• Geomechanics and Engineering
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• 제33권5호
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• pp.507-518
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• 2023

The effects of various supporting arrangements have been investigated on an excavation support system using a numerical tool. The purpose of providing different supporting arrangements was to limit the pile wall deflection in the range of 0.5% to 1% of the excavation depth. Firstly, a deep excavation supported by sheet pile wall was modeled and the effects of sheet pile wall thickness, excavation depth and distance to adjacent footings from sheet pile wall face were explored on the soil deformation and wall deflection. Further analysis was performed considering six different arrangements of tieback anchors and struts in order to limit the wall deflections. Case-01 represents the basic excavation geometry supported by sheet pile wall only. In Case-02, sheet pile wall was supported by struts. Case-03 is a sheet pile wall supported by tieback anchors. Likewise, for the Cases 04, 05 and 06, different arrangements of struts and tieback anchors were used. Finally, the effects of different supporting arrangements on soil deformation, sheet pile wall deflection, bending moments and anchor forces have been presented.

• 한국농공학회지
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• 제38권5호
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• pp.140-154
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• 1996

In this study, displacement, deformation, and stability according to change of cohesion and internal friction angle were investigated through elasto-plastic method, finite-element method, and in-site experiment when excavating soft ground using sheet pile. The results of the study were as follows : 1. The horizontal displacement was 5.5% of the excavation depth by the elasto-plastic method and 3.9% of the excavation depth by the on-site experiment at the final excavation depth(GL-8.Om) on the condition of double stair strut after excavating GL-6.Om. 2. Relationships between cohesion(c) and internal friction angle $({\varphi})$ when safety factor to the penetration depth was 1.2 is shown in the following equations : (a) c= -O.0086$({\varphi})$+ O.3(D=3m) and (b) c=-0.00933$({\varphi})$+0.14(D=4m). 3. The results of elasto-plastic method and the experiment show that possible excavation depth was GL-6.Om after setting single stair strut in a short period in terms of possibility of carrying out on the condition of experimental site on the contrary general reinforcement method, setting double stair strut after excavating GL-4.0m. 4. After setting the strut, distribution of the horizontal displacement had concentrated on the excavation base and possible local failure which the shear strain caused decreased by the strut reinforced. 5. After setting strut, displacement of sheet pile was decreased by half, the limit of stable excavation depth of ground was GL-8.Om, and the maximum horizontal displacement at the GL-8.Om was 1.6% of excavation depth by the elasto-plastic method, 0.7% of excavation depth by the finite-element method.

• Geomechanics and Engineering
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• 제32권2호
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• pp.145-157
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• 2023

This paper aims at investigating the face stability of large-diameter underwater shield tunnels considering seepage in soft-hard uneven strata. Using the kinematic approach of limit upper-bound analysis, the analytical solution of limit supporting pressure on the tunnel face considering seepage was obtained based on a logarithmic spiral collapsed body in uneven strata. The stability analysis method of the excavation face with different soft- and hard-stratum ratios was explored and validated. Moreover, the effects of water level and burial depth on tunnel face stability were discussed. The results show the effect of seepage on the excavation face stability can be accounted as the seepage force on the excavation face and the seepage force of pore water in instability body. When the thickness ratio of hard soil layer within the excavation face exceeds 1/6D, the interface of the soft and hard soil layer can be placed at tunnel axis during stability analysis. The reliability of the analytical solution of the limit supporting pressure is validated by numerical method and literature methods. The increase of water level causes the instability of upper soft soil layer firstly due to the higher seepage force. With the rise of burial depth, the horizontal displacement of the upper soft soil decreases and the limit supporting pressure changes little because of soil arching effect.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1991년도 추계학술발표회 논문집 지반공학에서의 컴퓨터 활용 COMPUTER UTILIZATION IN GEOTECHNICAL ENGINEERING
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• pp.123-132
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• 1991

