Study On Hydro-thermal-mechanical Coupling Law Of Water-bearing Sand Strata During Multi-tube Cycles Freezing

Shaft excavation is the first technical difficulty to develop solid mineral resources under deep soil layer,and freezing method is the most important sinking method in that situation.The frost heave force caused by artificial freezing of deep saturated sand layer has caused more than ten major engineering disasters such as shaft wall fracture and frozen pipe fracture,but there is a lack of systematic and in-depth research.In order to obtain the variation law and numerical value of frost heave force,the coupling effect law of water,heat and force in saturated sand layer under the condition of multi-tube cycles freezing was studied by using theoretical analysis,numerical simulation and physical test methods.Firstly,the characteristics of the coupling effect of water,heat and force in the frozen zone and the unfrozen zone during actual multi-tube cycles freezing process were analyzed,and the basic model of the coupling action of water,heat and force in the multi-layer cylinders were established;Based on the coupled effect of water,heat and force,an integral formula for calculating pore water pressure and frost heave force in saturated sand layer was derived;For the basic model,using the theoretical analysis method,the evolution rules of frost heave force and water pressure during the process of freezing pure water and freezing saturated sand layer,as well as the influence rules of various parameters were obtained under the axisymmetric plane strain condition.Secondly,for the basic model of multi-layer cylinders by coupling effect of water,heat and force,a secondary development program of ANSYS was developed,which can simulate the water,heat and force coupling action in saturated sand during multi-tube cycles freezing;By using ANSYS,the variation rules and values of temperature,water pressure and frost heave force in the process of pure water freezing and saturated sand layer freezing were obtained through a large number of numerical calculations.Thirdly,for the basic model of coupling effect of water,heat and force of multi-layer cylinder,a frost heave force test-bed which can withstand 25 MPa water pressure was developed;Using the test-bed,unidirectional and bidirectional freezing tests were carried out respectively on pure water and saturated sand,and the evolution rules of temperature,freezing front,water pressure and frost heaving force during the freezing process were obtained.Finally,by comparing the results of theoretical analysis,numerical calculation and physical test,the correctness of the theoretical analysis method was verified;The calculation model of frost heaving pore water pressure and frost heaving force in saturated sand layer under single or multi tubes cycles freezing based coupling effect of water,heat and force was established,the calculation formula and the theoretical calculation method was proposed;Under the assumption of plane strain,the variation law of water pressure and frost heave force in the unfrozen zone under the condition of single or multi tubes cycles freezing was obtained by using typical engineering condition parameters.Research showed that during the freezing process of water-bearing sand,swelling of water freezing can increase pore water pressure by more than 30 MPa and increase radial stress by more than 10 MPa,which poses threat to the safety of borehole walls and freezing pipes.Therefore,in similar projects,measures such as released by hydrological hole and stepwise freezing in different cycles should be taken to prevent frost heave disastersThe research results of this thesis can provide theoretical basis and reference for improving the design theory and method of frozen shaft wall and frozen wall,optimizing multi-tube cycles freezing scheme,and developing fracture prevention technology of freezing pipe.308 figures,18 tables and 100 references are in the thesis.