BWFE2019-0228 Limited Geotechnical Evaluation-
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RECEIVED
NO\/ 1 I 2019
INTERWEST
coNluirrr'ro GRoUP
Mrs. Lisa Swenson
62 Ellenwood Avenue
Los Gatos, California 95030
Limited Geotechnical Evaluation
Gabion Basket Rockfall Wal!
Proposed Single Family Residence
77-2lO Loma Vista
The La Quinta Resort
La Quinta, Riverside County, California
April 24,20L8
O 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.: 301581-001
Doc. No.: L8-04-7LL
REVIEWED
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INTERWEST
CONSULT'NG GROUP
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Earth Systems
79-811Country Club Drive, Suite B I Berrnuda Dunes, CA 92203 | Ph: 760.345.1588 | www.earthsystems.com
April 24,20L8 File No.: 301681-00L
Doc No.: L8-04-7LL
Mrs. Lisa Swenson
62 Ellenwood Avenue
Los Gatos, California 95030
Attention: Mrs. Lisa Swenson
Project:Proposed Single Family Residence
77-zLO Loma Vista
The La Quinta Resort
La Quinta, Riverside County, California
Subject:Limited Geotechnical Evaluation
Gabion Basket Rockfall Wall
Earth Systems Pacific [Earth Systems] is pleased to submit this limited geotechnical evaluation
letter for the project located at77-2t0 Loma Vista, La Quinta, Riverside County, California. The
intent of this report is to provide limited geotechnical information for a potential rockfall wall
located at rockfall analysis location "CRSP Analysis uA,"" as shown in Figure 1 of this letter.
Rockfall walls in the form of Gabion Baskets are proposed in lieu of Portland Cement concrete
impact walls at the above location. Unless requested in writing, the Client is responsible to
distribute the report to the appropriate governing agency and other members of the design
team. Please review the Limitations of this report as it is vital to the understanding of this report.
ROCKFALL WALLS
Rockfall walls incorporate a variety of structural elements to withstand the often very-high-
energy impacts associated with rockfalls while striving to minimize the footprints of the
protection structure. Several types of structural walls are used for rockfall protection:
1. Masonry or Portland Cement Concrete Walls
2. Soldier Pile Walls
3. Mechanically Stabilized Earth (MSE) Walls
4. Gabion Walls
Previously for the site, rockfall wall types L and/or 2, as described above, were proposed for
rockfall protection. The first two walls are rigid and do not have the ability to deform to dissipate
impact energy, but have the advantage of saving space and potentially being compact in their
footprint. Cost however, can be prohibitive. lt is our understanding there may be space onsite
to fit an MSE or Gabion wall behind a conventional fence wall at the Figure 1 location onsite (CRSP
A location). Based on our experience, the more effective structural walls for moderate to high-
energy rockfall impacts are thick-sectioned, gravity-type walls that incorporate structural
reinforcement fabrics or elements with earthen materials. The most commonly used structural
walls include mechanically stabilized earth (MSE) walls and gabion walls with a height to base
ratio of about L. This requisite width, however, limits their potential use at many sites.
Apri! 24,2OL8 File No.: 30L581-001
Doc. No.: L8-04-7LL
As such Earth Systems was requested to perform additional evaluation on the sizing needed for
a Gabion wall to absorb rockfall impacts which could occur and which were modeled previously
in Reference No. 2. Due to the need for adequate room to construct, which does not exist at the
analysis location, MSE walls were not evaluated as a part of this letter.
Research involving full-scale field testing (Peila et a!. 2000) has been conducted on thick structural
walls to quantify their capacity, to understand their performance, and to develop a design
methodology. Research has shown that kinetic energy from a rockfall impact is dissipated
through slip along the internal layers within the zone of impact and by the development of
localized cratering of the wall face. Peila demonstrated that a rock block colliding with energy
approaching 5,000 kJ (1,850 ft-tons) can be safely stopped by a reinforced embankment with a
unit weight per meter of length that is twice the weight of the block without the overall stability
of the thick wall being compromised.
Earth Systems performed several rockfall analyses for this project (ESSW, 2013, Geotechnical
Report). A review of the project geotechnical report (Plate A-3) indicates two locations of rockfall
analysis: CRSP Analysis "A" and CRSP Analysis "B", see Figure 1 below. This report discusses only
analysis location "A", which the soils report indicates the wal! needs a minimum height of 7 feet.
The 7 feet criteria is based on estimated bounce height of the rocks falling near the stated area.
This analysis discusses the minimum size of the wall needed to provide the protection of the
anticipated size of the largest rock.
A review of the soil report's CRSP analysis for Section A-A' indicates the following assumption
for this estimate of wall size:
L. Maximum size of rock falling is a 4ft round by 5 feet long cylinder.
2. The density of the rock is estimated at 161.4 pcf.
3. The maximum kinetic energy approaches 79,176 ft-lb (40 ft-tons or 107 kJ)
EARTH SYSTEMS PACIFIC
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Figure 1 Rockfall Analysis Locations
Using a cylindrical formula (V = nr2h) for the volume of the rock and the density of the rock, Earth
System estimates the weight of the rock is approximately 10,200 lbs. Based on the criteria set
from Piela's research, the projects kinetic energy is less than 1,850 ft-tons and the unit weight of
the wall per meter should be approximately 20,4001bs/meter length of wall.
