HomeMy WebLinkAboutPD 2023-0012; VALLEY MIDDLE SCHOOL CAMPUS MODERNIZATION; RESPONSE TO GEOTECHNICAL REPORT REVIEW COMMENTS; 2023-09-08
GEOTECHNICAL
MATERIALS
SPECIAL INSPECTION DVBE SBE SDVOSB SLBE
4373 Viewridge Avenue, Suite B
San Diego, CA 92123 P: 858.292.7575
usa-nova.com 944 Calle Amanecer, Suite F
San Clemente, CA 92673 P: 949.388.7710
Chad Conrad, Bond Program Manager September 8, 2023
Carlsbad Unified School District NOVA Project No. 2022253
6225 El Camino Real
Carlsbad, California 92009
Subject: Responses to Geotechnical Report Review Comments
Valley Middle School Modernization
1645 Magnolia Avenue, Carlsbad, CA 92008
References: City of Carlsbad (2023), Valley Middle School Modernization (1st review), Grading
Permit No. GR2023-0021, Project ID: PD2023-0012, June 7.
NOVA (2023), Update Geotechnical Report, Valley Middle School Modernization,
1645 Magnolia Avenue, Carlsbad, California, 92008, NOVA Project No. 2022253,
February 16.
Pasco Laret Suiter & Associates (2022), Precise Grading Plan, Carlsbad Unified School District, Valley Middle School, 1645 Magnolia Ave., Carlsbad California 92008, Campus Modernization, 100% DD Submittal, Sheets C-200 through C-205, Project 3483, December 5.
Dear Mr. Conrad:
NOVA Services, Inc. (NOVA) prepared this letter to response to geotechnical report review comments
from the City of Carlsbad (2023) for the Valley Middle School Modernization. NOVA is retained by the
Carlsbad Unified School District as the geotechnical consultant of record for the project. The review
comments and our responses are provided below.
Comment 1: Please provide the Seismic Design Category for the project in accordance with Section
1613 of the 2022 California Building Code.
Response: The Seismic Design Category is D.
Comment 2: Please provide recommendations for sulfate resistant concrete (compressive strength,
w/c ratio, type cement) based on the laboratory test results of the on-site soils and consistent with the
2022 California Building Code and ACI 318, Tables 4.2.1 and 4.3.1.
Response: Based on the results of our soluble sulfate testing and according to ACI 318, the sulfate
exposure class is S0, and the exposure severity is N/A. For sulfate exposure class is S0, a minimum
concrete compressive strength (fc’) of 2,500 psi is recommended with no maximum w/c ratio or cement
type restrictions according to ACI 381.
Response to Geotechnical Report Review Comments Valley Middle School Modernization, Carlsbad, CA NOVA Project No. 2022253
September 8, 2023
2
Comment 3: With respect to the remedial grading for proposed the site walls, shade structures, and
hardscape/pavement improvements; please clarify if the entire thickness of the existing fill beneath the
improvements should be removed down to Old Paralic Deposits and replaced as compacted fill as part
of the preparation for the placement of the proposed improvements.
Response: The entire thickness of existing fill beneath the proposed site walls, shade structures, and
hardscape/pavement improvements does not need to be removed down to old paralic deposits
provided the remedial grading recommendations contained in our referenced geotechnical report are
followed. Note that a NOVA representative should observe the conditions exposed in the bottoms of
excavations and confirm that suitable materials are encountered. Additional excavation may be
recommended based on the conditions exposed.
Comment 4: Please clarify if the value for lateral resistance (350 psf/ft) that is provided in the report is
the recommended parameter for both Old Paralic Deposits and compacted fill.
Response: The lateral resistance of 350 psf/ft is recommended for both old paralic deposits and
compacted fill.
Comment 5: Please provide the minimum reinforcement requirements for new foundations from a
geotechnical standpoint.
Response: Minimum two No. 5 bars at top and bottom is recommended. However, the project structural
engineer should design the actual reinforcement of foundations.
Comment 6: For any interior concrete floor slab associated with the project, please clarify if a capillary
break is recommended per Section 1805 of the 2022 California Building.
