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This paper describes an experimental investigation on the use of ground granulated blast furnace slag (GGBFS) and lime as stabilizers for cement-bentonite (CB) slurry used in constructing vertical barrier walls. The primary objective is to develop a blended material, which can reduce the permeability and also enhance the strength of CB slurry walls with a shortened curing time. Mixtures comprising various proportions of cement, bentonite, GGBFS, and lime were prepared and tested for particle size distribution (PSD), liquid limit, plastic limit, permeability, unconfined compressive strength (UCS), and constrained modulus. For each mixture, the effect of varying curing time on the results of the aforementioned tests was also investigated. The research results demonstrate that blending CB with optimum fractions of GGBFS and lime lead to decreased permeability and increased UCS of the mixture, without any adverse consequences. Thus, subject to satisfaction of other requirements, it is concluded that a potenti...

Soil–bentonite slurry-trench cutoff walls using backfill consisting of on-site sandy soil and Na-bentonite are extensively used as engineering barriers for the purpose of achieving relatively low hydraulic conductivity. The amendments such as zeolite to backfill are considered to improve the contaminant sorptive capacity. At some sites, local clayey soil, Ca-bentonite and natural zeolite may be available for an alternate backfill. However, studies on the workability (in terms of slump), compressibility and hydraulic conductivity of such zeolite-amended clayey soil/Ca-bentonite backfills for the cutoff walls are very limited. This paper presents a comprehensive laboratory investigation on the workability, compressibility, and hydraulic conductivity of fine-grained zeolite-amended clayey soil/Ca-bentonite backfills using several series of slump and oedometer tests. Kaolin is used as the model clayey soil, and it is amended with various amounts of Ca-bentonite (7.8–8.4%) and zeolite (10–40%) to prepare zeolite-amended kaolin–bentonite backfills. The test results are compared with previous studies on zeolite-amended sandy soil/Na-bentonite backfills as well as compacted zeolite–bentonite liners to assess the effects of zeolite content and zeolite grain-size on the compressibility and hydraulic conductivity. The results indicate that the water content required to achieve a target slump (100–150 mm) for the backfills increases with increasing zeolite content. Liquid limit can be a useful index for a preliminary estimation of the water content required to achieve the target slump for the backfills presented in this study and zeolite-amended sandy soil/Na-bentonite backfills reported in previous studies. The results reveal that the hydraulic conductivity of the zeolite-amended clayey soil/Ca-bentonite backfills with void ratio ranging from 0.54 to 1.45 is generally lower than the typical regulatory limit (10− 9 m/s). The addition of fine-grained zeolite has insignificant influence on the compressibility and hydraulic conductivity of both clayey soil/Ca-bentonite and sandy soil/Na-bentonite backfills. A proposed empirical method based on the framework of Kozeny–Carman equation can predict the hydraulic conductivity of zeolite-amended clayey soil/Ca-bentonite backfills values within the range of 1/3 to 3 times those calculated from the oedometer tests. The proposed method is also shown to estimate the hydraulic conductivity of the compacted zeolite–bentonite liners from previous studies with reasonable accuracy. Additional research is recommended to evaluate the proposed zeolite-amended backfill using tap water and also by direct measurement of hydraulic conductivity using falling-head or constant-head testing method.

The ageing and stability behaviour of Bentonite slurries were evaluated under the influence of Mg2 +, Ca2 + and Ba2 + ions at concentration ranging from 0.005 to 1 M. Stable gels were formed at low metal ion concentration of

A remediação de contaminações em águas subterrâneas e no solo tem sido alvo de estudos devido ao alto impacto e custo de recuperação. Um dos métodos utilizados para a contenção de plumas contaminantes é a cortina vertical. O presente trabalho tem por objetivo escolher a partir de dados de propriedades índice, hidráulicas, físico-químicas e mecânicas, o melhor material, entre quatro alternativas, a ser utilizado nas cortinas verticais com a função de contenção de plumas contaminantes. Os quatro tipos de materiais analisados foram um solo natural (SN), um solo natural com bentonita (SB), um solo natural com bentonita e cimento (SBC) e bentonita pura (B). O Método de Análise Hierárquica (AHP) foi utilizado como ferramenta de tomada de decisão para escolha da melhor solução de contenção, sendo utilizados dois critérios (caracterização e permeabilidade) e três subcritérios para a caracterização (caracterização geotécnica, físico química e resistência). Devido à indisponibilidade de dados de resistência da bentonita foram realizadas três análises, as quais indicaram o solo natural (SN) como sendo a melhor alternativa devido à influência relativa da permeabilidade.

