Response Of Earth Dams Research Articles

Application of the Time Step Optimization Method in Seismic Liquefaction Analysis and Its Evaluation Method for Computational Efficiency Improvement

In order to solve the time step setting problem in seismic liquefaction numerical analysis, the time step optimization method was introduced into seismic liquefaction numerical analysis platform, and the seismic response of earth dam was analyzed. The results show that the time step optimization method can effectively solve the time step setting problem. In addition, in order to evaluate the computational efficiency improvement of the optimized seismic response, a new method was proposed, and an example with analytical solution was selected to verify it. And the proposed method was used to evaluate the calculation efficiency of the optimized seismic response. The results show that the computing efficiency is greatly improved after the seismic liquefaction numerical analysis program is optimized by the time step optimization method.

Analysis the dynamic response of earth dam in free vibration and forced by introducing the effect of the interaction dam foundation

The present study concerns the analysis of the dynamic response of earth dam, in free and forced vibration (under the effect of earthquake) using the finite element method. The analysis is carried out at the end of dam construction without filling. The behavior of the dam materials and the foundation is linear elastic. In free vibration, to better understand the effect of the dam foundation interaction, we will take into account different site conditions and see their influence on the free vibration characteristics of the dam. In forced vibration, to study the seismic response of the dam, the system is subjected to the acceleration of the Boumerdes earthquake of May 21, 2003 recorded at the station n ° 2 of the dam of Kaddara in the base, with a parametric study taking into account the influence of the main parameters such as the mechanical properties of the soil: rigidity, density.

Effects of Upstream Water Level on Dynamic Response of Earth Dam

The island of Taiwan is located between the boundaries of the Eurasia and the Philippines Plates and thus earthquakes occurred frequently. The excitation of earthquake affects the integrity of earth dams situated in the mountainous area of the island. A study was conducted to evaluate the dynamic response and safety of one of the earthquake dams. The computer program and soil model used were calibrated for their appropriate use for the subject dam against a well-instrumented centrifuge model. Numerical simulation was then conducted to examine the influence of upstream water storage level on the response of the earth dam. The numerical results identified three locations in the dam where attentions are required because these locations were found susceptible to liquefaction.

3D Valley Site Effect on the Nonlinear Seismic Response of Earth Dam

A three dimensional numerical model for a typical earth dam and its valley site was established and the nonlinear seismic response of this model was performed. Experimental data of cyclic triaxial tests were adopted to determine the curves of modulus ratio and damping ratio that vary with dynamic strain amplitude. Free-field artificial boundary and viscous artificial boundary were employed and the input waves were the revised ground motions obtained from the station near the dam. Distributions of the PGA, displacement, residual deformation, shear strain increment and element failure state were presented. Results demonstrate that the 3D local valley site effect has a significant influence on the seismic response of earth dam.

Numerical analysis of nonlinear dynamic behavior of earth dams

A numerical study is conducted to investigate the dynamic behavior of earth dams. The numerical investigation employs a fully nonlinear dynamic finite difference analysis incorporating a simple elastic perfectly plastic constitutive model to describe the stress-strain response of the soil and the Rayleigh damping to increase the level of hysteretic damping. The extended Masing rules are implemented into the constitutive model to explain more accurately the soil response under general cyclic loading. The soil stiffness and hysteretic damping change with loading history. The procedures for calibrating the constructed numerical model with centrifuge test data and also a real case history are explained. For the latter, the Long Valley (LV) earth dam subjected to the 1980 Mammoth Lake earthquake as a real case-history is analyzed and the obtained numerical results are compared with the real measurements at the site in both the time and frequency domains. Relatively good agreement is observed between computed and measured quantities. It seems that the Masing rules combined with a simple elasto-plastic model gives reasonable numerical predictions. Afterwards, a comprehensive parametric study is carried out to identify the effects of dam height, input motion characteristics, soil behavior, strength of the shell materials and dam reservoir condition on the dynamic response of earth dams. Three real earthquake records with different levels and peak acceleration values (PGAs) are used as input motions. The results show that the crest acceleration decreases when the dam height increases and no amplification is observed. Further, more inelastic behavior and more earthquake energy absorption are observed in higher dams.

