The Study On The Influence Of Shearing Strength For The Carbonate-Salinized Soil Containing Different Content Of Carbonate,Sulfate And Salt Under Freeze Thaw Cycles Condition,Nongan,Jilin Province

Nong,an county of Jilin province is a typical seasonal frozen soil area,the reason is cold in winter and hot in summer.Because annual evaporation is greater than the annual rainfall,the depth of soil salinity is accumulated through the migration of water.Saline soil in Nong,an area belongs to be carbonate saline soil by testing.Due to the range of temperature between summer and winter is too large in the area,the freeze-thaw cycle for soil increases the harm of saline soil.Taking the carbonate saline soil in Nong,an county of Jilin province as the research object,studies on the change regulation of carbonate,sulfate and it,s content on shear strength combined with the freezing-thawing cycle test indoor and the rapid direct shear test and the size distribution test.The factors influencing the shear strength of carbonate soil were evaluated by using BP neural network model established by MATLAB.The following conclusions:(1)Under the influence of freezing-thaw cycling,the cohesion of soil with carbonate,sulfate and mixed salt decreases with the increasing of freeze-thaw cycling;the internal friction angle increases with the increasing of freeze-thaw cycling.At the beginning of the freeze-thawing cycle the cohesion and internal friction angle of soil containing carbonate,sulfate and mixed salt soil are inversely proportional to the salt content in the same compaction degree;The cohesion and internal friction angle of the soil are proportional to the compaction degree under the same degree of compaction.(2)In the process of freezing-thaw cycling,the cohesion of carbonate,sulfate and mixed soil cuts down sharply from 0~6 times,decreases slowly from 6~10 times,the cohesion tends to stabilize after 10 times;The inner friction angle increases rapidly from 0 to 6 times,the internal friction angle increases slowly from 6 to 10 times,and the friction angle of the soil tends to be stable after the 10 time.The internal friction angle of soil increases little by freeze-thawing cycle.(3)In the same degree of compaction equal salt content,it can be concluded that the degree of cohesion of the sulphate-bearing soil is the largest,and the degree of cohesion of the mixed soil is the second,and the degree of cohesion of the carbonate-bearing soil is the smallest.So it can be concluded that the effect of soil cohesion is ordered: sulfate> mixed salt> carbonate;In the same degree of compaction equal salt content,the effect of sulfate on the friction angle of soil is slightly larger than that of carbonate and mixed salt,the influence of carbonate and mixed salt on the internal friction angle of soil is flat.(4)In the same salt content,the greater the decrease in cohesion,the greater the increase in internal friction angle;the critical salt content is 1.5%.(5)The common characteristics of the different types of saline soils under freezethawing cycles are:——When containing carbonate,granule group converted into coarse powder crushed,coarse clay,colloidal agglomeration together in saline soil containing carbonate.——When containing sulphate,granule group converted into coarse powder crushed,coarse clay,colloidal agglomeration together in saline soil,the agglomeration of fine particles is enhanced with the increase of salt content and the increase of freeze-thawing cycles.——When containing mixed salt,granule group converted into coarse powder crushed,coarse clay,colloidal agglomeration together in saline soil containing carbonate,with the increase in salt content,agglomeration increased.The intensity of agglomeration occurred in various salts: sulfate> mixed salt> carbonate.(6)In the measured data,288 data were randomly selected to train BP neural network,and randomly selected 144 data for prediction,the input layer of BP neural network is 3,the hidden layer is 11,and the output layer is,and the simulation precision is up to 0.001.In the carbonate,sulfate,mixed salt under the action,the correlation coefficient between the measured value and the predicted value of the shear strength parameters trained by BP neural network is 0.8112 and 0.825,0.8447 and 0.857,0.8374 and 0.8431.The error between the measured value and the predicted value is small.The results show that the established BP neural network model is suitable for the analysis of the factors affecting the shear strength of carbonated saline soil under the action of freeze-thaw cycling.(7)By considering the correlation coefficient R2,the degree of compaction and the salt content respectively in the model,the order of the cohesion and the internal friction angle under the action of carbonate,sulfate and mixed salt is given as follows: freezing-thaw cycling> compaction degree> salt content.