| Artificial ground freezing method is the most widely used method of deep vertical shaft of coal mine special construction in our country.During the deep-seated freezing method,Excessive groundwater seepage velocity always leads to vertical well freezing accident,for instance,frozen wall hard to form a circle and developmental delay,even lead to large economic losses.It can be seen that groundwater velocity has an important influence on the distribution and formation of temperature field of frozen wall of deep shaft.The topsoil of Xinxi ventilation shaft in Huainan pansan Mine was constructed by freezing method.Three-coil pipes freezing programme was adopted.The maximum groundwater velocity reaches 7.96m/d,and the original freezing scheme does not consider the influence of groundwater seepage.This will undoubtedly bring some risk to the shaft freezing method.Accordingly,This paper is based on the coupled mathematical model of freezing temperature field and seepage field.And the finite element program of COMSOL Mutiphysics was used to study the distribution and formation law of the temperature field of deep-wall freezing well under groundwater seepage conditions.On this foundation,optimizing multi-coil pipes freezing programme of Xinxi air shaft in pansan mine.The main research contents and results are as follows:(1)In view of the original freezing scheme of Xinxi air shaft in Pansan Mine,the numerical simulation of multi-coil pipes freezing under five different groundwater seepage velocities(0m/d?2m/d?4m/d?6m/d?8m/d)is carried out.The difference of freezing temperature field with seepage and no seepage(0m/d)conditions is obvious.When there is no seepage,the frozen temperature field and the frozen wall are symmetrical?uniform and regular.When there is seepage flow,the freezing temperature field and borehole temperature show the phenomenon that the downstream temperature is low and the upstream temperature is high and the downstream frozen wall thickness is large and the upstream frozen wall thickness is thin.(2)The results of multi-tube freezing temperature field of groundwater with different seepage velocity shows that the more seepage velocity is,the more irregularities of freezing temperature field is.The higher seepage velocity is,the lower temperature is in the downstream area.The higher temperature is between the frozen tube and the frozen wall in the upstream outer ring,and the longer time is used of freezing wall closure.And in the same freezing time,the lower thickness of the frozen wall in the downstream area,the higher average temperature of the frozen wall,and the intercrossing time of frozen wall increases exponentially with the increase of the groundwater seepage velocity.(3)The optimization of the outermost main freezing pipe in the original freezing scheme of Xinxifengjing well in Pansan Mine was carried out.The 24 freezing holes uniformly distributed in the left half circle were increased from 6 to 30 uniform freezing holes and the spacing of freezing holes was reduced from 1.674 m to 1.34 m.The numerical simulation results of the optimization scheme show that the intersecting time of the frozen wall is advanced from 69 days to 44 days in the original freezing scheme at the maximum groundwater flow rate,after freezing for 140 days,the minimum effective thickness of the frozen wall increased by 2.861 m,and the optimized freezing solution satisfied the desired effect.By comparing the freezing effect of the original freezing scheme and the optimized freezing scheme,it was found that the optimized freezing scheme can effectively reduce the temperature of the the ground freezing temperature field in the upstream area,reduce the flow velocity of the seepage field in the upper and middle reaches of the stream.It can save the time cost of freezing construction,improve the development effect of freezing wall,and improve the efficiency of freezing method construction,It can provides reference and basis for future freezing engineering problems encountered in groundwater seepage. |
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