Clay Core Research Articles

Investigation of seepage near the interface between an embankment dam and a concrete structure: monitoring and modelling of seasonal temperature trends

Seasonal subsurface temperature monitoring, which exploits the fact that increased seepage flow may locally alter the temperature distribution, is a useful approach for leakage monitoring and evaluation within embankment dams and their foundations. At the Mactaquac Generating Station, New Brunswick, Canada, spatial and temporal variations of temperature have been monitored and modelled at the steeply inclined interface between the compacted clay till core of the embankment dam and an abutting concrete diversion sluiceway. Over a 4-year period, two seasonally recurring anomalies at different depths were observed by fibre optic distributed temperature sensing in the concrete structure close to the interface. A 3D coupled flow and heat transport model was developed in FEFLOW to simulate temperature distribution within the dam resulting from seasonal variations in air and reservoir temperature. Leakage zones near the interface were simulated in the concrete and embankment. At a depth of 13 m below the crest, the significant lag time between temperature variations in the reservoir and dam core shows that the leakage responsible for an observed temperature anomaly must be limited to enhanced flow within the concrete. At much shallower depths, where seasonal reservoir and dam core temperatures fluctuate nearly in phase, seepage paths are more challenging to determine.

Deformation and Stability Analysis of a Core Rockfill Dam with Leakage

The No. 4 clay core rockfill dam of the Gongming Reservoir experienced leakages when the reservoir water level was low. To analyze the leakage causes, a series of seepage tests were conducted on the dam materials in this paper. And a three-dimensional finite element stress-seepage coupled calculation model of the dam was established to study the deformation and stresses of the dam under the condition of normal storage water level and the sharp drop in the storage level. The test results show that the permeability coefficient of the clay core material is close to that of the dam shell material, resulting in the leakage of the dam under the condition of the low-water level. The simulation results show that the dam deforms a little under the condition of normal storage water level and the sharp drop in the storage level, and the stress distribution under the condition of the sharp drop in the storage level is basically consistent with that under the condition of normal storage water level. The safety factors of the dam under the two conditions meet the requirements of the specification, but the margin of the safety factor is small.

An Experimental Study for Swelling Effect on Repairing of Cracks in Fine-Grained Clayey Soils

Earth-dam failure starts with cracking in the clay core, and this cracking is not easy to detect and prevent. Therefore, swellable clay is a feasible solution, which helps to close the cracks automatically based on the self-healing process. The presented study utilizes experimental procedures to analyze the swelling behavior of fine-grained clayey soils to prevent structural failure regarding crack generations. In this regard, the clayey materials were modified using Kaolin and Bentonite mixed with various weight percentages (2.5, 5.0, 7.5, 10.0, and 12.5%) and extracted the geotechnical characteristics of the studied soils, which included 90 specimens and 85 tests, such as physical properties, consolidation, particle-size analysis, hydrometry, Atterberg limits, compaction, odometer, and pinhole. The experimental results revealed that the swelling of the Bentonite is more than Kaolin satisfied for self-healing features in clayey soils. Regarding the numerous swelling tests, Bentonite provides optimum results (attained 10%) compared to Kaolin. As a verification procedure, the pinhole test was performed on samples, which revealed that Bentonite was dominant in controlling the water flow through the samples.

A Simplified Method for Leakage Estimation of Clay Core Dams with Different Groundwater Levels

Clay core dams are widely applied in reservoir construction, regulating water resource and provide electric power. Leakage is a common problem in reservoir construction, and the leakage amount, which not only affects the economic benefits of the project, but also relates to the safety of the dam body, is difficult to estimate. According to Darcy’s law and stable seepage theory, an analytical method can be proposed to calculate the leakage of the clay core dam to gain the seepage flux in a short time. By making some reasonable assumptions, we propose formulae for seepage calculation in different conditions of the position of the groundwater levels, below or above the reservoir bottom. Both sets of formulae contain two parts of leakage calculation, i.e., leakage from the reservoir bottom and leakage from the dam body. By using the proposed analytical method, the leakage of clay core dams can be estimated considering the influence of the groundwater level. To prove the rationality of the analytical method, a simple numerical model can be established using Geo-studio 2020 to calculate the seepage flux of the clay core dam, where relative errors between numerical solutions and analytical solutions are less than 10%. To verify the feasibility in engineering applications, the proposed method was applied to calculate the seepage of a clay core dam in Sichuan, China, which was also calculated using numerical methods by establishing a three-dimensional model. The results show the rationality of the analytical method, which can strike a balance between precision and efficiency.