Understanding the changes in permeability of soil, when soil is subjected to high confining pressure and flow pressure, which may alter the textural and geomechanical characteristics of soil, is of great importance to many geo-engineering activities such as, construction of high-rise buildings near the coast or the water bodies, earthen dams, pavement subgrades, reservoir, and shallow repositories. It is now possible to evaluate the changes in permeability of soil samples under varying conditions of confining pressure and flow pressure using flexible wall permeameter (FWP). In the present study, investigation was carried out on a cylindrical sample of granular soil employing FWP under varied conditions of confining pressure (σ3)—50–300 kPa, which can simulate the stress conditions equivalent to depth of about 20 m under the earth’s crust, and a flow pressure (fp)—20–120 kPa, which is mainly present near the small earthen embankment dams, landfill liners, and slurry walls near the soft granular soil with high groundwater table. The obtained results indicate a linear relationship between hydraulic conductivity (k) with effective confining pressure (σeff.), k, decreasing linearly with an incremental change in σeff.. Further, k increases significantly with an increase in fp corresponding to each σeff., and q increases significantly with increase in the fp corresponding to each (σ3). It was also observed that corresponding to the low fp of 20 kPa, the reduction in k is nonlinear with σ3. The percentage reduction in k is observed to be 9, 13, and 27% corresponding to σ3 of 50–100, 100–200, and 200-300 kPa, respectively.

In the concrete diaphragm wall (CDW) construction, the L-shaped diaphragm wall is used to form an enclosed retaining structure. Due to the complicated stress change in trenching, the L-shaped trench has the lower stability than the regular rectangular trench. This paper investigates the trench instability during the L-shape slurry trench excavation based on the upper bound analysis. A 3D kinematically admissible mechanism defining the failure for the L-shaped trench is constructed. The safety factor on the trench and corresponding failure pattern are obtained through the upper bound analysis. The influence of trench geometries and the soil properties on the trench stability are discussed by the parameter analysis.

Bei der Herstellung von Schlitzwänden im Zweiphasenverfahren ergeben sich aus baubetrieblichen Gründen immer wieder Situationen, in denen Schlitze suspensionsgestützt lange stehen bleiben, bevor mit dem Betoniervorgang begonnen werden kann. Es herrscht die Vorstellung, dass sich mit zunehmender Standzeit unter Flüssigkeitsstützung der Filterkuchen an der Schlitzwandung, welcher später zwischen der fertig betonierten Wand und dem Boden verbleibt, verstärkt ausbildet und reibungsmindernde Eigenschaften hat. Aus dieser Annahme heraus wird in den Regelwerken verlangt, dass der Wandreibungswinkel für die statische Berechnung der Schlitzwand bei planmäßig langen Standzeiten des suspensionsgestützten Schlitzes von mehr als 30 Stunden mit k = 0 anzusetzen ist. Bleibt die Standzeit des suspensionsgestützten Schlitzes dagegen unter 30 Stunden, ist je nach Beschaffenheit des Bodens ein Ansatz des Wandreibungswinkels ohne weiteren Nachweis von bis zu k = ½ ‘k möglich. In diesem Beitrag werden Untersuchungen an Filterkuchenmaterial vorgestellt, das bei einer laufenden Baumaßnahme an zwei Schlitzwandlamellen gewonnen wurde. Diese Lamellen unterscheiden sich bei sonst gleichen Randbedingungen durch unterschiedlich lange Standzeiten des suspensionsgestützten Schlitzes (16 Stunden, 70 Stunden). Die Untersuchungen zeigen, dass sich bei den anstehenden Verhältnissen infolge der längeren Standzeit keine signifikanten Änderungen in der Ausbildung und in der Zusammensetzung des Filterkuchens ergeben.

Conducting deep excavations for underground construction inside the cities requires diaphragm wall due to space limitation. The ground surface is affected by the trenching process. The construction of the diaphragm walls near deep foundations may not be avoided specially in the crowded cities. This research focuses on the deflection and bending moment of piled foundations near slurry trench. Since the trench is considered as a three-dimensional problem, a three-dimensional numerical analysis was used in this research. It was conducted using a commercial analysis software known as FLAC 3D. The numerical analysis method was verified using two case histories, one in Hong Kong and another one in Giza, Egypt. The results from the numerical analysis were in quite a good contrast with the field data results. This indicates that the trenching process could be numerically modeled with the proposed method and provides good results. The verified numerical analysis method was used to conduct a numerical parametric sric study that discusses the effect of multiple panels on adjacent connected pile groups or piled raft foundation. The parametric study showed that the pile deflection and bending moment are affected by the panel construction stages, pile location within the foundation. The pile deflection and bending moment are affected by the stages of construction. The piles near the trench are affected by the trenching process, while the piles far from the trench are affected by the dragging force of the pile near the trench.

