HomeMy WebLinkAboutCT 00-06; BRESSI RANCH; RECOMMENDED STABILITY FILLS ALONG EL FUERTE; 2004-03-22Leighton and Associates, Inc.
A LEIGHTON GROUP COMPANY
March 22, 2004
Project No. 971009-011
To: Lennar Communities
1575 Faraday Avenue, Suite 300
Carlsbad, California 92009
Attention: Mr. Jim Urbina
Subject: Recommended Stability Fills Due to Adverse Geologic Conditions of Cut Slopes
Along El Fuerte Street, Bressi Ranch, Carlsbad, California
References: Leighton and Associates, Inc., 2001, Supplemental Geotechnical Investigation for
Mass Grading, Bressi Ranch, Carlsbad, California, Project No. 971009-005, dated
March 14, 2001
Project Design Consultants (PDC), 2003, Mass Grading and Erosion Control Plans
for Bressi Ranch, Carlsbad Tract No. CT-00-06, Carlsbad, California, Drawing No.
400-8A, dated January 23, 2003
Introduction
Geologic mapping of the cut slopes during the mass grading of the Bressi Ranch project
indicated that some of the manufactured cut slopes along both sides of El Fuerte Street contained
adverse geologic conditions (such as out-of-slope bedding, remolded clayseams, and blocky
claystone). As a result, recommendations were made during the course of the grading operations
to stabilize the applicable cut slopes. Based on our recommendations, the following cut slopes
were constructed with stability fills:
East side of El Fuerte Street between Station Nos. 37+50 and 40+50
East side of El Fuerte Street between Station Nos. 43+50 and 51+00
Southwest side of El Fuerte Street between Station Nos. 16+85 and 21+70
West side of El Fuerte Street between Station Nos. 13+50 and 15+00
3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425
858.292.8030 • Fax 858.292.0771 • www.leightongeo.com
971009-011
Recommendations
Based on the recommendations presented in the project geotechnical report (Leighton, 2001), we
recommended that the stability fill keys be excavated a minimum of 15 to 20 feet wide at a depth
of 5 feet below the toe-of-slope elevation. In addition, the key bottoms were tilted a minimum of 2
percent into-the-slope. The backcuts were excavated at a 1:1 or flatter (horizontal to vertical) slope
inclination.
A subdrain for each stability fill key was placed along the back of the stability fill key. The
subdrains consisted of a 4-inch diameter perforated pipe surrounded by a minimum of 3-cubic feet
(per linear-foot) of crushed gravel and surrounded by a filter fabric (Mirafi 140N or equivalent).
The subdrains were placed with a minimum 1-percent fall toward the outlet location. The subdrains
were outletted with a 4-inch diameter solid pipe into proposed storm drain structures or at the slope
face. A concrete cut-off wall extending 6 inches around the subdrains were placed at the
connection point of the perforated and solid portions of the subdrain system. Additional subdrains
were constructed, as necessary, at approximate 30 feet vertical intervals where the slope was
greater than 30 feet in height.
Geologic mapping of the stability fill key and backcuts were performed prior to the placement of
fill. The subdrain placement was observed by a representative of Leighton and Associates and the
subdrain line and grade was surveyed by the project civil engineer.
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.
A KWAf~~
Randall K. Wagner CEG 1612
Senior Associate
Distribution: (2) Addressee
(2) Lennar Communities, Attention: Ms. Kristine Zortman
(I) J.T. Kruer, Attention: Mr. Chuck Knight
-2-
Leighton