Response: We recommend that floors with moisture-sensitive floor coverings are dampproofed using
a minimum 15-mil vapor barrier in accordance with Section 1805.2.1 of the 2022 California Building
Code. Refer to Section 7.3 of our geotechnical report (NOVA, 2023). A capillary break is not considered
necessary with the recommended dampproofing.
Comment 7: Please provide the test data from the percolation/infiltration testing that was performed
and discussed in the report.
Response: The percolation test data and infiltration calculations are attached.
Comment 8: Please provide the data and the results of the Seismic Shear Wave Survey that was
performed at the subject site.
Response: The data from the seismic shear-wave survey is attached.
Comment 9: Please provide a complete summery [sic] list of the geotechnical observation/testing
services that should be performed as part of the construction of this proposed development.
Response: The following geotechnical observation and testing services should be performed during
site grading and earthwork construction:
• Attend the grading preconstruction meeting.
Response to Geotechnical Report Review Comments Valley Middle School Modernization, Carlsbad, CA NOVA Project No. 2022253
September 8, 2023
3
• Observe ground preparation prior to fill placement.
• Observe and map the geologic conditions exposed during grading.
• Observe placement and compaction of fill, backfill, and paving materials and perform field
density testing.
• Perform laboratory tests on fill, backfill, and paving materials.
• Observe foundation excavations to evaluate conformance with the project plans and
geotechnical recommendations.
• 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.
NOVA appreciates the opportunity to be of service to Carlsbad Unified School District on this project.
If you have any questions regarding this letter, please call us at 858.292.7575 x 413.
Sincerely, NOVA Services, Inc.
_________________________ _________________________
Tom Canady, PE Melissa Stayner, PG, CEG
Principal Engineer Senior Engineering Geologist
Attachments: 1: Percolation Test Data and Infiltration Calculations
2: Seismic Shear-Wave Survey
Response to Geotechnical Report Review Comments Valley Middle School Modernization, Carlsbad, CA NOVA Project No. 2022253
September 8, 2023
ATTACHMENT 1
PERCOLATION TEST DATA AND
INFILTRATION CALCULATIONS
Test Number:P-1Tested By:TPDate Tested:1/30/2023
Presoak Time:24 HR
Drilled Depth (feet):
Time Initial Water Final Water Change in Water Percolation
Interval, ΔT Height, Ho Height, Hf Height, ΔH Rate
(min)(ft)(ft)(in)(min/in)
23 min/in2.6 in/hr
0.21 in/hr
0.10 in/hr
It =ΔH(60r)
ΔT(r + 2Havg)
ΔH = Change in water head height over the time interval = 1.3 in
r = Test hole radius = 4 in
ΔT = Time interval = 30 min
Havg= Average water height over time interval=12(Ho + Hf)/2 = 23.58 in
By:HP Date:Sep-23
1.90
Project Name:
0:30 2.04 1.90 1.68 18
1 0:30 2.06 1.95 1.32 23
Job Number:Date Drilled:
Drilling Method:
Test Hole Diameter (inches):
Gravel Pack:
10:20
PORCHET METHOD CALCULATION:
25
7
10:53
1.92 0.96 31
11:2411:54
11:55
12:25
1.44 21
1:00
1:30
1.97 1.32
0:30 2.00 1.88
5 0:30 2.00
0:30
1.20
Observed Percolation Rate:
12 0:30 2.02 1.91 1.32 23
Tested Infiltation Rate Using Porchet Method, It:
Infiltation Rate with Factor of Safety FS=2:
Values from Last Trial
23
2022253 Figure:1
0:30
4373 VIEWRIDGE AVENUE, SUITE BSAN DIEGO, CALIFORNIA 92123858.292.7575 Job No:
9 0:30 2.03 1.92 1.32 23
10 0:30 2.00 1.90 1.20 25
3:0511 0:30 2.00 1.89 1.32
Trial No.
