| This dissertation tested the main physical and mechanical parameters of the inspection hole sample of the mine shaft in Yuandatan coal mine,and analyzed the stress field evolutionary regularity of the frozen wall,and put forward the stability discriminant method and the plastic zone distribution and the thickness calculation method of the frozen wall,and deduced the internal temperature distribution equation and the original frost heaving force calculation equation of the frozen wall by fully using the frozen soil test,theoretical analysis,numerical simulation and the field practical monitoring research methods.In addition,the dissertation also discussed the relation of the converging deformation and the plastic zone distribution of frozen wall with it’s mechanics parameters,geometric parameters and it’s external forces and the exposure time of which is the main influence of the stability of the frozen wall,and calculated the formulas of the frozen wall convergence and plastic zone distribution by fitting.The brine temperature,the hole temperature and the sides temperature,the frozen wall convergence deformation and the wellbore pressure were measured in the Yuandatan coal mine.Finally,this dissertation analyzed the frozen wall stability characteristics from it’s formation to thaw,and summed up that the convergence deformation of the fine sand layer and the clay layer were greater than the convergence deformation of the siltstone layer and the sandy mud layer,and that the causes of the differences of the frozen wall convergence deformation for the main inclined shaft were the strength character changes of the frozen stratum.This dissertation was on the background of the main inclined shaft freezing construction of the Yuandatan coal mine.The frozen wall stability research contents and achievements of the main inclined shaft mainly based on the following aspects:1.The mass specific heat,volume specific heat,thermal conductivity,freezing temperature and frost heaving ratio of the frozen soil samples were tested by the physical and mechanical properties test of the stratum threaded by the main inclined shaft of the Yuandatan coal mine.The uniaxial compression and uniaxial creep test were also implemented.The uniaxial test results show that the uniaxial compressive strength of the frozen topsoil presented nearly linear increase with temperature decreasing,and that the strength growth rate was about 0.32 ~ 0.64 MPa / ℃.The uniaxial compressive strength of the frozen rock generally increase with temperature decreas ing,the frozen rock strength was influenced relatively great when the temperature was between-10 ℃ and-15 ℃.The elastic modulus of the frozen rock was greater than the surface soil’s when the temperature was low,and it showed a trend of growth generally when the temperature reducing and it’s discreteness was obvious.The creep deformation of the frozen ground was small in the condition of low temperature.When the level of the stress was low,it basically belonged to the category of attenuation creep;when the level of the stress was much higher,it gradually fell into the category of non attenuation creep.According to the axial creep strain and time relation curves under the co ndition of different temperature,the creep parameters of each tested layer under different temperature condition were acquired by establishing the creep mathematical model of frozen soil.2.The “tilt elastic thick wall cylinder model” was set up based on the theory of elastic mechanics,and the frozen wall stress field evolution law was analyzed with achieving the expression of the radial stress,hoop stress,tangential stress and axial stress of the frozen wall by considering different buried depth,and the frozen wall stability discriminant method was put forward from the aspects of strength condition and deformation condition.Based on the stress distribution characteristics of the frozen wall in the condition of elastic state,the border of the frozen wall was determined when it reached the plastic state,the maximum radius of the plastic extension of the frozen wall and it’s thickness calculation method were acquired according to the yield condition of it’s plastic zone which was confirmed by Mises yie ld criterion.The double orifice freezing temperature field mathematical model was established based on the circular tube stable heat conduction equation,and the vertical direct three-borehole temperature field distribution equation of the frozen wall and the whole row internal temperature equation of the frozen wall were inferred by using the superposition principle with predicting the vertical multi-row core temperature field distribution of the frozen wall of the inclined shaft.The inner edge frost heaving force can be divided into the normal frost heaving force,horizontal frost heaving force and tangential frost heaving force according to the the direction acted on the surface of the outer shaft wall.Based on the theory of elastic mechanics and combining the vertical direct borehole characteristics of the frozen curtain,the frost heaving force calculation model was established and the outer edge original frost heaving force calculation method was acquired by the analysis of the deformation coordination between the frozen wall and the unfrozen soil.3.It was analyzed that the relation of the converging deformation and the plastic zone distribution of frozen wall with it’s mechanics parameters,geometric parameters and it’s external forces and the exposure time of which is the main influence of the