HomeMy WebLinkAbout06244-12-01; Agua Hedionda Creek - Rancho Carlsbad; Agua Hedionda Creek - Rancho Carlsbad; 2002-09-05DNo
LIMITED
GEOTECHNICAL INVESTIGATION
AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
PREPARED FOR
RICK ENGINEERING COMPANY
SAN DIEGO, CALIFORNIA
SEPTEMBER 5, 2002
'FROM : Rick Engineering Company FAX NO. : 619 291 4165 Jan. 08 2003 03:56PM PI
RICKENGINEERING, COMPANY
Fax Transmittal
TO Dick Jacobs
Office Dick Jacobs Associates
From Roberta Cronquist
Date January 8, 2003
Time 9:15 am
Job Number 13182C
Receiving Fax No. (858) 720-0443
Pages to follow, including cover sheet 5_
Rick Engineering Company Fax No (619) 291-4165
Comments:
Dick.
Here is a copy of the GEOCON report addendum you requested.
Please let me know if you have any questions or need any additional information.
Thanks - Roberts
rcronquist@rickeng.com
(619)688-1454
cc:
5620 Friars Road • San Diego * California • 92110-2596 • (619)291-0707 • FAX {6!9)29M165 • www.rickeilgiiiccring.com
FROM : Rick Engineering Company FflX NO. : 619 291 4165 Jan. 08 2003 03:56PM P2
GEOCON
INCOHPOhATEil
GEOTECHNICAt CONSULTANTS
Project No. 06244-12-01
October 7, 2002
Rick Engineering Company
5620 Friars Road
San Diego, California 92110-2596
Attention: Mr. Tim Gabrielson
Subject: AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
ADDENDUM TO LIMITED GEOTECHNICAL INVESTIGATION
Reference: Limited Geotechnical Investigation, Agua Hedionda Creek, Rancho Carlsbad,
Carlsbad, California, prepared by Geocon Incorporated, dated September 5, 2002.
Gentlemen:
In accordance with your request, this letter is prepared to express our opinion with regard to the new
channel configurations. It is our understanding that the remedial grading of the channel would
involve lowering of the channel approximately 3 to 7 feel and creating a 3:1 (horizontal to vertical)
inclination for the channel side slopes.
In order to reduce the potential for surficial instability, it is recommended that the slopes be stabilized
by construction of stability fills. The recommended construction procedures arc as follows:
• The toe key for the slopes should be at least 10 feet wide and penetrate a minimum of 2 feet
below the bottom of the channel.
• It is understood that the grading and back cut excavations will be limited by the presence of
existing improvements and trees to be protected.
• The inclination of back cut slope will vary depending on the height and configuration of the
existing slopes but should maximize the width of the stability fill.
• To reduce the potential for back cut failure, it is recommended that the construction of the
stability fill be performed in segments. The length of the segments will be determined in the
field by the project soils engineer or geologist, based on the back cut inclination and
proximity of the existing improvements.
• The materials resulting from the excavation will consist of a range from cohesionlexs sand to
silty clay in saturated conditions. These soils are considered unsuitable in their present
6960 Flanders Drive. • Son Diego, California 92121-2974 • Tclephom. (858) 5584900 • Fox (858) 5584159
*
FROM : Rick Engineering Company FflX NO. : 619 291 4165 Jan. 08 2003 03:57PM P3
conditions to ba used in fill. Following mixing and moisture conditioning to approximately
optimum moisture content, the excavated soil can be placed and compacted in the stability fill
zone.
• The final slopes should be over built and trimmed back to the designed configurations.
• Excavations should not be left open overnight and should be backfilled as soon as practical.
We have modified Figure 3 of the referenced report to show the proposed grades along with the limits
of the recommended stability fill configurations. It should be noted that this letter is a supplement to
the referenced report. All other conclusions and recommendations presented in the referenced report
remain applicable.
If there are any questions regarding this report, or if we may be of further service, please contact the
undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
ASJJV:dmc
(2/Jcl) _^
(2/del) Rick Engineering Company
Attention: Mr, Dennis Bowling
(2/del) Dick Jacobs Associates
Attention: Mr. Dick Jacobs
Joseph ]. Vette!
GE 2401
Project No. 06244-12-01 -2-October 7,2002
FROM : Rick Engineering Company FfiX NO. : 619 291 4165 Jan. 08 2003 03:57PM P4
\
AGUAHEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
50'
vy L N
INCORPORATED
CROSS-SECTIONS A-A* AND B-B1
CEOTYCHNICAL CON'Sv'lTANTS
6960 FUNDERS DSIVE • SAN DIEGO. CALIFORNIA 9212J-297/
PHONE 858 358-6900 - FAX 858 S« 61SS>
PROJECT NO. 06244-12-01
FROM : Rick Engineering Company FAX NO. : 619 291 4165 Jan. 08 2003 03:58PM P5
A
70-
50'H
30'H
B
60'-,
40'H
20'-l
EXISTING GRADE
PROPOSED GRADE \A \\
EXISTING GRADE
PROPOSED GRADE
U in' j
SCALE : 1" = 20'
(HORiZ = VERT.)
GEOCON
INCORPOKATED
GEOTECHNICAL CONSULTANTS
Project No. 06244-12-01
September 5, 2002
Rick Engineering Company
5620 Friars Road
San Diego, California 92110-2596
Attention: Mr. Tim Gabrielson
Subject:AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
LIMITED GEOTECHNICAL INVESTIGATION
Gentlemen:
In accordance with your authorization and our proposal dated June 20, 2002, we have performed a
limited geotechnical investigation of subject project. The accompanying report presents the findings
of our study and our conclusions and recommendations pertaining to geotechnical and geologic
aspects of the project.