Response of Earth Dams to Rayleigh Waves Using Coupled FE-BE Method

The effects of Rayleigh waves on the response of earth dams are examined, with emphasis on the importance of the foundation flexibility and the spatial variability of the ground motion. The study is based on a rigorous hybrid numerical formulation that combines the efficiency and versatility of the finite-element (FE) method and the ability of the boundary element (BE) method to account for the radiation conditions. The two-dimensional (2D) formulation is used here in the frequency domain to investigate the response of infinitely long earth and rockfill dams subjected to Rayleigh waves traveling across the dam width. The study demonstrates the dramatic effect of the flexibility of the foundation rock in reducing the overall response of the dam. It also shows that the spatial variability of the vertical component of the ground motion caused by the Rayleigh waves induces additional rocking motion that contributes significantly to increasing the horizontal response, especially in the upper part of the dam body, while reducing the vertical vibration.

New techniques for modelling reservoir-dam and foundation-dam interaction

A hybrid numerical procedure is proposed for the dynamic frequency domain response of earth dams resting on a multi-layered foundation. The impounded fluid is assumed viscous to account for the internal viscosity and absorption at the reservoir bottom. A new technique is described to determine the frequencydependent added masses and loads contributed by the reservoir at the inclined upstream dam face. The impedance of the multi-layered foundation is obtained using the layer transfer matrix and the dam is modelled by finite elements. An interface function is defined using interpolating functions to maintain equilibrium of interface forces and the displacement compatibility at the interface nodes. Unlike other boundary elements, this procedure avoids any additional discretization of the fluid and the foundation except at their interfaces with the dam structure. Numerical results, including transient reponses to the S90W El-Centro earthquake groundmotion (1940), are presented to illustrate the modelling of reservoir-dam and soil dam interaction.

Wave passage effects on the response of earth dams : Dakoulas, P; Hashmi, H Soils FoundV32, N2, June 1992, P97–110

Wave passage effects on the response of earth dams : Dakoulas, P; Hashmi, H Soils FoundV32, N2, June 1992, P97–110

Lateral response of dams in semi-elliptical rigid canyons

An analytical closed-form solution is developed for the lateral response of earth and rockfill dams built in semi-elliptical canyons. The dam is idealized as a linearly hysteretic elastic body deforming only in shear, whereas the canyon is assumed to be rigid. The solution for the dam response is given in terms of prolate spheroidal radial and angular functions of the first kind and zero order. Results are presented for natural frequencies, modal displacement shapes, participation factors, and response to transient and steady-state harmonic base excitation for various dam length-to-height ratios. Comparisons are made of the effects of the length-to-height ratio and the canyon shape on the response of dams built in semi-elliptical and rectangular canyons. A subsequent study (Dakoulas, P. & Hsu, C.H., Response of earth dams in semi-elliptical flexible canyons to oblique SH waves, Report, Rice University, Houston, Texas, 1993) extends this model to a semi-elliptical canyon consisting of flexible elastic rock, subjected to obliquely incident harmonic SH waves.

Response of Earth Dams in Semicylindrical Canyons to Oblique SH Waves

An analytical solution is developed for steady‐state lateral response of earth and rockfill dams built in semicylindrical canyons and subjected to obliquely incident harmonic SH waves. The dam is idealized as a linearly hysteretic elastic body deforming only in shear, while the supporting canyon is modeled as an elastic medium, representing a deformable rock half‐space. The solution accounts in a rigorous way for the complex wave reflection, transmission, and diffraction phenomena associated with the presence of the dam‐filled canyon. For the displacement fields in the dam and the canyon, closed‐form expressions are derived involving a series expansion in terms of spherical‐Bessel and Legendre functions. A parametric investigation elucidates the effects of the dam‐to‐canyon material impedance ratio, of the angle of incidence, and of the frequency of excitation on the response along the crest of the dam. Similarities and differences are noted and explained with the response of the dam to “rigid‐base”‐type (“synchronous”) excitation, as well as with the response of an alluvial semicylindrical valley to oblique SH waves.

