• Geomechanics and Engineering
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• 제29권4호
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• pp.471-486
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• 2022

The effect of segmental joints is one of main importance for the segmental lining design when tunnels are excavated by a mechanized process. In this paper, segmental tunnel linings are analyzed by two numerical methods, namely the Beam-Spring Method (BSM) and the Solid-Interface Method (SIM). For this purpose, the Tehran Subway Line 6 Tunnel is considered to be the reference case. Comprehensive 2D numerical simulations are performed considering the soil's calibrated plastic hardening model (PH). Also, an advanced 3D numerical model was used to obtain the stress relaxation value. The SIM numerical model is conducted to calculate the average rotational stiffness of the longitudinal joints considering the joints bending moment distribution and joints openings. Then, based on the BSM, a sensitivity analysis was performed to investigate the influence of the ground rigidity, depth to diameter ratios, slippage between the segment and ground, segment thickness, number of segments and pattern of joints. The findings indicate that when the longitudinal joints are flexible, the soil-segment interaction effect is significant. The joint rotational stiffness effect becomes remarkable with increasing the segment thickness, segment number, and tunnel depth. The pattern of longitudinal joints, in addition to the joint stiffness ratio and number of segments, also depends on the placement of longitudinal joints of the key segment in the tunnel crown (similar to patterns B and B').

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.757-762
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• 2007

The lining segment which is the main structure of the shield tunnel consists of joints, not continua. Past international and domestic design data have been commonly used for design practices without specific verification about the structural analysis model, design load, and affection of the soil constant of the lining segment. In this study, the propriety is estimated through the comparison between analytical solution and numerical solution for segment analysis and design models of the shield tunnel which is being used internationally and domestically. As a result, the full. circumferential beam jointed spring model (1R-S0) is suggested by considering aspects of convenient use, application to field condition, and accuracy of analysis result. With suggested model, the parameter analysis was conducted for joint stiffness, ground rigidity, joint distribution, and joint number.

• 한국터널지하공간학회 논문집
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• 제17권6호
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• pp.695-702
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• 2015

원심모형시험은 최근의 기계적, 이론적 발전에 따라 그 활용도와 정확성이 높아지고 있다. 원심모형시험은 원지반 응력을 효과적으로 재현할 수 있으므로 주위 지반 또는 암반과 상호작용을 하는 터널과 같은 지하구조물의 거동을 모사하기 적합하다. 본 연구에서는 병렬 터널의 지진시 동적 거동을 원심모형시험을 통하여 분석하였다. 터널 모델링시 지진에 의해 발생하는 최대 가속도 저감을 위하여 Flexible segment를 고려하였으며 Flexible segment의 두께가 얇은 경우와 두꺼운 경우를 각각 고려하였다. 시험 결과 Flexible segment의 지진시 터널 구조물에 발생하는 최대 가속도 저감 효과를 확인하였다. 그러나 Flexible segment가 얇은 경우 단주기파 적용시 최대가속도의 저감효과는 없었고, 두꺼운 경우 기반암 가속도가 클 경우 보다 효과적임을 확인하였다. 또한 동일 모델에 대하여 3차원 수치해석을 수행하여 지진시 거동을 파악한 결과, 시험 결과와 유사한 경향을 보임을 확인할 수 있었다.

• Geomechanics and Engineering
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• 제15권3호
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• pp.833-839
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• 2018

Dynamic behaviour of a tunnel is one of the most important issues for the safety and it is generally subjected to the seismic response of the surrounding soil. Relative displacement occurred in tunnel lining during earthquake produces severe damage. Generally, it concentrates at the connecting area when two tunnels are connected in the ground. A flexible segment is a useful device for the mitigation of seismic loads on tunnel lining. In this study, 1-g shaking table tests are performed to investigate the acceleration response for the verification of the effect of flexible segment and to determine the optimum location of the flexible segment for connected tunnels. Four different seismic waves are considered; as a result, peak acceleration is reduced to 49% in case that flexible segment is implemented adjacent to connecting area. It also exhibited that the mitigation of acceleration response is verified in all seismic waves. Additionally, 3-dimensional numerical analysis is performed to compare and verify the results. And the numerical results show good agreement to those of the experimental study.

• Applied Biological Chemistry
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• 제41권8호
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• pp.583-586
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• 1998

Porous ceramic cups are used for monitoring ion concentration in soil solutions in various time course and depth. A soil solution sampler was constructed in laboratory by inserting pliable perfluoroalkoxy(PFA) tubings into porous cup through holes in PVC rod segment which plugged top opening of the porous cup. The system was installed in drip irrigated soil in a vertical position, and nitrogen movement below the drip basin was monitored. To collect soil solution, vacuum in the cup was applied with a hand vacuum pump. The samples obtained were sufficient enough to run quantitative analyses for a number of chemicals. Nitrogen transformation and movement could be well defined, and the system seemed to be relevant to the other soil solution samplers in monitoring chemical movement in soil. Although this system has general deficiencies found in the other samplers using ceramic cup, it could be easily constructed at a low cost. Since the tubing was pliable, the cups could be installed in horizontal position, and this allows installations of the cups at more precise depth increments and also more precise samplings of soil solution at each depth.

