Soil Water Retention Curves Of 12 Soils Investigate By Dynamic Dew-point Isotherm Method

Soil water retention curve（SWRC）refers to the relationship between soil gravity or volume water content and suction,and is the most important constitutive relationship of unsaturated soil.Most SWRCs are measured by the axis translation method which is suitable for suctions in the range of 0 to 1.5 MPa.However,in engineering practice,the relative humidity RH is often less than 95%,which means suctions larger than 6.8 MPa,so it is necessary to study the water retention curve of soil in the range of high suction.The SWRCs of Wyoming Bentonite,Ningming Bentonite,Denver Bentonite,Jingmen yellowish-brown soil,Denver Claystone,Xinyang clay,Wuhan clay,Sanmenxia silty clay,Zhengzhou silt,Calcined kaolin,Kaifeng Yellow River sand are determined by the dynamic dew point isotherm method under the high suction range of 6.8 to 510.9MPa.The gravitational water content w₉₅corresponding to the end point of moisture absorption（RH is 95%）is adopted to quantify the water retention capacity under high suction,SWRC hydraulic hysteresis area（HHA）,Maximum difference of gravity moisture content in adsorption and desorption processesΔw_maxis adopted to reflect the hysteresis effect strength,discusses w₉₅,HHA,Δw_maxand relationship between soil mechanical parameters,a polynomial of 12 kinds of mathematical description for the SWRC under high soil suction.The SWRCs of Wyoming Bentonite,Ningming and Jingmen Bentonite at different temperatures are measured by DDI method,and the temperature effect law of water retention capacity of expansive soil under high suction is discussed.Conclusions are as follows:（1）The water retention capacity under high suction is quantified by the relative humidity 95%corresponding to the gravity moisture content w₉₅.Calcined kaolin is1.0%,while Denver Bentonite is 22.5%,indicating that the water retention capacity of12 kinds of soils from sand to extremely plastic clay varies greatly under high suction,and is positively correlated with plasticity indexes（SSA,w _L,I_P）.（2）The hysteresis effect is quantified by using the hysteresis area HHA,which is 0for calcined kaolin and 13641 k Pa for Wyoming Bentonite,indicating that the hysteresis effect of 12 kinds of soils from sandy soil to extremely plastic clay varies greatly under high suction,and is also positively correlated with the plasticity indexes（SSA,w _L,I_P）.（3）Using cubic polynomial to fit the SWRC expressed by w-ψrelation under high suction of 12 soil samples,the results show that the R²is greater than 0.95 and the RMSE is less than 0.54%.（4）The water retention capacity(w₉₅)of the three kinds of expansive soils generally decreases with the increase of temperature,and the hysteresis effect(HHA,?w_max)of SWRC also decreases with the increase of temperature.An modified Fredlund-Xing（1994）model is used to simulate the SWRC of three expansive soils at different temperatures.