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This paper describes a series of laboratory tests performed to characterize the mechanical and hydraulic properties of plastic concrete (PL-C). PL-C is used in the construction of seepage cut-off walls in dams and it comprises cement, aggregate, and water mixed with sodium bentonite. The addition of sodium bentonite causes a reduction in strength a...
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... dams that require a foundation cut-off, the cut-off wall is typically constructed in the foundation by the slurry trench method, then the dam is built on top of the cut-off wall and foundation. Figure 2 shows the typical geometry. During embankment construction, both the foun- dation and PL-C compress under the weight of the earthfill structure. ...
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... PL-C, at least in compression. 5. Typical volume in and out during triaxial tests with per- meation: (a) full test; (b) response during compression from 1% to 2% axial strain, 3. 7. Stress-strain response of 0.95 MPa ( fcu) plastic concrete (sc = 400 kPa). The ratio of elastic modulus to unconfined compressive strength, E/f cu , is summarized in Fig. 12. Overall, the stiff- ness of the 0.6 MPa ( f cu ) and 0.95 MPa ( f cu ) PL-C is strongly influenced by s c as shown in this figure. The E/f cu ratio of both the 0.6 and 0.95 MPa specimens roughly dou- bles as s c is increased from the unconfined state to s c = 900 kPa. To put this into context, s c typically has a strong influence on ...
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... MPa PL-C specimens, however, there is a change in behaviour. The influence of s c on the E/f cu ratio of the 2.5 MPa PL-C is quite small and more comparable to that normally observed for conventional concrete (see Scott et al. 1982). It is noted that the Janbu (1963) parameters for the 0.6 and 0.95 MPa ( f cu ) PL-C mixes are also presented in Fig. ...
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... relaxation versus log-time response of 2.5 MPa ( fcu) plastic concrete (sc = 900 kPa). 12. Modulus ratio (E/fcu) of plastic concrete versus confine- ment pressure. ...
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... should be suitable for PL-C in compression. (3) The modulus of elasticity of PL-C is strongly influenced by s c for 0.6 and 0.95 MPa ( f cu ) mixes. Analogous beha- viour has been observed in soils and Janbu's equation (Janbu 1963) provides a reasonable fit for the observed behaviour. It is also noted that the Janbu parameters pro- vided in Fig. 12 of this paper could be considered when using numerical models to assess the effect of embank- ment construction on PL-C cut-off walls. (4) Variations in the modulus of 2.5 MPa ( f cu ) PL-C versus s c were more comparable to that observed for concrete (e.g., Scott et al. 1982) indicating that a pressure depen- dent elastic model may ...
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Citations
... Sivakumar et al. (2019) investigated the deformation behaviour of the cut-off wall for varying its location from the upstream end to the downstream end using a numerical model. Other literature has also investigated the effect of deformations and stresses in cut-off walls under various conditions (Alrowais et al. 2023;Hinchberger, Weck, and Newson 2010;Javanmard, Mottaghi, and Mir Mohammad Hosseinni 2018;Ostrowsky 2018). Long seepage barriers are sensitive to unbalanced deformations and settlements. ...
An analytical solution to the problem of two-dimensional steady-state seepage flow beneath a water-retaining structure is presented using conformal mapping and complex variables. The cutoff at the downstream end has a definite thickness, and this paper addresses the question of to what extent the cutoff thickness affects the values of seepage characteristics. Since the closed-form analytical equations are not explicit, they are calculated numerically. The analytical results have been validated by comparing them with the available exact solutions for finite-depth seepage. The resulting implicit equations, involving elliptic integrals, are used to create design diagrams. The results show that increasing the thickness can cause a reduction in hydraulic gradient, seepage discharge, and uplift pressure at the left tip of the cutoff. Furthermore, based on the method of fragments, a customized fragment type considering the cutoff’s thickness is developed using the analytical results to estimate seepage quantities and exit gradients. The form factor for this fragment is obtained in the form of dimensionless charts, which predict the flow rate and exit gradient more precisely than the existing solutions.
... In the application of dam seepage walls, plastic concrete can adapt well to soil deformations and exhibits excellent deformation coordination ability and impermeability performance [4]. In addition, plastic concrete has low elastic modulus, good toughness, certain strength and low material cost [5][6][7]. Plastic concrete has broad application prospects and good performance. ...
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... Once the compatible properties are set, the choice of the mixture is straightforward. According to the literature, the undrained cohesion of the plastic concrete varies between 500-1500 kPa [28,29,32]. Considering the interval of variation determined in this paper, most of the mixtures are located in this interval, with only two mixtures being outside of it, namely 137 and 442 kPa. ...
... The presence of additives can drastically modify the results given herein; therefore, this research direction should also be considered for future development on the subject of cutoff wall materials and mixtures. According to the literature, the undrained cohesion of the plastic concrete varies between 500-1500 kPa [28,29,32]. Considering the interval of variation determined in this paper, most of the mixtures are located in this interval, with only two mixtures being outside of it, namely 137 and 442 kPa. ...
