| Loess exhibit significant water sensitivity.And water is the most active factor inducing loess landslides.In recent years,it is a high trending that inextreme rainfall induced loess landslides.It is a key technological issue of preventing and controlling of loess landslides to conduct basic theoretical research on water sensitivity of loess and reveal the mechanism of water induced loess landslides.The author was lucky to participate in the professor’s projects,responsible for the collection of soil samples,on-site monitoring,laboratory test,and data processing in Qingyang.Based on summarizing the engineering geological characteristics of loess,the article improved the method for measuring the hydraulic characteristic curve of loess at the full suction range,revealing the water retention and permeability characteristics of loess at the full suction range,exploring the hydrological response process of loess profiles to rainfall and the mechanism of water induced loess landslides.The major contributions are as follows:（1）Systematically collected and tested typical profile samples of loess,and summarized the engineering geological characteristics of loess.A 250m deep exploration borehole was deployed and implemented in a well-developed section of the loess stratigraphic sequence in the Qingyang area,with continuous coring throughout the borehole and undisturbed soil samples taken from each layer.The representative loess and paleosol were selected to measure the basic physical and hydraulic property indexes,and the first-hand test data such as water content,particle gradation,liquid limit,plastic limit,plastic index,specific gravity,density,saturated permeability coefficient,mineral composition,chemical composition,and pore size distribution were obtained.（2）The measurement of soil water characteristics at the full suction range was proposed.And the water sensitivity characteristic of loess at the full suction range was revealed.Improved TRIM for traditional Soil and Water Characteristic Curve（SWRC）testing,combined with VSA,obtained the measured points of SWRC at the high suction range of 20 layers of loess in Qingyang Profile,as well as the measured points of SWRC at the full suction range of 7 layers of loess.Revealed the changes in hydraulic characteristic parameters,water retention capacity characteristic point RH0.95,maximum humidity reduction,hydraulic hysteresis area,and other characteristics parameters with depth under different hydrualic paths at the range of high suction and full suction,as well as their correlation with physical characteristic parameters.Based on SWRC,unsaturated hydraulic corffcient curve（HCC）were constructed using the Children&Collis-Geroge model,Fredlund&Xing model,and pore size distribution（PSD）cuve of soil samples,respectively.A water sensitivity classification scheme of loess was explored based on the high suction range,full suction range,and unsaturated characteristics of loess at different layers.（3）Established an analytical equation for typical loess profile infiltration,revealing the hydrological response process of rainfall.Based on the characteristics of water transport,the transient zone,steady-state zone,and saturation zone of the thick loess layer were divided into zones by on-site observation,large soil column tests,and hydraulic model tests.Combined with the constructed SWRC and HCC,an analytical equation for infiltration rate and recharge rate was established.The recharge rate and recharge time of groundwater under actual rainfall conditions were obtained,and verified using the Chloride Balance Method.Based on the small soil column test and ISVH-TRAP hysteresis model,the response process of water content field and matric suction field of loess under steady and intermittent recharge conditions was revealed,laying the foundation for the stability analysis of water induced loess landslides.（4）A hydraulic coupling equation between suction stress and water content was established,revealing the progressive failure mechanism of water induced loess landslides.By improving the transient desorption and absorption methods,the SWRC,HCC,and suction stress characteristic curve（SSC）of the full suction range were obtained.SWRC and SSCC was introduced into the Mohr-Coulomb strength theory to obtain the unsaturated shear strength formula.SWRC and HCC were introduced into the flow law to obtain the distribution of water content and suction of loess profile,revealing the progressive failure mechanism of water induced loess landslides,A method for calculating the probability of instability of loess landslides was proposed and applied in the Heifangtai Irrigation District of Gansu Province. |
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