• Tunnel and Underground Space
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• v.15 no.3 s.56
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• pp.185-194
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• 2005

Recently, the surrounding rock mass is understood as the major support system for the tunnel constructed in the rock mass. Generally, the rock mass contains many discontinuity planes such as joints, and thus, the tunnel behavior in the rock mass is governed by the characteristics of the discontinuity planes. In this study, the behavior of tunnel in jointed rock mass is studied by model tests and numerical analyses. The results shows that the behavior of tunnel depends on the different initial stress conditions, in case that the tunnel is excavated in the ground without any joints. When a joint is located near the tunnel, the pound stress and displacement tend to increase between the tunnel and the joint.

• Geomechanics and Engineering
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• v.27 no.5
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• pp.511-525
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• 2021

In the design of underground excavation, the shear strength (SS) is a key characteristic. It describes the way the rock material resists the shear stress-induced deformations. In general, the measurement of the parameters related to rock shear strength is done through laboratory experiments, which are costly, damaging, and time-consuming. Add to this the difficulty of preparing core samples of acceptable quality, particularly in case of highly weathered and fractured rock. This study applies rock index test to the indirect measurement of the SS parameters of shale. For this aim, two efficient artificial intelligence methods, namely (1) adaptive neuro-fuzzy inference system (ANFIS) implemented by subtractive clustering method (SCM) and (2) support vector regression (SVR) optimized by Harmony Search (HS) algorithm, are proposed. Note that, it is the first work that predicts the SS parameters of shale through ANFIS-SCM and SVR-HS hybrid models. In modeling processes of ANFIS-SCM and SVR-HS, the results obtained from the rock index tests were set as inputs, while the SS parameters were set as outputs. By reviewing the obtained results, it was found that both ANFIS-SCM and SVR-HS models can provide acceptable predictions for interlocking and friction angle parameters, however, ANFIS-SCM showed a better generalization capability.

• Tunnel and Underground Space
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• v.27 no.4
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• pp.195-204
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• 2017

This case study introduces the construction of large cross section tunnel for underground ventilation system in Sillim-Bongcheon Tunnel Project. In order to grant the safety and efficiency in connecting the ventilation shaft (7.8 m of width, and 6.6 m of height) to a tunnel for axial fan facility (20.8 m of width, and 12.3 m of height), gradual enlargement of tunnel cross section was employed between those and temporary support method was determined based on Q system. In addition, some original designs were revised during construction stage to improve the efficiency of excavation in large cross section tunnel. The advance length was optimized and top heading of the tunnel was excavated without partition in accordance with ground condition and numerical stability analysis results. It is believed that some experiences and considerations in this case study will be useful for the future design and construction in similar large cross section tunnel such as large underground ventilation system or road tunnel with four lanes.

• Geomechanics and Engineering
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• v.27 no.6
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• pp.561-571
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• 2021

Cofferdams made of teel sheet piles are commonly utilized as support structures for excavation of sea-crossing bridge foundations. As cofferdams are often subject to tide variation, it is imperative to consider potential effects of tide on stability and serviceability of sheet piles, particularly, ultralong steel sheet piles (USSPs). In this study, a real USSP cofferdam constructed using new construction technology in Nanxi River was reported. The design of key parts of USSP cofferdam in the presence of tidal action was first introduced followed by the description of entire construction technology and associated monitoring results. Subsequently, a three-dimensional finite-element model corresponding to all construction steps was established to back-analyze measured deflection of USSPs. Finally, a series of parametric studies was carried out to investigate effects of tide level, soil parameters, support stiffness and construction sequence on lateral deflection of USSPs. Monitoring results indicate that the maximum deflection during construction occurred near the riverbed. In addition, measured stress of USSPs showed that stability of USSP cofferdam strengthened as construction stages proceeded. Moreover, the numerical back-analysis demonstrated that the USSP cofferdam fulfilled the safety requirements for construction under tidal action. The maximum deflection of USSPs subject to high tide was only 13.57 mm at a depth of -4 m. Sensitivity analyses results showed that the design of USSP cofferdam system must be further improved for construction in cohesionless soils. Furthermore, the 5th strut level before concreting played an indispensable role in controlling lateral deflection of USSPs. It was also observed that pumping out water before concreting base slab could greatly simplify and benefit construction program. On the other hand, the simplification in construction procedures could induce seepage inside the cofferdam, which additionally increased the deflection of USSPs by 10 mm on average.

• Geomechanics and Engineering
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• v.34 no.6
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• pp.697-726
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• 2023

Brittleness as an important property of rock plays a crucial role both in the failure process of intact rock and rock mass response to excavation in engineering geological and geotechnical projects. Generally, rock brittleness indices are calculated from the mechanical properties of rocks such as uniaxial compressive strength, tensile strength and modulus of elasticity. These properties are generally determined from complicated, expensive and time-consuming tests in laboratory. For this reason, in the present research, an attempt has been made to predict the rock brittleness indices from simple, inexpensive, and quick laboratory test results namely dry unit weight, porosity, slake-durability index, P-wave velocity, Schmidt rebound hardness, and point load strength index using multiple linear regression, exponential regression, support vector machine (SVM) with various kernels, generating fuzzy inference system, and regression tree ensemble (RTE) with boosting framework. So, this could be considered as an innovation for the present research. For this purpose, the number of 39 rock samples including five igneous, twenty-six sedimentary, and eight metamorphic were collected from different regions of Iran. Mineralogical, physical and mechanical properties as well as five well known rock brittleness indices (i.e., B₁, B₂, B₃, B₄, and B₅) were measured for the selected rock samples before application of the above-mentioned machine learning techniques. The performance of the developed models was evaluated based on several statistical metrics such as mean square error, relative absolute error, root relative absolute error, determination coefficients, variance account for, mean absolute percentage error and standard deviation of the error. The comparison of the obtained results revealed that among the studied methods, SVM is the most suitable one for predicting B₁, B₂ and B₅, while RTE predicts B₃ and B₄ better than other methods.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.4
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• pp.479-499
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• 2019

