Dam Core Research Articles

Permeation grouting for remediation of dam cores

Grouting methods are known to effectively remediate the dam foundation or the abutment. However, remediation grouting of the deteriorated embankment earth-core itself has rarely been performed or studied. In this study, low-pressure permeation grouting is adopted to remediate the deteriorated central core layers of five aging dams. Technical features of each dam's deterioration are described, such as sinkholes, slope failures, fluidized clay cores, and wet zones on the downstream surface induced by excessive seepage. This study suggests several empirical standards for the application of permeation grouting to the improvement of core permeability, including grout mix, injection period per stage, injection rate, and maximum fluid pressure to prevent hydraulic fracturing. The results of this empirical case study can be applied to effectively remediate degraded dam embankment cores to decrease their permeability and minimize the risk of hydraulic fracturing, without requiring a reduction in the reservoir water level.

Numerical model for clay core dam breach process due to overtopping considering different failure modes of core wall

Based on the breach mechanism of clay core dam due to overtopping failure, a numerical model for dam breaching process is put forward. In this model, the initial scour position on the downstream slope is determined by means of the characteristics of dam figuration and overtopping flow, the broad-crested weir formula is adopted to calculate breach flow discharge, and a time averaged backward erosion formula is adopted to simulate the dam shell breach. The moment and mechanical equilibrium methods are utilized to model the overturning and sliding failures of the core, respectively. In order to simulate the actual failure mode of the dam, one-and two-sided erosion, as well as dam base erosion, are taken into account. The model adopts the iterative calculation method to simulate the coupling process of water and soil during dam breaching. 10 clay core dam overtopping failure cases which have measured data are adopted to testify the present model. The comparison of measured data and calculated results on peak breach flow, final breach width and failure time shows that the calculated results can meet the engineering requirements, and the statistics of model’s relative errors validate the reasonability of the present model.

FEASIBILITY, VALUE ENGINEERING, AND ROCK FILL DAMS CONSTRUCTION: A CASE STUDY

In this study details of structure of Shahr-e-Bijar concrete-faced rock-fill (CFRD) in Guilan (a province in the north of Iran) and the reasons to select CFRD are presented. To select CFRD first by investigation of 18 different types of dam based on local availability of materials and the ability of constructing by available technology (both Iranian and foreign available technology) six types of them were selected for value engineering. By attention to construction costs, execution time, durability, reliability and performance and ease of construction and operation; and also, the importance coefficient for local government were selected for value engineering. After that 3 types of dam structure (vertical clay core dam, asphalt core dam, and CFRD) had maximum scores. Finally, rock fill dam with concrete surface is selected because despite being more expensive in some cases than other options, it could be considered as a successful dam construction option in Iran because the construction needs no foreign technology and its technology of construction and materials are available. On the other hand, the necessary time for the project is 24 months. The main objective of this project is to avoid time loosing because of materials availability and local technology that needs no finance transferring and no foreign contract that may not be affected by some political condition that delays the project.

Large-deformation finite element analysis of the interaction between concrete cut-off walls and high-plasticity clay in an earth core dam

PurposeA large, uneven settlement that is unfavourable to dam safety can occur between a concrete cut-off wall and the high-plasticity clay of earth core dam built on alluviums. This issue has been often studied using the small-strain finite element (FE) method in previous research. This paper aims to research the interaction behaviour between a concrete cut-off wall and high-plasticity clay using large-deformation FE analyses.Design/methodology/approachThe re-meshing and interpolation technique with a small-strain (RITSS) method was performed using an independently developed program and adopted for large-deformation FE analyses, and a suitable element size for the high-plasticity clay region was suggested. The layered construction process of an earth core dam built on thick alluviums was simulated using the RITSS method incorporating a hyperbolic model for soil.FindingsThe RITSS method is an effective technique for simulating the soil–structure interaction during dam construction. The RITSS analysis predicted a higher maximum principle stress of the concrete cut-off wall and higher stress levels in the high-plasticity clay region than small-strain FE analysis.Originality/valueA practical method for large-deformation FE analysis was advised and was used for the first time to study the interaction between a concrete cut-off wall and high-plasticity clay in dam engineering. Large deformation in the high-plasticity clay was handled using the RITSS method. Moreover, the penetration process of the concrete cut-off wall into the high-plasticity clay was captured using a favourable element shape and mesh density.

