Design Of Arch Dams Research Articles

Numerical analysis method of equivalent deformation parameters for grouted arch dam abutment fractured rock masses considering scale effects and anisotropy

Research on the equivalent deformation parameters of grouted arch dam abutment rock masses has recently emerged as a key in the design, construction and stability assessment of arch dams. With the aim of synthetically considering scale effects and anisotropy of the rock mass equivalent deformation parameters after grouting, in this paper, a practical numerical calculation method is developed. First, the Latin hypercube sampling method is introduced to generate a network of fractures of the arch dam abutment rock mass. Subsequently, the finite element models of the rock masses with different sizes in various directions are constructed. On this basis, equivalent continuum theory and cohesive element model are applied for numerical calculation of grouting fractured rock masses. Then, the scale effect and anisotropy of the deformation modulus of rock mass under different grouting conditions are investigated. Finally, the Jinping super-high arch dam is taken as an example to validate the theoretical significance and application effect of the proposed method. The analysis results indicate that the process of fracture and fragmentation of grouted rock masses is characterized precisely, and the deformation of material units can be described as fully as possible to calculate more realistic equivalent deformation parameters of the fractured rock masses.

Nonlinear seismic response and index correlation of high arch dams under cross-stream oblique incidence of near-fault SV waves based on wavelet decomposition

This paper aims to propose an analysis framework for the response index correlation of high arch dams under cross-stream oblique incidence of near-fault pulse-like and non-pulse seismic waves. The influence of the dynamic pulse effect of near-fault seismic waves on the index correlation at different incidence angles is evaluated. Further, the seismic response through an arbitrary incident angle is quantitatively estimated. Several typical near-fault records of extracted strong velocity pulses are selected, and their decomposed non-pulse ground motions (GMs) are used to ensure the similarity and uniformity of the response spectra. Furthermore, a seismic input model of the oblique incidence of the SV wave is established based on the three-dimensional viscous-spring artificial boundary method, and its accuracy was confirmed through the numerical application. The engineering demand parameters (EDPs) of pulse-like SV waves and non-pulse SV waves, including dam damage, dynamic displacement, and joint opening, with cross-stream incident angles are discussed emphatically. Finally, the correlation between the response indices of near-fault SV waves at different incident angles is quantitatively analyzed. The numerical results indicate that pulse-like seismic waves with different input angles are more destructive than non-pulse seismic waves, and different response indices of the dam may have different most unfavorable incident angles. A prediction model of the dam response considering different input angles of seismic waves is proposed to roughly estimate the response index values of each input angle. The influence of the dynamic pulse characteristics on the correlation degree of response indices under different input angles is mainly divided into three types: no impact, increasing correlation degree, and decreasing correlation degree. In the seismic design and performance evaluation of arch dams, it should be suggested to comprehensively consider the influence of the oblique incident angle of GMs and near-fault pulse characteristics.

Shape Optimization of Single-Curvature Arch Dam Based on Sequential Kriging-Genetic Algorithm

Shape optimization of single-curvature arch dams using the finite element method (FEM) is often computationally expensive. To reduce the computational burden, this study introduces a new optimization method, combining a genetic algorithm with a sequential Kriging surrogate model (GA-SKSM), for determining the optimal shape of a single-curvature arch dam. At the start of genetic optimization, a KSM was constructed using a small sample set. In each iteration of optimization, the minimizing predictor criterion and low confidence bound criterion were used to collect samples from the domain of interest and accumulate them into a small sample set to update the KSM until the optimization process converged. A practical problem involving the optimization of a single-curvature arch dam was solved using the introduced GA-SKSM, and the performance of the method was compared with that of GA-KSM and GA-FEM methods. The results revealed that the GA-SKSM method required only 5.40% and 12.40% of the number of simulations required by the GA-FEM and GA-KSM methods, respectively. The GA-SKSM method can significantly improve computational efficiency and can serve as a reference for effective optimization of the design of single-curvature arch dams.