The paper presents the construction of anchorage foundation for the Second Humen Bridge. Overview of the project is descripted briefly for the Nizhou islands anchorage. This gravity anchorage is of the dimension as the Akashi strait suspension bridge. Retaining by diaphragm slurry wall top-down construction of inner lining-wall is adopted by the designer with the excavation of foundation pit. During excavation monitoring system for the slurry wall are installed. The measurements of the slurry wall include its inclination, nearby ground settlement, earth pressure on it with depth, as well as stress in reinforcement bars. Level of ground water outside foundation pit is also observed daily. These data could provide the on-site control of safe excavation, and could furthermore verify the design assumption later on.

Diaphragm walls are normally used for the deep excavations and underground construction inside the cities. The trenching process of diaphragm walls causes deformation in the ground surface. The construction of the diaphragm walls near deep foundations may not be avoided specially in the crowded cities. This research focuses on the deflection and bending moment of piled foundations near slurry trench. Since the trench is considered as a three dimensional problem, a three-dimensional numerical analysis was used in this research. It was conducted using a commercial analysis software known as FLAC 3D which is based on the finite different analysis method. Verification was made for the numerical analysis method using two case histories, one in Hong-Kong and another one in Giza, Egypt. The results from the numerical analysis were in quite a good contrast with the field data results. This means the trenching process could be numerically modeled with the proposed method and provides good results. The verified numerical analysis method was used to conduct a numerical parametric study that discusses the effect of a single or double panel(s) on the nearby piled foundation. The parametric study showed that the pile deflection and bending moment are affected by the panel length, pile diameter, pile location from the trench, groundwater level and the existence of a weak soil layer that could cause reduction in slurry pressure. The panel thickness did not show any influence on the pile bending moment or deflection. The decrease of the panel length and controlling the slurry level will reduce the influence of trenching on nearby piles. Lowering the groundwater level before trenching could probably reduce the influence on the pile as well.

Bentonite cake is commonly fabricated on trench surfaces that is originated from bentonite slurry during trench excavation for slurry wall construction. Construction defects in the soil-bentonite slurry wall such as insufficient keying to less permeable strata and highly permeable “windows” also may occur due to inappropriate construction procedures or improperly mixed soil-bentonite backfill. In this study, separate numerical models were developed to simulate the groundwater flow and contaminant transport through the soil-bentonite slurry walls of typical geometries with consideration of the bentonite cake and/or construction defects. Results of the groundwater simulations showed that the bentonite cake has no effect in the key insufficient cases. In the keyed wall cases, the bentonite cake with very low hydraulic conductivity significantly impedes groundwater flow through the wall. The presence of bentonite cake not only remedies the “window” defects but also renders the wall construction more effective in sealing the groundwater flow. In terms of contaminant transport, the steady-state normalized flux of a hypothetical non-reactive contaminant through the wall can be reduced by 13% to 62% along with the presence of bentonite cake in the most critical scenario. For the typical inorganic and organic (i.e., cadmium and toluene) contaminant transports, the bentonite cake can lessen the steady-state mass flux by 16% to 20% through a unit length of the slurry wall. These results show the significance of bentonite cake in a soil-bentonite slurry wall construction.

article Soil-bentonite vertical cutoff walls, consisting of a sandy soil mixed with Na-bentonite as backfill, are used extensively as engineered barriers for contaminant containment. However, suitable sandy soil and Na-bentonite may not be available at some sites. Consequently, locally available clayey soil and Ca-bentonite may be considered as an alternative backfill. The use of clayey soil/Ca-bentonite backfill may be advantageous to achieve relatively low hydraulic conductivity, which has equivalent performance as that of conventional sandy soil/Na-bentonite backfills. However, studies on the compressibility and hydraulic conductivity of these clayey soil-bentonite backfills are very limited. This paper presents a comprehensive laboratory investigation on the compressibility and hydraulic conductivity of clayey soil/Ca-bentonite backfill through a series of oedometer tests. Kaolin is used as the control clayey soil and it is amended with different contents of Ca-bentonite, 0 (kaolin alone), 5, 10, and 15% (by dry weight basis), to prepare the clayey soil/Ca-bentonite backfills. The initial water contents for the backfills are selected to be 0.75, 1.0, 1.25, and 1.50 times their corre- sponding liquid limits. The results reveal that the backfills exhibit a noticeable inverse 'S' shaped e-log(σ') compression curves attributed to the existence of the remolded yield stress (σ'yr). The compressibility, in terms of σ'yr and the compression index (Cc), is significantly affected by the initial water content and bentonite content.The voidratioataneffectiveverticalcompressionstress of 1 kPa (denotedase1) isa useful characteristic parameter touniquely correlate withCcfor theclayeysoil/Ca-bentonitebackfills inthis study as well asfor sandy soil/Na-bentonite and sandy soil-clay backfills that are reported in previous published studies. Unique relation- ships are also foundbetween the σ'yr,initial voidratio(e0), e1, andthevoidratioatliquidlimit(eL).The hydraulic conductivity of the clayey soil/Ca-bentonite backfills is significantly reduced by the bentonite content; generally to less than 10 �9 m/s. An empirical method based on the framework of Kozeny-Carman equation is proposed to predict the hydraulic conductivity of the clayey soil/Ca-bentonite backfills, and the predicted hydraulic conduc- tivity values using these methods are found to fall in the range of 1/3 to 3 times those obtained from the oedometer tests. The proposed method is shown to estimate the hydraulic conductivity for both the clayey soil/Ca-bentonite backfills inthisstudy and the sandy soil-bentonite backfills from published study with reason- able accuracy. Additional research is warranted to prepare the backfills to simulate typical field practice (e.g., use

