Plastic Concrete Cut-off Wall Research Articles

Experimental Study into the Mechanical Properties of Plastic Concrete: Compressive Strength Development over Time, Tensile Strength and Elastic Modulus

Plastic Concrete is a low-strength (fcm,28d≤ 1.0 MPa), low-stiffness, impervious concrete used for cut-off wall construction in earthen dams. To date, there has been no systematic study on the effect of mix design on the long-term time development of the mechanical properties (compressive strength, tensile strength, and elastic modulus) of Plastic Concrete. Therefore currently no Plastic Concrete specific constitutive law for cut-off wall design exists. The present study closes this gap. Ten Plastic Concrete mixes with two bentonite-cement ratios and three types of sodium bentonite were produced. Fresh concrete workability tests were performed for all mixes. Compressive strength tests were performed at ages 28 d, 56 d, 91 d and four years. Splitting tensile strength and elastic modulus tests were performed at 28 days. The workability results show a good linear correlation between slump and flow table tests. Plastic Concrete’s compressive strength development over time is notably slower than that of ordinary concrete, and a new time development model following fib MC 2020 is established using a fitted sC coefficient. The splitting tensile strength shows an overall good, linear correlation with compressive strength, with an approximate ratio of 0.135. Furthermore, the elastic modulus EC,S according to EN 12390-13 concrete tests show significantly higher elastic modulus than the available data, and a model approximation for the elastic modulus EC,S as a function of compressive strength is also provided. Overall, this study provides the first Plastic Concrete specific mechanical property models, confirming the critical role mix design plays on Plastic Concrete’s short and long-term mechanical properties. Thus, the developed models enable a more realistic Plastic Concrete cut-off wall design and provide an important basis for future research.

Investigating Deformation Mechanism of Earth-Rock Dams with InSaR and Numerical Simulation: Application to Liuduzhai Reservoir Dam, China

Ground deformation is the direct manifestation of the earth-rock dam's hazard potential. Therefore, it is essential to monitor deformation for dam warning and security evaluation. The Liuduzhai Dam, a clay-core dam of a large reservoir in China, was reinforced with plastic concrete cut-off walls between 13 January 2009 and 29 May 2010, as it was subject to leakage and deformation. However, the deformation development and the mechanism of the dam are still unclear. In this study, the deformation fields before and after the reinforcement of the Liuduzhai Dam were yielded by using the Interferometric Synthetic Aperture Radar (InSAR) technique. Furthermore, a numerical simulation method was employed to obtain the dynamic seepage field of the dam during the InSAR observation period. The results indicated that the average deformation velocity and maximum deformation velocity are −11.7 mm/yr and −22.5 mm/yr, respectively, and the cumulative displacement exceeds 100 mm, which shows typical continuous growth characteristics in a time series. In contrast, the dam deformation tended to be stable after reinforcement, with the average deformation velocity and maximum deformation velocity being −0.4 mm/yr and −1.2 mm/yr, respectively, behaving as cyclical deformation time series. According to the results of InSAR and seepage analysis, it is shown that: (1) dynamic seepage was the main mechanism controlling dam deformation prior to reinforcement; (2) the concentrated load caused by construction and the rapid dissipation of pore water pressure caused by the sudden drop of the infiltration line were the reasons for the acceleration of deformation during and after construction; and (3) the plastic concrete cut-off walls effectively reduced the dynamic seepage field, while the water level fluctuations were the main driving factor of elastic deformation of the dam after reinforcement. This study provides a novel approach to investigating the deformation mechanism of earth-rock dams. Furthermore, it has been confirmed that InSAR can identify the seepage deformation of dams by detecting surface movements. It is recommended that InSAR deformation monitoring should be incorporated into future dam safety programs to provide detailed deformation signals. By analyzing the temporal and spatial characteristics of the deformation signal, we can identify areas where dam performance has degraded. This crucial information aids in conducting a comprehensive dam safety assessment.

