• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1149-1156
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• 2011

A rockbolt is one of the most important reinforcement of on-site soil, as with the shotcrete and steel rib. The rockbolt by setting within the tunnel can prevent the deformation of the ground profile; furthermore it improves the structural behavior of soil and rock. In general, the rockbolt is mainly used with reinforced steel. However, steel pipe or the materials with the same strength can be used depending on the soil conditions, ground water outflow condition, and the surrounding of applying location. In Korea, most tunnel construction sites have used cement mortar or resin for steel reinforcement on the rock. Due to the ground water outflow in the construction site, the usability of steel reinforcement is poor and it requires curing time especially after installation. To improve exist above problems, this study introduces the development of a swelled steel pipe rockbolt, as well as presents the field testing and performance results.

• Journal of the Korean GEO-environmental Society
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• v.13 no.12
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• pp.81-89
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• 2012

The existing tunnel in urban area can be enlarged because of requirement of road-widening by traffic growth. The protector with rectangular cross section can be set up in the tunnel, which will be constructed for enlargement of width, to solve traffic jam around the tunnel. It is impossible to install the rockbolt in the lower area of tunnel due to a limited space between the protector and cutting surface. The objective of this study is to suggest the method of shotcrete thickness increase instead of rockbolt installation in the side wall of tunnel for the stability of tunnel. Numerical analysis was performed to evaluate displacement at the crown of tunnel, convergence of tunnel, and stress in shotcrete lining in 3-lane and 4-lane NATM tunnels enlarged from 2-lane conventional tunnel. There were three types of analysis condition, rockbolt installation, no rockbolt installation, and increase of shotcrete thickness without rockbolt in the side wall of tunnel. There was no difference on the displacement at the crown and the convergence of upper tunnel. In the lower tunnel, the convergence in case of no rockbolt installation was larger as maximum 1.3mm than that in case of rockbolt installation. The stress in shotcrete lining in case of no rockbolt installation was larger as maximum 1.3MPa than that in case of rockbolt installation. Numerical analysis was performed to compare the behavior of shotcrete with rockbolt with that of shotcrete, which its thickness was increased, without rockbolt. The shotcrete has an increase of 20%(250mm ${\rightarrow}$ 300mm, 4-lane tunnel)~25%(200mm ${\rightarrow}$ 250mm, 3-lane tunnel) in its thickness to reduce the stress in shotcrete lining. The behavior of shotcrete lining increased the shotcrete thickness by 20%~25% was similar to that of existing shotcrete lining with rockbolt.

• Journal of the Korean Geotechnical Society
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• v.33 no.3
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• pp.29-36
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• 2017

It has been known that rockbolt is one of important supports improving the support capacity with shotcrete in NATM tunnel. Also, it is necessary for the inclined system bolting to enhance the efficiency of installation in case of a narrow space such as cross passage and enlargement tunnel. However, there is no profound technical study for the effect of inclined rockbolt of systematic installation on the support mechanism and ground behaviour in NATM tunnel. In this study, the effects of the length and installation angle of rockbolt on the characteristics of support and ground reinforcement were analyzed by using 3D finite element numerical study. Through the numerical results for the parametric modelling of inclined rockbolt, the characteristics of mechanical behaviors between the axial force of rockbolt and the effect of ground reinforcement in regard to the various factors of the length and installation angle of rockbolt were verified and reviewed thoroughly. Also, it was shown that the installation angle of rockbolt for enhancing the arching effect in NATM tunnel was $45^{\circ}$, and the difference of the reinforcing effect for support between the installation angles of $75^{\circ}$ and $90^{\circ}$ was insignificant. The additional numerical studies for various condition would be carried out for practical design guideline of inclined rockbolt.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.869-886
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• 2018

Rockbolt is one of the most common supports used to reinforce discontinuous rock during underground excavation. Extra drain pipes are installed to improve excavation workability and the anchorage of rockbolts in water bearing ground. The drain pipe is effective in improving the workability by providing drainage path, but it is difficult to expect the reinforcement effect, increasing disturbance of the discontinuous rock mass and the construction cost. To solve this problem, dual purpose rockbolt (DPR) has been developed for the reinforcement of rock and the drainage of ground water. DPR was able to improve the mechanical and hydraulic stability of the rocks quickly and economically. Two kinds of DPRs using FRP (Fiber Reinforced Plastic) and steel were investigated for the mechanical and hydraulic performance. Also, the workability and stability of DPR were analyzed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.6
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• pp.637-652
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• 2012

