HomeMy WebLinkAbout3184; CANNON ROAD WEST; RESULTS OF INSTRUMENTATION MONITORING; 1999-09-30URS Greiner Woodward Clyde
A Division of URS Corporation
September 30, 1999
1615 Murray Canyon Road, Suite 1000
San Diego, CA 92108
Tel: 619.294.9400
Fax: 619.293.7920
Offices Worldwide
City of Carlsbad
Public Works - Engineering
2075 Las Palmas Drive
Carlsbad, CA 92009-1161
Attention: Ms. Sherri Howard
Subject: Results of Instrumentation Monitoring
Cannon Road Bridge Over Macario Canyon
Carlsbad, California
URSGWC Reference No. 58-9551 1302.03-OINST
I
Dear Ms. Howard:
This letter summarizes URS Greiner Woodward Clyde's (URSGWC) instrumentation
monitoring program for the approach embankment fill at the east abutment of the proposed
Cannon Road bridge over Macario Canyon. This work has been performed in accordance .with
our agreement dated January 29, 1999
The east approach embankment is underlain by deep alluvium that inclUdes soft and
compressible soils. Vertical drains were installed to accelerate consolidation of the compressible
soils. Instrumentation, consisting of piezometers and settlement plates, were' installed to monitor
consolidation of the soils. The embankment was also placed in two stages to mitigate potential
instabilities.
URSGWC installed four piezometers (designated P-i through P-4) within the footprint of the
east approach embankment on October 22 and 23, 1998, prior to placement of embankment fills.
The piezometers were installed to monitor the dissipation of excess pore pressures that would be
generated in the compressible soils due to placement of the fill soils. The piezometer locations
are shown on Figure 1, attached. Two settlement plates were also installed within the footprint
of the embankment prior to fill placement. The locations of these plates (designated DSPW and
DSPE) are also shown in Figure 1.
. Embankment fill was placed in two stages, with each stage receiving approximately 20 feet of
fill. Fill placement for Stage 1 commenced on November 6, 1998, and was completed, on
December 11, 1998. Stage 2 fill placement commenced on January 15, 1999 and was completed
by February 11, 1999. Piezometer and settlement measurements were made during and after
placement of fill at approximate intervals of one week. Settlement measurements were provided
\\SDG1\WPDATA\9551 1302\Oinst-a-Ldoc\30-Sep-99\SDG
Spencer-L. Price, R.C.E. 5
Senior Staff Engineer
URS Greiner Woodward Clyde
Ms. Sherri Howard
City of Carlsbad .
September 30, 1999
Page
to us by Simon Wong Engineering. Piezometer readings were made by URSGWC personnel
using a pneumatic indicator.
Settlement and piezometer measurements are presented on Figure 2, attached. The results of
measurements made through August 12, 1999 indicate the following:
Primary consolidation settlements appear to be substantially complete. The settlement
readings indicate a uniform rate of settlement (vs. log of time), indicative of near the end of
primary consolidation. In general, the responses of each piezometer were similar, with
excess pore pressures reaching a maximum near the end of fill placement and dissipating
over time. Stage 2 fill was approved to begin on January 14, 1999. The responses of
piezometers P-i and P-4 were somewhat anomalous; P-4 had a significantly higher pore
pressure increase, which may indicate a slower-draining material than the material in which
the other piezometers were installed. The readings for P-i indicate that the excess pore
pressure at that location did not fully dissipate after Stage 2 fill placement, although the pore
pressure did level off in a similar manner as the other piezometers. This response may be the
result of the piezometer having become damaged. Other subtle variations in the pore
pressure response can be attributed to variations in the static groundwater level, calibration
error of the pneumatic indicator, and the accuracy and precision of the readings.
The continuing settlements appear to be typical of secondary compression. This compression
occurs after the excess pore pressures have dissipated and is analogous to creep in other
materials. Projecting the current secondary compression rate, we estimate that rate may
contribute an additional three to six inches over a period of 50 years. Periodic overlays may
be required to alleviate the transition between the bridge and the approach embankment.
Should you require further assistance at this time, do not hesitate to give us a call.
Very truly yours,
URS GREINER WOODWARD CLYDE
rs
Senior Associate
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Attachments
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INDICATES APPROXIMATE LOCATION OF
PIEZOMETER
[ INDICATES DEEP SETTLEMENT PLATE
DSPW = DEEP SETTLEMENT PLATE WEST
DSPE = SEEP SETTLEMENT PLATE EAST
40 80
APPROXIMATE GRAPHIC SCALE
(FEET)
tINS Grelner Woodward Clyt
25
20
15
10
-10
-15
TV
-20.00
Piezometer 1 (elev. -11')
Piezometer 2 (elev. -33.5')
—A--- Piezometer 3 (elev. -23')
x Piezometer 4 (elev. +3')
0 - DSPW Settlement
- -0 - DSPE Settlement A
p _o°.G.G. - ..o
10 100
Elapsed Time (days, Day 0 = 11/6/98)
PIEZOMETER AND SETTLEMENT DATA
MACARIO CANYON BRIDGE - EAST EMBANKMENT
CARLSBAD, CALIFORNIA
FN: SITE PM: SLP I CHECKED BY: £.OI DATE: 9-29-99 1 PROJECT NO: 58-9551 1302.03—OINST I FIG. NO: 2
- -20
1000