Geosynthetic Reinforcement in the Mitigation of Pipeline Flotation - Reinforced Soil Engineering: Advances in Research and Practice - page 232

Table 1 Description of Testing Models

Test Descriptions

1 Control model. Sand as backfill material.

2 Sand as backfill. Geosynthetic reinforcement was used.

3 Gravel as backfill. Geosynthetic reinforcement was used.

4 Geosynthetic was used as reinforcement with a soil cement

block (30 cm thick) above the spring line.

5 Geosynthetic was used as reinforcement with a soil cement

block (30 cm thick) 30 cm below the spring line.

constructed in increments where each layer was of 10-cm thickness. In all tests,
the cover soil reached 70 cm above the crown. At the completion of backfilling,
the water was introduced into the test pit.
The behavior of the pipe was measured as the water table reached the
ground surface. It was confirmed that the pipe did not move with the rise of the
water table. The water table was then lowered to the spring of the pipe. The soil
above the pipe was removed at 10-cm increments until the pipe floated. The
critical overburden height of the soil cover was thus determined.
For tests 2 to 5, the geogrid was wrapped from the crown to the spring of the
pipe model. The length of the geogrid extended from the spring was about the
radius of the pipe.
Figure 3 shows the test where the geogrid was installed around the pipe in
the test pit. The backfill sand, gravel, or soil cement was placed on the grid. The
strain gauges were attached to both surfaces of the geogrid. The locations of
strain gauges in each test are shown in Fig. 4. The load cells were installed in the
ground and at the pipe to measure the load acting on them.

4 CRITICAL HEIGHT OF SOIL COVER

The results are summarized for each case of testing:

Test 1. When the overburden height was reduced from 70 cm to 30 cm, the
pipe floated. The cracks were observed in the soil along the longitudinal
direction of the pipe model. They occurred at a distance d apart, where d
is equal to the pipe diameter. The volume of the soil enclosed between
the cracks was lifted when the pipe floated. The ground surface after
lifting up is shown in Fig. 5 .