• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.40 no.1
• /
• pp.97-103
• /
• 2020

The newly improved multistep steel pipe grouting method was applied to an existing steel pipe-reinforced grouting method. It was applied in order to prevent a damage caused by ground failure from excessive grouting pressure in a tunnel construction. The tunnel goes under a highway and a ramp connected to a rest area on OO highway with 11.3~12.1 m depth cover and is a part of roadbed facility construction section ordered by OO public corporation. The improved grouting method provides pre-construction work condition assessment technique through new water injection limit test and grouting effect assessment technique by grouting type assessment. It also includes assessments on interval of joints, appropriate grouting pressure, and optimal operation time to be applied to current operations. Application of the grouting method allowed the smooth road management in shallow-depth grouting construction area located upper part of tunnel excavation. Moreover, the possibility of the application of the method not only to shallow-depth grouting construction but also to various steel pipe-reinforced grouting constructions was confirmed.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.12 no.5
• /
• pp.359-368
• /
• 2010

Unlike in Korea where steel pipe-reinforced multistep grouting is of commonly used methods for tunnel reinforcement, face bolt method is more widely used due to its better workability and lower construction cost in other countries. In this paper, the effects of both methods after tunnel failure were numerically analyzed and verified based on the oversea construction experiences. As a result it is concluded that the face bolt method may be effective to reinforcement especially when there are some fractured zones developed in the face of tunnel.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.12 no.6
• /
• pp.407-416
• /
• 2010

A new tunnel auxiliary method is proposed in this paper which utilizes the concept of cavity expansion for tuunel reinforcement by forming an umbrella arch on the roof of tunnel. When an inflatable pipe is inserted and expanded by pressure in the bore hole of umbrella arch, the ground around the bore hole can be compacted so that the stress condition above the tunnel perimeter is favorably changed. In order to verify the reinforcement effect of new concept, pilot-scale chamber test, trapdoor test and numerical analysis were performed and compared. In pilot-scale chamber test, three types of inflatable pipes are tested to verify the capability of expansion, and the results arc compared with analytical results obtained by applying cavity expansion theory and with results obtained from finite clement analysis, and the experimental results showed agreeable matches with analytical and numerical ones. Numerical analysis of a tunnel and trapdoor test applied with the inflatable pipes are also performed to figure out the reinforcement effect of the proposed techniques, and the results implied that the new method with 3 directional inflatable pipe (no pressure to downward direction) can contribute to reduce tunnel convergence and face settlement.

• Proceedings of the Korean Geotechical Society Conference
• /
• 1997.10a
• /
• pp.133-140
• /
• 1997

• Journal of the Korean Geotechnical Society
• /
• v.20 no.3
• /
• pp.97-106
• /
• 2004

In case of tunnel construction with a shallow soil cover in cohesionless soils or highly weathered rocks, reinforcement measures are required for a tunnel stability during the tunnel construction. Recent developments show that the use of Umbrella Arch Method(UAM) as tunnel reinforcement and water cut-off in domestic projects has increased. Unfortunately, guidelines for the design and construction of UAM have not been established, only empirical designs and applications in tunnel construction have been performed so far. In this study, behaviour of the steel pipes installed on the tunnel roof was analyzed through the monitoring of bending and axial stresses of the pipes with the advance of the tunnel face. The monitoring results were used in the establishment of the loading mechanism around the pipe. This paper suggests, the guidelines used in the determination of the total length, overlapping length and lateral spacing of the reinforcing pipes obtained from the established loading mechanism.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.3 no.1
• /
• pp.11-19
• /
• 2001

The purpose of this study is to improve the problems in Umbrella Arch Method, such as the oxidation, the difficulties in installation and cutting of the steel pipe. The applicability of the high strength FRP (Fiber-Reinforced-Plastic) materials composed of glass fiber as a substitute of steel pipe was investigated in this study. The results of this study show that FRP material is better than steel pipe in work performance and the durability of material except for its price. From the numerical analysis with various types of FRP, it was evaluated that the equiangular curve type is more efficient than the flat type developed abroad, and the supporting effect of FRP-grout mixture is similar to that of steel-grout mixture in results of bending strength test.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.5 no.1
• /
• pp.3-11
• /
• 2003

