Creep Characteristics Of Typical Silty Clay In The Middle And Lower Reaches Of The Yellow River And Prediction Of Foundation Pit Deformation

As the "foundation" of the project,the design and construction quality of underground engineering,especially the foundation pit and supporting structure,will affect the safety of the whole structure.Each step of the process needs strict quality control to ensure the safety of subsequent construction.Deformation is one of the most intuitive factors to detect the safety of deep foundation pit projects.The deformation of foundation pit will seriously affect the stability and safety of foundation pit.The fundamental cause of foundation pit deformation is the deformation of soil outside and bottom of pit.And the soil deformation is mainly composed of primary consolidation deformation and secondary consolidation deformation.The primary consolidation deformation is a process in which pore water is removed under consolidation pressure,excess pore water pressure dissipates and soil is compacted.The secondary consolidation is a process of rearrangement of soil particles caused by creep effect.With the development of engineering construction technology and the improvement of people’s understanding of engineering safety,it has gradually become an urgent need to ensure engineering safety to carry out real-time and accurate calculation and prediction of foundation pit deformation in view of secondary consolidation deformation(creep characteristic)of soil mass during foundation pit construction.On the basis of summarizing relevant researches at home and abroad,this paper relies on the shield well project of Yellow River Tunnel in Jinan City.The creep characteristics of typical silty clay in the middle and lower reaches of the Yellow River in Jinan were studied by one-dimensional consolidation creep test and triaxial confining pressure unloading creep test in this paper.And through the method of combining theoretical derivation and engineering site monitoring,the deformation of shield working well foundation pit in its excavation process changes with time.The main contents are as follows:(1)The creep characteristics of typical silty clay in the middle and lower reaches of the Yellow River in Jinan under lateral confinement were expounded through one-dimensional consolidation creep tests.The variation of strain with time was revealed by the experimental data.The variation of strain with load and deformation rate with time are also studied.At the same time,the boundary point of primary and secondary consolidation and the influencing factors of secondary consolidation coefficient are analyzed comprehensively.(2)The creep characteristics of silty clay in the middle and lower reaches of the Yellow River in Jinan City under simulated excavation stress are described by triaxial reduced triaxial compression creep tests.Based on the experimental data,the deformation of typical silty clay samples in the middle and lower reaches of the Yellow River was studied with time.The relationship between creep characteristics and deviatoric stress and the nonlinear characteristics of creep are analyzed.The experimental results were fitted and compared by three commonly used creep empirical models,and finally the creep model suitable for the silty clay in the middle and lower reaches of the Yellow River in Jinan City was obtained.(3)Take the shield well project on the south bank of the Yellow River Tunnel in Jinan City as an example.The automatic intelligent real-time monitoring system is used to obtain the real-time monitoring data of deep horizontal displacement in the excavation stage of working well foundation pit.The creep model is applied to the calculation of the deep horizontal displacement of the ground wall by defining the displacement time coefficient and the result curve of the model is obtained.By comparing the curve of derivation and the curve of monitoring,the applicability of the creep model in the excavation stage of foundation pit in practical engineering is demonstrated.The application range of the model and the obedience degree of the horizontal displacement and deformation law of the deep layer of the ground wall to the model are studied.