Discussion on the Safety Factors of Slopes Recommended for Small Dams

The design and assessment of the slope stability of small embankment dams is usually not carried out using slope stability calculations but rather by the comparison of proposed or existing dam slopes with those recommended by technical standards or guidelines. Practical experience shows that in many cases the slopes of small dams are steeper than those recommended. However, most of such steeper slopes at existing dams do not exhibit any visible signs of instability, defects or sliding. For the dam owner and also for dam stability engineers, the safety of the slope, expressed e.g. via a factor of safety, is crucial. The aim of this study is to evaluate the safety margin provided by recommended slopes. The factor of safety was evaluated for several dam shape and layout variants via the shear strength reduction method using PLAXIS software. The study covers various dam geometries, dam core and shoulder positions and parameter values of utilised soils. Three load cases were considered: one with a steady state seepage condition and two with different reservoir water level drawdown velocities – standard and critical. As numerous older small dams lack a drainage system, variants with and without a toe drain were assessed. Calculated factors of safety were compared with required values specified by national standards and guidelines.

Heterogeneous Influence on Hydro-Thermal Behaviors Within the Core of an Embankment Dam

Spatial variations of the hydraulic conductivity within compacted till cores are the result of heterogeneity, which are also the consequence of variability in source material and compaction conditions. This paper deals essentially with a numerical analysis of the influence of heterogeneity on hydro-thermal behaviors of dam QA-01 in northern Quebec. Input parameters from existing studies and a coupled heat and mass transfer formulation were used to model the monthly temperature profiles at the centerline of the core. Firstly, the parametric studies performed with the presence of more pervious layers within the core with different values of hydraulic conductivity were considered in the model. The obtained results of temperature distributions and time lags were used to evaluate the predictions for various conditions associated with the presence of pervious layers in the impervious core. Secondly, the model was then applied to dam QA-01 with the consideration of actual thermal and hydraulic properties. Modeled temperature profiles were finally compared with measurements to assess the heterogeneous influence. The close agreement between predictions and observations above the elevation of 340 m in the core was obtained. The numerical results also verify the existence of another more pervious zone below the elevation of 340 m.

Experimental Investigation of Suffusion in Dam Core Soils of Glacial Till

The main objectives of this study were to determine the susceptibility to suffusion of widely graded, non-plastic glacial till; to identify potential factors influencing susceptibility; and convers ...

MONITORING OF MASJED-SOLEIMAN EMBANKMENT DAM’S DEFORMATION USING A COMBINATION OF INTERFEROMETRIC SYNTHETIC APERTURE RADAR (INSAR) AND FINITE ELEMENT MODELING

The fresh water shortage is one the most important challenges in many countries like Iran. So there have been incentives to manipulate and manage water resources by constructing dams. Clay core embankments are one of the most popular dam structures. A layer of clay can be a reliable obstacle in front of water stream. However, because of the soil’s nature, these kinds of dams have the potential of instability. Thus deformation of clay core dams should be monitored frequently. The aim of this study is to use the combination of Interferometric Synthetic Aperture Radar technique (InSAR) and Finite Element Modeling (FEM) for dam’s deformation monitoring. For the InSAR analysis we used data from ENVISAT sensor and processed those using Small BAseline Subset (SBAS). We show that InSAR is an invaluable approach to monitor clay core dam’s deformation in specific circumstances. The deformation derived from InSAR was used as an initial condition in Finite Element Modeling. The case study is Masjed Soleiman Dam which is situated in South West of Iran. We used 19 ASAR images of ENVISAT sensor from 2003/8/22 to 2010/5/7. The process of ASAR images showed maximum velocity of 11 mm/year in LOS direction at central lower areas of dam. These results were compared with Geodetic Surveying Operations at four points on dam and the average agreement of 77 percent was obtained. The results of ENVISAT data have a good consistency with FEM results. Horizontal and vertical displacements derived from instrumentations and modeling are plotted versus depths. There is a good agreement between modeling results and instrumentations data.

