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Failure Mechanism of Unbonded Prestressed Thru-Anchor Cables: In Situ Investigation in Large Underground Caverns
Prestressed rock anchor cables are commonly utilized in geotechnical and mining engineering (Peliua et al. 2000; Tezuka and Seoka 2003; Koca et al. 2011) because their installation increases the effective strength and stability of the reinforced rock (Maejima et al. 2003; Li et al. 2012). Nevertheless, in some cases, prestressed cables have failed in large underground caverns or tunnels because of excessive deformation of the anchored rock mass or inadequate assumptions used when designing the cables (Li 2004; Lu et al. 2011; Gong et al. 2011). During the failure process of anchor cable, the stress redistribution and progressive deterioration of the reinforced mass rock can adversely affect the overall stability of the free surface, manifested as large deformation or indeed collapse of rock mass (Galvez et al. 2006; Zhu et al. 2010). Therefore, a deeper understanding of the mode and mechanism of prestressed anchor cable failure will better inform the design process of anchor cables to mitigate future failures. This paper focuses on evaluating the failure mechanism of UPTACs based on a case study of underground caverns in Sichuan Province, China. Several external failure modes of the UPTACs observed in this project are first presented and special design techniques for the UPTACs in the large underground caverns are summarized based on in situ investigation: failure depth of disabled UPTACs, break face, measured working load and installation method. An in situ failure investigation of UPTACs in large underground caverns shows that failure patterns occurred in various manners, including disjunction of the steel capping, strand penetration through the steel cap, and ejection of the steel strand from the cable. Field investigations and laboratory experiments indicated that the modes of failed anchor cables can be classified as tensile failure. From an engineering point of view, our case study of the Jinping II underground project can provide references for optimal UPTAC design for use in similar, large underground environments. Careful design of the prestressed ratio for UPTACs is key for avoiding cable failure. Our study in the Jinping II underground caverns suggests that a prestressed UPTAC ratio of 0.6-0.7 is optimal for preventing cable failure. In addition, a suitable supporting time is another important factor. Field experience indicates that the conditions, where the support system of rock bolts and shotcrete has already been installed and the current excavation-induced deformation in the surrounding rock trends to convergence is optimal for supporting time. Finally, applying an even preload for each of the strands of the anchor cables assists in avoiding partial failure of UPTACs.
Failure Mechanism of Unbonded Prestressed Thru-Anchor Cables: In Situ Investigation in Large Underground Caverns
Prestressed rock anchor cables are commonly utilized in geotechnical and mining engineering (Peliua et al. 2000; Tezuka and Seoka 2003; Koca et al. 2011) because their installation increases the effective strength and stability of the reinforced rock (Maejima et al. 2003; Li et al. 2012). Nevertheless, in some cases, prestressed cables have failed in large underground caverns or tunnels because of excessive deformation of the anchored rock mass or inadequate assumptions used when designing the cables (Li 2004; Lu et al. 2011; Gong et al. 2011). During the failure process of anchor cable, the stress redistribution and progressive deterioration of the reinforced mass rock can adversely affect the overall stability of the free surface, manifested as large deformation or indeed collapse of rock mass (Galvez et al. 2006; Zhu et al. 2010). Therefore, a deeper understanding of the mode and mechanism of prestressed anchor cable failure will better inform the design process of anchor cables to mitigate future failures. This paper focuses on evaluating the failure mechanism of UPTACs based on a case study of underground caverns in Sichuan Province, China. Several external failure modes of the UPTACs observed in this project are first presented and special design techniques for the UPTACs in the large underground caverns are summarized based on in situ investigation: failure depth of disabled UPTACs, break face, measured working load and installation method. An in situ failure investigation of UPTACs in large underground caverns shows that failure patterns occurred in various manners, including disjunction of the steel capping, strand penetration through the steel cap, and ejection of the steel strand from the cable. Field investigations and laboratory experiments indicated that the modes of failed anchor cables can be classified as tensile failure. From an engineering point of view, our case study of the Jinping II underground project can provide references for optimal UPTAC design for use in similar, large underground environments. Careful design of the prestressed ratio for UPTACs is key for avoiding cable failure. Our study in the Jinping II underground caverns suggests that a prestressed UPTAC ratio of 0.6-0.7 is optimal for preventing cable failure. In addition, a suitable supporting time is another important factor. Field experience indicates that the conditions, where the support system of rock bolts and shotcrete has already been installed and the current excavation-induced deformation in the surrounding rock trends to convergence is optimal for supporting time. Finally, applying an even preload for each of the strands of the anchor cables assists in avoiding partial failure of UPTACs.
Failure Mechanism of Unbonded Prestressed Thru-Anchor Cables: In Situ Investigation in Large Underground Caverns
Jiang, Quan (author) / Feng, Xia-Ting (author) / Cui, Jie (author) / Li, Shao-Jun (author)
Rock Mechanics and Rock Engineering ; 48 ; 873-878
2015
6 Seiten
Article (Journal)
English
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