HomeMy WebLinkAboutBLDG-2883-2023_STAMPED GEOTECHNICAL REPORT
Geotechnical Engineering Report
For
Proposed Detached Accessory Dwelling Unit
133 East Foothill Boulevard
San Luis Obispo, California
October 20, 2023
F-103345
Prepared For
Sterling Twisselman
By
Beacon Geotechnical, Inc.
P.O. Box 4814
Paso Robles, California 93447
02/27/2024November 1, 201 November 2, 201 November 6, 201 November 8, 201
REVIEWED FOR
CODE COMPLIANCE
City of San Luis Obispo
Building & Safety Division
October 20, 2023 F-103345
Sterling Twisselman
761 West Foothill Boulevard
San Luis Obispo, CA 93405
Project: Proposed Detached Accessory Dwelling Unit
133 East Foothill Boulevard
San Luis Obispo, California
Subject: Geotechnical Engineering Report
As authorized, we have performed a Geotechnical Study for the above
referenced project. The accompanying Geotechnical Engineering Report presents
the results of our subsurface exploration, laboratory-testing program and
conclusions and recommendations for geotechnical engineering aspects of
project design. Our services were performed using the standard of care ordinarily
exercised in this locality at the time this report was prepared.
Based on our study, it is our opinion that the site is suitable for the proposed
development from a geotechnical engineering standpoint provided the
recommendations of this report are successfully implemented.
We have appreciated this opportunity to be of service to you on this project.
Please call if you have any questions, or if we can be of further service.
Respectfully submitted,
Beacon Geotechnical, Inc.
Greg McKay
Project Manager
Copies: 3-Twisselman
1-File
Nicholas A. McClure
Geotechnical Engineer
October 20, 2023 F-103345
1
Contents
1 INTRODUCTION ....................................................................................... 2
1.1 Description................................................................................................. 2
2 SCOPE OF WORK ..................................................................................... 2
2.1 Purpose ..................................................................................................... 2
2.2 Report Contents ......................................................................................... 2
3 SITE SETTING .......................................................................................... 3
3.1 Location. .................................................................................................... 3
3.2 Site Description . ....................................................................................... 3
4 SITE CONDITIONS ................................................................................... 3
4.1 Soil Conditions ........................................................................................... 3
4.2 Groundwater .............................................................................................. 3
5 SEISMIC HAZARDS ................................................................................... 3
5.1 Nearby Faults ............................................................................................. 3
5.2 Liquefaction ............................................................................................... 4
5.3 Landslide Hazards ....................................................................................... 4
5.4 Seismic Design Parameters .......................................................................... 4
6 CONCLUSIONS AND RECOMMENDATIONS ................................................. 5
6.1 General Grading ......................................................................................... 5
6.2 Specific Site Development, Grading Pads, and Foundation Excavations ............ 6
6.3 Slope Construction ...................................................................................... 7
6.4 Utility Trenches .......................................................................................... 8
6.5 Structural Design – Foundations .................................................................. 8
6.6 Slabs on Grade ........................................................................................... 9
6.7 Structural Design – Lateral Resistance Parameters ........................................ 9
6.8 Structural Design – Settlement Considerations ............................................ 10
6.9 Structural Design – Retaining Walls ............................................................ 10
7 REFERENCES CITED ............................................................................... 11
8 ADDITIONAL SERVICES .......................................................................... 11
9 PROJECT LIMITATIONS AND UNIFORMITY OF CONDITIONS .................... 12
October 20, 2023 F-103345
2
1. INTRODUCTION
This report presents results of a Geotechnical Engineering Study performed for
the proposed detached accessory dwelling unit to be located in San Luis Obispo,
California.
1.1 Description
1.1.1. It should be noted that grading and foundation plans were not
provided for the purpose of this report. Prior to any construction, this
firm should review the grading and foundation plans to verify or
modify the recommendations offered herein. We anticipate that the
site will be developed by building at or near existing grade.
1.1.2. The proposed structure is assumed to be one (1) or two (2) stories of
wood framed construction.
1.1.3. Structural considerations for maximum wall loads of 1.75 kips per
square foot and maximum point loads of 22.0 kips were used as a
basis for the recommendations of this report. If actual loads vary
significantly from these assumed loads, Beacon Geotechnical, Inc.
should be notified as re-evaluation of the recommendations contained
herein may be required.