A Modified Strain Softening–Hardening Constitutive Model for Plastic Concrete Cut-off Wall

A Modified Strain Softening–Hardening Constitutive Model for Plastic Concrete Cut-off Wall

PbCl2 effects on the strength and permeability of plastic concrete cutoff walls

Plastic concrete walls are widely used in landfill and contaminated site pollution control engineering. Considering the prevalence of heavy metal lead ions contaminating the site, lead ions can affect the strength and permeability of plastic concrete walls. To this end, an experimental study on the effect of PbCl2 concentration on the strength, hydraulic conductivity and physico-chemical property indicators (pH and electrical conductivity) of plastic concrete walls composed of cement, bentonite, sand and PbCl2 solutions was carried out at different mix proportions and curing ages. The results show that the strength and pH of plastic concrete decrease with increasing PbCl2 concentration, and the hydraulic conductivity and electrical conductivity increases with increasing PbCl2 concentration at the same mix proportion and curing age. At the same PbCl2 concentration, the strength of plastic concrete increases with increasing plastic concrete cement content and curing age, and the hydraulic conductivity decreases with increasing plastic concrete cement content and curing age. Meanwhile, both pH and electrical conductivity decrease with increasing curing age, and both pH and electrical conductivity (σ) increase with increasing cement content. Consideration of pH and electrical conductivity (σ) can reflect the type of plastic concrete product and the degree of hydration reaction, which further reflects the degree of compactness and pore size of plastic concrete, thus affecting the strength and permeability of plastic concrete. Therefore, for plastic concrete with three cement contents, the strength of plastic concrete increases with increasing pH/σ, and the hydraulic conductivity decreases with increasing pH/σ at different PbCl2 concentrations and curing ages. In addition, pH/σ shows a good exponential function with plastic concrete strength and hydraulic conductivity.

Numerical Simulation Study on the Influence of Construction Load on the Cutoff Wall in Reservoir Engineering

Relying on the Beijing-Shijiazhuang Expressway widening project near the impervious wall of a reservoir, this paper uses FLAC3D two-dimensional and three-dimensional numerical simulation methods to establish the whole process model of the impervious wall of the reservoir affected by the construction load of the high-way reconstruction section. The stress and strain state of the cut-off wall in the high-way reconstruction section and the nearby reservoir is simulated in detail, the overall deformation of the cut-off wall in the reservoir is directly reflected, and the interaction and differential deformation between the wall structures are reflected. The safety and stability of the cutoff wall of the reservoir affected by the construction load are evaluated so that various advanced mechanical behaviors of the cutoff wall can be predicted. Research results show that the horizontal displacement value of the wall gradually increases from bottom to top, and the maximum value appears at the top of the wall. The horizontal displacement value of the 1–3 walls is relatively large, with the maximum value of 22.368 mm, and the horizontal displacement value of the 4–10 walls shows little difference. This is on account of the gravity of the backfill, the strata in the whole project area having settled, and the settlement at the bottom of the cut-off wall being 2.542 mm. At the root of the rigid cut-off wall, the compressive stress concentration occurs, with the maximum value between 1.75 MPa and 2.15 MPa. Due to the size of the structure, the maximum tensile stress of 0.237 MPa appears in the local area near the guide wall of the rigid cut-off wall, which will not endanger the rigid cut-off wall because of its small value. The maximum stress in the rigid impervious wall and the plastic impervious wall are 1.90–2.15 MPa and 1.00–1.12 MPa, respectively. Apart from the small tensile stress at the connecting guide wall between the rigid cut-off wall and the plastic concrete cut-off wall, the cut-off wall is under pressure, especially the plastic cut-off wall. Combined with the analysis of the stress state of the wall, it can be determined that the anti-seepage wall (rigid cut-off wall and plastic concrete cut-off wall) is stable and safe during the construction period.