If there are any questions regarding this report, or if we may be of further service, please contact the
undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
C
AS:JJV:dmc
(4/del) Addressee
(I/del) Rick Engineering Company
Attention: Mr. Dennis Bowling
Joseph J. Vettel
GE 2401
6960 Flanders Drive • San Diego, California 92121-2974 • Telephone (858) 558-6900 • Fax (858) 558-6159
TABLE OF CONTENTS
1. PURPOSE AND SCOPE 1
2. SITE AND PROJECT DESCRIPTION 1
3. SOIL AND GEOLOGIC CONDITIONS 2
4. GROUNDWATER 2
5. GEOLOGIC HAZARDS 2
5.1 Faulting and Seismicity 2
5.2 Liquefaction Potential 3
6. CONCLUSIONS AND RECOMMENDATIONS 4
6.1 General 4
6.2 Soil and Excavation Characteristics 4
6.3 Grading 5
6.4 Construction Procedures 5
6.4.1 Alternative I (2:1 or steeper side slopes) 5
6.4.2 Alternative II (4:1 or flatter side slopes) 6
LIMITATIONS AND UNIFORMITY OF CONDITIONS
MAPS AND ILLUSTRATIONS
Figure 1, Vicinity Map
Figure 2, Geologic Map (Map Pocket)
Figure 3, Geologic Cross Section
Figures 4 -6, Slope Stability Analyses
APPENDIX A
LABORATORY TESTING
Figure A-l, Gradation Curves
APPENDIX B
RECOMMENDED GRADING SPECIFICATIONS
LIMITED GEOTECHNICAL INVESTIGATION
1. PURPOSE AND SCOPE
The purpose of this study was to provide preliminary geotechnical and geologic information for
planning of regrading of the Agua Hedionda Creek, in the city of Carlsbad, California. Soils and
geologic constraints to future site development were identified and mitigating measures are presented
where appropriate.
The scope of our services consisted of a site reconnaissance and geologic mapping by an engineering
geologist and performing limited laboratory testing on soil samples collected from the site. In
addition, we have reviewed published geologic maps and reports, in-house aerial photographs (United
States Department of Agriculture, 1953 Series) and previous geotechnical reports of the projects
within the vicinity.
2. SITE AND PROJECT DESCRIPTION
The subject portion of Agua Hedionda Creek traverses the Rancho Carlsbad mobile home park in a
general east-west direction in the city of Carlsbad, California (Vicinity Map, Figure 1). The
alignment is bounded by the Rancho Carlsbad Drive bridge on the east and the El Camino Real
bridge on the west. We understand that the project consists of regrading the creek to maintain the
100-year flood level within the channel. The proposed regrading includes lowering the bottom of the
channel 3 to 7 feet and creating a 2:1 (horizontal to vertical) inclination for the channel side slopes,
except where grading will be limited by the presence of existing trees to be preserved. In these areas,
the slopes are planned as steep as 1.5:1.
The vegetation at the site consists of weeds, landscaped plants and trees on the side slopes. The
stream flows east to west. The elevations at the base of the channel ranges from approximately
42 feet Mean Sea Level (MSL) near the Rancho Carlsbad Drive bridge on the east to approximately
34 feet near the El Camino Real bridge on the west. The existing side slopes are generally less than
10 feet in height with inclination of 2:1 or flatter.
The locations and descriptions of the site and proposed development are based on a site
reconnaissance and a review of a plan entitled Agua Hedionda Creek, Grading Exhibit, prepared by
Rick Engineering Company revised dated July 1, 2002. This map is used here as a basis for our
Geologic Map (see Figure 2, map pocket).
Project No. 06244-12-01 -1 - September 5, 2002
3. SOIL AND GEOLOGIC CONDITIONS
Our site reconnaissance and a review of the available reports indicate that the area is underlain by
relatively thick alluvium. In addition, the bottom of the channel is filled with younger alluvium or
steam deposits. The alluvial soils typically consist of loose to moderately dense, dark brown, silty, to
clayey sand. These materials are exposed along the face of the existing side slopes of the channel.
Geologic cross sections are presented on Figure 3.
The stream deposits consist of various soil types ranging from loose, grayish brown fine to coarse
cohesionless sand, to soft dark gray to black clayey silt and loose, dark brown silty sand.
These soils are currently saturated. The thickness of the stream deposits is unknown. During our site
visit, soil samples were obtained from three locations and tested for grain size distribution. The
results are presented in Appendix A. Due to low in-place density and saturated conditions, grading
using conventional equipment will be very difficult.
4. GROUNDWATER
Surface water was observed within the creek channel at the time of our site reconnaissance. As a
result, groundwater levels within the channel bottom are expected to be within a foot or two of the
ground surface.
5. GEOLOGIC HAZARDS
5.1 Faulting and Seismicity
Based on our site reconnaissance, and a review of published geologic maps and reports, the site is
not located on any known active or potentially active fault trace. The closest known active faults and
their Maximum Earthquake Magnitude are indicated in Table 5.1. In order to determine the distance
of known faults to the site, the computer program EQFAULT (Blake, 1989, updated 2000) was
utilized. The program calculates the distance from the site within a specified search radius to known
"active" California faults that have been digitized in an earthquake catalog.
The results of the deterministic analysis indicate that the Rose Canyon Fault Zone is the closest
source for potential ground motion occurring at the site. The Rose Canyon Fault is located
approximately 7 miles to the west and is considered the dominant source due to its proximity. The
Rose Canyon Fault is postulated as having the potential to generate a Maximum Earthquake
Magnitude of 6.9. The "maximum earthquake magnitude" is defined as the maximum earthquake that
appears capable of occurring under the presently known tectonic framework (California Geological
Project No. 06244-12-01 -2- September 5, 2002
Survey, formerly known as CDMG, Notes, Number 43). The estimated peak site acceleration based
on attenuation relationships developed by Sadigh, et al, (1997) was determined to be 0.30g for the
Rose Canyon Fault Zone. Presented on the following table are the faults most likely to subject the
site to ground shaking.
