Viscoelastic-Plastic Analysis Of Mechanical Characteristics Of Frozen Wall Based On Improved Nishihara Model

According to the freezing engineering of auxiliary shaft in Gubei mine,Huainan,Anhui Province,this paper uses the method of theoretical analysis and field measurement to deeply explore the variation law of the freezing pressure of the freezing wall acting on the outer shaft wall.The main research contents and conclusions are as follows:(1)According to the field data of Gubei mine,the variation law of freezing pressure is analyzed.The monitoring results from two monitoring levels show that the change of the freezing pressure of the shaft wall roughly goes through three stages:the accelerated growth stage,the slow growth stage and the stable development stage.The accelerated growth stage occurs within 0-30 days after the excavation of the shaft wall.In this stage,the freezing pressure increases rapidly,and the growth rate is also increasing.The slow growth stage occurs within 30-90 days after the shaft wall is poured.In this stage,with the formation of the frozen wall,the growth rate of the frozen pressure slows down.The stable development stage occurs 90 days after the shaft wall is poured,and the influence of freezing pressure on the shaft wall decreases until the growth rate of freezing pressure is zero and no longer increases.(2)Based on DP criterion,the calculation formula of elastic-plastic mechanics of frozen wall in deep topsoil is derived,and the freezing pressure of auxiliary shaft in Gubei mine is calculated based on the formula.The calculation results show that the freezing pressure of the freezing wall increases continuously with the increase of the extension radius of the plastic zone,and eventually stabilizes;the freezing pressure value is related to the coefficient of the DP criterion and the value of ? and k.(3)The Nishimura model was improved by connecting a nonlinear rheological element in series with the model.There is an intermediate stress,When 0<???b,The model describes the decay creep stage of frozen soil;When ?b<???s,The model is the Burgers model,describing the attenuation and stable creep stages of frozen soil;When ?>?s,The model can reflect the three stages of frozen soil attenuation,stability and accelerated creep.It is applied to the derivation of the calculation formula of viscoelastic plasticity of the frozen wall of deep topsoil,and the calculation formula of the frozen pressure of the frozen wall acting on the outer shaft wall is given.(4)Based on the field measured data,the parameters of the improved constitutive model are inversed,and the variation law of the freezing pressure can be obtained by substituting the parameters into the expression of the freezing pressure.Compared with the measured results,the results show that the theoretical calculation is basically consistent with the field measurement results.Therefore,the calculation formula of the freezing pressure proposed in this paper is in line with the reality,which can better reflect the mechanical characteristics of the interaction between the freezing wall and the outer well wall,and provide theoretical support for the design of the freezing wall and the outer well wall.Figure 23 Table 14 Reference 80...