• Title/Summary/Keyword: Poor ground

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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.

Case Studies of Ground Subsidence Risk Ratings (GSRp) Applied to the Excavation Sites (지반함몰 위험등급 분류(GSRp)의 굴착현장 사례 연구)

  • Shin, Sang-Sik;Ihm, Myeong-Hyek;Kim, Hak Joon
    • The Journal of Engineering Geology
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    • v.29 no.3
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    • pp.289-302
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    • 2019
  • As the occurrence of ground subsidence near the excavation site increases recently, studies are being conducted to predict the possibility of ground subsidence prior to excavation. In this study, the ground subsidence risk rating for pre-excavation (GSRp) developed by the previous study was applied to actual excavation sites to verify its applicability. The final results for the evaluation of the ground subsidence risk level for five excavation sites revealed that GSRp scores were calculated between 40 and 79 points and classified mainly into grades II (Good Ground)~III (Fair Ground). In order to verify the evaluation method, the obtained GSRp grades were compared with the measured horizontal displacements. The horizontal displacements measured in five excavation sites were between 25% and 47% of the allowable displacement, which were well agreed with the low subsidence risk level obtained from GSRp calculation. It is expected that the GSRp method can be used as an evaluation tool for predicting the risk of ground subsidence before excavation if GSRp is verified and supplemented through the additional research for the poor soil with the high risk of ground subsidence.

Present Situation of School Turf Ground in Korea and Japan (한국과 일본의 학교 잔디운동장 현황)

  • ;Fujisaki, Kenichiro
    • Asian Journal of Turfgrass Science
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    • v.13 no.2
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    • pp.91-100
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    • 1999
  • School is the center for life of the students, 30% of Korean population. Students spend half of their daily life at school. However, amenity of school is not so good because school grounds in Korea are covered with soil while in USA and Europe with turf. This study was conducted to provide guidelines for constructing natural turf ground at school. 1. As of 1999, number of school grounds covered with turfgrass in Korea is only 130 out of 10,345. More turfs grounds should be constructed to improve amenity of school. Dept. of Education in Japan supports schools to establish turf grounds. 2. In Korea, only Zoysia japonica is used while in Japan several turfgrasses such as Zlysiagrass, bermudagrass and tall fescue are used. 3. In Korea and Japan, turfgrass at school is planted on soil based rootzone system resulting poor quality by heaby traffic. Recently in Japan, sand based rootzone systems such as Califonia and USGA systems are used at the schools with many students. 4. School turf both in Korea and Japan was managed by students and teachers. Turf quality of schools in Korea was not so good due to the poor management.

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Real-time Estimation of the Earthquake Magnitude Using the Bracketed Cumulative and Peak Parameters of the Ground-motion Acceleration of a Single Station (단일 지진관측소의 지반가속도 구간 누적값 및 최대값 파라미터를 이용한 실시간 지진규모 추정 연구)

  • Yun, Kwan Hee
    • Journal of the Earthquake Engineering Society of Korea
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    • v.18 no.1
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    • pp.29-36
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    • 2014
  • In industrial facilities sites, the conventional method determining the earthquake magnitude (M) using earthquake ground-motion records is generally not applicable due to the poor quality of data. Therefore, a new methodology is proposed for determining the earthquake magnitude in real-time based on the amplitude measures of the ground-motion acceleration mostly from S-wave packets with the higher signal-to-ratios, given the Vs30 of the site. The amplitude measures include the bracketed cumulative parameters and peak ground acceleration (As). The cumulative parameter is either CAV (Cumulative Absolute Velocity) with 100 SPS (sampling per second) or BSPGA (Bracketed Summation of the PGAs) with 1 SPS. The arithmetic equations to determine the earthquake magnitude are derived from the CAV(BSPGA)-As-M relations. For the application to broad ranges of earthquake magnitude and distance, the multiple relations of CAV(BSPGA)-As-M are derived based on worldwide earthquake records and successfully used to determine the earthquake magnitude with a standard deviation of ${\pm}0.6M$.

Ground motion intensity measure to evaluate seismic performance of rocking foundation system

  • Ko, Kil-Wan;Ha, Jeong-Gon
    • Earthquakes and Structures
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    • v.21 no.6
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    • pp.563-576
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    • 2021
  • The rocking foundation is effective for reducing structural seismic demand and avoiding overdesign of the foundation. It is crucial to evaluate the performance of rocking foundations because they cause plastic hinging in the soil. In this study, to derive optimized ground motion intensity measures (IMs) for rocking foundations, the efficiency of IMs correlated with engineering demand parameters (EDPs) was estimated through the coefficient determination using a physical modeling database for rocking shallow foundations. Foundation deformations, the structural horizontal drift ratio, and contribution in drift from foundation rotation and sliding were selected as crucial EDPs for the evaluation of rocking foundation systems. Among 15 different IMs, the peak ground velocity exhibited the most efficient parameters correlated with the EDPs, and it was discovered to be an efficient ground motion IM for predicting the seismic performance of rocking foundations. For vector regression, which uses two IMs to present the EDPs, the IMs indicating time features improved the efficiency of the regression curves, but the correlation was poor when these are used independently. Moreover, the ratio of the column-hinging base shear coefficient to the rocking base shear coefficient showed obvious trends for the accurate assessment of the seismic performance of rocking foundation-structure systems.

