HomeMy WebLinkAboutSDP 09-04; SHOPPES AT CARLSBAD; GEOTECHNICAL EVALUATION OF EXISTING SEWER AND STORM DRAIN PIPELINES; 2014-01-30Leighton Consulting, Inc.
A LEIGHTON GROUP COMPANY
January 30, 2014
Project No. 603522-001
Plaza Camino Real, GP
2049 Century Park East, 41st Floor
Century City, California 90067
Attention: Mr. Mike Sheller
Subject: Geotechnical Evaluation of Existing Sewer and Storm Drain Pipelines,
Proposed Retail Expansion (Reconfiguration and Additional Retail) Phase 1,
Westfield Plaza Camino Real Carlsbad, California
Reference: Leighton Consulting, Inc., 2013, Geotechnical Investigation, Proposed
Reconfiguration and Additional Retail, Westfield Plaza Camino Real,
Carlsbad, California, Project No. 603522-001, February 21, 2013
ANF & Associates, 2013, Structural Plans, Retail Expansion, Westfield
Plaza Camino Real Carlsbad, California, Sheets S6.6, S6.7, and S2.0
dated October 21, 2013
Hofman Planning & Engineering, 2014, Public Sewer Relocation and
Utility Plan, Westfield Phase 1, Carlsbad, California
In accordance with your request, we have performed a limited geotechnical evaluation
of the existing pipelines at the eastern end of the proposed retail expansion
(reconfiguration and additional retail) at Westfield Plaza Camino Real in Carlsbad
California (see Figure 1, Site Location Map). The purpose of this evaluation is to
address the concerns that the existing pipelines, a 54" RCP Storm Drain and 8" VCP
Sewer, that may be distressed due to the new proposed truck loading dock and trash
compactor area (i.e., increase loading and overburden pressures associated with the
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603522-001
additional fill). The current depth and slope of the existing pipelines are presented on
Figure 2, Existing Pipeline Profiles.
Based on our review of the referenced drawings, we understand that up to 18 feet of
new backfill will be placed over the pipelines and behind a new retaining wall to support
the new truck loading dock and trash compactor area. The new retaining wall, designed
by ANF & Associates, will be supported by conventional continuous footing, which is
utilizing an allowable bearing pressure of 3,500 pounds per square foot.
As background, we should note that this area is underlain by older documented fill
placed during original site grading and is within the limits of a 30 foot high surcharge fill
(Leighton, 2013). The surcharge fill was constructed to increase the rate of settlement of
the onsite alluvium material and fill material approximately 20 feet outside the building
limits that was monitored for 18 months and removed to site grades.
Given our current understanding of the site conditions and the proposed improvements,
we recommend that the existing 8" diameter VCP sewer pipe be relocated to minimize
potential negative impacts to the pipeline and surrounding improvements. In addition, the
VCP sewer pipe has a relatively gentle invert slope and intolerant to differential movement
and deflection. Note that current civil plans by Hofman Planning indicate that the sewer
will be relocated and replaced an 8" PVC sewer. In addition, the old existing sewer
pipeline beneath the new improvements should be properly abandoned (i.e., removed or
backfihled with a 2-sack sand cement slurry).
For the existing 54 inch RCP storm drain pipeline, we anticipate minimal settlement due to
additional fill loads (i.e., total static settlement of approximately % to 1/2 inch for the soil
below the pipeline). Therefore, it is our opinion the storm drain pipeline can remain in
place if it is structurally capable of supporting the additional loading. The existing storm
drain has an invert slope of approximately 1.5 percent which is tolerant to minor
differential movements and settlement. In addition, based on our understanding and
information provided by ANF and Associates, the proposed retaining wall foundation is
structural designed to accommodate retained soil loads and that additional reinforcement
has been provided for the footing located over the existing storm drain.
The conclusions and recommendations in this review are based in part upon data that
were obtained from a limited number of observations, site visits, excavations, samples,
and tests. Such information is by necessity incomplete. The nature of many sites is such
that differing geotechnical or geological subsurface conditions can and do occur.
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10 603522-001
Therefore, the findings, conclusions and recommendations presented in this review and
previous report can be relied upon only if Leighton has the opportunity to observe the
subsurface conditions during grading and construction of this project. Only with these
observations are we able to confirm that our preliminary findings are representative for
the site.
If you have any questions regarding our letter, please do not hesitate to contact this
office. We appreciate this opportunity to be of service.
Respectfully submitted,
LEIGHTON CONSULTING, INC.
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Project Geologist
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William D. Olson, RCE 45283
Associate Engineer
Attachments: Figure 1 - Site Location Map
Figure 2— Existing Pipeline Profiles
Distribution: (1) Addressee
(3) Hofman Planning, Ms. Haixin Li
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Project: 603522-001 Eng/Geol: MDJ SITE LOCATION MAP Figure
Scale: 1 "= 2,000 Date. January, 2014 Westfield Plaza Camino Real
Base Map. Microsoft Bing, 2012 Robinsons-May Renovation k4 Thematic Info: Leighton
Author Leighton Geomatics (mmurphy) Carlsbad, California Leighton
Mep Soveu as P \d101t:ng/603522\001/Maps\P003522001F01$ teL000t oi1Mup_GIS_2012.10-09.rn04 on 124/2012 10 02 21 AM