Improving the Behavior of Buried HDPE Pipe by Using EPS Geofoam

A buried thermoplastic pipe installed with conventional method deflects vertically downwards under soil load. Because the displacement of the pipe crown is more than that of the sidefill soil, differential settlements in the soil medium above the pipe crown level take place. Differential settlements lead to the development of a mechanism called “positive soil arching” within the soil medium and, consequently, a vertical stress smaller than the geostatic stress acts on the crown of the thermoplastic pipe. The degree of arching depends on the magnitude of the differential settlements. Therefore, the degree of arching can be increased by installing a zone or zones of a compressible material, which will increase the magnitude of the differential settlements, around the thermoplastic pipe when the pipe is being installed. The increase in the degree of arching will provide less vertical stress on the pipe crown and an improved pipe behavior. This paper presents a part of the findings obtained from true-scale laboratory model tests and finite element analysis which were performed to investigate the effects of compressible zone application on buried HDPE pipe behavior. EPS Geofoam with 10 kg/m³ nominal density was used as the compressible material. Compressible zone with proposed geometry provided a reduction in vertical pipe deflection of up to 89%, in horizontal pipe deflection of up to 96% and in vertical stress on the pipe crown of up to 77%. Finite element analysis showed that the compressible zone provided relatively very small bending moments and almost a uniform bending moment distribution around the pipe. Under 200 kPa surcharge stress, a reduction in the maximum bending moment around the pipe of 78% was provided.