벤토나이트 슬러리의 전기적 특성에 대한 영향인자 분석

유동주,오명학,김용성,박준범 한국지반공학회 2006 한국지반공학회논문집 Vol.22 No.10

Factors affecting the electrical properties of bentonite slurry were identified and electric conduction mechanism in slurry was examined. Electrical conductivity of bentonite and soil-bentonite slurry linearly increases with the bentonite content. Test result indicated that the change in electrical conductivity of slurry was mainly caused by dissolved cations from bentonite particles. The relationship between electrical conductivity and bentonite content was affected by the initial electrical conductivity of slurry solution and fine content in soil-bentonite mixture. Such influences were evaluated and the calibrated relationships were suggested. Based on the suggested relationship between electrical conductivity and bentonite content, bentonite content in various bentonite and soil-bentonite slurry can be quantitatively evaluated by using electrical conductivity measurement method.

해수가 슬러리 쉴드 TBM 공법 적용성에 미치는 영향

유영무,김해만,김도형,이인모 사단법인 한국터널지하공간학회 2019 한국터널지하공간학회논문집 Vol.21 No.2

Formation of filter cake with little slurry penetration into the tunnel face ground is an essential factor to successfully apply the slurry shield tunnel boring machine (TBM) for tunnelling work. However, when the bentonite slurry is in contact with seawater, it is not easy to guarantee the filter cake formation due to decrease of the swelling volume and viscosity of the slurry. In this study, in order to evaluate the effect of the seawater on the applicability of the slurry shield TBM method, the slurry injection tests were carried out with the variation of seawater percentage contained in the slurry samples as well as the variation of soil types. And then, the effect of these two factors on the slurry clogging phenomena was theoretically and experimentally figure out. As a result, it was found that the value of the slurry clogging criteria (SCC) indicating the applicability of the slurry shield TBM significantly decreases up to 67% as the percentage of seawater increases from 0% up to 20%. In addition, it was found to be necessary to take into account both the characteristics of slurry and soil types together when judging the applicability of the slurry shield TBM method by assessing the slurry penetration characteristics that will occur during tunnelling work. 슬러리 쉴드 TBM (Slurry shield TBM) 공법에서 벤토나이트 슬러리의 침투와 필터 케이크의 형성 여부는 공법의 적용성에 영향을 미치는 중요한 요소이다. 그러나 벤토나이트 슬러리는 해수와 접촉하였을 때 팽윤성과 점도가 저하되어 공법에 대한 적용성을 확보하기 어렵다. 본 연구에서는 해수의 영향에 따른 슬러리 쉴드 TBM 공법의 적용성 변화를 평가하기 위해 슬러리의 해수 비율을 다르게 하여 주입 실험을수행하였고 해수가 슬러리의 폐색 현상에 미치는 영향을 확인하였다. 그 결과, 해수의 비율이 0%에서 20%까지 증가할수록 폐색 효과에 의한 슬러리 쉴드 TBM 공법의 적용성을 나타내는 slurry clogging criteria (SCC)가 최대 67%까지도감소하는 것을 확인하였다. 또한 슬러리의 물리적 성질이 동일함에도 지반 조건에 따라 SCC값이 공법 적용에 문제가 없는 수준에서 공법 적용을 위해 슬러리에 추가적인 처리를 요하는 수준으로 변화하는 것을 통해 슬러리 쉴드 TBM의 적용성을 평가할 때 슬러리의 특성뿐만 아니라 지반 조건에 대한 고려도 필요함을 입증하였다.