Effect of Clay Core Configuration of the Rock Fill Dams Against Hydraulic Fracturing

Hydraulic fracturing occurred in Hyttejuvet dam in Norway during its first impounding. The water containing soil particle was emerging from the downstream toe of the dam. The water level on the reservoir was then lowered in order to reduce the potential of failure. Further investigation indicated that the clay core configuration was the main caused of the hydraulic fracturing to occur. The clay core material was moraine till soils. Due to the pore water pressure dissipation in the core was very slow, the upstream slope was steepened. This practice increased the arching effect and load transfer between embankment zones.This paper studies the effect of clay core configuration on the rock fill dams against hydraulic fracturing using numerical analysis. The configuration of the Hyttejuvet dam was analyzed using finite element method. Couple analyses between stress & deformation and seepage analyses were used. The stress and deformation during construction was then used as initial stress in the couple analysis with increasing water in the reservoir. When the effective vertical stresses in the upstream face of the clay core was less than the water pressure in the reservoir, hydraulic fracturing will occur. In order to investigate the effects of clay core materials in the analyses, the clay core material was replaced by clay core materials used in 5 major dams in Indonesia The variation of the clay materials were made in the 6 different fine contents. There were 30 variations of the clay core materials were analyzed.The results indicated that hydraulic fracturing was still occurred in the relatively same locations, event the clay core materials were replaced by 30 variations. The analyses results indicated that the configuration of clay core of the rock fill dam strongly influence to the hydraulic fracturing.

Analysis and Prediction of Asphalt-Concrete Core Wall Settlement of the Boguchany HPP Rockfill Dam During the Period of Construction Completion

Greatest core wall settlement to 2021 was predicted using field study data for settlement of the rockfill dam and asphalt-concrete core wall of the Boguchany HPP from 2011 to 2015.

Assessing suffusion susceptibilities of core dam soils by statistical analysis

La suffusion est l’un des principaux processus d’erosion interne dans les ouvrages hydrauliques en terre et leurs sols de fondation ce qui peut accroitre le risque de rupture. L’objectif de cette etude est d’estimer la variabilite spatiale de sensibilite a la suffusion des sols constituant le noyau d’un barrage hydraulique zone (noyau en moraine du Nord du Quebec). La sensibilite a la suffusion des sols est evaluee avec l’indice de resistance a l’erosion Iα. L’approche utilisant l’indice de resistance a l’erosion se concentre sur la sensibilite du materiau en caracterisant le potentiel de perte d’une portion de particules fines. L’avantage de cette approche est le caractere intrinseque de Iα. Une analyse statistique qui utilise plusieurs parametres physiques est utilisee afin d’estimer la valeur de Iα. Ces parametres, a savoir Finer KL issu de la courbe granulometrique complete, l’angle de frottement interne, la valeur au bleu de methylene et le poids volumique sec peuvent etre facilement mesures en laboratoire ou in-situ. Ainsi Iα a pu etre estime tout le long de la coupe transversale du noyau du barrage. Les resultats indiquent que les sols sont tres resistants a la suffusion et que la variabilite spatiale de Iα est relativement faible.

Geophysical investigation and its geological interpretation in the frame of an intergrated survey prior to a dam construction in Plati River Valley, Rethymno, Greece.

