Asphalt Concrete Core Research Articles

Static Parametric Stress-Strain Analysis for Asphaltic Concrete Core of Rockfill Dams

Abstract This study was conducted to investigate the effect of variations in the asphaltic concrete core Rockfill dam geometric parameters on the core behavior at different upper, middle, and lower points under two-dimensional static stress-strain analysis. The mentioned analysis was performed using SIGMA/W software. In the modeling and analysis process, the geometry of a large number of dams constructed around the world was studied and many numerical models with variations in eight classes of height, three dams upstream/downstream slope modes, and three different asphaltic core positions and thicknesses on a rigid foundation were created and analyzed. In addition, for each of the above models, four dam operation stages including “End of Construction”, “Full Reservoir”, “Half-Full Reservoir”, and “Rapid Drawdown” were considered. The results show, in four different stages of construction and impounding and three different slope modes, the maximum stress as well as horizontal and vertical displacements at the upper, middle, and lower points of the core increase with increasing height. In all models, increasing upstream and downstream slopes results in an increase in the amount of vertical displacement for all construction and impounding stages at the upper, middle, and lower points of the core. In the middle and lower points of the core, with increasing height, the amount of deviatoric stress increases for all construction and impounding conditions. In addition, for all operation cases, the maximum strain increases in all points of the vertical and tilted cores as the core thickness increases. Additional results are presented in the next sections.

Seismic performance assessment of high asphalt concrete core rockfill dam considering shorter duration and longer duration

The particular interest produced by the seismological characteristics impacting structural response has given a new challenge in the performance-based design of high dams. Recent research has shown that the seismological characteristics of frequency and amplitude inherent in ground motion (GM) records govern the dynamic response of high dams. Therefore, these seismological characteristics have been accepted and incorporated into the seismic design codes of high dams in most countries. However, the duration of strong GMs, as one of the critical seismological characteristics of earthquakes, also needs to be fully understood to carry out a more effective performance-based design of high dams. Based on this observation, the effect of the duration of strong GMs has been explored, investing in the seismic performance of high asphalt concrete core rockfill dams (ACCRDs) by employing an integrated duration (ID) concept that can reflect the duration of all components of GMs. A high ACCRD was firstly built in the commercial software ABAQUS considering the dam-reservoir-foundation interaction systems. Subsequently, the coupled multiple stripe analysis and maximum likelihood estimate method generate seismic fragility curves for a dam according to two damage indicators. Comparison of the results for the seismic performance of the high ACCRD revealed that the longer-duration GMs could give rise to the higher relative settlement ratio, stress demand-capacity ratios, and probability of exceedance (POE) of the dam than shorter-duration GMs. It is recommended that in the current seismic design and seismic performance evaluation, the effects of GM duration, frequency, and amplitude should be considered.

Experimental study of the role of interface element in earth dams with asphalt concrete core - Case study: Mijran dam

In recent years, the tendency to use asphalt concrete cores in earth dams is very common and is increasing. In such dams, the interaction between asphalt concrete core and soil materials has an important role in dam stability. The present study, as a case study of Mijran Dam located in Ramsar area in Iran, has evaluated experimentally the mechanical behavior of the interface between the filter soil material and the asphalt concrete core in the laboratory. In this regard, the samples were tested using large-scale direct shear machine in different normal stresses and in dry and saturation conditions. Also, tests have been performed on samples with different percentages of bitumen and relative density of filter materials at different shear rates and under different freeze-thaw cycles. In all the above conditions, the shear surface has been considered as the interface and the shear rate used in different tests varied in the amounts of 0.5, 1, 1.5 and 3 mm/min. The results of this study show that different percentages of bitumen used do not have such an effect on the shear strength parameters of interface. As the relative density increases, the values of the shear parameters increase. If the sample is dry or saturated, parameters such as dilation angle and shear stiffness increase with increasing density, but the interaction ratio increases in the dry state and decreases in the saturated state. As the shearing rate increases, the dilation angle and interaction ratio in the interface materials increase by about 2–3%. On the contrary, increasing the freeze-thaw cycles reduces the mentioned strength parameters.

Numerical Simulation of a 3D Seepage Field of an Asphaltic and Concrete Core Rockfill Dam in an Arid Area

This investigation focused on the three-dimensional (3D) seepage field simulation of an asphaltic concrete core rockfill dam (ACRD) under the design water level conditions. At first, the finite element theory of seepage is introduced in the arid area; then, a hydro-junction projection on the Nuer River in Xinjiang is selected as engineering background, the finite element model of a seepage field of an asphaltic and concrete core rockfill dam under the design water level condition is established, and a boundary condition is determined, and the next distribution of a seepage field of different profiles are plotted, and the monitoring value of different points is compared with the finite element solution; conclusions can be drawn that when the antiseepage system of the dam foundation is good, the water level at the downstream side of the core wall is greatly reduced; for the dam foundation, the effects of reducing head of the cutoff wall are rather obvious, and for the dam body, certain leakage defects at the joint of an impermeable body in the cross sections 0 + 456.5 m and 0 + 540 m can exist. For the dam-around seepage, the hydrogeological condition conforms to the actual conditions. These conclusions can provide great significance for the future design.