2 SCOPE OF WORK
2.1 The purpose of the geotechnical investigation that led to this report was to
evaluate the soil conditions of the site with respect to the proposed
development. These conditions include surface and subsurface soil types,
expansion potential, settlement potential, bearing capacity, and presence or
absence of subsurface water. The scope of our work included:
• Reconnaissance of the site.
• Drilling, sampling, and logging of two (2) borings to investigate soils and
groundwater conditions.
• Laboratory testing of soil samples obtained from subsurface exploration to
determine their physical and engineering properties.
• Geotechnical analysis of the data obtained.
• Consultation with owner representatives and design professionals.
• Preparation of this report.
2.2 Contained in the report are:
• Discussions on local soil and groundwater conditions.
• Results of laboratory and field tests.
• Conclusions and recommendations pertaining to site grading and
structural design.
October 20, 2023 F-103345
3
3 SITE SETTING
3.1 The site of the proposed development is located in San Luis Obispo,
California, with the approximate geographical coordinates 35°17’38.27” N
and 120°41’07.24” W. See the Vicinity Map in Appendix A.
3.2 The proposed building site is a relatively level back yard area.
4 SITE CONDITIONS
4.1 Soil Conditions
4.1.1 Evaluation of the subsurface indicates that soils are generally light
brown silty clayey sand overlain by brown silty clayey sand with gravel.
4.1.2 Soils encountered at approximate bearing depths should be designed
as Site Classification D in accordance with the local building code.
4.1.3 Expansion determination indicates that the bearing soils lie in the
“Low” range.
4.2 Groundwater
4.2.1 Groundwater was not encountered to a maximum depth of twenty (20)
feet.
5 SEISMIC HAZARDS
This portion of Central California is subject to significant seismic hazards from
moderate to large earthquake events. Ground shaking resulting from
earthquakes is the primary geologic hazard at the project site. Ground
displacement resulting from faulting is a potential hazard at or near faults.
5.1 Nearby Faults
5.1.1 The site does not lie within an Earthquake Fault Zone identified on a
State of California Earthquake Fault Zone Map.
5.1.2 Faults closest to the site, which would most affect the proposed
project:
Nearby Active Faults Approximate Distance (km) Magnitude MW
Los Osos Fault
San Luis Range Fault
Rinconada Fault
Hosgri Fault
San Andreas Fault Zone
3.4
12.6
13.4
23.1
58.8
6.9
7.1
7.5
7.3
8.0
October 20, 2023 F-103345
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5.2 Liquefaction
Earthquake-induced vibrations can be the cause of several significant
phenomena, including liquefaction in fine sands and silty sands. Liquefaction
results in a complete loss of strength and can cause structures to settle or even
overturn if it occurs in the bearing zone. If liquefaction occurs beneath sloping
ground, a phenomenon known as lateral spreading can occur. Liquefaction is
typically limited to the upper 50 feet of the subsurface soils and to soils that
have a relative density of less than 70%.
5.2.1 Based on the quality and conditions of the in-place soils and the
absence of groundwater in our boring explorations, it is our opinion
that the potential for liquefaction and/or lateral spreading is low at this
site.
5.3 Landslide Hazards
5.3.1 The site topography and exposed soil types indicate that the potential
for landslides is minimal at this site. Furthermore, no evidence of
previous landslides was observed at the site.
5.4 Seismic Design Parameters
The following estimated ground motion parameters have been established using
the methods outlined in the 2022 California Building Code with reference to the
acceleration contour maps provided by the U.S. Geological Survey (USGS) and
the National Earthquake Hazards Reduction Program (NEHRP-2015). These
ground motion parameters represent the Maximum Considered Earthquake
(MCE) spectral response of seismic events experiencing 5 percent damped
acceleration and having a 2 percent probability of exceedance within a 50-year
period.
2022 California Building Code Seismic Parameters
Parameter Value
Seismic Design Category D
Site Class D
Short Period Spectral Acceleration, Ss 1.035
1-second period spectral acceleration, S1 0.383
Short period site coefficient, Fa 1.086
1-second period site coefficient, Fv 1.917
Adjusted short period spectral acceleration, Sms 1.124
Adjusted 1-second period spectral acceleration, Sm1 0.734
Short period design spectral acceleration, SDS 0.750
1-second period design spectral acceleration, SD1 0.489
October 20, 2023 F-103345
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6 CONCLUSIONS AND RECOMMENDATIONS
The site is suitable for the proposed development from a geotechnical
engineering standpoint provided the recommendations contained herein are
properly implemented into the project.
