• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.73-81
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• 2002

Nowadays , the grouted-reinforcing method, which is called FRP(Fiberglass-reinforced-plastic) pipe .reinforcing method, has been introduced in the community of pound reinforcements. The resistance to corrosion and chemical attack high strength to weight ratio, and ease of handling make these pipes a better alternative to steels in tunnel. However, to fully utilize FRP pipes as grouted reinforcing members at the face and the crown in tunnel, their mechanical properties and behaviors and the grout-reinforced underground have to be verified. Laboratory shear tests were conducted to evaluate the mechanical properties for FRP pipes, the grout-reinforced members and the grout-reinforced body of FRP pipes. According to the test results, it was observed that FRP pipes play a dominant role in shearing behavior of the grout-reinforced members and that their shearing resistance exerts after the shearing displacement increases to some extent.

• Tunnel and Underground Space
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• v.34 no.2
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• pp.143-153
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• 2024

Tunnel Boring Machine (TBM) method is a tunnel excavation method that produces lower levels of noise and vibration during excavation compared to drilling and blasting methods, and it offers higher stability. It is increasingly being applied to tunnel projects worldwide. The disc cutter is an excavation tool mounted on the cutterhead of a TBM, which constantly interacts with the ground at the tunnel face, inevitably leading to wear. In this study quantitatively predicted disc cutter wear using geological conditions, TBM operational parameters, and machine learning algorithms. Among the input variables for predicting disc cutter wear, the Uniaxial Compressive Strength (UCS) is considerably limited compared to machine and wear data, so the UCS estimation for the entire section was first conducted using TBM machine data, and then the prediction of the Coefficient of Wearing rate(CW) was performed with the completed data. Comparing the performance of CW prediction models, the XGBoost model showed the highest performance, and SHapley Additive exPlanation (SHAP) analysis was conducted to interpret the complex prediction model.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.1
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• pp.135-144
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• 2020

Since the depth of tunneling with tunnel boring machine (TBM) becomes deeper and deeper, the expense for site investigation for coring and geophysical survey increases to obtain the sufficient accuracy. The tunnel ahead prediction methods have been introduced to overcome this limitation in the stage of site investigation. Probe drilling can obtain the core and borehole images from a borehole. However, the space in TBM for the probe drilling equipment is restricted and the core from probe drilling cannot reflect the whole tunnel face. Seismic methods such as tunnel seismic prediction (TSP) can forecast over 100 m ahead from the tunnel face though the signal is usually generated using the explosive which can affect the stability of segments and backfill grout. Electromagnetic methods such as tunnel electrical resistivity prospecting system (TEPS) offer the exact prediction for a conductive zone such as water-bearing zone. However, the number of electrodes installed for exploration is limited in small diameter TBM and finally the reduction of prediction ranges. In this study, the theoretical equations for the electrical resistivity survey whose electrodes are installed in the face and side of TBM to minimize the installed electrodes on face. The experimental tests were conducted to verify the derived equations.

• The Journal of Engineering Geology
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• v.24 no.4
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• pp.643-648
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• 2014

Understanding of fracture networks and rock mass properties during tunnel construction is extremely important for the prediction of dangers during excavation, and for deciding on appropriate excavation techniques and support. However, rapid construction process do not allow sufficient time for surveys and interpretations for spatial distributions of fractures and rock mass properties. This study introduces a new statistical approach for predicting joint distributions at foreside of current excavation face during the excavation process. The proposed methodology is based on a cumulative space diagram for joint sets. The diagram displays the cumulative spacing between adjacent joints on the vertical axis and the sequential position of each joint plotted at equally spaced intervals on the horizontal axis. According to the diagram, the degree of linearity of points representing the regularity of joint spacing; a linear trend of the points indicates that the joints are evenly spaced, with the slope of the line being directly related to the spacing. The linear points which are stepped indicates that the fracture set show clustered distribution. A clustered pattern within the linear group of points indicates a clustered joint distribution. Fractures surveyed from an excavated space can be plotted on this diagram, and the diagram can then be extended further according to the plotted diagram pattern. The extension of the diagram allows predictions about joint spacing in areas that have not yet been excavated. To test the model, we collected and analyzed data during excavation of a 10-m-long tunnel. Fractures in a 3-m zone behind the excavation face were predicted during the excavation, and the predictions were compared with observations. The methodology yielded reasonably good predictions of joint locations.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.71-83
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• 2009

