The Experts below are selected from a list of 2892 Experts worldwide ranked by ideXlab platform
Biswajeet Pradhan - One of the best experts on this subject based on the ideXlab platform.
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assessment of multi scenario rockfall hazard based on mechanical parameters using high resolution airborne laser scanning data and gis in a tropical area
Environmental Earth Sciences, 2016Co-Authors: Ali Mutar Fanos, Biswajeet Pradhan, Azlan Abdul Aziz, Mustafa Neamah Jebur, Hyuckjin ParkAbstract:Rockfall hazard is a main threat for mountainous and hilly areas that can cause loss of life, damage to infrastructures, and traffic interruption. Rockfall frequency and magnitude vary both spatially and temporally; therefore, multi-scenarios related to rockfall characteristics (trajectories, frequency and kinetic energy) can provide early warnings by identifying the areas at risk for mitigation purposes. The aim of this study is to predict the areas at risk from future rockfall incidents and suggest suitable mitigation measures to prevent them. The most significant elements in rockfall analysis are slope topography interpretation or the digital elevation model (DEM) and the rockfall modeling approach. Light detection and ranging (LiDAR) techniques have been widely used in rockfall studies because of their capability to provide high-resolution information regarding slope surfaces. In the current study, airborne laser scanning (ALS) is used to obtain a high-density point cloud (4 pts./m2) of the study area for the construction of an accurate DEM via a geographic information system. Rockfall source areas were identified based on multi-criteria method including DEM derivatives (e.g., slope, aspect, curvature and topographic contrast) in addition to terrain type and aerial photos. A 3D rockfall model has been established to determine rockfall multi-scenarios based on their characteristics according to a range of restitution coefficient (normal and tangential) and friction angle values; these parameters are particularly crucial in rockfall simulation to delineate the spatial prediction of rockfall hazard areas along the Jelapang corridor of the North–South Expressway in Malaysia. In addition, a barrier location was suggested based on limited rockfall height and kinetic energy to mitigate rockfall hazards. Results show that rockfall trajectories (stopping distance) and, subsequently, their frequency and energy are increased; moreover, barrier efficiency is reduced when the values of the mechanical parameters (Rn, Rt, and friction angle) are increased. Nonetheless, the suggested barrier location is an efficient and mitigative measure to eliminate the rockfall effect.
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multi scenario rockfall hazard assessment using lidar data and gis
Geotechnical and Geological Engineering, 2016Co-Authors: Ali Mutar Fanos, Biswajeet PradhanAbstract:Transportation corridors that pass through mountainous or hilly areas are prone to rockfall hazard. Rockfall incidents in such areas can cause human fatalities and damage to properties in addition to transportation interruptions. In Malaysia, the North–South Expressway is the most significant expressway that operates as the backbone of the peninsula. A portion of this expressway in Jelapang was chosen as the site of rockfall hazard assessment in multiple scenarios. Light detection and ranging techniques are indispensable in capturing high-resolution digital elevation models related to geohazard studies. An airborne laser scanner was used to create a high-density point cloud of the study area. The use of 3D rockfall process modeling in combination with geographic information system (GIS) is a beneficial tool in rockfall hazard studies. In this study, a 3D rockfall model integrated into GIS was used to derive rockfall trajectories and velocity associated with them in multiple scenarios based on a range of mechanical parameter values (coefficients of restitution and friction angle). Rockfall characteristics in terms of frequency, height, and energy were determined through raster modeling. Analytic hierarchy process (AHP) was used to compute the weight of each rockfall characteristic raster that affects rockfall hazard. A spatial model that considers rockfall characteristics was conducted to produce a rockfall hazard map. Moreover, a barrier location was proposed to eliminate rockfall hazard. As a result, rockfall trajectories and their characteristics were derived. The result of AHP shows that rockfall hazard was significantly influenced by rockfall energy and then by frequency and height. The areas at risk were delineated and the hazard percentage along the expressway was observed and demonstrated. The result also shows that with increasing mechanical parameter values, the rockfall trajectories and their characteristics, and consequently rockfall hazard, were increased. In addition, the suggested barrier effectively restrained most of the rockfall trajectories and eliminated the hazard along the expressway. This study can serve not only as a guide for a comprehensive investigation of rockfall hazard but also as a reference that decision makers can use in designing a risk mitigation method. Furthermore, this study is applicable in any rockfall study, especially in situations where mechanical parameters have no specific values.
