Research On Deformation And Stability Of High-filling Foundation In Loess Gully Region

The Loess Hilly and Gully Region,which has complex geological conditions,is the most extensive landform in the Loess Plateau.With the implementation of China's western development strategy,the construction of various infrastructures is being carried out in the Loess Plateau of Northwest China.There is a shortage of available land resources,so the land levelling projects are gradually increasing.It is bound to cause a lot of geotechnical engineering problems with deep cut and high fill,which must be sufficient attention.Relying on a loess high fill engineering in the gully of Yanan area,this dissertation will focus on the physical and mechanical properties and porosity microstructure changes of compacted loess,the settlement deformation law of high-filling foundation in loess gully region and the deformation and stability of high fill slope,the foundation settlement calculation and prediction,and the mechanism of layered settlement of high-filling foundation.The main research content and results are as follows:(1)The physical and strength properties of the loess are researched through the basic tests,direct shear test and high pressure consolidation test.The variation regularities of porosity microstructures of compacted loess,which has the same optimum water content and different dry density,are investigated by the ESEM and Image-Pro Plus image processing software.By the multiple linear regression method,the correlations between microstructural parameters of compacted loess pores and strength are analyzed.The pore structure characteristic parameters which have a key influence on the strength of compacted loess have been established.(2)Carry out the centrifugal model tests and analyze the settlement deformation law of high-filling foundation in the gully under the conditions of natural water content and rising groundwater level.Study the influence of the lapping joint methods between the filling and the original gully slope on the foundation settlement and raise the method of treatment on the lapping between the filling and the original rock.(3)The centrifugal model tests are carried out on the high fill slope and reinforced loess slope.The deformation features and the potential failure surfaces of two kinds of slopes are compared and analyzed.The distribution of tensile strain of each geogrid in the reinforced loess slope is learned.In addition,when there is the lateral recharge of water,the variation of groundwater level in the slope is also explicated.(4)Based on the finite element numerical simulation,the centrifugal model tests would be verified and supplemented.A comparative study is made on the settlement deformation law of high-filling foundation with different original slope gradients,and the effects of original slope gradient on the settlement deformation are summarized.The deformations of high fill slope and reinforced loess slope are simulated,the settlement characteristics and potential failure surface of slope are analyzed.(5)By the laboratory tests,finite element numerical simulation and field monitoring,the layered settlement deformation of high-filling foundation in loess gully region is studied.The methods are established for the foundation settlement calculation and prediction for the high fill engineering in this loess area.Then,the relationship between the layered settlement deformation and dry density,void ratio of each layered underlying filling,the height of the overlying filling is analyzed,and the mechanism of layered settlement of high-filling foundation is revealed.