Effects of Phosphate Dispersants on the Liquid Limit, Sediment Volume and Apparent Viscosity of Clayey Soil/Calcium-Bentonite Slurry Wall Backfills

Yan-Jun Du,Yu-Ling Yang,Ri-Dong Fan,Fei Wang 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.2

Soil-bentonite slurry-trench wall, usually consisting of sandy soil and Na-bentonite, is used extensively as in-situ engineered barriers for contaminant containment. Clayey soil/Ca-bentonite may be considered as an alternative backfill when Na-bentonite is scarce at some sites. Adding trace amount of phosphate dispersant to clayey soil/Ca-bentonite backfills may be advantageous to maintain the deflocculated structure of bentonite, which is benefit to minimizing increases in hydraulic conductivity of the backfills when attacked by contaminants. However, studies on the application of phosphate dispersants to the clayey soil/Ca-bentonite backfills are very limited. A series of laboratory tests are conducted for the measurements of liquid limit, sediment volume and apparent viscosity of the phosphate dispersant-amended backfills. The phosphate dispersants tested are sodium hexametaphosphate, sodium tripolyphosphate and sodium pyrophosphate with contents ranging from 0 to 2%. The results demonstrate that the values of liquid limit, sediment volume and apparent viscosity of the backfills decrease sharply when the dispersant content is relatively low (≤ 0.1 to 0.5%), while they change slightly at relatively high dispersant content (> 0.1 to 0.5%). The type and content of the dispersant as well as Ca-bentonite content have significant effects on the liquid limit, sediment volume and apparent viscosity of the backfill. The sodium hexametaphosphate is shown to have higher dispersibility compared with the others in terms of greater reduction in apparent viscosity, and its optimum content is suggested in a range of 0.1% to 0.5%. A power function is proposed which well quantifies the relationship between the measured apparent viscosity and liquid limit.

A novel calculation model for the permeability coefficient of soils conditioned with foam and bentonite slurry

Fanlin Ling,Shuying Wang,Xiangcou Zheng,Jiazheng Zhong,Yujia Chen 대한토목학회 2024 KSCE Journal of Civil Engineering Vol.28 No.5

Both foam and bentonite slurry are commonly employed in soil conditioning to prevent water spewing during earth pressure balance (EPB) shield tunnelling. A novel calculation model to estimate the permeability coefficient of soils conditioned with foam and bentonite slurry is developed. In this model, bentonite particles are assumed to adhere to the foam film in a monolayer of bridging particles, and the permeation channels within the conditioned soil are updated using the Kozeny-Carman equation. A series of permeability tests on conditioned soil, varying conditioning parameters and water heads, validate the accuracy of the model. The measured results that the value of permeability coefficient can be well captured by the calculation results, which indicates that the model can accurately predict the permeability of soil conditioning by foam and bentonite slurry. While there is a slight reduction in accuracy for conditioning states with high foam and bentonite slurry injection ratios, the model remains conservative for tunnelling engineering safety due to calculated values consistently exceeding measured ones. Furthermore, the model performs well in cases of foam-conditioned soil from previous studies. Additionally, the model underscores the significant influence of bentonite slurry on the permeability coefficient by altering soil grain gradation.

Influence of Cutting Tools on Filter Cake Formation during Slurry Shield Tunnelling

Jiahua Mao,Dajun Yuan,Dalong Jin,Shengnan Liu 대한토목학회 2021 KSCE Journal of Civil Engineering Vol.25 No.6

The filter cake on excavation face would be destructed periodically by cutting tools during slurry shield tunneling. The broken filter cake has a risk for face stability. The influence of cutting tools on filter cake was studied in this paper. A slurry-soil interaction model based on a multiphase flow theory which considers the solid particles and fluid in slurry was developed. The whole process of slurry penetration and filter cake formation on the excavation face of slurry shield can be described by this model. The motion state of cutting tools can be combined with this model and the effect of cutting tools on the slurry-soil interaction and pressure transfer mechanism was analyzed. Subsequently, the comparative calculations were presented to discuss the influence of tunneling parameters and the design of cutting wheel on filter cake formation during slurry shield tunnelling. The results indicate that the total area of filter cake on excavation face increases with the decreasing of revolutions per minute of cutting wheel and shield machine advance rate. The area ratio of filter cake on the center of excavation face always larger than other zone due to the lesser amount of cutting tools within one track in the center of cutting wheel. The results can provide a better understanding of how to set the shield tunneling parameters and design the layout of cutting tools for the stability of tunnel face.

