• Tunnel and Underground Space
• /
• v.34 no.4
• /
• pp.283-300
• /
• 2024

Due to the revitalization of urban development, the number of cases of excavating tunnels adjacent to existing subways is increasing. This may affect the structure and track of the existing subway, resulting in reduced stability and usability. In this study, we verified the adequacy of the proximity evaluation range to ensure the stability of new tunnels and existing subways when excavating adjacent to tunnels, and proposed a quantitative correction rate considering various conditions. Conditions for applying the correction rate considered rock grade, geologically weak section, structurally weak section, and structural deterioration section. It is hoped that a more accurate proximity evaluation will be performed by applying a quantitative correction rate that considers rock and geological conditions, structure status, etc. to the proximity evaluation standard.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.16 no.2
• /
• pp.125-133
• /
• 2014

In this study, TBM selection methods to meet soil and site conditions were presented. Factors and excavation equipment affecting TBM selection by soil and environmental condition were selected and classified. Weights between equipment and influencing factors selected were calculated by applying the AHP (Analytic Hierarchy Process) method. The results of the analysis influence factors, Ground condition was a major factor in objective factors and strength was a major factor in the hard condition of criteria factors and water pressure was a major factor in the soft ground condition of criteria factors. In Environment condition, existence of adjacent structures was evaluated more important than existence of feasible site. Lastly, Adequacy was verified through the deduction of results that coincide with input equipment by applying derived weights to actual site conditions.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.10 no.4
• /
• pp.397-404
• /
• 2008

Excessive amount of groundwater flowed into tunnel, while constructing Incheon international airport railway. Tunnel passes under subway line no. 2 with only 1.76 m below. To protect the existing structure, TRcM excavation method was applied. As station and construction shaft are already constructed, which are located back and forth of TRcM section, 86.4 ton per day of groundwater inflow is against expectation. To identify mechanism of excessive water inflow, hydraulic back analyses were performed. Then, hydro-mechanical coupled analysis were also performed with the hydrogeologic parameters identified, whose results are investigated for checking the stability of adjacent structures to the tunnel under construction. And a number of mechanical analyses were also performed to check the hydro-mechanical coupling effect. The result from the mechanical analysis shows that subsidence and tunnel ceiling displacement will be 0.85 mm and 1.32 mm. The result of hydro-mechanical couple analysis shows that subsidence and maximum tunnel ceiling displacement will be 1.2 mm and 1.72 mm. Additional displacements caused by groundwater draw down were identified, however, displacement is minute.

• The Journal of Engineering Geology
• /
• v.28 no.1
• /
• pp.81-99
• /
• 2018

Excessive groundwater discharge by tunneling and tunnel operation can lead to groundwater exhaustion and ground subsidence. Therefore, it is very important to evaluate environmental impact and to establish mitigation measures of the impact related to tunnel excavation based on hydrogeological and modeling approaches. This study examined the depletion of surface reservoirs and valley water due to tunnel excavation through field survey, water quality analysis, tracer test, and groundwater modeling. As a result of field water quality test, the concentration of chemical constituents in groundwater discharge into the tunnel is slightly higher than that of valley water. By the result of laboratory water analysis, both valley water and the groundwater belong to $Ca^{2+}+HCO_3{^-}$ type. Tracer test that was conducted between the valley at the injection point and the tunnel, indicates valley water infiltration into the ground and flowing out to the tunnel, with maximum electrical conductance changes of $70{\mu}S/cm$ in the first test and of $40{\mu}S/cm$ in the second test. By groundwater modeling, the groundwater discharge rate into the tunnel during tunnel construction is estimated as $4,942m^3/day$ and groundwater level recovers in 3 years from the tunnel completion. As a result of particle tracking modeling, the nearest particle reaches the tunnel after 6 hours and the farthest particle reaches the tunnel after 9 hours, similarly to the case of the field trace test.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.17 no.2
• /
• pp.141-151
• /
• 2015

A new rock excavation method using an abrasive injection waterjet system has been developed to enhance the efficiency and reduce the vibration of tunnel excavation. The abrasive feed rate is an important factor for the cutting performance and the economical efficiency of waterjet-based excavation. In this study, various experiments were performed to explore the effects of major process parameters for both the abrasive feed rate and the suction pressure occurring inside the mixing chamber when the abrasives are inhaled. Experimental results reveal that the abrasive feed rate is affected by geometry parameters (abrasive pipe height, length, and tortuosity), abrasive parameters (abrasive particle size), and jet energy parameters (water pressure and water flow rate). In addition, the relation between the cutting performance and the abrasive feed rate was discussed on the basis of the results of an experimental study. The cutting performance can be maximized when the abrasive feed rate is controlled appropriately via careful management of major process parameters.

