Research On The Mechanism Of Pore Water Action Within Unsaturated Soil And The Corresponding Slope Stability

The type of pore water action is a solid and considerable factor which couldinduce to the physical property change of soil or rock mass. This thesis wascompleted by basing the experimental results and some typical phenomenon gotfrom the project which named Rainfall induce shallow landslide in unsaturated soilslope (it is the co-project fulfilled by the USGS and CSM). In order to demonstratedthe action mechanism of pore water within unsaturated soil and the correspondingcharacteristics of soil mass, three types of methods was used in this research work,namely, the analytical method, laboratory test method and numerical simulationmethod. Major conclusions that got from this thesis can be seen as follows:(1) To calculate the seepage state data by using the deduced equation and byselected parameters, the rainfall intensity q, the inverse value of air-entry pressureand the ration of rainfall intensity with saturated hydraulic conductivity, respectively,we can see that the seepage state within soil layer is more sensitive with rainfallintensity. Furthermore, take research on several types of soil for getting insight intothe steady seepage condition within these different type of soil layers, comparedwith the other two factors, the rainfall event will take more influence on the seepagestate of soil layer, and as for the three type of soil: sandy soil, silty soil or clay soil,the last one could take more sensitive on the rainfall event, and the correspondingsoil strength is also has the same characteristic. Combined the deduced boundarycondition, initial condition and Laplace transform equation, we can take solution fora partial differential equation of second order, and get a equation to calculate thetransient seepage condition, finally. Select the un-linear Boussinesq equation todemonstrate the unsteady seepage state profile of soil layer which is under theinfluence of water level fluctuation with specified velocity, and based the knownresults, this thesis provide an equation for the location calculation of water tablewithin soil layer. From the expression we can see that the range of variation isconsiderable influence by the velocity of water level fluctuation, hydraulicconductivity and specific yield.(2) TWRI tests were conducted for several types of soil which collected in alandslide site. Experimental results need to be taken as input data in HYDRUS-1Dcomputer code, the influence of HAE disk and pore air within water were also taken into consideration. Some major hydraulic parameters were obtained from these tests,and huge hysteresis effect could be found between these parameters related wettingprocess and drying process, respectively.(3) Claiming at the micro-structure point, we can get some insights into the samediameter two-particle unsaturated soil system and the different diameter two-particlesunsaturated soil system, obtained expressions from these known data that can be used toestablish the relationship among contact angle, water content and matric suction. Usingthese expressions to validate the hysteresis effect of unsaturated soil and to experiencethe same issue for different grading level soil.(4) By combining the methods of common type of soil test and micro-structureanalysis into research work, the contribution type and contribution rule of matric suctionto soil strength can be obtained. And according to the special characteristic ofunsaturated soil, the micro-structure survey work was conducted on some soil sampleswith different water contents. The interactive relation and related mechanism forstrength contribution that provided by pore water were also detected and demonstratedby this test.(5) The difference between wetting process and drying process were consideredduring taking experimental data into slope model. The research results show us thataccording to different range type of water level variation, the slope stability will act asdifferent type of developments. As for the slope that under the influence of differentrainfall conditions, the slope stability will reduce gradually with the rainfall intensityincrease or with the rainfall time elapse. The rainfall with low intensity but long actiontime could induce to landslide in deep location, in the other way, shallow landslideoccurs usually for the influence of high intensity but short action time. The two-phaserainfall event also shows us that all of the rainfall action time, rainfall intensity and theslope soil properties are important in landslide forecast work.Each part of this thesis can take tightness interactive and comprise an initial butreasonable theory system; the related researcher could take this work as a benefitedreference or based on it to further their study work.