• Journal of the Korean Geotechnical Society
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• v.32 no.11
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• pp.83-96
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• 2016

The surface settlement of the back ground of a braced wall due to the ground excavation has the great influence on the safety of the surrounding area. But it is not easy to predict the settlement of the surrounding area due to proud excavation. Estimation of the settlement of the surface ground induced by the deformation of the braced wall is performed by FEM and empirical method (Peck, Clough etc). In this research, surface settlement of the back ground braced wall depending on the joint dips in rocks during excavating the composit ground was measured at the large scale model test (standard: $0.3m{\times}0.3m{\times}0.5m$). The scale of model test was 1/14.5 and the ground was excavated in ten steps. Earth pressure on the braced wall and ground surface settlement on the back ground of a braced wall were investigated. The surface settlement during the excavation depended on the joint dips in rocks on of the ratio of rock layer. Maximum earth pressure and maximum surface settlement were masured at the same excavation step. In accordance with the increase of the rock layer dips and rock layer ratio, the ground surface settlement increased. The maximum ground surface settlement was 17 times larger at 60 degree joint dips in rocks than that of the horizontal ground conditions. And the position of the maximum surface settlement by empirical method was calculated at the point, which was 17%~33% of excavation depth. In accordance with the increase of the rock layer dips and rock layer ratio, the ground maximum surface settlement increased. The ground surface settlement of composite ground is smaller than that of the empirical.

• Tunnel and Underground Space
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• v.18 no.6
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• pp.465-479
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• 2008

For the quantitative identification of rock behavior in shallow tunnels, we recommend using the rock behavior index (RBI) by the analytic hierarchy process (AHP) and the Rock Engineering Systems (RES). AHP and RES can aid engineers in effectively determining complex and un-structured rock behavior utilizing a structured pair-wise comparison matrix and an interaction matrix, respectively. Rock behavior types are categorized as rock fall, cave-in, and plastic deformation. Seven parameters influencing rock behavior for shallow depth rock tunnel are determined: uniaxial compressive strength, rock quality designation (RQD), joint surface condition, stress, pound water, earthquake, and tunnel span. They are classified into rock mass intrinsic, rock mass extrinsic, and design parameters. An advantage of this procedure is its ability to obtain each parameter's weight. We applied the proposed method to the basic design of Seoul Metro Line O and quantified the rock behavior into RBI on rock fall, cave-in, and plastic deformation. The study results demonstrate that AHP and RES can give engineers quantitative information on rock behavior.

• Tunnel and Underground Space
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• v.10 no.4
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• pp.544-552
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• 2000

Norway has the geological of condition of hard bedrocks, high mountains, deep valleys and fjords. In this background many tunnels and rock caverns are developed. In this process of constructing tunnels and rock caverns Norway seems to have strong competitiveness in the construction of tunnels. In spite of high salaries to the tunnel workers, Norwegian contractors are probably producing the cheapest tunnels and rock caverns in the world. Besides benefit of hard-rock geology, Norwegian cost-saying is owing to the Norwegian excavation technique in hard rocks such as unlined pressure tunnels, air cushion chambers, underwater piercing, and reasonable contract system and organization of workers developed from the accumulated experience. Brief analytical description of them are given in this paper in order to stimulate the utilization of the underground spaces.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.4
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• pp.421-435
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• 2012

Rock excavation (removal) tests are performed with effective parameters using an abrasive waterjet. For verification of the field rock excavation capabilities, the removal performance and level of efficiency are analyzed for hard granite rock in terms of the water pressure, exposure time of the jet, and the standoff distance. In particular, experimental tests are performed with a long standoff distance required condition in the real excavation field. The rock removal performance level changes according to the rock properties. In this study, various rock specimens are used and P-wave velocities are measured in order to determine the correlation between the removal performance and the P-wave velocity. As a result of the experimental study, the effect of waterjet parameters on rock removal is analyzed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.505-513
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• 2014

This paper investigated the effect of joint on the earth pressure against an excavation wall in rockmass with the consideration of various rock and joint conditions. For this purpose, this study briefly reviewed of the previous earth pressure studies, and then numerical parametric studies were conducted based on the Discrete Element Method (DEM) to overcome the limitations of the previous studies. The numerical tests were carried out with the controlled parameters including rock types and joint conditions (joint shear strength, joint inclination angle, and joint set), and the magnitude and distribution characteristics of the induced earth pressure were investigated considering the interactions between the ground and the excavation wall. In addition, the earth pressures induced in rock stratum were compared with Peck's earth pressure for soil ground. The results showed that the earth pressure against an excavation wall in jointed rockmass were highly affected by different rock and joint conditions and thus different from Peck's empirical earth pressure for soil ground.