Face stability of a tunnel is a main concern during tunnel excavation. However, there has been only a few studies on this problem while a lot of researches on the support systems have been carried out. In addition, when tunneling is performed below the groundwater level, the groundwater flows into the tunnel so that the seepage forces generated on the tunnel face might give rise to a serious potential for the face instability. In this study, the face stability was evaluated by simultaneously considering two factors: one is the effective stress calculated by upper bound theorem; the other is the seepage forces acting on the tunnel face obtained by numerical analysis under the condition of steady-state groundwater flow. Tunneling in difficult geological conditions often requires auxiliary techniques to guarantee safe tunnel excavations and/or to prevent damage to structures and services around the tunnel. The steel pipe-reinforced multistep grouting has been recently applied to tunnel sites in Korea. Face stability of a tunnel with the steel pipe-reinforced multistep grouting was also analyzed in this study.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.4
• /
• pp.121-131
• /
• 2003

Tunneling in difficult geological conditions is often inevitable especially in urban areas. Ground improvement and reinforcement techniques are often required to guarantee safe tunnel excavations and/or to prevent damage to adjacent structures. The steel pipe-reinforced multistep grouting method has been recently applied to tunnel sites in Korea as an auxiliary technique. In this study, the face stability with steel pipe-reinforced multistep grouting was evaluated emphasizing the effect of seepage forces. The study revealed that the influence of the steel pipe-reinforced multistep grouting on the support pressure in dry condition is not significant while there is relatively a large amount of reduction in seepage forces by adopting the technique in saturated condition. The effect of the anisotropy of permeability on the seepage force acting on the tunnel face was also estimated by conducting the coupled analysis. It was found that a higher horizontal permeability compared with the vertical one causes reduction in the seepage farce acting on the tunnel face.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.15 no.3
• /
• pp.187-199
• /
• 2013

Umbrella arch method (UAM) used for improving the stability of the tunnel ground condition has been widely applied in the tunnel construction projects due to the advantage of obtaining both reinforcement and waterproof. The purpose of this study is to develop the evaluation technique of the integrity of bore-hole in UAM by using a non-destructive test and to evaluate the possibility of being applied to the field. In order to investigate the variations of frequency depending on grouted length, the specimens with different grouted ratios are made in the two constraint conditions (free boundary condition and embedded condition). The hammer impact reflection method in which excitation and reception occur simultaneously at the head of pipe was used. The guided waves generated by hitting a pipe with a hammer were reflected at the tip and returned to the head, and the signals were received by an acoustic emission (AE) sensor installed at the head. For the laboratory experiments, the specimens were prepared with different grouted ratios (25 %, 50 %, 75 %, 100 %). In addition, field tests were performed for the application of the evaluation technique. Fast Fourier transform and wavelet transform were applied to analyze the measured waves. The experimental studies show that grouted ratio has little effects on the velocities of guided waves. Main frequencies of reflected waves tend to decrease with an increase in the grouted length in the time-frequency domain. This study suggests that the non-destructive tests using guided ultrasonic waves be effective to evaluate the bore-hole integrity of the UAM in the field.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.2
• /
• pp.301-321
• /
• 2019

The development of a rapidly hardening seal material applicable to steel pipe multistage grouting is described in this paper. In the multistage technique, seal materials are inserted to prevent the backflow of main grouting material. The grouting material must be inserted only after sufficient time has passed for the seal material to reach a gel state. Otherwise, the fluid seal material mixes with the main grouting material and a backflow of the grouting material occurs, thereby making its in situ insertion difficult. Furthermore, if the seal material remains in the gel state for too long a time, it solidifies; and the main grouting material will not be able to seep into the soil. The gel time, i.e., the time needed for the fluid seal material to turn into a gel state, determines the construction period of steel pipe multistage grouting. The gel time is one of the important factors in this technique, because it impacts the total tunnel construction period significantly. This study develops a rapidly hardening calcium aluminate material, which can reduce the gel time and shorten the construction period while retaining proper sealing function. It also presents a method to determine whether the seal material has reached the gel state as well as the quality standard and bleeding rate testing method for the seal material in the gel state.