Use of the concept of capillary barriers to optimize the support systems of deep vertical excavations in unsaturated soils

Abstract

In deep excavations, it is necessary to guarantee stability against catastrophic failure and to ensure that the deformations in the surrounding are within acceptable limits. Excavations done above the groundwater table can be supported with simple structures such as soldier pile walls. But the stability of the structure is affected by the infiltration of rainwater. If the infiltration of rainwater can be reduced the construction of a deep vertical excavation support system can be optimized. A Capillary Barrier (CB) which consists of a fine layer lying on top of a coarse layer at the ground level can cut off the infiltration into the lower layers. In this research study, initially, attempts were made to establish the critical parameters through parametric studies. A laboratory model of a Capillary Barrier was constructed with instrumentation and a rainfall pattern was applied. Experimental results were verified with GeoStudio, 2012 SEEP/W software and there was a very good agreement. A deep excavation supported by a soldier pile wall in an unsaturated soil was modelled thereafter with Midas GTS NX 3D software and the effectiveness of the capillary barrier in optimizing the design of the support system during a prolonged rainfall was illustrated.