• International Journal of Naval Architecture and Ocean Engineering
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• 제8권2호
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• pp.177-187
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• 2016

To evaluate the tractive performance of tracked trencher on seafloor surface, a new shear stress-displacement empirical model was proposed for saturated soft-plastic soil (SSP model). To validate the SSP model, a test platform, where track segment shear test can be performed in seafloor soil simulacrum (bentonite water mixture), was built. Series shear tests were carried out. Test results indicate that the SSP model can describe the mechanical behavior of track segment with good approximation in seafloor soil simulacrum. Through analyzing the main external forces applied to seafloor tracked trencher during the uniform linear trenching process, a drawbar pull prediction model was deduced with the SSP model. A tracked walking mechanism of the seafloor tracked trencher prototype was built, and verification tests were carried out. Test results indicate that this prediction model was feasible and effective; moreover, from another side, this conclusion also proved that the SSP model was effective.

• 식물병연구
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• 제23권1호
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• pp.65-68
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• 2017

2단계의 nested PCR 방법을 이용하여 보리 및 벼 재배 토양에서 Barley yellow mosaic virus (BaYMV)를 검출하였다. BaYMV 분절 RNA1 외피단백질 영역의 특이 프라이머로 1차 PCR을 하고 내부서열로부터 작성된 프라이머로 2차 PCR을 실시하여 확보된 372 bp의 PCR 산물이 BaYMV 외피단백질 영역과 98%-100% 염기서열이 일치하여 BaYMV를 검출할 수 있음을 확인하였다. 이 결과는 토양으로부터 BaYMV 검출에 관한 최초의 보고이며 토양전염성 바이러스의 정확한 진단과 예찰에 적용될 수 있을 것으로 생각한다.

• 한국토양비료학회지
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• 제24권2호
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• pp.102-108
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• 1991

나지상태(裸地狀態)에서 관수량(灌水量)에 따른 양분(養分)의 수직이동(垂直移動) 양상(樣相)을 구명하기 위하여 본량사양토(本良砂壤土)(Typic Udifluvents)의 작토층(作土層)을 공시토양(供試土壤)으로 하여 microplot(지름 20cm, 길이 85cm)시험(試驗)을 수행하였다. 시비량(施肥量)를 기준으로 하여 각(各) 성분(成分)이 (각(各) 토층(土層)으로 이동(移動)된 양(量))/(시비량(施肥量))${\times}$(시비지점에서 각(各) 토층(土層) 중심점까지의 거리)의 화(和)를 평균(平均) 이동(移動)거리라 했을때, 평균이동(平均移動)거리는 관수량(灌水量)과 수직적(直線的)인 관계가 있었다. 1 pore volume(piston front 10cm)물의 이동(移動)에 대한 각(各) 성분(成分)의 평균(平均) 이동(移動)거리는(cm)는 Cl, 7.52>무기태(無機態) N, 6.03>K, 3.50>Mg, 2.69>Ca, 1.19>유효인산(有效燐酸), 0.29순이었다. 여러 성분중(成分中) Cl이 가장 활발하게 하향이동(下向移動)되어 물의 piston front 이동(移動)거리의 75%가 되었고, 인산(燐酸)은 거의 이동(移動)되지 않아 물의 piston front 이동(移動)거리의 3%에 불과하였다. 양분이동(養分移動)의 결과 토양 pH는 관수량(灌水量)이 많아질수록 표층(表層)에서 낮아지고 심층(深層)에서 높아지는 경향인데 토양(土壤)깊이별 pH변화는 치환성(置換性) Ca과 Mg보다는 $NH_4-N$의 함량변화와 같은 경향을 보였다.

• Coupled systems mechanics
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• 제3권2호
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• pp.213-232
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• 2014

Pounding is a major cause of bridge damage during earthquakes. In an extreme situation, it can even contribute to the unseating of bridge girders. Long-span bridges will inevitably experience spatially varying ground motions. Soil-structure interaction (SSI) may play a significant role in the structural response of these structures. The objective of this research is to experimentally investigate the effect of spatially varying ground motions on the response of a three-segment bridge considering SSI and pounding. To incorporate SSI, the model was placed on sand contained in sandboxes. The sandboxes were fabricated using soft rubber in order to minimise the rigid wall effect. The spatially varying ground motion inputs were simulated based on the New Zealand design spectra for soft soil, shallow soil and strong rock conditions, using an empirical coherency loss function. The results show that with pounding, SSI can amplify the pier bending moments and the relative opening displacements.

• Geomechanics and Engineering
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• 제29권3호
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• pp.229-236
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• 2022

In this study, a model experiment and field experiment was conducted to introduce the optimal tensile force when constructing a non-open cut tunnel according to the ground conditions of sandy soil. CMR (Concrete Modular Roof) method is economical because of the high precision and excellent durability, and corrosion resistance, and the inserted parts can be used as the main structure of a tunnel. In addition the CMR method has a stable advantage in interconnection because the concrete beam is press-fitted compared to the NTR (New Tubular Roof) method, and the need for quality control can be minimized. The ground conditions were corrected by adjusting the relative density of sandy soil during the construction of non-open cut tunnels, and after introducing various tensile forces, the surface settlement according to excavation was measured, and the optimal tensile force was derived. As a result of the experiment, the amount of settlement according to the relative density was found to be minor. Furthermore, analysis of each tensile force based on loose ground conditions resulted in an average decrease of approximately 22% in maximum settlement when the force was increased by 0.8 kN per segment. Considering these results, it is indicated that more than 2.0 kN tensile force per segment is recommended for settlement of the upper ground.