Experimental Study On Artificial Frozen Soil Moisture Migration Of The Single Pile&soil System And The Frost Heave Properties

Along with the increase of construction and the enlargement of investment of foundation engineering in cold religion, construction difficulty and disease problems are becoming increasingly prominent in frozen soil region at the same time. Thermal disturbance of permafrost affected by the engineering construction and change of temperature, moisture, etc in the process of refreezing bring influence to bearing capacity and settlement of the pile foundation on field, which puts forward challenge to the design and the construction units.Meanwhile, the research on moisture migration of frozen soil has become a hot topic in recent years, which has attracted the interest of scholars at home and broad.In order to investigate the moisture migration regularity and formation mechanism of the ice film at the interface between pile and soil at different conditions of soil around pile, a device testing moisture migration of freezing process of unsaturated soil and its simplified using method are self developed in this paper. Based on the indoor model test and numerical model, the temperature change of soil around pile in the process of freezing and thawing at different conditions of soil around pile and interface between pile and soil, the variation law of moisture content of different positions of soil around pile at different conditions of refreezing temperature in the process of refreezing and the change of frost heaving force and frost heaving amount of the soil around pile in this closed environment are researched. In the following are some aspects of main research results of this paper:(1) Based on the engineering practice of K1047 Chuma river section of Qinghai-Tibet railway, ohmic heating of the scale model pile, embedded within electrical bar, is used to simulate the concrete hydration heat generated by the on-site bored pile. Low temperature environment is provided by the low temperature model box, which has a freezing and thawing cycle function; by means of self-made freezing and thawing sample model box,temperature sensor, temperature patrol instrument, electro mechanical dial indicator, earth pressure cell, NV2312 N wireless static strain gauge and other testing instruments, indoor model test device of moisture migration at the interface between pile and soil at different conditions of soil around pile is designed and assembled.(2) In the following are separately three different working conditions of indoor model test of moisture migration at different conditions of soil around pile: Lanzhou loess;medium-fine sand; and loess in the upper layer and medium-fine sand in the lower layer.Temperature change of freezing, melting and refreezing stages is obtained by temperature monitoring; soil mass is extracted from the model box at separate refreezing temperatures of-0.5℃、-1℃、-1.5℃、-2℃、-2.5℃, with which to test the moisture content of different position through slice test. And then moisture migration law of different conditions of soil around pile is summarized; the regularity of frost heaving of different conditions of soil around pile isobtained by testing frost heaving force and frost heaving amount of the soil from the box at the temperature of refreezing to-2.5℃ of each working condition.(3) The change of the temperature field and moisture field in the process of freezing and thawing and refreezing of frozen soil is researched through the indoor model test in this paper.Using ABAQUS software, the finite element analysis of site temperature field of practical engineering, relied on by the model test, is performed; and the change of temperature field in the process of thermal disturbance of soil mass, caused by the hydration heat produced by pouring pile, is analyzed, which provide guidance to the engineering practice.Through self-designed test scheme in this paper, indoor model tests of three different working conditions-at different conditions of soil around pile are measured, the finite element analysis of site temperature field is performed, and regularity of the change of temperature field and moisture field in the process of moisture migration at different conditions of soil around pile, which provides reference for further study on multi-field coupling problem of frozen soil.