BWFE2019-0028 Geotechnical Report UpdateI
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Earth Systems
Southwest
July 26,20LG
Lisa Swenson
52 Ellenwood Avenue
Los Gatos, California 95030
Dear:
Subject:
Project:
RECElVED
79-8118 Country Club Drive
Bermuda Dunes, CA92203
(750) 34s-1s88
(800) 924-701s
FAX (760) 34s-737s
File No.: L2L24-OL
Doc. No.: 16-07-7L3
NO\/ 1 g z0lg
INTERWESTReferences:
CONSULTTNG GROUP
1. Earth Systems Southwest, 2013, Geotechnical Engineering Report, Swenson Residence,
77-2L0 Loma Vista, The La Quinta Resort, La Quinta, Riverside County, California, dated
March 26, 20L3, File No.: 12124-0L, Doc No. : L3-03-737 .
2. Earth Systems Southwest, 20L3, Grading Plon Review, Swenson Residence, TT-2L0 Loma
Vista, The La Quinta Resort, La Quinta, Riverside County, California, dated October 23,
20t3, File No.: 12724-0L, Doc No.: 13-10-730.
3. Earth Systems Southwest,20L4, lnfiltrotion Testing for Stormwater Retention Feasibility,
Proposed Residence, TT-210 Loma Vista, La Quinta, Riverside County, California, dated
February LL,20L4, File No.: 12124-0L, Doc No.: L4-O2-708.
4. Earth Systems Southwest, 2015, Plon Review ond Response to City Review Comment
lncluding Retaining Wall Evoluotion ond Grouted Anchor General Specificotions, Swenson
Residence,TT-2L0 Loma Vista, La Quinta, Riverside County, California, dated May 7,2OLS,
File No.: L2L24-0L, Doc No.: 15-05-706.
5. Earth Systems Southwest, 2016, Geotechnicol Engineering Plon Review, Retoining Woll
with Rock Clodding, Swenson Residence,TT-210 Loma Vista, La Quinta, Riverside County,
California, dated July 13, 2OL6, File No.: L2L24-0L, Doc No.: 15-O7-7O8.
In accordance with your request and authorization, Earth Systems Southwest [Earth Systems] has
reviewed the above referenced geotechnical reports for providing updated recommendations in
accordance with the 2013 California Building Code. This update applies to a proposed new
residential structure as documented in more detail in each of the reports referenced above. To
validate this update report, Earth Systems recommends that we review the foundation ptans
once they become available. Additionally, please review the limitations section of this report as
INTERWEST
CONSULTING GROUP
Mrs. Swenson
Geotechnical Engineering Report Update
Proposed Single Family Residence
77-zLO Loma Vista
The La Quinta Resort
La Quinta, Riverside County, California
RECEIVED
Noy 0 8 20tg
R E v I E \ffi E*,T,!i,?r?i,ffi pARTr,,Eilr
'JAN 0 2 2020
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July 26,2OL6 File No.: L2L24-OL
Doc No.: t6-07-7L3
the information presented is integral to the understanding of this document. Our conclusions
and recommendations are provided below.
The original geotechnical report was produced in 20L3 (Earth Systems, Geotechnical Engineering
Report, Swenson Residence). That report used the 2010 California Building Code (CBC) as the
standard for design. This report updates the geotechnica! design to reflect the 2OL3 CBC. We also
reviewed the 2013 CBC code values for setbacks and as shown in a plan review (Earth Systems,
2OL6, Geotechnical Engineering Plan Review, Retaining Wall with Rock Cladding) in which Earth
Systems provided alternative recommendations for setbacks along slopes for the proposed
retainingwalls noted in the cited plan reviews (Earth Systems 2OL3 and 2015). Also, note in the
cited plan review, the 2013 CBC allowed alternative recommendations for slope setbacks is
dependent on the approval of the Building Official.
We recommend the structural engineer review the 2OL3 CBC for slab thickness and
reinforcement as these designs considerations are still the responsibility of the structural
engineer or architect. The reader will also find that we updated dynamic pressures and coefficient
friction values for retaining walls.
To date, Earth Systems released four (a) additional plan review/reports after release of the
original geotechnical report:
1. Grading PIan Review, Swenson Residence
2. !nfiltration Testing for Stormwater Retention Feasibility, Proposed Residence
3. Plan Review and Response to City Review Comment lncluding Retaining Wal! Evaluation
and Grouted Anchor Genera! Specifications.
4. Geotechnical Engineering Plan Review, Retaining Wall with Rock Cladding
This report updates items L and 3, but not item 2 (infiltration testing report). At this time, storm
water disposal locations are not understood at this time, so a separate update report will follow
once these locations are understood. Since item 4 was written in 2OL6,there is no need to update
this report. Earth Systems should review the fina! grading plans, foundation plans, or other plans
when available.