Analysis on Construction Method of Asphalt Concrete Core Wall in Reservoir Dam

Analysis on Construction Method of Asphalt Concrete Core Wall in Reservoir Dam

Seismic Response of Asphalt Concrete Core Dam Considering Spatial Variability of Overburden Foundation Materials

Seismic Response of Asphalt Concrete Core Dam Considering Spatial Variability of Overburden Foundation Materials

Parametric stress-strain analysis for upstream slope of the asphaltic concrete core rockfill dams in static state

In this study, the effects of various geometric parameters of a dam in 2D static analysis of stress-strain on the upstream slope of the asphaltic concrete core rockfill dams were investigated. For this purpose, first the geometric characteristics of a large number of world's dams were collected and assessed, then by geometric modeling of these dams, many numerical models were developed for static analysis using GeoStudio software in eight height classes, three cases of upstream and downstream slopes, three different shape and thickness of the asphaltic concrete core under different Impounding states including "Full Reservoir", "Half full Reservoir", "End of construction and "Rapid Drawdown on a rigid type of foundation. The results of this study demonstrated that in four different construction and impounding states and in three different cases of slopes, Increasing the height parameter, causes increasing the Maximum total stress, Maximum total strain, Shear strain and Maximum shear stress for all construction and impounding states. The Maximum total stress decreased for all operating situations as the upstream slope reduced. According to the obtained results from the static stress-strain analysis, increasing both vertical and inclined asphaltic concrete core thicknesses, leads to decreasing the Maximum shear stress in Full Reservoir state but it increases in other state of impoundment. Moreover, by comparing the displacements related to specified points on the upstream slopes, increasing the height parameter, leads to increasing both horizontal and vertical displacements, the volumetric strain, deviator strain and deviator stress for all impounding conditions. In the following, the additional results were provided along with diagrams for further analysis.

Performance evaluation of asphalt concrete core earth-rock fill dam relative to clay core earth-rock fill dam in the case of Megech Dam, Ethiopia

Performance evaluation of asphalt concrete core earth-rock fill dam relative to clay core earth-rock fill dam in the case of Megech Dam, Ethiopia

Creep Behavior of Asphalt Concrete Core Materials in Embankment Dams under a Stepped Loading Path

AbstractUnderstanding the long-term creep behaviors of asphalt concrete core materials is crucial to the safety of embankment dams. This study systematically analyzes the creep behavior of asphalt ...

An approach for simulating the interaction between soil and discontinuous structure with mixed interpolation interface

Structural discontinuities are common (e.g. cracks, segmented structures) especially in large-scale geotechnical structures, which can lead to the discontinuous soil-structure interaction (SSI) problems. Thus, in this paper a mixed interpolation interface with non-matching nodes is introduced for effectively simulating discontinuous SSI problems. This paper provides a conveniently executed numerical implementation of the introduced approach within a finite element method (FEM) analysis platform. The high flexibility and precision of the developed method are demonstrated through fine analyses of 2D and 3D concrete faced rockfill dams (CFRDs). Furthermore, a cracking evolution analysis for a high pedestal of the Quxue asphalt concrete core dam is conducted by coupling the method with a cohesive zone model (CZM). The mixed interpolation interface is verified as an effective tool for solving discontinuous SSI problems. The modeling also sheds light on the process of cracking evolution and the primary failure mechanism for high pedestal.

Discussion on deformation monitoring method of asphalt concrete core wall of high earth-rock dam

The deformation of asphalt concrete core wall of earth rock dam is an important monitoring item of safety management in the construction and operation period of the project. This paper summarizes the conventional monitoring methods and principles of the deformation of asphalt concrete core wall, analyzes the application scope and existing problems of the conventional monitoring methods, and introduces a new method and principle of the deformation monitoring of asphalt concrete core wall of high earth rock dam, which effectively solves the problems The problems of conventional monitoring methods are solved, and the three-dimensional deformation monitoring of asphalt concrete core wall is realized.

