Experimental study on the modulus of soil reaction for plastic pipes buried in lightweight cellular concrete backfill

• PVC and HDPE pipes had different behavior under and after compressive loads. • Modulus of soil reaction of LCC depended on pipe and trench fill properties. • Modulus of soil reaction of LCC had a linear relationship with LCC strength. • Modulus of soil reaction of LCC at small deformation was higher than granular fill. The modulus of soil reaction, representing the stiffness of a soil surrounding pipes, is a critical parameter in the design of buried flexible pipes. This study conducted plate loading tests on corrugated polyvinyl chloride, smooth polyvinyl chloride, and high-density polyethylene pipes buried in lightweight cellular concrete (LCC) backfills at densities of 400, 475, 550, and 650 kg/m 3 to investigate the pipe deformation behavior and moduli of soil reaction. In addition, this study examined the effects of the narrow trench condition on the pipe deformation and modulus of soil reaction. In these tests, the vertical and horizontal diameter changes of pipes under the vertical pressures applied through a hydraulic jack were measured. Test results reveal that the average moduli of soil reaction of plastic pipes within a wide trench backfilled by the LCCs at densities of 400, 475, 550, and 650 kg/m 3 were back-calculated as 66, 99, 133, and 205 MPa, respectively, using the modified Iowa formula. Furthermore, the back-calculated moduli of soil reaction for LCCs exhibited linear relationships with their densities and unconfined compressive strengths and were higher than the recommended values for the commonly used soil backfills. Based on the vertical deformation criterion of 5% pipe diameter, the ultimate bearing capacities of flexible pipes buried in wide LCCs at densities of 475, 550, and 650 kg/m 3 exceeded 500 kPa. The LCC with a narrow trench exhibited a lower modulus of soil reaction and ultimate bearing capacity but a larger pipe diameter change.