HomeMy WebLinkAboutCT 97-02; Rancho Carrillo Villages A, B, C & D - Continental; Rancho Carrillo Villages A, B, C & D - Update; 1997-07-141
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UPDATE REPORT
RANCHO CARRILLO
VILLAGES A, B, C AND D
CARLSBAD, CALIFORNIA
PREPARED FOR
CONTINENTAL RANCH INC.
SAN DIEGO, CALIFORNIA
JULY 1977
GEOCON
INCORPORATED
GEOTECHNICAL CONSULTANTS
Project No. 05845-12-04
July 14, 1997
Continental Ranch Inc.
12636 High Bluff Drive, Suite 300
San Diego, California 92130
Attention: Mr. Dave Lother
Subject: RANCHO CARRILLO
VILLAGES A, B, C, AND D
CARLSBAD, CALIFORNIA
UPDATE REPORT
Reference: 1. Preliminary Geotechnical Investigation for Rancho Camilla Villages A, B, C,
and D, Carlsbad, California, prepared by Geocon Incorporated, dated March 3,
1993 (Project No. 04787-12-05)
2. Supplemental Geotechnical Investigation [for] Rancho Carrillo, Carlsbad,
California, prepared by Geocon Incorporated, dated June 20, 1996 (Project
No. 04787-12-09)
3. Tentative Map C. T. 97-02/P. U. D. 97-02, Rancho Carrillo Villages A, B, C, and
D, prepared by Rick Engineering Company, stamp dated July 1, 1997
Gentlemen:
In accordance with your request, we are providing this update to the above-referenced geotechnical
report. This update is required to meet the requirements of the City of Carlsbad in that a period of
three years has elapsed since the referenced preliminary geotechnical report was issued.
As a part of this update, we have reviewed the referenced tentative map indicating the planned finish
grade conditions. For reference purposes, the geologic mapping from the geotechnical reports has
been overlain on the attached 80-scale version of the tentative map.
It is our opinion that the conclusions and recommendations, as presented in the referenced
geotechnical reports are valid and remain applicable to the proposed development. Furthermore,
based on our review of the 40-scale tentative map, it is our opinion that the proposed grading is in
general conformance with the recommendations of the referenced geotechnical reports.
6960 Flanders Drive • San Diego, California 92121-2974 • Telephone (619) 558-6900 • Fax (619) 558-6159
For clarity purposes, the attached letter prepared by Geocon Incorporated, dated May 14, 1997, is
included in this update to aid in understanding the intent and implementation of placing "granular"
soil within fill slopes as discussed in the geotechnical report.
If you have any questions regarding this correspondence, or if we may be of further service, please
contact the undersigned at your convenience.
Very truly yours,
GEOCQN INCORPORATE
David F. Leake
RCE_22527
DFL:dmc
(6) Addressee
(2) Rick Engineering Company
Attention: Mr. Craig Kahlen
Project No. 05845-12-04 -2-July 14, 1997
GEOCON
INCORPORATED
GEOTEOHNICAL CONSULTANTSProject No. 05845-12-01
May 14, 1997
VIA FACSIMILE AND U. S. MAIL
Mr. Dave Lother
Continental Ranch Inc.
12636 High Bluff Drive, Suite 300
San Diego, California 92130
Subject: RANCHO CARRJJLLO
CARLSBAD, CALIFORNIA
CONSULTATION - GRANULAR SOIL
Gentlemen:
In accordance with your request, this correspondence has been prepared to discuss the intent and
implementation of placing "granular" soil in the outer 15 feet of fill slopes on the subject project.
The intent of our recommended "granular" slope zone was to provide a completed slope with shear
strength characteristics that under normal conditions would not be susceptible to surficial sloughing or
shallow slope failure. Therefore, soils with low compacted shear strength- or soils which may lose
strength due to subsequent excessive expansion after placement are not desirable in the slope zone.
Additionally, even though a thin layer of such soil may not be sufficient to significantly reduce the
strength of the overall slope zone, such a condition could cause subsurface water to perch on the layer
and create a nuisance slope seepage condition or destabilize a localized portion of the slope. Since silty
clayey soils are most susceptible to a loss of strength due to soil expansion and often possess low
strength characteristics even in a properly compacted condition, their placement within the slope zone
should be kept to a minimum to reduce the risk for slope distress.
Essentially all material on the project site can be used in the slope zone provided it is adequately mixed
or blended with other materials to yield a soil condition which contains at least 30 percent sand size
particles and/or does not possess an Expansion Index in excess of 90. It has been our experience that
when soil meets such conditions, its shear strength characteristics will be sufficient to provide
acceptable surficial slope stability. Where the soil does not meet the above criteria, lengthy laboratory
testing would be required to determine that the long term shear strength of the soil actually used is
acceptable.
The term "granular" was used in the project soil report to preclude the use of very clayey, highly
expansive soil in the slope zone unless such materials were altered (by mixing or blending with sandy
soils) to yield a granular texture. It has been common practice on most grading projects in San Diego
County to limit the placement of low strength, highly expansive clayey soils to fill areas beyond the
slope zone. The use of "false" slopes to meet the "granular" slope zone criteria is typically not
necessary and the implementation of the recommendation is not normally a separate pay item.
6960 Flanders Drive • San Diego, California 92121-2974 • Telephone (619) 558-6900 • Fax (619) 558-6159
From a practical viewpoint, the stiff, clayey soils that comprise a majority of the on-site topsoils,
colluvium and alluvium, will be very difficult to blend and/or mix with sandy soils due to their
plasticity characteristics. Alternatively, the mixing of fonnational claystones and siltstones with sandy
soils should be less difficult and is frequently accomplished, particularly when the mixing occurs in the
cut area prior to placement
If you have any questions regarding this letter, or if we may be of further service, please contact the
undersigned at your convenience.
Very truly yours,
GEOCON INCORPORATED
Thomas V.
RCE 20427
TVLisc
(1) Addressee
(1) Continental Ranch Inc. (via Facsimile)
Attention: Mr. Mike Lombardi
Project No. 5845-12-01 - 2 - May 14,1997