A series of centrifuge model tests exploring the effects of different types of slurry on long-trench stability in soft clay were conducted. The influence of groundwater conditions relative to trench stability was examined by constructing long trenches using different slurries. The soil deformation and surface settlement induced by the excavation of the trench are found to be closely related to slurry type and excavation depth of the long trench. Increasing the bentonite concentration of the slurry has beneficial effects on stability: 1) larger particles can improve local and global stability in cases where filter cakes do not form, and 2) larger viscosity can promote filter cake formation on the walls of long trenches excavated in soft clay and enhance their stability.

Modern urban policies, particularly in major towns, involve the active use of underground space that poses the problem of assessing the impact of excavation on the existing buildings as one of the most urgent. Surface and semi-closed construction methods are currently widespread in the process of urban civil and transport underground facilities construction. The depth of excavation can reach 30 m, but more often, in everyday practice common foundation pits have shallower depth, accommodating 2-4 underground levels (6-12 m). In the process of solving such problems not only the forces occurring in the foundation pit fence are of great interest, but also a quantitative change in the stress-strain state of the rock mass. In modern engineering practice in order to solve them numerical methods based on the finite element method are widely applied, which can quantify soil stress-strain state. In this study, the authors present the investigation of the influence of various factors within their variation on the additional deformations of adjacent buildings located in the influence zone, using the design of experiment method. The study is based on 3-dimensional numerical simulation with the use of finite element method. Such calculated factors were taken: the depth of excavation (X ), modulus of deformation (X ), the distance to the building (X ) and distributed load of the building (X ). As a result, regression equations to determine the maximum additional deformationof building and horizontal displacement of the pit fence were derived from the calculations carried out. Also, the graphs describing these dependencies and illustrating the effect of each factor were presented.

A synthesized investigation is conducted of trench formation machine’s effect on trench wall in soft soil area. The failure pattern of the slurry-trench is analyzed by means of 3D FEM based on strength reduction method. The investigation shows that the global instibility occurs in the superficial layers and speads along the trench segment. The grab movement in slurry has an instant impact on the trench wall and may cause local instability. The overload and construction technique of trench formation equipment are both important concerns during trench construction to ensure safetry.

In this study, we applieorithmd the inverse analysis alg to the prediction of displacement shape in the example construction and verified the feasibility of suggested algorithm. For this purpose, as information processing knowledge in the field of IT is required and the need for convergence with the major is emerged, it is intended to try to apply the algorithm to the construction sector. Prediction of displacement shape is very important since it is related to the earth pressure of slurry wall and effecting on the safety of slurry wall after anchor removal. 3 levels of inverse analysis were applied to the slurry walls in 3 sites and compared the measured displacement shape with predicted displacement shape of the last excavation construction. As the predicted displacement shape was matched well with the measured one, the applied analysis algorithm in this study can be applied to the excavation construction.

In this study, we compared and analyzed the displacement of final excavation with measured value through an inverse analysis method used in urban excavation construction. We maximized the effectiveness of the inverse analysis method, and plan to achieve cost-effective and practical construction management in the field with identical conditions. As the first stage, we suggest an example of a field which has the inverse analysis method. We applied the inverse analysis method to three different fields on which construction and measuring were finished. Of these three fields, two fields showed a very satisfactory result. However, in one field, there were significant differences between the analysis and measured value. The result of our analysis indicated that, we should unite the conditions of the inverse analysis method and field construction. We need to thoughtfully reconsider the RANKINE earth pressure application in a triangle type. This is because the uniformity of earth pressure is made by its arching effect, in the condition of the displacement of lower underground occurring widely, which is differentiated with the earth pressure conditions of RANKINE, even if the slurry wall has stiffness. Also, when recalculating the soil parameter, we should emphasize the adhesion of the weathering zone, and give experimental consideration to ground water level.

