• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.19-37
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• 2024

Rockbolts are the primary-supports in NATM tunnels and are widely used at tunnel construction sites. Among the rockbolts methods applied in domestic tunnel design, fully grouted rockbolts are the most representative and frequently used. Fully grouted rockbolts exhibit relative behavior between the bolt and the ground due to the grout material. However, during numerical analysis for tunnel design, fully grouted rockbolts are often modeled in a way that does not reflect their behavior characteristics. This may result in underestimating or overestimating the force of the supports. Based on a literature review, it was analyzed that fully grouted rockbolts are modeled using truss element or cable element. To analyze the effect of grout properties of cable elements on rockbolts behavior, this paper compared the behavior of rockbolts in two models: one estimating grout properties based on rockbolt pull-out test data, and another assuming complete adhesion between the rockbolts and the ground by applying large grout properties. Under identical tunnel conditions, the numerical analysis was conducted by modeling the fully grouted rockbolts differently using truss and cable elements, and the tunnel behavior was analyzed. The research results suggest that modeling fully grouted rockbolts as a function of the interface effect between the bolts and the ground, specifically considering grout, is desirable. The use of pull-out test data to simulate the behavior of actual fully grouted rockbolts was considered as a valid approach.

• Tunnel and Underground Space
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• v.5 no.2
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• pp.123-133
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• 1995

A two dimensional visco-plastic finite element model capable of handling the multistep excavaton was developed for investigating the effect of excavation-support sequences on the behaviour of underground openings in the jointed rock mass. Ubiquitous joint pattern was considered in the model and joint properties in each set were assumed to be identical. Passive, fully-grouted rockbolts were considered in the model. Visco-plastic deformations of joints and rockbolts were assumed to be governed by Mohr-Coulomb and von Mises yield criteria, respectively. With the ability of removing elements, the model can von Mises yield criteria, respectively. With the ability of removing elements, the model can simulate the multi-step excavation-support sequences. The reliability of the model to the stability analysis for the underground excavation in practice was checked by simulating the behavior of underground crude oil storage caverns under construction.