Search Results (11)

Slope stability analysis requires particular attention to groundwater effects, where seepage–stress coupling fundamentally alters mechanical responses. This investigation develops a field-calibrated numerical model using monitoring data from a water diversion project in Yunnan, using finite element analysis based on seepage–stress coupling theory. Comparative stability assessments through strength reduction methodology evaluate three scenarios: non-seepage conditions, seepage–stress interaction, and cutoff wall implementation. Results demonstrate the cutoff wall’s effectiveness, achieving optimal slope ratios of 1:1.41 compared to 1:2.21 under seepage–stress coupling. Parametric analyses reveal quantitative relationships between wall characteristics and stability metrics. Elastic modulus optimization within practical ranges (9362.63 MPa peak performance) enables steeper 1:1.37 slopes while maintaining safety factors. Strategic width reduction from 0.6 m to 0.4 m decreases concrete usage by 33% without compromising stability thresholds, proving cost-efficiency in large-scale applications. The methodology provides actionable guidelines for deep excavation projects facing similar hydrogeological challenges. Optimized cutoff walls enhance slope stability sustainably through ecological preservation and resource efficiency, providing actionable frameworks for eco-conscious geotechnical design aligned with global sustainability objectives. Full article

Plastic Concrete is a low-strength ($f_{cm,28\mathrm{d}}$ ≤ 1.0 MPa), low-stiffness impervious concrete used for cut-off walls in earthen dams worldwide. These properties are achieved through a very high w/c ratio (w/c ≥ 3.0) and water-binding additions (e.g., bentonite). To date, the effect of mix design, especially w/c ratio, as well as bentonite content and type, on the long-term time development of the microstructural properties and corresponding compressive strength of Plastic Concrete has yet to be systematically studied. Furthermore, in the literature, mercury intrusion porosimetry (MIP) and X-ray diffractometry (XRD) have yet to be applied systematically to Plastic Concrete for this purpose. The present study closes this gap. Ten Plastic Concrete mixes with two bentonite–cement ratios, three types of sodium bentonite and two swelling times were produced. MIP and XRD measurements and compressive strength tests were performed at sample ages of 7 d, 28 d, 56 d, 91 d and four years. The results show that both MIP and XRD can be successfully used; however, meticulous sample preparation and data analysis must be considered. The porosimetry results show a bi-modal pore size distribution, with two age-dependent peaks at approximately 10,000–20,000 nm and 100–700 nm. The results also exhibit a clear pore refinement over time, with coarse porosity dropping from 26% to 15% over four years. In addition, the fine porosity peak is significantly refined over time and positively correlates with the significant increase in compressive strength. The XRD results show no unexpected crystalline phases over the same period. Overall, this study links MIP and corresponding compressive strength data specifically for Plastic Concrete for the first time, confirming the key role that the mix design of Plastic Concrete plays in defining its long-term microstructural and mechanical properties and ensuring more realistic cut-off wall design in the future. In addition, the experimental boundaries for MIP testing on Plastic Concrete are set out for the first time, enabling future research in this field. Full article

Dam foundations are prone to leakage damage after being exposed to long-term water action, which seriously affects the operation safety of the dam. At present, concrete cut-off walls serve an important means of anti-seepage for dam foundations. However, due to construction challenges, the cut-off wall needs to be poured segment-by-segment during the construction process, and the joints between adjacent segments become weak parts for seepage prevention. Therefore, it is crucial to clarify the stress state of segmented discontinuous concrete cut-off walls. Based on the Lee-Fenves framework and the tension–compression constitutive relationship of fracture energy, a plastic damage calculation method was established in this paper to characterize the mechanical behavior of discontinuous cut-off walls. The method was then used to analyze the mechanical performance of discontinuous walls with segment joints containing slurry cake. The research results showed that compared to the continuous cut-off wall, the vertical settlement in the middle part of the discontinuous cut-off wall increased by 5.8%, and the displacement along the river flow direction decreased by 35.3%. As the wall segment width decreased, the joint opening and the degree of tensile damage were reduced accordingly, while the compressive damage in the middle and lower parts of the wall was intensified. As the wall depth decreased, the constraints and load on the bottom of the wall showed obvious changes, leading to a reduced stress and damage level of the wall. The findings provide reference for the design and safety control of cut-off walls. Full article

