• Title/Summary/Keyword: 공벽 안정성

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Experimental Study on Effect of Injected Drilling Fluid for Bore Hole Collapse Prevention (모형실험을 이용한 안정액 주입 시 공벽붕괴방지 효과 분석)

  • Choi, Jung-Hyuk;Yoo, Chung-Sik;Han, Yun-Su
    • Journal of the Korean Geosynthetics Society
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    • v.15 no.4
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    • pp.53-62
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    • 2016
  • This paper presents the results of a reduced-scale physical model investigation into the effect of drilling fluid with different mix designs for use in offshore bore hole collapse prevention. Compare the bentonite and Attapulgite use. Reduced-scale model tests were then carried out considering field procedures for cases with decomposed granitic soil with fines and a sand with various drilling fluids with different mix designs. The results were indicated that the addition of polymer to the bentonite based drilling fluid decreases the amount of injected drilling fluid and increases the final depth of excavation. Also revealed that the effect of polymer on the performance of drilling fluid is more pronounced in the decomposed granite soil with fines than sand. Practical implications of the findings from this study are discussed in detail.

Numerical Analysis of Borehole Stability Depending on Drilling Fluid (Drilling Fluid를 적용한 시추공의 안정성에 대한 수치해석)

  • Sin, Chun-won;Yoo, Chung-Sik
    • Journal of the Korean Geosynthetics Society
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    • v.16 no.2
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    • pp.183-194
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    • 2017
  • When a borehole is drilled, the load distributed by the removal is taken to re-establish equilibrium. As a result, the stresses around the borehole is redistributed. If there is no hydrostatic support pressure by drilling fluid (mud) introduced into the borehole, failure in the formation may take place. The mud pressure boundary that keeps the borehole stable is defined as a mud window. To predict the potential for failures around the borehole, a series of numerical analysis were performed and compared with a mud window. The effect of failure criterion and the intial stress ratio adopted on the mud window was also studied.

Using a Borehole Stability Device for Hydraulic Testing in Unconsolidated Alluvium (공벽 유지장치를 이용한 미고결 충적층의 수리특성 평가)

  • Won, Kyoung-Sik;Kim, Chunsoo;Chae, Soo-Yong;Shin, Dong-Min
    • The Journal of Engineering Geology
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    • v.26 no.1
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    • pp.15-22
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    • 2016
  • Hydraulic falling head and slug tests were carried out in an alluvium aquifer using a borehole stability device. The hydraulic testing had proved difficult in alluvial formations of sands and gravels due to borehole collapse and unstable borehole walls within the test section. This study aims to improve the hydraulic test results by using a borehole stability device. The device can minimize the collapse of borehole walls, and the use of a filter with a constant opening ratio improves the calculations per unit area of the test section. Permeability obtained from the falling head test without a borehole stability device was 8.82 × 10−5m/sec. When the borehole stability device was installed in the same test section the measured permeability increased to 4.00 × 10−4m/sec, which is 4.5 times that obtained without the borehole device. The relatively low permeability obtained using the conventional test method is attributed to the presence of a fine-grained slime generated during drilling and a reduction of the test area in the test interval due to a gradual collapse of the borehole walls. This study considers how the use of a borehole stability device to prevent borehole collapse can influence the results of hydraulic tests in alluvial formations. It is expected that the results can be used as a basis for improving the reliability and applicability of hydraulic tests performed in alluvial aquifers.

A Basic Study on Borehole Breakout under Room Temperature and High Temperature True Triaxial Compression (상온 및 고온 하 진삼축압축실험을 이용한 시추공의 파괴 거동 기초 연구)

  • Yoon, Jeonghwan;Min, Ki-Bok;Park, Eui-Seob;Jung, Yong-Bok
    • Tunnel and Underground Space
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    • v.30 no.6
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    • pp.559-572
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    • 2020
  • This paper performs laboratory experiments for borehole stability considering temperature and true triaxial stress condition, and observes a thermo-mechanical behavior of the rock under stress and temperature conditions of deep underground. China yellow sandstone and Hwangdeung granite specimens were used to perform a true triaxial compression test. Mechanical tests were carried out under nine confining pressure conditions, and thermo-mechanical tests using granite samples were carried out under six confining pressure conditions at 60-100℃. In the mechanical tests, maximum principal stress at borehole breakout was proportional to intermediate principal stress. In the thermo-mechanical tests, it was confirmed that thermal stress is added to the stress field of the borehole with the increase in temperature, resulting in additional breakout progress. To analyze the results of the laboratory experiment, Mogi-Coulomb failure criterion was used. The results of traditional triaxial compression test on cylindrical specimens and borehole breakout under true triaxial compressions matched well with Mogi-Coulomb failure criterion.

A Study on Engineering Characteristics of the Drilling Fluid Dependingon the Mix Water (배합수에 따른 안정액의 공학적 특성 분석)

  • Choi, Jung-Hyuk;Yoo, Chung-Sik;Han, Yun-Su
    • Journal of the Korean Geosynthetics Society
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    • v.15 no.4
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    • pp.43-52
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    • 2016
  • This paper presents the results of a engineering characteristic to the effect of drilling fluid with different mix designs for use in bore hole collapse prevention. The bore hole collapse prevention mechanism for the bentonite based drilling fluid was first discussed together with the effect of conditioning with different additives on engineering characteristics of bentonite based drilling fluid. As result, bentonite with polymer have a outstanding characteristics as compared to CMC Properties thickening effect In the case of sea water with attatulgite be superior to bentonite. Therefore, in this paper presented qualitative result on the performance of the drilling fluid depending on the water.