The GEOKST program was used to solve the tunnel example problem. The package can solve such geotechnical problem as excavation, embankment, foundations, etc., in which the soil can be modeled by various elastoplastic geomaterial models. The main objective was to consider the effects of excavation depth to the face of the tunnel on the stability of the ground and support system. Depended on the strength of the ground materials, the limit excavation depth without any support system could be established by analyzing three-dimensional excavation problem. In this given example problem, the strengths of the ground materials were enough for the stability of the tunnel without any support system up to fairly deep excavation and the maximum tunnel section displacement was stabilized as the excavation proceed. The asymptotic value was approximately the same as that of the plane strain analysis. Thus, assuming the plain strain condition and simulation the actual excavation procedure, the maximum tunnel section displacement was caculated after final step. The maximum calculated displacement occured at the top section of the tunnel geometry and was about 8mm.

• 한국지반신소재학회논문집
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• 제5권3호
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• pp.37-44
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• 2006

지반굴착에 의한 일반적인 흙막이공과 친환경성을 만족시키기 위한 조경 및 보강옹벽 등의 시공을 동시에 적용하게 되면 시공기간이 증가하고, 이에 따른 비용도 커지게 된다. 이러한 단점을 극복하여 흙막이벽과 옹벽구조물의 기능을 동시에 가지는 옹벽겸용 흙막이벽 공법이 제시된 바 있다. 하지만 기존에 제시된 공법은 굴착깊이에 대한 한계성을 가지고 있기 때문에 본 연구에서는 기존 공법을 응용한 설계패턴을 제시하였고, 시공사례를 통하여 응용설계법에 대한 시공성 및 안정성을 평가하였다. 그 결과, 배면의 여유공간이 부족한 현장의 경우 일반적인 흙막이벽이 갖는 말뚝의 변위 및 굴착한계깊이가 다소 해결될 수 있는 공법으로서의 적용이 가능함을 확인할 수 있었다.

• 농업과학연구
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• 제23권1호
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• pp.25-38
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• 1996

연약지반상에 시공되는 용 배수로 굴착사면의 안정문제를 구명하기 위하여 굴착사면의 경사에 따른 지반의 거동을 한계평형법 및 유한요소법에 의하여 해석하고 실제 현장실험과 비교 분석한 결과 다음과 같은 결론을 얻었다. 1. 수로에서 수위를 급강하시켰을 때 과잉공극수압의 영향으로 균열이 발생하였고, 그 이후에 공극수압의 감소는 완만하게 나타났다. 2. 연직굴착시는 굴착폭이 클수록 균열의 폭도 커지고, 굴착깊이가 깊어지면서 진행성 파괴형태를 나타냈다. 3. 연약지반에서 소규모의 굴착공사를 할 때 최소안전율은 굴착사면의 경사(1:1, 1:1.5, 1:2)보다는 점착력(1.0, 1.5, 2.0, 2.5, $3.0t/m^2$)에 더 큰 영향을 받는 것으로 나타났다. 4. 굴착이 진행되면서 소성영역이 발달하는 상부사면에서는 침하가 발생하였으며, 굴착저면에서는 히빙현상이 나타났다. 5. 최대전단응력은 저부지반으로 갈수록 크게 나타났으며, 이와같은 현상은 인장영역을 발생시켜서 국부적인 파괴 가능성을 증가시킴을 알 수 있었다. 6. 최대전단변형은 굴착깊이에 따라 증가하며, 굴착저면에서 가장 큰값을 나타내고 굴착사면의 중앙저부에 집중되는 분포형태를 나타냈다.