2.00
10:51
Pipe Diameter (inches):
Time
9:199:49
9:502
8
23
3 0:30 2.05 1.94
6 0:30 2.00 1.89 1.32 23
4
10:21
2.0811:23
1.32 23
REPORT OF BOREHOLE PERCOLATION TESTING
Storm Water Infiltration
Valley Middle School Modernization
1645 Magnolia Avenue, Carlsbad, California 92008
3:05
3:35
1/29/20232022253Valley Middle School Modernization
8-inch Hollow Stem Auger
5.0
8
Y
3
1:332:032:04
2:342:35
12:2612:56
Jill ~-~ NOVA
Test Number:P-2Tested By:TPDate Tested:1/30/2023
Presoak Time:24 HR
Drilled Depth (feet):
Time Initial Water Final Water Change in Water Percolation
Interval, ΔT Height, Ho Height, Hf Height, ΔH Rate
(min)(ft)(ft)(in)(min/in)
83 min/in0.7 in/hr
0.05 in/hr
0.02 in/hr
It =ΔH(60r)
ΔT(r + 2Havg)
ΔH = Change in water head height over the time interval = 0.4 in
r = Test hole radius = 4 in
ΔT = Time interval = 30 min
Havg= Average water height over time interval=12(Ho + Hf)/2 = 28.50 in
By:HP Date:Sep-23
Valley Middle School Modernization
1645 Magnolia Avenue, Carlsbad, California 92008
4373 VIEWRIDGE AVENUE, SUITE BSAN DIEGO, CALIFORNIA 92123858.292.7575 Job No:2022253 Figure:2
15:21
Observed Percolation Rate:
Tested Infiltation Rate Using Porchet Method, It:
Infiltation Rate with Factor of Safety FS=2:
PORCHET METHOD CALCULATION:
Values from Last Trial
14:51
12 14:51 0:30 2.39 2.36 0.36 83
14:21
11 14:21 0:30 2.40 2.39 0.12 250
13:51
10 13:51 0:30 2.43 2.40 0.36 83
25013:21
9 13:21 0:30 2.46 2.43 0.36 83
0.24 12512:51
8 12:51 0:30 2.47 2.46 0.12
12:21
7 12:21 0:30 2.49 2.47
0.24 12511:51
6 11:51 0:30 2.50 2.49 0.12 250
11:21
5 11:21 0:30 2.52 2.50
0.36 8310:51
4 10:51 0:30 2.54 2.52 0.24 125
10:21
3 10:21 0:30 2.57 2.54
0.24 1259:51
2 9:51 0:30 2.58 2.57 0.12 250
Pipe Diameter (inches):3
Trial No.Time
1 9:21 0:30 2.60 2.58
Drilling Method:8-inch Hollow Stem Auger
5.0
Test Hole Diameter (inches):8
Gravel Pack:Y
REPORT OF BOREHOLE PERCOLATION TESTING
Storm Water Infiltration
Project Name:Valley Middle School ModernizationJob Number:2022253Date Drilled:1/29/2023
Jill ~-~ NOVA
Test Number:P-3Tested By:TPDate Tested:1/30/2023
Presoak Time:24 HR
Drilled Depth (feet):
Time Initial Water Final Water Change in Water Percolation
Interval, ΔT Height, Ho Height, Hf Height, ΔH Rate
(min)(ft)(ft)(in)(min/in)
50 min/in1.2 in/hr
0.08 in/hr
0.04 in/hr
It =ΔH(60r)
ΔT(r + 2Havg)
ΔH = Change in water head height over the time interval = 0.6 in
r = Test hole radius = 4 in
ΔT = Time interval = 30 min
Havg= Average water height over time interval=12(Ho + Hf)/2 = 26.70 in
By:HP Date:Sep-23
Valley Middle School Modernization
1645 Magnolia Avenue, Carlsbad, California 92008
4373 VIEWRIDGE AVENUE, SUITE BSAN DIEGO, CALIFORNIA 92123858.292.7575 Job No:2022253 Figure:3
15:45
Observed Percolation Rate:
Tested Infiltation Rate Using Porchet Method, It:
Infiltation Rate with Factor of Safety FS=2:
PORCHET METHOD CALCULATION:
Values from Last Trial
15:14
12 15:15 0:30 2.25 2.20 0.60 50
14:42
11 14:44 0:30 2.25 2.20 0.60 50
14:11
10 14:12 0:30 2.25 2.21 0.48 62
3613:41
9 13:41 0:30 2.25 2.22 0.36 83
0.72 4213:10
8 13:11 0:30 2.27 2.20 0.84
12:36
7 12:40 0:30 2.25 2.19
