• Journal of Korean Society of Disaster and Security
• /
• v.10 no.1
• /
• pp.19-27
• /
• 2017

In recent years, ground subsidence has been frequently occurred by underground cavities due to the excessive groundwater inflow, caused by poor construction and management, during tunnel excavation and underground structure construction. In this study, a numerical model (SEEFLOW3D) was developed to estimate groundwater fluctuations for saturated-unsaturated poros media, evaluates the impact on ground excavation with open cut and non-open cut scenarios. In addition, the visual MODFLOW was applied to demonstrate the verification of the model compared with both results. Our results indicated that the RMSE and NRMSE was obtained to range over -3.95~5.7% and 0.56~4.62%, respectively. The developed model was expected to estimate groundwater discharges and apply analysis tool for optimum design of waterproof wall in future.

• The Journal of Engineering Geology
• /
• v.31 no.2
• /
• pp.135-148
• /
• 2021

Ground subsidence risk ratings obtained from the site investigation during pre-excavation stages could be changed depending on the parameters revealed during construction activities. A method of correcting the pre-excavation ground subsidence risk ratings based on the site conditions observed in the field is suggested in this study. The elevation of groundwater table during the excavation may be different from the predicted value depending on the application of waterproofing methods and construction conditions. The drastic drawdown of groundwater table during the excavation could cause ground subsidence due to soil volume decrease related to consolidation or compression of the ground, whereas the rising of groundwater table caused by the intense rainfall may result in a high potential for ground subsidence due to heaving or boiling of the excavation bottom. Excessive displacements of retaining walls or ground settlements may cause ground subsidence, which also results in a high risk of ground subsidence caused by the destruction of buried pipelines. Reevaluation of ground subsidence risk ratings is suggested considering the fluctuation of groundwater table, condition of groundwater leakage, measured ground displacements, and soil types. Finally, the ground subsidence risk rating system is improved for better evaluation by using 12 factors in 5 categories.

• Journal of the Korean Geotechnical Society
• /
• v.15 no.4
• /
• pp.43-56
• /
• 1999

The use of berms can be an effective method to restrain excessive movements of wall and ground caused by deep excavations in urban area. But generally in construction sites, no berm remains for the sake of construction convenience or the geometry and magnitude of remaining berm is determined by individual experiences due to scarce research results. In this research, laboratory model tests and numerical analyses are used mainly for sandy soils. And efficient berms for restraining excessive movements by deep excavations are analyzed. Model tests were performed for the cases of cantilever and braced wall excavations, and the behaviors of retaining wall were analyzed according to the geometry and magnitude of berms. And also, numerical methods were used for analyzing efficient berms which are available in the soil and construction conditions in urban areas of Korea.

• The Journal of Engineering Geology
• /
• v.11 no.1
• /
• pp.1-11
• /
• 2001

The geological characteristics of Korea are that we can encounter the rock layer only after 10m of excavation, methods to presume the rock pressure distribution of the rock layer is urgently needed. When using the existing empiric science of Terzaghi-Peck, Tschebotarioff to measure the rock pressure of the rock layer, underestimate the real strength because of the cohesion is ignored. Therefore calculating the horizontal sliding force of wedge block, which includes the dips and shear strength of discontinuities and surcharge load etc., think to be to getting a closer rock stress of the real rock pressure acting upon the earth structure in rock mass. This research use Coulomb soil pressure theory assuming that the backfill soil will yield wedge failure when it has cohesion, applying Prakash-Saran(l963), and then it uses equilibrium of force and shear strength $\tau$=c+$\sigma$tan $\Phi$ of the cliscontinuities. Analyzing shear strength and dips of cliscontinuities using calculated theory according to the status of discontinuities aperture, we were able to find out that because the cohesion and friction angle of the rock layer itself is large enough, how the dip directions and dips facing the excavation face is the only factor deciding whether or not the rock stress is applied. The evaluated theory of this research should be strictly estimated, so that the many parameters such as c, $\Phi$value, types and structures of rock class, excessive lateral pressure, dynamic load, earthquake, needed later when calculating shear strength of discontinuities and especially the ground water effect acting on rock layer should be coumpted with many measuring data achieve at the insite to study the application.

• Journal of the Korean Society of Costume
• /
• v.50 no.7
• /
• pp.129-139
• /
• 2000

The Chonmachong (Tumulus No. 155 in Whangnam-dong, Kyungju, Korea), which was unearthed in 1973, is an ancient tomb built in the Shilla Era between the 5th∼6th centuries by the method of Juk-suk-mok-gwak. With the excavation of this tomb more than 11,500 articles of luxurious and splendid relics including gold and silver ornaments, weaponry and horse gears were obtained. Among the excavated articles, the saddle flap with a drawing of flying horse on it is the first relic of its kind from the Shilla Era. and 'Chonma'(a flying horse), the name of the tomb. was named after this drawing. The saddle flap is highly valuable in that it provides the idea of how goad the people of Shilla were at drawing. Although a lot of researches have been released about the relics from the Chonmachong, this study is to focus on the fabrics from the excavation, all of which are in the Kyongiu Museum's collection. The findings of this study are as follows : 1 The subject of this study is mainly on the fabrics used in horse gears, the pieces of cloth that were used to spread on a saddle or to underlay beneath a saddle. As the Shilla Dynasty tried to restrict excessive ornamentation on horses and it is assumed that the fabrics used are different. according to the social status. 2. The subject articles are four plain fabrics, three fabrics of combined -construction and one braid, the warp-faced compound woven silks of combined-construction was found for the first tinge in Korea, and is the typical quality sick with patterns woven with dyed threads in different colors. 3. It is ascertained by the Chonmachong excavation that polychrome woven silk was used not only for the clothes of the upper classes but also for the ornaments of their horses in the Era of the Three Kingdoms.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.14 no.1
• /
• pp.55-77
• /
• 2012

