HomeMy WebLinkAboutBaker St_Geotechnical Entitlement Level Evaluation131 Calle Iglesia, Suite 200, San Clemente, CA 92672 (949) 369-6141 www.lgcgeotechnical.com
January 31, 2024 Project No. 23160-01
Mr. Trygg Danforth
Ecosystem Investment Partners
5550 Newbury Street, Suite B
Baltimore, Maryland 21209
Subject: Preliminary Geotechnical Subsurface Evaluation and Recommendations, Proposed
Approximate 65‐Acre Industrial Development, Baker Street, Lake Elsinore,
California
In accordance with your request, LGC Geotechnical, Inc. has performed a preliminary geotechnical
subsurface evaluation and recommendations for the proposed approximately 65-acre industrial
development located on Baker Street in the City of Lake Elsinore, California. The purpose of our study
was to evaluate the existing onsite geotechnical conditions and to confirm that the site can be developed
from a geotechnical perspective. This report presents the results of our evaluation and geotechnical
analysis and provides a summary of our conclusions and recommendations relative to the proposed
development of the site.
Should you have any questions regarding this report, please do not hesitate to contact our office. We
appreciate this opportunity to be of service.
Sincerely,
LGC Geotechnical, Inc.
Ryan Douglas, GE 3147 Barry Graham, CEG 2749
Project Engineer Project Geologist
RLD/BPG/BPP/amm
Distribution: (1) Addressee (electronic copy)
Project No. 23160‐01 Page i January 31, 2024
TABLE OF CONTENTS
Section Page
1.0 INTRODUCTION ...................................................................................................................................... 1
1.1 Purpose and Scope of Services ............................................................................................................... 1
1.2 Project Description ..................................................................................................................................... 1
1.3 Field Evaluation .......................................................................................................................................... 2
1.4 Laboratory Testing ..................................................................................................................................... 3
2.0 GEOTECHNICAL CONDITIONS ............................................................................................................. 5
2.1 Regional Geology ......................................................................................................................................... 5
2.2 Site Specific Geology .................................................................................................................................. 5
2.2.1 Undocumented Artificial Fill (afu)........................................................................................ 5
2.2.2 Topsoil/Colluvium (Qcol) ....................................................................................................... 5
2.2.3 Quaternary Alluvium (Map Symbol: Qal) .......................................................................... 6
2.2.4 Tertiary Silverado Formation (Map Symbol: Tsi) .......................................................... 6
2.3 Geologic Structure....................................................................................................................................... 6
2.4 Groundwater ................................................................................................................................................. 7
2.5 Preliminary Field Infiltration Testing ................................................................................................. 7
2.6 Seismicity and Faulting ............................................................................................................................ 8
2.6.1 Liquefaction and Dynamic Settlement ................................................................................. 9
2.6.2 Lateral Spreading ......................................................................................................................... 9
2.7 Rippability ..................................................................................................................................................... 9
2.8 Oversized Material .................................................................................................................................. 10
2.9 Expansive Soil Characteristics ........................................................................................................... 10
3.0 ENGINEERING ANALYSES .................................................................................................................. 11
3.1 Seismic Parameters for Structural Design .................................................................................... 11
3.2 Soil Shear Strength Parameters ........................................................................................................ 12
3.3 Slope Stability Analyses ........................................................................................................................ 13
3.4 Surficial Stability Analyses .................................................................................................................. 14
4.0 CONCLUSIONS ........................................................................................................................................ 15
5.0 PRELIMINARY RECOMMENDATIONS ............................................................................................ 17
5.1 Site Earthwork .......................................................................................................................................... 17
5.1.1 Site Preparation ......................................................................................................................... 17