TABLE 5.1
Fault
Rose Canyon Fault Zone
Newport -Inglewood
Elsinore (Julian)
Coronado Bank
Elsinore (Glen Ivy)
Elsinore (Temecula)
Distance From
Site (miles)
7
8
22
23
34
37
Maximum
Earthquake Magnitude
6.9
6.9
7.1
7.4
6.8
6.8
Peak Site
Acceleration (g)
0.30
0.27
0.13
0.16
0.07
0.11
The site could be subjected to moderate to severe ground shaking in the event of an earthquake along
any of the faults listed in Table 6.1 or other faults in the southern California/northern Baja California
region. However, we do not consider the site to possess any greater seismic risk than that of the
surrounding developments. While listing of maximum earthquake magnitudes and peak accelerations
is useful for comparison of potential effects of fault activity in a region, other considerations are
important in seismic design, including the frequency and duration of motion and the soil conditions
underlying the site.
5.2 Liquefaction Potential
Liquefaction is a phenomenon in which loose, saturated and relatively cohesionless soil deposits lose
strength during strong ground motions. Primary factors controlling the development of liquefaction
include intensity and duration of ground motion, characteristics of subsurface soil, in situ stress
conditions and the depth to groundwater.
Due to the depth of the groundwater and the presence of loose cohesionless and soft soils,
liquefaction potential of the alluvial soils is considered to be high.
Project No. 06244-12-01 -3-September 5, 2002
6. CONCLUSIONS AND RECOMMENDATIONS
6.1 General
6.1.1 No geologic hazards or significantly adverse soil conditions were observed during the site
reconnaissance or noted in review of the referenced documents that, in our opinion, would
preclude the re-construction of the channel, provided the recommendations of this report
are followed.
6.1.2 The Grading Exhibit shows that the bottom of the channel will be lowered between
approximately 3 to 7 feet with 2:1 (horizontal to vertical) side slopes. The slope at certain
locations will be steeper due to the presence of trees.
6.1.3 The Grading Exhibit also shows that the proposed bottom elevation of the creek will be
approximately 3 feet below the El Camino Real bridge flow line. Therefore, water will be
ponding within the western portion of the creek. This situation may have a significant
impact on the stability of the side slopes.
6.1.4 The site is underlain by stream deposits and deep alluvium. In general, the materials
exposed at the bottom of the channel (stream deposits) are variable in nature, consisting of
cohesionless sands to clayey silts in a saturated state. This will make the grading with
conventional methods and equipments difficult.
6.1.5 Groundwater is currently within 1 to 2 feet of the existing channel insert, and is considered
to be a constraint to project development.
6.2 Soil and Excavation Characteristics
6.2.1 The prevailing soil conditions are anticipated to vary from "very low" expansive sands to
"medium" to "high" expansive silty clays.
6.2.2 In general, the on-site soil can be excavated with a moderate effort using conventional
heavy-duty grading equipment. However, saturated conditions may require special
equipment or handling methods.
Project No. 06244-12-01 - 4 - September 5, 2002
6.3 Grading
6.3.1 All grading should be performed in accordance with the Recommended Grading
Specifications contained in Appendix B. Where the recommendations of Appendix B conflict
with this report, the recommendations of this report should take precedence.
6.3.2 Prior to commencing grading, a preconstruction conference should be held at the site with
the owner or developer, grading contractor, civil engineer, and geotechnical engineer in
attendance. Special soil handling and the grading plans can be discussed at that time.
6.4 Construction Procedures
6.4.1 Alternative I (2:1 or steeper side slopes)
6.4.1.1 Re-grading the channel to the currently proposed configuration will require extensive
dewatering. Prior to the start of grading operations the groundwater level should be
lowered by diverting the stream flow outside of the channel or other approved methods.
The contractor is responsible to provide proper methods for dewatering. The grading
operations may start when groundwater is lowered to at least 3 feet below the deepest
excavations.
6.4.1.2 Our slope stability analysis for the proposed excavated slopes indicate that the side slopes
will posses an adequate factor of safety against deep seated failures (Figure 4). However,
they may be susceptible to progressive surficial failures (Figure 5). Therefore, it is
recommended that the side slopes be overexcavated and replaced with properly compacted
fill. The toe key for the proposed slopes should be at least 10 feet wide and 2 feet below
the bottom of the channel. Reconstruction of the slope adjacent to existing homes or
improvements should be performed in segments or slots, to reduce the potential for slope
failure and resultant damage. The width of the segments or slots should be evaluated
during construction by the geotechnical engineer.
6.4.1.3 The slopes should be brought to final grade elevations with structural fill compacted in
layers. In general, soils native to the site are suitable for re-use as fill provided adequate
moisture conditioning is performed. Following excavation, these soils need to be moisture
conditioned and mixed to approximately optimum moisture content before being used as
fill. Layers of fill should be no thicker than will allow for adequate bonding and
compaction. All fill, including backfill and scarified ground surfaces, should be compacted
to at least 90 percent of maximum dry density and slightly above optimum moisture
content, in accordance with ASTM Test Procedure D 1557-00.
Project No. 06244-12-01 - 5 - September 5, 2002
6.4.1.4 As an alternative to the construction of the stability fills, as discussed above, the excavated
side slopes should be covered and protected by using rip rap or synthetic measures such as
"Three Dimensional Geocells" or equivalent.
