Effects of grass on induced soil suction during Evapotranspiration and ponding

Abstract

Soil suction induced by grass Evapotranspiration (ET) in vegetated landfill covers is recognised to potentially reduce percolation (due to the decrease in water permeability) and also improve slope stability (due to the increase in soil shear strength) upon rainfall. However, grass-induced suction is generally ignored when analysing a vegetated cover because effects of root-water uptake on suction is less understood. In this study, a series of laboratory tests were conducted to measure suction induced during ET and suction retained during ponding. Compacted silty sand with and without vegetated with a grass species, Cynodon dactylon, were tested in an atmospheric-controlled room. Responses of suction were monitored by 12 tensiometers. By investigating water flow mechanism in vegetated soil, vertical and horizontal influence zones of suction are identified in relation to grass root characteristics. Measurements from bare and vegetated soil are compared to quantify the effects of grass on suction retention upon ponding.