DEPTH IDENTIFICATION OF THE ACTIVE AND CRACKING ZONES IN EXPANSIVE SOILS FROM IN-SITU SUCTION MEASUREMENT

In order to assess the active zone depth and the cracking zone depth of expansive soil below ground surface,Mithchell formulation and crack expansion equation are used.Through excavating observation wells in two inartificial slopes in Ankang area,the suction values at different depths were measured by tensiometer.According to the Mithchell formulation,the active zone depth is calculated.According to the theory of tensile strength of unsaturated soil,the equation of crack expansion is formulated.The theoretical solution is obtained through calculation from the results of suction measurement.The results indicate that the suction curves of expansive soil do not change significantly with the increase of depth.The curves undulate with depth.The active zone depth of expansive soil is found to be between 3.17 m and 3.32 m.The crack depth is found to be between 3.06 m and 3.14 m.Therefore,the results of the two methods are close.