Construction of Plastic Concrete Seepage Cut-Off Wall for Polavaram Earth Cum Rockfill Dam

Abstract: Polavaram Project is being executed on River Godavari near Ramayyapeta village of Polavaram Mandal, West Godavari District, Andhra Pradesh. This multipurpose major project envisages construction of 2454m long Earth-cum-Rock fill (ECRF) dam across river Godavari near Polavaram with a maximum height of 50.32m. The proposed ECRF dam will be founded on a bed of sand. The depth of sand bed over the underlying rock strata varies from 30m to 90m at different location. To restrict the flow of seepage water through the sand bed, a plastic concrete diaphragm wall/Cut-Off wall is proposed with its top end embedded in the clay core of the ECRF Dam and the bottom end embedded into underlying hard rock. The wall was constructed of plastic concrete using panel construction method. Plastic concrete was selected to provide a seepage Cut-Off wall that has sufficient strength to withstand both static and seismic stresses beneath the new embankment, and yet is flexible enough to undergo seismic deformations, without cracking, with the surrounding soils. This paper illustrates the construction of the plastic concrete Cut-Off wall for the Polavaram ECRF dam, including the field and laboratory testing performed to confirm design wall stiffness, strength, and hydraulic conductivity requirements. The trial laboratory and field testing programs to determine plastic concrete mix design, and the QA/QC testing conducted during construction are presented. Keywords: ECRF, Plastic concrete, Cut-Off wall, Hydraulic grab, Trench cutter, Koden, Tremie

Quantitative study on the influence of foundation valley shape on the behaviour of concrete cut-off walls

Concrete cut-off walls are the main seepage control measures for the alluvial foundation of earthen dams. Its mechanical behaviour, which is affected by many factors, is complicated, in which foundation valley shape is one of the main factors. To analyse the influence of the foundation valley shape on the behaviour of the cut-off walls quantitatively, this study defines the foundation valley width coefficient μ, foundation valley steepness coefficient δ and foundation valley asymmetric coefficient γ. A series of numerical calculations on the cut-off wall behaviour with different foundation valley shape parameters was performed on the basis of a core earthen dam. The influence of the foundation valley shape was studied quantitatively by combining it with the numerical results and measured data of the case histories. The behaviour difference between ordinary concrete and plastic concrete cut-off walls was also discussed. Results indicate that the cut-off wall mainly experiences bending deformation. Large tensile stress occurs near the interface between the cut-off wall and the bedrock. The plastic concrete cut-off wall can effectively reduce the tensile stress. The foundation valley width affects the wall behaviour through the bedrock arching effect. μ = 1.5 can be used as the critical value to distinguish the wide and narrow valley foundation. When δ > 1.0, the cut-off wall is subjected to large tensile and shear stresses near the contact part of the wall and bedrock. The foundation valley asymmetry causes uneven deformation and large tensile stress on the cut-off wall near the steeper bank slope.

Numerical analyses of embankment dams containing plastic concrete cut-off walls using finite difference method (A case study: The Karkheh Embankment Dam)

In this paper, numerical analyses have been performed on the Karkheh embankment dam with a clayey core and plastic concrete cut-off wall during construction, impounding, and permanent seepage stages. The dam has 127 meters height and is located in a high seismic hazard zone in Iran. Different stages of construction, water impounding, and steady state seepage were modelled and analyzed using the hyperbolic and Mohr-Coulomb models with the two dimensional finite difference method (FDM). So, nonlinear analyses were performed using FLAC 2D to investigate the settlements and the pore water pressure changes in different zones of the dam during above-mentioned stages and the results were compared to those of the other studies. The results show that at the end of the construction stage, the maximum settlement equal to 1.45m occurs inside the clay core at the height of 65m. Then, after impounding of the reservoir and steady state stage, the maximum magnitude of the horizontal deformations occurs in the downstream of the dam equal to 0.55m; however, these magnitudes reach to 0.17m at the crest of the dam. Moreover, it was shown that the maximum horizontal displacement of the plastic concrete cut-off wall has happened at the top of the wall in the clay core which is in a good agreement with the other studies’ result.

