HomeMy WebLinkAboutCT 12-05; LA COSTA RESIDENTIAL; GEOTECHNICAL PARAMETERS FOR RETAINING WALL; 2013-08-12Table 6
Static Equivalent Fluid Weight (pci)
Conditions Level 2:1 Slope
Active 40 65
At-Rest 55 90
Passive
*200
(Maximum of 3 ksf)
140
(Sloping Down)
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LOG FA Geotechnical, Inc. l
6~- 1~1- 095
August 12, 2013 VQ21 Project No. 12043-01
Ms. April Tornillo
Taylor Morrison
8105 Irvine Center Drive, Suite 1450
LI Irvine, California 92618
Subject: Clarification of Geotechnical Parameters for Retaining Wall Design Adjacent to Bio-
Retention Basins Proposed La Costa Town Center Residential Development, Carlsbad,
California
Introduction
In accordance with your request, LGC Geotechnical, Inc. has prepared this letter to clarify our geotechnical
parameters for retaining wall design for the walls adjacent to the proposed bio retention basins.
TI Geotechnical Parameters for Retaining Wall Desi'n
For design purposes, the following lateral earth pressure values for level or sloping backfill are
recommended for retaining walls backfihled with onsite soils of Low expansion potential. For the bio
retention basins only, we recommend the design engineer ignore all of the passive pressure attributed to the
planting media material. Full passive pressures may be used for the gravel below this planter mix.
* Ignore the upper 18" (all planting media)
LI Unrestrained (yielding) cantilever walls up to 15 feet in height should be designed for an active ecpi'iv
pressure value provided in table above. If conditions other than those covered herein are anticipated,
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equivalent fluid pressure valUes should be'rovided on an individual case basis by the geotechnical engineer.
A surcharge load for a restiamed&iinrstramed wall resulting from automobile traffic may be assumed to
be equivalent to a uniform ho'?izonti pressure of 75 psf which i is in addition to the equivalent fluid pressure V.11
given above For other nifoii surcharge loads, a uniform horizontal pressure equal to 0.35q should be
applied to the wall (where q is the surcharge pressure in psf). To account for potential redistribution of forces
during a seismic event, basement walls, if any, that fall within the requirements of ASCE 7-05 Section 15.6.1
should also be checked considering an additional uniform seismic pressure distribution equal to 101-1 psI,
where 1-1. equals the overall retained, height in feet. The wall prestires assume walls are backlilled with
free draining materials and water is not allowed to accumulate behind walls A typical wall drainage design
is provided in Appendix ft Importing or selective grading may be necessary to obtain retaining wall backfill
material.
Wall backfill should be brought to at least 3 percent above the optimum moisture content and compacted by
mechanical methods to at least 90 percent relative compaction (based on ASTM 131557). Wall footings
should be designed in accordance with the foundation design recommendations and reinforced in accordance
with structural considerations.
The allowable bearing pressure for retaining walls should be limited to 2,500 psf for footing founded in
compacted fill on the gravel storage blanket below the basins. Footing embedment depth should be at least
18 inches below the lowest adjacent grade.
Lateral soil resistance developed against lateral structural movement can be obtained from the passive
pressure value provided above Further, for sliding resistance, the friction coefficient of 0.33 may be used at
the concrete and soil interface. These values may be increased by one-third when considering loads of short
duration including wind or seismic loads. The total resistance may be taken as the sum of the frictional and
passive resistance provided that the passive portion does not exceed two-thirds of the total resistance.
Should you have any questions, please do not hesitate to contact our office. We appreciate this opportunity to
be of service.
ES
Sincerely, /.20 4Y
LGC Geolechnica!, Inc. co
Z5 NO. 26's .
iTi---- cc EXP 06/30/13
Tirn Lawson, CEG 1821, GE 2626 CAO
Geotechn ical Engineer/Geologist
TJL/kmh
Distribution: (1) Addressee (via email)
(I) Latitude 33 Planning and Engineering (via email)
Attn: Mr. Armando Urquidez
(I) Orco Block, Inc.
Attn. Mr. Tim Mallis (via email)
Project No. 12043-01 Page 2 August 12, 2013