Research On Collapsibility Of Loess Based On Water Immersion Test

Collapsible loess has the characteristics of softening,subsidence and rapid loss of strength in contact with water.With the loess area project in full swing,the loess collapsibility problem encountered in the project has become more and more prominent,which has brought new problems and challenges to researchers and engineers.T his problem is mainly manifested in the insufficient understanding of the collapsibility characteristics of loess after water infiltrating,causing incomplete evaluation methods of loess collapsibility.In recent years,due to the needs of projects such as subways and tunnels in Taiyuan,the research on collapsible loess in the area has gradually been enriched.However,through the literature review,the relevant information and data of field flooding tests are rare in Taiyuan.The existing research results cannot meet the needs of engineering construction in Taiyuan.In view of the above reasons,this paper takes the loess of the Dongshan Loess Plateau in Taiyuan as the research object.On the basis of collecting and analyzing the geological data and engineering data in the study area,the geotechnical test in laboratory and the field immersion test are designed and carried out.The surface and deep collapse deformation characteristics of collapsible loess,the botom boundary of collapsible loess,the relationship between self-weight collapsibility coefficient and physical properties,and the difference between the microstructure before and after collapsibility were systematically studied,and the numerical simulation analysis of the field scale was carried out.And the conclusions are as follows:(1)The quantitative relationship between the physical properties of loess and the self-weight collapsibility coefficient was established,and the change characteristics of the loess microstructure before and after collapse were qualitatively analyzed.The void ratio has a positive correlation with the self-weight collapsibility coefficient,while the dry density and water content have a negative correlation with the self-weight collapsible coefficient.The compressive action makes the loess more closely after collapsing contact with the loess before collapsing,and the pores become smaller.(2)Based on the field immersion test,the surface subsidence of the collapsible loess site after water immersion was obtained,and the settlement of the deep loess was detected according to the preset deep punctuation points,and the settlement law of the deep soil layer after encountering water and the surrounding area of the test pits were obtained.The test results show that the growth law of the collapsible volume of the middle and deep loess is consistent with the law of the surface loess,and the trend is low-high-low-smooth.The loess site has obvious boundary effect in the process of flooding and collapsing.The tensile effect of the deformed loess on the surface loess is the main reason for the formation of cracks.(3)Based on the analysis and comparison of the results of the indoor test and the field immersion test,the water diffusion range of the immersion test is obtained,which proves the existence of "residual collapsibility" after a collapse,and the site is a severe self-weight collapsible site,which is the Taiyuan wetland Provide important technical support for sinking loess disposal.(4)The Hydro-mechanical formulation model(HM)was used to simulate the loess flooding test.Combined with the field test data,the water-mechanical coupling behavior of the loess at the field scale was analyzed,revealing the relationship between water infiltration and collapsibility deformation,and the collapsibility of the upper and lower soil layers.Deformation laws and causes.