• Title, Summary, Keyword: Ground surface settlement

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A Trend of Back Ground Surface Settlement of Braced Wall Depending on the Joint Dips in Rocks under the Soil Strata (복합지반 굴착 시 암반층 절리경사 각도별 흙막이 벽체 배후 지표침하의 경향)

  • Bae, Sang-Su;Lee, Sang-Duk
    • 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.

Critical face pressure and backfill pressure in shield TBM tunneling on soft ground

  • Kim, Kiseok;Oh, Juyoung;Lee, Hyobum;Kim, Dongku;Choi, Hangseok
    • Geomechanics and Engineering
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    • v.15 no.3
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    • pp.823-831
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    • 2018
  • The most important issue during shield TBM tunneling in soft ground formations is to appropriately control ground surface settlement. Among various operational conditions in shield TBM tunneling, the face pressure and backfill pressure should be the most important and immediate measure to restrain surface settlement during excavation. In this paper, a 3-D hydro-mechanical coupled FE model is developed to numerically simulate the entire process of shield TBM tunneling, which is verified by comparing with real field measurements of ground surface settlement. The effect of permeability and stiffness of ground formations on tunneling-induced surface settlement was discussed in the parametric study. An increase in the face pressure and backfill pressure does not always lead to a decrease in surface settlement, but there are the critical face pressure and backfill pressure. In addition, considering the relatively low permeability of ground formations, the surface settlement consists of two parts, i.e., immediate settlement and consolidation settlement, which shows a distinct settlement behavior to each other.

지하수 채수에 따른 지반침하 사례분석

  • 정하익;구호본
    • Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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    • pp.168-171
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    • 2001
  • It is a common practice to extract water from the ground for domestic, agricultural or industrial uses or to lower the groundwater level for construction work. An accurate prediction of ground settlement Is sometimes crucial when groundwater is pumped. This case study have shown that drawdown of the groundwater table may cause ground subsidence. Many settlement gauges was installed in the vicinity of a pumped well to measure the surface settlement. The relationships between the level of groundwater drop and surface settlement is investigated In this research.

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A simple model for ground surface settlement induced by braced excavation subjected to a significant groundwater drawdown

  • Zhang, Runhong;Zhang, Wengang;Goh, A.T.C.;Hou, Zhongjie;Wang, Wei
    • Geomechanics and Engineering
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    • v.16 no.6
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    • pp.635-642
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    • 2018
  • Braced excavation systems are commonly required to ensure stability in construction of basements for shopping malls, underground transportation and other habitation facilities. For excavations in deposits of soft clays or residual soils, stiff retaining wall systems such as diaphragm walls are commonly adopted to restrain the ground movements and wall deflections in order to prevent damage to surrounding buildings and utilities. The ground surface settlement behind the excavation is closely associated with the magnitude of basal heave and the wall deflections and is also greatly influenced by the possible groundwater drawdown caused by potential wall leakage, flow from beneath the wall, flow from perched water and along the wall interface or poor panel connections due to the less satisfactory quality. This paper numerically investigates the influences of excavation geometries, the system stiffness, the soil properties and the groundwater drawdown on ground surface settlement and develops a simplified maximum surface settlement Logarithm Regression model for the maximum ground surface settlement estimation. The settlements estimated by this model compare favorably with a number of published and instrumented records.

Evaluation of Foundation Settlement of Gyungbu High Speed Concrete Track Under Construction (건설 중인 경부고속철도 콘크리트궤도 기초침하 평가)

  • Kim, Dae-Sang;Yoo, Chung-Hyun;Kim, Hwan-Ki
    • Proceedings of the KSR Conference
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    • pp.365-370
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    • 2007
  • Foundation settlements(settlements at the embankment surface and ground) has been evaluating to satisfy the strict allowable residual settlement level from the start of the construction of Gyungbu high speed railway. This is because both embankment and ground settlement could be important to minimize the residual settlement after the construction of concrete track. Ground settlement is caused by the increase of effective stress resulting from embankment. The causes of embankment settlement could be come from different sources, for example, the increase of effective stress, rainfall, creep behaviors. Based on the field measured data, this paper analysed the settlement of ground and embankment settlement. The biggest settlement at the embankment surface was 9.7mm during 246days at the STA 000k922.5. The calculated settlement of embankment itself was 8.6mm at the same places. These results conclude that the compressive settlement of embankment could not negligible.

