Centrifuge model studies on the performance of earthen dams with geocomposite internal drain subjected to pseudostatic seismic loading

Abstract

This paper evaluates geocomposite (GC) as an internal drain for seepage control in earthen dams subjected to upstream impoundment and inertial loading through centrifuge model tests. A total of five centrifuge tests were performed on a homogeneously built small earthen dam section having prototype height of 7.2 m with 1H:1V side slopes at 30 g-level using a 4.5 m radius large beam geotechnical centrifuge available at the Indian Institute of Technology Bombay, India. The studied earthen dam models had an internal drain in the form of (a) a geocomposite horizontal drain (GC HD); (b) a sand-sandwiched geocomposite horizontal drain (SSGC HD); (c) a geocomposite chimney drain (GC CD); and (d) a sand-sandwiched geocomposite chimney drain (SSGC CD). The seepage-deformation response of the GC equipped earthen dam models is presented in terms of the development of pore-water pressure (PWP), phreatic surfaces, surface settlements (sc), and downstream slope face movements (sf). The behavior of the earthen dam model without any internal drain is also presented for comparison. In the case of an earthen dam with GC internal drain both as HD and CD, it was found to be efficient up to some extent in restricting phreatic surfaces, but phreatic surfaces were observed to be close to downstream side slope. However, a sand-sandwiched GC internal drain HD and CD seemed more promising in restricting the phreatic surface much within the downstream region and imparting higher stability even during sustained inertial loading conditions. The study concludes that SSGC chimney drain can be safely adopted for seepage control in small earthen dams and similar geotechnical structures viz levees, raw water reservoirs (RWRs), coastal protection structures, etc.