0.60 5012:05
6 12:06 0:30 2.25 2.18 0.84 36
11:34
5 11:35 0:30 2.23 2.18
0.36 8311:03
4 11:04 0:30 2.25 2.19 0.72 42
10:32
3 10:33 0:30 2.25 2.22
0.36 8310:01
2 10:02 0:30 2.25 2.12 1.56 19
Pipe Diameter (inches):3
Trial No.Time
1 9:31 0:30 2.25 2.22
Drilling Method:8-inch Hollow Stem Auger
5.0
Test Hole Diameter (inches):8
Gravel Pack:Y
REPORT OF BOREHOLE PERCOLATION TESTING
Storm Water Infiltration
Project Name:Valley Middle School ModernizationJob Number:2022253Date Drilled:1/29/2023
Jill ~-~ NOVA
Test Number:P-4Tested By:TPDate Tested:1/30/2023
Presoak Time:24 HR
Drilled Depth (feet):
Time Initial Water Final Water Change in Water Percolation
Interval, ΔT Height, Ho Height, Hf Height, ΔH Rate
(min)(ft)(ft)(in)(min/in)
8 min/in7.7 in/hr
0.64 in/hr
0.32 in/hr
It =ΔH(60r)
ΔT(r + 2Havg)
ΔH = Change in water head height over the time interval = 3.8 in
r = Test hole radius = 4 in
ΔT = Time interval = 30 min
Havg= Average water height over time interval=12(Ho + Hf)/2 = 22.08 in
By:HP Date:Sep-23
Valley Middle School Modernization
1645 Magnolia Avenue, Carlsbad, California 92008
4373 VIEWRIDGE AVENUE, SUITE BSAN DIEGO, CALIFORNIA 92123858.292.7575 Job No:2022253 Figure:4
15:47
Observed Percolation Rate:
Tested Infiltation Rate Using Porchet Method, It:
Infiltation Rate with Factor of Safety FS=2:
PORCHET METHOD CALCULATION:
Values from Last Trial
15:16
12 15:17 0:30 2.00 1.68 3.84 8
14:45
11 14:46 0:30 2.00 1.69 3.72 8
14:14
10 14:15 0:30 2.00 1.72 3.36 9
813:44
9 13:44 0:30 2.00 1.70 3.60 8
4.08 713:13
8 13:14 0:30 2.00 1.69 3.72
12:41
7 12:43 0:30 2.09 1.75
3.84 812:10
6 12:11 0:30 2.00 1.71 3.48 9
11:38
5 11:40 0:30 2.00 1.68
2.88 1011:08
4 11:08 0:30 2.05 1.70 4.20 7
10:35
3 10:38 0:30 2.15 1.91
3.60 810:00
2 10:05 0:30 2.18 1.94 2.88 10
Pipe Diameter (inches):3
Trial No.Time
1 9:30 0:30 2.00 1.70
Drilling Method:8-inch Hollow Stem Auger
5.0
Test Hole Diameter (inches):8
Gravel Pack:Y
REPORT OF BOREHOLE PERCOLATION TESTING
Storm Water Infiltration
Project Name:Valley Middle School ModernizationJob Number:2022253Date Drilled:1/29/2023
Jill ~-~ NOVA
Response to Geotechnical Report Review Comments Valley Middle School Modernization, Carlsbad, CA NOVA Project No. 2022253
September 8, 2023
ATTACHMENT 2
SEISMIC SHEAR-WAVE SURVEY
DVBE SBE SDVOSB SLBE
GEOTECHNICAL
MATERIALS
SPECIAL INSPECTION
4373 Viewridge Avenue, Suite B San Diego, CA 92123 P: 858.292.7575
www.usa-nova.com
24632 San Juan Avenue, Suite 100 Dana Point, CA 92629 P: 949.388.7710
Mr. Derrick Anderson January 24, 2020 Carlsbad Unified School District NOVA Project 2020006 6225 El Camino Real Carlsbad, California 92009 Subject: Seismic Shear-Wave Survey Valley Middle School Solar Project City of Carlsbad, California Dear Mr. Anderson: NOVA Services, Inc. (NOVA) is pleased to present the attached report for the above-referenced
project. The site-specific shear-wave data was requested by Carlsbad Unified School District
(CUSD) to aid in engineering in conformance with the seismic code, which has been updated in
the 2019 California Building Code and ASCE Standard 7-16.