Study on dynamic contact model and force transfer mechanism of hydraulic spherical keyway

In the design of hydraulic structures, keyway are often arranged between adjacent structures to increase their integrity. Spherical keyway is more and more used in the transverse joints of high arch dams. However, the layout of keyway is dense in transverse slot and the simulation workload is huge. Very few reports have been reported on accurately pointing out the working mechanism and force mechanism of transverse joint keyway in high arch dam during earthquake. In this paper, the contact force transmission characteristics of spherical keyway are studied and the contact mechanics equation of spherical keyway is derived. A three-dimensional finite element fine simulation model of spherical keyway is established by using parametric modeling technology, and high performance calculation is carried out by using parallel computing technology. Real-time dynamic simulation of the working behavior of spherical keyway in earthquake reveals the variation of contact position, contact stress and contact mode of spherical keyway in parallel and vertical joints. The research results lay a solid foundation for in-depth seismic response analysis and seismic safety design of high arch dams.

Shape design of arch dams under load uncertainties with robust optimization

Due to an increased need in hydro-electricity, water storage, and flood protection, it is assumed that a series of new dams will be build throughout the world. The focus of this paper is on the non-probabilistic-based design of new arch-type dams by applying means of robust design optimization (RDO). This type of optimization takes into account uncertainties in the loads and in the material properties of the structure. As classical procedures of probabilistic-based optimization under uncertainties, such as RDO and reliability-based design optimization (RBDO), are in general computationally expensive and rely on estimates of the system’s response variance, we will not follow a full-probabilistic approach but work with predefined confidence levels. This leads to a bi-level optimization program where the volume of the dam is optimized under the worst combination of the uncertain parameters. As a result, robust and reliable designs are obtained and the result is independent from any assumptions on stochastic properties of the random variables in the model. The optimization of an arch-type dam is realized here by a robust optimization method under load uncertainty, where hydraulic and thermal loads are considered. The load uncertainty is modeled as an ellipsoidal expression. Comparing with any traditional deterministic optimization method, which only concerns the minimum objective value and offers a solution candidate close to limit-states, the RDO method provides a robust solution against uncertainty. To reduce the computational cost, a ranking strategy and an approximation model are further involved to do a preliminary screening. By this means, the robust design can generate an improved arch dam structure that ensures both safety and serviceability during its lifetime.

Static analysis of a high arch dam

The paper presents the design and static analysis of a high arch dam. A feasibility study was conducted on the dam in the 90s and a preliminary layout was designed. However, the dam’s construction phase has been never started. In this paper, the design and layout of the dam under consideration are in accordance with the US manuals for the design of arch dams. The structure’s three-dimensional model was entered into the program SAP2000 and three-dimensional solid finite elements were used to discretize the model. This paper considers the hydrostatic pressure of the water reservoir and concrete self-weight. The analysis was performed for both the maximum and the minimum designed water level and for the case when the reservoir is empty. Special attention is given to the boundary conditions of the dam at its abutments and foundation. The results show that the planned layout is good for the dam’s construction. The arch dam’s curve transfers the loads to the abutments. The significant role of the foundation rigidity and the reservoir water level in the stress distribution and nodal displacements within the arch dam is observed.

An Elastic-plastic Constitutive Model of Concrete Based on Thermodynamic Principles and Its Application in Arch Dam Design

An Elastic-plastic Constitutive Model of Concrete Based on Thermodynamic Principles and Its Application in Arch Dam Design

Viscous Damping and Contraction Joint Friction in Underwater Explosion Resistant Design of Arch Dams

The aim of this study is to clarify the parameter-determination issue with regard to the viscous damping and contraction joint friction in the underwater explosion (UNDEX) resistant design of arch dams. A 141-m-high double-curvature arch dam is chosen as the study subject, and the finite-element program ABAQUS/Explicit is employed. Both the dam-reservoir interaction and the contraction-joint nonlinearity are considered. The calculation results suggest that in a routine range of values for the viscous damping ratio (less than 0.05), the damping effect on the UNDEX-induced displacement and damage responses of the arch dam seem limited. To be conservative in the design, the viscous damping ratio could be assigned a zero value (neglecting the damping effect). The calculation results have highlighted the importance of the monolith-to-monolith friction to the tensile damage to the dam base. We believe that a value of 0.65 assigned to the friction coefficient should be appropriate for the UNDEX resistant design of an arch dam in case the shear keys’ shear-transferring roles are not considered.

