• Title, Summary, Keyword: Underpinning

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Importance of Construction Sequence in Numerical Modeling for Underground Structure

  • Park, Yang-Hoo;Cho, Kook-Hwan
    • International Journal of Railway
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    • v.9 no.1
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    • pp.21-26
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    • 2016
  • When excavation under existing structure is planned for a new construction project, the underpinning method is one of the most applicable construction methods. This study introduces a new modified underpinning method which is applied to construct a new subway line in Seoul Metropolitan. The new subway line was designed to pass underneath the existing subway line. Existing subway line carries about 2 million passengers daily, which is 33% of total passengers using subway in Seoul, and is the only circulation line in Seoul. Subway trains are passing 540 times through this section in a day. By applying a new underpinning method, the subway box structure of line is exposed 54m in the air supported by bearing piles. The proposed method was carefully monitored using heavy instrumentation system during construction. This study proposed and verified the application of the modified underpinning method, which can reduce construction period by 1.5 times and the construction cost by 1.2 times comparing with conventional method. The importance of considering construction sequence is investigated and verified by analyzed data non-considering construction sequence. The unexpected heaving which can bring up a dangerous situation for train running stability were measured, so this study shows that the upward movement has to be analyzed in designing process. As the use of underground space increases, the proposed method can be a good example of underground development.

A Case Study of Underpinning for Building Settlement Reduction (건물 침하방지를 위한 Underpinning 사례연구)

  • 박병기;이인모
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.57-62
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    • 1993
  • Settlements of maximum 23cm have occurred in and Apartment building consturcted on a fill layer with pile foundations. The main reason of the settlements was due to the negative skin friction applied to the pile, and settlement of adjacent ground since most pile tips are acted as a floating foundation founded on the stratum where the SPT N value was mostly less than 30. To underpin this building, the Jumbo Special Pile grouging was adopted, and instrumented data showed little differential settlement after the JSP underpinning.

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A Study on the Grouting for the Underpinning of Open Caisson of Existing Bridge (기존 교량구조물의 유지관리를 위한 우물통 기초 보강주입에 관한 연구)

  • Chun, Byung-Sik;Yeoh, Yoo-Hyeon
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.4 no.1
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    • pp.131-138
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    • 2000
  • In this study, physical and engineering properties of ordinary portland cement and microcement were investigated to verify reinforcing effect of underpinning of open caisson foundation by using microcement grouting. Laboratory injection tests such as infiltration and injection in case of seepage for the stream bed soil at ${\bigcirc}{\bigcirc}$ Great Bridge in Seoul were carried out. Field injection tests to reinforce open caisson foundation at ${\bigcirc}{\bigcirc}$ Great Bridge were performed and the ability of application by microcement grouting was evaluated. From the test results, physical and engineering properties of microcement are better than those of ordinary portland cement. Also, the ability of infiltration and solidity in case of seepage is better than that of ordinary portland cement. Therefore, it is concluded that microcement is an excellent material to reinforce open caisson foundation of the existing bridge structure under the water and can be used as underpinning material of general foundations.

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Numerical Analysis of Effect of Waveform Micropile on Foundation Underpinning During Building Vertical Extension Remodeling (수치해석을 통한 수직증축 리모델링시 파형 마이크로파일의 보강효과 분석)

  • Wang, Cheng-Can;Jang, Youngeun;Kim, Seok-Jung;Han, Jin-Tae
    • Journal of The Korean Society of Civil Engineers
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    • v.39 no.2
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    • pp.335-344
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    • 2019
  • Micropiles are widely used for foundation underpinning to enhance bearing capacity and reduce settlement of existing foundation. In this study, the main objective is to evaluate underpinning performance of a newly developed micropile called waveform micropile for foundation underpinning during vertical extension. Finite element method (FEM) was used to evaluate the underpinning performance of waveform micropile in terms of load-settlement response of underpinned foundation and load sharing behavior. For comparison, underpinning effects of three conventional micropiles with different lengths were also discussed in this study. Numerical results of load-settlement response for single pile demonstrated that bearing capacity and axial stiffness of waveform micropiles were higher than those of conventional micropiles because of the effect of shear keys of waveform micropiles. When additional loads 20 %, which is according to design loads of the vertical extension, were applied to the underpinned foundation, load sharing capacity of waveform micropile was 40 % higher than conventional micropile at the same size. The waveform micropile also showed better underpinning performance than the conventional micropile of length 1~1.5 times of waveform micropile.

A Study on the Ground Improvement by Compaction Grouting System (C.G.S에 의한 기초지반보강효과에 관한 연구)

  • 천병식;여유현;최현석;오일석
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.1-13
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    • 1999
  • The use of Compaction Grouting evolved in the 1950's to correct structural settlement of buildings. Over the almost 50 years, the technology has developed and is currently used in wide range of applications. Compaction Grouting, the injection of a very stiff, 'zero-slump' mortar grout under relatively high pressure, displaces and compacts soils. It can effectively repair natural or man-made soil strength deficiencies in variety of soil formations. Major uses of Compaction Grouting include densifying loose soils or fill voids caused by sinkholes, poorly compacted fills, broken utilities, improper dewatering, or soft ground tunneling excavation. Other application include preventing liquefaction, re-leveling settled structures, and using compaction grout bulbs as structural elements of minipiles or underpinning. The technique replaced slurry injection, or 'pressure grouting', as the preferred method of densification grouting. There are several reasons for the increased use of Compaction Grouting which can be summarized in one word: CONTROL. The low slump grout and injection processes are usually designed to keep the grout in a homogeneous mass at the point of injection, while acceptable in some limited applications, tends to quickly get out of control. Hydraulic soil fracturing can cause extensive grout travel, often well beyond the desired treatment zone. So, on the basis of the two case history constructed in recent year, a study has been peformed to analyze the basic mechanism of the Compaction Grouting and verify the effectiveness of the ground improvement using some test methods.

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