6.1 General Grading
6.1.1 Grading, at a minimum, should conform to Chapter 18, and any
additional locally approved appendices relating to grading, of the 2022
California Building Code.
6.1.2 The existing ground surface should be initially prepared for grading by
removing all vegetation, trees, large roots, debris, non-complying fill,
and all other organic material. Voids created by removal of such
material should not be backfilled unless the underlying soils have been
observed by a representative of this firm.
6.1.3 The bottom of all excavations should be observed by a
representative of this firm prior to processing or placing fill.
6.1.4 Fill and backfill placed at near optimum moisture in layers with loose
thickness not greater than eight (8) inches should be compacted to a
minimum of 90% of maximum dry density obtainable by the ASTM D
1557 Test Method.
6.1.5 Import soils used to raise site grade should be equal to or better than
on-site soils in strength, expansion, and compressibility characteristics.
Import soils can be evaluated but will not be pre-qualified by the
geotechnical engineering firm. Final comments on the characteristics of
the import soils will be offered after the material is at the project site.
6.1.6 Due to the expansive soils present within the building area,
roof draining systems should be designed so that water is
collected and diverted into solid drain lines discharging into
an approved drainage area away from the structures.
6.1.7 Final site grade should be such that all water is permanently diverted
away from the structure and is not allowed to pond. The ground
immediately adjacent to the building shall be sloped 5% for a
minimum of ten (10) feet measured perpendicular to the face of the
wall. All diverted water is to be directed to an approved drainage.
Alternative grading methods can be found in 2022 California Building
Code Section 1804.4.
6.1.8 It should be noted that uniform soil moisture conditions around the
perimeter of the structure will help decrease the potential for
differential swelling and heaving associated with expansive soils. Post-
construction care should be taken to create long-term landscaping and
irrigation solutions that do not allow for frequent changes in soil
moisture content or irregular application of water around the perimeter
of the structure.
October 20, 2023 F-103345
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6.1.9 The above referenced site drainage conditions should be maintained
over the course of the life of the structure. Proper long-term
performance of the foundation and building pad may be compromised
if the surrounding site drainage and grading is adversely modified.
6.1.10 It is recommended that Beacon Geotechnical, Inc. be retained to
provide intermittent geotechnical engineering services during site
development, grading, and foundation construction phases of the work
to observe compliance with the design concepts, specifications, and
recommendations, and to allow design changes in the event that
subsurface conditions differ from those anticipated prior to the start of
construction.
6.1.11 Should soils become unstable during grading due to excessive
subsurface moisture, alternatives to correct instability may include
aeration or the use of gravels and/or geotextiles as stabilizing
measures. Recommendations for stabilization should be provided by
this firm as needed during construction.
6.1.12 Plans and specifications should be provided to Beacon Geotechnical,
Inc. prior to grading. Plans should include the grading plans, and
foundation details. Structural loads should be shown on the foundation
plans.
6.1.13 All water associated with drainage and runoff should not be discharged
onto slope faces. All outflow of drainage structures and drainage
facilities should be designed by the project Civil Engineer to minimize
erosion.
6.2 Specific Site Development, Grading Pads, and Foundation Excavations
6.2.1 Due to the presence of low density soils at shallow bearing depths,
overexcavation and recompaction of soils in the building area
(including covered deck areas) will be necessary to decrease the
potential for differential settlement and to provide more uniform
bearing conditions. Soils should be overexcavated to a depth of two
(2) feet below the bottom of footings, five (5) feet below existing
grade, through the brown topsoil (noted as soil type A1 in the boring
logs), or 75% of the deepest fill thickness, whichever is greater. The
over-excavation should extend to a distance of five (5) feet beyond the
building perimeter. The resulting surface should be scarified to a depth
of one (1) foot, moisture conditioned and recompacted to a minimum
of 90% of maximum dry density. The intent of these recommendations
is to provide a minimum of two (2) feet of compacted soils below the
bottom of all footings, and recompact the loose topsoil.