Lu Liu - One of the best experts on this subject based on the ideXlab platform.
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research on a seepage monitoring model of a high core Rockfill dam based on machine learning
Sensors, 2018Co-Authors: Xiang Cheng, Zhiwei Zhou, Zhixiang Luo, Ming Liu, Lu LiuAbstract:The seepage of a Rockfill dam with a high core wall is an important and difficult issue in the safety monitoring of a core Rockfill dam, something about which managers are immensely concerned. Seepage of a high core Rockfill dam is mainly affected by factors such as water level, rainfall, temperature, filling height, and aging. The traditional research method is to establish a multiple linear regression model to analyze the influence factors of seepage. However, the multicollinearity between these factors affects parameter estimation, and random errors in the data cause the regression model to fail to be established. This paper starts with data collected by an osmometer, uses the 3δ criterion to process the outliers in the sample data, uses the R language to perform principal component analysis on the processed data to eliminate the multicollinearity of the factors, and finally uses multiple linear regression to model and analyze the data. Taking the Nuozhadu high core Rockfill dam as an example, the influencing factors of seepage in the construction period and the impoundment period were studied and the seepage was then forecasted. This method provides guidance for further studies of the same type of dam seepage monitoring model.
Li Min Zhang - One of the best experts on this subject based on the ideXlab platform.
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discussion on the allowable safety factor of slope stability for high Rockfill dams in china
Engineering Geology, 2020Co-Authors: Chen Chen, Li Min Zhang, Liang PeiAbstract:Abstract The allowable safety factors of slope stability for Rockfill dams in Chinese design codes are defined irrespective of dam heights and are mainly based on the engineering experiences with respect to the Rockfill dams which are lower than 200 m. It is well known that safety margins for different structures are not comparable when safety factors are taken as the measure of safety margin. Thus whether the current allowable safety factors are applicable to the Rockfill dams with heights of over 200 m has been controversial in the engineering and academic field. Reliability is well known as a unified measure of safety margin for different structures. Therefore, the slope safety margins of Rockfill dams with different heights can be compared in terms of slope reliability indices derived from probabilistic methods. Based on the statistical analysis of nonlinear shear strength parameters of Rockfills from 14 Chinese dams, the slope reliabilities of fictitious Rockfill dams of different heights designed with equal allowable safety factor are calculated and compared in this paper. It is shown that the slope failure risk of higher dams is larger than that of lower dams if the dams are designed with equal allowable safety factor rather than equal reliability. Therefore, from the perspective of maintaining consistent slope reliability levels among Rockfill dams with different heights, the allowable safety factors should be prescribed in terms of dam height, i.e. the allowable safety factor for higher dams should be larger than that for lower dams.
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seepage failure mechanism of the gouhou Rockfill dam during reservoir water infiltration
Soils and Foundations, 2006Co-Authors: Li Min Zhang, Qun ChenAbstract:The catastrophic failure of the 71-m high Gouhou concrete-faced Rockfill dam in Qinghai Province, China, has drawn many studies. This paper aims at providing new understanding on the modes and process of this failure, which could be applicable to similar dam failures. The geometrical and hydraulic criteria for internal erosion in Rockfill materials are assessed. Unsaturated-saturated seepage theory is used to analyze the Gouhou dam since the Rockfill materials of the dam were unsaturated before reservoir water infiltration. The water infiltration is simulated by several cases of transient seepage analyses. According to the study, a perched-water table formed in the dam when the reservoir water infiltrated into the Rockfill from the top of the concrete face. The perched water spread nearly horizontally along stratifications in the Rockfill and exited from the downstream slope at a high elevation as observed before the breach of the dam. The hydraulic gradient of the perched water table was the highest near the wetting front, which might provide necessary hydraulic conditions to trigger internal erosion and piping failure. Based on the geometrical conditions of the Rockfill materials and the hydraulic conditions in the dam, the susceptibility of internal erosion is evaluated and the possible modes and process of seepage failure of the dam are described.
