HomeMy WebLinkAboutCT 03-02; CARLSBAD RANCH PA 5; RECOMMENDED 85-PERCENT RELATIVE COMPACTION RELATIVE TO THE PLACEMENT OF THE HIGHLY EXPANSIVE CLAY SOILS; 2006-11-22C-T°3z
Leighton and Associates, Inc.
A LEIGHTON GROUP COMPANY
November 22, 2006
Project No. 040575-005
To: Grand Pacific Carlsbad
5900 Pasteur Court, Suite 200
Carlsbad, California 92008
Attention: Mr. Bruce Zelenda
Subject: Recommended 85-Percent Relative Compaction Relative to the Placement of the
Very Highly Expansive Clay Soils in the Private Parking Lot West of Hotel 1 and
the Conference Facility, Proposed Grand Pacific Resort, Carlsbad Ranch Planning
Area PA-5, Carlsbad, California
Reference: Leighton and Associates, 2005, Geotechnical Investigation, Proposed 53-Acre
Resort Development.- Phase 1, Carlsbad Ranch, Planning Area No. 5, Carlsbad,
California, Project No: 040575-003, dated April 11, 2005
This letter presents our geotechnical recommendations concerning the placement of the very
highly expansive soils in the triangular-shaped private parking lot located west of Hotel 1 and the
Conference Facility at the proposed Grand Pacific Resort in Carlsbad, California. Very highly
expansive soils (haying expansion potentials in the 150 to 250+ range) were encounterèdbeneath
the, basement of Hotel 2. Based on our previous recommendations presented in the project
preliminary geotechnical report (Leighton, 2005), these very highly expansive soils were
recommended to. be removed to a depth of 10 feet below and 10 feet outside the limits of any
building or other improvement and replaced with low expansive sandy soils. During the grading
operations when these highly expansive soils were encountered, they were placed in a deep fill
area (ie. an area greater than 10 feet below the proposed finish grade elevation). However, as the
site rough and fine grading has been completed, the only practical location to place these very
highly expansive soils is in the large private parking lot located west of Hoel 1 and the
Conference Facility. Since highly expansive soils are already located below a depfh of 10 feet in
this parking lot, we recommend that the very highly expansive soil (from the Hotel 2 excavation)
be placed below a depth of 5 feet in this parking lot.
1'
3934 Murphy Canyon Road, Suite B205 • San Diego, CA 921234425'
858.292.8030 • Fax 858.292.0771 • www.leightongeo.com
040575-005
As you are aware, the placement of these highly expansive clays within 10 feet of the parking lot
pavement section and other improvements may result in differential heaving of the
improvements. In order to reduce the heaving potential, we recommend that the clay soils be
placed at a minimum 85 percent relative compaction and a minimum moisture content of 6-
percent over the optimum moisture content of the clay. The clay soils should not be placed with 5
feet of the parking lot subgrade elevation. Within the upper 5 feet of the parking lot subgrade
elevation, we recommend that sandy low expansive soils be placed at a minimum 90-percent
relative compaction with at least a moisture content of 27percent over the optimum moisture
content.
If you have any questions regarding this letter, please do not hesitate to contact this office We
appreciate this opportunity to be of service.
Respectfully submitted,
LEIGHTON AND, ASSOCIATES, INC.
• Randall K. Wagner, CEG 1612
Principal Geologist
Distribution: (3) Addressee
(2) City of Carlsbad, Attention Mr. Patrick Vaughan