HomeMy WebLinkAboutCT 90-03; SHELLEY PROPERTY; PROPOSED WICK DRAIN INSTALLATIONS AND SETTLEMENT MONITORING; 1999-02-08,^ ^^•i^^^^k^^^^^^^^M^ ^^^B A GTG Company
Leighton and Associates
m GEOTECHNICAL CONSULTANTS
PROPOSED WICK DRAIN INSTALLATIONS
AND SETTLEMENT MONITORING,
SHELLEY PROPERTY,
CARLSBAD TRACT NO. 90-3
CARLSBAD, CALIFORNIA
Project No. 851855-008
February 8, 1999
Prepared For
MR. DAN SHELLEY
c/o Mr. Chuck DuVivier
P.O. Box 230638
Encinitas, California 92024
3934 MURPHY CANYON ROAD, SUITE B205
SAN DIEGO, CA 92123-4425
(619) 292-8030 • FAX (619) 292-0771
A GTG Company
February 8, 1999
Project No. 4851855-008
Leighton and Associates
GEOTECHNICAL CONSULTANTS
To: Mr. Dan Shelley
c/o Mr. Chuck DuVivier
P.O. Box 230638
Encinitas, California 92024
Subject: Proposed Wick Drain Installations and Settlement Monitoring, Shelley Property,
Carlsbad Tract No. 90-3, Carlsbad, California
Reference: Leighton and Associates, Inc., 1998, Update Geotechnical Investigation, Shelley
Property, Carlsbad Tract No. 90-3, Carlsbad, California, dated September 8,1998.
Introduction
In accordance with your request, we have reviewed our update geotechnical investigation of the
Shelley Property to estimate the number and depth of wick drain installations required for the
proposed improvements. This letter presents our estimation of wick drain installations and
additional recommendations for the monitoring of settlement.
Wick Drains
Based on our review, if the wick drain alternative is selected, alluvial removals will be completed in
areas to receive improvements before the installation of wick drains. Removals will be completed
to within two feet (or closest feasible removal) of the surface of the groundwater table. Fill
materials should then be placed to provide a uniform working pad. The surface of the fill pad
should be graded to meet with the toe of proposed fill slopes and have an overall gradient of no less
that one percent, draining to the toe of the proposed slopes. Wick drains will then be installed from
this grade to the base of alluvial materials or competent formational materials.
After installation of the wick drains, select fill consisting of clean granular sands derived from the
on site Torrey Sandstone materials or approved substitute should then be placed to one to two feet
above the elevation where wick drains were installed to facilitate evacuation of water draining out
of the alluvial materials.
We have reviewed the subsurface data and site grading plans to estimate the areas and amounts of
wick drains. The attached Plate No. 1 indicates the areas proposed for wick drain installation and
the length of wick drain in each area. We have estimated the total length of drain needed to be
between 200,000 and 250,000 linear feet of wick drain in approximately 4,700 locations. These
installations are spaced in accordance with the schedule recommended in our update geotechnical
report. Based on our experience with similar projects, the cost for installation of wick drains can
vary between 40 to 75 cents per foot depending on the amount of drains installed, with an additional
$25,000 mobilization fee. We have provided these estimated costs as a convenience to our client;
however, these costs should be verified before precisely estimating the entire cost of the installation.
3934 MURPHY CANYON ROAD, SUITE B205
SAN DIEGO, CA 92123-4425
(619) 292-8030 • FAX (619) 292-0771
851855-008
Based on conversations with an installer, we understand that wick drains can be installed at a rate of
approximately 12,000 feet per day per machine.
Settlement Monitoring
Settlement monitoring is required for all three alternatives (wick drains, surcharging, and
monitoring only). Monitoring will be performed in all areas where alluvial soils are left in place
after site grading achieves the finished grade or surcharge elevation. A minimum of 10 to 15
settlement monuments will need to be installed to monitor the settlement of alluvial materials left in
place. Surveying of the settlement monuments should be performed by the project civil engineer
with data provided to the geotechnical consultant for review. After review of the settlement data
indicates the completion of the primary settlement, the area(s) will be released for construction.
Settlement monuments can be installed for approximately One Hundred Fifty Dollars ($150.) each.
Monitoring costs will be dependent on the length of the monitoring period. As noted in the project
geotechnical report, the monitoring period will be 18 to 24 months for monitoring if fill soils are
placed to the design grade without surcharging or wick drain installation. The monitoring period is
estimated to be 9 to 12 months for the surcharge and wick drain alternatives. Surveying should be
performed at approximately 2-week intervals during the monitoring period. Geotechnical costs for
data reduction and analyses will be approximately Two Hundred Dollars ($200.) per reading with
summary letters prepared as requested at a cost of Four Hundred Dollars ($400.) per letter.
If you have any questions regarding our report, please contact this office. We appreciate this
opportunity to be of service.
Respectfully submitted,
LEIGHTON AND ASSOCIATES, INC.
t _
JL
Michael R. Stewart, CEG 1349
Director of Geology/Managing Principal
1 NO. 1349 1
CERTIFIED
ENGINEERING,
AGEOLOGIST. t
JAD/MRS
Attachment: Plate 1 - Geotechnical Map (In Pocket)
Distribution: (1) Addressee
(1) Project Design Consultants, Attention: Mr. Mark Campbell