BWFE2019-0228 Slope GradingI
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RECEIVI)
Nov 1 8 2019
INTERWEST
coNluu-iruo GRoUP
Mrs. Lisa Swenson
62 Ellenwood Avenue
Los Gatos, California 95030
Slope Grading Exhibits Review
Proposed Swenson Residence
77-2L0 Loma Vista
La Quinta, Riverside County California
June 25,ZOLB
RECEIVED
Noy 0 I 20ru
oilor Lq QurltrA
DESIGN AIID DEVEIOPMENT DEPARII,,IENIREVIEWED
UAN 0 2 2020
INTERWEST
CONSULTING GROUP
@ 2018 Earth Systems Pacific
Unauthorized use or copying of this document is strictly prohibited
without the express written consent of Earth Systems Pacific.
File No.: 301681-001
Doc. No.: 18-06-716 ,tw In
ta
t
Ea rt h Syste m s
79-SllCountryClubDrive,SuiteB I BermudaDunes,CA 92203 | Ph:750.345.1588 | wwwearthsystems.com
June 25,20L8 File No.: 301681-001
Doc. No.: L8-06-7L6
Mrs. Lisa Swenson
62 Ellenwood Avenue
Los Gatos, California 95030
Attention: Mrs. Lisa Swenson
Subject: Slope Grading Exhibits Review
Project:Proposed Swenson Residence
77-27O Loma Vista
La Quinta, Riverside County California
ln accordance with the request of the design team, Earth Systems Pacific [Earth Systems] has
reviewed references 8 and 9 (see Reference Section in the back of this report) in relation to the
project soi! reports. ln addition, Earth Systems attended a meeting held by the design staff on June
L9, 2OL8 at 3:30 pm. Our review of the exhibits was performed from a geotechnical perspective.
Our conclusions from the exhibit reviews and meeting interpretations are provided below.
Background
Earth Systems received three exhibits from The Altum Group via email on May 25,201,8. The three
exhibits are titled:
1. Exhibit #1 (from The Altum Group)
2. Exhibit #2 (from The Altum Group)
3. Walker Martin Exhibit (from Mocon Corporation)
The Altum Group prepared two exhibits based on a meeting at John Vuksic' s office. The email
stated both exhibits utilize the original Land Suitability Study Exhibit as a base, which identifies the
proposed limits of potential disturbance. Also, the emai! references another exhibit called "Walker
Martin's 41 3Ol L8 Exhibit".
Exhibit #1 identifies the 2:L, L.5:L, and L:1 slope inclination limits based on the proposed site and a
proposed bench for boulders at the top of the slope (see Walker Martin's 4l3OlL8 Exhibit). Exhibit
#L is based on the Altum and John Vuksic discussion prior to Earth Systems receiving these
exhibits. Exhibit #1 provides a comparison of new grading !imits in comparison to the potential
disturbance area. Exhibit #2 is a potential proposed solution, utilizing retaining walls and various
slopes to generally stay within the limits of potential disturbance.
Earth Systems understanding of the Walker Martin Exhibit is a "fully captive fill" slope having a tie-
back bolt placed perpendicular to a bedrock slope or possibly at least L0 feet of fill. The bolt is shown
having a standard #10 size and grade 75 that are bonded into 3 feet of bedrock or 10 feet of soi!. A
r,
June 25,2OL8 2 File No.: 301681-001
Doc. No.: 18-06-7L6
concrete mat is laid along the face of the slope and the bolts placed into the slope and bedrock have
washers securing the concrete mat to the slope. Boulders are placed on top of the bar heads and
concrete mat. The top of the slope indicates a boulder cast in concrete. At the bottom of the rock
cladding, the exhibit shows rock cladding supported by bedrock or shear pin or grade beams. Also
included in the Walker-Martin Exhibit are two drain lines located at the bottom of the slope: one on
top of the concrete mat and the other within the "fully captive fill".
A meeting occurred on June L9, 2OL8 with attendees from "John Vuksic", Earth Systems, Altum,
Knapp Structural Engineering, and Mocon. Both attendee companies (The Altum Group and Mocon
Corporation) provided a discussion of their exhibits. A discussion from John Vuksic indicated the
intent of the meeting was to reduce the cost of a previous concept utilizing walls and rock cladding.
At this meeting Earth Systems indicated clarification with regards to the following:
a. The soils report is based on benching soil into competent bedrock according to the
California Building Code.
b. Slopes should have all undocumented fill removed and replaced with engineered fill.
c. Slopes should not be steeper than L-L/2:1. Earth Systems is concerned L:1 slopes will fai!
or creep.
i. Earth Systems recommends the use of a mechanically stabilized (geogrid
reinforced or similar) slope if the 1:L slope is desired.
ii. Earth Systems also recommends a retaining wall at the location of L:1 slopes if
stabilized slopes are not utilized. The Mocon solution is not considered suitable
for l,:1 slopes.
d. Bond strengths should be determined during design and confirmed during construction.
