Abstract Collapse and clearance invasion events occurred repeatedly during the construction at the section of ZK152+433-ZK152+463 of left tube of Baizhang tunnel passing through a flow-plastic fracture zone with abundant water, which brought unprecedented challenges to the engineers. The various measures adopted in the construction are described in detail, and an analysis on structure safety is conducted by numerical method. The results show that:(1) as for the flow-plastic water-rich fracture zone, dense advance support is the most effective measure to prevent large deformation or collapse of surrounding rocks during excavation, a ring of ?51 self-drilling anchor bolts with unit length of 3.5 m are installed between steel arches (with the steel arch interval of 50 cm), that is to say there are 7 layers of advance support for each tunnel section, effectively controlling the rock mass deformation after excavation, avoiding collapse and clearance invasion of tunnel lining; (2) it is significant to reinforce the surrounding rocks,especially at sidewall and tunnel floor, since it can effectively decrease the integral subsidence of tunnel lining during construction. A combination of jackstone treatment and grouting is adopted to reinforce the surrounding rocks at sidewall and tunnel floor and the effect is much better than that only with grouting; (3) as for the tunnel with explicit external load, the parameters of lining support should be determined by both calculation analysis and engineering experience, which will guarantee the safety of tunnel structure and also make it economical and reasonable; (4) as for the two-lane tunnel, three-bench method is taken and the bench length should be shortened as much as possible in order to form an enclosure of primary support in time so as to control the deformation of surrounding rocks better.
Abstract：
Collapse and clearance invasion events occurred repeatedly during the construction at the section of ZK152+433-ZK152+463 of left tube of Baizhang tunnel passing through a flow-plastic fracture zone with abundant water, which brought unprecedented challenges to the engineers. The various measures adopted in the construction are described in detail, and an analysis on structure safety is conducted by numerical method. The results show that:(1) as for the flow-plastic water-rich fracture zone, dense advance support is the most effective measure to prevent large deformation or collapse of surrounding rocks during excavation, a ring of ?51 self-drilling anchor bolts with unit length of 3.5 m are installed between steel arches (with the steel arch interval of 50 cm), that is to say there are 7 layers of advance support for each tunnel section, effectively controlling the rock mass deformation after excavation, avoiding collapse and clearance invasion of tunnel lining; (2) it is significant to reinforce the surrounding rocks,especially at sidewall and tunnel floor, since it can effectively decrease the integral subsidence of tunnel lining during construction. A combination of jackstone treatment and grouting is adopted to reinforce the surrounding rocks at sidewall and tunnel floor and the effect is much better than that only with grouting; (3) as for the tunnel with explicit external load, the parameters of lining support should be determined by both calculation analysis and engineering experience, which will guarantee the safety of tunnel structure and also make it economical and reasonable; (4) as for the two-lane tunnel, three-bench method is taken and the bench length should be shortened as much as possible in order to form an enclosure of primary support in time so as to control the deformation of surrounding rocks better.
TIAN Zhiyu1 TIAN Shangzhi1 YANG Feng1 ZHANG Zhaojie1 WANG Bo2
.Engineering Measures and Safety Evaluation of Baizhang Tunnel Passing through Flow Plastic Water-rich Fracture Zone[J] MODERN TUNNELLING TECHNOLOGY, 2020,V57(2): 176-183
2020, Vol. 57 