls that are
6 feet or less are considered suitable. NOVA anticipates that massive metasedimentary/metavolcanic
rock (Mzu) will be exposed at backcut of these retaining wall.
Comment 11: Please provide a discussion addressing seismically induced landsliding with respect to
the proposed project.
Response: See Section 5.2.3 of NOVA, 2018.
Comment 12: Please provide updated seismic design parameters in accordance with the 2022
California Building Code and ASCE 7-16.
Response: See response to Comment #1.
Comment 13: Site Class B (“Rock”) per Table 20.3-1 of Chapter 20 of ASCE 7-16 is not a typical
classification for bedrock units in the coastal plain region of northern San Diego County. Please justify
the use of Site Class B (in accordance with Section 1613 of the 2020 California Building Code and
Chapter 20 of ASCE 7-16) for the determination of the seismic design parameters provided in the
report. Please provide the shear wave velocity and/or data from site-specific investigation/testing that
supports Site Class B.
Response: NOVA determined that the site is classified as Site Class C.
Comment 14: Please provide recommendations for temporary cuts (maximum allowed height of
vertical cut, inclination of cut, etc.) necessary to construct the proposed up to approximate 12’ high
DRAFT Responses to City of Carlsbad Geotechnical Report Review Comments (1st Review) Guinn Residence Addition, 7500 Cadencia Street, Carlsbad, CA NOVA Project No. 2022270
September 30, 2024
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cuts that will apparently be required to construct the building retaining walls associated with the
proposed garage/ADU structure and other site retaining walls. Please provide specific
recommendations for the temporary cuts to prevent any adverse impact of the construction on adjacent
off-site property and promote worker safety.
Response: NOVA anticipates planned excavations into the hillside will expose competent, massive
metasedimentary/metavolcanic rock (Mzu).
Temporary excavations 4 feet deep or less can be made vertically. Deeper temporary excavations
should be laid back no steeper than 1:1 (horizontal:vertical) (h:v). The faces of temporary slopes should
be inspected daily by the contractor’s Competent Person before personnel are allowed to enter the
excavation.
Comment 15: Please provide the minimum reinforcement requirements for new foundations from a
geotechnical standpoint.
Response: Minimum one No. 4 bar at top and bottom is recommended. However, the project structural
engineer should design the actual reinforcement of foundations.
Comment 16: Please evaluate and discuss the potential for storm water infiltration at the subject site
as part of the proposed development.
Response: Proposed stormwater infiltration BMPs have been eliminated from the site design.
Comment 17: Please provide geotechnical recommendations for the proposed keystone retaining wall and biofiltration area proposed locally within the sloping ground along the northwest side of the existing
driveway.
Response: The keystone retaining wall and biofiltration basin have been eliminated from the plans.
Comment 18: Please provide a complete summary list of the geotechnical observation/testing services
that should be performed as part of the construction of this proposed development.
Response: The geotechnical observation and testing services during the construction of the proposed
development should conform to the local jurisdictional agency and Chapter 17 of the 2022 CBC. We
recommend that the following geotechnical observation and testing services be performed during site
grading and earthwork construction:
• Attend the grading pre-construction meeting.
• Observe ground preparation prior to fill placement.
• Observe and map the geologic conditions exposed during grading.
• Observe placement and compaction of fill, backfill, and perform field density testing.
• Perform laboratory tests on fill and backfill.
• Observe foundation excavations to evaluate conformance with the project plans and
geotechnical recommendations.
• Observe temporary cuts and retaining wall subdrains.
DRAFT Responses to City of Carlsbad Geotechnical Report Review Comments (1st Review) Guinn Residence Addition, 7500 Cadencia Street, Carlsbad, CA NOVA Project No. 2022270
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• Prepare daily field reports summarizing the day's activity with regard to earthwork.
• Prepare supplemental reports and letters as needed and a final report upon completion of the
earthwork summarizing the results of our geotechnical observation and testing and our
conclusions regarding conformance with the project plans and specifications.
Closure
NOVA appreciates the opportunity to be of continued service. If you have any questions regarding this
letter, please call us at 858.292.7575 x 409.
Sincerely,
NOVA Services, Inc.
_______________________ _______________________ Wail Mokhtar John F. O’Brien, PE, GE Regional Manager Principal Geotechnical Engineer
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www.usa-nova.com 944 Calle Amanecer, Suite F San Clemente, CA 92673 P: 949.388.7710
Mr. Rick Guinn December 20, 2022
7500 Cadencia Street NOVA Project No. 2018049
Carlsbad, CA 92009
Subject: Update Letter
Guinn Residence Additions
7500 Cadencia Street, Carlsbad, California
References:
SE 2022. Guinn ADU, 7500 Cadencia St., Carlsbad, California, Solidforms Engineering, Job
#22-381, dated December 08, 2022.
NOVA 2018. Report, Preliminary Geotechnical Investigation, Guinn Residence Additions, 7500
Cadencia Street, Carlsbad, California, NOVA Services, Inc., Project No. 2018049, June 05,
2018.
Dear Mr. Guinn:
NOVA Services, Inc. (NOVA) has reviewed the Guinn ADU plans (SE 2022). The review was limited to the geotechnical aspects of the plans, reviewing for conformance with the referenced geotechnical reporting by NOVA. Based on this review, the recommendations provided in NOVA 2018 geotechnical report remain applicable to the proposed Guinn ADU project.
Additionally, NOVA is providing updated seismic design parameters in accordance with the 2019 California Building Code (CBC). These recommendations are provided by NOVA Services, Inc. (NOVA) for Guinn ADU project. NOVA is retained by Mr. Guinn as the geotechnical engineer-of record for this project. The updated seismic parameters are presented below. Table 1. 2019 CBC and ASCE 7-16 Seismic Design Parameters
Site Coordinates
Latitude: 33.0875 ° Longitude: - 117.23849 °
Site Coefficients and Spectral Response Acceleration Parameters Value
Site Class B
Site Coefficients, Fa 1.00
Site Coefficients, Fv 1.00
Mapped Spectral Response Acceleration at Short Period, Ss 0.956g
Mapped Spectral Response Acceleration at 1-Second Period, S1 0.349g
Mapped Design Spectral Acceleration at Short Period, SDS 0.683g
Design Spectral Acceleration at 1-Second Period, SD1 0.233g
Site Peak Ground Acceleration, PGAM 0.417g
Source: OSHPD/SEAOC www.Seismicmaps.org
Updated Letter Guinn Residence Additions, Carlsbad, CA NOVA Project No. 2018049 December 20, 2022
2
Closure
NOVA appreciates the opportunity to be of continued service to Guinn Residence. Should you
have any questions regarding this submittal or other matters, please do not hesitate to contact us
at 858.292.7575.
Sincerely, NOVA Services, Inc.
____________________________ ___________________________
Wail Mokhtar John F. O’Brien, PE, GE Regional Manager Principal Geotechnical Engineer
Report
Geotechnical Investigation
Guinn Residence Additions 1714 West Arbor Drive, San Diego, California
PREPARED FOR Mr. Rick Guinn
7500 Cadencia Street Carlsbad, Ca 92009
PREPARED BY
NOVA Services, Inc.
4373 Viewridge Ave, Ste. B San Diego, California 92123
NOVA Project No. 2018049
June 05, 2018
G E O T E C H N I C A L ■ M A T E R I A L S ■ S P E C I A L I N S P E C T I O N S
S B E ■ S L B E ■ S C O O P
4373 Viewridge Avenue, Ste. B San Diego, CA 92123
858.292.7575 Mr. Rick Guinn June 05, 2018
7500 Cadencia Street NOVA Project 2018049 Carlsbad, CA 92009 Subject: Report Preliminary Geotechnical Investigation Guinn Residence Additions
7500 Cadencia Street, Carlsbad, California
Dear Mr. Guinn:
NOVA Services, Inc. (NOVA) is pleased to present this report of its preliminary geotechnical investigation for the above-referenced single-family residence additions.
NOVA appreciates the opportunity to be of service on this most interesting project. Should you have any questions regarding this report or other matters, please do not hesitate to contact the undersigned at (858) 292-7570.
Sincerely, NOVA Services, Inc.