This survey was conducted per the scope of work outlined in NOVA’s proposal dated January 6,
2020. Written notice to proceed was issued by CUSD on January 8, 2020.
The objective of the shear-wave survey is to assess the one-dimensional average shear-wave
velocity structure to a depth of at least 100 feet. This survey employed the multi-channel
analysis of surface waves (MASW) and microtremor array measurements (MAM) commonly
referred to as ReMi (Refraction Microtremor) surveys. Attachment 1 provides the scope,
location, and results of the seismic shear-wave survey.
NOVA appreciates the opportunity to be of continued service to Carlsbad Unified School District.
Should you have any questions regarding this proposal or other matters, please do not hesitate
to contact the undersigned at 858.292.7575.
Sincerely, NOVA Services, Inc.
_______________________
Melissa Stayner, PG, CEG Senior Geologist
Distribution: Addressee; Mr. Vinnie Aguelo, CUSD
Seismic Shear-Wave Survey Valley Middle School Solar, Carlsbad, CA NOVA Project 202006 January 24, 2020
ATTACHMENT 1
SEISMIC SHEAR-WAVE SURVEY BY
TERRA GEOSCIENCES
SEISMIC SHEAR-WAVE SURVEY CARLSBAD UNIFIED SCHOOL DISTRICT SOLAR PROJECT VALLEY MIDDLE SCHOOL
1645 MAGNOLIA AVENUE, CARLSBAD, CALIFORNIA Project No. 203356-1 January 17, 2020
Prepared for: NOVA Services, Inc. 4373 Stevens Avenue, Suite B Solona Beach, CA 92075
Consulting Engineering Geology & Geophysics -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
P.O. Box 1090, Loma Linda, CA 92354 • 909 796-4667
TERRA
GEOSCIENCES
Project No. 203356-1 Page 1
TERRA GEOSCIENCES
NOVA Services, Inc. 4373 Stevens Avenue, Suite B Solona Beach, CA 92075
Attention: Ms. Melissa Stayner, Senior Geologist Regarding: Seismic Shear-Wave Survey Carlsbad Unified School District Solar Project
Valley Middle School
1645 Magnolia Avenue, Carlsbad, California NOVA Project No. 2020006 INTRODUCTION
As requested, this firm has performed a seismic shear-wave survey using the multi-
channel analysis of surface waves (MASW) and microtremor array measurements (MAM) methods for the above-referenced site. The purpose of this survey was to assess the one-dimensional average shear-wave velocity structure, at various depth intervals, beneath the subject survey area, to a depth of at least 100 feet. Geologic
mapping by Tan and Kennedy (1996), indicates the local survey area to be mantled by
Pleistocene age terrace deposits, generally described as being comprised of poorly- to moderately-indurated, sandstone, siltstone, and conglomerate. The location of the seismic traverse has been approximated in the field using Google™
Earth Imagery (2020) and GPS coordinates, and then transferred to the provided site
plan, which is presented as the Seismic Line Location Map, Plate 1. This line is also shown on a Google™ Earth Imagery Map (see Plate 2) for clarity. Photographic views of the survey line are presented on Plate 3, for visual and reference purposes.
As authorized by you, the following services were performed during this study: Review of available pertinent published and unpublished geologic and geophysical
data in our files pertaining to the site. Performing a seismic surface-wave survey by a licensed State of California Professional
Geophysicist that included one traverse for shear-wave velocity analysis purposes. Preparation of this report, presenting the results of our findings with respect to the
shear-wave velocities of the subsurface earth materials. Accompanying Maps, Illustrations, and Appendices Plate 1 - Seismic Line Location Map Plate 2 - Google™ Earth Imagery Map Plate 3 - Survey Line Photographs
Appendix A - Shear-Wave Model and Data
Appendix B - References
Project No. 203356-1 Page 2
TERRA GEOSCIENCES
SUMMARY OF SHEAR-WAVE SURVEY
Methodology The fundamental premise of this survey uses the fact that the Earth is always in motion at various seismic frequencies. These relatively constant vibrations of the Earth’s surface are called microtremors, which are very small with respect to amplitude and are
generally referred to as background “noise” that contain abundant surface waves. These microtremors are caused by both human activity (i.e., cultural noise, traffic, factories, etc.) and natural phenomenon (i.e., wind, wave motion, rain, atmospheric pressure, etc.) which have now become regarded as useful signal information. Although these signals are generally very weak, the recording, amplification, and
processing of these surface waves has greatly improved by the use of technologically improved seismic recording instrumentation and recently developed computer software. For this application, we are mainly concerned with the Rayleigh wave portion of the seismic signals, which is also referred to as “ground roll” since the Rayleigh wave is the dominant component of ground roll.