Experimental Investigation on Seepage Characteristics of Clay-Structure Interface after Shear Deformation.

There exist shear and seepage behaviors on the interface between clay core and concrete slab in clay core dams. In order to investigate the seepage characteristics of the clay–structure interface after shear deformation, a shear-seepage test system is proposed, in which the seepage direction is perpendicular to the shear direction. The shear test and shear-seepage test are performed on clay–metal and clay–mortar interfaces under different normal stresses (100, 200, 400, 800, and 1600 kPa). The shear stress-deformation curves of two clay–structure interfaces exhibit softening behavior and residual friction behavior. The interface roughness can enhance peak and residual shear strength and increase peak displacement. The shear-seepage test results show that specimen permeability decreases first and then increases to a stable value as shear deformation increases under low normal stress, while it decreases continuously and then retains stability under high normal stress. The interface roughness enhances specimen permeability under low normal stress, whereas it has a weak effect on specimen permeability under high normal stress. Compared with initial permeability, shear deformation reduces specimen permeability rather than raise it. The ratio of stabilized permeability coefficient to initial value ranges from 0.6 to 0.8. The clay–structure interface still has a good resistance to seepage failure after shear deformation. The shear dilation features and interface pore decrease caused by shear behavior are the internal attributions of clay–structure specimen permeability evolution.

Evaluation of the Effect of Varying the Angle of Asphaltic Concrete Core on the Behavior of the Meijaran Rockfill Dam

The use of asphaltic concrete cores for sealing embankments and rockfill dams is very important. The self-healing properties of bitumen, simple construction in cold and rainy conditions compared to clay cores, good flexibility and connection with embankment materials are the essential characteristics of asphaltic concrete. The main concern regarding the use of asphaltic concrete cores in Iran is mainly the performance of these dams under seismic loads. The evaluations of the performance of these types of dams in other countries show that asphaltic concrete cores perform satisfactorily in the static state, but in earthquake conditions, the situation may be different. In this paper, the static and seismic behavior of the Meijaran dam in Iran, Mazandaran, is evaluated for three core angles of 90°, 60° and 45°. This evaluation was conducted at the end of the impounding stage and after applying seismic loads using FLAC 2D software and Mohr–Coulomb consitutive models. The results were matched with the ICOLD recommendation to use angled cores in dams with asphaltic cores and showed that the dam performs better with angled cores. Finally, for the Meijaran dam, the results from the dynamic analysis are compared with the results from the centrifuge test.

Effect of engineering geological properties on dam type selection of the Qadis Khordak Dam, Afghanistan

This paper deals with engineering geological properties of Qadis Khordak dam site in Northwest Afghanistan. This study is based on on-site and laboratory tests, surface discontinuity surveying, drilled borehole and permeability test of dam foundation. The engineering geological properties at the dam site were studied in order to evaluate geotechnical characteristics of rock masses at dam foundation, geotechnical properties of alluvium at dam axis, reservoir and borrow materials. The structural geological studies also carried out due to stability and safety of dam on their abutments reservoir and seismicity. Existence of a fault, high permeable zone at dam foundation and the thickness of alluvium at dam axis, are the most engineering geological issues that cause change on dam type selection. In the feasibility phase, the dam type was chosen as the concrete face rock-fill dam, because of state of engineering geological properties of dam site. However, in the design phase dam type has been changed as a rock-fill with a clay core.

The Utilization of Self-Crosslinkable Nanoparticles as High-Temperature Plugging Agent in Water-Based Drilling Fluid