Numerical analyses of embankment dams containing plastic concrete cut-off walls using finite difference method (A case study: The Karkheh Embankment Dam)

Numerical analyses of embankment dams containing plastic concrete cut-off walls using finite difference method (A case study: The Karkheh Embankment Dam)

Construction Technology and Application of Plastic Concrete Cutoff Wall in Water Conservancy and Hydropower Projects

Construction Technology and Application of Plastic Concrete Cutoff Wall in Water Conservancy and Hydropower Projects

Effects of pH and EC on the strength and permeability of plastic concrete cutoff walls.

At present, plastic concrete is widely used in anti-seepage engineering, and its strength and hydraulic conductivity are important indexes of plastic concrete cutoff walls. The pondus hydrogenii (pH) and electrical conductivity (EC) have an important effect on the strength and hydraulic conductivity of plastic concrete cutoff walls. However, it is not clear why the pH and EC are related to the strength and permeability of these walls. For this reason, plastic concrete composed of sand, cement, water, and bentonite was taken as the research object to study the influence of different mix ratios and curing ages on the unconfined compressive strength and permeability of plastic concrete. The pH and EC of the corresponding mix ratio and curing age were measured. The effects of the pH and EC on the strength and permeability of plastic concrete were studied, and the internal reason was explored from the product type and hydration reaction degree of plastic concrete. Furthermore, the quantitative relationship between pH and EC and the strength and hydraulic conductivity of plastic concrete was established. With increasing cement content, the strength, pH, and EC of plastic concrete increase continuously, while the hydraulic conductivity decreases. With increasing curing age, the strength increases, the hydraulic conductivity decreases, and both the pH and EC show a trend of first increasing and then decreasing. The pH value and electrical conductivity can reflect the product type and hydration reaction degree of plastic concrete, further affecting its strength and hydraulic conductivity. Under different dosage and curing age conditions, the pH showed three stages, namely, 11.7-12.27, 12.27-2.5, and 12.5-12.75, and there is a good power functional relationship among the EC and strength and hydraulic conductivity at each stage.

Design of a Plastic Concrete Cutoff Wall as a Remediation Plan for an Earth-Fill Dam Subjected to an Internal Erosion

Abstract This paper deals with the procedure to determine the required mechanical properties of plastic concrete used to build a new cutoff wall as a remediation measure in an earth-fill dam constr...

Determination of plastic concrete behavior at different strain rates to determine Cowper-Symonds constant for numerical modeling

Strain rate investigations are needed to calibrate strain-rate-dependent material models and numerical codes. An appropriate material model, which considers the rate effects, need to be used for proper numerical modeling. The plastic concrete cut-off wall is a special underground structure that acts as a barrier to stop or reduce the groundwater flow. These structures might be subjected to different dynamic loads, especially earthquake. Deformability of a structure subjected to dynamic loads is a principal issue which need to be undertaken during the design phase of these structures. The characterization of plastic concrete behavior under different strain rates is essential for proper designing of cut-off walls subjected to dynamic loads. The Cowper-Symonds model, as one of the most commonly applied material models, complies well with the behavior of a plastic concretes in low to moderate strain rates and will be useful in explicit dynamics simulations. This paper aims to present the results of an experimental study on mechanical responses of one of the most useful types of plastic concrete and Cowper- Symonds constant determination procedures in a wide range of strain rate from 0.0005 to 107 (1/s). For this purpose, SHPB, uniaxial, and triaxial compression tests were done on plastic concrete samples. Based on the results of quasi-static and dynamic tests, the dynamic increase factors (DIF) of this material in different strain rates and stress state conditions were determined for calibration of the Cowper - Symonds material models.