October 20, 2023 F-103345
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6.2.2 Any excavated material from foundation and septic or drainage
systems should be properly recompacted in accordance with all the
recommendations for engineered fill. Alternatively, excavated soil may
be hauled off site when adequate placement area is not available at
the project location.
6.2.3 Areas outside the building area to receive fill, exterior slabs-on-grade,
sidewalks, and paving should be overexcavated to a depth of one (1)
foot below finish subgrade or existing grade whichever is deeper. The
exposed surface should be scarified, moisture conditioned and
recompacted.
6.2.4 On-site soils may be used for fill once they are cleaned of all organic
material, rock, debris, and irreducible material larger than eight (8)
inches.
6.2.5 Although not encountered in our borings, should any trash, debris or
subsurface structures be encountered during grading, removals will be
necessary to adequate depths and horizontal limits as recommended
by this firm at the time of grading.
6.2.6 Grading inspections shall be performed in accordance with the 2022
California Building Code Table 1705.6. See Appendix B for project
specific grading observation requirements.
6.3 Slope Construction
6.3.1 All hillside grading and construction of fill slopes should conform to the
minimum standards listed in Chapter 18 of the 2022 California Building
Code. It is recommended that a representative of this firm review the
grading plans prior to grading and site development.
6.3.2 Fill slopes should be keyed and benched into firm natural ground when
the existing slope to receive fill is 10:1, horizontal to vertical, or
steeper. The keys should be tilted into the slope, should be a minimum
of one equipment width wide, and should extend a minimum of three
(3) feet deep at the outside edge.
6.3.3 Fill slopes should be overfilled, compacted, and cut back to planned
configurations. This will yield better compaction on the slope faces
than other methods.
6.3.4 Lined drainage swales and down drains should be provided at the tops
of all cut and fill slopes to divert drainage away from the slope faces.
6.3.5 Cut and fill slopes should not be constructed steeper than 2:1
(horizontal to vertical). Setbacks of structures from slopes should be
maintained as per the 2022 California Building Code.
October 20, 2023 F-103345
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6.4 Utility Trenches
6.4.1 Utility trench backfill should be governed by the provisions of this
report relating to minimum compaction standards. In general, service
lines inside of the property lines may be backfilled with native soils and
compacted to a minimum of 90% of maximum dry density. Backfill of
offsite service lines will be subject to the specifications of the
jurisdictional agency or this report, whichever is more stringent.
6.4.2 A representative of this firm is to monitor compliance with these
recommendations.
6.5 Structural Design – Foundations
6.5.1 Conventional interconnected continuous footings may be used for
support of the structure.
6.5.2 Footings should bear entirely into firm recompacted soils.
6.5.3 Based on the project expansive soil conditions, it is assumed that the
footings will extend a minimum of eighteen (18) inches below lowest
adjacent grade. The structural engineer of record may incorporate
additional and/or alternative means of mitigating the expansive soils
and should clearly state the design conditions on the project
foundation plans and details.
6.5.4 Conventional continuous footings may be designed based on an
allowable bearing value of 1750 psf.
6.5.5 Allowable bearing values are net (weight of footing and soils surcharge
may be neglected) and are applicable for dead plus reasonable live
loads.
6.5.6 Bearing values may be increased by one-third when transient loads
such as wind and/or seismicity are incorporated into designs using the
alternate load combinations in 2022 California Building Code Section
1605.3.2.
6.5.7 Lateral loads may be resisted by soils friction on floor slabs and
foundations and by passive resistance of the soils acting on foundation
stem walls. Lateral capacity is based on the assumption that any
required backfill adjacent to foundations and grade beams is properly
compacted.
6.5.8 For structures to be constructed above slopes, the outside faces at the
bottom of footings should provide a minimum horizontal distance of
ten (10) feet from the slope face.
6.5.9 Conventional continuous footings for buildings where the ground
surface slopes at 10:1, horizontal to vertical, or steeper should be
stepped so that both top and bottom are level.
October 20, 2023 F-103345
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6.5.10 Reinforcement of footings bottomed in soils in the “Low” expansion
range should be designed by the Project Structural Engineer to
properly resist the effects of the expansive soil. Additionally, soils
should be presaturated to 120% of optimum moisture content to a
depth of twenty-one (21) inches below lowest adjacent grade.
6.5.11 Foundation excavations should be observed by a
representative of Beacon Geotechnical, Inc. after excavation,
but prior to placing reinforcing steel or forms.
