Lateral rock mass pressure calculation method for extra deep vertical shafts
The design and construction of highway tunnel shafts in China mainly relies on the experience of coal,metallurgy,and other industries.Despite significant accomplishments in constructing ultra-deep shafts,the design theory in this area significantly lags behind engineering practice.Throughout the construction of super-deep shafts in many long tunnels,numerous challenges have been faced.In order to address the issue of calculating the surrounding rock pressure in super-deep shafts for tunnel engineering,a three-dimensional finite difference simulation method was utilized based on the design parameters of the Tiantaishan No.2 Shaft.The measured stress and damage characteristics of the surrounding rock was used,assumed alm range for the blasting damage zone and a 560 m-deep numerical model of the shaft(comprising grade Ⅲ-Ⅴ surrounding rock)was established.The analysis focused on the stress distribution characteristics of the surrounding rock and developed a calculation method for the lateral pressure of ultra-deep shafts.The results show that the plastic zone of the surrounding rock extended 1 to 2.5 m beyond the shaft excavation line,with the range of the plastic zone increasing with burial depth in the same level of surrounding rock and decreasing near changes in surrounding rock grade.The inner surrounding rock exhibited lower stress compared to other areas,with the major principal stress being tangential stress and a significant ring formation effect in the surrounding rock.Additionally,the major principal stress in the plastic zone outside the damage area is vertical stress.After the excavation and support of the shaft,there is a noticeable change in the stress state of the surrounding rock.Radial stress increases with depth,decreases near the changing point of rock mass level and the bottom of the shaft.Variations in the surrounding rock level have a significant impact on tangential and vertical stress levels,while radial stress remains relatively unaffected.The proposed calculation method in this study showed smaller surrounding rock pressure,compared to the current recommended method in the Guidelines for Design of Highway Tunnel(JTG/T D70-2010),and closely matched measured and simulated results from similar projects.This method can serve as a valuable reference for calculating rock pressure in ultra-deep shaft enclosures.3 tabs,19 figs,21 refs.
tunnel engineeringvertical shaftlateral rock mass pressureradial stresstangential stress