Deflection Mechanism and Treatment Technology of Permanent Derrick of Freeze Sinking on Deep Alluvium

Aiming at the problems of deflection and operation safety of permanent derrick of freeze sinking shafts, the mechanism analysis of uneven settling of the derrick foundations in frost-thawed soil was conducted. In addition, research on ground stabilization and derrick deviation rectification technologies was also studied in this paper based on the engineering practice of derrick of auxiliary shaft in the Dingji Coal Mine. Firstly, since the soil texture and artificial freeze temperature field are uneven, the bearing capacity and compression modulus of soil mass decrease after freeze thawing, resulting in uneven settlement of the foundation soil of the derrick footing and causing the deflection of the derrick. The finite element numerical analysis indicates that, in the event of uneven settling, the greatest tensile stress in the derrick structure of Dingji auxiliary shaft increased by 39.83% and the largest pressure stress increased by 33.33%. Secondly, this study used sleeve valve pipe single-fluid static pressure grouting technology to reinforce the foundation of the derrick footing. The reinforced depth of grouting is 32 m, and every derrick foundation has adopted three circles of grouting holes for grouting reinforcement. Meanwhile, the hydraulic synchronous jacking system was used to rectify the deviation of the derrick, restoring the centre line of derrick ascension to the original design state. Finally, the practice of grouting, foundation consolidation, and derrick deviation rectification projects of the Dingji auxiliary shaft suggest that, after grouting reinforcement, the rate of foundation settlement is gradually decreased and tends to be stable. This has resulted in uniform settlement, and through four basic jacking, the deflection of the derrick has been corrected to its initial design state.

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