Use of interlocked EPS block geofoam for sandy slopes subjected to seepage flow

Abstract

Expanded polystyrene (EPS) geofoam (geofoam block) is a closed cellular lightweight fill material and has been used in many slope rehabilitation projects in various countries. It is known that, due to its low density, geofoam blocks cannot resist hydrostatic sliding forces. Increasing overburden stress acting on geofoam blocks, implementing permanent drainage system or anchoring the blocks can be counted as viable techniques to increase resistance against hydrostatic sliding. In this study, an alternative technique which involved the increasing of the interface friction properties between geofoam blocks was investigated by using a geofoam block slope system subjected to seepage. For this purpose, an interlocked geofoam block design was implemented, and its effect on interface shear behavior was quantified through laboratory direct shear tests. Two different interlocked geofoam block configurations based on typical construction practice where the interlocked geofoam blocks were placed on the face of the sandy slope were tested in the laboratory under seepage condition. For this reason, a lysimeter with dimensions of 60 cm height, 20 cm width, and 200 cm length was constructed in the laboratory. Constant head seepage condition was provided through a water tank located at one side of the lysimeter. The dimensions of the interlocked geofoam blocks used in the laboratory lysimeter model tests were 2.5 cm high, 5 cm wide, and 15 cm long to ensure a 1:20 scale of geofoam blocks which corresponds to a common manufactured sizes of 0.5 m high, 1.0 m wide, and 3.0 m long. The geofoam blocks had a density of 20 kg/m3. The adjacent slope material was comprised of sand that was packed into the lysimeter with a dry unit weight of 14 kN/m3, and slope angle of 45 degrees (1 horizontal to 1 vertical). Piezometric pressures developed inside the slope by seepage flow were measured by pencil size tensiometers and recorded through pressure transducer-datalogger setup. The laboratory experiments showed that even though the designed interlocked geofoam block system has significantly higher interface friction resistance when compared with the typical (non-interlocked) geofoam blocks, they were not able to prevent deep-seated slope failures occurred at the end of the lysimeter tests. It was concluded that increasing interface friction resistance between the geofoam blocks was ineffective against deep-seated failures on its own. It is recommended that interlocked geofoam blocks should be used in conjunction with aforementioned measures in slope rehabilitation projects.