Measurement of hydraulic properties of bentonite cake formation deposited on base soil medium

Lee, D.,Kim, K.,Lee, H.,Lim, J.,Lee, I.M.,Choi, H. Elsevier 2016 Applied clay science Vol.123 No.-

<P>Bentonite cake and filter cake on the surface of porous media result from the filtration of stabilizing slurry into the adjacent porous formation. This paper provides measurements of hydraulic conductivities of bentonite cake formed on Korean standard sand under various pressure levels. Two types of bentonite (Tixoton and Bentonil GTC4) were used to create the slurries with three different concentrations (4, 6, and 8% by weight). An estimation of the hydraulic conductivity of the bentonite cake based on the filtration theory was carried out. The range of hydraulic conductivities of the bentonite cake was from 2.1 x 10(-11) m/s to 5.7 x 10(-10) m/s. The hydraulic conductivity of the bentonite cake deposited on Korean standard sand were compared with that of the bentonite cake deposited on filter paper to show the effect of the filter medium. The slurry concentration of 6% seems to be a value that most stimulates the effect of the filter medium on the permeability of the Bentonil GTC4 bentonite cake. In addition, a simple approach was developed to characterize the hydraulic properties of the filter cake, which has usually been confused with the bentonite cake in recently published literature. (C) 2016 Elsevier B.V. All rights reserved.</P>

수정 fluid loss 시험을 이용한 연직 차수벽에 생성된 벤토나이트 필터케익 특성 평가

웽테바오,최항석,박문서,임지희,한신인 한국지반공학회 2011 한국지반공학회논문집 Vol.27 No.2

During the construction of vertical cutoff walls, filtration of bentonite slurry into the adjacent soil formation fabricates a layer of bentonite filter cake on the wall surface. The bentonite filter cake possesses much lower hydraulic conductivity compared to that of backfill materials in the cutoff wall. Hydraulic conductivity of bentonite filter cakes formed with three different types of bentonites has been measured by performing the modified fluid loss test under various pressure levels. Three different mixture ratios, 4, 6, and 8%, were selected for fabricating bentonite filter cakes to represent common field conditions. Two analysis methods for interpreting the experimental data from the modified fluid loss tests were employed to estimate hydraulic conductivity of the bentonite cakes. The range of hydraulic conductivities of the three bentonite cakes is between 2.15×10-11 m/s and 2.88×10-10 m/s which is 1 to 2.7 orders of magnitude lower than that of the design cutoff wall backfill. The stress distribution and thickness of the bentonite cakes were also evaluated in this paper.

소성가공한 폐 벤토나이트 슬러리의 건축재료 활용방안에 관한 기초적 연구

김효열,안화행,정영호 동의공업대학 2001 論文集 Vol.27 No.1

This study aims to propose a fundamental report for pozzolan reaction of discarded Bentonite slurry by heat-treatment as concrete mineral admixture. To find out pozzolan reaction ability of discarded Bentonite slurry by heat-treatment, the experiment is excuted Phenolphtalein test, setting test, pH test and the analysis by X-ray diffractor. As a result of this study, discarded Bentonite slurry can be utilized as concrete mineral admixture by heat-treatment and especially, pozzolan reaction ability of discarded Bentonite slurry is superior to the situation of 500℃·60min, 600℃·60min and 700℃·60min.