Dynamic Centrifuge Modelling Tests for Asphalt Concrete Core Dam

Dynamic centrifuge modelling tests are carried out to study the seismic behaviour of a sand-gravel dam with asphalt concrete core wall. The acceleration response, deformation, core wall stress and stability are analysed under design and check seismic intensity. The crest acceleration amplification factor is 2.7~3.0. The crest settlement rate is 0.442% and 0.481%, respectively under design and check intensity. Maximum seismic stress is recorded in core wall of 2/3~4/5 dam height. Under design intensity, failure cracks appear in crest and upstream dam revetment at water level. Under check intensity, more cracks are found. Furthermore, landslide occurs in upstream slope above 2/3 dam height under check intensity. Downstream slope is stable. No evident separation is observed between dam shell materials and core wall. The dam is unstable under design and check earthquake. Aseismic measures are necessary according to test results.

Improvement Methods for Reduction of the High Stress of Ultra-High Asphalt Concrete Core Dams

With the rapid development of asphalt concrete core rockfill dams (ACCRDs), the construction of ultra-high asphalt concrete core rockfill dams (UACCRDs) has been improved significantly. However, the security problems of asphalt concrete core (ACC) become very prominent with the increase of dam height. The shear failure control standard and tensile failure control standard of ACC are suggested. The mechanisms of ACC that generate high shear stress and high tensile stress are investigated. Based on the definition of stress level and the transmission mechanism of arch structures, the improvement methods that reduce the high shear stress and high tensile stress of ultra-high asphalt concrete core (UACC) are proposed and investigated. The results show that the stress level of ACC can be reduced significantly by the increase of the strength parameters of ACC (failure ratio, cohesion, and internal friction angle). The following value ranges of the failure ratio, cohesion, and internal friction angle of ACC for the suitable construction of UACCRDs are recommended: Rf ≥ 0.75, C ≥ 0.30 MPa, and φ ≥ 28.5° (h = 150 m), with the growth gradient adjusted by 5%, 15%, and 5%/25 m. The tensile stress and tensile stress area can be reduced obviously by the new type of dams (curved asphalt concrete core rockfill dams (CACCRDs)). The value ranges of the curvature of CACC (k ≥ 1.0 × 10−3) for the suitable construction of UACCRDs are recommended.

Investigation for the key technologies of ultra-high asphalt concrete core rockfill dams

The mechanical characteristics of ultra-high asphalt concrete core rockfill dams (UACCRDs) at different periods is investigated via Rankine’s earth pressure theory, and a shear safety control standard for UACCRDs is proposed. The reasonable material parameters of the asphalt concrete core (ACC) and transition material that independently and comprehensively satisfy the shear safety control standard are back-calculated. The engineering measures that reduce the stress level (shear stress) of the ACC are given. Moreover, the engineering measures (straight asphalt concrete core rockfill dams (SACCRDs) are designed as curved asphalt concrete core rockfill dams (CACCRDs)) that reduce the tensile stress of the ACC are proposed. Based on the theory of the straight beam and curved beam on Winkler elastic foundation, the simplified mechanical models of straight asphalt concrete core (SACC) and curved asphalt concrete core (CACC) are established. The improvement effect of CACC that reduces tensile stress is also investigated. The results show that the following value ranges of the internal friction angle, cohesion of ACC and the internal friction angle of transition material for the suitable construction of UACCRDs are recommended: φa ≥ 30.5°, Ca ≥ 0.25 MPa and φt ≤ 43.5° (h = 200 m), with the growth gradient adjusted by 0.5%, 1.5% and −0.5%/25 m. The stress level of ACC can be obviously reduced by increasing the internal friction angle and cohesion of ACC, and reducing the internal friction angle of transition material. The simplified mechanical models of SACC and CACC can estimate the force and deformation characteristic of the ACC (SACC and CACC) well. The CACC can significantly reduce tensile stress to a level approximately 42.8% lower than that of SACC.

Effect of water on the triaxial behavior under dynamic loading of asphalt concrete used in impervious barriers

Abstract Dams with an asphalt concrete core are a viable alternative in the construction of rockfill dams; therefore, characterization of the materials used in their construction is required. Part of this characterization requires obtaining the response parameters upon applying cyclic loads under different stress and temperature conditions. The objective of this research is to determine the effect of water on the dynamic properties of asphalt concrete after prolonged contact. To this end, an extensive program of laboratory tests was carried out in which specimens of this material were prepared, saturated and exposed to water. After the saturation process, the results of the tests indicated that the asphalt concrete presented a decrease in the shear modulus of 6.5% and an increase in the damping ratio of 16.1%, on average, with respect to the values obtained for the dry material. No significant change in the mechanical response was observed as a result of exposure to water for a period of up to 12 months.

