The Research Of Water Physical And Mechanical Properties' Of Xigeda Clay Rocks

The Xigeda Formation is formely known as "HunDan Strata", because of it's outcrop Xigada Village was renamed as "Xigeda Formation" in the year 1958。It was developed in the Large rivers and the tributaries in the southeastern coast of Qinghai-Tibet Plateau and is a set of discontiguous lacustrine facies half-diagenesis sedimentary layer.Xigeda Strata is the product of slope planation and landform remolding of the transit area between the first level and second level of the three steps in China, is the sedimentary response of the uplif process of Qinghai-Tibet Plateau, and mainly developed in barrier lake area and faulted lake basin area。Because distribution areas are scattered, mineral composition and internal structure of Xigeda strata in different parts are very different, and so the engineering characteristics. The Xichang Xigeda Formation clay rocks distribute widely, and the engineering hazard is serious. So doing the deeply research of the water physical and mechanical properties of Xichang Xigeda formation clay rock is very significant to strengthening the understanding of the Xigeda strata and avoiding the security hidden trouble.At present, the reserarch about the Xigeda Formation Clay rocks is not complete, the influent factors are still not clear. In this paper, mainly by the water physical and mechanical propreties two aspects, the research about the influence of water content to the the mechanical behavoir of Xigeda formation clay rocks and the Xigada Formation clay rocks'water-rock interaction damage mechanism have been done in differernt way. The aim of the paricle is to show that water is major controling factor to the Xichang Xigeda Formation clay rocks'water physical and mechanical properties. The main research results are as follows:(1) The expantion tests of the Xichang Clay rock have been done, results show that the the discrete degree of the it's free expansio ration is high, but the data lower than the disctimination standard of expansive soil. It's plastic limit, liquid limit and plastic index are all less than the average value of Panzhihua Xigeda Formation Clay rock's. It show the imcomprabality of the Xigeda Formation in different places.(2) The shear test results of Xichang Xigeda Formation Clay rock indicate that,the average value of it's c andφis obviusly lower than those of the Xichang Xigeda Clay rock, because of it's relative low diagenesis degree. The change rule of the average value of c and (p under four conditions is basic as follows:the c and cp value of consolidated quick shear test is lower than that under consolidated quick shear test, which is lower than that of the water immersion consolidated quick shear test, lower than that of the water immersion quick shear test.Theφis average value is completely follow that rule, it shows thatφvalue is more sensitively to the soil's water content.(3) Through the test and analysis of the bearing capacity of Xigeda Formation, it can be found that, the bearing capacity of soft rock determined by the in-situ rock loac test is far higher than the saturated uniaxial compressive strength value tested of the rock under the no laeral restraint uniaxial compressive stress state. The decreasing rang of fomation's bearin capacity is very large, it shows that water sensitivity of this formation is strong. So the protect to excavated foundation pit and basis the should be paid attetion during the engineering.(4) Xigeda Formation is the early quaternary fomation sedimanted in the standing water environment in southwest area. The cements and the and sources are different because of the differences of the sedimantary and time. According the analysis of the in-situ test results, with the increase of the sampling depth, the compression coefficient and compression modulus'value respectively become lower and higher. This appearance is mainly controlled by unloading springback effect of the Xigeda Formation.(5) The research of clay rock'damage test show that, the water cause the clay rock's solidfication cohesion and original cohesive strehth both reduced.Water content's influence to the cohesive strehth of Xichang Xigeda Formation clay rock is obvious, the integeral tent reduced stagely. The increase of water content leads the particle's surface friction and the occlusive friction between the particles to reduce, which cause the internal friction angle reduce. The reduce degree of friction angle with the increase of water content show the quickly earliyer and sllowly latter change tent. Untill the soil body is close to saturated, the internal friction angle is close to the const value.(6) Mechanics analysis shows that, in shearing process,the soil shear strength is combined controlled by double stresses (net stress and the suction),cohessive strength and internal friction angle. With the increase of water content, the matrix cohessive strength of soil body reduces continually, the shear strength nonlinear decreases.(7) According the research about the microscopic mineral chemistry effect, When the soft rock is under the water immesion action, the viscous cohessive body and the mineral structure firstly generate structural vacant holes, such as microcrack and microfissure and so on. And then with the intersity of the damage, the irreversible themordynamic process conduct the chemical disequilibrium, which change the rock's physical state and microscopic structrure, corroses the crystal lattice, and weaken the connaction between mineral paticles. The multiple fracture directional pierces and converge, and macroscopic structrual plane, and then cause the irreversible material damage to the rock. The change of microcosmic miterial and damage of microcosmic structural cause the the macroscopic physical and mechanical properties change...