Summary The increasing exploration of oil/gas resources in unconventional reservoirs, such as deep layers and shale formation, hinges on the development of high-performance drilling fluids under harsh environments. In this work, self-crosslinkable nanoparticles [poly(methyl methacrylate/styrene/2-acrylamido-2-methyl-1-propanesulfonic acid (PMS)/N-(hydroxymethyl)acrylamides (PMSNs)] were prepared and utilized as a plugging agent to realize micropore plugging at high temperatures. The obtained PMSN possesses long-term colloidal stability in conventional storage and high-temperature aging cases. Incorporating thermal crosslinking property brought PMSN post-crosslinking behavior during thermal treatment and improved the thermal stability, as verified by Fourier transform infrared spectrometer (FT-IR) and thermogravimetric analysis (TGA) tests. Additionally, PMSN is emulsifier-free and compatible with bentonite-based drilling fluid without foaming problems. Compared with conventional rigid nanosilica (NS) and flexible nanopolyester (NP-1), PMSN can improve the hole-cleaning efficiency of sodium bentonite (Na-Bent) dispersion by increasing viscosity and yield point (YP), especially after thermal aging. Its filtration-reduction and clay core plugging performance at room temperature are between NS and NP-1, ascribing to the rigid core and partial flexible shell structures of PMSN. However, at high-temperature, high-pressure (HTHP) conditions, PMSN with self-crosslinked structures have superior micropore plugging performance over NS and NP-1. A statistical-significant model was established based on response surface methodology (RSM) to illustrate the main and interactive effects of PMSN dosage, aging temperature, and time on the HTHP micropore fluid loss. The optimal plugging can be obtained after high-temperature aging when self-crosslinking happened. The specific self-crosslinking plugging mechanism of PMSN is the combination of interior self-crosslinking in water and interparticle crosslinking in the deposited plugging layer.

Adjustment Design of Gangou Shantang Clay Core Dam

Adjustment Design of Gangou Shantang Clay Core Dam

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

Evaluation Indices and Design Method to Determine the Rolling Density of Dam Shell Sandy Gravel Material

AbstractSandy gravel dams with clay core walls are a widely used dam type, and the rolling density of sandy gravel material is evaluated by the relative density Dr. Consequently, designing the opti...

Common Problems and Quality Requirements of Clay Core Weathered Material Dam Body Filling

Common Problems and Quality Requirements of Clay Core Weathered Material Dam Body Filling

Effect of stress on permeability of clay silty cores recovered from the Shenhu hydrate area of the South China Sea

Hydrate saturation and effective stress are the most important key factors in controlling permeability by altering the pore structure of hydrate reservoirs. However, the understanding of the dependence of the permeability on these factors in fine-grained hydrate reservoirs is not comprehensive due to limited experimental conditions. In this study, clay silty cores recovered from the Shenhu hydrate area of the South China Sea were used as skeletons to synthesize tetrahydrofuran (THF) hydrate-bearing sediments with hydrate saturations of 0–0.6. A series of step-by-step loading and water permeability measurements were conducted on a customized permeability measurement system. The results showed that the water permeability was in the range of 0.005–4 mD, approximately 0.03–1.47 mD near the value of the in situ effective stress of ∼2 MPa. The water permeability increased with increasing effective porosity and conformed to a modified Kozeny-Carmen equation, while the effective porosity increased exponentially with hydrate saturation and effective stress. Permeability stress sensitivity analyses showed that the normalized permeability stress sensitivity coefficient increased with the increase of hydrate saturation. Pore space compression and pore throat clogging were the important factors in the reduction in the water permeability, which dropped by approximately 95% when the effective stress increased from 0 to 8 MPa. This study provides insight into the evolution of pore space and permeability during gas recovery from hydrate-bearing clay silty sediments.

Cracking of unsaturated clays using a newly developed small-beam bending apparatus and analysis by digital image correlation

This research presents a comprehensive investigation on the impact of initial imposed suction both on the applied tensile force and the cracking phenomenon of unsaturated clayey soil samples. The proposed experimental approach is based on using a new developed apparatus for testing the indirect tensile force on small-beam bending. Several sets of bending tests have been carried out on small clay beams initially submitted to different levels of suction (361 MPa, 110 MPa and 38 MPa). The approach consisted first to study the global behaviour by estimating the maximum tensile force Fmax which controls the initiation of tensile cracks. The results show that Fmax varies with the initial imposed suction level as well as the consolidation stress direction representing the initial loading applied to the sample during the stage of clay core preparation. Then, unload–reload cycles allowed to describe the reversibility of beam’s behaviour versus the initial imposed suction. Finally, by using digital image correlation technique, the formation and propagation of cracks were precisely captured through the measurement of the local strain variations, especially close the crack tip.

Metallurgical activity in the Early Bronze Age period on the hilltop settlement of Pod near Bugojno

In the present article attention is drawn to several finds from the Early Bronze Age period, which in our opinion represent clear indications for a bronze casting workshop at the hilltop settlement of Pod near Bugojno, situated in the valley of the river Vrbas. These represent ceramic cylindrical objects, which we associate with identical finds from the workshop of a bronze founder in the Early Bronze Age phase at the settlement of Feudvar near Mošorin in Vojvodina. They can be interpreted as clay core supports, used as a casting instrument during the production of bronze objects.