A geophysical survey using electrical resistivity tomography (ERT) method(25 ERT profiles of 240m total length and 2 ERT profiles of 1000m total length) in the area of Plati River valley gave valuable information regarding the stratigraphy, related to loose sediments, various faces of flysch and limestone, the tectonic status and the detection of areas of thick and extensive sheared siltstone, that geoelectrically is similar to clay,material useful for the core of the future dam. Both branches of river and valley and in greater detail the area near the position of the dam have detected showing the underground in a 2D and 3D manner. The thickness of neogene andflysch exceeds 40m. Alternations of siltstones-sandstones are met in flysch and in places cohesive sandstones are also met without continuation in an extended area. The siltstonelayers due to their shear character present clayey characteristics in respect of their resistivities. In general zones of limestone uplift have not been detected, which may create problems of leakages apart of the dam area where lateral inhomogeneity between flysch and limestone has been detected (probable fault). The various limestone bodies met in flysch or neogene do not have continuation in depth and they are isolated.

Seismic Resistant Effects of Composite Reinforcement on Rockfill Dams Based on Shaking Table Tests

In this article, the seismic resistant effect of a new reinforcement measure on rockfill dams, the Composite Reinforcement, is investigated based on 1-g large-scale shaking table tests. A 1 m high rockfill dam, which is scaled from the Yele rockfill dam in China, is tested by inputting a series of motions designed from a realistic Wenchuan earthquake record. The model dam is divided into two sections, with one section representing a normal rockfill dam (RD) while the other section employing the Composite Reinforcement (composite reinforced rockfill dam (CRRD)). The seismic-resistant effect of the Composite Reinforcement is investigated by comparing the recorded dynamic response of the two dams, in terms of the peak acceleration amplification factor distribution along the dam core, the crest settlement, and the visualized failure pattern. Results show that the application of the Composite Reinforcement can effectively mitigate the seismically induced deformation of the rockfill dam by reducing the peak crest acceleration and residual crest settlement by 18% and 55%, respectively, when subjected to a 0.5 g input motion. The investigation of the captured failure pattern on the two dams further indicates the effective reinforcing effect of the Composite Reinforcement on preventing the sliding failures of rockfill materials in the top 20% height of the dam body.

Dynamic tensile test of mass concrete with Shapai Dam cores

Static and dynamic tensile tests of dam concrete cores were carried out to investigate the dynamic properties as well as the tensile stress–strain relationship under either monotonic or cyclic load. The test specimens were prepared from the cylindrical cores drilled from Shapai Arch Dam, which was built with three-graded roller compacted concrete and survived the strong shaking of Wenchuan Earthquake. Direct tensile tests were performed on an MTS servo controlled testing machine and the system displacement was used as the control command for all tests. The test results indicate a significant increase in strength compared with static ones, from 2 to 47 % under strain rate roughly from 10−4 to 10−2/s, and more fracture energy is consumed by the concrete under dynamic or cyclic loading than static monotonic loading. Furthermore the static preload on the specimens shows little influence on their dynamic tensile strengths. Based on the experimental data, a simple analytical model was proposed for entire stress–strain relationship under both monotonic and cyclic tensile loading, the calculated stress–strain path gives a satisfactory approximation which can be used in dynamic numerical analysis of concrete dams.

Simplified material model for analysis of asphalt core in embankment dams

Asphalt concrete exhibits time- and temperature-dependent viscoelastoplastic behavior which is difficult to model and implement in practical dam design analyses. The main goal of the paper is to develop a simplified material model for the various types of loading conditions experienced by an asphalt core in an embankment dam. The types of loading conditions are simulated by conducting long-term triaxial creep tests with stepwise loading corresponding to the slow construction of the asphalt core and dam embankment; unloading-reloading cycles corresponding to seasonal reservoir fluctuations, and dynamic cyclic tests corresponding to earthquake loading. The results of the long-term triaxial creep tests show that creep strains accumulate until a “creep-stable state” is reached when virtually no further creep is occurring at that level of sustained deviator stress and temperature, and a corresponding “creep-stable stress-strain modulus” is defined. Based on the test results, a simplified material model expressed in terms of deviator stress is proposed and formulated analytically with a plastic yield boundary (PYB). The unloading-reloading and dynamic behavior was found to be almost linearly elastic, and the unloading-reloading modulus and dynamic secant modulus to be in the order of 20 and 40 times the creep-stable modulus, respectively. The proposed simplified material model and equivalent secant moduli may be used in finite element analyses of the asphalt core and its interaction with adjacent gravel and rockfill zones in the dam.