6.6 Slabs on Grade
6.6.1 Due to expansive soils present at the project, concrete slabs shall be a
minimum of four (4) inches thick, reinforced with a minimum of #3
bars spaced at eighteen (18) inches on center, each way.
6.6.2 Concrete slabs should be supported by compacted structural fill as
recommended earlier in this report.
6.6.3 Reinforcement dowels shall be provided at the connection between
concrete slabs on grade and continuous footings.
6.6.4 Slabs should be underlain with a minimum of four (4) inches of clean
and free draining sand. Areas where floor wetness would be
undesirable should be underlain with a 10mil moisture barrier to
reduce moisture transmission from the subgrade soils to the slab. The
membrane should be placed at mid-height in the clean sand.
6.6.5 Reinforcement and slab thickness should be determined by the Project
Structural Engineer.
6.6.6 Soils underlying slabs in the “Low” expansion range, as a minimum,
should be presaturated to 120% of optimum moisture content to a
depth of twenty-one (21) inches below lowest adjacent grade.
6.7 Structural Design – Lateral Resistance Parameters
6.7.1 Resistance to lateral loading may be provided by friction
acting on the base of foundations. A coefficient of friction of
0.34 may be applied to dead load forces. This value does not include a
factor of safety.
6.7.2 Passive resistance acting on the sides of foundation stems equal to
300 pcf of equivalent fluid weight may be included for resistance to
lateral load. This value does not include a factor of safety.
6.7.3 A one-third increase in the quoted passive value may be used when
considering transient loads such as wind and seismicity.
October 20, 2023 F-103345
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6.8 Structural Design – Settlement Considerations
6.8.1 Maximum expected settlements approximately 3/4 inches are
anticipated for foundations and floor slabs designed as recommended.
6.8.2 Differential settlement between adjacent load bearing members should
be less than one-half the total settlement.
6.8.3 The majority of settlement should occur during construction. Post
construction settlement should be minimal.
6.9 Structural Design – Retaining Walls
6.9.1 Conventional cantilever retaining walls bearing in soils prepared in
accordance with the “Grading Pads – Site Development and
Foundation Excavations” section of this report and backfilled with
compacted soils may be designed for the lateral pressures listed
below:
Active Case 40 pcf
At Rest Case 60 pcf
Passive Case 300 pcf
Max. Toe Pressure 1750 psf
Coefficient of Sliding Friction 0.34
6.9.2 Retaining walls extending greater than six (6) feet in height should be
designed for an additional seismic horizontal line load of 12H2 (#/ft-of-
wall) assumed to be acting at a height of 0.33H (ft) above the base of
the wall, where H is the height of the wall in feet. This seismic
surcharge should be added to an active pressure design utilizing an
active pressure of 40 psf.
6.9.3 It should be noted that where structural retaining walls would
otherwise be designed based on an at-rest pressure case, the seismic-
and-active design results should be compared to the at-rest design
results and the governing conditions should be used for the purpose of
the project.
6.9.4 In addition to the static soil pressures described above, it is important
to note that the active pressure condition will only fully develop if the
retaining wall structure is allowed to move a sufficient distance. The
necessary lateral movements required to establish the active pressure
condition are shown below,
Non-Expansive Granular Soil 0.001H – 0.004H
Expansive Cohesive Soil 0.01H – 0.04H
October 20, 2023 F-103345
11
where H represents the height of the wall. At-rest pressures should be
used for design purposes where retaining wall systems connected or
adjacent to building structures would be adversely affected by the
above referenced lateral displacements.
6.9.5 Design pressures noted above are applicable to a horizontally retained
surface behind the wall. Walls having a retained surface that slopes
upward from the wall should be designed for an additional equivalent
fluid pressure of 1 pcf for the active case and 1.5 pcf for the at-rest
case, for every two degrees of slope inclination. Walls positioned on or
near descending slopes should be evaluated by this firm on an
individual basis.
6.9.6 The pressures listed above were based on the assumption that
backfilled soils will be compacted to 90% of maximum dry density as
determined by ASTM D 1557 Test Method.
6.9.7 The lateral earth pressure to be resisted by the retaining walls or
similar structures should include the loads from any structures or
temporary loads that influence the wall design.
