Experimental Study On Ground Settlement And Compressive Rebound Characteristics Of Deep Soil In Xianyang City

In the early stage of Xianyang City,excessive groundwater was extracted,which caused geological disasters such as land subsidence and ground fissures.However,land subsidence is a dynamic process of change,and its development law,influencing factors and genetic mechanism of ground subsidence need further study.This paper summarizes the characteristics of land subsidence in Xianyang City through field geological survey and data collection.On this basis,deep hole drilling was carried out,and soil samples of different depths of XG65 drilling were selected,and relevant physical parameter indexes were determined.The compression test and springback test of cohesive soil and saturated sandy soil were carried out respectively,and comparative analysis was carried out.Therefore,the characteristics of land subsidence and deep-reverse soil compression and rebound in Xianyang City are summarized.The conclusions are as follows:(1)By analyzing the development relationship of groundwater,precipitation funnel and settlement leakage in Xianyang area,it is found that all three have experienced three stages of continuous decline,stable fluctuation and slow recovery,and the corresponding time points in the same stage are more consistent.Settlement is mainly caused by a drop in the water table.(2)The severe land subsidence area in Xianyang area is the main urban area along the two sides of the Weihe fault,but the annual mean shape of the settlement is not large,and the annual average settlement variable is less than 10 mm.Other areas outside the main urban area belong to the relatively stable area,and obvious settlement deformation occurs in some areas.(3)The second-order terrace sand layer is mainly composed of coarse sand and medium sand with coarser particles,while the third-order terrace sand layer is mainly composed of fine-grained silt and fine sand.The lower strata of the second-order terrace are mainly composed of river facies,and the third-order subterranean strata are mainly composed of lacustrine sediments.Comparing the basic physical parameter indexes of the two borehole soils,it is known that the second-order terrace is more susceptible to compression than the third-order terrace,which is consistent with the second-order terraces than the third-order terraces.(4)Soil compression deformation has experienced three stages of rapid-slowstationary compression.Under the influence of the buried depth of the soil,the shallower the buried depth,the greater the compressive deformation of the soil.Comparing the compression parameters of the second-order terrace clay soil and sandy soil,it can be seen that the ground settlement of Xianyang is mainly compressed by the sandy soil layer.(5)As the load on the soil is reduced,the rebound point of the soil is continuously increased and the rebound amount is increased.The resilience of cohesive soil is worse than that of sandy soil.The rebound ratio of cohesive soil is about 9% to 11.3% of the total compression,while the rebound of saturated sandy soil accounts for 12.9%.~ 15.6%.However,the amount of rebound generated by the soil has a certain mitigation effect on the occurrence of land subsidence.