The structural engineer raised concerns too that strength resistance of the bolts is
needed too.
e. Slope analysis of any slope steeper than 2:1 should be performed.
f. Connection between the slope and rock cladding should be provided.
After the meeting, Earth Systems reviewed the Milliken lnfrastructure website and noted the
concrete mat has severa! functions:
a. Ditch lining
b. Erosion control and slope protection
c. Berm protection and secondary containment
d. Culvert lining
The Milliken website is found at link:http://infrastructure.milliken.com/concretecloth/. Based on
this information, Earth Systems understands the concrete mat is very thin and is used for erosion
control and aiding in slope protection, but not as a "compression" device to apply an overburden
load function to the "captive fill.
Concl usion
At this time and based on references 8 and 9 reviews, the June L9 meeting, research of the project
reports, and discussions with additional Earth Systems staff, it is our professional opinion that, from
EARTH SYSTEMS PACIFIC
June 25,2OL8 File No.: 301681-001
Doc. No.: 18-06-7t6
a geotechnical standpoint, the exhibits reviewed have not been completely prepared in substantial
conformance with the intent of the recommendations in the referenced project soit reports. Earth
Systems provides the list below showing itemized discrepancies between the project soil reports
and the proposed exhibits:
1. Slope Steepness: Normal engineered fill slopes should be no steeper than L-L/2:L if
protected from erosion and shown to be globally stable. tf 1:l slopes are needed, then they
should be mechanically stabilized and a specialty contractor, like Tensar Corp, should be
hired to design these specialized slopes.
2. Benching: All fill placed along slopes should be benched according to the project soits report
and the Z.OLG California Building Code.
3. Earth Systems wants to make clear that undocumented fill locations have been provided in
the project soils reports. These areas must be over-excavated and recompacted as
engineered fill per the project soils report. Undocumented fills and lose soil onsite are not
suitable for structural support.
4. Bolt Reinforcement lnformation: During design, the bolt type and structural properties of
the bolt should be provided as well as what the intent of the bar is (shear, compression,
etc.). The spacing of the bars should be determined along with minimum bonding strength.
Embedment into only fill is not recommended.
5. Slope Stability Analysis: The final design of the slope should require a stope stability anatysis
under various loading conditions and shear strength based on engineering judgement.
6. Boulder Facing Connection: The facing of the boulders placed on the face slope and concrete
mat should be provided. The weight should be added to the slope stability analysis.
7. Engineered Fill: Engineered fill should be shown on cross sections.
8. The grade beam dimensions should be provided and resistance strengths prescribed for the
stability analysis.
9. Earth Systems can provide design strength of bonding between steel bars and rock or soit,
as well as the required construction procedures for testing bond strength.
Additionally, it is our opinion that the recommendations provided in the project soil reports remain
applicable to the proposed project. Earth Systems structural plan review approvat is only valid if
Earth Systems performs the observation and testing during grading to substantiate the soit
conditions are as anticipated and provide further recommendations if needed. lf not, the new
Geotechnical Engineer of record must accept this plan review.
Prooer seotechni cal obselvation and testing durins construction is imp erative to allow the
3
eeotechnica!engineer the opportu nitv to verifv assumptions made durins the desisn process and
that our eotechni mmendations h en ro e inte r and im lemente
EARTH SYSTEMS PACIFIC
June 25,zOLg 4 File No.: 301681-001
Doc. No.: 18-06-7L6
during construction and is required bv the 2016 ea[fornia Buildine Code. Observation of grading
and fil! placement by the Geotechnical Engineer of Record should be in conformance with Section
L7 of the 2016 California Building Code. California Building Code requires full time observation by
the geotechnical consultant during site grading (fill placement) and in accordance with the
requirements of the project plans. Therefore, we recommend that Earth Systems be retained during
the construction of the proposed improvements to observe compliance with the geotechnical
recommendations, and to allow design changes in the event that subsurface conditions or methods
of construction differ from those assumed while completing our study. Please review the limitations
presented below as they are vital to the understanding of this letter.
EARTH SYSTEMS PACIFIC
June 25,2OL8 File No.: 301681-00L
Doc. No.: 18-06-7LG
1. Earth Systems Southwest, 2013, Geotechnica! Engineering Report, Swenson Residence,TT-
210 Loma Vista, The La Quinta Resort, La Quinta, Riverside County, California, dated March
26, 20L3, File No.: 12 t24-OL, Doc No. : L3-03-737 .
