Study Of The Desiccation Crack For Granite Residual Soils Evolution Considering Effect Of Grain Size

There are serious rainfalls-induced erosion and granite residual soils disintegration in the collapsing area of southern jiangxi,which cause great water and soil loss.Numbers of studies have been carried out on the man-made or natural disasters caused by collapse erosion in this area,including the mechanism and process of collapse erosion in southern jiangxi province,and the disintegration characteristics of granite residual soils under the combined action of drying-wetting and acid rain.It is found that the erosion and disintegration characteristics of collapsed regions are often accompanied by the formation and evolution of cracks via the above research.The development of cracks in turns accelerates the process of rainfall-induced erosion and disintegration.Studies of desiccation cracks with granite residual soils are limited at present,especially for the effect of grain size.Researches of desiccation cracks formation and evolution for granite residual soils with four grain sizes are performed.Besides,the corresponding mechanism analysis are conducted as well,the main conclusions are shown as follows:(1)According to the necessity of desiccation cracks study for different grain sizes and sample thickness,corresponding-condition laboratory geotechnical tests,such as sieve drying test,liquid limit test,specific gravity test and splitting test,are carried out to obtain the corresponding geotechnical parameter of granite residual soils..(2)Based on the granite residual soil property parameters obtained from the laboratory geotechnical test,the critical moisture content of soil sample with different grain size and sample thickness on crack development is theoretically derived,which on the basis of three relationships,namely,the relationship between particle size distribution and matric suction,the relationship between matric suction and the tensile strength of soil,and the relationship between soil cracking and its tensile strength.Then the laboratory desiccation crack tests are carried out with granite residual slurry samples,and the critical water content model parameters were analyzed based on the test results.(3)Binarization extraction of holes and cracks are conducted with the help of the recognition software PCAS and CIAS,the binarization images are then repaired and rogued with Photoshop,and the number and size of cracks and holes of these images are extracted in the form of data,which is later plotted to study the effect of bubble-bursts holes on formation and evolution of desiccation cracks.The fractal theory is used to analyze the fractal dimension of the cracks for four grain size.Meanwhile,three indexes as crack length,crack width and crack number are analyzed.(4)On the basis of the tests results of this paper and the reference to relevant literature,studies the cause of formation and mode of crack development are performed.With the help of matric suction and tensile strength,the causes of fractures were explained macroscopically,and the differences in fracture morphology characteristics were analyzed micromechanically according to sampling process and the process of mechanical analysis.At the same time,mechanical simulation analysis of the samples with holes is carried out via finite element method.The results will provide reference for the cause of formation and development of granite residual soil crack in a certain.