Coupling Of Temperature, Stress And Moisture Migration In Shallow Tunneling Using Multi-Freezing Pipes

Based on the research achievements of the artificial ground freezing in the past, combined with the ground freezing engineering practice of the tunnel of Yan'an Dong road, Shanghai, and by a series of methods including laboratory tests, site observation, theoretical analysis and numerical simulation, author has systematically studied the coupling mechanism and law of three fields ( temperature, stress, moisture migration) and got some important results about soft soil and freezing processFirstly, according to the requirement of theoretical study and engineering practice, the physical and mechanical properties of three kinds saturated soft clay in Shanghai area in the frozen and unfrozen conditions have been tested in laboratory. The influencing factors of initial freezing temperature of soft clay which is in natural condition and the thermal conductivity, thermal diffusion ratio of frozen and unfrozen clay are analyzed. The quantitative relationship between the temperature and the unfrozen water content, elastic modulus and Poission's ration are obtained. The frost heave behaviors of the soft clays are also discussed. By means of the unconfined compression test and tri-axial shear test, the strength variation law of frozen clay is studied.Secondly, by means of the systemizing to the site surveying data oftemperature, stress, surface deformation and soil layers displacement, the variation law of temperature field and stress field and the interference and effect of multi-freezing pipes are analyzed. According to the distribution characteristics of soil layers and installing place and depth of freezing pipes, the coupling properties of temperature, stress, the phase transition of pore water and ground deformation are studied.Thirdly, according to the development of the frozen soil, the coupling model of single freezing pipe of axial symmetry of temperature field, stress field and moisture migration is put forward firstly. Then, by means of the progressing principle of potential field, the coupling model of temperature field, stress field and moisture migration which is under the condition of the multi-freezing pipes is extended. At last, the energy balance equation, stress balance equation, quality balance equation, geometric equation, physical equation, initial and boundary conditions etc are adopted to give the analytic solution to the problem of plane axial symmetry of single freezing pipe.At last, based on the analysis of Galerkin finite element method and some simplification and hypothesis, the numerical solution of three fields coupling of shallow tunnel with multi-freezing pipes is obtained. By means of the finite element program for the freezing process in dynamic static, the numerical simulation is made, and the results agree well with the site survey results.