Homogeneous Earth Dam Research Articles

Artificial Neural Network Model to Predict the Factor of Safety in Earth Dams Subjected to Rapid Drawdown

Rapid drawdown has been identified as one of the most frequent causes of slope failures due to the effects associated with drought and operational changes when incorporating hydroelectric plants, which influence the filling level of earth dams. The main goal of this research is to obtain predictive models based on Artificial Neural Networks that return the factor of safety of the upstream slope in homogeneous earth dams in the face of the effect of rapid drawdown. Three geometries and 40 soils were defined to form the embankment, from which hybrid numerical models of transient water flow with unsaturated soils were built, considering three discharge speeds. From these results, a database was built to develop the predictive models, by means of the KNIME program and an algorithm based on Artificial Neural Networks. The behavior of the factor of safety as a function of time is also analyzed to establish its recovery intervals. Main results show that the minimum factor of safety is obtained between 52 % and 88 % of the total drawdown time. Regarding the predictive models, the adjusted R2 determination coefficients were greater than 95 % in all cases and the errors remained below 10 %. This demonstrates a high effectiveness of this algorithm and the validity of its application to geotechnical problems.

Analysis of Homogenous an Earth Dam Using Finite Element Method (Case Study, Arus Missan Dam), Northern Missan, Iraq

Arus Missan is a suggested earth dam that will be constructed in Ali-Al-Garbi city, northern Missan, Iraq, to avoid flood risks in the study area. In the same way, to harvest flooding and rainwater that comes from Iran territories. The finite element model SEEP/W is utilized to simulate seepage through the dam and the results of the model were analyzed to check the effectiveness of a homogenous earth dam in the proposed site. This model is an attempt to design a homogeneous earth dam comprised of silts. The material type of the model is the common soil type in the study area. Arus Missan dam is relatively safe according to the results of a simulation model, in the case of a homogenous silt dam. At the same time, to avoid an accumulation of silt sediment by the influence of slope, the dam needs careful design. For instance, slurry trench under the dam and drilling wells to minimize pore-water pressure in the dam foundation.

Reliability Analysis of the Slope Stability of Homogeneous Earth Dam under Seismic Loading

Earth dams are widespread throughout the world and their safety is the overriding concern of civil engineers, especially in regions with high seismic activity. This contribution presents a deterministic and reliability-based approach of the slope stability analysis of homogeneous earth dam under seismic loading. The hydrostatic loading as well as the saturation line in the dam body is considered for different design situations to investigate the effects of water level fluctuations on earth dam slope stability. Seismic loading is introduced by horizontal and vertical pseudo-static forces, while the considered failure mode is circular slip, analyzed with the classical method of slices. Given the nature of the soils, uncertainties about their properties must be considered in the assessment of the slope stability. These uncertainties can be quantified by a reliability analysis. The proposed reliability method is approached by the failure probability assessment of the slope stability of an earth dam based on Monte-Carlo simulation. The used random variables are the mechanical shear properties of the embankment body as well as the acceleration coefficient of the seismic zone. For the failure probability evaluation, the log-normal distribution law was used to generate the random variables. A computer program was developed using Matlab®. The developed approach was applied, for a practical example, to analyze the slope stability of an earthen dam located in Médéa (Algeria), whose dimensions are realistic. The results obtained with the developed analytical model were compared with those obtained with the Flac2D© software. The confrontation turned out to be satisfying.

Influence of factors on filtration regime of an earth dam under headwater drawdown

Introduction. As the statistics of observations of groundwater retaining structures shows, one of the most significant factors of emergencies in these structures is the occurrence of filtration deformations in the dam body. This often results in the appearance of moves of concentrated filtration. The occurrence of these phenomena can be provoked by a rapid decrease of the headwater level known as reservoir drawdown. It can be caused either by the technological requirements of the operation of the hydraulic unit or by the occurrence of an emergency situation. Modern design standards require mandatory consideration of the case of rapid drawdown with an assessment of the filtration regime and stability of the structure.
 