5.1.2 Remedial Grading ...................................................................................................................... 18
5.1.3 Over-Excavation of Pads and Streets ................................................................................. 19
5.1.4 Temporary Excavations ......................................................................................................... 19
5.1.5 Removal Bottoms and Subgrade Preparation ................................................................ 20
5.1.6 Material for Fill ........................................................................................................................... 20
5.1.7 Fill Placement and Compaction ........................................................................................... 21
5.1.7.1 Oversized Placement ............................................................................................. 22
5.1.8 Trench and Retaining Wall Backfill and Compaction .................................................. 22
Project No. 23160‐01 Page ii January 31, 2024
5.1.9 Preliminary Shrinkage and Bulking .................................................................................. 23
5.2 Slope Stability ............................................................................................................................................ 24
5.2.1 Fill Slopes ..................................................................................................................................... 24
5.2.2 Cut Slopes ..................................................................................................................................... 24
5.2.3 Existing Native Slopes ............................................................................................................. 25
5.2.4 Slope Maintenance Guidelines ............................................................................................. 25
5.3 Preliminary Tieback Anchor Retaining Wall Design for Slope Stability Mitigation ...... 26
5.3.1 Testing of Tieback Anchors ................................................................................................... 26
5.4 Foundation Recommendations .......................................................................................................... 27
5.4.1 Preliminary Foundation Design Parameters ................................................................ 27
5.4.2 Slab Underlayment Guidelines ............................................................................................ 28
5.4.3 Shallow Foundation Maintenance .................................................................................... 28
5.5 Foundation Setback From Slopes ..................................................................................................... 29
5.6 Soil Bearing and Lateral Resistance ................................................................................................ 29
5.7 Lateral Earth Pressures for Retaining Walls ............................................................................... 30
5.8 Preliminary Soil Nail Wall Design Parameters ............................................................................. 32
5.9 Control of Surface Water and Drainage Control .......................................................................... 33
5.10 Preliminary Pavement Sections ........................................................................................................ 33
5.11 Preliminary Portland Cement Concrete Pavement Sections ................................................ 34
5.12 Soil Corrosivity .......................................................................................................................................... 35
5.13 Nonstructural Concrete Flatwork ...................................................................................................... 36
5.14 Subsurface Water Infiltration ............................................................................................................ 36
5.15 Geotechnical Plan Review .................................................................................................................... 37
5.16 Geotechnical Observation and Testing During Construction ................................................. 37
6.0 LIMITATIONS ......................................................................................................................................... 39
Project No. 23160‐01 Page iii January 31, 2024
LIST OF ILLUSTRATIONS, TABLES, & APPENDICES
Figures
Figure 1 – Site Location Map (Page 4)
Figure 2A – Retaining Wall Backfill Detail (Rear of Text)
Figure 2B – Retaining Wall Backfill Detail – 2:1 Backfill (Rear of Text)
Tables
Table 1 – Summary of Infiltration Testing (Page 7)
Table 2 – Structural Seismic Design Parameters (Page 12)
Table 3 – Soil Shear Strength Parameters (Page 13)
Table 4 – Estimated Shrinkage and Bulking (Page 23)
Table 5– Allowable Soil Bearing Pressures (Page 29)
Table 6 – Lateral Earth Pressures – Approved Select Sandy Material (Page 31)
Table 7 – Preliminary Asphalt Concrete Paving Section Options (Page 34)
Table 8 – Preliminary Portland Cement Concrete Pavement Section Options (Page 35)
Appendices
Appendix A – References
Appendix B – Boring Logs, Excavations by Others
Appendix C – Laboratory Test Results
Appendix D – Slope Stability & Geotechnical Seismic Analysis
Appendix E – Infiltration Testing Results
Appendix F – General Earthwork and Grading Specifications for Rough Grading
Sheets
Sheet 1 – Preliminary Geotechnical Map
Sheet 2 – Geotechnical Cross Sections
Project No. 23160‐01 Page 1 January 31, 2024
1.0 INTRODUCTION
1.1 Purpose and Scope of Services
This report presents the results of our preliminary geotechnical evaluation for the proposed
approximately 65-acre industrial development located along Baker Street in Lake Elsinore,
California (Figure 1).
