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

• Geomechanics and Engineering
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• v.19 no.2
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• pp.153-165
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• 2019

A case study of monitoring and analysis of surface settlement induced by tunneling of Tabriz metro line 2 (TML2) is presented in this paper. The TML2 single tunnel has been excavated using earth pressure balanced TBM with a cutting-wheel diameter of 9.49 m since 2015. Presented measurements of surface settlements, were collected during the construction of western part of the project (between west depot and S02 station) where the tunnel was being excavated in sand and silt, below the water table and at an average axis depth of about 16 m. Settlement readings were back-analyzed using Gaussian formula, both in longitudinal and transversal directions, in order to estimate volume loss and settlement trough width factor. In addition to settlements, face support and tail grouting pressures were monitored, providing a comprehensive description of the EPB performance. Using the gap model, volume loss prediction was carried out. Also, COB empirical method for determination of the face pressure was employed in order to compare with field monitored data. Likewise, FE simulation was used in various sections employing the code Simulia ABAQUS, to investigate the efficiency of numerical modelling for the estimating of the tunneling induced-surface settlements under such a geotechnical condition. In this regard, the main aspects of a mechanized excavation were simulated. For the studied sections, numerical simulation is not capable of reproducing the high values of in-situ-measured surface settlements, applying Mohr-Coulomb constitutive law for soil. Based on results, for the mentioned case study, the range of estimated volume loss mostly varies from 0.2% to 0.7%, having an average value of 0.45%.

• Geomechanics and Engineering
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• v.29 no.5
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• pp.509-522
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• 2022

Tail-grouting is an effective measure in shield engineering for filling the gap at the shield tail to reduce ground deformation. However, the gap-filling ratio affects the value of the gap parameters, leading to different surface settlements. It is impossible to adjust the fill ratio indiscriminately to study its effect, because the allowable adjustment range of the grouting quantity is limited to ensure construction site safety. In this study, taking the shield tunnel section between Chaoyanggang Station and Shilihe Station of Beijing Metro Line 17 as an example, the correlation between the tail-grouting parameter and the surface settlement is investigated and the optimal grouting quantity is evaluated. This site is suitable for conducting field tests to reduce the tail-grouting quantity of shield tunneling over a large range. In addition, the shield tunneling under different grouting parameters was simulated. Furthermore, we analyzed the evolution law of the surface settlement under different grouting parameters and obtained the difference in the settlement parameters for each construction stage. The results obtained indicate that the characteristics of the grout affect the development of the surface settlement. Therefore, reducing the setting time or increasing the initial strength of the grout could effectively suppress the development of surface subsidence. As the fill ratio decreases, the loose zone of the soil above the tunnel expands, and the soil deformation is easily transmitted to the surface. Meanwhile, owing to insufficient grout support, the lateral pressure on the tunnel segments is significantly reduced, and the segment moves considerably after being removed from the shield tail.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.171-182
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• 2007

For minimizing the effect on the focus of civil traffic and environment conditions related to the excavation at the traffic jamming points, an underground station tunnel was planned with 35.5 m in length and bigger area than $200\;m^2$ in sedimentary rock mass. It faced the case that the overburden was just under 13 m. Not based on a pattern design but on the case histories of similar projects and arching effect, the design of large section tunnel under shallow overburden was investigated on three design subjects which are shape effect on the section area, application method of support pressure, and supporting and tunnel safety. According to the mechanical effect from section shape, a basic design and a preliminary design was obtained, and then supporting method of large section was planned by the supporting of NATM and a pipe roof method for subsidence prevention and mechanical stability. From the comparative study between both designs, it was found that the basic design was suitable and acceptable for the steel alignment of tunnel lining, safety and the design parameter restricted by the limit considered as partition of the excavation facilities. Through the analysis result of preliminary design showing the mechanical stability without stress concentration in tunnel arch level, it also was induced that shape effect of the large section area and yielding load obtained from deformation zone in the surrounding rock mass of tunnel have to be considered as major topics for the further development of design technique on the large section tunnel.