 Materials and methods. The results of numerical studies of unsteady filtration in a homogeneous earth dam under reservoir drawdown are considered. Numerical studies were carried out on the basis of the finite element method using the PRAXIS software package. Test calculations were carried out, which showed the reliability of the results obtained. The influence of the soil filtration coefficient of the dam, the rate of drawdown and the slope of the structure on the change in the position of the depression curve and the value of the maximum pressure gradient is analyzed.
 
 Results. For the considered variants of earth dams with different characteristics, the parameters of the filtration flow are obtained when the headwater level changes: the position of the depression curve and the values of the maximum pressure gradients. An assessment of the possibility of occurrence of filtration deformations of soils of the upper prism of the dam is given.
 
 Conclusions. The use of the PLAXIS software package for solving problems of unsteady filtration under reservoir level changes allows to obtain reliable results that are well comparable with the results of other proven methods. At certain rates of runoff for soils of different permeability in the upper prism of an earth dam, large values of pressure gradients exceeding critical values may occur. This indicates the necessity to control the process of drawdown and the use of antifiltration measures.

Analysis and Estimation of Seepage through Homogeneous Earth Dams Using Neural Network and Empirical Equation

In this investigation, the quantity of seepage through a homogeneous earth dam with a vertical drain on a permeable foundation was studied using the SEEP/W program. Moreover, the effects of the geometrical and geotechnical parameters (upstream slope, dam height, top width, free board, and permeability ratio) on leakage flow were analyzed with SPSS 20. To begin with, leakage flow values through an earth dam were estimated using SEEP/W by taking three values of each parameter, and then statistical analysis was performed with the help of dimensional analysis. In addition, an empirical equation and a neural network model dubbed q_ANN were developed to calculate leakage flow through an earth dam with a vertical drain. The validation of these models (empirical equation and q_ANN) is made by their applications to real case studies such as El-Haimeur and Boubrik dams located in Ghardaia City. In conclusion, the values of these models can prove that the performance of the models is high and accurate to predict leakage flow through a homogeneous earth dam with a vertical drain on a permeable base.

Numerical simulation using the finite element method to investigate the effect of internal cutoff walls on seepage and hydraulic gradients in homogeneous earth dams

Numerical simulation using the finite element method to investigate the effect of internal cutoff walls on seepage and hydraulic gradients in homogeneous earth dams

Mathematical Modeling of Seepage–Temperature Field for Earth Dam Using Experimental Test

Monitoring the seepage field is essential to characterize the operation of the earth dam. However, conventional seepage monitoring typically involves the use of a piezometer tube or pressure sensor for point distribution. A mathematical model incorporating the feedback of the temperature field on the seepage field was proposed based on experimental test observations. First, a theoretical analysis of the mathematical model is conducted, which includes examining the relationship between the variation of temperature field and factors, such as hydraulic gradient, water and soil temperature difference, hydraulic conductivity, thermal conductivity, specific heat, and time. Second, a homogeneous earth dam model is constructed in the laboratory with a distributed temperature sensor system to obtain synchronous information of the seepage–temperature field. Finally, the parameters of the mathematical model are quantified using observations from experimental tests, demonstrating good agreement between calculated and measured values. The experimental results indicate the feasibility of inferring seepage field monitoring information from the temperature field and elucidation of the interaction mechanism of the coupled fields. The quantitative mathematical model of the temperature field feedback on the seepage field is validated for its applicability in earth dams.

Study on the Influence of Water Level on Earth Dam Reinforced by Cut-Off Wall: A Case Study in Wujing Reservoir

The construction of a cut-off wall is a common reinforcement method for earth rock dams. At present, compared with the in-depth study on homogeneous earth dams, more and more attention is being paid to the stability and deformation of earth dams strengthened by a concrete cut-off wall. In this study, aiming at the Wujing project of the earth dam strengthened by cut-off wall, the influence of the water level rise and fall on the stability of the dam slope, the deformation of the dam body, and the crack width on dam crest were analyzed by numerical calculation and in situ measurement. The analysis results show that when the reservoir encounters a sudden drawdown, the safety factor of the dam slope decreases sharply. The faster the sudden drawdown, the faster the safety factor decreases. When the reservoir water level rises, the dam’s horizontal displacement shifts to the upstream direction, and the change of horizontal displacement of the downstream slope is significantly larger than that at the measuring point of the upstream slope. The water level of the reservoir rises, and the surface of the dam body rises, and the fluctuation of settlement deformation shows that the upstream side is larger than the downstream side, especially during the period of abrupt change in the reservoir water level. The longitudinal cracks on the dam crest show a tendency of shrinkage when the reservoir water level rises, and opening decreases with the decrease of deformation gradient increment and increases with the increase of gradient increment.

