Safe Thickness of Pregrouting Curtain for Vertical Shaft Ground and Its Application in Tunnel Ventilation Shaft:A Case Study of No.4 Ventilation Shaft of Tianshan Shengli Tunnel
The No.4 ventilation shaft of the Tianshan Shengli tunnel intersects a water-rich stratum,presenting high construction challenges and risks.To mitigate this issue,a ground pregrouting technology is employed to create a grouting curtain.Considering the blasting disturbance effect during shaft excavation,the safe thickness of the ground pregrouting curtain is categorized into invalid and effective thicknesses.A mechanical analysis model of the grouting curtain is established under the combined action of horizontal formation pressure and pore water pressure.Subsequent analysis of the radial displacement of the effective grouting curtain is conducted using the elastic-plastic mechanics theory.The invalid thickness of the grouting curtain is determined by predicting the range of the surrounding rock's crushing area post shaft excavation blasting.Utilizing the thick-walled cylinder theory and considering the displacement coordination condition of the effective grouting curtain at the elastic-plastic interface,the effective thickness of the grouting curtain is determined and strength and stability of the curtain are verified.This theory is applied to the calculation of the safe thickness of the grouting curtain for the No.4 ventilation shaft of the Tianshan Shengli tunnel,which is determined to be 6.5 m.The field test outcomes affirm that the thickness of the grouting curtain meets the engineering requirements and curtain's water stop effect is good,thereby ensuring the safe and rapid construction of ventilation shafts.
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