HomeMy WebLinkAboutCDP 2020-0007; TERRA BELLA DEVELOPMENT; GEOTECHNICAL ADDENDUM FOR TEMPORARY EXCAVATION; 2021-06-21
GEOTECHNICAL | ENVIRONMENTAL | MATERIALS
June 21, 2021
Project No. 3630-SD
Terra Bella Development, LLC
P.O. Box 232458
Encinitas, California 920243
Attention: Ms. Meng Xu
Subject: Geotechnical Addendum for Temporary Excavations
6479 Surfside Lane
Carlsbad, California
References: See Page 2
Dear Ms. Xu:
As requested, GeoTek, Inc. (GeoTek) has prepared this letter to comment upon the project
rough grading plan that proposes temporary excavations for a project retaining wall. As noted
in GeoTek’s 2019 report, temporary excavations were recommended to be limited to a vertical
height of four feet. GeoTek understands that the project does not desire to construct
temporary shoring to facilitate the excavation and has alternatively proposed a temporary
excavation as indicated on the rough grading plan. The excavation generally consists of an
overall cut of approximately 8.5 feet. Specifically, the excavation detail indicates a 1:1 (vertical:
horizontal) excavation, one foot into the side property, with a maximum vertical excavation of
six foot below the base of the 1:1 excavation, which includes the excavation for the wall
footings.
In preparation of presenting this addendum, a global slope stability analysis was performed
based upon the proposed excavation detail. Soil shear strength parameters used were selected
from laboratory testing performed for the site and GeoTek’s engineering judgement. Results of
the analysis indicate the temporary excavation shown on the plan possesses a factor of safety
greater than 1.2, which is typically required for a short-term condition (see attached). Thus,
excavations are globally stable up to a vertical excavation of 6.0 feet.
It should be noted that global stability does not analyze surficial stability. Based upon
experience, the geology underlying the site and local area contain soils that are potentially
“friable” and susceptible to erosion. Friable formational material is prone to surficial instability
and sluffing into excavations. As such, each contractor, person, and employer will need to
GeoTek, Inc.
1384 Poinsettia Avenue, Suite A Vista, CA 92081-8505
(760) 599-0509 Off, (760) 599-0593 Fa. www.geotekusa.com
Terra Bella Development, LLC Project No. 3630-SD
Geotechnical Addendum June 21, 2021
6479 Surfside Lane, Carlsbad, California Page 2
comply with California Occupational Safety and Health Act (CalOSHA) guidelines as mandated
by law. GeoTek is not a responsible person beyond those persons employed with GeoTek.
Should you have any questions after reviewing this letter, please feel free to contact our office
at your convenience.
Respectfully Submitted,
GEOTEK, INC.
Christopher D. Livesey Edward LaMont
CEG 2733, Exp. 05/31/23 CEG 1892, Exp. 7/31/22
Project Geologist Principal Geologist
Bruce A. Hick
GE 2284, Exp. 12/31/22
Geotechnical Engineer
Attachment: Temporary Excavation @ Side Yard Static Slope Stability Analysis
Distribution: (1) Addressee via email
REFERENCES
GeoTek, Inc, 2019, “Preliminary Geotechnical Evaluation, 6479 Surfside Lane, Carlsbad,
California”, dated March 9.
HWL Planning & Engineering, 2020, Preliminary Grading Plan for 6479 Surfside Lane, Carlsbad,
CA 92011, 1 Sheet, plot dated March 5, 2020.
Jack Bian Architect, 2020, Architectural Plans for Surfside Family Residence, 6479 Surfside Lane,
Carlsbad, CA 92011, 8 Sheets, A2-101 through A3-102, received February 2020.
GEOTEK
1.2441.2442500.00 lbs/ft675.00 lbs/ft1.2441.244Method NameMin FS Bishop simplified1.244Material NameColorUnit Weight(lbs/3)Strength TypeCohesion(psf)Phi(deg)Af125MohrCoulomb15027Qop125MohrCoulomb32429.35' CMU Retaining WallAPN 214-021-12-30-25-20-15-10-50510BRMCompanyGeoTek, Inc.Slope StabilityProjectTemporary Excavation @ Side Yard - StaticSLIDEINTERPRET 7.0380 CX) 0 r--. LO <O 0 <O LO LO □ □ ~i--------------0 GEOTEK