HomeMy WebLinkAboutCT 02-28; La Costa Condominiums; Tentative Map (CT) (12)Leighton and Associates, Inc.
A LEIGHTON GROUP COMPANY
June 17,2003
Project No. 980161-002
To:
Subject:
Reference:
Mr. Kwan So
2683 Costebelle Drive
La Jolla, California 92037
Evaluation of Proposed Detention Basin, Lot 185, La Costa Avenue South Unit 1,
Carlsbad, California
Leighton and Associates, 2002, Updated Preliminary Geotechnical Report,
Lot 185, La Costa Avenue South Unit 1, Carlsbad, California, Project No.
9801 61-002
As requested, we have performed an additional stability analysis of the proposed fill slope located
above the proposed detention basin for Lot 185 of La Costa Avenue South Unit 1, located south of
La Costa Avenue and north of Sacada Circle, in Carlsbad, California. The proposed detention
basin, as shown on Tentative Tract Map prepared by O’Day Consultants, dated May 2003, is
located at the southeast corner of the project in the vicinity of our Geological Cross-Section D-
D’ (Leighton, 2002).
In summary, this area is currently underlain by landslide deposits that are considered to be
unstable in their present condition and will require remedial measures (i.e. buttressing with fill
andor removals of the unstable and potentially compressible portions). Recommendations for
the stabilization of the landslide are presented in Section 5.2, and indicated on the Geotechnical
Map (Plate 1) and Cross-sections (Plate 2) of the Updated Preliminary Geotechnical Report.
Given the results of our previous investigation and the proposed grades for detention basin, the fill
slope (i.e., a remediated fill slope with a buttress) was analyzed for gross stability utilizing the
slope stability program SLOPE/W (Geo-Slope, 2002). Our analysis, assuming homogeneous slope
conditions and an elevated groundwater level, indicates that the designed fill slopes constructed at
2: 1 (horizontal to vertical) slope inclinations up to a maximum proposed height of 50 feet will have
a calculated factor of safety of 1.5 or greater with respect to potential, deep rotational failure. The
slope stability calculation is presented in Appendix A. Note that the proposed slopes should be
constructed in accordance with the recommendations of this report, the General Earthwork and
3934 Murphy Canyon Road, Suite B205 = San Diego, CA 921 234425
858.292.8030 rn Fax 858.292.0771 rn www.leightongeo.com
h
980161-002
Grading Specifications for Rough Grading (Updated Preliminary Geotechnical Report,
Appendix E), and City of Carlsbad grading requirements.
If you have any questions regarding this letter, please contact this office. We appreciate this
opportunity to be of service.
Respectfully submitted,
LEIGHTON AND ASSOCIATES, INC.
William D. Olson, RCE 45283
Senior Project Engineer
Attachment: Appendix A - Slope Stability
Distribution: (2) Addressee
(6) Hoffman Planning, Attention: Mr. Roy Publico
(1) O’Day Consultants, Attention: Mr. George O’Day
-2- Leighton and Associates, Inc.
A LEIGHTON GROUP COMPANY
F
5
W w
z 0
s 4
W
La Costa Cross Section D-D'
Proposed Grading June 2003
File Name: La Costa DD Static 6-16-03 2.slz
Analysis Method: Bishop
Factor of Safety: 1.59
Scale = 1" : 60'
240
m
160
120
en
40
0
Artificial Fill (Af)
Unit Weight: 125
Piezometric Line #: 1
** ;;:esm:250 1'
*
/ /
Santiago Formation (Tsa)
Unit Weight: 130
Cohesion: 500
'hi:
lie2
240
m
160
120
80
40
0
29
rometric
i=
k
W W
z 5 s W
Line #: I
I
SECTION D-D
N3 E