Rheological Experimental Study And Mechanism Research On Gentle-dipped Landslides Of Jurassic Red Strata In Wanzhou City

ChuanJiang river (part of Yangtse Rive from Yibin to Yichang) has always been one of China's geological disaster-prone areas. Following with the civil engineering for transmigrates of the Three Gorges Project; many engineering geological explorations revealed that the mechanics of some ancient landslides in complex geological environment are not as simple as formerly proposed.The sliding of solid rocks on a continuous claystone dipping towards valley at 3-5°, the steepest is not more than 10°. Such gentle-dipped landslides are not common in other areas that have nearly horizontal strata. However, the formation mechanism of these landslides has been debatable. The landslides formation mechanisms are important in prevention and treatment sliding. So it is significant to learn the mechanisms of this kind of landslides. There are eight chapters in this dissertation.Chapter 1 "introduction", Makes an introduction about the situation and tendency in domestic and foreign research, and then schemes the research content. On of the famous views about the formation of landslide occurred in nearly horizontal strata was that the head of water raised by rainfall in steep fissure pushed the landslide to translate, so this kind of landslide also was named "pushed translation landslide". But this view cannot explain why there are many steep fissures in the rear of slope. In this dissertation, the rheology characters of rocks and soils were considered for the formation of landslide is a long geologic age. So in this chapter the idea of research the landslide mechanics based on the f rocks and soils rheology theory was proposed.Chapter 2 "Regional geological, lithology, and rainfall character in Wanzhou area" In this chapter describes the geographic, lithology, and climate in Wanzhou. The occurrence of landslide lies on the lithology, tectonic, geomorpholo and the groundwater. Human activities and rainfall will change these conditions and triggered the landslide failure. Wanzhou lies Chuangdong arcuate strutural zone which formed by the sedimentary covers thrust into each other along the sliding planes between the cover and basement. During the movement, many incompetent beds may become shear zone between strata. It is an advantage to form landslide. The rockmass in red beds can change to soil under the inner and outer effects of geological processes. Many engineering geological exploration reveals that the mudstone changed to soil and become the landslide slip surface. Wanzhou area is the center of rainstorm of Three Gorges reservoir area and profuse rainfall is an important factor result in landslide.Chapter 3 "experiment study on representative rock in Wanzhou area" The samples of red plagioclase quartz sandstone, muddy fine sandstone and sliding zone soil in Wanzhou were taken, their physical attribute mineral components and mechanics attribute were studied. The results show that angle of shearing resistance of the sliding zone soil is larger than the angle of slip surface gradient. The strength of sandstone obeies the Mohr-Coulomb failure criterion, the shear strength parameters are abtained by experiments. One axis compact tests point load tests are performed in study muddy fine sandstone and the shear strength parameters are also abtained.Chapter 4 "Rheological Experiments on red sandstone in Wanzhou of Three Gorges Reservoir area" In order to discover the cause of these landslides, rheological experiments were conducted on the sandstone of Erchengyan landslide bedrock in Wanzhou with RLM-2000 triaxial rheology test machine. Before the specimen failures, there was an accelerated creep stage, which lasted about 8 hours, this course is similar to the deformation of some approximately horizontal slip surface landslides failure. Tautochrone of test data indicates this kind of rock is close to liner visco-elastoplastic materials. Burgers rheology model was used to identify the curves, and the Burgers three dimensional rheology model and its parameters were obtained. The results show that the proposed Burgers rheology model exactly presents the rheology characterization of Jurassic red strata in Wanzhou. And it can also describe the mechanism of the approximately horizontal slip surface landslides occurring in Jurassic red strata in Wanzhou. There was a nearly linear correlation between the creep strain rate and time in the beginning of accelerative creep stage and a nonlinear rheological model NBurgers was proposed to describe this accelerative creep stage. The creep strain rate behaved close to exponential growth with time in the last of accelerative creep stage. That accelerative creep stage was highly nonlinear chracterastic, the creep strain rate showed a discontinuous form, which occurred in jumps change. Furthermore, the experimental results reveal the fact the long-term strength of the rock is only 44 percent of the peak strength in triaxial tests. This conclusion is very helpful for the research on the mechanism and prevention on the horizontal slip surface landslides.Chapter 5 "Creep experimental study on sliding zone soil of Anlesi landslide." Creep text have been carried out to study the rtheology property of sliding zone soils. Burgers model, Singh-Mitchell model and Mesri model have been used to describe the creep character of sliding zone soils. Each model is evaluated compared with the test data.Chapter 6 "Experimental study on stress relaxation of Anlesi landslide in Wanzhou". Triaxiality stress relaxation experiment on GDS Unsaturated Triaxial Testing Systems was carried out to investigate the stress relaxation properties of slide zone soils of Anlesi landslide. During relaxation tests the soil volume deformation is almost could to be ignored. Test data shows stress relaxation is direct ratio to initial strain but independent of confining pressure. Based on stress relaxation tests, a new constitutive model for the stress-strain-time behavior of slide zone clays was introduced by assuming a hyperbolic stress-strain relationship and a logarithmic time-tress relationship. The comparison between the rheology model and experimental result shows that the new rheology model presents the relaxation characterization of the slide zone clays nicely. That also provides the model and parameter for the further researches about approximate level landslides exist in Jurassic red strata in Sichuan basin. The new relaxation model indicates the shear stress of this kind of clay will relaxat to zero. That is significance for approximate level landslides research and control.Chapter 7 "mechanism research on approximately horizontal slip surface rockslides" Flac3D was used to simulate typical approximately horizontal slip surface landslide in Jurassic red strata in Wanzhou city. After synthetize the numberic results about the stress and strain distributing and changing, and many phenomena about landslide, a new viewpoint was brought out on the point of rock and soil Rheological mechanics. This new opinion point considers that this kind of rockslide slide not result from the failure of sliding zone, but be caused the sliding zone cannot exert its strength enough. So the gentle- dipped slope instabilities must be connected to following conditions: (1) landslides have plastic substratum and rigid layer over, so the landslide body have viscosity great larger than the sliding zone soils; (2)landslides lies on wide water gap,so the landslide bady have to bear enough tension stress;(3) landslides's lateral erosion by river, so the landslides has weak lateral restrict.Chapter 8 "conclusion and prospecf'In this chapter the conclusions and innovations of this dissertation have been summed. And some suggestions have been proposed for further research about the mechanics of gentle-dipped landslides of Jurassic red strata in Wanzhou city.In this paper, the rheology charactes of the red rocks and soils in the Wanzhou area were studied based on experiments. Along with the deformation characteristics landslide site, from the perspective of rheological mechanics the mechanism of approximately horizontal landslides were discussed.