Study On The Collapsibility Characteristics Of Coarse-grained Saline Soil Foundation

Based on the laboratory collapsibility test of cement improved coarse-grained saline soil,the collapse characteristics of coarse-grained saline soil with 0%,2%,4%,6% and 8% cement under the load of 25 kpa,50kPa,100 kPa and 200 kPa are studied.The test results show that: when the cement content is the same,the sample settlement is the smallest at the 7d curing age,which is the relatively optimal curing age.Considering "rebound",the relative optimal cement content is 4%.The reshaped compacted sample used in the test showed non-collapsible properties under the indoor collapsing test conditions,and the result of on-site immersion load test is slight collapsibility,reflecting the great difference in the structural aspects between the undisturbed soil and the remolded soil.Combined with the data of the cement improved laboratory test and the field in-situ immersion load test of the coarse-grained saline soil,the numerical analysis and verification of in-situ immersion load test of coarse-grained saline soil are carried out.The numerical calculation results show that at the end of the immersion,the shape of the influence area of the Shanshan site is approximately "U" shape,and the vertical permeability is significant.With the increase of immersion time,the horizontal and vertical immersion range of the test pit does not change much.At the end of immersion,the vertical settlement range of the foundation is about 0.35 m,which is basically consistent with the boring results of the field.After the pressing plate of Shanshan site is loaded with200 kPa and immersed in water,the measured and calculated values of the cumulative settlement of the site are basically consistent with the numerical calculation.At the end of the project,the coefficient of collapsibility is about 0.002,which is a non-soluble coarse-grained saline soil site.The initial shape of the soil layer of Shenhuo site is approximately circular.Due to the influence ofthe sand mudstone impervious layer at the lower part of the site,the water immersion range gradually evolved into a large bell mouth shape.At the end of the test under water pressure,the vertical settlement range of the foundation is basically consistent with the result of the field excavation.At the end of the immersion test,the maximum dissolution coefficient in the center of the test pit is about 0.004,which is a insoluble coarse-grained saline soil site.Finally,based on the numerical analysis model and in-situ collapse test,this paper discusses the characteristics of influence of soluble salt content,collapse coefficient and skeleton particle content on the collapsibility of coarse-grained saline soil.And the following knowledge is obtained: the soluble salt content and permeability coefficient have a positive correlation with the collapsibility of coarse-grained saline soil.The soluble salt content and permeability coefficient are positively correlated with the dissolution of coarse-grained saline soil.With the decrease of the permeability coefficient,the influence depth of collapsibility shows the characteristics of nearly exponential attenuation.There is a negative correlation between the content of skeleton particles and the collapsibility of coarse-grained saline soil.When the content of skeleton particles is lower than about 55%,the subsidence coefficient is higher than0.01,and the coarse-grained saline soil base begins to show collapsibility.