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Numerical simulation of the effect of confining pressure and tunnel depth on the vertical settlement using particle flow code (with direct tensile strength calibration in PFC Modeling)

  • Haeri, Hadi;Sarfarazi, Vahab;Marji, Mohammad Fatehi
    • Smart Structures and Systems
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    • v.25 no.4
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    • pp.433-446
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    • 2020
  • In this paper the effect of confining pressure and tunnel depth on the ground vertical settlement has been investigated using particle flow code (PFC2D). For this perpuse firstly calibration of PFC2D was performed using both of tensile test and triaxial test. Then a model with dimention of 100 m × 100 m was built. A circular tunnel with diameter of 20 m was drillled in the middle of the model. Also, a rectangular tunnel with wide of 10 m and length of 20 m was drilled in the model. The center of tunnel was situated 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, 45 m, 50 m, 55 m and 60 m below the ground surface. these models are under confining pressure of 0.001 GPa, 0.005 GPa, 0.01 GPa, 0.03 GPa, 0.05 GPa and 0.07 GPa. The results show that the volume of colapce zone is constant by increasing the distance between ground surface and tunnel position. Also, the volume of colapce zone was increased by decreasing of confining pressure. The maximum of settlement occurs at the top of the tunnel roof. The maximum of settlement occurs when center of tunnel was situated 15 m below the ground surface. The settlement decreases by increasing the distance between tunnel center line and measuring circles in the ground surface. The minimum of settlement occurs when center of circular tunnel was situated 60 m below the surface ground. Its to be note that the settlement increase by decreasing the confining pressure.

Effects of Reinforced Pseudo-Plastic Backfill on the Behavior of Ground around Cavity Developed due to Sewer Leakage (하수관 누수에 의해 발생되는 공동 주변 지반의 거동에 대한 가소성유동화토의 보강효과)

  • Oh, Dongwook;Kong, Sukmin;Lee, Daeyoung;Yoo, Yongseon;Lee, Yongjoo
    • Journal of the Korean Geoenvironmental Society
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    • v.16 no.12
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    • pp.13-22
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    • 2015
  • Developed ground cavity due to leakage of decrepit old sewer pipe causes ground surface settlement and brittle fracture of pavement. Recently, for 5 years, frequency of occurrence of ground subsidence phenomenon tends to increase rapidly and/or steadily. It is difficult to investigate ground surface settlement and/or subsidence in urban area because most ground surfaces are covered with asphalt or concrete pavement. In this research, therefore, ground surface settlement, influence zone and settlement of sewer pipe were analyzed using finite element method. Not only reinforced effect of pseudo-plastic backfill that is applied to prevent ground surface settlement or subsidence spot, was compared and analyzed using numerical analysis program, but also direct shear test was carried out to determine strength parameters of pseudo-plastic backfill.

Reliability analysis of surface settlement by groundwater drawdown from tunnel excavation (터널굴착시 지하수위저하에 의한 지표침하의 신뢰성 해석)

  • Jang, Yeon-Soo;Kim, Hong-Seong;Park, Jeong-Yong;Park, Joon-Mo;Lee, Seong-Ki
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.1426-1433
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    • 2005
  • In this paper, reliability analysis of surface settlement by ground water drawdown is performed using a reliability-groundwater flow numerical model. The result is compared with that of the deterministic model to evaluate the influence of the uncertainty from hydraulic conductivity in the soft ground as well as to determine the range of hydraulic conductivity of grouted ground. From the analyses, it was found that probability of failure to exceed the tolerable settlement was very high, if the hydraulic conductivity of grouted ground is decided from the deterministic flow model only. Reliability analysis which evaluates variance of hydraulic conductivity should be used together with the deterministic model for grouting design of tunnels to prevent ground water drawdown.

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Development of Automated Monitoring System for Soft Ground Settlement Based on Hole Senor (홀센서 기반의 연약지반 자동 지반침하 계측시스템 개발)

  • Jeon, Je-Sung;Lee, Keun-Ho;Yoon, Dong-Gu
    • Journal of the Korean Geotechnical Society
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    • v.28 no.6
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    • pp.39-52
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    • 2012
  • Magnetic sensing system and automated monitoring system based on digital hall sensor for ground settlement are developed to change traditional method for monitoring surface settlement and underground settlement by manual type and to overcome technical limits of existing automated settlement monitoring system. It's possible to monitor surface settlement and underground settlement with multi-points at the same time in a single hole with NX size. It was possible to verify technical confidence and stability by several case studies of soft ground improvement project.

A Prediction Method for Ground Surface Settlement During Shield Tunneling in Cohesive Soils (점성토 지반에서의 실드 터널 시공에 따른 지표침하 예측 기법)

  • Yoo, Chung-Sik;Lee, Ho
    • Geotechnical Engineering
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    • v.13 no.6
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    • pp.107-122
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    • 1997
  • This paper presents a ground surface settlement prediction method for shield tunneling in cohesive soils. In order to develop the method, a parametric study on shield tunneling was performed by using a threetimensional elasto-plastic finite element analysis, which can simulate the construction procedure. By using the results of the finite element analysis, the ground movement mechanism was investigated and a base which relates the ground surface settlement and iuluencing factors was formed. The data base was then used to formulate semi -empirical equations for both surface settlement ratio above tunnel face and imflection point by means of a regression analysis. Furthermore, a prediction method for transverse and longitudinal surface settlement profiles was suggested by using the leveloped equations in conjunction with the normal probability curve. Effectiveness of the developed method was illustrated by comparing settlement profiles obtained by using the developed method with the results of finite element analysis and measured data. Based on the comparison, it was concluded that the developed method can be effectively rosed for practical applications at least within the conditions investigated.

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