The purpose of our study was to provide a preliminary geotechnical evaluation relative to the
proposed industrial development. As part of our scope, we have: 1) reviewed available
geotechnical background information including in-house regional geologic maps; 2) performed
a subsurface geotechnical evaluation in the area of the proposed development; 3) performed
laboratory testing of select soil samples obtained during our subsurface evaluation; 4)
incorporated field and laboratory data into our analysis; and 5) prepared this preliminary
geotechnical summary report presenting our findings, preliminary conclusions and
recommendations for the development of the proposed project.
The findings, conclusions, and recommendations presented herein should be considered
preliminary and will need to be confirmed/updated as part of a future 40-scale grading plan
review report. Additional fieldwork and laboratory testing may be required. It should be noted
that LGC Geotechnical does not provide environmental consulting services and did not address
the environmental conditions of the subject site.
1.2 Project Description
The subject property is located on an approximately 65-acre site along the southwest side of
Baker Street, in the city of Lake Elsinore, California (Figure 1). Site elevations range from
approximately 1,392 in the southwest portion of the site to approximately 1,260 in the northeast
portion of the site. The site is mostly undeveloped with one existing structure in the eastern
portion of the site. The site is covered by low lying vegetation and manmade (dirt) trails
throughout.
The proposed development will include grading and construction of two industrial buildings
totaling approximately 1,000,000 square feet, associated drive aisles, retaining walls, and parking
areas (RGA, 2023). The proposed grading will include cutting into the hillsides on the southwest
portion of the site. The proposed cut slopes will be up to approximately 70 feet tall. Proposed
slope inclinations will be at 2:1 (horizontal to vertical) inclinations or flatter. Retaining walls are
proposed along all sides of the site. One approximately 45-foot-tall retaining wall is proposed
along the southwest portion of the site (KWC, 2024). The proposed industrial buildings are
anticipated to be at-grade concrete tilt-up structures with estimated maximum column and
wall loads of approximately 150 kips and 10 kips per linear foot, respectively. Please note no
structural loads were provided to us at the time of this report.
The preliminary recommendations given in this report are based upon the provided
preliminary grading information and the estimated structural loads as indicated above.
We understand that the project plans are currently being developed at this time. LGC
Project No. 23160‐01 Page 2 January 31, 2024
Geotechnical should be provided with updated project plans and the actual structural
loads when they become available, in order to either confirm or modify the
recommendations provided herein. This may include, but is not limited to, additional
subsurface field work, laboratory testing, and analysis to provide a design level 40‐scale
grading plan review geotechnical report.
1.3 Field Evaluation
The field portion of our evaluation included excavation of three large-diameter borings, fourteen
small-diameter hollow-stem auger borings, and fourteen exploratory test pits.
Three large-diameter, bucket-auger borings (BA-1, BA-1B, and BA-2, ) were excavated on the site
by Big Johnny & Pam’s Drilling under subcontract to LGC Geotechnical (Sheet 1). The maximum
depth of the bucket-auger borings was approximately 100 feet below existing grade. The bucket-
auger borings were excavated to evaluate the geologic structure of the underlying bedrock
materials and to obtain samples for laboratory testing. Samples were obtained at select locations
for laboratory testing. The large-diameter boreholes were surface logged during excavation and
downhole logged by an engineering geologist in order to obtain structural geologic information.
Borings were subsequently backfilled with cuttings and tamped.