• Geomechanics and Engineering
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• 제35권5호
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• pp.525-538
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• 2023

The development of a city is closely linked to the construction and operation of its subway system. However, constructing a new subway tunnel under an existing station is an extremely complex task, and the deformation characteristics and mechanical behavior of the new subway tunnel during the excavation process can greatly impact the normal operation of the existing station. Although the previous studies about the case of underpass engineering have been carried out, there is limited research on the condition of a newly-built subway tunnel that closely undercrossing an existing station with zero distance between them. Therefore, this study analyzes the deformation law and mechanical behavior characteristics of the preliminary lining of the underpass tunnel during the excavation process based on the real engineering case of Chengdu Metro Line 8. This study also makes an in-depth comparison of the influence of different excavation methods on this issue. Finally, the accuracy of numerical simulation is verified by comparing it with on-site result. The results indicate that the maximum bending moment mainly occurs at the floor slab of the preliminary lining, while that of the ceiling is small. The stress state at the ceiling position is less affected by the construction process of the pilot tunnel. Compared to the all-in-one excavation method, although the process of partial excavation method is more complicated, the deformation of preliminary lining caused by it is basically less than the upper limit value of the standard, while that of the all-in-one excavation method is beyond standard requirements.

• Geomechanics and Engineering
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• 제33권1호
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• pp.53-63
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• 2023

Rock disturbance caused by blasting and stress relaxation is commonly observed during excavation. As the distance from the source of disturbance increases, the degree of disturbance decreases, and rock at a large depth does not experience disturbance. However, in stability analyses, a single value of disturbance is often applied to the entire rock mass, which leads to underestimated results. In this study, this modeling mistake is addressed by considering realistically varying rock disturbance. The safety of infinite slopes in a disturbed rock mass with a strength governed by the Hoek-Brown failure criterion is investigated based on the kinematic approach of limit analysis. The maximum disturbance is assigned to the outermost slope face because it is directly exposed to blasting damage and dilation, and the disturbance progressively decays with distance in the rock mass. The safety analysis results indicate that the assumption of uniform disturbance in the entire rock mass leads to underestimation of the rock strength and safety on infinite rock slopes. A critical slip surface appears to be within the disturbed rock layer as well as the interface between the disturbed upper rock and undisturbed lower rock.

• 한국환경과학회지
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• 제27권8호
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• pp.677-688
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• 2018

The purpose of this study was to minimize salt water intrusion into freshwater aquifers and limit the development of freshwater aquifers, by selecting an appropriate excavation depth of in the western coastal area of Jeju Island. The study site was mostly basaltic lava, which was mainly composed of trachy basalt. A vertical logging test was conducted to investigate the vertical distribution of the groundwater and saline groundwater interface in the study well. It was found that freshwater groundwater, saline groundwater, and freshwater groundwater are distributed from the surface to approximately 16 m, 16~50 m, and 50~60 m, below the ground, respectively. In order obtain saline groundwater and minimize the inflow of freshwater into this well, the drilling depth should be limited in the range of 16~50 m from the surface. Thus, saline groundwater well development should be carried out with reference to the measurement results, which depend on the drilling depth and EC (electrical conductivity) obtained with drilling apparatus for geology and ground handling.

• Coupled systems mechanics
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• 제2권1호
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• pp.23-51
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• 2013

An analytical algorithm for the estimation of the resistance forces exerted on the dipper of a cable shovel and the specific energy consumed in the cutting-loading process is presented. Forces due to payload and to cutting of geomaterials under given initial conditions, cutting trajectory of the bucket, bucket's design, and geomaterial properties are analytically computed. The excavation process has been modeled by means of a kinematical shovel model, as well as of dynamic payload and cutting resistance models. For the calculation of the cutting forces, a logsandwich passive failure mechanism of the geomaterial is considered, as has been found by considering that a slip surface propagates like a mixed mode crack. Subsequently, the Upper-Bound theorem of Limit Analysis Theory is applied for the approximate calculation of the maximum reacting forces exerted on the dipper of the cable shovel. This algorithm has been implemented into an Excel$^{TM}$ spreadsheet to facilitate user-friendly, "transparent" calculations and built-in data analysis techniques. Its use is demonstrated with a realistic application of a medium-sized shovel. It was found, among others, that the specific energy of cutting exhibits a size effect, such that it decreases as the (-1)-power of the cutting depth for the considered example application.