Investigating effects of water salinity on geotechnical properties of fine-grained soil and quartz in a sandstone case study: Ajichay project in northwest Iran

The effect of water salinity on the geotechnical properties of a CL soil and mechanical properties of a quartz sandstone has been studied using samples from the Ajichay project, located in the northwest of Iran. The purpose of this investigation is to investigate the feasibility of using saline water in processing the clay core of earthen dams in this area. One-dimensional consolidation, swelling, and uniaxial compressive strength tests were performed on the soil with distilled, half-saline, and saline water. To evaluate the effect of water salinity on the sandstones placed in the abutments of the dams, the slake durability index and uniaxial compressive strength were investigated. Results indicated that the compressibility index decreased, hydraulic conductivity decreased, and uniaxial compressive strength of the soil increased with increasing water salinity. The soil swelling percent with all three waters was less than 1 % after 24 h. However, swelling percent increased by 23 % with saline water and decreased by 32 % with half-saline water. Some damage in the rock texture such as disaggregation, weathering, and corrosion of the feldspars along with the dissolution of carbonate cement was observed in thin sections after 6 months of immersion in saline water. The strength of the sandstones exposed to saline water for 5 months decreased by between 5 and 13 %.

Design considerations and behavior of reinforced concrete core dams during construction and impounding

Reinforced concrete core dams can be an alternative solution to conventional dam designs either for permanent impounded reservoirs or flood protection and flood-retaining dams. Dams of this type have been constructed in Austria for various reasons and have shown good behavior during operation. For a better understanding of the load-deformation behavior of this type of dams during construction and impounding, numerical simulations were carried out. The interaction between the thin reinforced concrete core and the dam fill material as well as the influence of fill material properties and other main parameters, such as the roughness of the concrete surface and bedding conditions of the concrete core, on the deformation behavior of dams were examined. The results show that high compressive stress is mainly induced by arching effects in the dam body during construction. During the reservoir impounding, the compressive stresses in the core are reduced significantly while the bending moment in the core footing increases. The results also show that the maximum bending moments occur at the core footing and can be significantly reduced by design improvements. The findings in this study can provide general design recommendations for small dams with a central concrete core as a sealing blanket.

중심코어형 필댐의 코어재 현장 물성에 대한 통계학적 분석

중심코어형 필댐의 코어재 현장 물성에 대한 통계학적 분석

Pore Pressure Dissipation in the Core of the Nurek Dam

The Nurek HPP has been in operation for 30 years. Observations are being carried out on pore pressure dissipation in the dam core. Pore pressure dissipation and changes in the seepage factor resulting from the dissipation process are examined.

Dam and wet-screened concrete creep in compression: in situ experimental results and creep strains prediction using model B3 and composite models

Abstract This paper proposes a methodology for the prediction of the compressive creep strains of dam concrete based on wet-screened experimental results at constant elevated temperature conditions measured in situ. Due to its large aggregate dimensions, the experimental characterization of dam concrete has particular constraints. The wet-screened concrete, obtained by sieving the aggregates larger than a given dimension, after mixing, is used to cast standard specimens and to embed monitoring devices. An experimental in situ installation using creep cells was used to obtain the compressive creep strain development over time for the maturing conditions of the dam core. The study of the effect of wet-screening procedure on creep in compression considers three types of concrete, dam concrete and two wet-screened concretes tested at three loading ages, 28, 90 and 365 days. The comparison between different types of concrete at different maturing conditions requires the definition of a reference state given by the maturity method, using the equivalent age, and relies on the fit of compressive creep strains to the RILEM recommended model B3. To take into account the effect of the aggregate content on the deformability properties of dam concrete, an equivalent two-phase composite model was applied. The equivalent composite model considered the equivalent matrix as the wet-screened concrete and the inclusions as the larger aggregates that are removed during the wet-screening procedure. Predictions obtained with the composite model are close to the dam concrete experimental results, for the tested loading ages.