Swelling properties and coefficient of permeability of friction-reducing polymer for pull-out of temporary sheet piles

Abstract

Harmful cracks and settlements occur after the pull-out removal of temporary sheet piles. This is because a large amount of soil is discharged from the ground due to the significant skin friction at the steel surface. In order to prevent these cracks and settlement problems, a friction-reducing polymer was developed. After a sheet pile coated with the polymer is installed into the ground; the polymer absorbs ground water and transforms to a swollen gel layer which separates the soil and the sheet piles. In this investigation, a newly designed column type test apparatus was used to simulate ground conditions. The swelling test was carried out, followed by a continuous permeability test. Based on the obtained test results, the swelling properties and coefficient of permeability of the friction-reducing polymer in the ground were determined. The main conclusions are as follows. The values of the water-absorbing ratio, Ramax, decrease with increasing earth pressure, p′, independent of the pore water pressure, u. Equations to determine the values of Ramax are proposed as functions of p′ only. The maximum swelling pressure, at which the friction-reducing polymer cannot absorb water and swell, is p′max = 560 kPa. Even at a depth of approximately 100 m, the polymer absorbs ground water, and the swollen gel layer forms. The approximate range of coefficient of permeability, k, of the swollen gel layer is 10−13–10−11 m/s; these are extremely small values. The swollen gel can be considered an impermeable material. Depth distributions of the thickness and the coefficient of permeability of the swollen gel layer are illustrated in practical charts, based on the test results.