The Mechanical Properties Tests Of Saturated Silty Soft Clay In Shanghai Under Artificial Freezing Method

With the development of underground structures in Shanghai, the artificial freezing method is more and more widely used in tunnel construction (such as the soil reinforcement of by-pass and pump house of tunnels). In order to avoid the problems of geological disaster which may happen in the frozen construction, like the freezing accident happened in shanghai tunnel Line 4, the artificial freezing technology should be utilized safelier, more economically and more effectively to serve the Shanghai city. it is very important and necessary for us to study the microstructure, the instantaneous uniaxial compressive strength, the frost heave and thaw collapse, the creep of frozen soil and its' engineering mechanism quality. The result will be beneficial to the functional safety of underground engineering in the future.So far, no scholar has studied the physical and mechanical character of saturated silty soft clay under artificial freezing method in Shanghai. In this paper, we mainly discuss contents in four aspects as following:(1) Through instantaneous uniaxial compressive strength tests, the strength of the frozen soil was analyzed and the relationship between strength and freezing temperature were discussed. In a certain temperature range, the strength of the frozen soil and freezing time interact in a quadratic parabola relation in early period. Besides, it is also a linear relationship between the time and Young's modulus as well as Poisson's ratio.(2) Exploring characteristic of frost-heaving of artificial freezing soil is a key-technology and important basal research about artificial freezing method for municipal underground space. After the frost-heaving test, the paper studies the soil's frost-heaving's relationship with freezing end temperature. The frost-heaving ratio and the frost-heaving stress are linear with the freezing end temperature. The paper also measured the freezing temperature of soil by freezing temperature test, established freezing temperature distribution field of the soil sample, and further revealed the relationship between the freezing front and time. (3) The frozen grey silty clay of the 4th storey has the obvious creep characteristic, the frozen soil creep is the most prominent characteristic of frozen soil mechanical behavior. By analyzing the creep test result of the frozen soil and using the empirical method, the paper has obtained creep equation. From the analysis of the same-time long-term creep curves and the same- temperature long-term creep curves of strain-stress, relationship between stress-strain is farther discussed.(4) In this paper, the microscopic behavior of grey silty clay of the 4th storey is studied by means of scanning electronic microscope. The shape, size and contact condition of the basic elements of the soil microscopic structure, the shape and the size of the pore are further studied. In addition, through the information obtained from the SEM photo by means of computer Vector processing soft, the quantitative analysis method of microstructure of silty clay soils is presented. The analysis result shows that the shape and directionality of the pore changes little compared with undisturbed soil, but the pore diameter increases with freezing temperature declines.