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Showing 8 results for Rockfill

M.h. Baziar, Sh. Salemi, T. Heidari,
Volume 4, Issue 3 (9-2006)

Seismic behavior of a rockfill dam with asphalt-concrete core has been studied utilizing numerical models with material parameters determined by laboratory tests. The case study selected for these analyses, is the Meyjaran asphalt core dam, recently constructed in Northern Iran, with 60 m height and 180 m crest length. The numerical analyses have been performed using a nonlinear three dimensional finite difference software and various hazard levels of earthquakes. This study shows that due to the elasto-plastic characteristics of the asphalt concrete, rockfill dams with asphalt concrete core behave satisfactorily during earthquake loading. The induced shear strains in the asphalt core, for the case presented in this research, are less than 1% during an earthquake with amax=0.25g and the asphalt core remains watertight. Due to large shear deformations caused by a more severe earthquake with amax=0.60g, some cracking may occur towards the top of the core (down to 5-6 m), and the core permeability may increase in the top part, but the dam is safe.
A. Soroush, R. Jannatiaghdam,
Volume 10, Issue 2 (6-2012)

This paper studies thoroughly and deeply the results of about one hundred triaxial compression tests on thirty types of rockfill
materials. The materials are categorized in accordance with their particles shape (angular / rounded) and gradation
characteristics. The main tool of the study is the Hyperbolic Model developed by Duncan and Chang. The focus of the study is
on the variations of deformation modulus of the materials (Ei and Et) with confining stress (&sigma3). Features of the mechanical
behavior of the rockfill materials, as compared with the general behavior of soils, are highlighted through the exponent
parameter (n) of the Hyperbolic Model. It is shown that high confining stresses may have adverse effects on the deformation
modulus of the rockfill materials and make them softer. The particle breakage phenomenon which happens during compression
and shearing is found as the main factor responsible for the above effects and, in general, responsible for controlling the
behavior of the materials. For the rockfill materials of this study, two correlations for estimating the initial elasticity modulus (Ei)
and the internal friction angle (&phi) in terms of particles shape, confining pressure (&sigma3), and coefficient of uniformity (Cu) are

R. Mahin Roosta, A. Alizadeh,
Volume 10, Issue 2 (6-2012)

In the first impounding of rockfill dams, additional settlements occur in upstream side in saturated rockfills due to collapse
phenomenon even high rainy seasons can cause additional deformation in the dumped rockfills. Unfortunately these
displacements are not taken into account in the conventional numerical models which are currently used to predict embankment
dam behavior during impounding. In this paper to estimate these displacements, strain hardening-strain softening model in Flac
is modified based on the laboratory tests, in which same impounding process in such dams is considered. Main feature of the
model is reproduction of nonlinear behavior of rockfill material via mobilized shear strength parameters and using collapse
coefficient to display induced settlement due to inundation. This mobilization of shear strength parameters associated with some
functions for dilatancy behavior of rockfill are used in a finite difference code for both dry and wet condition of material. Collapse
coefficient is defined as a stress dependent function to show stress release in the material owing to saturation. To demonstrate
how the model works, simulation of some large scale triaxial tests of rockfill material in Gotvand embankment dam is presented
and results are compared with those from laboratory tests, which are in good agreement. The technique could be used with any
suitable constitutive law in other coarse-grained material to identify collapse settlements due to saturation

H. Ghiassian, M. Jalili, I. Rahmani, Seyed M. M. Madani,
Volume 11, Issue 4 (12-2013)

The concept of Geosynthetic Cellular Systems (GCS) has recently emerged as a new method in construction of breakwaters and coastal protective structures. The method potentially has significant advantages compared to conventional systems from the standpoint of constructability, cost effectiveness, and environmental considerations. This paper presents the results of physical model testing on the hydraulic responses of GCS structures under wave action. A series of model tests were carried out in a wave flume on GCS models with different shapes and soil types, subjected to various wave characteristics. Horizontal wave forces acting on the models were measured at different elevations. The maximum horizontal force in each test was calculated and compared with conventional formula of predicting wave pressure on breakwaters. The results show that Goda’s equation overestimates the hydrodynamic water pressure on these structures. This can be attributed to the influence of seeping water through the GCS models because of relative permeability of the GCS.
Farzin Kalantary, Javad Sadoghi Yazdi, Hossein Bazazzadeh,
Volume 12, Issue 3 (7-2014)

