Effect of Clogging on Large Strain Consolidation with Prefabricated Vertical Drains by Vacuum Pressure

Yupeng Cao,Jianwen Xu,Xia Bian,Guizhong Xu 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.10

Clogging will inevitably occur while using vacuum preloading method to process super-soft soils with high water content. How to quantitatively evaluate the effect of clogging on the consolidation behavior is a key issue to be solved. Based on NALSC (negative axisymmetric large-strain consolidation) model, considering the “internal clogging” and the “external clogging”, a calculation method by using parameter “clogging rate” to reflect clogging problem is proposed for single-well consolidation theory. Effects of clogging rate and clogging occurred time on Us (degree of consolidation defined by strain) and Up (degree of consolidation defined by stress) are investigated. Differences of the effect of clogging on consolidation degree are determined between large-strain and small-strain consolidation theory. The results show that, the larger the clogging rate, the smaller the degree of consolidation of the soil at the same consolidation time. Effect of clogging on Up is greater than Us. The earlier the clogging occurs, the smaller the degree of consolidation at the same clogging rate. Influences on the degree of consolidation for large-strain and small-strain theory are the same. Consolidation rate of soil is determined to a certain extent by the “generalized clogging parameter μ”. The “external clogging” has a greater influence on the degree of consolidation than the “internal clogging” at the same clogging rate.

천변여과지 모형에서 여재모래의 폐색현상 실험연구

정재민(Jae Min Jeong),김승현(Seung Hyun Kim) 大韓環境工學會 2013 대한환경공학회지 Vol.35 No.9

천변여과지에서 표류수 유속이 여재의 폐색에 주는 영향을 파악하기 위하여 파일럿 규모의 실험을 수행하였다. 표류수 유속을 0~40 cm/sec 범위에서 단계적으로 변화시키면서 설비를 운전하여 폐색이 발달하는 현상을 관측하였고, 관측결과를 수치해석코드로 해석하여 폐색계수를 얻었다. 연구결과 이 범위의 표류수 유속에서는 표류수 유속이 폐색발달에 영향을 주지 않는 것으로 나타났고, 폐색은 주로 표층에서 발생함을 알 수 있었다. 여과수 산출율이 5 m3/m2-day에서 3 m3/m2-day까지 감소하는 동안 표층 50 cm에서의 폐색계수는 약 30,000 sec까지 증가하였으며, 이는 전체 여재두께 2.4 m가 가지는 폐색계수의 87%에 해당되었다. 표층 50 cm의 폐색계수에서 표면폐색이 90% 정도를 차지하여 내부폐색은 약 10%에 불과함을 알 수있었다. 운전지속에 따라 표면폐색은 심화되었지만 내부폐색은 일정함도 알 수 있었다. 또한, 폐색이 진행되어도 여과깊이에 따른 탁도분포는 일정함을 알 수 있었다. A pilot-scale sand-box experiment was performed in order to investigate the effect of cross-flow velocity on the clogging of the filter sand in a model filtration pond. The clogging phenomenon was observed during the operation with the cross-flow varied in stages in a range of 0~40 cm/sec, and the experimental result was analyzed using a numerical code. Results showed that the cross- flow velocity in this range had no influence on the development of clogging and that clogging occurred mostly on the filter-surface. It was found that while the production rate decreased from 5 m3/m2-day to 3 m3/m2-day the clogging coefficient of the top 50 cm layer increased up to about 30,000 sec, which corresponded to 87% of the clogging coefficient of the total 2.4 m layer. Of the clogging coefficient of the top 50 cm layer, surface clogging constituted 90% while the other 10% was intermediate clogging. It was also found that the surface clogging increased while the intermediate clogging remained constant as the operation continued, and that filtrate turbidity along the filtration depth remained constant in spite of the increase in clogging.

Clogging mechanism of poly(styrene) particles in the flow through a single micro-pore

Kim, Youngseok,Ahn, Kyung Hyun,Lee, Seung Jong Elsevier 2017 Journal of membrane science Vol.534 No.-

<P><B>Abstract</B></P> <P>In this study, the clogging mechanism of poly(styrene) particles in the flow through a single micro-pore was investigated. Together with the microscopic observation, the pressure drop was also measured. The pressure drop fluctuated according to the amount of particles deposited inside the channel. When the particles deposited and blocked the channel, the channel was clogged and the pressure drop increased sharply. During the clogging process, the particles were often detached by the flow, and interesting behaviors, such as “rolling” and “stick and detach”, were found to be the key factors that determine whether the clogging completely occurs or not. Above a certain flow rate, the channel was not clogged and the pressure drop did not increase further. The particles deposited in the upstream had an influence on the flow path. When the particles were deposited in the upstream, the flow detoured and the vortex was formed. The effect of viscosity was examined by controlling the concentration of glycerol solution. As the viscosity and the flow rate increased, the shear stress applied to the particles became larger and it was more difficult for the particles to get accumulated. The normalized clogging pressure drop decreased exponentially with shear stress. It was unity above a certain shear stress, in which the particles did not clog the channel completely.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The clogging mechanism of poly(styrene) particles in the flow through a single micro-pore was investigated. </LI> <LI> The particles deposited near the contraction caused the pressure drop to increase and the formation of the vortex. </LI> <LI> As the shear stress increased, it became easier for the particles to be washed away and the channel was rarely clogged. </LI> <LI> There exists a critical stress that determines whether the clogging will occur or not. </LI> </UL> </P>

