2-D Freezing Heave Test And Theoretical Research Of Saturated Fine-grained Soils

The research on frost heave mechanism and its effect on the engineering structure have always been a hotspot and difficulty in the field of frozen soil.Most of the previous theoretical analyses and experimental studies on frost heave focused on one-dimensional(1-D)freezing problems under different boundary conditions.However,two-dimensional(2-D)freezing phenomena widely exist in the actual engineering in frozen soil area.Distinguishing from the conventional 1-D heat exchange from the natural ground surface,the frost heave mechanism,distribution character of frost heave force and its interaction with the supporting structure will surely change under the 2-D freezing condition.Due to the complexity of physical and mechanical properties of frozen soils and the diversity of the actual engineering environment,the theories and research results based on 1-D freezing conditions have obvious limitations in explaining the complex frost heave phenomenon in the actual engineering environment.Considering actual engineering conditions,the authors found studying the mechanism of 2-D frost heave and its coupling evolution behavior with engineering structures has great significance and scientific value in the engineering construction of frozen soil area.Based on the 2-D freezing phenomenon involved in the frozen soil projects,the 2-D frost heave mechanism,characteristics and its coupling behavior with engineering structures of saturated fine-grained soils were systematically studied through the theoretical analysis,laboratory sample test and physical simulation test in this paper.Then,a new visualized test system of 2-D frost heave with dual functions of centralized control and constraint was developed;A series of 2-D frost heave tests on saturated fine-grained soils were carried out;2-D frost heave simulation tests of the deep foundation pit in the seasonal frozen soil area were conducted,which reveals the forming and evolution mechanism of 2-D freezing segregation ice of saturated fine-grained soils.Distribution characteristics of frost heave force of the supporting structure in the foundation pit was obtained.Finally,a 2-D freezing coupled heat-moisture-stress separate ice frost heave model was established.The main research results are as follows.(1)A 2-D visualized freezing test system of frozen soils which is coupled controlled by temperature and constrained boundary was developed.The control precision of the system temperature is ±0.1?.The lowest operating temperature is-40 ?.It can achieve bidirectional temperature and stress/displacement boundary independent control.Real time digital photography is achieved during the freezing process.By means of image analysis and CT scanning technology,the visualized and accurate measurement of evolution rules and distribution characteristics of segregation ice of frozen soil 2-D frost heave are realized.(2)A series of 2-D frost heave tests of saturated fine-grained soils were carried out.Through these tests,the authors have obtained the variation of the temperature,stress and deformation fields during the 2-D freezing process of two typical saturated fine-grained under different freezing temperatures.The forming process,growth rate and distribution characteristics of 2-D frost heave segregation ice of saturated fine-grained soils were analyzed,which revealed the 2-D frost heave mechanism of saturated fine-grained soils under lateral constraints from macroscopic and microscopic perspectives.(3)A 2-D coupled heat-moisture-stress separate ice frost heave model of the soil was established.On the basis of the 1-D separate ice frost heave model,the concept of separation pressure is extended to the 2-D case.The formation criterion of ice crystals in 2-D freezing process was analyzed.The basic theory of 2-D separate ice frost heave model was developed.The theoretical model can well reveal the coupled heat-moisture-stress in the 2-D freezing process and predict the development of ice lenses.Based on Matlab,a 2-D freezing process program was developed.The 2-D freezing process of a square area was numerically calculated,and the variation rules of temperature field,equivalent water pressure field and displacement field were analyzed.(4)2-D freezing simulation tests of deep foundation pit projects in the seasonally frozen area were carried out.Taking the deep foundation pit projects in the typical seasonally frozen area as the research background,the authors obtained the data of 2-D freezing temperature gradient,water migration and distribution of stress and displacement fields under different freezing temperatures and engineering constraint modes.Then,the frost heave force size,distribution and development rule with time of the two support system,namely pile-anchor support and diaphragm wall support of foundation pit under the 2-D freezing condition were analyzed.(5)Based on the results of the theoretical analysis,laboratory and simulation tests,the distribution and evolution of 2-D freezing temperature,water and deformation field of saturated fine-grained soil and their coupling characteristics and nonlinear evolution behavior with engineering environment were analyzed.The 2-D freezing characteristics and internal physical mechanism of saturated fine-grained soil were clarified.