Easy Equation for Estimating Seepage Discharge through Earth Dams Based on Impermeable Foundation

The goal of this work was to develop an easy and reliable equation for calculating seepage discharge through homogeneous earthen dams that operate with toe drains. For this purpose, many data were generated using (SEEP/W) program depending on the geometrical variables that affect this seepage, such as dam height (h), upstream water depth (H), dam top width (b), upstream and downstream slopes, and base length of toe drain. The seepage discharge quantity for 728 cases was determined using three different values for each of the aforementioned geometric variables. A straightforward and precise equation was created for computing the discharge via a homogeneous earth dam with chimney drain system using the dimensional analysis method and SPSS software, with an (R2) coefficient of 0.986. Then the dimensional analysis was applied to this information. A simple and accurate equation was obtained to calculate the discharge through a homogenous earth dam with a toe drain system with a coefficient (R2) of 0.986. The results indicated that the seepage discharge increases with an increase in the upstream water depth, the toe drain’s base length, and the angle of the upstream and downstream slopes, while it decreases with an increase in the dam top width.Additionally, utilizing the produced data, the artificial neural network model (ANN) was implemented. The results of this model revealed varying percentages of importance for the independent geometrical variables on the seepage quantity, where the upstream water depth (H) has the most important and amounted to 66.9%, while the upstream slope was the least important, where the importance percentage for this factor was 0.7%. The (ANN) model and predicted empirical equation results show excellent agreement when compared.

Classification of Scouring Form of Homogeneous and Sticky Earth Dams in Overtopping

Classification of Scouring Form of Homogeneous and Sticky Earth Dams in Overtopping

Assessing the Suffusion Susceptibility of the Homogeneous Earth Dam Body Considering Spatial Variability of Soil Properties

The suffusion susceptibility of the soil samples is evaluated through an erosion resistance index. The erosion resistance index is estimated from several soil parameters thanks to existing statistical analyses. In actual exploitation, the soil properties with the input parameters are related to the grain distribution of the soil. Vary greatly from the original design value due to the influence of many factors. One of the factors is the inherent variability. Inherent soil variability is modeled as a random field. The usual problems used to assess the suffusion susceptibility maybe not give accurate results or fully evaluate the actual working ability of the ground in each case. That is one of the reasons why dams are still eroded when they are put into use. The paper aims to assess the suffusion susceptibility of the earth dam body using a two-dimensional (2D) Stochastics random field, modeling the initial problem, considering the variability spatial of soil properties, using the assumption of a Normal random field of soil characteristics parameters. The research goals predict the two-dimensional spatial variability of erosion resistance index of the dam body, probability of suffusion susceptibility, and the variability spatial of density and internal friction angle. An illustration of a numerical simulation of a homogeneous earth dam body is presented in this paper. The scientific novelty of the paper shows the predicted results of the two-dimensional spatial variability of erosion resistance index with a contour map and probability of suffusion susceptibility of the homogeneous earth dam body. Furthermore, the two-dimensional spatial variability maps of density and internal friction angle are also shown.

Sensitivity Study of the Computational Parameters for the Deformation of Homogeneous Earth Dams

The deformation of dams has always been the focus of dam safety research. To more accurately study the effect of the Duncan–Chang model on the deformation of homogeneous Earth dams, this paper simulates the displacement variation of a homogeneous Earth dam through the finite element method based on the Duncan–Chang E-B model. The sensitivity of the Duncan–Chang E-B model parameters and the dam material density on the displacement of a homogeneous earthen dam in Gansu Province, China, were investigated using single-factor and multifactor analysis methods. The results show that the displacement variation of the dam during the completion and operation periods is consistent with the general rule for Earth and rock dams; the three parameters R f , φ 0 , and Δ φ are more sensitive to dam deformation; and the three parameters m , n , and K are less sensitive to dam deformation.