Trench stability is a conventional geotechnical problem; however, current evaluations are often based entirely on empiricism. This paper uses numerical finite-element upper and lower bound limit analysis to produce stability charts for two-dimensional and three-dimensional homogeneous and inhomogeneous undrained diaphragm wall trenches. Using the limit theorems cannot only provide a simple and useful way of analyzing the stability of the trench, but also avoid the shortcomings and arbitrary assumptions underpinning the limit equilibrium method. By considering the effects from the bentonite slurry pressures, the collapse load in this study has been bracketed to within ±8.5% or better by the numerical upper and lower bound limit analyses. The chart solutions can be used to predict either the critical depth or the safety factor of the trench and provide a convenient tool for preliminary designs by practicing engineers.

The bi-layer diaphragm wall is a new type of slurry wall, designed to improve watertightness and to counter leakage problems. These walls consist of two bonded concrete layers: the first, a conventional Reinforced Concrete (RC) diaphragm wall and the second, a sprayed Steel Fibre Reinforced Concrete (SFRC) layer with a waterproof additive. Here, we analyse and quantify the influence of different construction process parameters on the effectiveness of the bi-layer diaphragm wall technique. Thirty numeric simulations were conducted with an uncoupled structure-section analysis, placing special emphasis on the SFRC layer contribution. The results show that, in all cases, the main flexural strength is provided by the RC layer, with a secondary flexural contribution (between 8% and 15%) by the sprayed SFRC layer. Using satisfactory spraying sequences (detailed herein), a reduction in the steel reinforcement of the RC layer can be obtained in every structural configuration and construction sequence, reaching a maximum percentage reduction of 7.0% of the total bending reinforcement. The displacements are almost completely governed by the thickness of the first layer, and a minor reduction (less than 7.3%) is obtained, when the second layer is included.

Thispaperpresentstheresultsofalaboratorystudyonthesubaqueousdepositionofsandparticlesfromsediment-ladencircularjets on horizontal and inclined beds. Four sets of experiments were carried out to investigate the effects of jet characteristics, bed slope, sediment size, and sediment concentration on the growth and development of the sediment mound. Three distinct flow regimes can be identified as de- veloping regime, spreading regime, and backup regime. It was found that in the developing regime, deposition height and width formed by the continuous release of sediment particles grow faster than the mound length. Slurry jet flow in the spreading regime was diverted from the axial direction to the sides and caused more deposition on both sides of the mound. Backup regime started when the deposition height and width reachedtheirmaximumvalues.Inthiscondition,aslurryjetpushedsedimentbacktothenozzleandeventuallyblockedthe flow.Theinitiation of sediment deposition was estimated, and predictions were compared with experimental results. Variations of the deposition length scales, moundbasearea,andangleofdepositionwithtimeweremeasured.Empiricalformulationswereintroducedtopredictdepositiondevelopment

The development of industry has brought serious heavy metal pollution in the soil. There are various kinds of site contamination remediation technologies. The slurry wall barriers technology has many advantages, such as low permeability, good chemical compatibility, and low cost, so it was widely used in groundwater and soil pollution control projects. In this paper, the application status of vertical barrier technology in contaminated sites is reviewed. Currently, those research progress at home and abroad payed more attention on barrier materials, barrier mechanisms, and site types.

Geomembrane–bentonite composite barrier is known as one of the most reliable and effective technologies for containing underground contamination. Analytical solution for one-dimensional diffusion of an organic solute in the three-layered composite barrier is presented for the case in which the barrier is keyed in aquitard. Parametric analyses were conducted to investigate the effects of partition coefficient and installation location of high-density polyethylene (HDPE) geomembrane, retardation factor, and thickness of bentonite slurry wall on the barrier performance using this analytical solution. The analysis results demonstrate that the containment performance of the composite barrier depends much on the partition coefficient of HDPE geomembrane over the target pollutant. The HDPE geomembrane exhibits an excellent resistance to the hydrophilic organics, which have a low partition coefficient. However, the hydrophobic organics, which have a high partition coefficient, can diffuse readily through ...

When constructed the bored pile in sand layer, it is easily to appear the under-reaming and hole collapsed phenomenon. Then it will lead to the engineering disasters, such as hole collapsed, burying drilling and super party amount of concrete. Through the mechanics analysis of the fine sand in the hole process, we found that the mud turbulence will be broken in the drilling process which can cause the water in the hole to be turbulent fluctuation. The result of turbulent fluctuation is making the slurry wall inside and outside the test pressure difference exceeds the wall shear strength which results in the wall off block. At the end, the sand soil collapse dropping leads to the engineering disaster.