6.4.2 Alternative II (4:1 or flatter side slopes)
6.4.2.1 As an alternative to the proposed grading configurations, the side slopes may be graded to
an inclination of 4:1 (horizontal to vertical) or flatter. Surficial slope stability analysis
indicates that these slopes will have a factor of safety in excess of 1.5 for a maximum
height of 20 feet (Figure 6).
6.4.2.2 In lieu of dewatering and conventional grading operations other methods for excavation
such as dredging should be taken into consideration.
Project No. 06244-12-01 -6- September 5, 2002
LIMITATIONS AND UNIFORMITY OF CONDITIONS
1. The recommendations of this report pertain only to the site investigated and are based upon
the assumption that the soil conditions do not deviate from those disclosed in the
investigation. If any variations or undesirable conditions are encountered during
construction, or if the proposed construction will differ from that anticipated herein, Geocon
Incorporated should be notified so that supplemental recommendations can be given. The
evaluation or identification of the potential presence of hazardous materials was not part of
the scope of services provided by Geocon Incorporated.
2. This report is issued with the understanding that it is the responsibility of the owner, or of his
representative, to ensure that the information and recommendations contained herein are
brought to the attention of the architect and engineer for the project and incorporated into the
plans, and the necessary steps are taken to see that the contractor and subcontractors carry
out such recommendations in the field.
3. The findings of this report are valid as of the present date. However, changes in the conditions
of a property can occur with the passage of time, whether they be due to natural processes or
the works of man on this or adjacent properties. In addition, changes in applicable or
appropriate standards may occur, whether they result from legislation or the broadening of
knowledge. Accordingly, the findings of this report may be invalidated wholly or partially by
changes outside our control. Therefore, this report is subject to review and should not be relied
upon after a period of three years.
Project No. 06244-12-01 September 5, 2002
SOURCE : 2002 THOMAS BROTHERS MAP
SAN DIEGO COUNTY, CALIFORNIA
REPRODUCED WITH PERMISSION GRANTED BY THOMAS BROTHERS MAPS.
THIS MAP IS COPYRIGHTED BY THOMAS BROS. MAPS. IT IS UNLAWFUL TO COPY
OR REPRODUCE ALL OR ANY PART THEREOF, WHETHER FOR PERSONAL USE OR
RESALE, WITHOUT PERMISSION NO SCALE
GEOCON
INCORPORATED
GEOTECHNICAL CONSULTANTS
6960 FLANDERS DRIVE - SAN DIEGO, CALIFORNIA 92121-2974
PHONE 858 558-6900 - FAX 858 558-6159
VICINITY MAP
AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
AS/TA DSK/EOOOD DATE 09-05-2002 [PROJECT NO. 06244-12-01 FIG. 1
1VICMAP
60-
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o
Z40-\
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20—'
B
60-i
~50-
°40-
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UJ
30-
20 -1
AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
GEOCON
INCORPORATED
GEOTECHNICAL CONSULTANTS
6960 FLANDERS DRIVE • SAN DIEGO, CALIFORNIA 92121 - 2974
PHONE 858 558-6900 • FAX 858 558-6159
PROJECT NO. 06244-12-01
FIGURE 3
DATE 09-05-2002
E/2002/6244_ASl.DWG/<,ml
PROJECT NO. 06244-12-01
ASSUMED CONDITIONS:
Slope Height
Slope Inclination
Total Unit Weight of Soil
Angle of Internal Friction
Apparent Cohesion
No Seepage Forces
H = 20 feet
2:1 (Horizontal:Vertical)
Yt = 130 pounds per cubic foot
<)> = 20 degrees
C = 200 pounds per square foot
ANALYSIS:
Equation (3-3), Reference 1
Equation (3-2), Reference 1
Calculated Using Eq. (3-3)
Determined Using Figure 10, Reference 2
Factor of Safety Calculated Using Eq. (3-2)
REFERENCES:
(1) Janbu, N., Stability Analysis of Slopes with Dimensionless Parameters, Harvard Soil Mechanics,
Series No. 46, 1954.
(2) Janbu, N., Discussion of J. M. Bell, Dimensionless Parameters for Homogeneous Earth Slopes,
Journal of Soil Mechanics and Foundation Design, No. SM6, November 1967.
SLOPE STABILITY ANALYSIS FOR 2:1 SLOPES
AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
FIGURE 4
PROJECT NO. 06244-12-01
ASSUMED CONDITIONS:
Slope Height
Depth of Saturation
Slope Inclination
Slope Angle
Unit Weight of Water
Total Unit Weight of Soil
Angle of Internal Friction
Apparent Cohesion
Slope saturated to vertical depth Z below slope face.
Seepage forces parallel to slope face
ANALYSIS:
FS =
H
Z
2:1
i
Yw
Yt
20
3 feet
(Horizontal :Vertical)
= 26.5 degrees
= 62.4
= 130
= 20
= 200
pounds per cubic foot
pounds per cubic foot
degrees
pounds per square foot
ytZsinicosi = 1.31
REFERENCES:
(1) Haefeli, R. The Stability of Slopes Acted Upon by Parallel Seepage, Proc. Second International
Conference, SMFE, Rotterdam, 1948, 1, 57-62.
(2) Skempton, A. W., and F. A. Delory, Stability of Natural Slopes in London Clay, Proc. Fourth
International Conference, SMFE, London, 1957, 2, 378-81.
SURFICIAL SLOPE STABILITY ANALYSIS FOR 2:1 SLOPES
AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
FIGURE 5
PROJECT NO. 06244-12-01
ASSUMED CONDITIONS:
Slope Height
Depth of Saturation
Slope Inclination
Slope Angle
Unit Weight of Water
Total Unit Weight of Soil
Angle of Internal Friction
Apparent Cohesion
Slope saturated to vertical depth Z below slope face.