• Journal of the Korean Geotechnical Society
• /
• v.30 no.7
• /
• pp.17-26
• /
• 2014

Tunneling-induced displacement in a jointed rock mass is an important factor to control tunnel stability and to secure a demanded space and construction quality. The magnitude of the inducible displacements is significantly affected by an elastic modulus and therefore, in a rock mass where a joint controls tunnel behavior, it is very important to estimate an elastic modulus of jointed rock mass reliably. Elastic modulus of jointed rock mass is affected by many factors such as rock type, joint condition, and loading condition. Nevertheless, most existing studies were focused on rough empirical relationships based on compressive loading conditions, which are different from tunnel excavation loading conditions, without a systematic approach of rock, joint, and loading conditions together. Therefore, this study considered rock and joint conditions systematically to estimate an elastic modulus of jointed rock mass under tunnel excavation loading. The controlled factors considered in this study are rock types and joint conditions (joint shear strength, joint inclination angle, number of joint sets, and joint spacing). Numerical parametric studies have been carried out with a consideration of different rock and joint conditions; the results have been compared with existing empirical relationships; and charts of elastic modulus change of different rock and joint conditions have been provided. The results are expected to have a great practical use for estimating the convergence induced by tunnel excavation in jointed rockmass.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.5 no.4 s.19
• /
• pp.49-57
• /
• 2005

The purpose of this study is to closely examine the influence of the surcharge load applied to the retaining wall through some model tests, in which wall stiffness in each stage of excavation, horizontal displacement of the retaining wall and surface displacement of the backfill according to wall stiffness and ground conditions, and change and distribution of the earth pressure applied to it were measured and their values were produced, then these values were mutually compared with their theoretical values and their values after analysis of the data obtained at the field, and they were analytically studied, in order to closely examine the influence of the surcharge load applied to the retaining wall. Findings from this study are as follows: The shape of ground surface settlement curve on the model ground under surcharge load, different from the distribution curve of regular probabilities which is of a shape of ground surface settlement under no surcharge load, appears in that settlement in an arching shape shows where the center part of surcharge load shows the maximum settlement. In examining the maximum horizontal displacement with the surcharge load applied to each stage of excavation, it occured at the point of 0.8H(excavation depth) when finally excavated. Regarding the range in which the displacement of the retaining wall increases according to application of surcharge load, the increment of displacement showed till the point of depth which is of two times of the distance of load from the upper part of the wall. Also since each displacement of the foundation plate caused by the ground surface settlement according to each stage of excavation occured most significantly at the final stage. Also since regarding wall stiffness, the wall of its thickness of 4mm(flexible coefficient $p:480m^3/t$), produced maximum 3 times of wall stiffness than its thickness of 9mm(flexible coefficient $p: 40m^3/t$), it was found out that influence of wall stiffness is so significant.

• Explosives and Blasting
• /
• v.37 no.2
• /
• pp.22-30
• /
• 2019

On sites where explosives are used, the effects of noise and vibration produced by the blast wave are subject to a number of operational restrictions. Recently, the number of civil complaints has increased and the standard of environmental regulations on secure goods has been greatly tighten. Therefore, work is generally carried out by machine excavation in case of close proximity of safety thing. Machine excavation methods have the advantage as reducing noise and vibration compared to blasting methods, but depending on the conditions of rock intended to be excavated, they are sometimes less constructive than planned. In general, the closer a rock type is to hard rock, the less constructible it becomes. In this paper, we are going to explain the construction of a construction section with a close proximity to a safety thing using electronic detonators. While the project site was designed with a machine excavation methods due to the close(9.9m) proximity of safety thing(the railroad), construction using electronic detonators was reviewed as an alternative method for improving rate of advance time and construction efficiency when expose to hard rock. Through blasting using electronic detonators, construction and economic efficiency were maximized while minimizing impact on surrounding safety things. Because $HiTRONIC^{TM}$, which is produced by Hanwha, has innovative stability and high explosion reliability, it is able to explode with high-precision accuracy. Electronic detonators are widely used in construction sites of railway or highway, other urban burrowing areas and large limestone mines.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.11
• /
• pp.83-96
• /
• 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
• /
• v.32 no.6
• /
• pp.373-385
• /
• 2022

The drum cutter, which is used in the form of an attachment of a excavator, is very useful in that it can be used in connection with a excavator that can perform various tasks in the field. This study estimated the load and torque acting on the drum cutter attachment by measuring the hydraulic pressure and strain that appear during excavation on the exposed rock slope using the drum cutter installed in the excavator. Working conditions such as the operation angle between the boom and arm of the excavator were divided into eight working modes. And as a result of analyzing the variations in hydraulic pressure and action force according to the working mode, it was confirmed that the hydraulic pressure and flow rate can be driven without any problems within the range considered in the manufacturing specifications of the drum cutter. The average load and torque acting on the drum cutter were within the range of the manufacturing specifications, but the maximum load was up to four times the specification. Because sumping was not properly performed due to the high ground strength and the ground included discontinuous surfaces in some locations, no trend of load and torque was found depending on the angle between the boom and arm of the excavator. However, it is believed that this result can be used to determine the range of loads and torques that appear on the drum cutter when excavating a high-intensity rock.