Relative Performance Evaluation of Asphaltic Concrete Core Embankment Dam and Clay Core Embankment Dam: By Plaxis Software Application

This paper investigates asphaltic concrete core embankment dam in relative to the clay core embankment dam so that it is vital from the perspective of safety and controlling seepage. Plaxis 8.5, finite element based software was employed for analysis of the dam and Geostudio 2012 for seepage analysis. Relatively the result of analysis shows that good result of safety factor has been found in asphalt concrete core dam with regard to the stability of the dam during steady-state condition and end of construction. During steady-state condition, the factor of safety computed for clay core dam was 1.466, and the dam fails to attain the minimum factor of safety recommended by USACE. But, under this similar condition stability analysis result of asphalt concrete core dam gave a good result of 1.661 which is found within the recommended range. Likewise, at the end of construction, the factor of safety computed for clay core dam was 1.553, but, under this loading condition (end of construction) stability analysis result of asphalt concrete core dam gave a good result of 1.600 which keeps the dam more stable. The seepage analysis result of asphaltic concrete core dam is also insignificant. Generally, application of asphalt concrete core in rock fill dam can fulfill the basic requirement and minimum factor of safety under all loading condition, and dam of such types is seepage free as it shown here and approved by many other researchers’ extensive works.

Research and Application on Seepage Detection and Repair of Anti-Seepage System for Earth-Rockfill Dam with Asphalt Concrete Core

The asphalt concrete core wall has been widely used in various kinds of high dams because of its good performance of anti-seepage, deformation and rapid construction speed. In recent years, the leakage phenomena of some asphalt concrete core dams begin to occur, endangering dam safety. To determine the leakage status, location and access of the bituminous concrete core, drilling holes are arranged in the upper and lower reaches of the bituminous concrete core wall. With water as the medium, underwater sonar, color TV observation in hole, consecutive test of tracer, water level analysis in the dam body and physical detection and other methods were used for detection. Then the leakage state of asphalt concrete core wall of dam body is comprehensively analyzed and determined according to a variety of test results. At the same time, aiming at the problems existing in the direct repair of asphalt concrete core wall in the dam body, repairing project of concrete seepage cut-off wall, controlling grouting repair scheme, as well as its key control factors, construction process and technical parameter indexes were studied. Through the application of multiple engineering examples, the treatment effect was remarkable, which can provide a reference for the treatment of similar engineering problem.

OPTIMIZATION OF PRESERVATIVE FOR PROTECTION OF CONCRETE PAVEMENT OF HIGHWAYS

Disadvantages of road concrete pavement quite well known professionals-standards. They were mainly low elasticity modulus asphaltic concrete, as well as a fairly rapid aging of asphalt concrete core component-bitumen. And, as a consequence, is relatively low durability of the coating, the need for frequent repair. To some extent, cement concrete cover signifi cantly outperform this index of asphalt, convinces experience roads of Germany, the United States and other countries. The correct structure of concrete, overall compliance technology laying concrete, comprehensive quality control production work, sufficient technical personnel qualifications provide long defect-free work road re-coated. However, violations by manufacture of works or in the process of exploitation, particularly in the harsh conditions of freezing and thawing, saturation-drying, especially under the influence of salts-defrosting, cause defects, reduce its durability. There are two directions of increase of durability of the coating. Firstly, it is the primary protection is the creation of concrete with minimal possible on data components mixture water cement ratio that provides reception of concrete with minimum porosity and consequently with maximum durability. Secondly, the secondary protection, providing increased resistance already ready-mixed concrete cover external aggressive actions. In this case against the background of other ways quite promising looks impregnation of the surface concrete integrated structure. Composition must contain multiple components, primarily water repellents, preventing penetration of fluid into the body of the concrete, and finely dispersed silica sol in particular silica, providing reduction of the porosity of the surface layers of concrete by interacting with the free calcium hydroxide. The problem of optimization of impregnation structure and is dedicated to this work.

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.

Causes of the abnormal seepage field in a dam with asphaltic concrete core

Asphaltic concrete core (ACC) dams are widely built in China. Many ACC dams perform well, but others have experienced significant leakage including the case in western China studied herein. A numerical model of saturated-unsaturated water flow was adapted to simulate the seepage through the dam. By comparing the normal and abnormal seepage fields under different conditions, the main causes for the actual abnormal seepage field were identified and attributed to a defect in the ACC and an unintended, low permeability layer (LPL) in the transition zone (TZ) and the downstream dam shell. These conclusions are consistent with the situation and performance of the dam. Inadequate ACC construction processes might have caused defects in the ACC. An abrupt change of the ACC thickness probably induced stress concentrations and caused the ACC to fail. Material sources for the TZ and dam shell were complex and varied from specifications, and soil gradation for the TZ was inadequately controlled. In particular, tests show that the permeability varies over large ranges in these two parts of the dam. An unexpected LPL probably exists in both areas, and extends continuously.