In this paper, a novel numerical model for characterizing the seepage and dissolution coupling effect on the durability of anti-seepage walls of earth-rock dams is proposed. The model considers the influence of hydraulic gradient-driven seepage on the non-equilibrium decomposition of the calcium dissolution in concrete, as well as the effects of seepage dissolution on pore structure, permeability, and diffusivity. The reasonableness of the model is validated by experimental and literature data, which is then applied to analyze the deterioration and failure processes of a concrete cutoff wall of an earth-rock dam in Zhejiang Province, China. On this basis, the seepage dissolution durability control indices of anti-seepage walls are identified. The findings demonstrate that the suggested method accurately explains the calcium leaching process in concrete. Under the seepage and dissolution coupling effect, calcium in the wall continuously decomposes and precipitates, leading to varying degrees of increases in structural performance parameters, which weaken the seepage control performance of the walls and consequently result in an increase in seepage discharge and hydraulic gradient. By proposing the critical hydraulic gradient as a criterion, the service life of the wall is projected to be 42.8 years. Additionally, the upstream hydraulic head, the initial permeability coefficient, and the calcium hydroxide (CH) content are three crucial indices affecting the durability of walls, and these indices should be reasonably controlled during the engineering design, construction, and operational phases. Full article

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. Full article

Plastic concrete is a ductile material with a low elastic modulus (1000–3000 MPa), good flexibility, a and strong ability to adapt to the surrounding soil deformation. Hydraulic concrete mainly serves in a watery environment, so the leaching behavior of plastic concrete is crucial and cannot be neglected. Meanwhile, improving the crack resistance and effect of anti-seepage is also a primary task for cut-off walls. In this paper, in order to investigate the mechanical performance and leaching behavior of plastic concrete, a uniaxial compressive strength test was performed on plastic concrete specimens of a specific age (28 days) and different percentages of replacement cement by single bentonite (40%, 50%, and 60%) and bentonite (30%) together with clay (10%, 20%, and 30%), and the compressive strength, elastic modulus, pH value of the leaching solution, ultrasonic transmit time, electrical resistivity, and calcium ion dissolution concentration of plastic concrete have been evaluated. Moreover, the quantitative relationship between pH value and calcium ion concentration change was built through the electrochemical accelerating leaching method. According to the results, adding 40–60% soil materials can entirely meet the compressive strength (2–7 MPa), elastic modulus (below 3000 MPa), and relative permeability coefficient (below 1 × 10⁻⁷ cm/s) of plastic concrete used for cut-off walls while the compressive strength and elastic modulus of plastic concrete with 30% replacement cement by bentonite would be higher than 7 MPa and 3000 MPa, respectively. The leaching resistance of plastic concrete can be improved by more than 30% by adding bentonite coupled with clay, and three representative zones were observed through SEM and energy spectrum analysis, and Ca/Si molar ratio decreased by 30% after leaching. Full article

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. Full article

In the past thirty years many mining projects in Chile and Peru have used: (i) polymeric geomembranes and (ii) design-and-build cutoff trenches, plastic concrete slurry walls, and grout curtain systems to control seepage at tailings storage facilities (TSFs). Geosynthetics are a viable alternative at a TSF dam for clay cores or impermeable materials, mainly because of their marked advantages in cost, installation, and construction time. This article describes the use of geosynthetics liners and cutoff trench–plastic concrete slurry walls–grout curtain systems in TSF dams in Chile and Peru mining, with the objective to decrease seepage to the environment, considering different dam material cases such as: cycloned tailings sand dams, borrow dams, and mine waste rock dams. Finally, this article discusses aspects of geosynthetic technology acceptance in the local regulatory frameworks, lessons learned, and advances. It focuses on the use and implementation of geosynthetics in TSFs in Chile and Peru, which have some of the highest TSF dams in the world, as well as a wet environment, dry environment, extreme topography, and severe seismic conditions. These conditions constitute a challenge for manufacturers, engineers, and contractors, who must achieve optimal technical solutions, while being environmentally aware and economic. Full article

