祁南矿东风井冻结温度场时空演化规律分析

Analysis on spatio-temporal evolution law of freezing temperature field in eastern shaft of Qinan Coal Mine

  • 摘要: 以安徽祁南矿东风井冻结法凿井为工程背景,以多圈管冻结的不同土性表土层为研究对象,基于冻结孔实际成孔位置,应用有限元软件COMSOL Multiphysics分别建立埋深218 m钙质黏土层位、埋深225 m细砂层位和埋深259 m砂质黏土层位3个不同土性、不同埋深的冻结温度场数值计算模型,并结合现场实测数据,分层计算分析了其冻结壁温度场时空演化规律,结果表明:在相同冻结条件下,埋深225 m细砂层位冻结壁有效平均温度比埋深259 m砂质黏土层位和埋深218 m钙质黏土层位分别低0.09~0.72℃和0.44~1.95℃,埋深225 m细砂层位平均有效厚度比埋深259 m砂质黏土层位和埋深218 m钙质黏土层位分别厚0.17~0.38 m和0.29~0.47 m;现场实测与数值计算均表明,各个层位冻结壁开挖时,其平均温度均低于–15℃,有效厚度均大于6.2 m,200 m以下深部表土层井帮温度低于–4℃,满足施工要求,冻结壁强度和稳定性均处于安全状态;冻结孔沿径向将冻结温度场划分为3个区域(A区、B区、C区),B区在冻结孔冷量叠加的影响下降温速度最快,A区降温速度适中,C区距离冻结管较远,且外部土体源源不断向其输入热源,降温速度最慢。该研究可为冻结法凿井中冻结壁的施工提供一定的理论参考。

     

    Abstract: Three numerical calculation models of the freezing temperature fields with different soil nature and different burial depths, i.e. the calcareous clay horizon with the burial depth of 218 m, the fine sand horizon with the burial depth of 225 m and the sandy clay horizon with the burial depth of 259 m, were established respectively using the finite element software COMSOL Multiphysics based on the actual forming locations of freezing holes, with the engineering background of using the freezing method in shaft sinking for the eastern air shaft of Qinan Coal Mine Anhui Province and the study object of the surface soil with different soil nature that was frozen by multi-circle-pipe method. In combination with the field measured data, the space-time evolution regularity of the freezing wall temperature field was calculated and analyzed. As indicated by the results, under the same freezing conditions, the effective average temperature of the fine sand horizon with the burial depth of 225 m was 0.09-0.72℃ and 0.44-1.95℃ lower than those of the sandy clay horizon with the burial depth of 259 m and the calcareous clay horizon with the burial depth of 218 m, respectively; the effective average thickness of the fine sand horizon with the burial depth of 225 m was 0.17-0.38 m and 0.29-0.47 m larger than those of the sandy clay horizon with the burial depth of 259 m and the calcareous clay horizon with the burial depth of 218 m, respectively. According to both the field measurement and numerical calculation, when the freezing wall of each horizon was excavated, the average temperature was lower than −15℃ for each, the effective thickness was larger than 6.2 m for each, and the flank temperature at the deep surface soil below 200 m was lower than −4℃, which met the construction requirements; both the freezing wall strength and the stability were in safe status; the freezing temperature field was divided into 3 areas radially by the freezing hole. The temperature of area B dropped fastest due to the effect of the cooling capacity superposition of freezing holes; the temperature drop in area A was moderate; the temperature drop of area C was the slowest, as the area was far away from the freezing pipe, and the external soil continued to transfer heat to it. The study can provide certain theoretical references to the construction of the freezing wall in the shaft sinking using the freezing method.

     

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