________________________ __________________________ Wail Mokhtar Bryan Miller-Hicks, C.E.G. 1323
Project Manager Senior Geologist
_________________________ John F. O’Brien, P.E., G.E. Principal Engineer
Report of Preliminary Geotechnical Investigation June 05, 2018 Guinn Residence Additions, 7500 Cadencia Street, Carlsbad NOVA Project 2018049
Report Preliminary Geotechnical Investigation Guinn Residence Additions 7500 Cadencia Street, Carlsbad, California ______________________________________________________________
Table of Contents
1.0 INTRODUCTION.............................................................................................................. 1
1.1 Terms of Reference ......................................................................................................................... 1
1.2 Objective, Scope, and Limitations of This Work ......................................................................... 1
1.2.1 Objective ...................................................................................................................................................... 1 1.2.2 Scope ............................................................................................................................................................ 2 1.2.3 Limitations ................................................................................................................................................... 2
1.3 Understood Use of This Report...................................................................................................... 3
1.4 Report Organization ....................................................................................................................... 3
2.0 PROJECT INFORMATION ............................................................................................ 4
2.1 Site Description ............................................................................................................................... 4
2.1.1 Location ....................................................................................................................................................... 4 2.1.2 Current Condition ........................................................................................................................................ 4
2.2 Planned Additions ........................................................................................................................... 5 2.2.1 General ......................................................................................................................................................... 5 2.2.2 Structural ...................................................................................................................................................... 5 2.2.1 Potential for Earthwork ................................................................................................................................ 6
3.0 FIELD EXPLORATION AND LABORATORY TESTING ........................................ 7
3.1 Overview .......................................................................................................................................... 7
3.2 Engineering Borings and Test Pits ................................................................................................ 8 3.2.1 General ......................................................................................................................................................... 8
3.2.2 Logging and Sampling ................................................................................................................................. 8 3.2.3 Closure ......................................................................................................................................................... 8
3.3 Laboratory Testing ......................................................................................................................... 8 3.3.1 General ......................................................................................................................................................... 8 3.3.2 Gradation ...................................................................................................................................................... 9 3.3.3 Moisture Density .......................................................................................................................................... 9
3.3.4 Expansion Potential ...................................................................................................................................... 9
Report of Preliminary Geotechnical Investigation June 06, 2018 Guinn Residence Additions, 7500 Cadencia Street, Carlsbad NOVA Project 2018049 ________________________________________________________________________________________________________
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3.3.5 Corrosivity ................................................................................................................................................... 9
4.0 SITE CONDITIONS ........................................................................................................ 10
4.1 Geologic and Seismic Setting ....................................................................................................... 10 4.1.1 Regional ..................................................................................................................................................... 10 4.1.2 Site Specific .............................................................................................................................................. 10
4.2 Site-Specific Conditions ................................................................................................................ 11
4.2.1 Surface ....................................................................................................................................................... 11 4.2.2 Subsurface .................................................................................................................................................. 11 4.2.3 Groundwater............................................................................................................................................... 12 4.2.4 Surface Water ............................................................................................................................................. 12
5.0 REVIEW OF GEOLOGIC AND SOIL HAZARDS .................................................... 13
5.1 Overview ........................................................................................................................................ 13
5.2 Geologic Hazards .......................................................................................................................... 13 5.2.1 Strong Ground Motion ............................................................................................................................... 13 5.2.2 Fault Rupture.............................................................................................................................................. 13 5.2.3 Landslide .................................................................................................................................................... 14
5.3 Soil Hazards ................................................................................................................................... 15 5.3.1 Embankment Stability ................................................................................................................................ 15
5.3.2 Seismic ....................................................................................................................................................... 15 5.3.3 Expansive Soils .......................................................................................................................................... 16
5.3.4 Expansion Potential .................................................................................................................................... 16 5.3.5 Hydro-Collapsible Soils ............................................................................................................................. 16
5.3.6 Corrosive Soils ........................................................................................................................................... 16
5.4 Other Hazards ............................................................................................................................... 17
5.4.1 Flood .......................................................................................................................................................... 17 5.4.2 Tsunami ...................................................................................................................................................... 17 5.4.3 Seiche ......................................................................................................................................................... 17
6.0 EARTHWORK AND FOUNDATIONS ........................................................................ 18
6.1 Overview ........................................................................................................................................ 18
6.1.1 Soil and Geologic Hazards ......................................................................................................................... 18 6.1.2 Foundations ................................................................................................................................................ 18 6.1.3 Review and Surveillance ............................................................................................................................ 18
6.2 Seismic Design Parameters .......................................................................................................... 18
6.2.1 Site Class .................................................................................................................................................... 18 6.2.2 Seismic Design Parameters ........................................................................................................................ 18
6.3 Corrosivity and Sulfates ............................................................................................................... 19
Report of Preliminary Geotechnical Investigation June 06, 2018 Guinn Residence Additions, 7500 Cadencia Street, Carlsbad NOVA Project 2018049 ________________________________________________________________________________________________________
iii
6.3.1 General ....................................................................................................................................................... 19 6.3.2 Metals ......................................................................................................................................................... 19 6.3.3 Sulfates and Concrete ................................................................................................................................. 20 6.3.4 Limitations ................................................................................................................................................. 21
6.4 Site Preparation and Earthwork ................................................................................................. 21
6.4.1 General ....................................................................................................................................................... 21 6.4.2 Clearing and Grubbing ............................................................................................................................... 21 6.4.3 Excavation Characteristics ......................................................................................................................... 22 6.4.4 Select Fill ................................................................................................................................................... 22 6.4.5 Remedial Grading ...................................................................................................................................... 22 6.4.6 Maintenance of Moisture in Soils During Construction ............................................................................. 22 6.4.7 Trenching and Backfilling for Utilities ...................................................................................................... 22 6.4.8 Flatwork ..................................................................................................................................................... 23
6.5 Shallow Foundations ..................................................................................................................... 23
6.5.1 General ....................................................................................................................................................... 23 6.5.2 Conventionally Reinforced Concrete Slab ................................................................................................. 23
6.5.3 Conventional Foundations ......................................................................................................................... 23 6.5.4 Moisture Barrier ......................................................................................................................................... 24
6.6 Control of Drainage and Moisture Around Structures ............................................................. 25 6.6.1 General ....................................................................................................................................................... 25 6.6.2 Landscaping ............................................................................................................................................... 25 6.6.3 Drainage ..................................................................................................................................................... 25 6.6.4 Surface Grades ........................................................................................................................................... 26 6.6.5 Backfills ..................................................................................................................................................... 26
6.7 Retaining Walls ............................................................................................................................. 26 6.7.1 General ....................................................................................................................................................... 26 6.7.2 Shallow Foundations .................................................................................................................................. 26 6.7.3 Lateral Earth Pressures ............................................................................................................................... 26 6.7.4 Foundation Uplift ....................................................................................................................................... 26 6.7.5 Resistance to Lateral Loads........................................................................................................................ 27 6.7.6 Wall Drainage ............................................................................................................................................ 27 6.7.7 Seismic ....................................................................................................................................................... 28
6.8 Temporary Shoring ...................................................................................................................... 28
7.0 REFERENCES ................................................................................................................. 29
7.1 Site Specific .................................................................................................................................... 29
7.2 Design ............................................................................................................................................. 29
7.3 Geologic and Site Setting .............................................................................................................. 29
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List of Plates
Plate 1. Subsurface Investigation Map
List of Appendices Appendix A Use of this Report
Appendix B Soil Exploration Logs
Appendix C Laboratory Analytical Results
List of Tables
Table 3-1. Abstract of the Engineering Borings
Table 3-2. Qualitative Descriptors of Expansion Potential Based on EI
Table 6-1. Seismic Design Parameters, ASCE 7-10
Table 6-2. Summary of Corrosivity Testing of the Near Surface Soil
Table 6-3. Soil Resistivity and Corrosion Potential
Table 6-4. Exposure Categories and Requirements for Water-Soluble Sulfates
Table 6-5. Lateral Earth Pressures
List of Figures Figure 1-1. Vicinity Map
Figure 2-1. Site Location and Limits
Figure 2-2. Proposed First Floor Plan
Figure 2-3. Foundation Plan for the Planned Addition to the Existing Residence
Figure 3-1. Location of the Borings and Test Pits
Figure 4-1. Geologic Mapping of the Site Vicinity
Figure 4-2. Surface Conditions in the Area of the Planned Additions
Figure 5-1. Faulting in the Site Vicinity
Figure 5-2. Flood Mapping of the Site Area
Figure 6-1. Conceptual Design for Wall Drainage
Report of Preliminary Geotechnical Investigation June 05, 2018 Guinn Residence Additions, 7500 Cadencia Street, Carlsbad NOVA Project 2018049
1.0 INTRODUCTION
1.1 Terms of Reference
The report presents the findings of a preliminary geotechnical investigation for additions to the single-family residence at 7500 Cadencia Street in Carlsbad, California (hereafter, also referenced as ‘the site’).
The work reported herein was completed by NOVA Services, Inc. (NOVA) for Mr. Rick Guinn (hereafter, ‘the Owner’). Figure 1-1 provides a graphic that depicts the site vicinity.
Figure 1-1. Vicinity Map
1.2 Objective, Scope, and Limitations of This Work
1.2.1 Objective
The objectives of the work reported herein are twofold, as described below.
1. Objective 1, Site Characterization. Characterize the subsurface conditions within the limits of the planned proposed additions.
2. Objective 2, Geotechnical. Provide recommendations for geotechnical-related development, including foundations and earthwork.
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1.2.2 Scope
In order to accomplish the above objectives, NOVA undertook the task-based scope of work described below.
• Task 1, Background Review. Reviewed readily available background data regarding the site area, including geotechnical reports, topographic maps, geologic data, fault maps, and preliminary concept plans for the project.
• Task 2, Subsurface Exploration. The exploration includes the following subtasks.
o Subtask 2-1, Reconnaissance. Prior to undertaking any invasive work, NOVA conducted a site reconnaissance, including layout of the exploratory borings used to explore the subsurface conditions. Underground Service Alert was notified for underground utility mark-out services.
o Subtask 2-2, Borings and Test Pits. Using hand excavation methods, completed two engineering borings and two test pits to depths of 1 to 3 feet below existing ground surface (bgs) in the area of the proposed additions.
• Task 3, Laboratory Testing. Laboratory testing addressed soil gradation, expansion potential, compressibility, strength, and corrosivity.
• Task 4, Engineering Evaluations. The findings of Tasks 1-3 were utilized to support geotechnical related evaluations.
• Task 5, Reporting. This report presents the findings of all work and completes NOVA’s scope of work.
1.2.3 Limitations
The recommendations included in this report are not final. These recommendations are developed by NOVA using judgment and opinion and based on the limited information available from the borings. NOVA can finalize its recommendations only by observing actual subsurface conditions revealed during construction. NOVA cannot assume responsibility or liability for the report's recommendations if NOVA does not perform construction observation.
This report does not address any environmental matters; including, but not limited to assessment or investigation for the presence or absence of hazardous or toxic materials in building materials, soil, groundwater, or surface water within or beyond the site.