For the purposes of this study, there are two ways that the surface waves were recorded, one being “active” and the other being “passive.” Active means that seismic energy is intentionally generated at a specific location relative to the survey spread and recording begins when the source energy is imparted into the ground (i.e., MASW
survey technique). Passive surveying, also called “microtremor surveying,” is where the seismograph records ambient background vibrations (i.e., MAM survey technique), with the ideal vibration sources being at a constant level. Longer wavelength surface waves (longer-period and lower-frequency) travel deeper and thus contain more information about deeper velocity structure and are generally obtained with passive survey
information. Shorter wavelength (shorter-period and higher-frequency) surface waves travel shallower and thus contain more information about shallower velocity structure and are generally collected with the use of active sources. For the most part, higher frequency active source surface waves will resolve the shallower velocity structure and lower frequency passive source surface waves will better resolve the deeper velocity
structure. Therefore, the combination of both of these surveying techniques provides a more accurate depiction of the subsurface velocity structure. The assemblage of the data that is gathered from these surface wave surveys results in development of a dispersion curve. Dispersion, or the change in phase velocity of the
seismic waves with frequency, is the fundamental property utilized in the analysis of surface wave methods. The fundamental assumption of these survey methods is that the signal wavefront is planar, stable, and isotropic (coming from all directions) making it independent of source locations and for analytical purposes uses the spatial autocorrelation method (SPAC). The SPAC method is based on theories that are able
to detect “signals” from background “noise” (Okada, 2003). The shear wave velocity (Vs) can then be calculated by mathematical inversion of the dispersive phase velocity of the surface waves which can be significant in the presence of velocity layering, which is common in the near-surface environment.
Project No. 203356-1 Page 3
TERRA GEOSCIENCES
Field Procedures One seismic shear-wave survey traverse (Seismic Line SW-1) was performed along an accessible area proximal to the proposed construction, as approximated on the Seismic
Line Location Map, as presented on Plate 1, and the Google™ Earth Imagery Map, as shown on Plate 2. For data collection, the field survey employed a twenty-four channel Geometrics StrataVisorTM NZXP model signal-enhancement refraction seismograph (Geometrics, 2004). This survey employed both active (MASW) and passive (MAM) source methods to ensure that both quality shallow and deeper shear-wave velocity
information was recorded (Park et al., 2005). Both the MASW and MAM surveys used
the same linear geometry array that consisted of a 161-foot long spread using a series of twenty-four 4.5-Hz geophones that were spaced at regular seven-foot intervals. For the MASW survey, the ground vibrations were recorded using a one second record length at a sampling rate of 0.5-milliseconds. Two seismic records were obtained using
a 25-foot offset from the beginning and end of the survey line utilizing a 16-pound
sledge-hammer as the energy source to produce the seismic waves. Each of these shot points used multiple hammer impacts (stacking) to improve the signal to noise ratio of the data.
The MAM survey did not require the introduction of any artificial seismic sources and
only background ambient noise was recorded. The ambient ground vibrations were recorded using a thirty-two second record length at a two-millisecond sampling rate with 20 separate seismic records being obtained for quality control purposes. The seismic-wave forms and associated frequency spectrum that were displayed on the
seismograph screen were used to assess the recorded seismic wave data for quality
control purposes in the field. The acceptable records were digitally recorded on the in-board seismograph computer and subsequently transferred to a flash drive so that they could be subsequently transferred to our office computer for analysis.