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three dimensional analysis of water infiltration into the gouhou Rockfill dam using saturated unsaturated seepage theory
Canadian Geotechnical Journal, 2006Co-Authors: Qun Chen, Li Min ZhangAbstract:The Gouhou Dam was a concrete-faced Rockfill dam built in a steep canyon that collapsed in 1993 due to internal erosion during the initial reservoir filling. In this paper, the process of water infiltration into the originally unsaturated Rockfill dam is studied using three-dimensional saturatedunsaturated seepage theory. The three-dimensional characteristics of seepage through the dam bounded by steep abutments, the effect of material anisotropy, and the effect of Rockfill stratifications are studied. The three-dimensional results are compared with those from two-dimensional analyses. The three-dimensional simulations show that seepage water flows faster and the hydraulic gradients are greater near the abutment boundary in the dam. As such, the evolution of the seepage failure in the three-dimensional cases is faster than that in the two-dimensional analyses, and the two-dimensional analyses will underestimate the risk of seepage failure, particularly near the abutment boundary. If the materials in the ...
K. G. Sharma - One of the best experts on this subject based on the ideXlab platform.
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modeling the triaxial behavior of riverbed and blasted quarried Rockfill materials using hardening soil model
Journal of rock mechanics and geotechnical engineering, 2016Co-Authors: N P Honkanadavar, K. G. SharmaAbstract:Abstract Riverbed modeled Rockfill material from Noa Dehing dam project, Arunachal Pradesh, India and blasted quarried modeled Rockfill material from Kol dam project, Himachal Pradesh, India were considered for this research. Riverbed Rockfill material is rounded to sub-rounded and quarried Rockfill material is angular to sub-angular in shape. Prototype Rockfill materials were modeled into maximum particle size (dmax) of 4.75 mm, 10 mm, 19 mm, 25 mm, 50 mm and 80 mm for testing in the laboratory. Consolidated drained triaxial tests were conducted on modeled Rockfill materials with a specimen size of 381 mm in diameter and 813 mm in height to study the stress–strain–volume change behavior for both Rockfill materials. Index properties, i.e. uncompacted void content (UVC) and uniaxial compressive strength (UCS), were determined for both Rockfill materials in association with material parameters. An elastoplastic hardening soil (HS) constitutive model was used to predict the behavior of modeled Rockfill materials. Comparing the predicted and observed stress–strain–volume change behavior, it is found that both observed and predicted behaviors match closely. The procedures were developed to predict the shear strength and elastic parameters of Rockfill materials using the index properties, i.e. UCS, UVC and relative density (RD), and predictions were made satisfactorily. Comparing the predicted and experimentally determined shear strengths and elastic parameters, it is observed that both values match closely. Then these procedures were used to predict the elastic and shear strength parameters of large-size prototype Rockfill materials. Correlations were also developed between index properties and material strength parameters (dilatancy angle, ψ, and initial void ratio, einit, required for HS model) of modeled Rockfill materials and the same correlations were used to predict the strength parameters for the prototype Rockfill materials. Using the predicted material parameters, the stress–strain–volume change behavior of prototype Rockfill material was predicted using elastoplastic HS constitutive model. The advantage of the proposed methods is that only index properties, i.e. UCS, UVC, RD, modulus of elasticity of intact rock, Eir, and Poisson's ratio of intact rock, νir, are required to determine the angle of shearing resistance, ϕ, modulus of elasticity, E 50 ref , and Poisson's ratio, ν, of Rockfill materials, and there is no need of triaxial testing. It is believed that the proposed methods are more realistic, economical, and can be used where large-size triaxial testing facilities are not available.
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testing and modeling the behavior of riverbed and blasted quarried Rockfill materials
International Journal of Geomechanics, 2014Co-Authors: N P Honkanadavar, K. G. SharmaAbstract:AbstractModeled Rockfill materials were obtained from nine sites (two riverbed and seven quarried) from different projects in India and Nepal, and drained triaxial tests were conducted with specimens that were 381 mm in diameter and 813 mm high. Index properties of the Rockfill materials, namely, unconfined compressive strength (UCS) and uncompacted void content (UVC), were determined. An elastoplastic hierarchical singe-surface (HISS) constitutive model was used to characterize the behavior of modeled Rockfill materials. The predicted stress-strain-volume change behavior was compared with the observed behavior, and it was found that both observed and predicted behavior matched closely. Procedures have been developed to predict the shear strength and elastic parameters of Rockfill materials using the index properties, namely, UCS, UVC, and relative density (RD), and predictions were made satisfactorily. Predicted shear strength and elastic parameters were compared with the experimental values, and it was ...