Appendix A provides additional discussion regarding limitations and use of this report.
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1.3 Understood Use of This Report
NOVA expects that the findings and recommendations provided herein will be utilized in decision-making regarding design and construction of the planned addition to the residence.
NOVA’s recommendations are based on our current understanding and assumptions regarding project development. Effective use of this report should include review by NOVA of the final design. Such review is important for both (i) conformance with the recommendations provided herein, and (ii) consistency with NOVA’s understanding of the planned addition.
1.4 Report Organization
The remainder of this report is organized as abstracted below.
• Section 2 reviews available project information.
• Section 3 describes the field investigation and laboratory testing.
• Section 4 describes the surface and subsurface conditions.
• Section 5 reviews geologic and soil hazards that may affect the site.
• Section 6 provides recommendations for earthwork and foundation design.
• Section 7 lists the principal references utilized in the development of the report. The report is supported by three appendices. Appendix A provides guidance regarding the use and limitations of this report. Appendix B presents logs of NOVA engineering borings and test pits. Appendix C provides records of the geotechnical laboratory testing.
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2.0 PROJECT INFORMATION
2.1 Site Description
2.1.1 Location
The subject property is a developed residential lot located at 7500 Cadencia Street in Carlsbad, California. The lot is about 0.78 acre in size, occupied by a one- and two-story single-family residence. The APN is 223-260-0900. Figure 2-1 depicts the location and limits of the site.
Figure 2-1. Site Location and Limits
2.1.2 Current Condition
The site currently supports a one-and two-story single-family residence with an attached garage and a swimming pool with a spa. A concrete covered driveway provides access to the home via Cadencia Street.
Other residences surround the property to the north, east and south.
The existing residence was constructed in 1984 on a level graded cut-and-fill pad. The residential pad is at elevation 252 msl. An approximately 24-foot high fill slope was constructed on the west side of the pad, and slopes downwards to Cadencia Street. To the east of the pad, an approximately 18-foot high cut slope ascends to the neighboring property to the west. Based on NOVA’s review of the approved grading plans (approval date of October 29, 1984, by the City of Carlsbad), both cut and fill slopes have a 2:1 (H:V)
inclination.
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2.2 Planned Additions
2.2.1 General
Concept level architectural design for the planned additions is provided in Architectural Plans for Guinn Residence, 7500 Cadencia Street, Carlsbad, (Progress Set, John Alan Baker, Architect, 6 April 2018,
hereafter, ‘JAB 2018a’). JAB 2018a indicates that the additions will consist of adding a one-and two-story addition to the existing residence. The additions to the home will comprise about 1,000 square feet. Figure 2-2 shows the plan of the first floor of the house incorporating the new one-and two-story addition.
Figure 2-2. Proposed First Floor Plan
(source: JAB 2018a)
In addition, based on discussions with Mr. Guinn, NOVA understands that it is also proposed to excavate into the existing cut slope at the east of the property in order to construct both (i) a detached garage with an apartment above; and, (ii) a cantilevered retaining wall. The detached garage with the second-story apartment will be constructed to the northeast of the home. The retaining wall will be constructed to the east of the new addition.
2.2.2 Structural
NOVA was provided with the structural plan and related calculations for the one- and two-story addition (Structural Plans for Guinn Residence, 7500 Cadencia Street, Carlsbad, John Alan Baker, 1 April 2018, hereafter ‘JAB 2018b’).
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JAB 2018b indicates that the addition will be supported by spread footings designed for an allowable
contact stress of 1,500 psf. The footings will have a have a minimum width of 24 inches and be embedded a minimum of 24 inches below lowest adjacent grade. The ground level of the addition will employ a 5-inch thick conventional on-grade (ground-supported) slab. No structural information was
provided for the detached garage and site retaining wall. Figure 2-3 below provides a plan view of the foundation plan for the planned addition to the existing residence.
Figure 2-3. Foundation Plan for the Planned Addition to the Existing Residence (source: JAB 2018b)
2.2.1 Potential for Earthwork
Civil and grading plans are not yet developed. It is anticipated that grading for the one- and two-story addition will be minimal. Grading for the proposed detached garage and site retaining wall will require cuts into the slope of up to 8 feet to (i) establish a level pad to support the detached garage; and (ii) expanding the rear yard.
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3.0 FIELD EXPLORATION AND LABORATORY TESTING
3.1 Overview
NOVA’s field exploration was completed on May 8, 2018. That work included two hand-augered engineering borings and two hand-excavated test pits, referenced herein as ‘B-1’ and ‘B-2’, and ‘TP-1’ and ‘TP-2’.
Figure 3-1 presents a plan view of the site indicating the locations of the engineering borings and test pits. A plate that depicts the locations of the borings and test pits on a larger scale is provided immediately following the text.
Figure 3-1. Location of the Engineering Borings & Test Pits
KEY TO SYMBOLS
Mzu METASEDIMENTARY & METAVOLC1\NIC ROCKS
B-2
8 APPROXIMATE LOCATION OF GEOTECHNICAL BORING
TP-2 IXI APPROXIMATE LOCATION OF TEST PIT
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3.2 Engineering Borings and Test Pits
3.2.1 General
The engineering borings and test pits were completed under the direction of a geologist from NOVA who directed sampling and maintained a log of the subsurface materials that were encountered. The
engineering borings and test pits were advanced by hand auger equipment and hand tools.
Boring and test pit locations were determined in the field by the NOVA geologist. Elevations of the ground surface at the boring locations were estimated. Table 3-1 provides an abstract of the engineering
borings and test pits.
Table 3-1. Abstract of the Engineering Borings
Boring Reference
Approximate Ground Surface Elevation (feet, msl)
Total Depth Below Ground Surface (feet)
Depth to Groundwater (feet)
B-1 +252 1.0 not encountered
B-2 +252 3.0 not encountered
TP-1 +262 1.2 not encountered
TP-2 +254 1.0 not encountered
3.2.2 Logging and Sampling
The borings and test pits were completed under the direction of a geologist from NOVA who directed sampling and maintained a log of the subsurface materials that were encountered.
Bulk (disturbed) samples were recovered from the surface soils and underlying formational materials, providing composite samples for testing of soil characteristics.
Logs of the borings and test pits are provided in Appendix B. The group symbols for each soil type are indicated in parentheses following the soil descriptions on the logs. The stratification lines designating the interfaces between earth materials on the trench, boring logs and profiles are approximate; in-situ, the
transitions may be gradual.
3.2.3 Closure
Each boring and test pit was backfilled to the ground surface with cuttings upon completion. The area of
each boring was restored as closely as possible to its approximate condition before drilling.
3.3 Laboratory Testing
3.3.1 General
Soil samples were returned to the laboratory where a geotechnical engineer reviewed the field logs and classified each soil sample on the basis of texture and plasticity in accordance with the Unified Soil Classification System (‘USCS,’ ASTM D2487). Representative soil samples were selected and tested in
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NOVA’s materials laboratory to check visual classifications and to determine pertinent engineering
properties. The laboratory testing program included index testing on selected soil samples. Results of the testing are presented in Appendix C.
3.3.2 Gradation
The visual classifications were supplemented by soil gradation analyses after ASTM D 6913. The results of these analyses were used to support soil classification after ASTM D 2488.
A representative bulk sample of Unit 2 soil was found to be a sandy, with about 25% by weight clay-sized
particles, classified as SC after ASTM D2488.
3.3.3 Moisture-Density
A representative bulk sample of the Unit 2 soil that covers the area of the planned improvements was tested to determine its compaction characteristics. This testing indicates an optimum dry density of 112.0 pounds per cubic foot (pcf) at an optimum moisture content of 18.2%.
3.3.4 Expansion Potential
An Expansion Index (‘EI’, after ASTM D4829) test was performed to evaluate the potential for expansion of the Unit 2 weathered rock that overlies the project area. The expansion test was performed on a remolded sample of the Unit 2 weathered rock, indicating EI = 71.
EI has been adopted by the California Building Code (‘CBC’, Section 1803.5.3) for characterization of expansive soils. Table 3-2 summarizes the qualitative descriptors of expansion potential as included with ASTM D 4829 and the 2016 CBC, from which it can be seen that the upper, weathered portion of rock has ‘Medium’ expansion potential after ASTM D 4829.
Table 3-2. Qualitative Descriptors of Expansion Potential Based on EI
Expansion Index (‘EI’), ASTM D 4829 Expansion Potential, ASTM D 4829 Expansion Classification, 2016 CBC
0 to 20 Very Low Non-Expansive
21 to 50 Low
Expansive 51 to 90 Medium
91 to 130 High
>130 Very high
3.3.5 Corrosivity
Resistivity, sulfate content and chloride contents were determined to estimate the potential corrosivity of on-site soils. These chemical tests were performed on a representative sample of the near-surface soils by Clarkson Laboratory and Supply, Inc. The testing indicated low levels of soluble sulfates and chlorides in soils. Section 6 discusses the indications of this testing in more detail.
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4.0 SITE CONDITIONS
4.1 Geologic and Seismic Setting
4.1.1 Regional
The project area is located in the coastal portion of the Peninsular Range geomorphic province. This geomorphic province encompasses an area that extends approximately 900 miles from the Transverse Ranges and the Los Angeles Basin south to the southern tip of Baja California. The province varies in width from approximately 30 to 100 miles.
4.1.2 Site Specific
Geologic units encountered by the subsurface investigation include a veneer a few inches of topsoil below which occur metavolcanic and metasedimentary rock.
Figure 4-1 reproduces geologic mapping of the site area, from which it can be seen that metavolcanic and
metasedimentary rock (MzU) are mapped to occur widely in this portion of Carlsbad.
