Study And Application Of Spatial Distribution Of Unsaturated Soil And Pit Support Design Method In Jinan

Theoretical research on unsaturated soils has made significant progress in recent years,and the relevant results have demonstrated that the effect of matrix suction can reduce engineering investment in pit support and other aspects,while the existing pit design codes cannot provide effective guidance for such projects.Unsaturated soils are widely distributed in Jinan city,and with the high quality development of urban construction,unsaturated soil foundation pit projects are gradually receiving attention,therefore,it is of great theoretical significance and engineering value to carry out research on the design of unsaturated soil foundation pit support in Jinan area.Relying on engineering examples,the thesis uses data research,experimental testing,theoretical analysis and numerical simulation to clarify the design method of unsaturated soil foundation pit,establish the calculation formula of non-linear shear strength of unsaturated soil,analyse the law of force and deformation of unsaturated soil foundation pit,and suggest the optimisation measures of support system.The following progress was achieved.(1)Clarified the spatial distribution pattern of unsaturated soils in Jinan.According to the topography and groundwater conditions,the area south of the fourth system boundary,east of Metro Line 7 and south of Xiaoqing River were classified as the main unsaturated soil engineering construction areas in Jinan.(2)Mastered the elastic pivot method and three-dim ensional finite element method for the design of unsaturated soil foundation pits.The former is realized by the total cohesion method;the latter is realized by establishing scientific soil-water characteristic curves in the software soil definition stage in combination with experiments,and setting the saturation of soil at different burial depths according to the characteristics of the actual matrix suction distribution of the project.(3)Obtained the shear stress-strain law and shear strength calculation method for unsaturated soils.The soil partial stress is positively correlated with the net perimeter pressure and matrix suction,and the non-linearity of different soil strengths has different sensitivity to matrix suction;the two-parameter shear strength formula can take into account the non-linearity of soil strengths,and the calculation results are accurate and the parameters can be easily determined,which has good applicability.(4)Revealed the differences in the mechanical properties of the support structure between current design methods and unsaturated soil conditions.Unsaturated soil characteristics have a significant effect on the deformation of the upper soil and support piles in the pit,reducing the deformation and ground settlement of the support structure by 40-45%and the internal force by 25-45%compared to the current method;it is recommended that the design of the unsaturated soil pit optimises the upper support and enclosure section.