Site Visit
On Thursday, July 2L, 20L6, an Earth Systems' engineer and geologist arrived on-site and
conducted a site visit (see Figure L) to observe existing surficial conditions, erosion damage, and
debris flow potential. From the site visit, the pad is vacant and was graded in the past. The past
grading was found to be undocumented fill.
Earth Systems' staff walked the site for visual signs of changes. No noticeable signs of changes
have occurred on the site since the publication of the reports referenced above.
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EARTH SYSTEMS SOUTHWEST
L
BACKGROUND
July 26,201,6 File No.: LZL24-OL
Doc No.: L6-O7-7L3
Figure L. Swenson Residence, Access Road, 77-2tO Loma Vista, La Quinta, CA. Looking northerly.
It is our opinion that the recommendations provided in the project soils report (Earth Systems,
2OL3, Geotechnica! Engineering Report, Swenson Residence), as supplemented and superseded
below, remain applicable provided the following recommendations are incorporated into the
design and construction. The following is a summary of our conclusions and professional opinions
for each of the referenced reports being updated based on the data.
1. Geotechnical Eneinee ring Report, Swenson Residence. dated Ma rch 26, 20L3, File No.:
3
L2L24-O1, Doc No.: 13-03-737
with conditions as outlined in Earth Systems, 2016, Geotechnicol Engineering Plan
Review, Retoining Wall with Rock Clodding. This setback applies only to retaining walls
foundations as shown in a plan referenced in the stated 2016 plan review.
o Dynamic lateral earth pressures and based on Al Atik and Sitar,
o L00 psf uniform surcharge live load and the increase in lateral earth pressure
should be taken at 50% of the surcharge load,
o Factor of Safety,
o Dynamic pressures and wall heights,
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2. Earth Svstems . 2OL3.Gradinq Plan Review Swenson Residence,dated October 23, 20L3,
4
3
File No .: L2L24-0L Doc No.: 13-1-0-730
outlined in Eorth Systems, 2016, Geotechnicol Engineering Plan Review, Retoining
Wall with Rock Clodding. This setback applies only to retaining walls foundations as
shown in a plan referenced in the stated 2016 plan review.
MS 2015 Plan Review R to Review Comment lncludin
Retoinino Wall Evaluotion ond Grouted Anchor Generol Specifications, dated Mav 7 ,20L5,
File No.: L2L24-OL.Doc No.: 15-05-706.
SUPPLEM ENTAL RECOMM EN DATIONS
The following recommendations are intended to supplement and supersede the respective
recommendations in the referenced geotechnical report and plan review letters (Reference No.:
L,2,4, and 5) for new structures and should be incorporated into the design and construction of
the project. The remaining conclusions and recommendations contained within the referenced
geotechnical reports should be referred to and are still considered applicable and valid for
current project design. The conclusions and recommendations presented in this report are
subject to the limitations presented in our previous report and herein.
Pools with Maximu m Allowable Differential Settlement of 0.-inches (Section 5.1)
To provide a uniform and compacted subgrade for the support of the pool shell, the existing fill
soils below the pool shell and foundation areas should be removed to bedrock. At this time, our
understanding, based on Cross Section No. 6 presented on the following page (Earth Systems,
2OL6, Geotechnical Engineering Plan Review, Retaining Wall with Rock Cladding), the proposed
pool area will require a maximum lO-feet of fill with an additiona! S-feet of artificial fill removed
to bedrock. At this time, the dimensions of the pool is unknown and our assumptions are as
follows:
L. Maximum Pool Dimension is 40-feet or less.
2. Maximum depth of pool is 8-feet or less.
3. The poo! excavation occurs after engineered fill is placed to top of the pools water surface.
4. The material used to backfill is sandy materia! having a rate of consolidation that provides
95o/o of the expected settlement prior to pool excavation.
Based on the items above and Cross Section No. 6 noted above, we provide two possible grading
scenarios. lf a construction scenario is different from these two scenarios selected or any of the
above items are not true, then Earth Systems requests to evaluate the geotechnical issues of the
varying scenario and items above.
EARTH SYSTEMS SOUTHWEST
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)uly 26,2OtG 5 File No.: t2L24-O1,
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Figure 2, Cross Section No. 6
m
IE
PROPOSTD FINISH GRADE
E6
86
84
82
6- S.D.