6.9.8 A back drain or an equivalent system of backfill drainage should be
incorporated into the retaining wall design. Backfill immediately behind
the retaining structure should be a free-draining granular material.
Alternatively, the back of the wall could be lined with a geodrain
system.
6.9.9 Compaction on the uphill side of the wall within a horizontal distance
equal to one wall height should be performed by hand-operated or
other lightweight compaction equipment. This is intended to reduce
potential “locked-in” lateral pressures caused by compaction with
heavy grading equipment.
6.9.10 Water should not be allowed to pond near the top of the wall. To
accomplish this, the final backfill site grade should be such that all
water is diverted away from the retaining wall.
7 REFERENCES CITED
USGS, Online, Geologic Hazards Science Center, United States Geological
Society, in Cooperation with California Geological Society (CGS),
www.geohazards.usgs.gov/qfaults/ca/California.php
8 ADDITIONAL SERVICES
This report is based on the assumption that an adequate program of monitoring
and testing will be performed by Beacon Geotechnical, Inc. during construction
to check compliance with the recommendations given in this report. The
recommended tests and observations include, but are not necessarily limited to
the following:
October 20, 2023 F-103345
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8.1 Review of the building and grading plans during the design phase of the
project.
8.2 Observation and testing during site preparation, grading, placing of
engineered fill, and foundation construction.
8.3 Consultation as required during construction.
9 PROJECT LIMITATIONS AND UNIFORMITY OF CONDITIONS
9.1 The analysis and recommendations submitted in this report are based in
part upon the data obtained from the borings drilled on site. The nature
and extent of variations between and beyond the borings may not become
evident until construction. If variations then appear evident, it may be
necessary to re-evaluate the recommendations of this report.
9.2 The scope of our services did not include environmental assessment or
geological study. The scope of services did not include investigation for the
presence or absence of wetlands, hazardous or toxic materials in the soil,
surface water, groundwater, or air. Any statements in this report or on the
soil boring logs regarding odors, unusual or suspicious items or conditions
observed are strictly for the information of the client.
9.3 Findings of this report are valid as of this date, however, changes in a
condition of a property can occur with passage of time whether they be due
to natural processes or works of man on this or adjacent properties. In
addition, changes in applicable or appropriate standard may occur whether
they result from legislation or broadening knowledge. Accordingly, 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 one (1) year.
9.4 In the event that any changes in the nature, design, or location of the
structure and other improvements are planned, the conclusions and
recommendations contained in this report shall not be considered valid
unless the changes are reviewed and conclusions of this report modified or
verified in writing.
9.5 This report is issued with the understanding that it is the responsibility of
the owner or his representatives to ensure the information and
recommendations offered herein are called to the attention of the project
architect and engineers. It is also the responsibility of the owner or his
representatives to ensure the information and recommendations offered
herein are incorporated into the project plans and specifications and the
necessary steps are taken to see that the contractor and subcontractors
carry out such recommendations in the field.
October 20, 2023 F-103345
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9.6 Beacon Geotechnical, Inc. has prepared this report for the exclusive use of
the client and authorized agents. This report has been prepared in
accordance with generally accepted geotechnical engineering practices. No
other warranties, either expressed or implied, are made as to the
professional advice provided under the terms of this agreement.
9.7 It is recommended that Beacon Geotechnical, Inc. be provided the
opportunity for a general review of final design and specifications in order
that earthwork and foundation recommendations may be properly
interpreted and implemented in the design and specifications. If Beacon
Geotechnical, Inc. is not accorded the privilege of making this
recommended review, we can assume no responsibility for
misinterpretation of our recommendations.
END OF TEXT
Appendices
APPENDIX A
Vicinity Map
Site Plan
Quaternary Fault Map
Investigation Parameters
Unified Soil Classification Table
Boring Logs
PROJECT #: F-103345
SITE
PROJECT #: F-103345
2
1
PROJECT #: F-103345
SITE
Map Showing Nearby Quaternary Aged Faults (USGS, Online)
QUATERNARY FAULT MAP
INVESTIGATION PARAMETERS
• The borings were drilled to a maximum depth of twenty (20) feet below the
existing ground surface to observe the soil profile and to obtain samples for
laboratory analysis. The borings were drilled on October 2 and 5, 2023 using
a mobile drill rig and/or hand auguring equipment. The approximate
locations of the borings were determined in the field by pacing and sighting
and are shown on the Site Plan in this Appendix.