Field Evaluation of the Swelled Steel Tube Rockbolts (튜브형 강관 록볼트의 현장 적용성 평가)

  • Son, Sung-Gon;You, Jin-O;You, Joung-Hoon;Chung, Jae-Min
    • Proceedings of the KSR Conference
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    • 2011.10a
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    • pp.1149-1156
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    • 2011
  • A rockbolt is one of the most important reinforcement of on-site soil, as with the shotcrete and steel rib. The rockbolt by setting within the tunnel can prevent the deformation of the ground profile; furthermore it improves the structural behavior of soil and rock. In general, the rockbolt is mainly used with reinforced steel. However, steel pipe or the materials with the same strength can be used depending on the soil conditions, ground water outflow condition, and the surrounding of applying location. In Korea, most tunnel construction sites have used cement mortar or resin for steel reinforcement on the rock. Due to the ground water outflow in the construction site, the usability of steel reinforcement is poor and it requires curing time especially after installation. To improve exist above problems, this study introduces the development of a swelled steel pipe rockbolt, as well as presents the field testing and performance results.

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The Application of Nonlinear 3-D Tunnel Analysis Program for the Improved Efects of Steel Pipe Reinforced Multi Step Grouting Method (3차원 터널해석에 의한 강관 다단 그라우팅의 보강효과)

  • Kim, Hyeong-Tak;Lee, Bong-Yul;Kim, Hak-Moon
    • Proceedings of the Korean Geotechical Society Conference
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    • 1995.10a
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    • pp.25.2-38
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    • 1995
  • the Effect of steel pipe reinforced multi-step grouting(SPRG) technique to inrove the ground far ahead of the excavation face was investigated by means of numerical analysis. It was found taht the nonlinear 3-D FEM program performed well to evaluate the usefulness of the SPRG technique in soft ground tunnelling, and about 20% of settlement control in this particular case possible. Therefore in urban subway tunnel construction, the New Austirial Tunnelling Method can be satisfactorily applied even in poor ground conditon with aid of the SPRG technique.

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Developing Sea-Ground Cargo Linkages for Facilitating Coastal Transportations (연안운송의 활성화를 위한 연계체계 구축방안에 관한 연구)

  • Ha, Hun-Koo;Min, Jung-Ung
    • Journal of Korea Port Economic Association
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    • v.22 no.2
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    • pp.19-33
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    • 2006
  • The efficiency and effectiveness of freight transportation within and across Northeast Asia playa key role to achieve competitive advantages against other competing hubs in this area. However, the majority of local freight has been carried by ground transportation and the share of costal shipping has been decreasing for its transportational complexity and poor cargo works. In this paper, we discuss the prerequisites of efficient cargo linkage system from the perspectives of road, rail, ocean, and the service providers. Specifically, we identify that the balanced capacity of road/rail transportation system with costal freight system is a crucial component for facilitating coastal shipping. Other requirements such as the efficient on-dock container yard (ODCY), dedicated ports and ships, and the service provider of door-to-door transportation for short sea shipping are highlighted in order to secure the serviceability and availability of streamlined costal shipping. Further, we elaborate these requirements to facilitate costal cargo shipping in Korea.

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Application of Low Voltage High Resistance Grounding in Nuclear Power Plants

  • Chang, Choong-Koo;Hassan, Mostafa Ahmed Fouad
    • Nuclear Engineering and Technology
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    • v.48 no.1
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    • pp.211-217
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    • 2016
  • Most nuclear power plants now utilize solid grounded low voltage systems. For safety and reliability reasons, the low voltage (LV) high resistance grounding (HRG) system is also increasingly used in the pulp and paper, petroleum and chemical, and semiconductor industries. Fault detection is easiest and fastest with a solidly grounded system. However, a solidly grounded system has many limitations such as severe fault damage, poor reliability on essential circuits, and electrical noise caused by the high magnitude of ground fault currents. This paper will briefly address the strengths and weaknesses of LV grounding systems. An example of a low voltage HRG system in the LV system of a nuclear power plant will be presented. The HRG system is highly recommended for LV systems of nuclear power plants if sufficient considerations are provided to prevent nuisance tripping of ground fault relays and to avoid the deterioration of system reliability.