Shotcrete is an important primary support for tunnelling in rock. The quality control of shotcrete is a core issue in the safe construction and maintenance of tunnels. Although shotcrete may be applied well initially onto excavated rock surfaces, it is affected by blasting, rock deformation and shrinkage and can debond from the excavated surface, causing problems such as corrosion, buckling, fracturing and the creation of internal voids. This study suggests an effective non-destructive evaluation method of the tunnel shotcrete bonding state applied onto hard rocks using the impact-echo (IE) method and ground penetration radar (GPR). To verify previous numerical simulation results, experimental study carried out. Generally, the bonding state of shotcrete can be classified into void, debonded, and fully bonded. In the laboratory, three different bonding conditions were modeled. The signals obtained from the experimental IE tests were analyzed at the time domain, frequency domain, and time-frequency domain (i.e., the Short- Time Fourier transform). For all cases in the analyses, the experimental test results were in good agreement with the previous numerical simulation results, verifying this approach. Both the numerical and experimental results suggest that the bonding state of shotcrete can be evaluated through changes in the resonance frequency and geometric damping ratio in a frequency domain analysis, and through changes in the contour shape and correlation coefficient in a time-frequency analysis: as the bonding state worsens in hard rock condition, the autospectral density increases, the geometric damping ratio decreases, and the contour shape in the time-frequency domain has a long tail parallel to the time axis. The correlation coefficient can be effectively applied for a quantitative evaluation of bonding state of tunnel shotcrete. Finally, the bonding state of shotcrete can be successfully evaluated based on the process suggested in this study.

• Explosives and Blasting
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• v.36 no.3
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• pp.29-38
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• 2018

With the recent industrial developments and economic development nationally, there has been a rapidly increasing demand for the use of underground space as locations for establishing social infrastructure and various convenience facilities. In this study, a mist-control system was developed to reduce the generation of dust in underground blasting. To enhance the dust-reduction effect, a guiding device was developed which is capable of adjusting the direction of the spray toward's the blasting face of mine or tunnel. A numerical analysis was performed by using the AUTODYN software, and results were compared with those published in basic experiments. To verify the mist-diffusion effect according to the position of explosives in a water bag, numerical analyses were conducted for the following cases: Explosives were set in the middle, and in the bottom of the water bag. The optimum condition was external detonation and center charge. The mist particle size from the result was suitable for the reduction of dust after blasting in underground mine and tunnel.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.09a
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• pp.117-123
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• 2005

An in-hole seismic tests, which has been developed for measuring dynamic properties of soils and rock mass, is a bore hole seismic method that has cost effectiveness and practicality. The upgraded features include the motorized triggering system rather than the manual prototype version in the previous studies and a damper between source and receiver in the module. The performance of the probe has been verified through extensive cross-hole tests and in-hole tests at various sites. The dynamic stiffness of subsurface materials and rock mass have been evaluated and recently, the measurement of shear wave velocity was successfully adopted at horizontal holes of tunnel-face to install explosives. So the application of in-hole seismic test for various soil materials was certified.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.605-614
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• 2015

A room-and-pillar underground structure is characterized by its grid-type array of room and pillar. As a result, its construction and economical efficiency can be governed by excavation sequence. In this study, the construction period by the drill and blast method which can be treated as a main sequence for excavation was examined by considering the regulation for blasting and construction standard of estimation in Korea. To evaluate the construction period for the room-and-pillar underground structure constructed in 4 kinds of square-type area ($30{\times}30{\sim}57{\times}57m$), the concurrent excavation pattern which was suggested in the previous researches was used. From the suggested condition, the total construction period by drill-and-blast method can be estimated with the consideration of the construction area, number of jumbo drill and faces in operation.

• 한국지구물리탐사학회:학술대회논문집
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• 1999.08a
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• pp.1-20
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• 1999

In Japan, geophysical exploration methods have been widely applied to civil engineering and construction fields for a long time. In particular, seismic refraction has long played a significant role in geotechnical site investigations for tunnels, dams and landslides. However, our growing interest on the social and natural environment makes the methods available and its application fields diversify. Digital technologies such as personal computer have revolutionized our ability to acquire large volumes of data rapidly, and to produce more reliable results for subsurface image. Also, color graphics easily visualizes survey results In a more understandable manner, These days geophysical methods are essential to assessing grouting effects, predicting the front of tunnel cutting face, monitoring the movement, pollution and purification process of groundwater. Now three-dimensional exploration techniques have developed for the site characterization in civil engineering and construction needs.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.273-280
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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 multi-step 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 multi-step grouting was evaluated by simultaneously considering two factors: one is the effective stress acting on the tunnel face calculated by limit theorem and limit equilibrium method; the other is the seepage force obtained by means of numerical analysis. The study revealed that the influence of the steel pipe-reinforced multi-step 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 force acting on the tunnel face.