Figure 4-1. Geologic Mapping of the Site Vicinity
METASEDIMENTARY & OLD ALLUVIAL
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4.2 Site-Specific Conditions
4.2.1 Surface
The ground surface in the area of the planned one and two-story addition is relatively level at about elevation +252 feet msl. An approximately 18-foot high cut slope is located in the area to support the
planned detached garage and site retaining wall. Elevations at the slope range from about +252 feet msl to +270 feet msl. Figure 4-2 depicts surface conditions.
Figure 4-2. Surface Conditions in the Area of the Residential Additions
4.2.2 Subsurface
For the purposes of this report, the subsurface may be generalized to occur as the sequence of soil and
rock described below.
1. Unit 1, Topsoil The level pad area of the subject property explored by the borings are covered by a very thin layer of topsoil, about 1 to 3 inches in thickness. The unit is predominantly loose sands.
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2. Unit 2, Metasedimentary and Metavolcanic Rock (MzU). Metasedimentary and metavolcanic
bedrock lies beneath the topsoil in the areas to support the residential additions. As encountered in the borings and test pits, the unit grades from weathered to unweathered fractured bedrock. The upper weathered portions consisted of dense/hard, clayey sand/sandy clay. The unweathered rock will be
difficult to excavate using conventional equipment. The rock may need to be loosened by ripping prior to excavation.
4.2.3 Groundwater
No groundwater was encountered by the exploration. It is likely that groundwater first occurs at depths greater than 10 feet, such that groundwater should not affect construction.
Infiltrating storm water from prolonged wet periods can ‘perch’ atop localized zones of lower permeability soil or bedrock that exist above the static groundwater level. No perched groundwater was observed during drilling of the borings and excavation of the test pits.
4.2.4 Surface Water
No surface water was evident on the site at the time of NOVA’s work. NOVA did not observe any visual evidence of seeps, springs, erosion, staining, discoloration, etc. that would indicate recent problems with surface water.
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5.0 REVIEW OF GEOLOGIC AND SOIL HAZARDS
5.1 Overview
This section provides review of soil and geologic-related hazards common to this region of California, considering each for its potential to affect the planned development. The primary hazards identified by this review are abstracted below.
1. Seismic. The site is at risk for moderate-to-severe ground shaking generated by large-magnitude earthquakes during the lifetime of the planned residential additions. While there is no risk of liquefaction or related seismic phenomena, strong ground motion could affect the site. This circumstance is common to all civil works in this area of California. Seismic design parameters are provided in Section 6.
2. Near Surface Rock. As is discussed in Section 4, the area of the planned additions is underlain at shallow depth by hard metasedimentary and metavolcanic bedrock. In addition, a large outcrop was observed in the area of the proposed site retaining wall. The outcrop is evident in Figure 4-2.
The unweathered rock will be difficult to excavate using conventional equipment. The rock may need to be loosened by ripping or other use of special tools prior to excavation.
The following subsections address review of these and other potential soil and geologic hazards.
5.2 Geologic Hazards
5.2.1 Strong Ground Motion
The site is located in a seismically active area, as is the majority of southern California, and the potential for strong ground motion is considered significant during the design life of the proposed structure. The City of San Diego’s tectonic setting includes north and northwest striking fault zones, the most prominent
and active of which is the Rose Canyon fault zone. Major known active faults in the region consist generally of en echelon, northwest striking, right-lateral, strike-slip faults. These include the San Andreas, Elsinore, and San Jacinto faults located northeast of the site, and the San Clemente, San Diego
Trough, and Agua Blanca-Coronado Bank faults located to the west of the site.
The Rose Canyon fault is located approximately 6.9 miles west of the site. The Rose Canyon fault can generate an earthquake with a moment magnitude (MW) of up to MW = 7.2 (California Geological Survey, 2002). The web-based analytical tool provided by the USGS was used to estimate a corresponding risk-based Peak Ground Acceleration (PGAM) of PGAM ~ 0.40 g.
5.2.2 Fault Rupture
Figure 5-1 (following page) maps faults in the vicinity of the residence. The site is not underlain by any known active faults, such that the risk of fault rupture is negligible.
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Figure 5-1. Faulting in the Site Vicinity
5.2.3 Landslide
As used herein, ‘landslide’ describes downslope displacement of a mass of rock, soil, and/or debris by sliding, flowing, or falling. Such mass earth movements are about 10 feet thick and larger than 300 feet across. Landslides typically include cohesive block glides and disrupted slumps that are formed by translation or rotation of the slope materials along one or more slip surfaces.
The causes of classic landslides start with a preexisting condition- characteristically, a plane of weak soil or rock- inherent within the rock or soil mass. Thereafter, movement may be precipitated by earthquakes, wet weather, and changes to the structural or loading conditions on a slope (e.g., by addition of structures, erosion, cutting, filling, release of water from broken pipes, etc.).
Areas underlain by dense metasedimentary and metavolcanics are not generally susceptible to deep-seated landslides.
KEY TO SYMBOLS
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5.3 Soil Hazards
5.3.1 Embankment Stability
General
As used herein, ‘embankment stability’ is intended to mean the safety of localized natural or man-
made embankments against failure. Unlike landslides described above, embankment stability can include smaller scale slope failures such as erosion-related washouts and more subtle, less evident processes such as slope ‘creep.’
An approximately 24-foot high fill slope was constructed on the west side of the pad in the mid-1980s, and slopes down to Cadencia Street. To the east of the pad, an approximately 18-foot high cut slope ascends to the neighboring property to the west. Based on NOVA’s review of the
approved grading plans (approved October 29, 1984, by the City of Carlsbad), both cut and fill slopes have a 2:1 (H:V) inclination.
At the time of NOVA investigation, no evidence of slope failures or erosion was observed at the
site.
5.3.2 Seismic
Liquefaction
‘Liquefaction’ refers to the loss of soil strength during a seismic event. The phenomenon is observed in areas that include geologically ‘younger’ soils (i.e., soils of Holocene age), shallow water table (less than about 60 feet depth), and cohesionless (i.e., sandy and silty) soils of looser consistency. The seismic ground motions increase soil water pressures, decreasing grain-to-grain contact among the soil particles, which causes the soils to lose strength.
Resistance of a soil mass to liquefaction increases with increasing density, plasticity (associated with clay-sized particles), geologic age, cementation, and stress history. The very dense metasedimentary and metavolcanics units at this site have no potential for liquefaction.
Seismically Induced Settlement
Apart from liquefaction, a strong seismic event can induce settlement within loose to moderately dense, unsaturated granular soils. The metavolcanics/metasediments of the Unit 2 bedrock are
sufficiently dense and not prone to seismic settlement.
Lateral Spreading
Lateral spreading is a phenomenon in which large blocks of intact, non-liquefied soil move downslope on a liquefied soil layer. Lateral spreading is often a regional event. For lateral spreading to occur, a liquefiable soil zone must be laterally continuous and unconstrained, free to move along sloping ground. Due to the absence of a potential for liquefaction, there is no
potential for lateral spreading.
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5.3.3 Expansive Soils
Expansive soils are clays characterized by their ability to undergo significant volume changes (shrinking or swelling) due to variations in moisture content¸ the magnitude of which is related to both clay content and plasticity index. These volume changes can be damaging to structures. Nationally, the value of
property damage caused by expansive soils is exceeded only by that caused by termites.
As is discussed in Section 3, the upper, weathered portion of the Unit 2 rock has been characterized by testing to determine Expansion Index (‘EI’, after ASTM D 4829), showing the soil to be EI = 71 and
indicative of ‘Medium’ expansion potential.
5.3.4 Expansion Potential
Expansive soils are characterized by their ability to undergo significant volume changes (shrinking or swelling) due to variations in moisture content¸ the magnitude of which is related to both clay content and plasticity index. These volume changes can be damaging to structures. Nationally, the annual value of real estate damage caused by expansive soils is exceeded only by that caused by termites.
The soils have been characterized by testing to determine Expansion Index (‘EI’ after ASTM D 4829). Originally developed in Orange County in the 1960s, EI is a basic soil index property, comparable to indices such as the Atterberg limits of soils. EI has been adopted by the 2016 California Building Code (‘CBC’, Section 1803.5.3) for characterization of expansive soils.
The EI testing of the remolded sample of the Unit 2 weathered rock (0-3 feet depth) indicates EI = 71, indicating ‘Medium’ expansion potential.
5.3.5 Hydro-Collapsible Soils
Hydro-collapsible soils are common in the arid climates of the western United States in specific
depositional environments- principally, in areas of young alluvial fans, debris flow sediments, and loess (wind-blown sediment) deposits. These soils are characterized by low in situ density, low moisture contents, and relatively high unwetted strength.
The soil grains of hydro-collapsible soils were initially deposited in a loose state (i.e., high initial ‘void ratio’) and thereafter lightly bonded by water sensitive binding agents (e.g., clay particles, low-grade cementation, etc.). While relatively strong in a dry state, the introduction of water into these soils causes
the binding agents to fail. Destruction of the bonds/binding causes relatively rapid densification and volume loss (collapse) of the soil. This change is manifested at the ground surface as subsidence or settlement. Ground settlements from the wetting can be damaging to structures and civil works. Human activities that can facilitate soil collapse include irrigation, water impoundment, changes to the natural drainage, disposal of wastewater, etc.
The consistency and geologic age of the Unit 2 rock are such that there is no potential for hydro-collapse.
5.3.6 Corrosive Soils
The near surface soils were tested to show low levels of sulfates and chlorides. The potential for sulfate attack to embedded concrete is negligible. The potential for corrosion of embedded metals is relatively low. The indications of this testing are discussed in more detail in Section 6.
