Calculation Method of Unsaturated Loess Matrix Suction by In-situ Soaking Test

When the permeability coefficient of unsaturated soil is calculated by a relatively accurate algorithm considering the suction head value of the soil matrix in the project, it is difficult to accurately measure the suction head value of the matrix, and the measurement results of the laboratory test are quite different from the head value measured in the field. A new algorithm was used to calculate the soil matrix suction by using the in-situ water immersion test data. It is different from various traditional testing methods such as the indoor tensiometer method. Instead, it uses the Green-Ampt infiltration model combined with the immersion pit. The suction head value of the formation matrix is calculated from the difference between the water surface falling rate and the water infiltration rate measured by the moisture sensor. Select a loess paleosol interlayer site for in-situ immersion testing. The suction head value of the first layer of loess matrix with a thickness of 4 meters is 233 cm, and the value of the second layer of paleosol with a thickness of 2 meters is 124 cm. Using this algorithm, the suction head value of each layer of soil matrix can be predicted and calculated, and finally it is predicted that the suction of the stratum matrix will decrease to zero at 8.4 m below the immersion pit. This is a new attempt to calculate the suction of soil matrix in loess strata.