The construction of a cut-off wall is a common reinforcement method for earth rock dams. At present, compared with the in-depth study on homogeneous earth dams, more and more attention is being paid to the stability and deformation of earth dams strengthened by a concrete cut-off wall. In this study, aiming at the Wujing project of the earth dam strengthened by cut-off wall, the influence of the water level rise and fall on the stability of the dam slope, the deformation of the dam body, and the crack width on dam crest were analyzed by numerical calculation and in situ measurement. The analysis results show that when the reservoir encounters a sudden drawdown, the safety factor of the dam slope decreases sharply. The faster the sudden drawdown, the faster the safety factor decreases. When the reservoir water level rises, the dam’s horizontal displacement shifts to the upstream direction, and the change of horizontal displacement of the downstream slope is significantly larger than that at the measuring point of the upstream slope. The water level of the reservoir rises, and the surface of the dam body rises, and the fluctuation of settlement deformation shows that the upstream side is larger than the downstream side, especially during the period of abrupt change in the reservoir water level. The longitudinal cracks on the dam crest show a tendency of shrinkage when the reservoir water level rises, and opening decreases with the decrease of deformation gradient increment and increases with the increase of gradient increment. Full article

As urban development requires groundwater table isolation of various historically polluted sources, the necessity of building effective, strong, flexible, and low-permeability cutoff walls raises the question of choosing optimum construction materials. Various authors have proposed water–cement–bentonite mixtures, which are often chosen by experience or a trial-and-error approach, using classical methods for testing (Marsh funnel) and representation of results (water–cement ratio, water–bentonite ratio). The paper proposes a more precise approach for assessing the viscosity and global representation of the three components. Moreover, this approached is exemplified with a better documented recipe for the choice of materials based on laboratory results. The representation of the mixtures was undertaken on a limited domain of a ternary diagram, where the components are given in terms of mass percentage. The derived properties (viscosity, permeability, and compressive strength) are presented on a grid corresponding to the physically possible mixtures. Based on this representation, the most efficient recipes are chosen. Because the mixture contains only fine aggregates, the viscosity was determined using a laboratory viscosimeter. Full article

Hardening slurries (water-bentonite-binder mixtures) constitute a well-established material used broadly, i.a., for cut-off walls in civil and water engineering. Although they usually contain Portland cement, similar to common concrete, their properties differ greatly, mostly due to a much higher water content. This characteristic of hardening slurries creates unique opportunities for the utilization of significant quantities of industrial by-products that are deemed problematic in the concrete industry. This article investigates the effect of the addition of by-products of fluidized-bed combustion of hard, brown coal and municipal sewage sludge, as well as ground granulated blast furnace slag, on the properties of slurries. Unconfined compressive strength tests, as well as mercury porosimetry, scanning electron microscopy, and X-ray diffraction analyses were performed. The results suggest that it is possible to design hardening slurry mixes of desired properties, both in liquid and solid state, containing at least 100–300 kg/m³ of industrial waste. This includes cement-free slurries based entirely on industrial by-products as binders. In addition, the analyzed slurries exhibited good chemical resistance to landfill eluates, at the same time effectively immobilizing heavy metals. It was concluded that hardening slurry technology can ensure the safe deposition of significant amounts of waste that would be otherwise difficult to manage, thus contributing to the circular economy concept. Full article