연주공정 침지노즐 막힘 감지 기술

김기원,강영훈,신남호 제어로봇시스템학회 2011 제어로봇시스템학회 국내학술대회 논문집 Vol.2011 No.5

The objective of this study is to detect a blocked state(clogging) of SEN during continuous slab casting. SEN is installed between tundish and mold to transfer melting steel. A clogging of SEN gives bad effect to productivity and slab quality. So that clogging must be exactly noticed, that nozzle must be changed when nozzle is clogged. In this study, we develop a technology to notice nozzle clogging through method which makes interrelation between frequency variation and clogging. To realize that method, laser vibrometer is installed near to SEN and FFT is done to analyze frequency. We identify that frequency become lower when nozzle is clogged. Reasonable match result is made between estimation clogging thickness and real measured clogging thickness. That result has been guided to operators as a reference tool for identifying a real clogged thickness of SEN.

Experimental Investigation of the Effects of Aperture Ratio, Chamber Pressure and Soil Conditioning on the Clogging Behavior of EPB Shields

Gongyun Xu,Yong Fang,Yubo Wang,Liupan Dou,Ruyong Deng,Fangchuang Geng 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.10

Earth pressure balance (EPB) shield excavation in cohesive strata frequently encounters cutterhead clogging, consuming time and economic costs. Engineering practice shows that cutterhead aperture ratio, soil chamber pressure and soil conditioning have important influences on the clogging behavior of EPB shields. In order to study these factors, a series of laboratory tests were conducted using a setup that can closely simulate the shield tunnelling process. The indicators analyzed were excavation speed, torque, specific energy and soil distribution on the cutterhead. The results indicate that cutterhead aperture and cutter arrangement are important factors in clogging potential. Clogging creates a significant reduction in excavation speed. Torque is not a sensitive parameter reflecting clogging because of the effect of the consolidated soil on the cutters. The presence of soil chamber pressure makes it difficult to remove the clogging through the shearing action of the excavation surface. The injection of a sufficient amount of foam can reduce the risk of shield clogging, but it may lead to an increase of soil adhesion on the cutterhead. The amount of soil that adheres to the cutterhead cannot be used as a classification criterion for clogging potential. Based on experimental phenomena and established studies, a mechanical model called ‘beam-bridge’ was proposed to study the behavior of the soil through the cutterhead opening and damage form of clogging. The results will help to the excavation control of EPB shields.

도시 지역특성을 고려한 빗물받이 유입구의 막힘계수 산정

김정수,송주일,윤세의,Kim. Jung-Soo,Song. Ju-Il,Yoon. Sei-Eui 한국방재학회 2007 한국방재학회 학술발표대회논문집 Vol.2007 No.1

Urban storm water collection and conveyance systems are critical components of the urban infrastructures. During a storm event, street grate inlets are usually loaded with debris by the first-flush runoff volume. Grate inlets are subject to clogging effects. Effective interception area of grate inlets was decreased by clogging. It also decreased the interception capacity of grate inlets and increased the inundation area in street. Therefore, it is necessary to analyze the clogging characteristics and interception capacity change by clogging for appropriate design and management of grate inlets. In this study, field survey was executed to investigate debris and clogging pattern of grate inlet in 9 areas. The clogging factor with consideration of urban area characteristics was estimated with the field survey results.

