Structural analysis of closure cap barriers: A pre-test study for the Bentonite Mat Demonstration Project

According to the EPA-recommended closure cap design a waste site can either be covered with a single layer cap made of 36 inches of compacted soil (clay) or with a multilayer cap consisting of an upper vegetative layer underlain by a drainage layer over a low permeability layer. The Bentonite Mat Demonstration Project (BMDP) is a field demonstration study to determine the construction/installation requirements, permeability, and subsidence performance characteristics of a composite barrier. The composite barrier will consist of on-site sandy-clay blanketed by a bentonite mat and a flexible High Density Polyethylene (HDPE) liner (also called flexible membrane liner). Construction of one control test pad and three bentonite test pads are planned. The control test pad will be used to establish baseline data. Underneath the composite clay cap is a four-foot loose sand layer in which cavities will be created by evacuation of sand. The present work provides a mathematical model for the BMDP. The mathematical model will be used to simulate the mechanical and structural responses of the composite clay cap during the testing processes. Based upon engineering experience and technical references, a set of nominal soil parameters have been selected. Currently, detailed soil test data and cavity configuration data are not available to validate the mathematical model. Since the configuration of the cavities created in the testing process is irregular and unpredictable, two extreme configurations are considered in this mathematical model, viz., the circular cavity and the infinitely long trench in the sand underneath the cap. This approach will provide bounds for the testing results