Modeling the effect of central impervious core and downstream filter geometry on seepage through earth dams

This investigation aims to identify the seepage discharge in the earth dam resting on an impervious foundation. Twenty-one models of a homogenous earth dam with and without horizontal filter and a central impervious core of different width were constructed in a hydraulic flume. In the present study, fluid and geometrical parameters of the dam, horizontal filter’s and the central impervious core were varied to find their effect on seepage. It was observed that with increasing the dam’s height, filter’s length, downstream slope, and longitudinal slope, there was an increase in seepage discharge and vice versa with upstream slope, clay core’s thickness, the viscosity of the fluid, and the earth dam’s length. Several studies have neglected the variation in fluid's viscosity for the seepage study in earth dam modeling, which is included in this study. Using Slope/w, the stability of the upstream and downstream faces was checked under full reservoir conditions.

Architectural design of core-shell nanotube systems based on aluminosilicate clay.

A nanoarchitectural approach to the design of functional nanomaterials based on natural aluminosilicate nanotubes and their catalysis, and practical applications are described in this paper. We focused on the buildup of hybrid core–shell systems with metallic or organic molecules encased in aluminosilicate walls, and nanotube templates for structured silica and zeolite preparation. The basis for such an architectural design is a unique Al2O3/SiO2 dual chemistry of 50 nm diameter halloysite tubes. Their structure and site dependent properties are well combined with biocompatibility, environmental safety, and abundant availability, which makes the described functional systems scalable for industrial applications. In these organic/ceramic hetero systems, we outline drug, dye and chemical inhibitor loading inside the clay nanotubes, accomplished with their silane or amphiphile molecule surface modifications. For metal–ceramic tubule composites, we detailed the encapsulation of 2–5 nm Au, Ru, Pt, and Ag particles, Ni and Co oxides, NiMo, and quantum dots of CdZn sulfides into the lumens or their attachment at the outside surface. These metal–clay core–shell nanosystems show high catalytic efficiency with increased mechanical and temperature stabilities. The combination of halloysite nanotubes with mesoporous MCM-41 silica allowed for a synergetic enhancement of catalysis properties. Finally, we outlined the clay nanotubes’ self-assembly into organized arrays with orientation and ordering similar to nematic liquid crystals, and these systems are applicable for life-related applications, such as petroleum spill bioremediation, antimicrobial protection, wound healing, and human hair coloring.

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.

Stability analysis of embankment dams with defective internal geomembrane liners

ABSTRACT Internal geomembranes are alternatives to traditional clay cores and upstream geomembranes. In this research, numerical analysis is performed to assess the impact of leakage through 2-D geomembrane defects such as slits, tears and faulty stitches. Five possible applications of internal geomembranes and an upstream geomembrane were modelled to compare their performance with that of clayey cores. The results show that use of upstream or internal geomembranes significantly decreases the pore pressure developed at the downstream slope thus improving its stability. The effects of leakage through both internal and upstream geomembranes on the stability of embankment slopes under steady state and drawdown at a rate, conditions were analysed. Stability of the downstream slope reduces significantly due to defective geomembranes depending on the defective seam locations. Drawdown simulations show that internal geomembranes can cause instability in steep upstream slopes of dams.

Experimental and theoretical investigations of seepage reduction through zoned earth dam material with special core

Seepage through earth dams is one of the main causes of failure of earth dams through the internal movement of granules and their transport by seepage. The core in earthen dams has an important role in reducing leakage through the dam body and lowering the phreatic line. In this research, an alternative to the clay soil used in the core of the dam was innovated by conducting multi experiments for testing the permeability of the light-textured, sandy soil which is more available, with additives and it proposed as a suitable alternative. Then the innovative soil model was then used to represent the dam experimentally by means of a permeability device to measure the amount of seepage through the dam body and represent the seepage line. A finite element numerical model using Geo-Studio SEEP/W software was adopted to simulate and investigate soil with different percentages of additives and comparing the numerical and experimental results to predict the innovation model of soil. It was found that the type C sandy soil model has permeability very close to the permeability of clay soils, by using 10% Cement kiln dust (CKD) and 5% cement as additives. Moreover, soil type C was hypothetically tested as a core soil for HIMREEN earthdam of clay core soil. The result of the comparison between seepage for the hypothesis case and the real case was acceptable and they were very close.