PROPOSED
POOL
PROPOSEO FINISH GRAOE
80
78 --* -
76
74
72
70
I
. -tt-
1
ExEnNG
68
66
a
(
64
62
1 +00 t +20 l,:;' I
SECTION NO. 6
H0R.: l'=5', VERT.: l"=5''l[-ot
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Scenario L
!f the bedrock is located more than 2-feet from any portion of the bottom of the pool shell, then
the following recommendation is applicable:
Remove all existing artificial fill down to competent bedrock (as determined by the project
geologist). Bedrock should be removed such that the bedrock subgrade elevation below the pool
shell bottom has a level differential elevation of no more than 1l-feet across any span of the
pool. Fill compacted, to at least 95% relative compaction (ASTM D 1557), at near optimum
moisture content using heavy compaction equipment, should then be placed to the top of the
pool deck's subgrade as needed. The pool/spa shell excavation may then proceed. Compaction
should be verifled by testing. The project geotechnical engineer or geologist should review the
bottom of the excavation and excavation sidewalls prior to re-compaction. Soft or loose zones
may warrant additional removals.
lf Scenario No. L experiences deep bedrock causing excessive bedrock removal elsewhere within
the pool area, then Earth Systems should be informed of this condition to provide further
recommendations. Additional recommendations wi!! require the project geotechnical engineer
or geologist to evaluate the exposed conditions.
lf the bedrock is located 2-feet or less from the bottom of the pool shell, then the following
recommendation is applicable:
The bottom of the over excavation should be over excavated at least 2-feet into bedrock.
Engineered fill shall then be placed in maximum loose 8" lifts, moisture conditioned near
optimum moisture content, and be compacted, to finish subgrade as needed. The engineered fill
should be compacted to at least 95Yo relative compaction (ASTM D 1557) using heavy compaction
equipment. The pool/spa shell excavation may then proceed. Compaction should be verified by
testing.
The project geotechnical engineer or geologist should review the bottom of the excavation and
excavation sidewalls prior to re-compaction. Soft or loose zones may warrant additional
removals.
Retainine Walls (Section 5.51
The following table presents lateral earth pressures for use in retaining wall design. The values
are given as equivalent fluid pressures without surcharge loads or hydrostatic pressure. Values
are based on a soil having an internal friction angle of at least 32 degrees and a total unit weight
of approximately L22pcf . Passive resistance and frictional resistance may be used in combination
if the friction coefficient is reduced by one-third.
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EARTH SYSTEMS SOUTHWEST
Scenario 2
Lateral Pressures and Stiding Resistance 1 Granular Backfill
Passive Pressure 350 pcf - level ground
Active Pressure (cantilever walls)
Use when wall is permitted to rotate 0.1 to O.2% of wall height for
granular backfill
40 pcf - level ground
At-Rest Pressure (restrained walls)60 pcf - level ground
Dynamic Lateral Earth Pressure 2
Acting at 0.6H, where H is height of backfill in feet
20 pcf - flexible wall
30 pcf - rigid wall
Base Lateral Sliding Resistance
Dead load x Coefficient of Friction:0.25
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Notes:1 A factor of safety of 1.5 should be used in stability analysis (permanent condition) except for dynamic
earth pressure where a factor of safety of 1.1 is acceptable.2 Dynamic pressures are based on the Al Atik and Sitar, 2010 method considering PGAv, additive to earth
pressures. Walls retaining less than 6-feet of soil and not supporting inhabitable structures need not
consider this increased pressure.
Upward sloping backfil! or surcharge loads from nearby footings can create larger lateral
pressures. Should any walls be considered for retaining sloped backfill or ptaced next to
foundations, our office should be contacted for recommended design parameters. Surcharge
loads should be considered if they exist within a zone between the face of the wall and a plane
projected 45 degrees upward from the base of the wall. The increase in lateral earth pressure
should be taken as 50% of the surcharge load within this zone. At a minimum, the described
retaining walls should include a uniform surcharge live load equivalent to 100 psf.
Seismic Desisn Criteria (section 5.71
This site may be subject to severe ground shaking due to potential fault movements along
regional faults. The site soils are not subject to liquefaction induced bearing failure. As such, the
minimum seismic design should comply with the 2013 edition of the CBC using the seismic
coefficients given in the table below.
Seismic parameters are based upon computation by the Ground Motion Porameter Colculator
provided by the United States Geological Survey [USGS]:
http ://eeohaza rds. usss.qov/d esi gnmaps/us/application. ph p (July, 20L61.