In recent years, because of the continuous expansion of urban areas, an increased necessity to isolate historically polluted sites by means of artificial, flexible, low-permeability barriers has emerged. Moreover, due to cost and efficiency considerations, various combinations of materials that fulfill the previously stated requirements have been proposed. On the basis of a literature review, this paper analyses the relationships between water, cement, and bentonite, and the physical and mechanical properties of the resulting material created in combination with standard sand introduced in the mixture using a ratio of 2:1 with respect to the solid part of the mixture (cement and bentonite). The quantity of standard sand was established following previous research conducted by the authors. The relation between water, cement, and bentonite is analyzed through properties such as viscosity, permeability, and undrained cohesion, and the representation of mixtures and their corresponding parameters was carried out using a ternary diagram. This paper provides a graphical approach to finding the optimum water/bentonite/cement mixture required for barrier design, taking into account permeability, undrained cohesion, and mixture viscosity.
... Similarly to ordinary concrete, the elastic modulus of Plastic Concrete increases with increasing compressive strength and thus with decreasing w/c-ratio or increasing cement content [1]. In literature, various studies have investigated the elastic modulus of Plastic Concrete [10,11,13,14,16,17,36]. Still, as reported by the authors in [1], the testing procedure used has a major influence on the test results. ...
... In Fig. 14, the results of the present study with the stabilised elastic modulus E C,S , the tangent elastic modulus E ci and the secant elastic modulus E c1 are shown against the corresponding compressive strength. In addition the available literature data reported in [1] and based on [10,11,13,14,16,17,36] is shown in grey. ...
... The primary function of a plastic concrete cutoff wall is to serve as a barrier to prevent or reduce groundwater flow. The constituents of plastic concrete include cement, aggregates, water, clay, and bentonite, which is mixed at a high-water cement ratio to provide ductility [4,[53][54][55]. Plastic concrete has a lower cement content compared to ordinary concrete and contains clay and bentonite [20]. ...
... Plastic concrete is one of the commonly used materials for the construction of cutoff walls. The materials used for the construction of plastic concrete walls are selected based on the required wall performances such as very low hydraulic conductivity and excellent ductility after reaching failure compared with conventional concrete [1], construction facilities, and surrounding ground properties [2]. Along with strain compatibility, water resistance is a crucial parameter, related to the strength of concrete structures under hydrostatic conditions [3]. ...
... To batch the plastic concrete mixes, the obtained ratio of water and Na-bentonite was mixed thoroughly until a consistent slurry was attained. The resultant water-bentonite slurry was allowed to complete water adsorption and swelling for 24 hours [17][18]1]. Subsequently, the fine and coarse aggregates were mixed in a concrete mixer for 5 min and the obtained amount of cement with water was added to the mixture and mixed for 3 min. ...
... Subsequently, the fine and coarse aggregates were mixed in a concrete mixer for 5 min and the obtained amount of cement with water was added to the mixture and mixed for 3 min. Then, the prepared bentonite slurry was added to the concrete and the batch was mixed until a homogeneous mixture was obtained (Hinchberger et al. 2010). In meantime, retarders and described different proportions of PRAH were added with the separate mixes. ...
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... Water tightening and seepage control are important factors to consider when designing and building secant pile walls. Plastic concrete is made up of aggregate particles, cement, water, and bentonite that are combined at a high water-to-cement ratio to create a ductile construction mixes (Hinchberger et al., 2010;Liu et al., 2011;Xiong et al., 2011). Plastic concrete walls mainly act as a barrier to prevent or reduce groundwater flow Huang et al., 2010;Sandoval et al., 2017;Wu et al., 2016). ...
Sand-bentonite-cement are commonly used as cut-off walls to isolate polluted soils or in ground improvement technologies and as retaining structures as secant pile wall. In this research, a laboratory program consisted from 105 sample were prepared and tested between different tests, such as hydraulic conductivity, porosity, and compressive strength to monitor the mechanical behavior of sand-bentonite-cement at different ages. Based on the experimental relationships between hydraulic conductivity coefficient and samples age; there were reduction due to added bentonite to mixture reach about 35.0% at 7 days. Moreover, the average reduction in the compressive strength of plastic concrete samples with bentonite was lower by average range about 51.0% than the compressive strength of plastic concrete samples without bentonite at 7 days. In this study, proposed formulas were derived to estimate the splitting tensile strength based on the compressive strength and the hydraulic conductivity in terms of the bentonite/cement ratio and testing age. The predicted values showed well agreement with the experimental records for samples of sand-bentonite-cement mixtures where the standard deviation and coefficient of variation were 0.02, and 0.94%, respectively.
... Plastic concrete is formable concrete that is obtained from the combination of water, cement, sand, and bentonite [1]. The purpose of using this type of concrete in many researches [2][3][4][5] is to reduce water seepage and facilitate drilling. Due to the use of bentonite in plastic concrete, this type of concrete usually has more ductility and less permeability than normal concrete. ...
