• Journal of Korean Tunnelling and Underground Space Association
• /
• v.21 no.4
• /
• pp.455-478
• /
• 2019

In this paper, we conducted experimental investigation on the field applicability through the verification of reinforcement effect of the steel pipe reinforcement grouting using high strength steel pipe. SGT275 (formerly known as STK400) steel pipe is generally applied to the traditional steel pipe reinforcement grouting method. However, the analysis of tunnel collapse cases applying the steel pipe reinforcement grouting shows that there are cases where the excessive bending and breakage of steel pipe occur. One of the reasons causing these collapses is the lack of steel pipe stiffness responding to the loosening load of tunnels caused by excavation. The strength of steel pipe has increased due to the recent development of high strength steel pipe (SGT550). However, since research on the reinforcement method considering strength increase is insufficient, there is a need for research on this. Therefore, in this study, we conducted experiments on the tensile and bending strength based on various conditions between high strength steel pipe, and carried out basic research on effective field application depending on the strength difference of steel pipe through the conventional design method. In particular, we verified the reinforcement effect of high strength steel pipe through the measurement results of deformed shape and stress of steel pipe arising from excavation after constructing high strength steel pipe and general steel pipe at actual sites. The research results show that high strength steel pipe has excellent bending strength and the reinforcement effect of reinforced grouting. Further, it is expected that high strength steel pipe will have an arching effect thanks to strength increase.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.24 no.6
• /
• pp.699-714
• /
• 2022

The objective of this study is to suggest a safe and economical pillar reinforcement method when very near-twin tunnels with a minimum interval of 1 m passes through a soft zone such as weathered soil or weathered rock. A standard cross-sectional view of a two-lane road tunnel was applied to suggest a pillar reinforcement method for the very near-twin tunnels. The thickness of the pillar was 1 m. The ground condition around the tunnel was weathered soil or weathered rock. There were four reinforcement methods for pillar stability evaluation. These were rock bolt reinforcement, pre-stressed steel strand reinforcement, horizontal steel pipe grouting reinforcement, horizontal steel pipe grouting + prestressed steel strand reinforcement. When the ground condition was weathered soil, only the pillar reinforced the horizontal steel pipe grouting + prestressed steel strand did not failed. When the ground condition was weathered rock, there were no failure of the pillar reinforced the horizontal steel pipe grouting or the horizontal steel pipe grouting + prestressed steel strand. It is considered that the horizontal steel pipe grouting reinforcement played a role in increasing the stability of the upper part of the pillar by supporting the upper load applied to the upper part of the pillar.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.26 no.4
• /
• pp.345-363
• /
• 2024

Steel pipe reinforced grouting method has been widely used to strengthen the crown of tunnel face and prevent groundwater leakage during tunnel excavation. Various injection procedures without sealing have recently been suggested to enhance efficiency. There are two representative injection methods. One is simultaneous injection in segmented batches, and the other is multiple injection using the external packer. The pros and cons of each method were discussed in terms of construction duration and equipment. However, it has yet to be discussed how the injection procedure affects the grout diffusion range in the ground. This study aims to evaluate the grout diffusion range quantitatively by considering the practical grouting sequences. The grout viscosity was measured by laboratory testing. Then, the numerical modeling was structured using the commercial computational fluid dynamics software. Finally, the grout diffusion range affected by the injection procedure and ground conditions was evaluated by performing the numerical parametric study. The results showed that the injection method highly affected the grout diffusion range, especially for inhomogeneous soil. Consequently, it is anticipated that the proper method of steel pipe reinforced grouting will be suggested.

• Tunnel and Underground Space
• /
• v.26 no.6
• /
• pp.466-474
• /
• 2016

Pre-reinforcement with umbrella arch grouting is conducted around a tunnel where a portion of the upper part of the tunnel is located in a sand and gravel layer. Surroundings of a first tunnel situated below groundwater table are reinforced with LW or SSM that is composed of ultra-fine cement and injected into multi-stages through large diameter steel pipes. With them, a first tunnel is safely excavated without both leaking of groundwater and fallings of sand and gravel from the arch. A second tunnel where groundwater is drained down to the bedrock is reinforced with jet grouting. The effect of the pre-grouting reinforcement is monitored by checking whether groundwater is dripping or sand or gravel is falling from the arch of the tunnels.

• 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.24 no.6
• /
• pp.495-512
• /
• 2022

Due to the concentration of population in the city center, the aboveground structures are saturated, and the development of underground structures becomes important. In addition, it is necessary to apply the reinforcement construction method for the pillar part of the adjacent tunnel that can secure stability, economy, and workability to the site. In this study, the tunnel pillar reinforcement method using prestress and grouting was reviewed. There are various reinforcement methods that can compensate for the problems of the side tunnel, but as the tunnel pillar construction method using prestress and grouting is judged to be excellent in field applicability, stability, and economic feasibility, it is necessary to review the theoretical and numerical analysis of the actual behavior mechanism. Therefore, a scaled-down model experiment was conducted. The reduced model experiment was divided into PC stranded wire + steel pipe reinforcement grouting + prestress (Case 1), PC strand + steel pipe reinforcement grouting (Case 2), and no reinforcement (Case 3), and the displacement of the pillar and the earth pressure applied to the wall were measured. Through experiments, it was confirmed that the PC stranded wire + steel pipe reinforcement grouting + prestress method is the most excellent reinforcement method among various construction methods. It was judged that it could be derived.

• 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.

• Geotechnical Engineering
• /
• v.27 no.3
• /
• pp.29-39
• /
• 2011

• 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 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.