Temperature Monitoring And Numerical Analysis Of Freezing Shaft In Soft Rock Formation In Mengcun Coal Mine

In recent years,in the construction of new mines in China,complex and special formations have been encountered.The wellbore should pass through rock layers with different thickness and large water content,causing the wall thickness to be too large,increasing the amount of excavation work,significantly increasing the cost of the wellbore and extending the construction period by more than 1/3.These engineering problems have brought the wellbore construction.Great difficulty.It can be seen that the variation law and deformation mechanism of borehole temperature field during construction of weakly cemented soft rock are studied.The temperature variation law of wellbore structure suitable for weakly cemented soft rock under freezing conditions is proposed,and the optimal hole spacing scheme is determined under reasonable freezing strength,And to ensure the freezing of the wall crossing time,controlling the high and empty time of the excavation section has important engineering guiding significance for ensuring the safety of freezing and sinking construction.This paper takes the frozen sinking well of Mengcun Coal Mine as the engineering background,through the theoretical analysis of the physical and mechanical properties of the frozen rock and the continuous long-term monitoring of the long-range freezing temperature,combined with theoretical analysis and on-site monitoring results.The inversion calculation of the soft rock thermal parameters of freezing and sinking in coal mine is carried out.Based on this result,the variation law of temperature field in freezing method is numerically simulated.Based on this,the influence of concrete hydration heat on the strength of frozen wall and sinking well are analyzed.The rheological deformation law of the frozen wall during the process.The results of the study indicate that the temperature diffusion coefficient of sandstone under the condition of freezing the ground is kh=-0.317℃/d,and the temperature diffusion coefficient of sandy mudstone kh=-0.213℃/d.Using this coefficient,the required excavation and freezing time for this formation is 60～75 days,the thawing temperature diffusion coefficients of different rock formations were obtained by linear regression:sandstone kj =0.103℃/d,conglomerate,mudstone conglomerate interbed kj = 0.121℃/d,and using this coefficient,the frozen layer of this formation returned to zero.The time required for °C is approximately 180 days.From the law of freezing,it is found that the temperature of rock and soil in each area mainly experiences four stages:slowly decreasing→accelerating and decreasing→slowing down rate→maintaining stability;the flow of groundwater will take part of the energy so that the development speed of the post-freezing peak is significantly lower than that of the frozen forward.