Laboratory Modelling of Plastic Landfill Leachate Drainage Pipes

The structural performance of plastic pipelines used for landfill drainage is difficult to predict due to the complex stress transmission provided by the unusually inhomogeneous overburden (i.e. waste) and variable degrees of local confinement provided by the mounded gravel surrounds. Also the gravel-waste interaction controls the applied stress and degree of support afforded to the pipe-gravel system. Attempts have been made to model such cases using large-scale tests and idealised waste fills combined with finite element analyses, although field measurements demonstrated that the deformed shape in the smaller gravel surrounds differed greatly and classical theory was found greatly to underpredict pipe deformation. Consequently, smaller-scale laboratory tests have been conducted at the University of Birmingham with the aims of recreating the patterns of deformation found in the field and defining support mechanisms. Simulated waste was created to produce an accurate and repeatable degree of compression. Model tests were then carried out in a rigid steel box with a glass face through which photographs of the pipe, gravel mound and overlying waste were taken. This paper aims to describe the test procedures and the first results emanating from this test programme, and thereby to demonstrate that some of the patterns of deflection seen in the field can be recreated by careful variation of installation procedures. When combined with the field measurements, it is possible to determine the structural action of the pipes in different construction and loading scenarios and to make recommendations for the design and installation of such pipes in practice.