Research On The Failure Mechanism Of Short-term Permafrost Zone Of Granite Residual Soil Slope

The coastal area of Southeast China granite is widely distributed. Domestic short-term permafrost region are mainly distributed in Nanping City, Sanming City and Ningde City. Nearly twenty years, in order to meet the needs of the national economic rapid growth, in the short-term permafrost region, the development of the highway, railway and other transportation infrastructure construction is swift and violent, but in the construction process, there were appeared many engineering problems, such as soil cut slope is the multiple zone of engineering diseases. Therefore, it is urgent need to carry out the research about the mechanism of the granite residual soil slope shallow instability induced by short-term freezing and thawing cycle, otherwise it has the very outstanding application value and practical significance.The paper based on the heat transfer theory, the seepage theory, and the theory of unsaturated soil mechanics, respectively through the indoor experiment and numerical simulation method, did the system research about Short-term permafrost region granite residual soil engineering characteristics and the temperature field and moisture field of Wuyishan area’s typical slope and the stability of the slope, the main conclusions are as follows:(1) We took two kind of classic granite residual soil in Nanping Wuyishan typical areas to analyse:No. I soil is a kind of poor gradation and low liquid limit gravelly clay soil, its proportion is 2.425, the maximum dry density is 1.79 g/cm3, the optimum water content is 14.95%; No. II soil is a kind of poor gradation and low liquid limit gravelly clay soil, its proportion is 2.316, the maximum dry density is 1.84 g/cm3, the optimal water content is 15.02%.(2) With the increase of moisture content, the shearing strength of soil is Sharply reduce, and the internal friction Angle influence the shearing strength a few; The shearing strength along with the rise of compaction degree is obviously increasing trend.Along with the freezing and thawing cycle times increasing, soil samples shear strength parameters including cohesive force and Angle of internal friction are tending to decline, but change amplitude is more and more small, ultimately remain unchanged.(3) Under the action of freezing and thawing, the shallow ground water content change amplitude is the largest, and 10 cm under the surface soil, the curve of the water content is gentle, the total water content and unfrozen water content dropped slightly or unchanged,Wuyishan area’s frozen layer thickness is about 10 cm.In freezing and thawing state,slope soil temperature and humidity are obvious change when temperature, initial moisture content and thermal conductivity change, and when compactness and specific heat capacity change,it is not obvious.(4) In short-term permafrost region when the shallow permafrost melt completely, its physical parameters including density, and the shear strength reduced to a certain value, can happen shallow instability, and its stability with the increase of freezing and thawing depth is significant decline.Along with the slope soil freezing and thawing cycle times increase,the stability will be reduced, and the decline range is more and more small, but as a result of the freezing and thawing influence depth of Wuyishan area’s slopes is limited, we can think the freezing and thawing cycle has a little influence on the deep layer of slope stability,but it makes a greet difference to the shallow layer.(5) To instability mechanism, wu put forward to three kinds of technical measures,such as:improve the temperature and humidity environment, slope conditions and setting of retaining structures.