Seepage forces parallel to slope face
ANALYSIS:
FS =
H
Z
4:1
i
Yw
Yt
= Infinite
3 feet
(Horizontal: Vertical)
= 14 degrees
62.4
130
20
200
pounds per cubic foot
pounds per cubic foot
degrees
pounds per square foot
Z sin i cos i
= 2.9
REFERENCES:
(1) Haefeli, R. The Stability of Slopes Acted Upon by Parallel Seepage, Proc. Second International
Conference, SMFE, Rotterdam, 1948, 1, 57-62.
(2) Skempton, A. W., and F. A. Delory, Stability of Natural Slopes in London Clay, Proc. Fourth
International Conference, SMFE, London, 1957, 2, 378-81.
SURFICIAL SLOPE STABILITY ANALYSIS FOR 4:1 SLOPES
AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
FIGURE 6
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APPENDIX
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APPENDIX A
During our site reconnaissance, three samples were obtained from the bottom of the channel for
laboratory testing. The results of the grain size analysis are presented on Figure A-l.
Project No. 06244-12-01 September 5, 2002
PROJECT NO. 06244-12-01
1003
90
80
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MEDIUM FINE SILT OR CLAY
U. S. STANDARD SIEVE SIZE
16 30 500 | 20 40 60 100 200
^ 1
^5
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GRAIN SIZE IN MILLIMETERS
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SAMPLE
TP-1
TP-2
TP-3
Depth (ft)
0.0
0.0
0.0
CLASSIFICATION
(SP) Gray, fine to coarse SAND
(SC) Black to dark gray, Clayey SAND
(SM) Dark brown, Silty SAND
fATWC LL PL PI
GRADATION CURVE
AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
RCARL Figure A-1
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APPENDIX
APPENDIX B
RECOMMENDED GRADING SPECIFICATIONS
FOR
AGUA HEDIONDA CREEK
RANCHO CARLSBAD
CARLSBAD, CALIFORNIA
PROJECT NO. 06244-12-01
>*•»
RECOMMENDED GRADING SPECIFICATIONS
1. GENERAL
1.1. These Recommended Grading Specifications shall be used in conjunction with the
Geotechnical Report for the project prepared by Geocon Incorporated. The recom-
mendations contained in the text of the Geotechnical Report are a part of the earthwork and
grading specifications and shall supersede the provisions contained hereinafter in the case
of conflict.
1.2. Prior to the commencement of grading, a geotechnical consultant (Consultant) shall be
employed for the purpose of observing earthwork procedures and testing the fills for
substantial conformance with the recommendations of the Geotechnical Report and these
specifications. It will be necessary that the Consultant provide adequate testing and
observation services so that he may determine that, in his opinion, the work was performed
in substantial conformance with these specifications. It shall be the responsibility of the
Contractor to assist the Consultant and keep him apprised of work schedules and changes
so that personnel may be scheduled accordingly.
1.3. It shall be the sole responsibility of the Contractor to provide adequate equipment and
methods to accomplish the work in accordance with applicable grading codes or agency
ordinances, these specifications and the approved grading plans. If, in the opinion of the
Consultant, unsatisfactory conditions such as questionable soil materials, poor moisture
condition, inadequate compaction, adverse weather, and so forth, result in a quality of work
not in conformance with these specifications, the Consultant will be empowered to reject
the work and recommend to the Owner that construction be stopped until the unacceptable
conditions are corrected.
2. DEFINITIONS
2.1. Owner shall refer to the owner of the property or the entity on whose behalf the grading
work is being performed and who has contracted with the Contractor to have grading
performed.
2.2. Contractor shall refer to the Contractor performing the site grading work.
2.3. Civil Engineer or Engineer of Work shall refer to the California licensed Civil Engineer
or consulting firm responsible for preparation of the grading plans, surveying and verifying
as-graded topography.
GI rev. 07/02
2.4. Consultant shall refer to the soil engineering and engineering geology consulting firm
retained to provide geotechnical services for the project.
2.5. Soil Engineer shall refer to a California licensed Civil Engineer retained by the Owner,
who is experienced in the practice of geotechnical engineering. The Soil Engineer shall be
responsible for having qualified representatives on-site to observe and test the Contractor's
work for conformance with these specifications.
2.6. Engineering Geologist shall refer to a California licensed Engineering Geologist retained
by the Owner to provide geologic observations and recommendations during the site
grading.
2.7. Geotechnical Report shall refer to a soil report (including all addenda) which may include
a geologic reconnaissance or geologic investigation that was prepared specifically for the
development of the project for which these Recommended Grading Specifications are
intended to apply.
3. MATERIALS
3.1. Materials for compacted fill shall consist of any soil excavated from the cut areas or
imported to the site that, in the opinion of the Consultant, is suitable for use in construction
of fills. In general, fill materials can be classified as soil fills, soil-rock fills or rock fills, as
defined below.
3.1.1. Soil fills are defined as fills containing no rocks or hard lumps greater than 12
inches in maximum dimension and containing at least 40 percent by weight of
material smaller than 3/4 inch in size.
3.1.2. Soil-rock fills are defined as fills containing no rocks or hard lumps larger than 4
feet in maximum dimension and containing a sufficient matrix of soil fill to allow
for proper compaction of soil fill around the rock fragments or hard lumps as
specified in Paragraph 6.2. Oversize rock is defined as material greater than 12
inches.
3.1.3. Rock fills are defined as fills containing no rocks or hard lumps larger than 3 feet
in maximum dimension and containing little or no fines. Fines are defined as
material smaller than 3/4 inch in maximum dimension. The quantity of fines shall
be less than approximately 20 percent of the rock fill quantity.