Stability Analysis for the Pohang Deep Geothermal Borehole (포항 심부 지열 시추공의 안정성 분석 연구)

  • Lee, Min-Jung;Chang, Chan-Dong;Lee, Jun-Bok;Lee, Tae-Jong;Hwang, Se-Ho
    • Geophysics and Geophysical Exploration
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    • v.11 no.3
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    • pp.204-213
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    • 2008
  • This paper presents the analysis about the stability of the Pohang deep geothermal borehole drilled in 2006. Severe wellhole instability problems such as collapse and tight hole occurred in weak rocks while drilling. Optimal mud pressure (mud window) required to prevent instability problems during drilling is obtained from analysis on in-situ stress and rock strength. The window is bounded by vertical stress in its upper limit and by either collapse pressure or pore pressure in its lower limit. Mud window varies with different types of rocks. In the top-most semi-consolidated mudstone formation, no mud window can secure borehole stability. In some weak rock types (basic dyke and crystal tuff), the borehole pressure needs to be higher by $50{\sim}60%$ than hydrostatic pressure. That means a mud density of 1.5 g/$cm^3$ or higher should be applied during drilling in order to prevent excessive collapse around the borehole.

Evaluation of Load Transfer Characteristics of Barrette Pile Based on Bi-directional Loading Tests (양방향 재하시험결과를 활용한 바렛말뚝의 하중전이특성 평가)

  • Park, Seong Wan;Lim, Dae Sung
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.2C
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    • pp.41-49
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    • 2009
  • Due to the increased size of civil infrastructure and the cost of materials, the needs exists for utilizing large sized cast-inplace piles in lieu of conventional precast piles. Among them, the barrette pile has become more commonly used in fields where a diaphragm wall is the retaining wall, to improve workability and economical efficiency, and to ensure hole stability under deep soil layers. In this paper, the bearing capacity and displacement characteristics of the barrette pile are evaluated by using the bi-directional loading test data obtained from four different sites. In addition, the design value of pile shaft resistance, ${\beta}$, is assessed with previous literatures and load transfer analysis. Finally, numerical analyses were performed to analyze the load-displacement behavior, and the interface effect on the piles, using the 3-dimensional finite element method.

Borehole Image Processing System(BIPS)를 이용한 사면 안정성 해석

  • Yu, Byeong-Ok;Kim, Byeong-Seop
    • Journal of the Korean Geophysical Society
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    • v.5 no.2
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    • pp.111-129
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    • 2002
  • Generally, investigation methods of cut slope are conucted only geological surface survey to gain engineering geological data of cut slopes. These methods have many problems such as limitations of investigation for a special area. So geophysical investigations such as geotomography, seismic and electrical resistivity methods have been used to search for failure surface in potential failure slopes or failed slopes. But investigation method using the borehole camera is recently a used method and it is thought that this method is more reliable method than other investigation methods because of being able to see by the eyes. Therefore, this paper was conducted investigations of borings and BIPS(Borehole Image Processing System) to search for potential sliding surfaces and was applied to obtain information of discontinuity on failed and potential failure slope in highway. As the results of BIPS, we could decide potential sliding surface in the slope, conducted to check slope stability and decided slope stability measures.

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A Study on Application and Stability Analysis of Spiral Pipe Nailing System (스파이럴 파이프 네일링 시스템의 안정해석 및 적용성에 관한 연구)

  • Park, Si-Sam;Park, Sung-Chul;Jung, Sung-Pill;Kim, Hong-Taek
    • Journal of the Korean GEO-environmental Society
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    • v.5 no.2
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    • pp.41-49
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    • 2004
  • In this study, a newly modified soil nailing technology named as the SPN (Spiral Pipe Nailing) system, is developed to self drilling method can apply to ground which is hard to keep shape of bore hole. And limit equilibrium analysis with simplified trial wedge method while length ratio and bond ratio being altered was performed to evaluate slope stability considered of tensile strength and bending stiffness. Also, using $FLAC^{2D}$ program, superiority of the SPN system was compared to the GSN (General Soil Nailing) system about an example section. And effects of various factors related to the design of the SPN system, such as the type of drilling method and the bit, are examined throughout a series of the displacement-controlled field pull-out tests. As a result, the SPN system is better than the GSN system in slope stability because of having larger bending stiffness, tensile strength and unit skin friction. And results of simplified trial wedge method are similar to results of TALREN 97 program, commercial limit equilibrium analysis computer software, about an example section. Consequently, it will find out of that the SPN system reduce displacements and settlements in down excavation process as well as to increase the global stability.

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An experimental study on the viscosity features of sealant (bentonite-cement slurry) in umbrella arch method (강관다단공법에 적용되는 씰링재 (벤토나이트-시멘트 슬러리)의 점성 특성에 대한 실험)

  • Sagong, Myung;Lee, Jun S.;Park, Jeongjun;Cho, Chungsik
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.20 no.5
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    • pp.773-786
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    • 2018
  • In this paper, viscosity features of sealant (bentonite-cement slurry), which is used for umbrella arch method in tunnel, were studied. The sealant must secure optimal strength and capacity for the waterproof and stabilization of borehole as well as to satisfy groutability. In this study, the variation of viscosity was measured with different mixing processes. With an increase of initial mixing period with water and bentonite mixture, the required time for the rapid increase of viscosity of the sealant is shorten. With increase of mixing period, the possibility of swelling of bentonite will increases and this can lead increase of the viscosity of the mixture. In addition, the behaviors of sealant vary with a drastic increase of the viscosity: thixotropy and rheopexy. Furthermore, the bentonite/water mixing period influences on the bleeding features of the sealant. Further study is required to introduce the guideline, which can be applicable in the field in the aspect of required capacity of the sealants and mixing processes of the ingredients.