A Comparative Study of the Cracking Effect of Induced Joints of Various Spatial Formations

The use of induced joints is a common cracking control measure used in the design of roller compacted concrete arch dams. Currently, in some projects in which radial twisted joints were used, during the construction period, some cracks appeared around the induced joints while the joints themselves failed to open. From the fracture mechanics point of view, this problem is related to the variations in the spatial formation of the induced joint planes. In this study, we formulated numerical examples involving square plate and cylindrical arch dam with joints of various planar spatial formations and used the virtual crack-closure technique and the Richard brittle fracture criterion to obtain the equivalent stress intensity factor of the joint plane, and we studied the joint plane stress intensity factor based on the variations in the joint plane formation angle. Based on the reciprocal of the normalized stress intensity factor, we obtained the equivalent strength correction coefficient for induced joints of varying plane angles, referred to in this study as the joint plane formation factor ψα, in order to reflect the influence of varying joint plane formations on the induced joint cracking. Our study results show that as the joint plane angle continuously increases, it is more difficult for the induced joints to open, which implies a gradual increase in the equivalent strength of the joint plane. Therefore, in the actual design of rolled concrete arch dams, the straight transverse joint layout should be used for induced joints. If the use of the radial twisted joint layout is necessary, the joint plane angle should not exceed 10°.

Research On Slope Stability Analysis Method Based On Limit State Design Method Of Partial Coefficient

The arch dam design specification (SL282-2003) provides an allowable safety factor of 3.5 in abutment stability analysis, whether at the same safety level with value of 3.0 specified for gravity dams. The approach of ‘Ratio of Safety Margin’ can compare the safety factor with reliability index. The researches confirm that allowable reliability index of 4.45 and the allowable safety factor of 3.5 at the same level of risk control.

Seismic design of Xiluodu ultra-high arch dam

The 285.5 m-high Xiluodu Arch Dam is located in a seismic region along the Jinsha River in China, where the horizontal components of peak ground accelerations for design and checking earthquakes have been estimated to be 0.355g and 0.423g, respectively (g is the gravitational acceleration). The ground motion parameters of design and checking earthquakes are defined by exceedance probabilities of 2% over 100 years and 1% over 100 years, respectively. The dam shape was first selected and optimized through static analysis of the basic load combinations, and then adjusted after taking into account the seismic loads. The dam should be operational during and after the design earthquake with or without minor repairs, and maintain local and global stabilities during an extreme earthquake. Both linear elastic dynamic analysis and nonlinear dynamic analysis considering radiation damping, contraction joints, and material nonlinearity were conducted to assess the stress in the arch dam. The dynamic analysis shows that the maximum dynamic compressive stresses are less than the allowable levels, while the area with tensile stress over the limit is less than 15% of the dam surface and the maximum contraction openings range from 10 mm to 25 mm. The arch dam has sufficient earthquake-resistance capacity and meets the safety requirements. Nevertheless, steel reinforcement has been provided at the dam toe and in the zones of high tensile stress on the dam surface out of extra precaution.

