| Large-scale and super-huge type glacial deposit body are widely distributed in the Zagunao river valley of Li county, which formed in Pleistocene. Influenced by historical sedimentary environment, these accumulation often have more complex material composition and structural characteristics.at the same time, the special geological conditions and frequent seismic activities in the area make the continuous deformation and destruction of these glacial deposit body occurred in varying degrees and gradually evolved to form an unstable slope or landslide. With the accelerate development strategy of the construction of large projects in western region, the glacial deposit body has become the geological background of the construction of human engineering and the geological hazards associated with the glacial deposit body are becoming more and more serious. Therefore, it has important theoretical significance and application value to study the shear strength characteristics of this kind of glacial deposit body.Through the survey and analysis of typical glacial deposit body of material composition, particle size composition and structure characteristics in Taoping,Li County, Sichuan province this paper discussed the causes, formation and evolution of the representative Taoping glacial deposit body; Based on the completion of a series of field and laboratory tests, the strength characteristics and the mechanism of shear strength attenuation about the glacial deposit body in Taoping were studied and analyzed, the following conclusions were obtained:1)The glacial deposit body in Taopingr is usually composed of coarse grain and fine grain. It has the characteristics of layered deposition in the space distribution. Coarse grained(crushed stone, gravel and sand) content with the elevation of the lower shows an increasing trend, and fines(silt and clay) content decreases.2)On the basis of summarizing the classification and origin of the ice deposits, the deposition characteristics of glacial deposit body and the variation characteristics of the structure, grain size composition and structure characteristics of the bulk material in spatial distribution, find out the Zagunao River along the sides outwash accumulation mainly due to Glacier Valley on both sides of the outwash kame terrace. To deduce the evolutionary process of the formation of the glacial deposit body body under different transportation and accumulation dynamic conditions by using reverse method to analyze the characteristics of climate change in this area during this period.3)Through a series of indoor physical property tests, the results show that the glacial deposit body of fine grained soil is a hard plastic silty clay. Field shear test results show that the cohesion of gravel(gravel content is 8.6% containing water 7.9%) is 20.54 kPa and friction angle is equal to 19.42 degrees; when the water content is 32.7%, the cohesion is 14.11 kPa and the friction angle is 15.75 degrees; the cohesion of the silty clay(gravel content of 0%, containing water 16.9%) is 17.62 kPa and the friction angle is 19.40 degrees; when the water content is 31.5%,the cohesion is 11.49 kPa and the friction angle is 18.70 degrees.4)Completed a series of the breccia soil triaxial tests of different gravel content and water content of glacial deposit body and combined with the Mohr Coulomb strength formula, get the shear strength parameters-the cohesion is between 32kPa~35kPa and the friction angle is between 19.8 degrees and 26.6 degrees; I obtained the influence of the various factors against shear strength parameters, acquired the optimal value of gravel content or clay content and put forward the content of water and gravel suggestions; revealed that at low confining pressures should force under the ice bulk strength envelope of breccia soil linear, with the Mohr Coulomb failure criterion of the theory.5)Based on the shear strength test of a series of silty clay, it is found that there is a certain structural strength in the undisturbed soil. With the change of water content, the content of [17.6, 21.2] is the maximum of the structural damage degree of soil.6)By using X-ray diffraction, electron microscope scanning and soil water chemical reaction ion concentration test and other methods to analyze the microscopic mechanism of glacial deposit body, we found the clay mineral and cement with water dissolved chemical reaction, caused by the change of clay mineral particles of fine microstructure, exacerbated the internal reflection of the deterioration of soil physical and mechanical properties.7) Based on the systematic summary of the ice water sediment shear strength of factors, strength parameters of the relationship and the combination of micro and macro analysis method, it is found the attenuation of the anti-shear strength against glacial deposit body results of internal structure change caused by soil water physical and chemical effects, which is also the reason why sticky cohesion of water sensitivity is stronger in friction angle; it is obtained the function formula of shear strength parameters(the value of C and ?) and immersion time t at the same time and determined that the 36 h and the 84 h are the two critical value which cause the shear strength reduction in glacial deposit body and the change of ion concentration in aqueous solution. |
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