Wave Passage Effects on the Response of Earth Dams

An analytical model is presented for steady-state lateral response of earthfill and rockfill dams in canyons subjected to a steady train of harmonic SH waves incident at an arbitrary angle θ. The dam is idealized as a 2-dimensional shear beam with a triangular cross-section, while the canyon is considered rectangular and consisting of elastic rock. A parametric study is undertaken to investigate the influence on the steady-state response of (a) the angle of incidence θ of the incoming waves, (b) the impedance ratio and (c) the canyon narrowness. It is shown that the acceleration amplification is considerably less for a dam built in flexible canyon than for a dam in a rigid canyon and, hence, the effect of radiation damping may be very important. For obliquely incident waves travelling from the left to the right, the response of the dam depends mainly on the interference of the waves transmitted through the base and the left boundary, leading to a maximum response at a θ about 30°-35°. For very long dams subjected to high frequency obliquely incident waves, it is found that there is no amplification of the motion by the dam. For low-frequency excitation, the response of the dam shows little variation along the crest and approaches the response of the elastic half-space. The results are in agreement with published results for the response of alluvial valleys subjected to incident SH waves.

Nonlinear response of dams founded on alluvial deposits in narrow canyons

This paper presents a simplified model for the response of earth dams founded on alluvial deposits at the base of canyons. The goal of the model is to capture the effect of the most important factors influencing the response and to provide a realistic and efficient tool for preliminary safety evaluations. The developed theoretical closed-form solution combines the effects on the response of: (a) the foundation layer, (b) the canyon narrowness, (c) the variation of soil stiffness within the dam versus depth, and (d) soil nonlinearity. The latter is incorporated in a simple piece-wise linear scheme, in which the soil shear moduli and damping ratios within the dam and the layer are continuously updated at small time intervals during the analysis. The presence of a soft foundation layer is found to have a dramatic effect on the natural periods of the dam. A series of parametric studies is undertaken to investigate the effect on the response of the fundamental geometric and material characteristics of the dam-layer-canyon system subjected to transient and harmonic motion. The results show that a foundation layer with an average S -wave velocity similar or less than that of the dam under moderate or strong base excitation may experience significant shear strains. Such strains are capable of inducing high excess pore water pressures and perhaps liquefaction within contractive saturated cohesionless soils in the foundation. The cost of the simplified analysis is about three orders of magnitude less than that of an elastoplastic FE analysis.

2‐D Elastoplastic Seismic Shear Response of Earth Dams: Applications

The method presented in the companion paper is applied herein to analyze the nonlinear earthquake response of an earth dam; the entire time history of the response quantities, including permanent deformation of the dam, are calculated. Two different input ground motion cases are considered: a moderate and a strong shaking with very different frequency characteristics. Comparative studies are conducted to examine the influence of two-dimensionality, nonlinearity, nonhomogeneity, modal expansion, modal coupling, and the multidimensional stress interaction on the response. The results are also compared to those obtained by an elaborate finite element analysis. The comparative study reveals significant response differences between one- and two-dimensional analyses, homogeneous and nonhomogeneous models, moderate and strong shakings, and one- and multi-mode solution expansions. In addition, the comparison indicates that the simplified method proposed can be used to realiably estimate the nonlinear earthquake response of earth dams modeled as 2-D shear wedges.

2‐D Elastoplastic Seismic Shear Response of Earth Dams: Theory

A simplified analytical‐numerical method for analyzing the nonlinear earthquake response of earth dams, modeled as two‐dimensional, nonhomogeneous shear wedges in rectangular canyons, is presented. The method takes into account the nonlinear, hysteretic, and strain‐dependent characteristics of the dam materials. The hysteretic stress‐strain behavior of the material is modeled using elastoplastic constitutive equations based on multisurface kinematic plasticity theory; no viscous or numerical (artificial) damping is employed. The method is based on a Galerkin formulation of the equation of motion in which the solution is expanded using the eigenmodes of the two‐dimensional linearized problem defined over the spatial domain occupied by the dam. The analysis can be used to calculate the entire time history of the response quantities, including permanent deformations of earth dams subjected to ground shaking. Finally, the efficiency and low computational cost make the technique very attractive.