Standard containment technologies for remediation of subsurface contaminants include slurry walls, reactive barriers, sheet piling, and grouting. Another less common technique is freezing contaminants in situ. Artificial freezing techniques can be used to create a frozen barrier that restricts migration of aqueous phase contaminants and, therefore, can provide subsurface containment at a variety of facilities, including underground tanks, nuclear waste sites, groundwater plumes, and in situ waste treatment areas. Frozen barriers are formed by using a series of subsurface freezing pipes. The adjacent soil forms a frozen column the length of the freezing pipe; and the diameter of the frozen soil column increases with time at a rate depending upon the specific soil properties, moisture content, and thermal conditions at a given site and refrigeration rate (i.e., pipe temperature). The barrier is completed once the increasing diameters of the frozen soil columns merge together, which is referred to as “freezing to closure”. A study was performed in Fairbanks, Alaska, to investigate how quickly a barrier can be created during the summer using actively cooled hybrid thermosyphons. Freezing to closure occurred after 42 days, the barrier was 1 m thick after approximately 49 days, and temperatures were below − 3 °C at the core of the barrier (in between the thermosyphons) after 60 days. The active system was turned off in the fall, and passive cooling of the ground continued through the winter. By the beginning of the following March, the frozen barrier was 3.8 m thick.

Slurry trenches are often used to impede groundwater flow or to contain soil and groundwater contamination. The stability of the slurry trench during excavation and prior to backfilling is a major concern in design. A horizontal slice method for stability analysis of slurry trenches, which allows consideration of soil stratification, is presented. Vertical force equilibrium for each slice of the sliding mass and horizontal force equilibrium for the whole sliding mass are considered on the basis of limit equilibrium. The factor of safety is obtained via the Newton–Raphson method and the critical slip surface corresponding to the minimum factor of safety is located by the pattern search method. The proposed method is verified via consideration of a previously reported problem. It is then applied to a full-scale field experiment in three-layer soils. The obtained minimum factor of safety and location of the slip surface of the sliding mass are in excellent agreement with the experimental measurements. Analyses of trenches having a weak layer at various depths demonstrate potential variations in slip surface inclination between soil layers.

The slug test is a viable method in estimating the hydraulic conductivity of the slurry trench wall backfill because of its ability to consider a more representative volume of the backfill and to reflect the in situ performance of the construction. A three-dimensional numerical model is developed to simulate the slug test in a slurry trench wall with the presence of bentonite cake on the interface boundary between the wall and the surrounding soil formation. Influential factors such as wall width (i.e., proximity of wall boundary), well deviation, vertical position of the well intake section, and compressibility of the wall backfill are taken into account in the model. The experimentally obtained hydraulic properties of the bentonite cake are also incorporated in a series of slug test simulations. The simulation results are then examined to evaluate the bentonite cake effect in analyzing practical slug test results in the slurry trench wall. The simulation results show that the modified line-fitting method can be used without any reduction factor for the slug test in the slurry trench wall with the presence of bentonite cake. A case study is reanalyzed with the assumption of existing bentonite cake. The results are compared with the previously reported results by the approaches used for the case of no bentonite cake (constant-head boundary) and upper-bound solution (no-flux boundary). The modified line-fitting method and the type curve method produce similar results for slurry walls with bentonite cakes. The case study results demonstrate the importance of the bentonite cake effect in estimating the hydraulic conductivity of the slurry wall backfill.

Slug tests can be adopted to estimate hydraulic conductivity of the slurry trench wall backfill for its abilities to reflect the in-situ performance of the construction. A comprehensive three-dimensional numerical model is developed to simulate the slug test in a slurry trench wall considering the presence of bentonite cake on the interface boundaries between the wall and the surrounding soil formation. Influential factors such as wall width (i.e., proximity of wall boundary), well deviation, vertical position of well intake section, compressibility of wall backfill, etc. are taken into account in the model. A series of simulation results are examined to evaluate the bentonite cake effect in analyzing practical slug test results in the slurry trench wall. The results show that the modified line-fitting method can be used without any correction factor for the slug test in the slurry trench wall with the presence of bentonite cake. A case study is reanalyzed with the assumption of existing bentonite cake. The results are compared with the previously reported results by the approaches assuming no bentonite cake (constant-head boundary) or upper-bound solution (no-flux boundary). The case study demonstrates the bentonite cake effect and the validity of the modified line-fitting method in the estimation of the hydraulic conductivity of the slurry wall backfill.