Data Reduction For analysis and presentation of the shear-wave profile and supportive illustrations, this study used the SeisImager/SWTM computer software program developed by Geometrics, Inc. (2016). Both the active (MASW) and passive (MAM) survey results were combined
for this analysis (Park et al., 2005). The combined results maximize the resolution and
overall depth range in order to obtain one high resolution Vs curve over the entire sampled depth range. These methods economically and efficiently estimate one-dimensional subsurface shear-wave velocities using data collected from standard primary-wave (P-wave) refraction surveys, however, it should be noted that surface
waves by their physical nature cannot resolve relatively abrupt or small-scale velocity
anomalies. Processing of the data proceeded by calculating the dispersion curve from the input data which subsequently created an initial shear-wave model based on the observed data. This initial model was then inverted in order to converge on the best fit of the initial model and the observed data, creating the final shear-wave model (Seismic
Line SW-1) as presented within Appendix A.
Project No. 203356-1 Page 4
TERRA GEOSCIENCES
Data Analysis Data acquisition went very smoothly and the quality was considered to be good. Analysis revealed that the average shear-wave velocity (“weighted average”) in the
upper 100 feet of the subject survey area was measured to be 1,284.4 feet per second, as shown on the Shear-Wave Model for Seismic Line SW-1, as presented within Appendix A. This average velocity classifies the underlying soils to that of Site Class “C” (Very Dense Soil and Soft Rock), which has a velocity range from 1,200 to 2,500 ft/sec (ASCE, 2017; Table 20.3-1). The “weighted average” velocity is computed from a
formula that is used by the ASCE (2017; Section 20.4, Equation 20.4-1) to determine the average shear-wave velocity for the upper 100 feet of the subsurface (V100). This formula is as follows:
V100’ = 100/[(t1/v1) + (t2/v2) + ...+ (tn/vn)] Where t1, t2, t3,...,tn, are the thicknesses for layers 1, 2, 3,...n, up to 100 feet, and v1, v2, v3,...,vn, are the seismic velocities (feet/second) for layers 1, 2, 3,...n. The shear-wave model displays these calculated layers and associated velocities (feet/second) to
the maximum obtained depth of 154 feet, where locally sampled (dark gray shaded area on shear-wave model represents the constrained data). The associated Dispersion Curves (for both the active and passive methods) which show the data quality and picks, along with the resultant combined dispersion curve
model are also included within Appendix A for reference purposes.
CLOSURE The field survey was performed by the undersigned on January 11, 2020, using "state of the art" geophysical equipment and techniques along a representative portion of the site proposed for the construction of the proposed solar carports. It is important to note that
the fundamental limitation for seismic surveys is known as nonuniqueness, wherein a specific seismic data set does not provide sufficient information to determine a single “true” earth model. Therefore, the interpretation of any seismic data set uses “best-fit” approximations along with the geologic models that appear to be most reasonable for the local area being surveyed.
It should be noted that when compared with traditional borehole shear-wave surveys, which use vertical body waves, the sources of error (if present) using horizontal surface waves for this project are not believed to be greater than 15 percent. Client should understand that when using the theoretical geophysical principles and techniques
discussed in this report, sources of error are possible in both the data obtained and, in the interpretation, and that the results of this survey may not represent actual subsurface conditions.
Project No. 203356-1 Page 5
TERRA GEOSCIENCES
These are all factors beyond Terra Geosciences control and no guarantees as to the results of this survey can be made. We make no warranty, either expressed or implied. If the client does not understand the limitations of this geophysical survey, additional input should be sought from the consultant.
Respectfully submitted,
TERRA GEOSCIENCES
Donn C. Schwartzkopf
Principal Geophysicist PGP 1002
SEISMIC LINE LOCATION MAP
Seismic shear-wave traverse SW-1 shown as red line. PROJECT NO. 203356-1 PLATE 1
GOOGLE™ EARTH IMAGERY MAP
Google™ Earth Imagery (2020); Seismic shear-wave traverse SW-1 shown as yellow line. PROJECT NO. 203356-1 PLATE 2
SURVEY LINE PHOTOGRAPHS
View looking southeasterly along Seismic Line SW-1.