Influence of Input Assumptions on the Evaluation of the Seismic Performance of Earth Dams

ABSTRACT The seismic performance of earth dams can nowadays be performed via dynamic analyses using constitutive models of sufficient accuracy in describing cyclic soil behavior. However, a number of assumptions different from soil model affect the problem as a whole. In this paper, a 2D model of a simplified homogeneous earth dam is developed, to assess the influence of bedrock compliance, vertical component of ground motion, stabilizing berms, and initial pore water pressure distribution on its seismic performance, thus providing some guidance on the choices that should be adopted for a safe assessment of the seismic performance of existing earth dams.

Modeling the effect of downstream drain geometry on seepage through earth dams

This research investigates the effect of downstream drain’s geometry on seepage through homogeneous earth dams founded on an impervious foundation. A permeability tank experimental model and SEEP2D numerical model are used in the study. The dam’s failure in the case of no drain is experimentally observed to point out the drain’s importance. The effect of the drain’s geometry on seepage characteristics is evaluated by considering different scenarios for its height, length, and angle. Three cases for reservoir filling are studied. Sensitivity analysis is performed to evaluate the drain’s most effective geometrical parameter. The results show that the most effective geometrical parameter of the downstream drain is its length, while its height and angle have no effect. Increasing the drain’s length increases the seepage discharge and the distance between the phreatic line and downstream face and reduces the pore water pressure leading to more safety. Design charts and equations are provided.

Numerical and experimental modelling of seepage in homogeneous earth dam with combined drain

ABSTRACT In this study, the use of combined drain has been suggested as an alternative for triangular toe drain in a homogeneous earth dam. The main idea used in this research is to reduce the volume of drain materials that are manufactured and simultaneously achieving better hydraulic performance. To study this idea, at first, the hydraulic performance of the combined drain and the influence of replacing the triangular toe drain with this type of drain is investigated using the small-scale physical modelling. Then large-scale numerical simulation was performed by developing a numerical model. The designed triangular toe drain height was reduced by 20, 30, 40 and 50%, and part of the remaining material was placed horizontally alongside the reduced triangular toe drain. The results showed that using combined drain with similar hydraulic performance to triangular toe drain models, saved 18 to 60% on the volume of drain materials for the models provided. Finally, the appropriate dimensions of combined drain are proposed based on the saving of material used. At the end, by applying dimensional analysis method, the dimensionless charts are presented to estimate the seepage quantity through the section of the homogeneous earth dam with combined drain.

Analysis and Peak Value Prediction of Rainfall Component Factors Influencing Seepage Flow for Homogeneous Earth Dams

The rainfall component of seepage flow is an important indicator for monitoring earth dam safety. Compared with previous practice of only analyzing rainfall, this paper divides the analysis dimensions into three categories according to the seepage process in the process of rainfall: the saturation permeability coefficient of the soil receiving the rainfall, the rainfall intensity and rainfall duration. This paper conducted FE simulation according to the principle of unsaturated seepage flow, and it is concluded that: the influence of different rainfall intensity on seepage flow is roughly linear and can be expressed by a first power factor; the influence of different saturation permeability coefficient and rainfall duration on seepage flow is obviously nonlinear, and should be expressed by multiple powers. Based on the above law, the model expression of peak seepage flow prediction was established, and both the fitting effect and prediction accuracy were good. The results show that the law of influence factors has been summarized correctly, and the research result can provide effective theoretical support for the seepage flow monitoring and early warning and safety monitoring for homogeneous earth dams.