도로공사 이수식 쉴드 TBM 굴착토 및 필터케이크 재활용방안 연구

남성민,박서영,안병철 사단법인 한국터널지하공간학회 2022 한국터널지하공간학회논문집 Vol.24 No.6

In order to excavate underground tunnel most safely such as Han river, the slurry shield TBM method is applied to cope with face of high water pressure for many metro projects. In downtown subway project most of excavated soil is discharged externally whereas in road construction excavated soil is used as filling materials so it becomes important factor for success of the project. After excavated soil, weathered rock and soft rock are discharged with bentonite through discharge pipe to slurry treatment plant then those soils are separated in separation plant according to those size. Fine grained soil has been discarded together with filter cake but it is not toxic and can be mixed with coarse aggregate in proper ratio so this study is performed to find use of qualified filling material to meet quality standard. Therefore, in this study, legal standards and quality standards for the utilization of excavated soil of the slurry shield TBM method were examined and test was conducted to derive recycling way for filter cake and aggregate. And a plan for using it as a filling material for road construction was derived. Because bentonite is a clay composed of montmorillonite, and the excavated soil in the tunnel is also non-toxic, disposal of this material can waste social cost so it is expected to be helpful in the underground space development project that carries out the TBM project by recycling it as a valuable resource. 한강과 같은 하저지반을 안전하게 굴착하기 위해서는 고수압 막장면에 대응할 수 있는 이수식 쉴드 TBM 공법을 적용한다. 이수식 쉴드 TBM 공법은 지하철 프로젝트에 널리 활용되어 왔는데 도심지 지하철 공사는 지하에서 연결되기 때문에 굴착토를 대부분 전량 사토해왔으며 필터케이크(벤토나이트)도 폐기물처리를 했다. 이와 달리 도로공사는 절성토의 최적화를 위해 굴착되어 나온 토석을 외부로 반출하는 것이 아니고 대부분 성토재로 활용하는 특징이 있어 굴착토의 활용방안이 프로젝트 성공의 중요한 요소가 된다. 이수식 쉴드 TBM 공법에서 굴착토는 이수재로 사용하는 벤토나이트와 굴착된 토사, 풍화암, 연경암 등이 섞여서 배니관을 통 해 이수처리플랜트로 운송되면 이수처리플랜트에서 처리과정을 거쳐 크기별로 분리 배출된다. 이러한 굴착토 중 세립질의 토사는 필터케이크와 함께 폐기되어 왔으나 그 성분에 독성이 없고 조립토와 적정 비율로 혼합하여 사용하면 성토재의 품질기준을 만족할 수 있어 그 활용방안에 대한 연구를 수행하였다. 본 연구는 이수식 쉴드 TBM 공법의 굴착토의 활용에 있어 제도적 ‧ 기술적 기준을 고찰하여 필터케이크와 골재를 도로공사의 성토재로 활용하는 방안을 도출하였다. 벤토나이트는 몬모릴로나이트로 구성된 점토이며 터널 원지반의 굴착토 또한 독성이 없는 상태로 이를 폐기물 처리하는 것은 사회적 비용이 낭비될 수 있기에 오히려 귀중한 자원으로 재활용하여 향후 이수식 쉴드 TBM 프로젝트를 수행하는 지하공간 개발사업에 도움이 되고자 기대한다.

시추 안정액 배합설계에 따른 공벽 붕괴방지 효과에 관한 실험적 연구

유충식,최정혁,한윤수 한국지반공학회 2015 한국지반공학회논문집 Vol.31 No.1

This paper presents the results of a reduced-scale physical model investigation into the effect of drilling fluid withdifferent mix designs for bore hole collapse prevention. The bore hole collapse prevention mechanism for the bentonitebased drilling fluid was first discussed together with the effect of conditioning with different additives on engineeringcharacteristics of bentonite based drilling fluid. Reduced-scale model tests were then carried out considering field proceduresfor cases with a decomposed granitic soil with 20% fines and a sand with various drilling fluids with different mix designs. The results indicated that the addition of polymer to the bentonite based drilling fluid decreases the amount of drilling fluidinjected, the drilling fluid infiltration thickness and increases the final depth of excavation. Also revealed is that the effectof polymer on the performance of drilling fluid is more pronounced in the decomposed granite soil with 20% fines thanthe sand. Practical implications of the findings from this study are discussed in great detail.