stability of the frozen wall by the numerical simulation research about the stability of the frozen wall,and the formulas of the calculation indexes and multi-factor were calculated by fitting.The frozen wall convergence deformation and plastic zone distribution range were mainly affected by multiple factors such as the intensity of frozen wall,the frozen wall thickness,the tunnel size of the inclined shaft,the excavation length,the external load of the frozen wall and the exposure time.The main factors that influenced the convergence deformation and plastic zone distribution range of the frozen wall were the roof load and horizontal load and the strength of the frozen wall,and the secondary factors were the excavation length and the exposure time.The incidence that the frozen wall thickness affected the convergence deformation and plastic zone distribution range of the frozen wall was much more complicated,and it was related to the level of the external load and the current thickness.When the level of the external load change,the influence of the frozen wall thickness to the convergence deformation was not significant,but its impact on the plastic zone distribution of the frozen wall was larger.The influence of the excavation length to the convergence deformation and the plastic zone distribution was interrelated to the level of the external load.The exposure time of the frozen wall to the convergence deformation and the plastic zone distribution was reflected in the initial exposure stage of the frozen wall,and the convergence deformation and the plastic zone distribution increased roughly linearly with the increase of the deformation time.On the exposed section of the frozen wall,the roof deformation was greater than that of the bottom,and the deformation on both sides was symmetrical.The maximum roof and floor deformation and the sides deformation were located in the 0.45 times of the excavation length from the head-on face,and the deformation decreased gradually near the ends of the head-on side and the supported section.The plastic zone distribution range was larger in the roof of the frozen wall,and the plastic zone distribution was less in the floor;the plastic zone distribution of the two sides was symmetrical in general,and the plastic zone distribution increased gradually near the direction of the head-on side and the supported section.In order to obtain more safety,economy and stability frozen wall,the external load of the frozen wall must be clear in different area and depth when the inclined shaft excavation size was determined,and the excavation length should be ensured by combining with the construction process and the schedule,so the strength of frozen soil can be improved.When the inclined shaft excavate,the strengthen supporting measures should be implemented on the 0.45 times of the excavation length from the head-on face.Meanwhile,unilateral increase the thickness of the frozen wall was insignificant.When determined the thickness of the frozen wall,it should be important to analyzed the tunnel size of the inclined shaft,the excavation length and the intensity of the frozen wall,the level of the external load and the deformation time comprehensively.4.The measure research was carried out in the Yuandatan coal mine.The measure contents mainly included the brine temperature,the hole temperature and the sides temperature,the frozen wall convergence deformation and the wellbore pressure,and the stability of the frozen wall was analyzed combined with the measured results.The average temperature of the frozen wall was calculated out according to the measured brine temperature,the hole temperature and the sides temperature.The monitoring results showed that the radial deformation of the frozen wall was not only related to the depth of the frozen soil,but also related to the soil properties.Near the fine sand layer and silty sandstone layer and near clay layer and sandy mudstone layer,the frozen wall radial convergence deformation was greatly reduced,and the frozen wall convergence deformation of the fine sand and clay layers were greater than that of the powder sandstone and sandy mudstone layers.The measured results of the rate of convergence deformation of the frozen wall were basically consistent with the rate of convergence deformation of the frozen wall which was calculated on the basis of the regression formula of the numerical simulation.The fluctuation range of the (?)_v/V_v was 0.75 ~ 1.69,and the fluctuation range of the (?)_v/V_v was 0.71 ~ 3.17,and the measured values were no different than the calculated values.The frozen wall stability change characteristics among the period of the formation to thaw was analyzed according to the stress monitoring of the vault,the arch springing and the floor of the frozen wall.The maximum pressure of the wall was in vault,and the pressure was very small in the floor and the arch springing.The bearing capacity of the frozen wall decreased gradually after the pressure test element burying about 70 ~ 80 days,and the bearing capacity disappeared completely until the fully thawed of the frozen wall.The causes of difference of the convergence deformation was mainly the difference of the frozen ground intensity.In the process of the frozen wall design under similar conditions,the stability of frozen wall can be determined by the strength condition when other factors were determined such as the frozen wall thickness,the excavatio n length and the exposure time. |
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