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5.4 Other Hazards
5.4.1 Flood
The site is not located within a FEMA-designated flood zone. The site area is designated “Zone X.” This designation means the site is within an area of minimal flood hazard. Figure 5-2 (following page) reproduces flood mapping by FEMA of the site area.
Figure 5-2. Flood Mapping of the Site (source: FEMA Panel No. 6073C1055G, effective on 05/16/2012)
5.4.2 Tsunami
Tsunami describes a series of fast-moving, long period ocean waves caused by earthquakes or volcanic eruptions. The California Geological Survey Tsunami Inundation Map, Encinitas Quadrangle (2009),
shows that the site is not within a tsunami inundation area.
5.4.3 Seiche
Seiches are standing waves that develop in an enclosed or partially enclosed body of water such as lakes or reservoirs. Harbors or inlets can also develop seiches. Most commonly caused by strong winds and rapid atmospheric pressure changes, seiches can be affected by seismic events and tsunamis.
The site is not located near a body of water that could generate a seiche.
KEY TO SYMBOLS
ZONEX Areas determined to be outside the 0.2% annual chance floodplain.
SPECIAL FlOOO HAZARD AREAS SUBJECT TO INUNDATION BY THE
1% ANNUAL O-wlCE A.00D
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6.0 EARTHWORK AND FOUNDATIONS
6.1 Overview
6.1.1 Soil and Geologic Hazards
Section 5 provides review of soil and geologic hazards common to civil works in this region. That review identifies the particular geologic and soil concerns abstracted below.
1. Seismic. The site is at risk for moderate-to-severe ground shaking generated by large-magnitude earthquakes during the lifetime of the planned development. While there is no risk of liquefaction or related seismic phenomena, strong ground motion could affect the site. This circumstance is common to all civil works in this area of California. Seismic design parameters are provided in Section 6.3.
2. Near Surface Rock. The area of the planned additions is underlain at shallow depth by hard
metasedimentary and metavolcanic bedrock. The upper weathered portions consisted of moderately expansive sandy clay. In addition, a large outcrop was observed in the area of the proposed site retaining wall. The unweathered rock will be difficult to excavate, posing a
challenge to site development and related foundation design.
6.1.2 Foundations
Based upon the indications of the field and laboratory data developed for this work, it is the opinion of
NOVA that the proposed additions to the subject residence can be developed on shallow foundations provided the geotechnical recommendations described herein are followed.
6.1.3 Review and Surveillance
It is intended that these recommendations provide sufficient geotechnical information to develop the project in general accordance with 2016 California Building Code (CBC) requirements.
NOVA should review the grading plan, foundation plan, and geotechnical-related specifications as they become available to confirm that the recommendations presented in this report have been incorporated into the plans prepared for the project. All earthwork related to site and foundation preparation should be completed under the observation of NOVA.
6.2 Seismic Design Parameters
6.2.1 Site Class
Though site-specific data is limited, the subsurface is well understood by virtue of the extensive development in this region. In consideration of this knowledge, the site is classified as Site Class B per ASCE 7 (Table 20.3-1).
6.2.2 Seismic Design Parameters
Table 6-1 (following page) provides seismic design parameters in accordance with 2016 CBC and mapped spectral acceleration parameters.
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Table 6-1. Seismic Design Parameters, ASCE 7-10
Parameter Value
Site Soil Class B
Site Latitude (decimal degrees) 33.0875
Site Longitude (decimal degrees) -117.23849
Site Coefficient, Fa 1.000
Site Coefficient, Fv 1.000
Mapped Short Period Spectral Acceleration, SS 1.032 g
Mapped One-Second Period Spectral Acceleration, S1 0.400 g
Short Period Spectral Acceleration Adjusted For Site Class, SMS 1.0325 g
One-Second Period Spectral Acceleration Adjusted For Site Class, SM1 0.400 g
Design Short Period Spectral Acceleration, SDS 0.688 g
Design One-Second Period Spectral Acceleration, SD1 0.267 g
Source: U.S. Seismic Design Maps, found at http://earthquake.usgs.gov/designmaps/us/application.php
6.3 Corrosivity and Sulfates
6.3.1 General
Electrical resistivity, chloride content, and pH level are all indicators of the soil’s tendency to corrode ferrous metals. These chemical tests were performed on a representative sample of the near-surface soils Records of this testing are provided in Appendix C. The results of the testing are tabulated in Table 6-2.
Table 6-2. Summary of Corrosivity Testing of the Near Surface Soil
Parameter Units Value
pH standard unit 7.2
Resistivity Ohm-cm 1400
Water Soluble Chloride ppm 53
Water Soluble Sulfate ppm 150
6.3.2 Metals
Caltrans considers a soil to be corrosive if one or more of the following conditions exist for representative soil and/or water samples taken at the site:
• chloride concentration is 500 parts per million (ppm) or greater;
• sulfate concentration is 2,000 ppm (0.2%) or greater; or,
• the pH is 5.5 or less.
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Based on the Caltrans criteria, the on-site soils would not be considered corrosive to buried metals.
Appendix C provides records of the chemical testing that include estimates of the life expectancy of buried metal culverts of varying gauge.
In addition to the above parameters, the risk of soil corrosivity buried metals is considered by
determination of electrical resistivity (ρ). Soil resistivity may be used to express the corrosivity of soil only in unsaturated soils. Corrosion of buried metal is an electrochemical process in which the amount of metal loss due to corrosion is directly proportional to the flow of DC electrical current from the metal into
the soil. As the resistivity of the soil decreases, the corrosivity generally increases. A common qualitative correlation (cited in Romanoff 1989, NACE 2007) between soil resistivity and corrosivity to ferrous metals are tabulated below.
Table 6-3. Soil Resistivity and Corrosion Potential
Minimum Soil Resistivity (Ω-cm) Qualitative Corrosion Potential
0 to 2,000 Severe
2,000 to 10,000 Moderate
10,000 to 30,000 Mild
Over 30,000 Not Likely
Despite the relatively benign environment for corrosivity indicated by pH and water-soluble chlorides, the resistivity testing suggests that design should consider that the soils may be severely corrosive to embedded ferrous metals.
Typical recommendations for mitigation of such corrosion potential in embedded ferrous metals include:
• a high-quality protective coating such as an 18-mil plastic tape, extruded polyethylene, coal tar enamel, or Portland cement mortar;
• electrical isolation from above grade ferrous metals and other dissimilar metals by means of dielectric fittings in utilities and exposed metal structures breaking grade; and,
• steel and wire reinforcement within concrete having contact with the site soils should have at least 2 inches of concrete cover. If extremely sensitive ferrous metals are expected to be placed in contact with the site soils, it may be desirable to consult a corrosion specialist regarding choosing the construction materials and/or protection design for the objects of concern.
6.3.3 Sulfates and Concrete
The soil sample tested in this evaluation indicated water-soluble sulfate (SO4) content of 150 parts per million (‘ppm,’ 0.015 % by weight). The American Concrete Institute (ACI) 318-08 considers soil with this concentration of SO4 to have no potential for sulfate attack to embedded concrete (i.e., Exposure Class ‘S0’). Table 6-4 (following page) reproduces the ACI guidance.
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Table 6-4. Exposure Categories and Requirements for Water-Soluble Sulfates
Exposure Category Class Water-Soluble Sulfate (SO4) In Soil (percent by weight)
Cement Type (ASTM C150) Max. Water-Cement Ratio Min. f’c (psi)
Not Applicable S0 SO4 < 0.10 - - -
Moderate S1 0.10 ≤ SO4 < 0.20 II 0.50 4,000
Severe S2 0.20 ≤ SO4 ≤ 2.00 V 0.45 4,500
Very severe S3 SO4 > 2.0 V + pozzolan 0.45 4,500
Adapted from: ACI 318-08, Building Code Requirements for Structural Concrete
6.3.4 Limitations
Testing to determine several chemical parameters that indicate a potential for soils to be corrosive to construction materials are traditionally completed by the Geotechnical Engineer, comparing test results with a variety of indices regarding corrosion potential.
Like most geotechnical consultants, NOVA does not practice in the field of corrosion protection, since
this is not specifically a geotechnical issue. Should you require more information, a specialty corrosion consultant should be retained to address these issues.
6.4 Site Preparation and Earthwork
6.4.1 General
Based upon the known condition of the site and the repair design concept that is currently considered, NOVA expects that grading for the one- and two-story addition will be minimal. Grading for the
proposed detached garage and site retaining wall will require cuts into the slope of up to 8 feet to (i) establish a level pad to support the detached garage; and (ii) expanding the rear yard.
Earthwork should be performed in accordance with Section 300 of the most recent approved edition of the
“Standard Specifications for Public Works Construction” and “Regional Supplement Amendments.”
All fill should be compacted to a minimum of 90 percent relative compaction after ASTM D1557 (the ‘modified Proctor’) following moisture conditioning to at least 2% above the optimum moisture content.
Fill should be placed in loose lifts no thicker than the ability of the compaction equipment to thoroughly densify the lift. For most self-propelled construction equipment that will be able to access the work area., this will limit loose lifts to on the order of 8-inches or less. Lift thickness for hand-operated and walk behind compactors will be limited to on the order of 4 inches or less.
6.4.2 Clearing and Grubbing
Prior to the start of earthwork, the site should be cleared of vegetation and related root systems, and any
existing pavement.