• Tunnel and Underground Space
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• v.33 no.3
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• pp.141-149
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• 2023

Recently, as the demand for urban underground space increases, urban tunnel planning is actively progressing. In particular, the application of the roadheader excavation method, which has favorable applicability to urban tunnel, is increasing. However, it is known that the roadheader excavation method has a limitation in that excavation efficiency for high strength rock with a Uniaxial Compressive Strength (UCS) of 100 MPa or more is lowered. In this study, The pre-cracked method was presented as a method to improve the excavation efficiency of roadheader for high strength rock and its applicability was evaluated. The net cutting rate was evaluated using the Bilgin prediction formula, which can calculate the net cutting rate by considering the UCS and RQD (Rock Quality Designation). It was found that the net cutting rate increased as the RQD decreased under the rock condition with the same UCS. This is judged to increase the excavation efficiency of the roadheader in the jointed high strength rock. Additionally, the field applicability of the pre-cracked method for high strength rock was verified through field tests. It was confirmed that the crack zone was formed around the charging hole, and it is considered that the pre-cracked method can be applied to the high strength rock.

• Geotechnical Engineering
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• v.11 no.1
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• pp.51-62
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• 1995

The use of TBM has been rapidly increased in recent years since TBM has been introduced to Korea in 1985 and Korea came to occupy 27% of TBM holding ratio in the world. Despite a lot of experience, study on promoting the efficiency of TBM excavation is insufficient. The factors that influence the efficiency of excavation are the mechanical farttor geotechnical factor and management factor. The study on the efficiency of excavation has focused on the improvement of mechanical factor. But geotechnical factor is also very important and by this factor engineer can estimate the applicability of TBM. The purpose of this paper is to understand the effectiveness of TBM excavation for vari orts rock quality by analysing relations between rock quality and TBM excavation.

• Tunnel and Underground Space
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• v.29 no.3
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• pp.148-156
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• 2019

In urban area, the use of mechanical excavators (e.g., TBM and roadheader) has been increasing in construction of tunnelling and underground space. The undercutting technology, which is modified from the conventional rock-cutting concept, has been developed by advanced countries. Therefore, research on the latest technology of mechanical excavation is required, and keeping carrying out research on conventional mechanical tunneling methods at the same time. In this study, as a fundamental study of the undercutting technique, the principle and concept of the undercutting were introduced, as well as the current status of the research of advanced countries. The undercutting is applicable as a full-face excavation method for the tunnels and underground spaces, as well as an auxiliary(partial-face excavation) method for extension of the existing tunnels.

• The Journal of Engineering Geology
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• v.23 no.1
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• pp.47-55
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• 2013

To analyze lateral displacement of excavation walls exposed during the construction of Subway Line 1 in the Daegu region, inclinometer measurement data for sites D4, D5, and Y6 are investigated from the perspective of engineering geology. The study area, in the Banyawol Formation, Hayang Group, Gyeongsang Supergroup, is in the lower part of bedrock of andesitic volcanics, calcareous shale, sandstone, hornfels, and felsite dykes that are unconformably overlain by soil. The rock mass around the D4 site is classified as RMR-V grade and the maximum lateral displacement of 101.39 mm, toward N34W, was measured at a bedding-parallel fault, at a depth of 12 m. The rock mass around the D5 site is classified as RMR-IV grade and the maximum lateral displacement of 55.17 mm, toward the south, was measured at a lithologic contact between shale and felsite, at a depth of 14 m. The rock mass around the Y6 site is classified as RMR-III grade and the maximum lateral displacement of 12.65 mm, toward S52W, was measured at an unconformity between the soil and underlying bedrocks, at a depth of 7 m. The directions of lateral displacement in the excavation walls are vector sums of the directions perpendicular to the excavation wall and horizontally parallel to the excavation wall. Lateral displacement graphs according to depth in the soil profile show curvilinear trajectories, whereas those in bedrock show straight and rapid-displacement trajectories.

• Journal of the Korean Geotechnical Society
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• v.31 no.12
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• pp.59-69
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• 2015

This study examined the magnitude and distribution of earth pressure on the support system in a jointed rock mass due to the different joint sets as well as varying the rock type and joint condition (joint shear strength and joint inclination angle). Based on a physical model test and its numerical simulation, a series of numerical parametric analyses were conducted using a discrete element method. The results showed that the induced earth pressure was affected significantly by a joint set depending on the inclusion of the joint inclination angle, which induces a joint sliding condition, but the number of joint sets alone was not important, even though the earth pressure could be increased slightly as the number of joint sets is increased. In addition, the study results were compared with Peck's earth pressure for soil ground, which indicated that the earth pressure in a jointed rock mass could be considerably different from that in soil ground. The study suggests that the effects of joint sets as well as rock type and joint condition are important factors affecting the earth pressure in a jointed rock mass and they should be considered when designing a support system in a jointed rock mass.