도심 강우유출수 침투시설 다공질 여재의 부유물 폐색 모델링

이병식,김이형,이관호,전평구,Segismundo Ezequiel Q 한국방재학회 2014 한국방재학회논문집 Vol.14 No.6

Infiltration facilities are applied increasingly as effective BMPs to the urban stormwater control. The important functions of the facilitiesare surface flow reduction, contaminants elimination and aquifer recharge resulting from filtration, retention and infiltration ofstormwater by porous media. A major obstacle in operating infiltration facilities is clogging. Filters of porous media in the facility areclogged by deposition of sediment over time. Clogging reduces infiltration rate and lifespan of the facility. Clogging, thus, needs to beconsidered as one of the important design factors in constructing infiltration facilities. In this study, 3 clogging models were chosen tosimulate clogging, which developed in different disciplines, environmental and geotechnical engineering. Since the models weredeveloped initially for fine media, applicability to coarse media interested in this study needed to be examined. To examine the applicabilityof models, analytical procedures of models were thoroughly reviewed. Parametric studies were also conducted to determineappropriate input parameters. Finally, the models represented relatively appropriate applicability to estimate clogging developed in anartificial infiltration as well as a real infiltration testing conditions. Although further studies are still needed for considerable aspects ininput parameters and equations, the models could be suggested as effective analytical tools to estimate clogging developed in infiltrationfacilities of urban stormwater. 비점오염 관리 및 도시 물 순환 체계 개선을 위한 효과적인 환경시설로서 침투시설의 적용이 증가되고 있다. 침투시설은 다공질 여재를 통해 강우유출수를 여과, 저류 및 침투시켜 표면유출수 저감, 오염물질 제거, 지하수 충전 등의 주요 기능을 수행한다. 이 시설의 운영에 있어 주요 문제는 폐색현상이다. 시설 내 다공질 여재 필터가 시간에 따른 퇴적물 증가로 인해 폐색된다. 폐색은 시설의 침투율과수명을 저하시킨다. 따라서 폐색현상은 침투시설 건설 시 필히 고려하여야 할 중요한 설계조건 중의 하나다. 이 논문에서는 환경, 지반등 서로 다른 학문분야에서 개발된 3가지 폐색모델을 선정하였다. 모델들이 당초 입경이 작은 여재에 대해 개발되었으므로 이 논문에서 다루는 굵은 여재에 대한 적용성 검토가 필요하였다. 적용성 검토를 위해 모델 해석 과정을 상세히 검토하였다. 적정한 입력자료를결정하기 위해 영향분석도 수행하였다. 결과적으로 모델들은 가상 침투실험 조건 및 실제 실험조건에서 발생하는 폐색현상 모델링에있어서 적정 수준의 적용성을 가지고 있음을 보였다. 입력자료와 방정식 등에 대한 후속 연구가 요구되지만 이 논문에서 다룬 모델들을 도심 강우유출수 침투시설에서 발생하는 폐색을 추정하기 위한 효과적인 해석방법으로 제안할 수 있었다.

석탄회 혼합 모래필터의 폐색 예측을 위한 신경망모델

이병식(Byungsik Lee) 한국방재학회 2023 한국방재학회논문집 Vol.23 No.3

Infiltration filters of LID facilities are frequently confronted with clogging of pores by contaminants. To avoid malfunctioning of LID facilities, filters should be maintained according to the degree of clogging. In this study, clogging was characterized by curves representing the correlation between infiltration rate and infiltration quantity. To estimate the degree of clogging, a regression neural network model was developed to estimate the label (infiltration quantity) corresponding to the selected features (ash mix ratio, infiltration rate, and variation of infiltration rate). According to the results obtained from the evaluation of accuracy and applicability of the final model trained over the whole training dataset, the following conclusions were drawn: 1) the training of the final model was verified to be correct according to mean absolute errors of 0.00445 and 0.00491 for the training and test datasets, respectively; 2) the final model could be applied to estimate multiple, multivariate clogging curves for arbitrary ash mixing ratios and trained range of time series in terms of infiltration rate; 3) given that the final model could not estimate the clogging curve for future time steps for which the model was not trained, a CNN model or LSTM-RNN model are suggested as an alternative.

다짐말뚝 시공 시 공극 막힘 현상 분석 연구

최정호,박성진,추연욱,김일곤,김병규 한국지반공학회 2022 한국지반공학회논문집 Vol.38 No.4

A series of model tests were performed in this study to demonstrate the clogging mechanism created during the installation of a compaction pile to improve soft ground. The application of an air-jet to extrude sand or aggregates from a casing during the installation of a compaction pile imposes a remarkably high-pressure difference between the composite soil layers of clay and sand (or aggregates), resulting in severe clogging. Therefore, a one-dimensional testing system was developed to simulate composite soil layers consisting of clay and sand (or aggregates) and to apply a high-pressure differential at both boundaries, thus replicating the extrusion process used in compaction pile installation. Herein, the performance of two construction materials for compaction piles of crushed stone and grading-controlled aggregates was compared. A series of one-dimensional model tests were performed under multiple pressure settings, with clogging depth and permeability measured in each case. Results indicate that, blinding clogging mechanisms and blocking defined by previous studies were observed for crushed stone, and a new mechanism of “infiltration” was revealed and defined. Whereas, the controlled aggregates performed excellently against clogging because only blinding was observed.

Engineering Characteristics of Crushed Stone and Coal Ash Mixture Compaction Piles

도종남,천병식 대한토목학회 2012 KSCE Journal of Civil Engineering Vol.16 No.4

Crushed stone compaction piles are widely used for soft ground improvement because the installed piles improve both overall composite capacity and discharge capacity. However, discharge capacity declines when clogging occurs due to clay penetrating into the voids of crushed stone compaction piles over time. In this study, research was performed to reduce clogging and minimize voids in a crushed stone compaction pile constructed in soft ground. An optimal mixing ratio was determined based on large scale direct shear tests that were conducted to identify strength and permeability levels that would provide the best mixing ratio of crushed stone and bottom ash. The test results indicated that the highest internal friction angles were obtained at an 80:20 mixing ratio of crushed stone and bottom ash. The internal friction angle declined when the mixing ratio of the bottom ash became greater than 20%. The results of clogging tests indicated that a mixture of 80:20 crushed stone and bottom ash is more effective than pure crushed stone for reducing clogging.