State assessment of an operational tunnel is usually done by performing visual inspection and durability tests by following the detailed guideline for safety inspection (SI) and/ or precision inspection for safety and diagnosis (PISD). In this study, 12 NATM tunnels, which have been operational for more than 10 years, were inspected to figure out the cause of longitudinal cracks for the purpose of modifying the scoring items in the state assessment NATM tunnel related to the longitudinal crack and the thickness of concrete lining. All investigated tunnels were classified into four groups depending on the shape and usage of each tunnel. The causes of longitudinal crack occurrence were analyzed by investigating the correlations between the longitudinal crack and the following four factors: the patterns of ground excavation; construction state of primary support system; characteristics of material properties of the concrete lining; and thickness of lining which was obtained by Ground Penetration Radar (GPR) tests. It was found that influencing factors causing longitudinal cracks in the lining were closely related with the construction condition of the primary support system, i.e. shotcrete, rockbolt, and steel-rib; crack occurrences were not much affected by the excavation patterns. As for the properties of concrete lining materials, occurrence of the longitudinal crack was mostly affected by the following three items: w/c ratio; contents of cement; and strength of lining. When estimating the lining thickness of the concrete lining by GPR tests and taking thickness effect into account in the statement assessment, it was concluded that increase of the index score by an average of 0.03 (ranging from 0.01 up to 0.071) is needed; a more realistic way of state assessment should be proposed in which the increased index score caused by lack of lining thickness should be taken into account.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.3
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• pp.239-247
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• 2005

A new railway line of about 17km length was planned between Dongbaeksan and the neighboring town Dokye to improve the existing decrepit railway system. New line about 17km of the distance will almost be in circular alignment tunnels owing to the difference of elevation about 380m. Since the geology of the area is rather unusual compared to the normal in South Korea, extensive geological investigations have been carried out to prepare geological maps and profiles along the planned tunnel routes. The tunnel will almost be in sedimentary rock formations, such as limestone, sandstone, shale, coal etc and be near abandoned mines Various rock formations have the complicated, alter ed those rocks, but are well developed with laminated formations. Each rock formations have been classified using the Q-system and the cost of tunnel excavation, support has been estimated and compared for three alternative routes in the design stage. Based on these estimates, the final route of t he railway line was chosen.

• Journal of the Korean Geosynthetics Society
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• v.10 no.2
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• pp.13-19
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• 2011

Precast culvert system is generally constructed with a series of process such as excavation, ground mitigation, placement of culverts, anti-leakage packing between adjacent culverts, post-tensioning for PS strands and backfilling. In this process inappropriate ground mitigation often causes differential settlement and, correspondingly, makes water-leakage to be occurred between adjacent boxes. This study was performed to understand the behavioral characteristics of recently proposed precast foundation plate to support precast culvert system through on-site pilot construction. The gap between two adjacent culverts, increment of earth pressure at the bottom of culvert, vertical settlement of top of the culverts were monitored using various sensors. The monitoring results showed that the proposed foundation plate provides better culvert system in the points of less gap development, earth pressure and settlement at the adjacent of two culverts.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.555-566
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• 2007

In general, RMR classification system is used for the support design of a tunnel. Face mapping during excavation and RMR-based rock classifications are conducted in order to provide information for complementary changes to preliminary survey plans and for continuous geological estimations in direction of tunnel route. Although they are ever so important, there are not enough time for survey in general and sometimes even face mapping is not available. Linear regression analysis for the estimation of mediating RQD and condition of discontinuities, which require longer time and more detailed observation in RMR, was performed and optimum regression equations are suggest as the result. The geological data collected from tunnels were analyzed in accordance with three rock types as sedimentary rock, phyllite and granite to see geological effects, generally not been considered in previous researches. Parameters for the regression analysis were set another RMR factor.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.1-8
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• 2019

Steel elevator pit was developed for the purpose of minimizing the excavation, simplifying the construction of the frame and economical efficiency by improving the problems that occurred in the existing reinforced concrete. It is common to apply conventional RC method through excavation to underground structures such as underground floor collector well and elevator pit. In recent years, the use of steel collector well and steel elevator pits to reduce construction costs by minimizing the materials of steel and concrete has been continuously increasing. The steel elevator pit is an underground structure and then the performance of the welding part and the structure system is important. Specimen with only steel plate and concrete without studs could support the load more than 3 times than the specimen with deck only. Therefore, even if there is no stud, the deck (steel plate) rib is formed and the effect of restraining the steel plate and the concrete during the bending action can be expected. However, since sudden fracture in the elevator pit may occur, stud bolt arrangement is necessary for the composite effect of steel plate and concrete. It is expected that the bending strength can be expected to increase by about 15% or more depending with and without stud bolts.