Hydrodynamic pressures on arch dam faces with irregular reservoir geometry

A scaled boundary finite element method is developed for the analysis of hydrodynamic pressures acting on arch dam faces with a reservoir of irregular geometry. Water compressibility and reservoir boundary absorption are considered simultaneously. The reservoir is idealized as composed of finite and infinite subdomains. Governing equations for evaluating hydrodynamic pressures of finite fluid domain have been established and the solution procedures are presented. In addition, the boundary conditions at the interface between finite and infinite subdomains are decided. Numerical examples validate the present method with high accuracy and show that the fairly irregular geometry of a reservoir has an important influence on the hydrodynamic pressures acting on the arch dam face. Frequency response functions of the hydrodynamic pressures in the stream and cross-stream directions are evidently influenced by reservoir geometry, while hydrodynamic pressures in the vertical direction are relatively less influenced. Another feature of the frequency response function of hydrodynamic pressures is that the amplitude of resonant peaks is affected much more by reservoir geometry as compared to the resonant frequency. Besides, peak value of hydrodynamic pressures in the arch direction and cantilever direction is also significantly influenced by reservoir geometry. Based on these facts, it can be concluded that the effect of reservoir geometry on hydrodynamic pressure should be considered for seismic design of arch dams.

Robust Optimization for Shape Design of Arch Dams Based on Strain Energy

The strain energy of dam body and its sensitivity to the deformation modulus of foundation are taken as objective functions, feasibility robust constraint of stress is taken into account with the consideration of uncertainty of foundation deformation modulus, and a robust optimization model for shape design of arch dams is established based on strain energy. A formula of sensitivity of dam strain energy to deformation modulus of foundation is derived and a relevant algorithm is proposed. The optimization of a planned arch dam indicates that, the dam strain energy and its sensitivity to foundation deformation modulus of optimal design are reduced 2.29% and 15.51%, respectively, of that of initial design, and the validity of the proposed model is demonstrated.

Optimization design of foundation excavation for Xiluodu super-high arch dam in China

With better understanding of the quality and physico-mechanical properties of rocks of dam foundation, and the physico-mechanical properties and structure design of arch dam in association with the foundation excavation of Xiluodu arch dam, the excavation optimization design was proposed for the foundation surface on the basis of feasibility study. Common analysis and numerical analysis results demonstrated the feasibility of using the weakly weathered rocks III1 and III2 as the foundation surface of super-high arch dam. In view of changes in the geological conditions at the dam foundation along the riverbed direction, the design of extending foundation surface excavation area and using consolidating grouting and optimizing structure of dam bottom was introduced, allowing for harmonization of the arch dam and foundation. Three-dimensional (3D) geomechanics model test and finite element analysis results indicated that the dam body and foundation have good overload stability and high bearing capacity. The monitoring data showed that the behaviors of dam and foundation correspond with the designed patterns in the construction period and the initial operation period.

Failure and overall stability analysis on high arch dam based on DFPA code

A code of practice for three dimensional cracking and a failure process analysis of high arch dams, based on the finite element method, dam failure process analysis (DFPA) has been developed. In this code, by changing mesh density, consideration of heterogeneity when calculating the elements is achieved. Random strength and elastic modulus are assigned to the elements in accordance with a Weibull distribution. A stress analysis is carried out based on consideration of the deformation of an elastic material containing an initial random distribution of microcracks, which simulates the progressive failure of solids. The dam cracking and failure process associated seismicity accumulation can be analyzed using acoustic emissions. The proposed method was applied in investigating the failure mechanism, and overall stability of the Xiluodu high arch dam. The numerical mesh model was fine, and the total number of hexahedral elements was 300million. The DFPA analysis results, when compared with those derived by the Tfine code, and the 3D geomechanical model test show that the DFPA code is effective in fully simulating the failure processes of the dam and foundation. The analysis results were used to successfully guide the design of the Xiluodu high arch dam. The proposed DFPA method may also be of value to the reinforcement design and construction of high arch dams, associated with similar hydropower projects worldwide which are also located in complicated rock foundation areas.