Assuming the cross section shown in Figure L above, the required dimension of a Gabion wall
should be selected from one of three scenarios presented below for varying wallsizes and heights
as we!! as density of infil!:
3
lnclination
of lmpact
Face
(H:V)
Density of Wall
lnfill
(pcf)
Top of Wall (T)
(ft)
Base of Wall (B)
(ft)
Height of Wall (H)
(ft)
Near
Vertical
110 8.0 8.0 7.O
Near
Vertical
110 7.5 7.5 7.5
Near
Vertical
95 8.0 8.0
EARTH SYSTEMS PACIFIC
File No.: 301681-001
Doc. No.: 18-04-7tL
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April 24,2OL8 File No.: 301581-001
Doc. No.: 18-04-71,L
Gabions are rock-filled wire baskets that can be stacked to form rigid barriers for protection from
rockfalls, see Figure 3. Gabions are durable and, consequently, are well suited for construction of
protection measures in areas with a high frequency of rockfall. Gabions also have demonstrated
an ability to withstand high-energy impacts (Turn er,2Ot2l.
The specifications for the gabion basket wal! should provide a concrete base a minimum of 4
inches thick (3,250 psi compression strength) for corrosion protection. The coarse aggregate used
to fill the baskets should have the following requirements:
1. Minimum specific gravity of 2.6.
2. Minimum unit weight of 95 or 110 pcl depending on wall size, or approved by the
geotechnical engineer of record.
3. Maximum void ratio of 35% or approved by the geotechnical engineer of record.
4. The gradation of the gabion basket infill should be consistent with the gabion basket
aperture (opening size). Rock/crushed concrete should be selected such that the rock
particles do not "fall out" of the basket.
5. The backside of the Gabion wall should be a minimum of 6 inches laterally away from any
fence or screen wal!.
Gabion walls are considered relatively maintenance free; however, as with any rockfall barrier,
cleaning of fallen rock from the back side of the wall periodically wil! be required to maintain
effectiveness. Periodic checks by the homeowner or their representative should be made to
assure rocks are not accumulating or stacking over L foot in height and depth behind the wall.
Large impacts may require straightening of the baskets. As well, if geofabric or wire mesh is used,
it should also be observed for corrosion deterioration or deterioration due to exposure to
sunlight and the elements.
The geotechnical engineer should test and review the anticipated gabion aggregate infill for unit
weight requirements of the proposed wall. Geotextiles or wire mesh may be required to keep
the fines particles within the gabion basket depending on the selected infill. Additional
information on gabion specifications are available at gabion suppliers such as "BIue Stone
Supply". A typical Gabion wall layout is presented in Figure2.
Gabion wall 5" Minimum+-T-+{
slope
Standard
Fence Wall
(if desired)
water control
and conveyance
4
t
H
+
Figure 2
EARTH SYSTEMS PACIFIC
concrete slab
Gabion Barriers
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April 24,2018 File No.: 301681-001
Doc. No.: 18-04-7LL
Figure 3 TypicolGabion Barrier 6ft High by 6ft Wide
L!MITATIONS
It is intended that this addendum report be utilized with our Geotechnical Engineering Report
(Doc. No.: 13-03-7371dated March 26,20L3. All conclusions, recommendations, and limitations
cited in the referenced Geotechnical Report remain valid and apply to this addendum report.
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5
EARTH SYSTEMS PACIFIC
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April 24,2OL8 File No.: 301681-001
Doc. No.: 18-04-7LL
REFERENCES
1. Colorado Department of Transportation (CDOT) and othe rs, Colorodo Rockfoll Simulation
Progrom (CRSP)Version 4.0, March 2000
2. Earth Systems Southwest, 20L3, Geotechnical Engineering Report, Swenson Residence,
77-zLO Loma Vista, The La Quinta Resort, La Quinta, Riverside County, California, dated
March 26, 2Ot3, File No.: 12124-0L, Doc No. : 73-03-737 .
3. 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.: L2L24-0L, Doc No.: 13-10-730.
4. Earth Systems Southwest, 2014, lnfiltration 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.
5. Earth Systems Southwest, 2015, Plan Review and Response to City Review Comment
lncluding Retaining Wall Evaluation and Grouted Anchor General Specifications, Swenson
Residence,TT-2L0 Loma Vista, La Quinta, Riverside County, California, dated May 7,20L5,
File No.: L2L24-01, Doc No.: 15-05-705.
5. Earth Systems Southwest, 2016, Geotechnical Engineering Plan Review, Retaining Wall
with Rock Cladding, Swenson Residence,TT-210 Loma Vista, La Quinta, Riverside County,
California, dated July 13, 2OL6, File No.: L2L24-0L, Doc No.: 16-07-708.
7. Earth Systems Southwest, 2OL6, 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.: 16-07-7L3.
8. Earth Systems Southwest, 2016, Retaining Wall Evaluation and Grouted Anchor General
Specifications Supplemental Report for Easterly Knob Vertical Cut, Swenson Residence,
77-2LO Loma Vista, The La Quinta Resort, La Quinta, Riverside County, California, dated
December 2L,2OL6, File No.: L2L24-01, Doc No.: 16-12-7L0.
9. Turner A. Keith and Schuster L. Robert, 20L2, Rockfall Characterization and Control,
Transportation Research Board of the National Academies, Washington, D.C.
EARTH SYSTEMS PACIFIC
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April 24,20L8 File No.: 301681-001
Doc. No.: 18-04-7LL
CLOSURE
We appreciate the opportunity to provide our professional services. Please contact our office if
there are any questions or comments concerning this report or its recommendations.
Respectfu I ly su bm itted,
EARTH SYSTEMS P
7
'N}n"
Anthony Colarossi
Project Engineer
PE 60302
GER/ac/klp/mr /cg1
Distribution: 4lMrs. Lisa Swenson
UThe Altum Group,
1/BD File
*
Email: Mr. James Bazua: iames.bazua@thealtumgroup.com
EARTH SYSTEMS PACIFIC