Design Theory Of Homogeneous Frozen Wall In Deep Alluvium At Wanfu Mine And Its Application

"Two walls and one drilling" problems are the core technology of the shaft freezing method,and the problems of frozen wall in deep alluvium,especially the design theory and construction technology of frozen wall is one of the difficulties.During the design and construction of deep alluvium frozen wall,the temperature field and deformation of the frozen wall are the key factors influencing the construction of the freezing method.Generally,the frozen wall formed by shaft freezing is used as a conventional arrangement of concentric circles of frozen holes.Under the condition of satisfying the design and construction requirements,the cold consumption is large and the force is unreasonable.This paper puts forward the concept of "homogeneous" frozen wall,which respectively devides inner and middle ring freezing holes into two rings(three rings in conventional method changes to five rings in new method),more uniform and lower temperature strip between inner ring and outer ring,which is called "core area",are formed therefore.Because the core area frozen wall is more homogeneous,and its average temperature is lower than that of conventional method,the core area can undertake more external soil pressure,so the frozen wall has smaller displacement,and frozen wall is more secure.Adopting homogeneous frozen wall method,the frozen wall thickness can be minimized using the least amount of freezing holes,the temperature of frozen wall can be lower on the premise of the same number of freezing holes.This dissertation studied the uniformity and related problems of homogeneous frozen wall,which is the key technology of freezing design and construction of deep alluvium wellbore,through the combination of indoor test,theoretical analysis,numerical simulation and field measurement method.Based on the analysis of the thermodynamic characteristics of the deep alluvium,the spatial and temporal evolution of the temperature field of the homogeous frozen wall and its deformation law,the design method of the homogeneous frozen wall was proposed.According to the undisturbed soil and remolded soil uniaxial compression test,triaxial compressive strength test,uniaxial creep test,the frost heave test as well as the coefficient of thermal conductivity,specific heat test and so on,mechanics parameters such as strength,deformation modulus,poisson’s ratio,creep rate,rate of frost heave and thermal physical parameters such as specific heat,coefficient of thermal conductivity were conducted.Space-time evolution characteristics of the temperature field of the traditional frozen wall and uniform frozen wall are compared using COMSOL Multiphysics software.It can be found that the inner ring and middle ring freezing holes in conventional method are divided into two rings respectively,so that the temperature of frozen wall between the inner ring and outer ring is relatively more uniform,and the average temperature of the frozen wall is lower in the early stage of freezing.On this basis,the concept of "core zone frozen wall"(frozen wall between inner ring and outer ring)was proposed.Through single factor analysis and orthogonal analysis,the influence of the parameters of the homogeneous frozen wall on the temperature field and its significant influencing factors were obtained;and through the multifactor regression analysis,the regression formulas of frozen wall thickness,frozen wall average temperature,core area frozen wall thickness,and the average temperature of core area frozen wall were put forward to analyse the homogeneous frozen wall.The comparison of homogeneous frozen wall and traditional frozen wall and the comparison of homogeneous frozen wall and frozen wall with uniform temperature were carried out using ANSYS software.It is found that the traditional method which analyses the frozen wall deformation using frozen wall thickness and everage temperature has certain error;the core area of frozen wall has a lower average temperature,so it has higher strength and can take more load to reduce the displacement of inner frozen wall.Moreover,it can be seen that the core of decreasing the displacement of frozen wall is to increase the strength of frozen wall in core area.Using single factor analysis and orthogonal analysis,the deformation law of deep alluvium in the process of excavation was obtained,and the regression formula of the maximum radial displacement of the frozen wall was put forward by taking the thickness of frozen wall in the core area and its average temperature as parameters.The concept,connotation and implementation way of homogeneous frozen wall were expounded,and design method of homogeneous frozen wall was put forward based on the laws of space-time evolution and deformation obtained above.Moreover,a design software of deep alluvium homogeneous frozen wall was developed adopting MATLAB software to design the homogeneous frozen wall efficiently.Through the comparison of the measured data of the main shaft of Wanfu coal mine and the auxiliary shaft of Longgu coal mine,it can be found that the development and evolution rules of frozen temperature field formed by arranging frozen holes in circles and flowers are quite different from traditional method.It can also be seen from the stress and deformation analysis of the frozen wall that the main shaft of Wanfu coal mine which arranges frozen holes in circles and flowers is better than the auxiliary shaft of Longgu coal mine which adopts the common concentric circular layout.Research results obtained in this paper may improve the deep alluvium shaft freezing theory and technology,improve the level of design and construction of frozen wall in deep overburden,which can be used to instruct the design and construction of deep alluvium shaft freezing.Meanwhile,the research results have certain theoretical and technical significance for the future construction of deep overburden shaft freezing project in east China.