| Among the many factors affecting the occurrence of loess landslide,water is the most positive factor to induce landslide,among which irrigation induced loess landslide is the most representative.At the same time,due to the salt content of loess in the northwest region,irrigation water dissolves and carries salt in the slope,especially in the area where there are more landslides,a large amount of salt precipitation and accumulation can be seen.In this paper,the influence of water-salt migration on soil strength of loess landslide is studied based on the appearance of salt analysis in landslide area.Based on the literature on the formation mechanism,water-salt migration characteristics of loess landslide induced by irrigation in Heifangtai area of Gansu province,the engineering geological conditions of landslide area were studied by field investigation.Water and soil chemical samples were collected to grasp the soil and water salinity background in landslide area.Saturation and non-saturated direct shear tests,triaxial tests,scanning electron microscopy(SEM)microstructural tests and quantitative pore analysis of salt infiltration samples were carried out in different ion types and concentration conditions.The relationship between salt type and concentration and soil strength in slip zone was studied.Department.The conclusions of the paper are as follows:(1)In-situ testing and sampling laboratory testing of soil and water chemical characteristics in landslide irrigation areas and surrounding non-irrigation areas were conducted.The results show that the water content of Huangshui River is slightly higher than that of Huangshui River,and the salinity of the same river is higher in winter than in summer.The soil samples in the non-irrigation area of this area are classified according to the chemical composition of salt and belong to sulfate-stained soil.All the detection data and ion content of the spring point and the leading stream are much higher than that of the non-irrigation river,and the Na++K+?SO42-?Cl-content of the leading stream is the most significant.The runoff velocity of landslide area decreased in winter and the data decreased."Salt washing" It is now a large amount of salt accumulation on the surface of landslide area.The Na+?Ca2+?Cl-and SO42-of soil-like ion types in landslide area were found.the test data were fitted.the conductivity and salt content showed an exponential function relationship,and the conductivity and the total dissolved solids showed a power function relationship.the water content of the back wall of the landslide shows a univariate function relationship with the salinity.Through the particle size detection,it was found that the water infiltration produced leaching on the back wall soil particles,while the salt and minerals bonded to the soil particle.Due to the influence of runoff,the mineral content in soil in different regions also changed.(2)The effects of different ion types and salt concentration on soil strength in saturated slip zone were tested.The soluble salt types include NaCl?KCl?Na2SO4 and CaCl2,every salt concentrations include 0%,10%,12%,14%,16%and 18%.The results show that the shear strength of soil sample is the largest when the concentration of salt is 12%,and when the concentration of soil sample is more than 12%,the strength of soil sample decreases with the increase of concentration.The NaCl salt increases the strength of the sample the largest,the Na2SO4 second and the lowest CaC12.When the soluble salt concentration is 12%,the cohesive force is greatly increased,and after 14%,the cohesive force value decreased.and the change amplitude of internal friction angle is within 2.60.Different ions increase the strength of soil samples in Na+>Ca2+>K+.Anionic Cl->SO42-.The strength law of soil sample under saturated direct shear test is similar to that of triaxial test,and the effect of soluble salt on the strength of saturated soil decreases gradually with the increase of axial load.(3)The influence of water content and salt concentration on the strength of unsaturated soil was tested.NaCl concentrations of 0%,10%,12%,14%,16%and 18%,and soil sample moisture content of 2%,7%,13%,18%,23%and 28%.The results showed that the strength of unsaturated soil was increased by soluble salt.When the salt concentration of soil sample is 16%,the strength increases the most,and beyond this concentration,the strength of soil sample is basically stable.The effect of the increase of soluble salt on the strength of soil samples decreased with the decrease of moisture content.The cohesive force and the angle of internal friction increase with the concentration of soluble salt.Variations in cohesive force The formula is exponential and the internal friction angle changes linearly.(4)Microstructure analysis and test of soil samples after shearing before and after adding salt.The results show:After the salt seeps into the soil,it will have a certain effect on the size of soil particles,contact relationship and soil-like pores.based on the quantitative analysis of the pores based on the PCAS system,the number,perimeter,fractal dimension,shape coefficient and other parameters of the pores under the hair change accordingly with the infiltration of salt solution concentration.And the infiltration of excess salt concentration will destroy the microstructure of soil,which will have a negative effect on soil strength. |
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