Soil-water Characteristics and Unsaturated Permeability Coefficient Related to Weak Expansive Soils of a Certain Highway

A laboratory test on soil-water characteristics has been carried out on certain weak expansive soils,which was obtained from a high slope along a highway in Hubei province.The osmotic technique and the vapour phase technique were employed for suction control.And the water retention curve(0.01~309MPa) was obtained of the tested soil.And then,the water retention curve for tested weak expansive soil was fitted according to the model proposed by Fredlund and Xing.Based on this,the coefficients of permeability were determined from this characteristic and the Childs and Collis-George model which is based on the random variation of pore size.The results show that the desorption curve of the specimen has significant boundary effecting segment and transition segment,whereas the residual segment is unobvious.The permeability of Hubei weak expansive soil varies nonlinearly with suction(water content),and it decreases quickly with increasing of suction(decreasing of water content).