View looking northwesterly along Seismic Line SW-1. PROJECT NO. 203356-1 PLATE 3
\
APPENDIX A
SHEAR-WAVE MODEL AND DATA
0
20
40
60
80
100
120
140
160
De
p
t
h
(
f
t
)
0 500 1000 1500 2000
S-wave velocity (ft/s)
S-wave velocity model (inverted) : 3356Final.rst Average Vs 100ft = 1284.4 ft/sec
1243
15.4
1308
38.5
1266
69.3
1306
107.8
1383
SEISMIC LINE SW-1
SHEAR-WAVE MODEL
700068006600
6400
6200
6000
5800
5600
5400
5200
5000
48004600
4400
4200
4000
3800
3600
3400
3200
3000
2800
26002400
2200
2000
1800
1600
1400
1200
1000
800
600
400 200
0
Ph
a
s
e
v
e
l
o
c
i
t
y
(
f
t
/
s
)
0 5 10 15 20 25 30 35 40
Frequency (Hz)
Dispersion curve : Combined.rst
SHEAR-WAVE MODEL SW-1
COMBINED DISPERSION CURVE
"' ""A.'"· A At f\/"IA ., ... ,,..r " ,rw, \N Y V V' I vvvrr' \ "-I \/ -' I V ,__,
\ -\/
,1,-; ~ ~ ,-._ ~ ,--_ ,--_ ,--_ ,--_ ,--_ ,-._ ~ ~ = '='~ --~ ~ ~ ~ ~ --
SEISMIC LINE SW-1
ACTIVE DISPERSION CURVE
Dispersion Curve: Active 203356.rst
0
2
3
4
5
6
7
8
9
10
11
12
~ 13 N E, 14 >-" C: 15 Q) ::, tr 16 Q) u:: 17
18
19
20
21
22
23
24
25
26
27
28
29
0 500 1000
Phase velocity (fVs)
1500 2000 2500 3000
SEISMIC LINE SW-1
PASSIVE DISPERSION CURVE
Dispersion Curve: Passive203356.rst
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
~ 7.0
N
E, 7.5
>-" C: 8.0 Q) ::, tr 8.5 Q) u::
9.0
9.5
10.0
10.5
11.0
11.5
12.0
12.5
13.0
13.5
14.0
14.5
15.0
500 1000
Phase velocity (ft/s)
1500 2000 2500 3000
APPENDIX B
REFERENCES
REFERENCES
American Society of Civil Engineers (ASCE), 2017, Minimum Design Loads and
Associated Criteria for Buildings and other Structures, ASCE Standard 7-16, 889pp. American Society for Testing and Materials, Intl. (ASTM), 2000, Standard Guide for Using the Seismic Refraction Method for Subsurface Investigation, Designation D 5777-00, 13 pp. California Building Standards Commission (CBSC), 2019, 2019 California Building Code, California Code of Regulations, Title 24, Part 2, Volume 2 of 2. California State Board for Geologists and Geophysicists, Department of Consumer Affairs, 1998, Guidelines for Geophysical Reports for Environmental and Engineering Geology, 5 pp. Crice, Douglas B., undated, Shear Waves, Techniques and Systems, Reprinted by Geometrics, Sunnyvale, California. Geometrics, Inc., 2004, StrataVisorTM NZXP Operation Manual, Revision B, San Jose, California, 234 pp. Geometrics, Inc., 2016, SeisImager/SW Analysis of Surface Waves, Pickwin Version
5.2.1.3. and WaveEq Version 4.0.1.0. Google™ Earth, 2020, http://earth.google.com/, Version 7.3.2.5776 (64-bit). Tan, S.S. and Kennedy, M.P., 1996, Geologic Maps of the Northwestern Part of San Diego County, California, California Division of Mines and Geology, Open-File Report 96-02, Scale 1: 24,000. Louie, J.N., 2001, Faster, Better: Shear-Wave Velocity to 100 Meters Depth From Refraction Microtremor Arrays, in, Bulletin of the Seismological Society of America, Volume 91, pp. 347-364. Okada, H., 2003, The Microtremor Survey Method, Society of Exploration Geophysicists, Geophysical Monograph Series Number 12, 135 pp. Park, C.B, Milner, R.D., Rynden, N., Xia, J., and Ivanov, J., 2005, Combined use of Active and Passive Surface Waves, in, Journal of Environmental and Engineering Geophysics, Volume 10, Issue 3, pp. 323-334.