Fourteen exploratory hollow-stem borings (HS-1 through HS-8 and I-1 through I-6) were
drilled to depths ranging from approximately 3 to 50 feet below existing grades. An LGC
Geotechnical engineer observed the drilling operations, logged the borings, and collected soil
samples for laboratory testing. The borings were excavated using a track-mounted CME 75 drill
rig equipped with both a 6 and 8-inch-diameter hollow-stem auger. Driven soil samples were
collected by means of the Standard Penetration Test (SPT) and Modified California Drive (MCD)
sampler generally obtained at 2.5 to 5-foot vertical increments. The MCD is a split-barrel
sampler with a tapered cutting tip and lined with a series of 1-inch-tall brass rings. The SPT
sampler and MCD sampler were driven using a 140-pound automatic hammer falling 30 inches
to advance the sampler a total depth of 18 inches. The raw blow counts for each 6-inch
increment of penetration were recorded on the boring logs. Bulk samples were also collected and
logged at select depths for laboratory testing. At the completion of drilling, the borings were
backfilled with the native soil cuttings and tamped. Some settlement of the backfill soils may
occur over time.
Fourteen exploratory test pits (TP-1 through TP-14) were excavated utilizing a standard backhoe
with a 3-foot bucket in order to estimate removal depths, geologic materials, and obtain samples
for laboratory testing. An engineering geologist observed the operation, logged the geotechnical
test pits, and collected the soil samples. Subsequent to logging, the test pits were backfilled with
native soils and compacted using a compaction wheel. Some settlement of the backfill soils may
occur over time.
Infiltration testing was performed within five of the borings (I-2 through I-6) at depths ranging
from approximately 3 to 12 feet below existing grade. Please note that infiltration test I-1 was
abandoned due to groundwater that was encountered at a depth of approximately 11 feet,
prior to the design depth of the infiltration test being reached. Test well installation consisted of
placing a 3-inch diameter perforated PVC pipe in each excavated borehole and backfilling the
Project No. 23160‐01 Page 3 January 31, 2024
annulus with crushed rock including the placement of approximately 2 inches of crushed rock at
the bottom of each borehole. Infiltration testing was performed in accordance with guidelines set
forth by the County of Riverside (2011). The PVC pipes were removed, and the holes were
subsequently backfilled with native soils at the completion of testing.
The approximate locations of our borings and test pits are shown on the Preliminary
Geotechnical Map (Sheet 1). Boring and test pit logs are presented in Appendix B.
1.4 Laboratory Testing
Representative bulk and driven samples were retained for laboratory testing during our field
evaluation. Laboratory testing included in-situ moisture content and in-situ dry density, grain
size analysis, Atterberg Limits, expansion index, laboratory compaction, consolidation, direct
shear, R-value, and corrosion testing.
The following is a summary of the laboratory test results.
Dry density of the samples collected ranged from approximately 87 pounds per cubic foot
(pcf) to 125 pcf, with an average of 110 pcf. Field moisture contents ranged from
approximately 3 percent to 26 percent, with an average of 15 percent.
Five fines content and sieve analysis tests indicated fines content (passing No. 200 sieve)
ranging from 27 to 73 percent. According to the Unified Soils Classification System (USCS),
the tested samples are classified as “coarse-grained” and “fine-grained” soil.
Five Atterberg Limit (liquid limit and plastic limit) tests were performed. Results indicated
Plasticity Index values ranging from 22 to 41.
Two Expansion Index (EI) tests indicated EI values ranging from 71 to 99, corresponding
to “Medium” to “High” expansion potential.
Laboratory compaction testing of two bulk samples indicated a maximum dry density
ranging from 113.5 to 116.5 pcf with an optimum moisture content ranging from 12.0 to
14.0 percent.
One consolidation test was performed on select samples. The deformation versus vertical
stress plot is provided in Appendix C.
Four direct shear tests were performed on select relatively undisturbed and disturbed
samples. The plots are provided in Appendix C.
One R-value test performed on a representative bulk sample indicates an R-value of less
than 5. The R-value plot is provided in Appendix C.
Corrosion testing indicated soluble sulfate contents less than approximately 0.03 percent,
chloride contents ranging from 180 to 220 part per million (ppm), pH values ranging from
6.57 to 7.91 and minimum resistivity values ranging from 735 to 1240 ohm-cm.
A summary of the results is presented in Appendix C. The moisture and dry density test results
are presented on the boring logs in Appendix B.