Analysis free surface of nonlinear seepage using the MQRBF method

In order to solve the characteristics of low accuracy and slow efficiency in traditional numerical solution the free surface problem, the multiquardatic radial base function collocation method(MQ RBF) is used to analyze the constant seepage and unsteady seepage of the homogeneous earth dam. Computation of transient problem of free surface of earth dam by the linear derivation of Richards equation. The results show that the calculation accuracy of the MQRBF is higher than that of the traditional numerical method. The solution process does not involve numerical integral calculation and grid reorganization, which greatly reduces the calculation amount. Compared with the Trefftz method, it has the advantage of solving boundary values and internal values at the same time. It is not limited by the solution of the Laplace equation, and its application is wider and simpler.

2-D steady seepage flow model to simulate the contaminates transportation through homogeneous earth dam using Geo–Studio software

Geo-Studio program is used in this study with its sub-programs named SEEP/W and CTRAN/W 2012 to represent and analyse the phreatic line, the amount of seepage through the dam, the pressure head, the discharge, the total head and the amount of contaminants that transport through the body of the dam. The problem of transportation of contaminants through homogeneous earth dam due to seepage flow was studied and simulated using the computational fluid dynamic technique with the help of Geo–slope programs. The paper also studied the prediction of future contaminants’ levels in the specified dam. The study also discusses the effect of pool water level fluctuation from maximum to a minimum level on the seepage flow and the time of pollution transmission. From the Geo-studio software, it is deduced that when the water level is at the maximum height (20m), it needs 12 days, at normal height (15m) it needs 30 days, while at a minimum height (8 m) it needs 100 days to reach the drain zone.

Seepage through earthen dams under different dam geometries and conditions

The study presents a method to carry out a new equation for the seepage rate of homogeneous earth fill dam with clay core using various geometry conditions. For this purpose the Slide 6.0 software has been used. The proposed program runs for (85) different geometrical cases of dam body to determine the seepage rate. The aim of the study is to examine the capabilities of slide 6.0 software in computing the rate of seepage and to find the impact of different structure geometry (e.g., upstream horizontal blanket length and thickness and, cutoff depth) on the reduction of the rate of seepage through the proposed earth dam. Dimensional analysis is conducted using Buckingham π theorem to find the dependent and non-dependent variables. Artificial Neural Network (ANN) model is developed that relates the output variables with the input variables which govern the rate of the seepage through homogenous earth dam with clay core. The results are analyzed using SPSS software. Three different heights of the dam, three different lengths of the upstream blanket with four different thickness of the blanket and four different cutoff depths with different conditions were used in this study and the results showed that the rate of the seepage decreased as the upstream blanket length, the cutoff depth and the thickness of the blanket are increased. Also, the impact of the upstream blanket length is greater than the cutoff depth and then the thickness of the blanket in decreasing the rate of seepage. While, the rate of the seepage were increased as the top width of the dam were decreased. The seepage rate obtained by the Slide 6.0 program was compared with its quantity calculated from an empirical equation developed in this study. This relation has a determination coefficient of (R2 = 0.8842).  

Rapid Drawdown in Homogeneous Earth Dam Considering Transient Flow and Suction

The present work intends to demonstrate the advantages of considering transient flow regime in the stability analysis of the upstream slope for the rapid drawdown situation of a homogeneous earth dam. Upstream slope stability evaluations were carried out, considering pore pressure and suction from transient flow analysis while simulating rapid drawdown of the reservoir. The evaluations comprised different geometries of the upstream slope (from 1V:1.1H to 1V:2.5H) and heights varying from 10 m to 50 m, as well as several low permeability materials (SM, SM-SC, SC, ML, ML-CL, CL, MH and CH). In addition, equations relating the safety factor to such slopes or dam height were adjusted to the analysis data, in order to define the minimum slope for a certain dam height or the maximum height for a given upstream slope. The results have shown that, considering the transient flow condition, including suction, within the slope stability analysis of the rapid drawdown situation, increases the safety factor in relation to the simplified analysis that is usually adopted. This also results in much steeper slopes (for a safety factor of 1.1) than the ones recommended by the U.S. Bureau of Reclamation (USBR), suggesting the importance of performing transient flow analysis for rapid drawdown situations and considering its results instability analysis.