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prediction of shear strength parameter for prototype quarried Rockfill material based on index properties
2011Co-Authors: N P Honkanadavar, K. G. SharmaAbstract:Rockfill materials are widely used all over the world in the construction of Rockfill dam to trap river water. These materials have advantages because of their inherent flexibility, capacity to absorb large seismic energy and adoptability to various foundation conditions. For the present study, Rockfill material is obtained from Kol dam site, Himachal Pradesh. The maximum particle size of the material used in the dam is 800 mm. For testing, the size is scaled down to smaller sizes of 4.75, 10, 19, 25, 50 and 80 mm maximum particle size (dmax) using parallel gradation technique. Drained triaxial tests are carried out with a specimen size of 381 mm diameter and 813 mm height with varying confining pressure (V 3) from 0.2 to 1.6 MPa. All the dmax are tested for 87% and 75% relative density (RD). The index properties of the Rockfill materials viz. unconfined compressive strength (UCS) and uncompacted void content (UVC) are determined. Stress-strain-volume change behaviour of the modelled Rockfill material is studied and presented. The shear strength parameter, angle of internal friction (I) is determined for all the dmax of modelled Rockfill materials tested with 87% and 75% RD. Strength law has been developed to determine the failure stresses using index properties of Rockfill materials viz. UCS, UVC and RD and then I-values are predicted for all the modelled Rockfill materials satisfactorily. The I-value of the prototype Rockfill material is predicted using the proposed strength law. The predicted I-value of prototype Rockfill material is compared with the I-value predicted by commonly used extrapolation technique (power law which requires laboratory triaxial test results) based on dmax and found that I-value match closely. Therefore, it is believed that the proposed method is more realistic, economical, and can be used where large size triaxial testing facilities are not available and is quick to determine I-value using index properties.
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Constitutive Model for Rockfill Materials and Determination of Material Constants
International Journal of Geomechanics, 2006Co-Authors: A. Varadarajan, K. G. Sharma, Syed Mohd Abbas, A. K. DhawanAbstract:Two types of Rockfill materials collected from seven sites are modeled and tested under triaxial loading. A constitutive model based on a disturbed state concept is used to characterize the behavior of modeled Rockfill materials. The model is shown to provide satisfactory prediction of the observed behavior of the modeled materials. Characteristics of the particles of the Rockfill materials are determined. Relationships are developed between the material constants of the modeled Rockfill materials and the characteristics of the particles and these are used to predict the material constants for the prototype size Rockfill materials.
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Testing and Modeling Two Rockfill Materials
Journal of Geotechnical and Geoenvironmental Engineering, 2003Co-Authors: A. Varadarajan, K. G. Sharma, K. Venkatachalam, Ashok Kumar GuptaAbstract:Modeled Rockfill materials consisting of rounded and angular particles obtained from two dam sites are subjected to drained triaxial tests using large size specimens. An elastoplastic constitutive model based on the disturbed state concept is adopted to characterize the behavior of the modeled Rockfill materials. The material parameters for the two Rockfill materials are determined from the experimental results. The variation of the material parameters with respect to the size of the particles for the Rockfill material with the rounded particle is, in general, opposite to that for the Rockfill material with the angular particles. The model is shown to provide satisfactory prediction of the behavior of the Rockfill materials tested. Material parameters are predicted for prototype size of Rockfill materials.
Erxiang Song - One of the best experts on this subject based on the ideXlab platform.
