Identification Of Seasonal Frozen Soil Ice Front Based On Parallel Plate Capacitance Test

The world's permafrost area accounts for about half of the entire land area.Due to the imbalance of national economic development and the process of economic globalization,China has successively put forward the strategy of developing the western region,revitalizing the old industrial bases in Northeast China,and the strategy of “One Belt,One Road”.Geographically speaking,the western and northeastern regions of China belong to the permafrost regions.With the implementation of these strategies,a large number of seasonal frozen soil projects will inevitably be involved.At present,the detection method of frozen soil in China basically adopts the method of artificial digging or frozen soil drilling.The disadvantages are inconvenient observation,high labor intensity,insufficient data density,and real-time monitoring of soil freezing and thawing depth and its development and changes.Affected by the harsh environment,many transportation projects and infrastructure construction in the frozen area are difficult to implement.The spatial position of the internal ice surface(the interface between frozen soil and melted soil)in the frozen soil will produce its engineering characteristics.The important influence,and therefore the discrimination of its position,especially non-invasive non-destructive discrimination,is an engineering problem that urgently needs to be solved.Based on this,this paper takes the ice front of the frozen soil as the test object.The parallel plate capacitor is used as the medium,and the measuring instrument based on the capacitance test circuit is used as the test tool.The non-invasive non-destructive discrimination method is used to explore the parameter of the capacitance value.Applied to the identification of the ice surface of the seasonal frozen soil.The main research work of this paper is as follows:(1)A system for frozen soil testing is designed in combination with the capacitor test circuit.The system consists of a capacitor test circuit and a frozen soil test device,which are used to test the capacitance of the soil sample and the soilsample placed for the test.In the design,the measurement accuracy of the capacitance test circuit and the insulation of the frozen soil test device are considered separately.The capacitance test circuit uses a self-balancing AC bridge capacitance measurement circuit.The capacitance test circuit has high measurement accuracy and can meet the accuracy requirements of the relevant tests involved in this paper.(2)Based on the test of capacitance of seasonal frozen soil under different temperatures,the change law of capacitance under temperature influence,namely“temperature-capacitance curve”,is established,and the temperature-capacitance model of seasonal frozen soil is established.The model is in accordance with Boltzmann function.A method for characterizing the temperature of seasonal frozen soil is proposed,which provides a new non-destructive identification method for the frozen ice front.(3)In the laboratory environment,the ice-frozen surface identification of the frozen soil was carried out.The experiment set up nine different volume ratios of frozen soil and soil(soil sample at room temperature).In each case,frozen soil was measured.The capacitance value of the area,the ice front and the fused area,combined with the temperature-capacitance model proposed in this paper,gives the method to identify the position of the ice front.