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2OL3 CBC (ASCE 7-10) Seismic Parameters
Maximum Considered Earthquake IMCE] Ground Motion
Short Period Spectral Response Ss:
1 second Spectral Response, Sr:
Site Location:
Site Class
Mean Peak Ground Acceleration (PGAv)
Design Earthquake Ground Motion
Short Period Spectral Respons€, Sos
L second Spectral Respons€, Sor
33.6935"N/116.3157"W
C
0.553 g
1.500 g
0.634 g
1.000 g
0.549 g
The intent of the CBC lateral force requirements are to provide a structura! design that will resist
collapse and therefore provide reasonable life safety from a major earthquake, but may
experience some structura! and nonstructural damage. A fundamental tenet of seismic design is
that inelastic yielding is allowed to adapt to the seismic demand on the structure. tn other words,
domoge is ollowed. The CBC lateral force requirements should be considered a minimum design.
The owner and the designer may evaluate the level of risk and performance that is acceptable.
Performance based criteria could be set in the design. The design engineer should exercise
special care such that all components of the design are fully met with attention to providing a
continuous load path. An adequate quality assurance and contro! program is urged during
project construction to verify the design plans and good construction practices are followed. This
is especially important for sites lying close to major seismic sources.
LIMITATIONS
Except as modified in this report, it is our opinion that the referenced documents, including
limitations, are applicable to the proposed development in regard to geotechnical constraints.
This report and our scope of services are not intended to address any environmental issues or
constraints related to the site or our observations. Earth Systems has striven to provide our
services in accordance with generally accepted geotechnical engineering practices in this locality
at this time. Observations reported are those existing at the time of our services and may not be
the same or comparable at other times. Our observation and opinions presented are not
insurance, nor do they guarantee construction of any type. This assessment does not include,
and specifically excludes, observation of inaccessible areas. Only those conditions apparent upon
reasonable visual observation are noted. lf additional information becomes available, we must
be consulted to review the effect of the information on our conclusions. No warranty or
guarantee, express or implied, is made.
Our findings and recommendations in this report are based on our points of previous field
exploration, laboratory testing, and our understanding of the proposed project. Furthermore,
our findings and recommendations are based on the assumption that soil conditions do not vary
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significantly from those found at specific exploratory locations. Variations in soil or groundwater
conditions could exist between and beyond the exploration points. The nature and extent of
these variations may not become evident until construction. Variations in soi! or groundwater
may require additional studies, consultation, and possible revisions to our recommendations. lt
is recommended that Earth Systems be retained during the construction of the proposed
improvements to observe compliance with the design concepts and geotechnical
recommendations, and to allow design changes in the event that subsurface conditions or
methods of construction differ from those assumed while completing this commission. lf we are
not accorded the privilege of performing this review, we can assume no responsibility for
misinterpretation of our recommendations. The above services can be provided in accordance
with our current Fee Schedule. The geotechnical engineering firm providing tests and
observations shall assume the responsibility of Geotechnical Engineer of Record.
Our evaluation of subsurface conditions at the site has considered subgrade soil and groundwater
conditions present at the time of our study. The influence(s) of post-construction changes to
these conditions such as introduction or removal of water into or from the subsurface will likely
influence future performance of the proposed project. lt should be recognized that definition
and evaluation of subsurface conditions are difficult. Judgments leading to conclusions and
recommendations are generally made with incomplete knowledge of the subsurface conditions
due to the limitation of data from field studies. The availability and broadening of knowledge
and professional standards applicable to engineering services are continually evolving. As such,
our services are intended to provide the Client with a source of professional advice, opinions and
recommendations based on the information available as applicable to the project location, time
of our services, and scope. tf the scope of the proposed construction changes from that
described in our reports, the conclusions and recommendations contained in this report are not
considered valid unless the changes are reviewed, and the conclusions and recommendations of
our reports are modified or approved in writing by Earth Systems.
Findings of this report are valid as of the issued date of the report and are strictly for the
client. Changes in conditions of a property can occur with passage of time, whether they are
from natura! processes or works of man, on this or adjoining properties. ln addition, changes in
applicable standards occur, whether they result from legislation or broadening of
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 year.
This report is issued with the understanding that the owner or the owner's representative has
the responsibility to bring the information and recommendations contained herein to the
attention of the architect and engineers for the project so that they are incorporated into the
plans and specifications for the project. The owner or the owner's representative also has the
responsibility to take the necessary steps to see that the general contractor and al!
subcontractors follow such recommendations and for submittal of this report to the appropriate
governing agencies.
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CLOSING
We appreciate the opportunity to provide our professiona! geotechnical services to you. lf you
should you have any questions concerning our report, please do not hesitate to give us a call and
we will be pleased to assist you.
Respectfu I ly su bm itted,
EARTH SYSTEMS SO
/.
hony Co
Project Engineer
RCE 60302
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Distribution: 1/Mrs. Lisa Swenson via email: (lisa_verde@yahoo.com)
L/ Mr. James Bazua via emai!: (james.bazua@thealtumgroup.com)
1/BD File
EARTH SYSTEMS SOUTHWEST