Effect of Matric Suction on Permeability and Shear Strength of Vegetated Soils

Abstract

AbstractMatric suction is an important parameter to designate the mechanical properties of unsaturated soil. To explore the influence of matric suction on the properties of unsaturated soil covered by vegetation, a series of laboratory tests were conducted to investigate the effects of matric suction on the permeability and shear strength indexes in vegetated soils. 8 test boxes compacted with sandy silt were prepared, six of which were covered with Cynodon dactylon and Indigofera amblyantha while two boxes were left bare as control. The results showed that the water retention capacity of vegetated soil was significantly improved compared with the bare soil. The variations in water infiltration amount presented a similar trend with time in bare and vegetated soils, and the water infiltration amount of vegetated soil (Herbs) and vegetated soil (Shrubs) was about 1/2 and 2/3 of bare soil when infiltration time was 2 h, respectively. The permeability coefficient of bare and vegetated soils gradually decreased as matric suction increased, and the permeability coefficient of vegetated soils was obviously lower than bare soil. Permeability coefficient of vegetated soils decreased to the magnitude of 1.00E-08 when soil matric suction was about 25 kPa. According to the soil-water characteristic curve of sandy silt, shear strength indexes of bare soil and vegetated soils increased as matric suction augmented in the boundary effect region and the transition region. The rate of increase in soil cohesion slowly diminished, and internal friction angle increased gradually as the matric suction augmented. The consequences are of great significance for using vegetation to prevent slope instability and other geological disasters, meanwhile furtherly enriching the hydraulic mechanism of vegetation in slope stability.KeywordsVegetated soilMatric suctionSoil-water characteristic curvePermeability coefficientShear strength