In comparison with other geomaterials, constitutive modeling of rockfill materials and its validation is more complicated. This is principally due to the existence of more intricate phenomena such as particle crushing, as well as laboratory test limitations. These issues have necessitated developing more complex constitutive models, with many parameters. Regardless of the type of model, the calibrations of the parameters in such models are considered as one of the most important and challenging steps in the application of the model. Therefore, the need for comprehensive and rapid methods for evaluation of optimum parameters of the models is deemed necessary. In this paper, a Neuro-Fuzzy model in conjunction with Particle Swarm Optimization (PSO) is used for calibration of the twelve parameters of Hierarchical Single Surface (HISS) constitutive model based on the Disturbed State Concept (DSC). The Neuro-fuzzy system is used to provide a high-degree nonlinear regression model between the deviatoric stress and volumetric strain versus axial strain that has been obtained from consolidated drained large scale tri-axial tests on rockfill materials. The model parameters are determined in an iterative optimized loop with PSO and ANFIS such that the equations of DSC/HISS are simultaneously satisfied. Material data used in this study are gathered from the results of large tri-axial tests for two rockfill dams in Iran. It is shown that the proposed method has higher accuracy and more importantly its robustness is exhibited through test predictions. The achieved improvement is substantiated in a comparison with the more widely used "Least-Square" method.
M. Derakhshandi, H. R. Pourbagherian, M. H. Baziar, N. Shariatmadari, A. H. Sadeghpour,
Volume 12, Issue 4 (12-2014)

In this study, the mechanical behavior of Vanyar dam was evaluated at the end of construction. A two-dimensional numerical analysis was conducted based on a finite element method on the largest cross-section of the dam. The data recorded by the instruments located in the largest cross-section were compared with the results of the numerical analysis at the place of instruments. The settlement, pore water pressure, and total vertical stress were the parameters used for evaluating the dam behavior at the end of construction. The results showed that the settlements obtained from the numerical analysis were in reasonable agreement with the data recorded by the instruments, which proved that the numerical analysis was implemented based on realistic material properties. In addition, the difference between the instruments and the numerical analysis in terms of total vertical stresses was discussed by focusing on the local arching around the pressure cells. Furthermore, the arching ratios were calculated based on the results of the numerical analysis and the data recorded by the instruments. Moreover, the pore water pressures and total vertical stresses, recorded by piezometers and pressure cells, respectively, were the two parameters utilized for evaluating the hydraulic fracturing phenomena in the core. The results demonstrated that the maximum settlement obtained from the numerical analysis was 1 m, which corresponded to 46 m above the bedrock on the core axis. The recorded data in the core axis indicated that maximum settlement of 0.83 m happened 40 m above the bedrock. In addition, maximum pore water pressure ratio recorded by the instruments (Ru =0.43) was more than that obtained from the numerical analysis (Ru =0.26) this difference was due to the local arching around the pressure cells. Furthermore, the arching ratios in Vanyar dam were found to be 0.83 to 0.90. In general, the results revealed that the dam was located on a safe side in terms of critical parameters, including settlement and hydraulic fracturing. In addition, results of the numerical analysis were consistent with those provided by the monitoring system

A.a. Heshmati, A.r. Tabibnejad, H. Salehzadeh, S. Hashemi Tabatabaei,
Volume 13, Issue 1 (3-2015)

To investigate the saturation induced collapse deformation behavior of rockfill material, a set of large-scale triaxial tests were conducted in saturated and dry-saturated conditions. Specimens were tested under various confining pressures. For dry-saturated tests, specimens were sheared in various stress levels. Results of all dry saturated tests indicate a sudden reduction in the specimen volume during the submerging process. The ratio of the minimum axial strength of a submerged specimen (at the end of the saturation process) to the shear strength of the specimen before saturation is defined as the coefficient of stress recovery, Csr. Results show that this ratio increases as the confining pressure increases, and decreases as the shear stress level increases. According to the results of dry-saturated tests, reduction values of the internal friction angle caused by saturation (c), the ratio of the elasticity modulus of the material after saturation to its elasticity modulus in dry condition, i.e., Ewet/Edry, and the saturation induced sudden volumetric strain (vc) decrease as the confining pressures increase. However the shear stress level does not have any meaningful effect on the variation of c, Ewet/Edry and (vc).
Mr. L. Yanlong, Mr. L. Shouyi, Mr. Y. Yang, Miss T. Xing,
Volume 13, Issue 4 (12-2015)

This study simulates the temperature field and temperature stress of concrete face slabs, considering the cold waves that occur during construction as well as the contact friction between the face slabs and the cushion layer. The results show that when a cold wave occurs during construction, the surface and center temperature of the face slabs continually drop with the outside air temperature, with the surface temperature drop being the largest. In addition, the surface and center of face slabs are subjected to tensile stress, with the maximum principal stress on the surface being greater than that on the center. The maximum principal stress of the surface and center occurs at approximately half of the dam height. This study also examines the surface insulation of concrete face slabs. Surface insulation can significantly improve the temperature drop range and the maximum principal stress amplitude caused by the cold wave. A stronger heat preservation results in smaller tensile stress and an increase in the amplitude of face slabs.

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