Three mixtures of cement–bentonite slurry containing 28, 36 and 44 % PFA (as a proportion of cementitious materials) were tested using the unconfined compressive strength and triaxial apparatus to determine the stress–strain and shear strength relationships for samples cured for various periods. The samples were batched using 4 % bentonite and 20 % cementitious materials (by mass of water) and allowed to cure underwater once extruded from sealed moulds. Curing periods of 14, 28 and 90 days were selected to investigate the changes in behaviour at durations commonly specified (28 and 90 days) as well as providing insight into changing behaviour with curing (additional curing periods of 7 and 60 days were investigated on a smaller number of samples to increase understanding). Two rates of displacement were used (1.0 and 1.3 mm/min) and four confining pressures (0, 50, 100 and 200 kPa). Shear strength and strain at peak deviator stress of the samples do not appear to vary considerably with confining pressure. For samples containing 28 % PFA, the majority of physical properties exhibited by the cement–bentonite samples change with curing period up to 60 days, where after the properties become similar to those cured for 90 days.

Despite the installation in the 1980s and 1990s of hydraulic containment systems around known source zones (four slurry walls and ten pump-and-treat systems), trichloroethene (TCE) plumes persist in the three uppermost groundwater-bearing units at the Middlefield-Ellis-Whisman (MEW) Superfund Study Area in Mountain View, California. In analyzing TCE data from 15 recovery wells, the observed TCE mass discharge decreased less than an order of magnitude over a 10-year period despite the removal of an average of 11 pore volumes of affected groundwater. Two groundwater models were applied to long-term groundwater pump-and-treat data from 15 recovery wells to determine if matrix diffusion could explain the long-term persistence of a TCE plume. The first model assumed that TCE concentrations in the plume are controlled only by advection, dispersion, and retardation (ADR model). The second model used a one-dimensional diffusion equation in contact with two low-permeability zones (i.e., upper and lower aquitard) to estimate the potential effects of matrix diffusion of TCE into and out of low-permeability media in the plume. In all 15 wells, the matrix diffusion model fit the data much better than the ADR model (normalized root mean square error of 0.17 vs. 0.29; r2 of 0.99 vs. 0.19), indicating that matrix diffusion is a likely contributing factor to the persistence of the TCE plume in the non-source-capture zones of the MEW Study Area's groundwater-extraction wells. © 2013 Wiley Periodicals, Inc.

A 2D and 3D kinematically admissible rotational failure mechanism is presented for homogeneous slurry trenches in frictional/cohesive soils. Analytical approaches are derived to obtain the upper bounds on slurry trench stability in the strict framework of limit analysis. It is shown that the factor of safety from a 3D analysis will be greater than that from a 2D analysis. Compared with the limit equilibrium method, the limit analysis method yields an unconservative estimate on the safety factors. A set of examples are presented in a wide range of parameters for 2D and 3D homogeneous slurry trenches. The factor of safety increases with increasing slurry and soil bulk density ratio, cohesion, friction angle, and with decreasing slurry level depth and trench depth ratio, trench width and depth ratio. It is convenient to assess the safety for the homogeneous slurry trenches in practical applications.

This paper presents a variational limit equilibrium closed-form solution for the stability of slurry-supported trenches in cohesive soil, frictional cohesive soil, and cohesionless soil. Study results indicate that the critical slip-surface geometry is either planar or log spiral. The normal stress distribution, which indicates the likely depth of a tension crack at the crest over the slip surface, was also obtained as part of the complete solution and as a function of groundwater-table level. The closed-form solution was used to produce stability charts for a practical range of parameters. The charts can be used to conveniently assess the stability of a given slurry trench for preliminary design. The paper gives two different examples for trenches to illustrate the influence of the slurry level on the trench stability. To introduce the analytical solution, this study is limited to a simple slurry trench problem; however, extension of the present framework to deal with complex problems would be st...

Although there are well-established methods for economic (cost) estimation of any process, the estimation of the environmental and the social effects is relatively less understood and rarely incorporated in engineering calculations. In this paper, the effectiveness of different types of vertical barrier system for a present waste dump is compared in terms of the embodied energy (EE) and carbon emission in addition to the targeted service life. The model used for the assessment is streamlined energy and emission assessment model (SEEAM). The project involved constructing the vertical barrier around Bingipura fill in order to prevent the contamination of nearby water body due to the leachate from the waste dump. Different types of barriers are analyzed: sheet pile walls, concrete barriers, and the slurry-based cutoff walls (Na-bentonite). The performance analysis was carried out in the well-established software POLLUTEv7 which indicated the effectiveness of the sodium bentonite (Na-B) slurry wall and Soil-Bentonite backfill over other two for the leachate containment.

