HomeMy WebLinkAboutCT 00-06; BRESSI RANCH; RECOMMENDED STABILITY FILLS ALONG POINSETTIA LANE; 2004-03-26Oto
Leighton and Associates, Inc.
A LEIGHTON GROUP COMPANY
March 26, 2004
Project No. 971009-009
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 Slopes Along
Poinsettia Lane, 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
Kimley-Horn, 2003, Grading and Erosion Control Plans for Poinsettia Lane at
Bressi Ranch, Carlsbad, California, Drawing No. 397-2J, dated January 24, 2003
Introduction
Geologic mapping of the slopes during the mass grading of the Bressi Ranch project indicated
that some of the manufactured cut slopes and natural slopes along both sides of Poinsettia Lane
contained adverse geologic conditions (such as out-of-slope bedding, blocky claystone,
oversteepened natural slopes). As a result, recommendations were made during the course of the
grading operations to stabilize the slopes containing adverse geologic conditions. Based on our
recommendations, the following slopes were constructed with stability fills:
North side of Poinsettia Lane between Station Nos. 86+30 and 91+25
South side of Poinsettia Lane between Station Nos. 87+25 and 90+00
3934 Murphy Canyon Road, Suite B205 • San Diego, CA 92123-4425
858.292.8030 • Fax 858.292.0771 • www.leightongeo.com
971009-009
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 system was placed along the back of the stability fill key and backcut on northern side
of Poinsettia Lane. The subdrain 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 subdrain was placed with a minimum I-percent fall toward the
outlet location. The subdrain was outletted with a 4-inch diameter solid pipe 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. A subdrain was constructed, as
necessary, at approximate 30 feet vertical interval 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.
4QU
frEG Randall K. Wagne 1612
Senior Associate
Distribution (2) Addressee
(2) Lennar Communities, Attention: Ms. Kristine Zortman
(1) J.T. Kruer, Attention: Mr. Chuck Knight
-2-
Leighton