A Modern Rock TBM is a tunnel excavation method combining the conventional tunnelling method with the mechanized tunnelling method. It is a hybrid system that excavates a tunnel with TBM and supports the ground by ring beam, wire mesh, rock bolt, shotcrete, i.e., conventional tunnelling method. In the Modern Rock TBM, a ring beam is similar to a steel rib in NATM in the way that uses H-beam. But using a ring beam is more effective than a steel rib because it is installed in a closed-circle. Therefore, improving the performance of the ring beam is a key factor for achieving tunnel stability. In this respect, this study introduces a pressurized ring beam that might be functioning more effectively by confining convergence during tunnel excavation. In order to verify the effect of the pressurized ring beam, a three-dimensional numerical analysis was conducted. The numerical analysis confirms an increase in the minimum principal stress and reduction in the plastic strain that triggers excessive displacement. The analysis result also indicates a decrease in the relative displacement occurring after installing the ring beam, and expansion in spacing between the ring beams.

• Journal of the Korean GEO-environmental Society
• /
• v.15 no.6
• /
• pp.49-56
• /
• 2014

The stability of tunnel construction depends entirely on the characteristics of the soil strength. If the soil strength is weak, collapse of tunnel occurs frequently under construction. In general, it copes with collapse by conducting half section excavation or reinforcement in advance under these conditions. Nevertheless, it can be collapsed under upper section excavation in the weathered fracture zone and it can be recovered through the application of reinforcement. As it has a bad influence on the upper section in case of upheaveal of tunnel bottom, it can be adversely affected on the overall stability of the tunnel. Thus, an in-depth review of reinforcement is needed in poor bottom ground. As the practices that has a bad affect on the stability of the tunnel due to upheaveal of tunnel bottom is increasing, research is needed for applicable standards for reinforcement. In this paper, it were investigated at actual field cases of upheaveal of bottom ground and characteristics of behavior and reinforcement measures were analyzed.

• Journal of the Korean GEO-environmental Society
• /
• v.7 no.2
• /
• pp.67-76
• /
• 2006

For a hydro power plant project, the headrace tunnel having a finished diameter of 3.3 m was constructed in volcanic rocks with well-developed vertical joint and high groundwater table. The intake facility was located 20.3km upstream of the powerhouse and headrace tunnel of 20km in length and penstock of 440m in height connected the intake and the powerhouse. The typical caldera lake, Lake Toba set the geology at the site the caving of the ground caused tension cracks in the vertical direction to be developed and initial stresses at the ground to be released. High groundwater table(the maximum head of 20bar) in the area of well-connected vertical joints delayed the progress of tunnel excavation severely due to the excessive inflow of groundwater. The excavation of tunnel was made using open-shield type TBM and mucking cars on the rail. High volume of water inflowraised the water level inside tunnel to 70cm, 17% of tunnel diameter (3.9m) and hindered the mucking of spoil under water. To improve the productivity, several adjustments such as modification of TBM and mucking cars and increase in the number of submersible pumps were made forthe excavation of severe water inflow zone. Since the ground condition encountered during excavation turned out to be much worse, it was decided to adopt PC segment lining instead of RC lining. Besides, depending on the conditions of the water inflow, rock mass condition and internal water pressure, one of the invert PC segment lining with in-situ RC lining, RC lining and steel lining was applied to meet the site specific condition. With the adoption of PC segment lining, modification of TBM and other improvement, the excavation of the tunnel under severe groundwater condition was successfully completed.

• Journal of the Korean GEO-environmental Society
• /
• v.15 no.2
• /
• pp.45-52
• /
• 2014

The tunnel construction is increasing in order to secure a good driving performance of the car and train. A cases of tunnel collapse and the tunnel excessive displacement are increasing with the increase in tunnel construction. In terms of empirical construction methods using the strength characteristics of soil, it is important for tunnel construction to analyze causes of collapse and displacement. In the paper, it was analyzed the causes of collapse and excessive displacement of tunnel in the fractured ground condition. The results of analysis is that the increase of rainfall and lasting increase of displacement and large scale fractured ground are interconnected.

• Journal of the Korean Geotechnical Society
• /
• v.20 no.7
• /
• pp.197-206
• /
• 2004

The ground anchor support system may not be occasionally used because of space limitations in urban excavation sites nearby the existing structures. In this case, soil nailing system with relatively short length of nails could be efficiently adopted as an alternative method. The general soil nailing support system, however, may result in excessive deformations particularly in an excavation zone of the existing weak subsoils. Pretensioning the soil nails then could play important roles to reduce deformations mainly in the upper part of the nailed-soil excavation system as well as to improve local stability. In this study, a newly modified soil nailing technology named as the PSN (Pretension Soil Nailing), is developed to reduce both facing displacements and ground surface settlements in top-down excavation process as well as to increase the global stability. Up to now, the analytical procedure and design technique are proposed to evaluate maximum pretension force and stability of the PSN system. Also, proposed are techniques to determine the required thickness of a shotcrete facing and to estimate probability of a failure against the punching shear, Based on the proposed procedure and technique, effects of the radius of a influence circle and dilatancy angle on the thickness of a shotcrete facing, bonded length and safety factors are analyzed. In addition, effects of the reduction of deformations expected by pretension of the soil nails are examined in detail throughout an illustrative example and the $FLAC^{2D}$ program analysis. And a numerical approach is proposed PSN system using the shear strength reduction technique with the $FLAC^{2D}$ program.