Study on the microscale structure and anti-seepage properties of plastic concrete for cut-off walls modified with silica fume: Experiment and modelling

A modified plastic concrete cut-off wall was synthesized using different mass ratios of silica fume (0–21.3%) and constant cement content (8%) based on the conventional soil-bentonite cut-off wall. The slump test, hydraulic conductivity and mechanical performance were analysed to determine the optimal material ratio. The hydraulic conductivity of the optimal sample could meet theanti-seepagerequirement (~10-9 m/s). The amended plastic concrete cut-off wall could obtain the appropriate compressive strength (0.896 MPa) and a low elastic modulus (1244.5 MPa). The characterization of the clayey soil materials and modified plastic concrete cut-off walls were analysed by X-ray diffraction (XRD) methods, which demonstrated that the clayey soil mainly contained quartz and feldspar (anorthite). The pozzolanic reaction between the silica fume and calcium hydroxide and the refinementofthe porestructure could increase the compressive strength and reduce the hydraulic conductivity. Microscale three-dimensional real geometry images of the modified plastic concrete for cut-off walls were obtained from X-ray microcomputed tomography. The internal structural parameters were analysed through pore-scale modelling. The hydraulic conductivity and velocity fields were simulated using the lattice Boltzmann method. The results showed that most of the pores and throats in the modified plastic concrete for cut-off walls were micropores and microflow paths (diameter ≤ 5 μm), and the connected porosity was approximately 25.89%. The simulated hydraulic conductivity was in good agreement with the measured value, and the velocity fields indicated that the microflow paths were tortuous and complex. The silica fume-modified plastic concrete for cut-off walls enabled the realization of the requirements for good controlof the waterseepage in hydraulic engineering construction applications at a low cost.

Application of plastic concrete cut-off wall in reinforcement of reservoir

Plastic concrete is a kind of suitable material for cut-off wall of earth dam, which has low elastic modulus and permeability, large ultimate deformation, and good workability. In this paper, the mix proportion of plastic concrete with 50% bentonite content, water-binder ratio of 1.00 and sand-aggregate ratio of 55% is proposed, and the plastic concrete cut-off wall has been successfully applied to the reinforcement project of Huizhou Zengbo Lianhe reservoir. All the indexes meet the design requirements. The seepage of the main dam was reduced by 67%, and the piezometric level behind the wall was reduced by 6-9 m.

Performance of a deep excavation in Lanzhou strong permeable sandy gravel strata

A large air shaft engineered between the Olympic Sports Center Station and Century Avenue Station of the Lanzhou Metro Line one, China, occurred in strong permeable sandy gravel complex strata. The short distance between the Yellow River and the pit (shaft) resulted in many challenges during construction. These challenges mainly included the quick recovery of the water level and the difficulty of plugging the water. Some measures for monitoring the structural safety and response of the surrounding environment were taken. As the data showed, the design combined a bottom-up method with a top-down method using a peripheral cut-off wall for anti-seepage treatment, the underground diaphragm wall and the concrete bracing had a large rigidity, good impermeability and little influence on the surrounding environment in the process of dewatering and excavation, the external plastic concrete cut-off wall could contribute to the groundwater drawdown inside the pit and reduce the soil pressure on the retaining structure of the pit.

Construction and Monitoring of Cement/Bentonite Cutoff Walls: Case Study of Karkheh Dam, Iran

Abstract Water seepage is one of the most important features of embankment dams. To prevent and reduce seepage, it is necessary to seal the dam. Plastic concrete cutoff walls are one of the most efficient methods in waterproofing the foundation of embankment dams on permeable alluvial substrates. Sufficient resistance to loads, low permeability to maintain dam sealing, high ductility compatible with the foundation and deformation under load without cracking are the main requirements in plastic concrete cutoff walls. In this paper, the construction and implementation of the cutoff wall of Karkheh Dam, which is one the world’s largest water sealing projects, was studied. In addition, a numerical model using Seep-3D software was developed to evaluate the efficiency of the cut-off wall to decrease the seepage over the dam’s foundation. The numerical results validated by instrumentation statistics resulted from 17-years dam operation. According to the results, after the drainage of the reservoir, the cutoff wall optimally reduced the hydraulic gradient by 0.08 from 2.35 and the water leakage by 3.1 m/s from 18.3 m/s.