• Blow counts were obtained within the test borings with Standard Penetration
Test (S.P.T.) equipment. The blow counts were obtained by driving the
sampler with a 140-pound hammer dropping thirty (30) inches in
accordance with ASTM D 1586-11.
• Bulk samples of the soils encountered were gathered from the auger
cuttings.
• The final logs of borings represent our interpretation of the contents of the
field logs and the results of laboratory testing performed on the samples
obtained during the subsurface investigation. The final logs are included in
this Appendix.
UNITED SOIL CLASSIFICATION (ASTM D-2487)
UNITED SOIL CLASSIFICATION CHART
F-103345
LOG OF BORING
for:
133 East Foothill Boulevard
Site Location: San Luis Obispo, CA F-103345
Driller/Helper:
Rig Type: Hand Auger BORING NO. 1
Auger Diameter: 4”
Date: October 2, 2023
GROUNDWATER Not Encountered SAMPLE TYPE
Time Depth SPT=Standard Penetration Test (uncorrected value, N/corrected value, N)
Depth
(ft.)
Blow
Type
Blows
per ft.
Drilling
comments
Voids Moisture Description USCS Beacon
Soil ID
0 Loose Brown silty clayey sand with gravel SM-SC A1
5
Medium Dense Light brown silty clayey sand SM-SC A2
Total Depth @ 7.0’
10
15
20
25
30
35
40
45
50
LOG OF BORING
for:
133 East Foothill Boulevard
Site Location: San Luis Obispo, CA F-103345
Driller/Helper:
Rig Type: Giddings BORING NO. 2
Auger Diameter: 4”
Date: October 5, 2023
GROUNDWATER Not Encountered SAMPLE TYPE
Time Depth SPT=Standard Penetration Test (uncorrected value, N/corrected value, N)
Depth
(ft.)
Blow
Type
Blows
per ft.
Drilling
comments
Voids Moisture Description USCS Beacon
Soil ID
0 Loose Brown silty clayey sand with gravel SM-SC A1
10
-4%
Medium Dense Light brown silty clayey sand SM-SC A2
17
-3%
5 20
-3%
10 26
-2%
15
20 Total Depth @ 20.0’
25
30
35
40
45
50
APPENDIX B
Laboratory Testing Parameters
Laboratory Results
Bench & Keyway Detail
Transition Lot Detail
2022 CBC -- Table 1705.6
LABORATORY PARAMETERS
• Samples were reviewed along with field logs to determine which would be
analyzed further. Those chosen for laboratory analysis were considered
representative of soils that would be exposed and/or used during grading,
and those deemed to be within the influence of the proposed structure. Test
results are presented in this Appendix.
• ASTM D2487-11 Standard Practice for Classification of Soils for Engineering
Purposes (Unified Soil Classification System)
• ASTM D1557-12e1 Standard Test Methods for Laboratory Compaction
Characteristics of Soil Using Modified Effort
• ASTM D2216-10 Standard Test Methods for Laboratory Determination of
Water (Moisture) Content of Soil and Rock by Mass
• ASTM D4318-10e1 Standard Test Methods for Liquid Limit, Plastic Limit, and
Plasticity Index of Soils
• ASTM D4829-11 Standard Test Method for Expansion Index of Soils
LABORATORY RESULTS
Boring Max. Opt.
Depth USCS Density Moisture E.I. P.I.
(pcf) (%)
Material A1 1@0’-6’ SM-SC 116.6 11.5 25 7
Material A2 2@2’-20’ SM-SC 119.2 11.3 26 6
PROJECT #: F-103345
Underlying soil material
per boring logs and
grading recommendations
PROJECT #: F-103345
TOPSOIL, COLLUVIUM OR WEATHERED
BEDROCK PER BORING LOGS AND
GRADING RECOMMENDATIONS
UNDERLYING SOIL OR BEDROCK
MATERIAL PER BORING LOGS AND
GRADING RECOMMENDATIONS
TOPSOIL, COLLUVIUM
OR WEATHERED
BEDROCK PER
BORING LOGS AND
GRADING
RECOMMENDATIONS
UNDERLYING SOIL OR BEDROCK
MATERIAL PER BORING LOGS AND
GRADING RECOMMENDATIONS