Geosynthetics October/November 2019 - 36

Repairing an oil well platform with a geogrid reinforced soil slope

The moisture content of the soils
ranged from 15% to 36%, except in the
lignite where moisture contents of 57%
and 93% were measured. Proctor tests
for the fine-grained soils determined the
optimum moisture contents to be between
19% and 22%. Three inclinometers and
three piezometers were installed during
the geotechnical investigation. The results
of the inclinometer measurements indicated the failure plane was at 38 feet (11.6
m) in boring S07 and at 36 feet (11.0 m) in
boring S08 (Figures 4a and 4b).

Slope stability failure analysis
FIGURE 2 The head scarp of the failed slope cutting through the gas flare

BLOW COUNT (N) vs. DEPTH
2170

2160

2150

ELEVATION

2140

2130

2120

2110

2100

2090

2080

0

5

10

15

20

25

30

35

40

45

BLOW COUNT (N)
S-01

S-02

S-03

S-04

S-05

S-06

S-07

S-08

FIGURE 3 Variation of blow counts with depth at the Mormon Butte site

S-09

50

The piezometer measurements and the
elevation of the creek were used in a seepage model to establish the groundwater
flow conditions in the slope. Using this
groundwater condition along with the
information from the inclinometers and
triaxial testing, a limit equilibrium slope
stability analysis was performed for the
prefailure geometry to determine the in
situ strength parameters of the backfill
slope. The parameters of the soil in the
failed slope were varied until a factor of
safety of 1.0 was achieved, indicating an
imminent failure condition.
The specified search limits required
the failure plane to exit the ground surface at the existing crack location. The
depth of the failure plane correlated well
with the depth and location of the failure surfaces found from the inclinometers, providing further confidence in the
parameters used in the analysis.

Trendline

Design
One of the constraints on the design of
the repair was that the head scarp was
only 50 feet (15 m) from the well. The
well was shut down and did not present
signs of damage; however, the construction of the repair needed to maintain the
integrity of the well. The integrity of the

36

Geosynthetics | October November 2019



Geosynthetics October/November 2019

Table of Contents for the Digital Edition of Geosynthetics October/November 2019

Geosynthetics October/November 2019 - Cover1
Geosynthetics October/November 2019 - Cover2
Geosynthetics October/November 2019 - 1
Geosynthetics October/November 2019 - 2
Geosynthetics October/November 2019 - 3
Geosynthetics October/November 2019 - 4
Geosynthetics October/November 2019 - 5
Geosynthetics October/November 2019 - 6
Geosynthetics October/November 2019 - 7
Geosynthetics October/November 2019 - 8
Geosynthetics October/November 2019 - 9
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Geosynthetics October/November 2019 - 11
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Geosynthetics October/November 2019 - 16
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Geosynthetics October/November 2019 - 20
Geosynthetics October/November 2019 - 21
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Geosynthetics October/November 2019 - 24
Geosynthetics October/November 2019 - 25
Geosynthetics October/November 2019 - 26
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Geosynthetics October/November 2019 - 35
Geosynthetics October/November 2019 - 36
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Geosynthetics October/November 2019 - 55
Geosynthetics October/November 2019 - 56
Geosynthetics October/November 2019 - Cover3
Geosynthetics October/November 2019 - Cover4
Geosynthetics October/November 2019 - Blank1
Geosynthetics October/November 2019 - GeoConf20_1
Geosynthetics October/November 2019 - GeoConf20_2
Geosynthetics October/November 2019 - GeoConf20_4
Geosynthetics October/November 2019 - GeoConf20_5
Geosynthetics October/November 2019 - GeoConf20_6
Geosynthetics October/November 2019 - GeoConf20_7
Geosynthetics October/November 2019 - GeoConf20_3
Geosynthetics October/November 2019 - GeoConf20_8
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