At the outset of site work, the Contractor should establish construction Best Management Practices
(‘BMPs’) to prevent erosion of graded/excavated areas until such time as permanent drainage and erosion control measures have been installed. Any existing utilities which are to be abandoned should either be (i) excavated and the trenches backfilled; or, (ii) the lines completely filled with sand-cement slurry. As is
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Stripped materials consisting of vegetation and organic materials should be removed from the site, or used
in landscaping non-structural areas.
6.4.3 Excavation Characteristics
The Unit 2 unweathered rock will be difficult to excavate by the limited size equipment that will be able
to access the area of the planned improvements.
6.4.4 Select Fill
Select Fill should be a mineral soil free of organics with the characteristics listed below:
• free of organics, with at least 40 percent by weight finer than ¼-inches in size and,
• maximum particle size of 4 inches; and,
• expansion index (EI) of less than 50 (i.e., EI < 50, after ASTM D 4829). It is expected that most of the soils now in place will not meet the above requirements, requiring the need for import of Select Fill for backfill behind the retaining walls.
6.4.5 Remedial Grading
NOVA recommends that the upper 12 inches of soil exposed in areas to support on-grade concrete slabs should be moisture conditioned to at least at least 3% above the optimum moisture content and densified to 90 percent relative compaction after ASTM D 1557. Rock greater than 6 inches in size should be
removed if encountered at pad grade.
6.4.6 Maintenance of Moisture in Soils During Construction
The subgrade moisture condition of the pad and foundation soils must be maintained at least 3% above optimum moisture content up to the time of concrete placement.
6.4.7 Trenching and Backfilling for Utilities
Excavation for utility trenches must be performed in conformance with OSHA regulations contained in 29 CFR Part 1926.
Utility trench excavations have the potential to degrade the properties of the adjacent soils. Utility trench
walls that are allowed to move laterally will reduce the bearing capacity and increase settlement of adjacent footings and overlying slabs.
Backfill for utility trenches is as important as the original subgrade preparation or engineered fill placed
to support either a foundation or slab. Backfill for utility trenches must be placed to meet the project specifications for the engineered fill of this project. Unless otherwise specified, the backfill for the utility trenches should be placed in 4 to 6-inch loose lifts and compacted to a minimum of 90 percent relative compaction after ASTM D 1557 (the ‘modified Proctor’) at soil moisture +2 percent of the optimum moisture content. Up to 4 inches of bedding material placed directly under the pipes or conduits placed in the utility trench can be compacted to 90 percent relative compaction with respect to the Modified
Proctor.
Compaction testing should be performed for every 20 cubic yards of backfill placed or each lift within 30 linear feet of trench, whichever is less.
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Backfill of utility trenches should not be placed with water standing in the trench. If granular material is
used for the backfill, the material should have a gradation that will filter protect the backfill material from the adjacent soils. If this gradation is not available, a geosynthetic non-woven filter fabric should be used to reduce the potential for the migration of fines into the backfill material.
6.4.8 Flatwork
Prior to casting exterior flatwork, the upper 12 inches of subgrade soils should be moisture conditioned to at least at least 3% above the optimum moisture content and densified to 95 percent relative compaction
after ASTM D 1557. Concrete slabs for pedestrian traffic or landscaping should be at least four (4) inches thick.
6.5 Shallow Foundations
6.5.1 General
Shallow foundations (i.e., isolated spread or continuous) footings for support of the additions may be established following penetration of at least 24 inches into the Unit 2 metavolcanic and metasedimentary
rock.
At grade, slabs may be supported at the surface of Unit 2 or on properly compacted Select Fill.
The following subsections detail recommendations for shallow foundations.
6.5.2 Conventionally Reinforced Concrete Slab
The ground level of the structure may employ conventional on-grade (ground-supported) slab. Conventionally reinforced on-grade concrete slabs may be designed using a modulus of subgrade reaction
(k) of 150 pounds per cubic inch (i.e., k = 150 pci).
The actual slab thickness and reinforcement should be designed by the Structural Engineer. NOVA recommends the slab be a minimum 5 inches thick, reinforced by at least #4 bars placed at 16 inches on center each way within the middle third of the slabs by supporting the steel on chairs or concrete blocks.
Minor cracking of concrete after curing due to drying and shrinkage is normal. Cracking is aggravated by a variety of factors, including high water/cement ratio, high concrete temperature at the time of placement, small nominal aggregate size, and rapid moisture loss due during curing. The use of low-slump concrete or low water/cement ratios can reduce the potential for shrinkage cracking.
6.5.3 Conventional Foundations
Shallow foundations (i.e., isolated spread or continuous) footings for support of the additions and site retaining wall may be established following penetration of at least 24 inches into the Unit 2 metavolcanic
and metasedimentary rock.
Conventional foundations, consisting of isolated and continuous footings, may be employed as described below.
Isolated Foundations
Isolated foundations for interior columns may be designed for an allowable contact stress of 5,000 psf. This value may be increased by one-third for transient loads such as wind and seismic.
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These foundation units should have a minimum width of 24 inches, embedded a minimum of 24
inches into Unit 2.
Continuous Foundations
Continuous foundations may be designed for an allowable contact stress of 5,000 psf, for footings
with a minimum of 24 inches in width and embedded 24 inches into the Unit 2 soils. This bearing value may be increased by one-third for transient loads such as wind and seismic.
Resistance to Lateral Loads
Lateral loads to shallow foundations cast neatly against Unit 2 may be resisted by passive earth pressure against the face of the footing, calculated as a fluid density of 400 psf per foot of depth, neglecting the upper 1 foot of soil below surrounding grade in this calculation. Additionally, a coefficient of friction of 0.35 between soil and the concrete base of the footing may be used with dead loads.
Settlement
If the new additions are supported as recommended above, these additions will settle less than 0.5 inch. This movement will occur elastically, as dead load (DL) and permanent live loads (LL) are applied. In usual circumstance, about 80% of this settlement will occur during the construction period. Angular distortion due to differential settlement of adjacent, unevenly loaded footings should be less than 1 inch in 40 feet (i.e., Δ./L less than 1:480).
6.5.4 Moisture Barrier
Capillary Break
Slabs that may receive moisture-sensitive floor coverings or may be used to store moisture-
sensitive materials should be underlain by a vapor retarder. The vapor retarder design should be consistent with the guidelines presented in the American Concrete Institute’s (ACI) Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials (ACI 302.2R-06). In addition,
the membrane should be installed in accordance with manufacturer’s recommendations and ASTM requirements and installed in a manner that prevents puncture. The vapor retarder used should be specified by the project architect or developer based on the type of floor covering that
will be installed and if the structure will possess a humidity-controlled environment.
The bedding sand thickness should be determined by the project foundation engineer, architect, and/or developer. However, NOVA should be contacted to provide recommendations if the bedding sand is thicker than 6 inches. The foundation design engineer should provide appropriate concrete mix design criteria and curing measures to assure proper curing of the slab by reducing the potential for rapid moisture loss and subsequent cracking and/or slab curl.
Vapor Barrier
Membranes set below floor slabs should be rugged enough to withstand construction. If a vapor barrier is desired, a minimum 15-mil polyethylene membrane should be placed over the porous
fill to preclude floor dampness.
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NOVA recommends that a minimum 15-mil low permeance vapor membrane be used. For
example, Carlisle-CCW produces the Blackline 400® underslab, vapor and air barrier, a 15-mil low-density polyethylene (LDPE) rated at 0.012 perms after ASTM E 96.
Limitations of This Recommendation
Recommendation for moisture barriers are traditionally included with geotechnical foundation recommendations, though these requirements are primarily the responsibility of the Structural Engineer or Architect.
If there is particular concern regarding moisture sensitive materials or equipment to be placed above the slab-on-grade, a qualified person (for example, such as the flooring subcontractor and/or Structural Engineer) should be consulted to evaluate the general and specific moisture vapor transmission paths and any impact on the proposed construction. NOVA does not practice in the field of moisture vapor transmission evaluation since this is not specifically a geotechnical issue.
6.6 Control of Drainage and Moisture Around Structures
6.6.1 General
Geotechnical, civil, structural, architectural and landscaping design for the areas around foundations and floor slabs must be undertaken with a view to the maintenance of an environment that encourages constant moisture conditions in the soils following construction. Roof and surface drainage, landscaping, and utility connections must be designed to limit infiltration and/or releases of moisture beneath or around
structures. This care should, at a minimum, include the actions described in the following subsections.
6.6.2 Landscaping
Landscaping adjacent to the structures should be limited. No new trees should be planted. If used, trees should be planted the greater of (i) 15 feet away from foundations; or (ii) 1.5 times its mature height away from foundations.
Do not plant flowers or shrubs closer than five (5) feet from foundations. Planters and other surface features which could retain water in areas adjacent to the buildings should be sealed or eliminated. Sprinkler systems should not be installed within 5 feet of foundations or floor slabs.
If trees are planted at locations that do not conform with the above, this action would be undertaken at the Designer’s/Owner’s sole risk. In such an event, the risk of such planting can perhaps be limited by utilizing root barriers, drought-resistant trees (to limit the need for watering) or trees with relatively
shallower root systems.
6.6.3 Drainage
Rainfall to roofs should be collected in gutters and discharged in a controlled manner through downspouts designed to drain away from foundations. Downspouts, roof drains or scuppers should discharge into splash blocks to slabs or paving sloped away from buildings.
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6.6.4 Surface Grades
In areas where sidewalks or paving do not immediately adjoin the structure, protective slopes should be provided with a minimum grade of approximately 3 percent for at least 8 feet from perimeter walls.
A minimum gradient of 1 percent is recommended in hardscape areas. In earth areas, a minimum gradient
of 5 percent away from the structure for a distance of at least 8 feet should be provided. Earth swales should have a minimum gradient of 2 percent. Storm water should be directed to approved drainage facilities. Proper surface and subsurface drainage will be required to minimize the potential for surface
water to seep to the level of the bearing soils under the foundations, pavements, and flatwork.