Plastic concrete is a type of concrete that usually has high ductility and low permeability and it can be used in the construction of tangential piles in the excavations that have a high groundwater level. In many cases, the project conditions for using plastic concrete with proper mixing plan are not considered. The aim of this research is to present the optimal mixing plan in terms of mechanical and economic characteristics for plastic concrete piles. For this purpose, five different mix designs were considered for plastic concrete and the properties were evaluated. Finally, the group of tangential piles, including structural and plastic concrete piles with strut, was simulated in the vicinity of the deep excavation and the deformation and flow rate passing through the excavation wall were investigated. In two-dimensional simulation, it is not possible to consider the characteristics of the plastic concrete pile in the modeling plane and check the deformation of the excavation wall between struts. For this reason, the simulation was done three-dimensionally. Results showed that if the groundwater level is kept constant, water infiltration into the project area is very low due to the very low permeability of plastic concrete piles and the subsidence and deformation created at the top of the piles as well as the swelling of the excavation bed is less than when the groundwater level is lowered. Also, by increasing the permeability of plastic concrete piles and soil, the flow rate through the excavation wall increases.
... Other construction techniques, such as diaphragm walls, pile walls and sheet piles, although made of reinforced concrete, may leak at the joints (interlocks) [1,5,7]. Some concrete cut-off walls have construction defects due to improper construction methods or material selection, resulting in the effective hydraulic conductivity of the wall being two to three orders of magnitude larger than the anticipated value [4,22]. The effective hydraulic conductivity of a cut-off wall refers to quantity of leakage through a unit area of the wall driven by a unit hydraulic gradient when considering the effects of wall materials, wall defects and cracks. ...
A fully penetrating cut-off wall is a vertical seepage barrier that fully penetrates an aquifer and is embedded in an underlying aquitard to a certain depth. Groundwater seepage with this type of wall occurs through three paths: leakage through the body of the wall in the aquifer, leakage through the body of the wall embedded in the aquitard, and seepage under the wall. Seepage through the first path can be simply treated as one-dimensional flow. However, due to the mutual influence of seepage through the latter two paths, the seepage problem is complicated and still needs to be studied. An analytical method is proposed to solve this problem in this study. Mathematic expressions for flow rate and head value are obtained by superposition of drawdowns of two exact models, namely, the model with only leakage through the wall body and the model with only seepage under the wall, respectively. Exact solutions are quoted or derived for the exact models, but they involve Legendre’s elliptic integrals of the first and third kinds. To facilitate an engineering application, approximate models of the exact models are introduced and their solutions are applied to the analytical formulas. The accuracy and applicability of the proposed method are verified compared with the numerical method. The proposed method provides a simple but effective method for quickly estimating the quantity of seepage in the aquitard (including leakage through the wall body and seepage under the wall) when simultaneously considering the effects of wall permeability and thickness.
... In geotechnical engineering, water seepage has become the main cause of the various engineering accidents [1][2][3][4][5]. e cut-off walls are the most commonly adopted antiseepage measurement [6][7][8]. e polymer cut-off wall technique is a newly proposed method that uses the two-component foaming polyurethane as an alternative to the traditional concretes to construct cut-off walls [9][10][11]. As shown in Figure 1, the two-component polymer (TFPU) cut-off wall is built in the soil using the grouting technology [9,10]. ...
... D l is derived from equation (7), and it represents the damage when the shear stress of the contact surface reaches the yield strength. e variation curves of D are drawn based on equation (6), and D l was calculated by (13). From Figure 7, one can see that D remains zero until c reaches a certain value, after which, it increases with the increasing c until up to 1. is observation corresponds well with the characteristics of the experimentally obtained τ-c curves ( Figure 2). ...
The newly developed two-component polymer (TFPU) cut-off walls have great application potential in civil engineering for water-seepage prevention. Investigating the mechanical interactions between TFPU and soil from the theoretical perspective can provide a basis for furtherly evaluating the stability of TFPU cut-off walls, which, however, has not been conducted. In this study, based on the shear testing results, the shear damage model of the TFPU-bentonite contact surface was established. Studies show that the TFPU-bentonite contact surface performs strain-softening behavior under shear and that the strain-softening behavior becomes less and less obvious when the normal stress increases. The theoretical shear stress-strain curves are in good consistent with the experimental ones, and the maximum differences between the theoretical shear stress and shear strain at yield and the experimental ones are about 3.88% and 3.40%, respectively, indicating that the shear damage model can reflect the mechanical properties of the TFPU-bentonite contact surface. The critical damage of the contact surface increases from 0.05 to 0.50 in the power function way when normal stress increases from 75 to 1200 kPa, implying that the shear failure of the contact surfaces changes from brittleness to ductility. This study provides a theoretical base for evaluating the influences of the TFPU-soil contact surface on the stability of the TFPU cut-off wall structures.
