Geosynthetic Reinforcement in the Mitigation of Pipeline Flotation - Reinforced Soil Engineering: Advances in Research and Practice - page 231

of reinforcement has been revealed through laboratory as well as field testings.
Many successful field constructions implied feasibility of extending geosynthetic
reinforcement to other important applications.
The uplift behavior of pipe has been studied, for example, by Trautmann
et al. (1985). The behavior of buried pipelines is affected by the groundwater. The
buoyancy of the water acts on the pipes so that a minimum depth of burial is
required. The designs conducted by considering force equilibrium between the
prism load and buoyancy are costly. The cost is accelerated if the diameter of
the pipes is larger because a deeper excavation is involved. To reduce the cost,
the burial depth of the pipe has to be minimized.
This paper deals with the flotation of pipelines where geosynthetics are
used to mitigate flotation. Full-scale tests were conducted, and the results are
reported and discussed herein.

2 MATERIALS

A large test pit available at the National Research Institute of Agricultural
Engineering (NRIAE) was used for the experiment. The test pit measured 3 m by
5 m and was 3m deep. This test pit was constructed to allow the control of water
table in it.
The full-scale pipe model was used in the tests. The inner diameter and
thickness of the pipe were 110 cm and 1.32 cm, respectively. It was manufactured
from fiberglass reinforced plastic mortar. Its gross weight was 1.27 kN/m. The
pipe was 290 cm long, to fit the width of the test pit.
The flotation of pipe model was mitigated by confining the backfill material
using a geosynthetic reinforcement. The sand, gravel, and soil cement were used
as backfill materials. The sand, gravel, and soil cement had a dry unit weight
g d ¼ 14.75 to 15.52 kN/m 3 , 19.61 kN/m 3 and 15.14 kN/m 3 , respectively.

A polypropylene biaxial geogrid was used. Its aperture size was 2.8 cm
(machine direction) by 3.3 cm (cross-machine direction). The mass per unit area
was 550 g/m 2 and the strength was 46 kN/m.

3 TESTING PROGRAM

Table 1 and Fig. 1 give the details and cross section for the five cases of
testing. Test 1 was conducted as a control case where the backfill soil was not
treated. Tests 2 and 3 used gravel as the backfill material. In tests 4 and 5, the soil
cement was used. The testing procedure is illustrated in Fig. 2.
In the test without geogrid, first the pipe model was placed on the
foundation in the test pit. A vibratory compactor was used. The backfill soil was