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3.2. Material of a perishable, spongy, or otherwise unsuitable nature as determined by the
Consultant shall not be used in fills.
3.3. Materials used for fill, either imported or on-site, shall not contain hazardous materials as
defined by the California Code of Regulations, Title 22, Division 4, Chapter 30, Articles 9
and 10; 40CFR; and any other applicable local, state or federal laws. The Consultant shall
not be responsible for the identification or analysis of the potential presence of hazardous
materials. However, if observations, odors or soil discoloration cause Consultant to
suspect the presence of hazardous materials, the Consultant may request from the Owner
the termination of grading operations within the affected area. Prior to resuming grading
operations, the Owner shall provide a written report to the Consultant indicating that the
suspected materials are not hazardous as defined by applicable laws and regulations.
3.4. The outer 15 feet of soil-rock fill slopes, measured horizontally, should be composed of
properly compacted soil fill materials approved by the Consultant. Rock fill may extend to
the slope face, provided that the slope is not steeper than 2:1 (horizontal:vertical) and a soil
layer no thicker than 12 inches is track-walked onto the face for landscaping purposes.
This procedure may be utilized, provided it is acceptable to the governing agency, Owner
and Consultant.
3.5. Representative samples of soil materials to be used for fill shall be tested in the laboratory
by the Consultant to determine the maximum density, optimum moisture content, and,
where appropriate, shear strength, expansion, and gradation characteristics of the soil.
3.6. During grading, soil or groundwater conditions other than those identified in the
Geotechnical Report may be encountered by the Contractor. The Consultant shall be
notified immediately to evaluate the significance of the unanticipated condition
4. CLEARING AND PREPARING AREAS TO BE FILLED
4.1. Areas to be excavated and filled shall be cleared and grubbed. Clearing shall consist of
complete removal above the ground surface of trees, stumps, brush, vegetation, man-made
structures and similar debris. Grubbing shall consist of removal of stumps, roots, buried
logs and other unsuitable material and shall be performed in areas to be graded. Roots and
other projections exceeding 1-1/2 inches in diameter shall be removed to a depth of 3 feet
below the surface of the ground. Borrow areas shall be grubbed to the extent necessary to
provide suitable fill materials.
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4.2. Any asphalt pavement material removed during clearing operations should be properly
disposed at an approved off-site facility. Concrete fragments which are free of reinforcing
steel may be placed in fills, provided they are placed in accordance with Section 6.2 or 6.3
of this document.
4.3. After clearing and grubbing of organic matter or other unsuitable material, loose or porous
soils shall be removed to the depth recommended in the Geotechnical Report. The depth of
removal and compaction shall be observed and approved by a representative of the
Consultant. The exposed surface shall then be plowed or scarified to a minimum depth of
6 inches and until the surface is free from uneven features that would tend to prevent
uniform compaction by the equipment to be used.
4.4. Where the slope ratio of the original ground is steeper than 6:1 (horizontal:vertical), or
where recommended by the Consultant, the original ground should be benched in
accordance with the following illustration.
TYPICAL BENCHING DETAIL
Finish Grade
Remove All
Unsuitable Material
As Recommended By
Soil Engineer
~~~\
'Original Ground
c
Slope To Be Such That
Sloughing Or Sliding
Does Not Occur
See Note 1 See Note 2'
DETAIL NOTES:(1) Key width "B" should be a minimum of 10 feet wide, or sufficiently wide to
permit complete coverage with the compaction equipment used. The base of the
key should be graded horizontal, or inclined slightly into the natural slope.
(2) The outside of the bottom key should be below the topsoil or unsuitable surficial
material and at least 2 feet into dense formational material. Where hard rock is
exposed in the bottom of the key, the depth and configuration of the key may be
modified as approved by the Consultant.
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4.5. After areas to receive fill have been cleared, plowed or scarified, the surface should be
disced or bladed by the Contractor until it is uniform and free from large clods. The area
should then be moisture conditioned to achieve the proper moisture content, and compacted
as recommended in Section 6.0 of these specifications.
5. COMPACTION EQUIPMENT
5.1. Compaction of soil or soil-rock fill shall be accomplished by sheepsfoot or segmented-steel
wheeled rollers, vibratory rollers, multiple-wheel pneumatic-tired rollers, or other types of
acceptable compaction equipment. Equipment shall be of such a design that it will be
capable of compacting the soil or soil-rock fill to the specified relative compaction at the
specified moisture content.
5.2. Compaction of rock fills shall be performed in accordance with Section 6.3.
6. PLACING, SPREADING AND COMPACTION OF FILL MATERIAL
6.1. Soil fill, as defined in Paragraph 3.1.1, shall be placed by the Contractor in accordance with
the following recommendations:
6.1.1. Soil fill shall be placed by the Contractor in layers that, when compacted, should
generally not exceed 8 inches. Each layer shall be spread evenly and shall be
thoroughly mixed during spreading to obtain uniformity of material and moisture
in each layer. The entire fill shall be constructed as a unit in nearly level lifts.
Rock materials greater than 12 inches in maximum dimension shall be placed in
accordance with Section 6.2 or 6.3 of these specifications.
6.1.2. In general, the soil fill shall be compacted at a moisture content at or above the
optimum moisture content as determined by ASTM D1557-00.
6.1.3. When the moisture content of soil fill is below that specified by the Consultant,
water shall be added by the Contractor until the moisture content is in the range
specified.
6.1.4. When the moisture content of the soil fill is above the range specified by the
Consultant or too wet to achieve proper compaction, the soil fill shall be aerated by
the Contractor by blading/mixing, or other satisfactory methods until the moisture
content is within the range specified.