6.6.5 Backfills
In order to reduce the possibility of moisture infiltration, backfill against foundation elements, exterior walls, and in utility and sprinkler line trenches should be with well compacted, non-expansive, low permeability soil that is free of all construction debris.
6.7 Retaining Walls
6.7.1 General
The following subsections provide guidance for design of cantilevered retaining walls, should planning change and such retaining structures are employed.
6.7.2 Shallow Foundations
Retaining walls should be developed on ground prepared in accordance with the criteria provided in Section 6.4. Continuous shallow foundations may be designed in accordance with the criteria provided in
Section 6.5.
6.7.3 Lateral Earth Pressures
Design may include smaller (perhaps 10 feet tall) cantilevered, conventionally reinforced concrete retaining walls. This section provides recommendations for wall pressures for those walls.
Lateral earth pressures for wall design are provided in Table 6-5 (following page) as equivalent fluid
weights, in psf/foot of wall height or pounds per cubic foot (pcf). These values do not contain a factor of safety.
6.7.4 Foundation Uplift
A soil unit weight of 125 pcf may be assumed for calculating the weight of soil over the wall footing.
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Table 6-5. Lateral Earth Pressures
Loading Condition
Equivalent Fluid Density (pcf) for
Approved ‘Native’ Backfill Notes A, B
Level Backfill 2:1 Backfill Sloping Upwards
Active (wall movement allowed) 35 60
“At Rest” (no wall movement) 65 100
‘Passive” (wall movement toward the soils) 260 220
Note A: ‘native’ means site-sourced soil with EI < 50 after ASTM D4546. Note B: assumes wall includes appropriate drainage.
6.7.5 Resistance to Lateral Loads
Lateral loads to wall foundations will be resisted by a combination of frictional and passive resistance as described below.
• Frictional Resistance. A coefficient of friction of 0.35 between the soil and base of the footing.
• Passive Resistance. Passive soil pressure against the face of footings or shear keys will accumulate at an equivalent fluid weight of 250 pounds per cubic foot (pcf). The upper 12 inches of material in areas not protected by floor slabs or pavement should not be included in calculations of passive resistance.
6.7.6 Wall Drainage
The recommended equivalent fluid pressures provided in the preceding subsection assume that constantly functioning drainage systems are installed between walls and soil backfill to prevent the uncontrolled buildup of hydrostatic pressures and lateral stresses in excess of those stated.
Design for wall drainage may include the use of pre-engineered wall drainage panels or a properly compacted granular free-draining backfill material (EI <50). The use of drainage openings through the
base of the wall (weep holes) is not recommended where the seepage could be a nuisance or otherwise adversely affect the property adjacent to the base of the wall.
Figure 6-1 (following page) provides a conceptual design for wall drainage. Numerous alternatives are
available for collection of water behind retaining walls. The intent of this Figure 6-1 is to depict the concepts described in the preceding paragraph.
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Figure 6-1. Conceptual Design for Wall Drainage
6.7.7 Seismic
The lateral seismic pressure acting on a cantilevered retaining wall should be applied as an inverted triangle with a magnitude of 11H, where H is the free height of the wall. The resultant dynamic thrust acts at a distance of 0.6H above the base of the wall. This equation applies to level backfill and walls that retain no more than 15 feet of soil.
6.8 Temporary Shoring
It is the sole responsibility of the Contractor to employ means and methods to retain temporary slopes provide an excavation that is safe and that causes acceptably small lateral and vertical soil movements.
Temporary slopes should be developed in conformance with OSHA requirements. The Unit 2 rock should be considered a Type B soil.
In general, special shoring requirements will not be necessary for temporary excavations less than 4 feet in height. Temporary excavations greater than 4 feet in height, however, should be either properly retained or sloped back at an appropriate inclination.
RETAINING
WALL
FINISHED
GRADE
CONCRETE
BROWDITCH
GROUND SURFACE
ATER PROOFING
PER ARCHITECT
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GEOTECHNICAL
CONSULTANT
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7.0 REFERENCES
7.1 Site Specific
JAB 2018a. Architectural Plans for Guinn Residence, 7500 Cadencia Street, Carlsbad, progress set, by John Alan Baker, 6 April 2018. JAB 2018b. Structural Plans for Guinn Residence, 7500 Cadencia Street, Carlsbad, by John Alan Baker, 1 April 2018.
7.2 Design
American Concrete Institute, Building Code Requirements for Structural Concrete, ACI 318-08.
American Society of Civil Engineers, Minimum Design Load for Buildings and Other Structures, ASCE 7-10.
American Public Works Association, 2015 Standard Specifications for Public Works Construction
(‘Greenbook’).
California Code of Regulations, Title 24, 2016 California Building Standards Code.
California Department of Transportation (Caltrans), 2015 Standard Specifications, Section 19-3.02G, Controlled Low Strength Material
California Department of Transportation (Caltrans), 2003, Corrosion Guidelines, Version 1.0, available at http://www.dot.ca.gov/hq/esc/ttsb/corrosion/pdf/2012-11-19-Corrosion-Guidelines.pdf.
USGS, Earthquake Hazards Program, Seismic Design Maps & Tools, accessed 13 August 2017 at: http://earthquake.usgs.gov/hazards/designmaps/.
7.3 Geologic and Site Setting
Jennings, C. W. and Bryant, W. A., 2010, Fault Activity Map of California, California Geological Survey, Geologic Data Map No. 6.
Tan, Siang S. and Kennedy, Michael P., 1996, Geologic Maps of the Northwestern Part of San Diego County, California, Open File Report 96-02, California Division of Mines and Geology.
Norris, R. M. and Webb, R. W., 1990, Geology of California, Second Edition: John Wiley & Sons, Inc.
United States Federal Emergency Management Agency (FEMA), 2012, FEMA Panel No. 6073C1055G, effective on 05/16/2012.
United States Geological Survey and California Geological Survey, 2011, Quaternary Fault and Fold database for the United States, http://earthquake.usgs.gov/regional/qfaults/.
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PLATES
B-1 B-2
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SAN DIEGO, CALIFORNIA
858-292-7575
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WWW.USA-NOVA.COM
PROJECT NO:
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Report of Preliminary Geotechnical Investigation June 06, 2018 Guinn Residence Additions, 7500 Cadencia Street, Carlsbad NOVA Project 2018049 ________________________________________________________________________________________________________
APPENDIX A
USE OF THE GEOTECHNICAL REPORT
Im ortant Information About Your
Geotechnical Engineering Report
Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.
The following information is provided to help you manage your risks.
Geotechnical Services Are Performed for
Specific Purposes, Persons, and Projects
Geotechnical engineers structure their services to meet the specific needs of
their clients. A geotechnical engineering study conducted for a civil engi-
neer may not fulfill the needs of a construction contractor or even another
civil engineer. Because each geotechnical engineering study is unique, each
geotechnical engineering report is unique, prepared solelyfor the client. No
one except you should rely on your geotechnical engineering report without
first conferring with the geotechnical engineer who prepared it. And no one
-not even you -should apply the report for any purpose or project
except the one originally contemplated.
Read the Full Report
Serious problems have occurred because those relying on a geotechnical
engineering report did not read it all. Do not rely on an executive summary.
Do not read selected elements only.
A Geotechnical Engineering R~port Is Based on
A Unique Set of Project-Specific Factors
Geotechnical engineers consider a number of unique, project-specific fac-
tors when establishing the scope of a study. Typical factors include: the
client's goals, objectives, and risk management preferences: the general
nature of the structure involved, its size, and configuration: the location of
the structure on the site: and other planned or existing site improvements,
such as access roads, parking lots, and underground utilities. Unless the
geotechnical engineer who conducted the study specifically indicates oth-
erwise, do not rely on a geotechnical engineering report that was:
• not prepared for you,
• not prepared for your project.
• not prepared for the specific site explored, or
• completed before important project changes were made.
Typical changes that can erode the reliability of an existing geotechnical
engineering report include those that affect:
• the function of the proposed structure, as when it's changed from a
parking garage to an office building , or from a light industrial plant
to a refrigerated warehouse,
• elevation, configuration, location, orientation, or weight of the
proposed structure,
• composition of the design team, or
• project ownership.
As a general rule, always inform your geotechnical engineer of project
changes-even minor ones-and request an assessment of their impact.
Geotechnical engineers cannot accept responsibility or liability for problems
that occur because their reports do not consider developments of which
they were not informed
Subsurface Conditions Can Change
A geotechnical engineering report is based on conditions that existed at
the time the study was performed. Do not rely on a geotechnical engineer-
ing reportwhose adequacy may have been affected by: the passage of
time; by man-made events, such as construction on or adjacent to the site;
or by natural events, such as floods, earthquakes, or groundwater fluctua-
tions. Always contact the geotechnical engineer before applying the report
to determine if it is still reliable. A minor amount of additional testing or
analysis could prevent major problems.
Most Geotechnical Findings Are Professional
Opinions
Site exploration identifies subsurface conditions only at those points where
subsurface tests are conducted or samples are taken. Geotechnical engi-
neers review field and laboratory data and then apply their professional
judgment to render an opinion about subsurface conditions throughout the
site. Actual subsurface conditions may differ-sometimes significantly-
from those indicated in your report. Retaining the geotechnical engineer
who developed your report to provide construction observation is the
most effective method of managing the risks associated with unanticipated
conditions.
