A construction strategy for a tunnel with big deformation

Abstract

By integrating literature reviews, site observation, field monitoring, theoretical analysis, summarization, etc., a construction strategy was proposed and verified for tunneling with big deformation in this paper. The tunnel was in phyllite, shotcrete cracks and steel arch distortion were observed, and a big deformation with a maximum of 2.0 m was monitored during the initial stage of the construction. Through carefully examining the site observation and laboratory test results, a construction principle was established for the tunneling on the basic concept of maintaining the rock strength/stiffness and keeping the rock dry, by providing confinement pressure to the rock, reducing the rock exposure time, keeping water out of the tunnel, etc. To achieve the construction principle, a set of specific construction measures with 11 items was further proposed and applied to the construction. To check the effectiveness of the construction measures, field monitoring was carried out, which showed that the rock deformation was well controlled and the tunnel became stable. An allowable deformation was then determined using the Fenner formulae and the monitored data in order to guide further construction, which received a good result. From this study, it can be concluded that providing quick strong initial support and reserving core soil at the working face are extremely important to control the rock deformation and keep the tunnel stable.

An Insight from Rock Bolts and Potential Factors Influencing Their Durability and the Long-Term Stability of Deep Rock Tunnels

“…For this reason, excessive deformations are generally common at great depth and rock bolts have to deal with them. In fact, some soft rocks often stabilize after visibly deforming [168], and rock bolts should support them in the long-term, otherwise tunnel failure can happen without delay. Colossal deformations of rocks have been observed in deep tunnels in such rock type.…”

“…Colossal deformations of rocks have been observed in deep tunnels in such rock type. For example, 2000 mm deformation has been measured during excavation of a diversion tunnel in Sichuan Province, China [168]. In addition, 2403 mm has been measured in Muzhailing tunnel, Gansu Province, China [169].…”

Prevention and Mitigation Management of Tunnel Collapse and Failure during Construction-A Review

“…(Kavvadas, 2003) has discussed some ground deformation measurements commonly used in tunneling in detail. Presetting bigger deformation can result in stable conditions, as noted in Dongsong Hydropower Station, China (Chen et. al., 2013).…”