At Kuwana illegal dumping site in Japan, where hazardous waste was illegally dumped, groundwater was severely contaminated by Volatile Organic Compounds (VOCs). Groundwater was already remedied by conducting Pump-and-Treat (P&T) after containment of all the waste by vertical slurry walls from 2002 to 2007. However, 1,4-dioxane was detected in both waste and groundwater outside of slurry walls after it was newly added into Japan environmental standards in late 2009, which suggested that the walls did not contain 1,4-dioxane completely. Our previous study developed a model to predict the 1,4-dioxane distribution in groundwater after the previous remediation at the site. In this study, numerical simulation was applied for remediation planning at the site based on the concept of Verified Follow Up (VF-UP) that had been proposed as a new approach to complete remediation effectively with consideration of future risks. The amount of waste to be removed and pumping plans were discussed by numerical simulation to achieve the remedial objective in which 1,4-dioxane in groundwater outside of walls is remedied within 10 years and 1,4-dioxane spreading throughout the walls is prevented in the case where a portion of waste is remained. Firstly, the amount of waste to be removed considering pumping plans for P&T was determined by scenario analysis. As a result, at least two-third of waste should be removed by combining with P&T. However, if the waste is remained, future risks of 1,4-dioxane spreading through the slurry walls may occur. Our simulation suggested that groundwater within the remaining waste must be pumped up at least 20 m3/d for containment of 1,4-dioxane within the remaining waste. In conclusion, our numerical simulation determined the amount of waste to be removed and the pumping plans for P&T to achieve the remedial objective effectively considering future risks based on the concept of VF-UP.

Several different phenomena are involved in the formation and performance of self-hardening slurry walls, including slurry contamination by soil, penetration of slurry into the ground, confining with the trench, filtration, sedimentation, consolidation, and chemical reactions between the slurry constituents. To evaluate the relative influence of these phenomena, a case study is analyzed—the cutoff wall of Santa Clara-a-Velha Monastery, built in 2001–2002. The performance of this wall is related to the in situ phenomena through data obtained during construction and from a site investigation conducted in 2011. An extensive laboratorial program was performed on samples cored from the wall and on laboratory-made samples. It was found that consolidation was the major contributor to the significant settlement of the wall that occurred after trench excavation, whereas filtration and sedimentation made only a secondary contribution. Contamination by sand only interfered with the physical properties and co...

This paper presents a reduced-scale shake table test on the seismic responses of a section of soil-cement-bentonite (SCB) slurry cutoff wall. The geometric scale of slurry wall width was chosen as 1∶3 (model:prototype). A section of a slurry wall with dimensions of 150 cm long, 20 cm wide, and 160 cm tall was constructed and tested on a one-dimensional shake table. A 187 cm (long)×150 cm (wide)×180 cm (tall) steel-frame box was anchored on the shake table and contained the slurry wall and sandy soil that was compacted on both sides of the wall. Spring-supported wood panels were installed at the bottom and on two sides of the box to create a boundary that has the stiffness of dense sand. The slurry wall and the confining soil were instrumented with accelerometers, LVDT, linear potentiometers, and dynamic soil stress gauges to respectively record the accelerations, vertical and horizontal deformations of the wall, and transient dynamic soil pressures on the wall during the simulated seismic excit...

This is an Accepted Manuscript of an article published by Taylor & Francis in [Journal of Civil Engineering and Management] on 2016, available online: http://wwww.tandfonline.com/10.3846/13923730.2014.914085. The bi-layer diaphragm wall, a new slurry wall type designed to cope with the problem of watertightness is studied in this paper. These walls consist of two bonded concrete layers, the first, a conventional Reinforced Concrete (RC) diaphragm wall, and the second, a Sprayed Steel Fibre Reinforced Concrete (SFRC). The main objective of this paper is to analyze the structural and sectional behaviour of these walls. A study in the form of an uncoupled structural-section analysis based on various hypothetical cases of bi-layer diaphragm walls was performed to fulfil the objective. It is concluded that there exists a potential of reduction in the reinforcement of the RC layer through the structural use of the SFRC layer. However, when the reduction is quantified, even though a reduction of between 3.2% and 1.7% in the RC reinforcement is confirmed, it appears insufficient to offer a cost-effective solution. Nonetheless, the system becomes a promising solution when particular conditions are taken into account, such as basement space limitations.

The Second Avenue Subway is currently under construction in Manhattan, New York. Spanning seven city blocks, the cut-and-cover station at 96th Street is the largest station in Phase 1. The station excavation is up to 68 feet deep and is typically within 20 feet of adjacent buildings. The station straddles areas of rock and deep soil at its invert and requires various forms of ground support, including both temporary and permanent secant pile and slurry walls. Construction was undertaken in a dense urban environment, adjacent to fragile buildings, with significant underground utility and traffic maintenance restrictions. Excavation and construction of the permanent earth support was recently successfully completed. This paper reviews the design and construction methodology for the ground support systems adopted and discusses the interfacing and construction challenges faced in a highly constrained environment from the perspectives of both the designer and contractor.