FEM Analysis of Stress Charecteristics of Cut-off Wall in Rushan River Groundwater Reservoir

In order to evaluate the safety of stress intensity of the plastic concrete cut-off wall in Rushan River underground reservoir, the most dangerous section of the cut-off wall was selected, the stress distribution characteristics of the cut-off wall were analyzed by ABAQUS finite element analysis method, the safety strength was rechecked, and the calculation results are compared with the stress calculation results of the elastic foundation beam method. The following conclusions are drawn. The calculation results of the two methods show that the water level difference between the two sides of the cut-off wall has a great influence on the stress of the cut-off wall. The maximum compressive stress of cut-off wall is less than 3 Mpa and the maximum tensile stress is less than 0.65 Mpa, which meets the design strength of plastic concrete cut-off wall. ABAQUS finite element analysis method is feasible in the stress analysis of cut-off wall. Compared with the results of elastic foundation beam method, the finite element method can better reflect the stress distribution and displacement deformation on both sides of cut-off wall. ABAQUS finite element analysis method has certain advantages in stress analysis of cut-off wall.

Evaluation of Penetration Depth for Cutoff Walls in the Core of Earth Dams

Seepage and water flow into soil are of the critical factors in the design of earth dams. There are various methods to control seepage in the dam foundation. One solution is the use of plastic concrete cutoff wall. Due to a higher hydraulic gradient in the union area and pressure increase of embankment above the wall by time, a considerable consolidation occurs in the wall. Therefore, crack in the wall, water seepage and erosion in the union area may occur. Hence, one of the items considered in earth the dams sealing system of design especially for plastic concrete cutoff walls is union area. This paper focuses on the effects of penetration depth of cutoff walls into the core of earth dams. To this aim, Anbaran dam located in the north-west of Iran was selected as a case study. Various penetration depths of cutoff walls including 0, 1, 2 and 3 m were considered. A two-dimensional model was defined and the results were compared together. For the numerical modeling and analysis of stresses and displacements in the mode of statics, including the construction stage and the first impoundment stage, GeoStudio-2007 and FLAC2D softwares were used, and for the dynamic stage FLAC2D was used. The results show that the penetration depth of wall plays an effective role in the flow rate of water, hydraulic gradient, stress and displacement of wall and union area. The results of numerical model revealed that, as the penetration depth increases, stresses and displacements of union area increase while the hydraulic gradient and seepage at the union area decrease. Finally, by analyzing the dam behaviorial parameters such as stress, displacement, seepage and hydraulic gradient, and also considering the economic and implementation aspects, the penetration depth of 2 m is chosen as an optimum penetration depth of this case. In this state, the maximum magnitudes of vertical and horizontal stresses are 2371 kPa and 728 kPa, respectively and the maximum magnitudes of vertical and horizontal displacements are 19.36 cm and 7.42 cm, respectively. The amount of seepage under the dam body is 3.330 × 10−6 m3/s/m and the maximum hydraulic gradient in the wall is 39.222. However, to find an optimum penetration depth of cutoff wall into the clay core, numerical analysis with corresponding specifications are strictly needed, indeed.

Effect of Dry and Saturated Bentonite on Plastic Concrete

Dams are rarely built on non-permeable lands, therefore usually reservoir leakage from dam foundations cause major problems for large dams which affect dams performances. One method of controlling the origin of leaks is to use plastic concrete cutoff walls. Bentonite is one of the most important materials used in constructing plastic concrete which act as a stabilizing agent. It is from clay materials having high water absorption and swelling of 300% properties even after contacting with water. These properties may cause negative effects on plastic concretes that include deep cracks and high reductions on its strength. In order to eliminate these effects, plastic concretes must be mixed with water at least 24 hours before usage and then they must be blended by special blades until they are totally saturated. This process costs huge time and money. Therefore, in this research, dry bentonite has been added to the mixer with particular method. It can be seen saving time and money and the properties of plastic concrete such as compressive strength, tensile strength, slump and permeability will not be slightly changed.