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full scale creep test and back analysis of the long term settlement of heavy loaded shallow foundations on a high Rockfill embankment
Computers and Geotechnics, 2019Co-Authors: Dehai Jin, Erxiang Song, Zhiping Shen, Zhenjie YangAbstract:Abstract The long-term settlement of heavy-loaded shallow foundations on a high Rockfill embankment was studied using a full-scale field creep test, in which four concrete platforms were constructed and loaded on the top of a 24-m-high Rockfill embankment. The test programme was introduced, and the long-term deformation of the high Rockfill embankment was analyzed based on the monitoring data. Then three-dimensional numerical simulation was performed, using a rheological model for the Rockfill. When the model parameters were derived from the laboratory creep tests, the numerical simulation seriously underestimated the long-term settlement compared with field measurements. The model parameters were further back-determined using a two-stage back-analysis method. Reasonable agreement was found between the predicted results and the field measurements, not only for the surface creep settlement but also for the sub-surface creep settlement.
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a random virtual crack dem model for creep behavior of Rockfill based on the subcritical crack propagation theory
Acta Geotechnica, 2016Co-Authors: Mengjia Zhou, Erxiang SongAbstract:The post-construction settlement of Rockfill dams and high filled ground of airport, which is a phenomenon of much significance, is mainly caused by the time-dependent breakage of the Rockfill material. In this paper, a random virtual crack DEM model is proposed for creep behavior of Rockfill in PFC2D according to the theory of subcritical crack propagation induced by stress corrosion mechanisms. The bonded clusters are adopted to represent the Rockfill particles so as to simulate their irregular shapes. Virtual cracks are set at the bonds of the clusters, and the length of the crack is considered as a random value, which leads the crushing strength of a single particle to follow the Weibull’s statistical model and the corresponding size rules. Oedometric creep tests for Rockfill are simulated by using this proposed model. The results show that the model, validated preliminarily by some test data, can reflect qualitatively the creep mechanism as well as the size effects reasonably. Particles can develop various breakage patterns during creep, including global breakage, local breakage and even complex mixed breakage. The increase in stress levels and particle size will lead to an obvious growth of the creep strain and creep rate of the Rockfill. The scale effects on the creep behavior of Rockfill are analyzed through 35 specimens, and formulas including the effects of scales and stress levels are tentatively proposed.
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particle mechanics modeling of creep behavior of Rockfill materials under dry and wet conditions
Computers and Geotechnics, 2015Co-Authors: Zhihong Zhao, Erxiang SongAbstract:Rockfill is an important construction material for infrastructure engineering, such as dams, railways and airport foundations, which display a long-term post-construction settlement. However, the main mechanisms for Rockfill creep and weathering influence still remain poorly understood. Particle mechanics method is used to understand the Rockfill creep process under dry and wet conditions. Different bond-aging models and wetting models that represent different degradation and weakening mechanisms are compared, in order to clarify the principle and secondary mechanisms for Rockfill creep and weathering influence. The results show that Rockfill aggregate breakage in terms of angularity abrasion is the main source for Rockfill creep under dry state. Wetting can induce additional strain mainly due to the reduction of contact friction coefficient, i.e. lubrication, and the bond strength reduction just plays a secondary role in producing additional strain. The earlier the wetting occurs during Rockfill creep, the more rapidly the Rockfill becomes stable. The wetting–drying cycles can induce strain evolution in a ‘stepped’ way, which is in agreement with experimental observation. The practical implications from the modeling and the outstanding issues in this study are also discussed.
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a large triaxial investigation of the stress path dependent behavior of compacted Rockfill
Acta Geotechnica, 2012Co-Authors: Ming Xu, Erxiang Song, Jinfeng ChenAbstract:Realistic prediction of the deformation of Rockfill structures becomes increasingly important, which requires improved knowledge about the mechanical properties of Rockfill materials. However, previous large triaxial tests were usually carried out with a constant cell pressure, and there is uncertainty about the behavior of Rockfill along other stress paths. This paper presents the results of a series of large triaxial tests conducted on limestone Rockfill specimens along different loading paths. The effect of previous loading history and moisture content has also been investigated. The results show that the stress–strain and volumetric behavior of Rockfill are significantly influenced by the loading directions as well as the confining pressures. However, the stress path appears to have only minor influence on the shear strength of Rockfill, while the strength envelope exhibits pronounced curvature at low confining pressures and the peak friction angle decreases approximately linearly with the logarithm of the corresponding confining pressure. The previous loading history is revealed to have considerable effect on the stress–strain behavior but small influence on the peak strength of Rockfill. In contrast, the moisture content of Rockfill has marked influence on both the deformation and the strength characteristics. The implications of the test results are discussed.
