Study On The Effcet Of Salinity Changes On Strength Character Of Loess

Loess, as a special project soil, would deteriorate in long-term nature physical andchemical effects as well as irrational excavating, which would seriously effect on itsengineering nature. And the deterioration of its engineering nature is the determinants andinternal factors in the loess structures's life time. As time goes by, the number of the old loessstructures grows increasingly, and the security issues become increasingly prominent. So thestudy on the loess's natrue degradation is urgently needed.In this experiment, the soil, whoes sanlinity changes in long-term seepage, is simulatedartificially by controling the soil salinity content. Study the strength properties under differentinitial moisture conten, confining pressure and dry density, by using the indoor conventionaltriaxial tests. And analyze the influence of the soluble salts and carbonate content change onsoil strength characteristics. The results will help forming the "whole life"design theory ofloess strucures, and provide a theoretical basis for the protection of the ancient erthe buildingsin the Northwest. At the same time, the results can provide a theoretical basis in theengineering applications of acid-contaminated soil.After the indoor simulated leaching test, the soluble salt decline frome1.024g/kg to0.010g/kg and the removement of soluble soil samples(S) is considered with no soluble saltcompared to ordinary siol(O). The three batches of different insoluble salt contentsoil(I-1,I-2,I-3) are acquired after the acetic acid with the pH=4treatment. The insoluble saltconten decreases from130g/kg to102g/kg,83g/kg,56g/kg respectively. There are a littlechanges in siol physical properties, when the treaded soil samples are compared with ordinarysoil. Specific gravity changes with the reduce of calcium carbonate content, it decrease from2.71to2.680,2.669and2.658separately for I-1,I-2and I-3, which comparede with S. Thesalinity change would affect the soil particles. And the results of paricle analysis showed thatthe major effect appeared in the grain group,whose particle size is less than0.02mm.The stress-strain cureve, the difference of extremum main stress and the shear strengthparameters of the five soil samples are aquired by laboratory triaxial test. By comparating theresults of O and S, the discipline of the influence of soluble salt in characteristics of loess canbe gotten. And the discipline of the influence of insoluble salt can also be gotten by comparating the results of S and I-1,I-2,I-3.The experiment results showed:(1) S, I-1, I-2and I-3have the same curve shape with O. The ultimate principal stressdifference were the axial strain got to15%corresponding the pincipal stress difference. Thepincipal stress difference of the five soil samples decreased in the order of O, S, I-1, I-2I-3.This phenomenon indicates that the strength of O is the biggst, the sthrength of S is samller,and the strength of I is the smallest when the samples damaged.(2)The effect of salinity changes on the strength increases as the moisture contentdecreases, the higher the moisture content the smaller the effect, instead the lower themoisture content the bigger the effect, under the same dry density and confining pressure.While the effect of insoluble salts(calcium carbonate) on the strength is the the biggest withthe optimum water cnontet of the ordineray soil. The effect of salinity changes on the strengthincreases with the confining pressure increases, in the case of same dry density and moisturecontent. The effect of soluble salts and in-soluble salts is the same, which increases withincreasing dry densty. The loess strength decreases with dacrearing calcium carbonate undersame dry density, confining pressure and moisture content.(3)The effect of salt on loess shear strength parameters changes with the moisturecontent and dry density changes. The impct of the soluble salts and insoluble salts on thecohension and the internal friction angle are associated with the moisture content decreasing,while the effect of insoluble salts can be the biggest in the optimum moisture content of theoriginal soil samples. The influence of soluble salts and insoluble salts increase withincreasing dry density, under the same moisture content. In the case of the same moisturecontent, the influence of soluble salts and insoluble salts increases with the increasing drydensity.(4)The calcium carbonate content influence the cohesion and internal friction angle. Andthe higher the calcium carbonate content the greater loess shear strength parameters, and viceversa.Through comparating and analyzing the test result, the conculusions can be drawed asfollowing. Salinity changes can influence the strength characteristics of loess to a certainextent, but also by factors such as moisture content and dry density. And the effect increseswith the decreasing moisture content and increasing dry density. Because the soluble saltscontent is low and the content of insoluble salts is higher, the effcet on the strength and shearstrength parameters, which caused by soluble salts, is lower than that of insoluble salts. Thedecrease of insoluble salt content has a of serious effect on the cohesion and internal frictionangle of loess. Calcium carbonate in loess can affect the strength of loess intensitily, the greater the content of calcium carbonate the higher the strength. Fit the the relationshipbetween changes in the amount of insoluble salt content and the shear strength parameterschanges, in the case of the serious loss. And the founction cae be used to approximatelycalculat the the biggest change in the amount of shear strength indexes.