• Tunnel and Underground Space
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• v.19 no.3
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• pp.181-189
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• 2009

This study is to evaluate an effect of supports with respect to these supports after comparing the characteristic of support between rock bolt of a widely used type and spiral bolt of a new type. For these purposes, we performed pull-out test in laboratory about rock and spiral bolts in the case of cement-mortar grout curing periods, 7 and 28 days, then calculated pull-out load, displacement, external pressure, inner pressure and shear stress using data obtained from the results of pull-out test, respectively. In relation between pull-out load and displacement, displacement of spiral bolt is larger than one of rock bolt. It is considered that mechanical property of rock bolt is due to larger than one of spiral bolt. In addition, displacement of supports shows nearly same or decreasing with curing periods. We found that because adhesive force between supports and cement-mortar grout is increasing with compressive strength of grout according to curing periods. The inner pressure of spiral bolt is represented larger than one of rock bolt at a step of same pull-out load. It is suggested that spiral bolt is more stable than rock bolt, maintaining stability of ground or rock mass, when supports are installed in a ground or rock mass under the same condition. Putting together with above results, we can consider that spiral bolt as a new support on an aspect of pull-out load and inner pressure is larger than rock bolt in a ground or rock mass under the same condition. Moreover, spiral bolt is more effective support than rock bolt, considering an economical and constructive aspects of supports, as well as ground or rock stability before or after installing supports.

• Wind and Structures
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• v.30 no.1
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• pp.69-83
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• 2020

Modelling incompressible, neutrally stratified, barotropic, horizontally homogeneous and steady-state atmospheric boundary layer (ABL) is an important aspect in computational wind engineering (CWE) applications. The ABL flow can be viewed as a balance of the horizontal pressure gradient force, the Coriolis force and the turbulent stress divergence. While much research has focused on the increase of the wind velocity with height, the Ekman layer effects, entailing veering - the change of the wind velocity direction with height, are far less concerned in wind engineering. In this paper, a modified k-ε model is introduced for the ABL simulation considering wind veering. The self-sustainable method is discussed in detail including the precursor simulation, main simulation and near-ground physical quantities adjustment. Comparisons are presented among the simulation results, field measurement values and the wind profiles used in the conventional wind tunnel test. The studies show that the modified k-ε model simulation results are consistent with field measurement values. The self-sustainable method is effective to maintain the ABL physical quantities in an empty domain. The wind profiles used in the conventional wind tunnel test have deficiencies in the prediction of upper-level winds. The studies in this paper support future practical super high-rise buildings design in CWE.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.6
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• pp.519-530
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• 2011

The screw conveyor system installed in EPB Shield TBM chamber was manufactured in small scale for pilot test to investigate the tunnel muck hauling system that could control the earth pressure and support face thrust force. In this experimental study, there were three different test conditions that include screw angles, screw pitch, and screw RPM. Through analysis on test results based on the muck hauling amount per unit time from screw conveyor, the optimum conditions of screw conveyor were proposed to be efficiently performed by the muck processing system. Finally, this study provided the meaningful results such as optimum screw angle, screw RPM, and screw pitch for anti-reverse flow of muck hauling.

• Tunnel and Underground Space
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• v.21 no.2
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• pp.138-144
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• 2011

Mine closure does often accompany the flooding of mine galleries due to ceasing a pumping operation. When a mine gallery is flooded, rocks around the gallery are fully saturated and the gallery is subject to a water pressure. The uniaxial unconfined compressive strength of a rock depends on its water content and decreases as the water content increases. A water pressure may originate the crack growth of a rock or the discontinuity growth of rock mass. Although the water in a gallery will give some support pressure inside the gallery, the degradation of rock mass properties caused by a water pressure will reduce the stability of the gallery. In this study, 2-dimensional discontinuous and 3-dimensional continuous numerical analyses have been conducted to evaluate an effect that a reduction of rock mass properties around the gallery induced by a water pressure has on the stability of mine gallery. The numerical analyses show that a reduction of rock mass properties caused by a water pressure increases displacements of rock mass around mine gallery. 2-dimensional model is found to give larger values of displacement than 3-dimensional model.

• 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.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.4
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• pp.651-668
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• 2017

For initial stability of the tunnel, the primary support, Shotcrete and rockbolt shall be placed in the most appropriate time. This is because the role of such support plays a vital role in long-term and short-term tunnel stability. In this study, the rock bolt is an important supporting system that receives the external pressure generated by the stress relaxation during tunnel excavation as axial force and transmits it to the shotcrete on the tunnel excavation surface. Until now, most of the materials of rock bolts have been used in the field, but there have been many problems such as uncertain quality of Chinese materials entering the market, poor packing due to falling down of rock bolts when filled with mortar, and corrosion due to water. Therefore, in this study, we have developed a high strength steel pipe rock bolt using Autobeam material to solve and improve various problems of existing rock bolts. In order to evaluate the performance of the developed bolt, field tests were carried out and the existing mortar filler in order to improve the performance of the rock bolt, the design and construction criteria were studied and the results were included in this paper.