2. Earth Systems Southwest, 20L3, Grading Plan Review, Swenson Residence, TT-2L0 Loma
Vista, The La Quinta Resort, La Quinta, Riverside County, California, dated October 23,20L3,
File No.: LZL24-01, Doc No.: 13-10-730.
3. Earth Systems Southwest, 2OL4, lnfiltration Testing for Stormwater Retention Feasibility,
Proposed Residence, 77-2L0 Loma Vista, La Quinta, Riverside County, California, dated
February LL,2OL4, File No.: 12124-01, Doc No.: L4-02-708.
4. Earth Systems Southwest, 2OL5, Plan Review and Response to City Review Comment
Including Retaining Wall Evaluation and Grouted Anchor General Specifications, Swenson
Residence,TT-2L0 Loma Vista, La Quinta, Riverside County, California, dated May 7,2OL5,
File No.: L2L24-0L, Doc No.: L5-05-706.
5. Earth Systems Southwest, 2016, Geotechnical Engineering Plan Review, Retaining Wall with
Rock Cladding, Swenson Residence, 77-2L0 Loma Vista, La Quinta, Riverside County,
California, dated July 13, 2OL6, File No.: L2L24-01, Doc No.: L5-07-708.
6. Earth Systems Southwest, 2016, Geotechnical Engineering Report Update, Proposed Single
Family Residence, TT-2L0 Loma Vista, The La Quinta Resort, La Quinta, Riverside County,
California, dated July 26,2OL6, File No.: L2L24-0L, Doc No.: 16-07-71,3.
7. Earth Systems Southwest, 2016, Retaining Wall Evaluation and Grouted Anchor General
Specifications Supplemental Report for Easterly Knob Vertical Cut, Swenson Residence, TT-
zLO Loma Vista, The La Quinta Resort, La Quinta, Riverside County, California, dated
December 2L,20L6, File No.: L2L24-0L, Doc No.: L6-12-7L0.
8. The Attum Group .,z}!8,Access Drive Stope Grading Study, Swenson Residence at the Enctave
Mountain Estates, 3 Sheets, No Date, No Signature.
9. Mocon Corporation, 2018, Retaining Wall Cross Section, Walker Martin, L Sheet, 04/30/18, No
Signature.
Limitations
Conclusions contained in this letter are based on our previously documented field observations and
subsurface explorations, laboratory tests, and our present knowledge of the proposed construction.
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 unti! construction. Variations in
soil or groundwater may require additional studies, consultation, and possible revisions to our
recommendations. lf during construction, soil conditions are encountered which differ from those
described, we should be notified immediately in order that a review may be made and any
supplemental recommendations provided.
lf the scope of the proposed construction changes from that described in this report, the conclusions
and recommendations contained in this report are not considered valid unless the changes are
5
EARTH SYSTEMS PACIFIC
REFERENCES
"June 25,20L8 File No.: 30L681-001
Doc. No.: 18-06-7L6
reviewed, and the conclusions of this report are modified or approved in writing by Earth Systems.
Additionally, this letter should be included with the project geotechnical (soils) report and
specification documents. 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. The recommendations
presented within are predicated upon the recommendations presented in the referenced project
soils reports. lnformation and recommendations presented in this supplement should not be
extrapolated to other areas or be used for other projects without our prior review and response.
lf Earth Systems is not retained to provide grading observation and testing during construction, we
can assume no responsibility for misinterpretation or the applicability 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.
Earth Systems has striven to provide our services in accordance with generalty accepted
geotechnical engineering practices in this locality at this time. No warranty or guarantee express or
implied is made. Please note that it is not within our scope of work to check the reviewed
documents for conformance to codes or other client and government requirements. As Earth
Systems does not practice architectural or structural design, we make no representation as to the
accuracy of dimensions, measurements, calculations, or any portion of the design.
We appreciate the opportunity to provide our professional services. Please do not hesitate to
contact our office if there are any questions or comments concerning this report or its conctusions.
Respectfu lly Su bm itted,
EARTH SYSTEMS PACIFIC
6
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Anthony Co
Project Engi
cE 60302
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neer -tytrx
LTR/aclklp/mr
Attachments: Altum Exhibits #L and #2
Mocon Walker-Martin Exhibit
Distribution: 3/Mrs. Swenson
E-ma i!:
Prest Vuksic: Mr. John Vuksic:
The Altum Group: Mr. Doug Franklin
Knapp Associates: Mr. Len Knapp:
Mocon Corporation: Mr. Walker Martin:
1/BD File
EARTH SYSTEMS PACIFIC
ioh nv@ restvuksica rch it ects.com
doue.franklin@th ealtumgrou p.com
Lknapp@kn appa ssociatesinc.com
walker .martin @moconroc kfa ll.com
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