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6.1.5. After each layer has been placed, mixed, and spread evenly, it shall be thoroughly
compacted by the Contractor to a relative compaction of at least 90 percent.
Relative compaction is defined as the ratio (expressed in percent) of the in-place
dry density of the compacted fill to the maximum laboratory dry density as
determined in accordance with ASTM D1557-00. Compaction shall be continuous
over the entire area, and compaction equipment shall make sufficient passes so that
the specified minimum relative compaction has been achieved throughout the
entire fill.
6.1.6. Soils having an Expansion Index of greater than 50 may be used in fills if placed at
least 3 feet below finish pad grade and should be compacted at a moisture content
generally 2 to 4 percent greater than the optimum moisture content for the material.
6.1.7. Properly compacted soil fill shall extend to the design surface of fill slopes. To
achieve proper compaction, it is recommended that fill slopes be over-built by at
least 3 feet and then cut to the design grade. This procedure is considered
preferable to track-walking of slopes, as described in the following paragraph.
6.1.8. As an alternative to over-building of slopes, slope faces may be back-rolled with a
heavy-duty loaded sheepsfoot or vibratory roller at maximum 4-foot fill height
intervals. Upon completion, slopes should then be track-walked with a D-8 dozer
or similar equipment, such that a dozer track covers all slope surfaces at least
twice.
6.2. Soil-rock fill, as defined in Paragraph 3.1.2, shall be placed by the Contractor in accordance
with the following recommendations: \ r> I S I ,1 ••> "4
/ *> " O* ~
6.2.1. Rocks larger than 12 inches but less than 4 feet in maximum dimension may be
incorporated into the compacted soil fill, but shall be limited to the area measured
15 feet minimum horizontally from the slope face and 5 feet below finish grade or
3 feet below the deepest utility, whichever is deeper.
6.2.2. Rocks or rock fragments up to 4 feet in maximum dimension may either be
individually placed or placed in windrows. Under certain conditions, rocks or rock
fragments up to 10 feet in maximum dimension may be placed using similar
methods. The acceptability of placing rock materials greater than 4 feet in
maximum dimension shall be evaluated during grading as specific cases arise and
shall be approved by the Consultant prior to placement.
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6.2.3. For individual placement, sufficient space shall be provided between rocks to allow
for passage of compaction equipment.
6.2.4. For windrow placement, the rocks should be placed in trenches excavated in
properly compacted soil fill. Trenches should be approximately 5 feet wide and 4
feet deep in maximum dimension. The voids around and beneath rocks should be
filled with approved granular soil having a Sand Equivalent of 30 or greater and
should be compacted by flooding. Windrows may also be placed utilizing an
"open-face" method in lieu of the trench procedure, however, this method should
first be approved by the Consultant.
6.2.5. Windrows should generally be parallel to each other and may be placed either
parallel to or perpendicular to the face of the slope depending on the site
geometry. The minimum horizontal spacing for windrows shall be 12 feet
center-to-center with a 5-foot stagger or offset from lower courses to next
overlying course. The minimum vertical spacing between windrow courses shall
be 2 feet from the top of a lower windrow to the bottom of the next higher
windrow.
6.2.6. All rock placement, fill placement and flooding of approved granular soil in the
windrows must be continuously observed by the Consultant or his representative.
6.3. Rock fills, as defined in Section 3.1.3., shall be placed by the Contractor in accordance with
the following recommendations:
6.3.1. The base of the rock fill shall be placed on a sloping surface (minimum slope of 2
percent, maximum slope of 5 percent). The surface shall slope toward suitable
subdrainage outlet facilities. The rock fills shall be provided with subdrains during
construction so that a hydrostatic pressure buildup does not develop. The
subdrains shall be permanently connected to controlled drainage facilities to
control post-construction infiltration of water.
6.3.2. Rock fills shall be placed in lifts not exceeding 3 feet. Placement shall be by rock
trucks traversing previously placed lifts and dumping at the edge of the currently
placed lift. Spreading of the rock fill shall be by dozer to facilitate seating of the
rock. The rock fill shall be watered heavily during placement. Watering shall
consist of water trucks traversing in front of the current rock lift face and spraying
water continuously during rock placement. Compaction equipment with
compactive energy comparable to or greater than that of a 20-ton steel vibratory
roller or other compaction equipment providing suitable energy to achieve the
GI rev. 07/02
required compaction or deflection as recommended in Paragraph 6.3.3 shall be
utilized. The number of passes to be made will be determined as described in
Paragraph 6.3.3. Once a rock fill lift has been covered with soil fill, no additional
rock fill lifts will be permitted over the soil fill.
6.3.3. Plate bearing tests, in accordance with ASTM Dl 196-93, may be performed in
both the compacted soil fill and in the rock fill to aid in determining the number of
passes of the compaction equipment to be performed. If performed, a minimum of
three plate bearing tests shall be performed in the properly compacted soil fill
(minimum relative compaction of 90 percent). Plate bearing tests shall then be
performed on areas of rock fill having two passes, four passes and six passes of the
compaction equipment, respectively. The number of passes required for the rock
fill shall be determined by comparing the results of the plate bearing tests for the
soil fill and the rock fill and by evaluating the deflection variation with number of
passes. The required number of passes of the compaction equipment will be
performed as necessary until the plate bearing deflections are equal to or less than
that determined for the properly compacted soil fill. In no case will the required
number of passes be less than two.
6.3.4. A representative of the Consultant shall be present during rock fill operations to
verify that the minimum number of "passes" have been obtained, that water is
being properly applied and that specified procedures are being followed. The
actual number of plate bearing tests will be determined by the Consultant during
grading. In general, at least one test should be performed for each approximately
5,000 to 10,000 cubic yards of rock fill placed.