The protector with the shape of '${\sqcap}$' in cross section can be set up in the tunnel, which can be constructed for enlargement of cross section, to keep traffic flow in the tunnel. It is impossible to install the rockbolt in the side wall of tunnel due to a limited space between the protector and cutting surface of side wall. The objective of this study is to suggest the optimum thickness of shotcrete lining without rockbolt on the side wall and to evaluate the stability of tunnel enlarged. Numerical analysis was performed to evaluate the displacement at the center of tunnel, the convergence of tunnel, and the stress in shotcrete lining in 4-lane NATM road tunnel enlarged from 3-lane NATM road tunnel. The vertical displacement at the center of tunnel and the convergence of crown in the tunnel with rockbolt in the side wall were almost similar to those in the tunnel without rockbolt in the side wall. The convergence of bench/invert and the stress in shotcrete lining without rockbolt on the side wall were greater maximum 0.57 mm and 1,300 kN/$m^2$ than those with rockbolt in the side wall. The increased convergence and the stress in shotcrete lining can be reduced in incerasing of thickness of shotcrete lining about 20% (5 cm) of standard thickness, 25 cm, of shotcrete lining.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.2
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• pp.189-198
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• 2003

For the huge section of tunnel, it is highly required to observe the role of each rock support and their effect of rock reinforcement in order to investigate more reasonable rock support structure. Especially for unstable tunnel situation with no shotcrete strength right after an excavation, sufficient investigation is needed for rock support structure. In this paper, we clarify the relations of compressive strength and material age, cohesion strength and material age, and cohesion stiffness and material age of grout with time-dependence through tests and numerical analysis simulation with trial rock mass considering hardening of bolt grouting material. By means of this process, effect of rock reinforcement for rockbolt is investigated right after an excavation and modelling and physical constants of young aged rockbolts are obtained. Additionally, the effect of rock reinforcement with hydraulic tensile friction bolt is examined right after an excavation, which grout effect is no need to be waited.

• The Journal of Engineering Geology
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• v.3 no.3
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• pp.215-230
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• 1993

In-situ rock mass demonstrates the variety of structural features, and especially the mechanical and spatial characteristics of joint (or joint system) greatly affect the deformation and fallure strength of the rock mass. In this study finite element model capable of analyzing the viscoplastic behavior of reinforced jointed rock mass has been developed based on equivalent material approach. Accuracy and reliability of the numerical model have verified by simuiating the behavior of simplified block model and comparing the results with analytic solutions. Practical applicability was also demonstrated by analyzing the time-dependent behavior of underground oil storage tunnel and assessing the reinforcement effect of rockbolt.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.10a
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• pp.366-373
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• 2002

This paper describes the load distribution and settlement of rockbolted-drilled shafts subjected to axial and lateral loads with the view to shortening the embedded depth of the pile shaft. The emphasis was on quantifying the reinforcing effects of rockbolts placed from the shafts to surrounding weathered rocks based on small-scale model tests peformed on instrumented piles. The major influencing parameters on reinforcing drilled shaft behavior are the number, the positions on the shaft, the grade, and the inclination angle at which the rockbolts are placed. The model tests was 1/40 scaled simulations of the behavior of the drilled shafts with varying combinations of the major influencing parameters. The incremental effects of reinforcement based on the various parameters have been weighed against load transfer characteristics before and after rockbolt installations.

• Journal of the Korean GEO-environmental Society
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• v.17 no.11
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• pp.15-21
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• 2016

Nowadays, some studies have been performed for rockbolt method widely used in Korea. To make large slopes, tunnels or rock structures stable, supporting systems, such as anchor bolt, rock bolt which are developed recently, are commonly used. In this study, laboratory pullout tests were carried out to compare the characteristics of rock bolt that is most widely used with ones of rock bolt by newly developed circular model testers. Re-pullout test for the rock bolt in which loading and unloading cycles are repeated several times showed that the maximum pullout load is almost constant irrespective of the number of loading cycles, which may be due to no failure between rock bolt and filler that is filled with soils and concrete as a substitute. A development of rock bolt fillers as supporters using to protect people in tunnels and slopes is reviewed as a probable man-made hazard after excavation works. The functions of the grouted rock bolts associated with reinforcement effects also should be assessed in this study, which develop the sealing apparatus preventing from overflowing mortar out of a rock bolt hole for securing safety in the tunnel and slopes in order to secure stability named the sealing packer.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.1
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• pp.41-56
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• 2017

Recently, the necessity of deep and double-deck tunnels has been grown day by day due to the increase of traffic volume at metropolitans and thus the study on the divergence of those tunnels becomes required. Therefore sensitivity analyses were conducted with FLAC 2D program by selecting ground condition, coefficient of lateral pressure, support pattern, and depth of rock cover as parameters. Ultimately, this study is to find the optimal shape and support method of a diverged section. As the results of this study, it turned out that the box type gave higher stability of the section than arch type unlike the general thought. It can be explained that the arch type has about 30% bigger excavation area than the box type. When the ground conditions are poor, steel pipe grouting reinforcement gives higher stability than rockbolt reinforcement, but its thickness and range do not give a great influence on the stability of the enlarged section.