Optimization design and measurement analysis on inter lining of high strength reinforced concrete frozen shaft lining with deep topsoil

Aiming at the problem of large design thickness of the inner wall of frozen shaft lining in deep topsoil,the force mechanism,design optimization method and field measurement results of high strength reinforced concrete inner wall are analyzed. The model of shaft lining is designed by using similarity theory and the loading test is carried out. Then,the stress,deformation and bearing capacity of high strength reinforced concrete inner wall are measured,and the stress mechanism of the shaft lining structure is studied. The results show that the inner wall of frozen shaft lining in the deep topsoil belongs to the thick-walled cylindrical structure buried deep in the ground. Due to the circular struc- ture of the inner surface,under the lateral pressure,the stress state of concrete in the shaft lining structure is trans- formed from the three-directional compression of the outer edge to the two-directional compression of the inner edge, and the concrete compressive strength is increased by 1. 592-1. 765 times,the bearing capacity of the shaft lining has been significantly improved. The calculation formula of the test value of concrete compressive strength improvement co- efficient is established,and the stress characteristics and strength characteristics of the inner lining of high strength re- inforced concrete are obtained. Based on the current concrete structure design code for concrete multi-axis strength checking requirements,according to the model test results and the inner wall force mechanism,the design optimization method of high strength reinforced concrete inner lining in deep topsoil is proposed,and the design value of concrete compressive strength improvement coefficient is given. The design optimization results apply to the inner wall control layer of freezing section of the west ventilation shaft in Panji No. 3 mine,the thickness of the shaft lining is reduced by 21. 74% and optimized from the original design of 1 150 mm to the current 900 mm. Finally,the field measurement of the west ventilation shaft in Panji No. 3 mine shows that the stress value of the hoop reinforcement in the shaft lining structure after optimization design is - 125. 8 - - 136. 9 MPa, and the vertical steel bar stress value is -39. 5--53. 2 MPa,which is much lower than the design value of steel bar strength of 300 MPa. The hoop strain of concrete in the shaft lining is -730×10-6 --790×10-6 ,and the vertical strain is -380×10-6 ~ -390×10-6 ,which is much lower than the ultimate compressive strain value of C70 concrete. The measured results show that the shaft lining structure af- ter design optimization is economical,reasonable,safe and reliable.