A Report's Recommendations Are Not Final
Do not overrely on the construction recommendations included in your
report. Those recommendations are not final, because geotechnical engi-
neers develop them principally from judgment and opinion. Geotechnical
engineers can finalize their recommendations only by observing actual
subsurface conditions revealed during construction. The geotechnical
engineer who developed your report cannot assume responsibility or
liability for the report's recommendations if that engineer does not perform
construction observation.
A Geotechnical Engineering Report Is Subject to
Misinterpretation
Other design team members' misinterpretation of geotechnical engineering
reports has resulted in costly problems. Lower that risk by having your geo-
technical engineer confer with appropriate members of the design team after
submitting the report. Also retain your geotechnical engineer to review perti-
nent elements of the design team's plans and specifications. Contractors can
also misinterpret a geotechnical engineering report. Reduce that risk by
having your geotechnical engineer participate in prebid and preconstruction
conferences, and by providing construction observation.
Do Not Redraw the Engineer's Logs
Geotechnical engineers prepare final boring and testing logs based upon
their interpretation of field logs and laboratory data. To prevent errors or
omissions, the logs included in a geotechnical engineering report should
never be redrawn for inclusion in architectural or other design drawings.
Only photographic or electronic reproduction is acceptable, but recognize
that separating logs from the report can elevate risk.
Give Contractors a Complete Report and
Guidance
Some owners and design professionals mistakenly believe they can make
contractors liable for unanticipated subsurface conditions by limiting what
they provide for bid preparation. To help prevent costly problems, give con-
tractors the complete geotechnical engineering report, but preface it with a
clearly written letter of transmittal. In that letter, advise contractors that the
report was not prepared for purposes of bid development and that the
report's accuracy is limited; encourage them to confer with the geotechnical
engineer who prepared the report (a modest fee may be required) and/or to
conduct additional study to obtain the specific types of information they
need or prefer. A prebid conference can also be valuable. Be sure contrac-
tors have sufficient time to perform additional study. Only then might you
be in a position to give contractors the best information available to you,
while requiring them to at least share some of the financial responsibilities
stemming from unanticipated conditions.
Read Responsibility Provisions Closely
Some clients, design professionals, and contractors do not recognize that
geotechnical engineering is far less exact than other engineering disci-
plines. This lack of understanding has created unrealistic expectations that
have led to disappointments, claims, and disputes. To help reduce the risk
of such outcomes, geotechnical engineers commonly include a variety of
explanatory provisions in their reports. Sometimes labeled "limitations"
many of these provisions indicate where geotechnical engineers' responsi-
bilities begin and end, to help others recognize their own responsibilities
and risks. Read these provisions closely Ask questions. Your geotechnical
engineer should respond fully and frankly.
Geoenvironmental Concerns Are Not Covered
The equipment. techniques, and personnel used to perform a geoenviron-
mental study differ significantly from those used to perform a geotechnical
study. For that reason, a geotechnical engineering report does not usually
relate any geoenvironmental findings, conclusions, or recommendations;
e.g., about the likelihood of encountering underground storage tanks or
regulated contaminants. Unanticipated environmental problems have led
to numerous project failures. If you have not yet obtained your own geoen-
vironmental information, ask your geotechnical consultant for risk man-
agement guidance. Do not rely on an environmental report prepared for
someone else.
Obtain Professional Assistance To Deal with Mold
Diverse strategies can be applied during building design, construction,
operation, and maintenance to prevent significant amounts of mold from
growing on indoor surfaces. To be effective, all such strategies should be
devised for the express purpose of mold prevention, integrated into a com-
prehensive plan, and executed with diligent oversight by a professional
mold prevention consultant. Because just a small amount of water or
moisture can lead to the development of severe mold infestations, a num-
ber of mold prevention strategies focus on keeping building surfaces dry.
While groundwater, water infiltration, and similar issues may have been
addressed as part of the geotechnical engineering study whose findings
are conveyed in this report, the geotechnical engineer in charge of this
project is not a mold prevention consultant; none of the services per-
formed in connection with the geotechnical engineer's study
were designed or conducted for the purpose of mold preven-
tion. Proper implementation of the recommendations conveyed
in this report will not of itself be sufficient to prevent mold
from growing in or on the structure involved.
Rely, on Your ASFE-Member Geotechncial
Engineer for Additional Assistance
Membership in ASFE/The Best People on Earth exposes geotechnical
engineers to a wide array of risk management techniques that can be of
genuine benefit for everyone involved with a construction project. Confer
with you ASFE-member geotechnical engineer for more information.
ASFE
The Best People an Earth
8811 Colesville Road/Suite G106, Silver Spring, MD 20910
Telephone: 301/565-2733 Facsimile: 301/589-2017
e-mail: info@asfe.org www.asfe.org
Copyright 2004 by ASFE, Inc. Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly prohibited, except with ASFE'S
specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of ASFE, and only for
purposes of scholarly research or book review. Only members of ASFE may use this document as a complement to or as an element of a geotechnical engineering report. Any other
firm, individual, or other entity that so uses this document without being an ASFE member could be commiting negligent or intentional (fraudulent) misrepresentation.
IIGER06045.0M
Report of Preliminary Geotechnical Investigation June 06, 2018 Guinn Residence Additions, 7500 Cadencia Street, Carlsbad NOVA Project 2018049 ________________________________________________________________________________________________________
APPENDIX B
SOIL EXPLORATION LOGS
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Report of Preliminary Geotechnical Investigation June 06, 2018 Guinn Residence Additions, 7500 Cadencia Street, Carlsbad NOVA Project 2018049 ________________________________________________________________________________________________________
APPENDIX C
LABORATORY ANALYTICAL RESULTS
Laboratory tests were performed in accordance with the generally accepted American Society for Testing and Materials (ASTM) test methods or suggested
procedures. Brief descriptions of the tests performed are presented below:
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Specimens were molded under a specified compactive energy at approximately 50 percent saturation (plus or minus 1 percent). The prepared 1-inch
thich by 4-inch diameter specimens were loaded with a surcharge of 144 pounds per square foot and were inundated with tap water. Readings of
volumetric swell were made for a period of 24 hours.
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and CT 422, respectively.
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ASTM D422. The grain size distributions of selected samples were determined in accordance with ASTM C 136 and/or ASTM D422. The results of the
tests are summarized on Appendix C.3 through Appendix C.5.
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... I 70 ++-+-+-+--+--+--+--~ll,.......-~~--+++-+-+---hl--+----+~1--+--~1--+-hl+-+--+-t--Tlt--+--t-~1---+-ar-+.-1+-+-+--+---+--+----+-t-+-a--+--+--+---+---+-------,
I ... :
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40 ++-+-+-+--+-+--+--+.---++-+-+---+-+.-+---+--+---+-+-<+-1--+-'~'~1+--+--+-~-t-+-h-+-+-i--------,f------+-----l------l-+-+-+-+-t---+-+----+-----+ 1,
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GEOTECHNICAL
MATERIALS
SPECIAL INSPECTION DVBE SBE SDVOSB SLBE
4373 Viewridge Avenue, Suite B San Diego, CA 92123 P: 858.292.7575
www.usa-nova.com 944 Calle Amanecer, Suite F San Clemente, CA 92673 P: 949.388.7710
Mr. Rick Guinn December 20, 2022
7500 Cadencia Street NOVA Project No. 2018049
Carlsbad, CA 92009
Subject: Update Letter
Guinn Residence Additions
7500 Cadencia Street, Carlsbad, California
References:
SE 2022. Guinn ADU, 7500 Cadencia St., Carlsbad, California, Solidforms Engineering, Job
#22-381, dated December 08, 2022.
NOVA 2018. Report, Preliminary Geotechnical Investigation, Guinn Residence Additions, 7500
Cadencia Street, Carlsbad, California, NOVA Services, Inc., Project No. 2018049, June 05,
2018.
Dear Mr. Guinn:
NOVA Services, Inc. (NOVA) has reviewed the Guinn ADU plans (SE 2022). The review was limited to the geotechnical aspects of the plans, reviewing for conformance with the referenced geotechnical reporting by NOVA. Based on this review, the recommendations provided in NOVA 2018 geotechnical report remain applicable to the proposed Guinn ADU project.
Additionally, NOVA is providing updated seismic design parameters in accordance with the 2019 California Building Code (CBC). These recommendations are provided by NOVA Services, Inc. (NOVA) for Guinn ADU project. NOVA is retained by Mr. Guinn as the geotechnical engineer-of record for this project. The updated seismic parameters are presented below. Table 1. 2019 CBC and ASCE 7-16 Seismic Design Parameters
Site Coordinates
Latitude: 33.0875 ° Longitude: - 117.23849 °
Site Coefficients and Spectral Response Acceleration Parameters Value
Site Class B
Site Coefficients, Fa 1.00
Site Coefficients, Fv 1.00
Mapped Spectral Response Acceleration at Short Period, Ss 0.956g
Mapped Spectral Response Acceleration at 1-Second Period, S1 0.349g
Mapped Design Spectral Acceleration at Short Period, SDS 0.683g
Design Spectral Acceleration at 1-Second Period, SD1 0.233g
Site Peak Ground Acceleration, PGAM 0.417g
Source: OSHPD/SEAOC www.Seismicmaps.org
Updated Letter Guinn Residence Additions, Carlsbad, CA NOVA Project No. 2018049 December 20, 2022
2
Closure
NOVA appreciates the opportunity to be of continued service to Guinn Residence. Should you
have any questions regarding this submittal or other matters, please do not hesitate to contact us
at 858.292.7575.
Sincerely, NOVA Services, Inc.
____________________________ ___________________________
Wail Mokhtar John F. O’Brien, PE, GE Regional Manager Principal Geotechnical Engineer