6.3.5. Test pits shall be excavated by the Contractor so that the Consultant can state that,
in his opinion, sufficient water is present and that voids between large rocks are
properly filled with smaller rock material. In-place density testing will not be
required in the rock fills.
6.3.6. To reduce the potential for "piping" of fines into the rock fill from overlying soil
fill material, a 2-foot layer of graded filter material shall be placed above the
uppermost lift of rock fill. The need to place graded filter material below the rock
should be determined by the Consultant prior to commencing grading. The
gradation of the graded filter material will be determined at the time the rock fill is
being excavated. Materials typical of the rock fill should be submitted to the
Consultant in a timely manner, to allow design of the graded filter prior to the
commencement of rock fill placement.
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6.3.7. All rock fill placement shall be continuously observed during placement by
representatives of the Consultant.
7. OBSERVATION AND TESTING
7.1. The Consultant shall be the Owners representative to observe and perform tests during
clearing, grubbing, filling and compaction operations. In general, no more than 2 feet in
vertical elevation of soil or soil-rock fill shall be placed without at least one field density
test being performed within that interval. In addition, a minimum of one field density test
shall be performed for every 2,000 cubic yards of soil or soil-rock fill placed and
compacted.
7.2. The Consultant shall perform random field density tests of the compacted soil or soil-rock
fill to provide a basis for expressing an opinion as to whether the fill material is compacted
as specified. Density tests shall be performed in the compacted materials below any
disturbed surface. When these tests indicate that the density of any layer of fill or portion
thereof is below that specified, the particular layer or areas represented by the test shall be
reworked until the specified density has been achieved.
7.3. During placement of rock fill, the Consultant shall verify that the minimum number of
passes have been obtained per the criteria discussed in Section 6.3.3. The Consultant shall
request the excavation of observation pits and may perform plate bearing tests on the
placed rock fills. The observation pits will be excavated to provide a basis for expressing
an opinion as to whether the rock fill is properly seated and sufficient moisture has been
applied to the material. If performed, plate bearing tests will be performed randomly on
the surface of the most-recently placed lift. Plate bearing tests will be performed to provide
a basis for expressing an opinion as to whether the rock fill is adequately seated. The
maximum deflection in the rock fill determined in Section 6.3.3 shall be less than the
maximum deflection of the properly compacted soil fill. When any of the above criteria
indicate that a layer of rock fill or any portion thereof is below that specified, the affected
layer or area shall be reworked until the rock fill has been adequately seated and sufficient
moisture applied.
7.4. A settlement monitoring program designed by the Consultant may be conducted in areas of
rock fill placement. The specific design of the monitoring program shall be as
recommended in the Conclusions and Recommendations section of the project
Geotechnical Report or in the final report of testing and observation 'services performed
during grading.
GI rev. 07/02
7.5. The Consultant shall observe the placement of subdrains, to verify that the drainage devices
have been placed and constructed in substantial conformance with project specifications.
7.6. Testing procedures shall conform to the following Standards as appropriate:
7.6.1. Soil and Soil-Rock Fills:
7.6.1.1. Field Density Test, ASTM D1556-00, Density of Soil In-Place By the
Sand-Cone Method.
7.6.1.2. Field Density Test, Nuclear Method, ASTM D2922-96, Density of Soil and
Soil-Aggregate In-Place by Nuclear Methods (Shallow Depth).
7.6.1.3. Laboratory Compaction Test, ASTM D1557-00, Moisture-Density
Relations of Soils and Soil-Aggregate Mixtures Using 10-Pound Hammer
and 18-Inch Drop.
7.6.1.4. Expansion Index Test, ASTM D4829-95, Expansion Index Test.
7.6.2. Rock Fills
7.6.2.1. Field Plate Bearing Test, ASTM Dl 196-93 (Reapproved 1997) Standard
Method for Nonreparative Static Plate Load Tests of Soils and Flexible
Pavement Components, For Use in Evaluation and Design of Airport and
Highway Pavements.
8. PROTECTION OF WORK
8.1. During construction, the Contractor shall properly grade all excavated surfaces to provide
positive drainage and prevent ponding of water. Drainage of surface water shall be
controlled to avoid damage to adjoining properties or to finished work on the site. The
Contractor shall take remedial measures to prevent erosion of freshly graded areas until
such time as permanent drainage and erosion control features have been installed. Areas
subjected to erosion or sedimentation shall be properly prepared in accordance with the
Specifications prior to placing additional fill or structures.
8.2. After completion of grading as observed and tested by the Consultant, no further
excavation or filling shall be conducted except in conjunction with the services of the
Consultant.
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9. CERTIFICATIONS AND FINAL REPORTS
9.1. Upon completion of the work, Contractor shall furnish Owner a certification by the Civil
Engineer stating that the lots and/or building pads are graded to within 0.1 foot vertically of
elevations shown on the grading plan and that all tops and toes of slopes are within 0.5 foot
horizontally of the positions shown on the grading plans. After installation of a section of
subdrain, the project Civil Engineer should survey its location and prepare an as-built plan
of the subdrain location. The project Civil Engineer should verify the proper outlet for the
subdrains and the Contractor should ensure that the drain system is free of obstructions.
9.2. The Owner is responsible for furnishing a final as-graded soil and geologic report
satisfactory to the appropriate governing or accepting agencies. The as-graded report
should be prepared and signed by a California licensed Civil Engineer experienced in
geotechnical engineering and by a California Certified Engineering Geologist, indicating
that the geotechnical aspects of the grading were performed in substantial conformance
with the Specifications or approved changes to the Specifications.
•**
GI rev. 07/02