Experimental Study on Cracking, Reinforcement, and Overall Stability of the Xiaowan Super-High Arch Dam

The Xiaowan super-high arch dam has faced challenging construction problems. Here, we provide a scientifically-based reference for applying geomechanical model testing to support the nonlinear design of super-high arch dams. We applied experimental similarity theory and techniques. Based on four 3D geomechanical model tests, the dam stress characteristics, deformation distribution, and the safety factors of the dam foundation were identified and compared. We also analyzed cracking characteristics of the up- and downstream dam surfaces and induced joints in the dam heel, the rock mass failure process of the dam-foundation interface, and the abutments. We propose foundation reinforcement measures for weak rock masses, alteration zones, and other faults in the abutments based on the 3D and plane tests each at a different elevation. The results show that all dam deformations remained normal with no yielding or tensile cracking under a normal water load. The reinforced rock mass increased the crack initial safety in the dam heel and toe by ~20 %. The minimum crack initial safety factor (K 1) of the dam heel was 1.4. The induced joint in the dam heel contributed to a reduction in tensile stress at the upstream dam heel, improving K 1. Compared with similar projects following reinforcement measures, the abutment stiffness and overall stability of the Xiaowan arch dam satisfy operational requirements. Four years of monitoring operations show that key areas near the dam remained normal and the dam foundation is functioning well. Our results may also be applicable to the design and construction of similar projects worldwide.

Discussion of Method for Computing Temperature Load during Operation Period on High Arch Dam

According to the existing arch dam design specification, the temperature load is obtained based on analytic solution of infinite long free plate, it only considers the average temperature and the equivalent linear temperature difference of dam section in operation period, the influence of non-linear temperature difference has not been considered. This kind of simplification has some approximation; especially it can not reflect spatial effect of larger temperature gradient changes in the upstream and downstream water level change area. This paper first takes the free plate as an example, has calculated the temperature field corresponding to analytical method, finite element method, standard method, explains the rationality of using written program to carry on finite element analysis. On this basis, take Xiluodu arch dam as an example, the dam temperature load and temperature stress has been analyzed by using finite element method and standard method, the difference between both has been discussed

Shape optimization of arch dams under earthquake loading using meta-heuristic algorithms

This paper presents efficiency of three meta-heuristic algorithms for large-scale shape optimization of double curvature arch dams under seismic loading condition with different constraints such as failure, stability and geometrical limitations. The earthquake load is considered by time variant ground acceleration applied in the upstream-downstream direction of the arch dam. Here, the Westergaard method is used to include the dam-reservoir interaction. For optimization, the Charged System Search (CSS), Particle Swarm Optimization (PSO), and a hybrid CSS and PSO (CSS-PSO) are utilized. Numerical results demonstrate the effectiveness of the meta-heuristic algorithms for optimal shape design of arch dams. Comparative studies illustrates that the superiority CSS-PSO algorithm compared to the standard PSO and CSS. A parametric study is also conducted to investigate the effect of water depth and earthquake intensity on the cost optimization of the arch dams.

'Toys that save millions' – a history of using physical models in structural design

Small-scale physical models have been used to determine the most efficient form of pure compression and tensile structures since the 17th century – and to predict structural behaviour of some full-size structures since the mid-19th century. This paper traces the development of model testing in the design of building structures from its origins in the design of bridges and ship hulls in the 19th century, to the design of gravity and arch dams in the early 20th century, through the early days of designing concrete shell roofs in the 1920s and 1930s, to its most sophisticated use in the 1960s and (in conjunction with computer modelling) the 1970s. The great strength of model testing was, and is, to deal with new types of structures without design codes and even without precedent.

A Discussion on the Differences between Arch Dam Design Standards of the United States, China and Vietnam

In arch dam design, every country has it own technical design standard. In Vietnam, the standard is far lessconprehensive compared with those of the United States and China. This research focus on analysis of the differences between three above standard systems, in order to give some suggestions to improve the Vietnamese standard for arch dam. Differnces in stability and strength analysis under static and seismic conditions is discussed in depth. A case study of Namchien arch dam in Vietnam, which has being constructed in Vietnam, is presented. The results show that if arch dam design based on the Vietnamese standard, stability and strength analysis should be paid more attention on the discussed differences. The research aims atcontributing constructive suggestions concerning to existing Vietnamese standard and providing some technical specifications for designer in arch dam design.