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The bearing capacity of large rectangular foundations on soil subjected to combined loading [simultaneously subjected to vertical load (V), overturning moment (M), and horizontal or lateral load (H)] is one of the central topics of interest to geotechnical engineers as it relates to the design of foundations such as ground anchorages of bridges, offshore structures, and gravity dams. To solve this problem, a combination of numerical simulation and theoretical research was used, and a stability evaluation model of large rectangular foundations on soil subjected to combined loading was established. First, an empirical equation for the failure envelope in the V‒M‒H loading space of rectangular foundations was developed. Second, the safety factor for load-path dependency (LPD) was established by considering the combined effects of V, M, and H, the stability evaluation model for large rectangular foundations on soil subjected to combined loading was constructed by proposing a method for calculating the LPD safety factor based on the V‒M‒H failure envelope. Last, the accuracy and effectiveness of the stability evaluation model proposed was verified. The proposed model provides a convenient means of calculating the stability of large rectangular foundations on soil under combined loading. The model was applied to the optimal design of a gravity anchorage project of a suspension bridge, which proves that the proposed model is rational and efficient. [ABSTRACT FROM AUTHOR]

This study aims to propose a seismic performance analysis framework based on the oblique incidence theory, estimate a normalized damage response (RDVR) through seismic parameters and incident angles, and explore the variation in dynamic responses of concrete dams with arbitrary incident angles under near-fault vertically polarized shear (SV) waves. Several near-fault pulse-like records were selected, and their decomposed nonpulse (residual) components were used to guarantee the similarity of the response spectra. Furthermore, a seismic input model of the SV wave oblique incidence was developed based on the viscous-spring artificial boundary method, and its accuracy was verified using a numerical application. The effects of the incident angles of SV waves (−30° to 30° at 5° intervals), seismic intensity, and polarity on the damage and displacement responses of a gravity dam–reservoir–foundation system under pulse-like and nonpulse motions were studied. Additionally, the relationships between the incident angle, seismic characteristics [including the peak ground velocity to peak ground acceleration (PGV/PGA) ratio and spectral acceleration Sa(T1)], and the proposed RDVR were established. The most unfavorable incidence angles for different cases were derived. The numerical results showed that the negative direction (from downstream to upstream) has a significant effect on the nonlinear responses of a dam. The seismic features of PGV/PGA exhibited a better correlation with RDVR than Sa(T1). Subsequently, the damage to the gravity dam was estimated using the multivariate fitted method according to the proposed prediction model. The results showed that the proposed prediction model with arbitrary incident angles provides a good estimation of the real results. Thus, it is important to consider the coupled effect of incident angles and seismological characteristics in the seismic assessment of concrete dams located in near-fault regions. [ABSTRACT FROM AUTHOR]

This paper proposes a progressive approach to assess the properties of large-scale roughness at dam–rock interfaces and the implementation of their effects into practical dam stability analyses. The analysis steps, ranked per increasing degree of complexity, consist of studying a gravity dam monolith using, first, the gravity method (GM), second, the finite element (FE) method (FEM) with a simplified horizontal planar dam–rock interface, and, third, the FEM with a detailed irregular geometry of the dam–rock interface. In the first two steps, the simplification of the rock foundation geometry is paired with the implementation of apparent cohesion and friction angle into the models. These apparent parameters are evaluated based on nonlinear shear strength criteria combined with an interface roughness coefficient (IRC) introduced to characterize the roughness of a dam–rock joint extending along the whole dam footprint. This coefficient is approximated herein numerically based on FE models. The inputs and steps of the progressive approach are illustrated through several examples of typical dam–rock systems and rock profiles based on bathymetric and LiDAR surveys. The results mainly show that the effects of rock foundation roughness on dam sliding stability can be efficiently represented with apparent cohesion and friction angles. The effectiveness of the simplified models coupled with the conservatism of the results they provide are likely to favor their adoption by practicing engineers. [ABSTRACT FROM AUTHOR]

The mathematical formulation of the problem describing the interaction between a dam and the reservoir during earthquakes is complex, and the solution requires the implementation of sophisticated numerical tools. The discussers claim that the transient FE analysis of a dam-reservoir system may not lead to a unique solution depending on the time integration method and the user-defined solution parameters. Impact of Dam Shape In the original paper, the authors only used a single dam shape (including five different heights) with the downstream slope of approximately 0.75 and the chimney width equal to 10% of the dam height. In the original paper, the authors incorporated three additional factors into the approximate Westergaard formulation through a set of multipliers: (1) the dam height, (2) the concrete elasticity, and (3) the reservoir bottom wave absorption. [Extracted from the article]

The error of the formula caused by those assumptions may have little effect on low gravity dams but can cause significant deviations for high dams from the nature of dam-reservoir interaction during earthquakes. It is well known that dam-reservoir interaction under earthquake forces is very complicated due to various influencing factors. Although the proposed Westergaard correction formula cannot give the exact solution of the hydrodynamic pressure on a gravity dam, the main affecting factors (e.g., dam body's elasticity, dam height) have been considered. Conclusions There are many complicated affecting factors to be considered in the analysis of gravity dam-reservoir water interaction problems. [Extracted from the article]

The bearing capacity of large strip foundations under combined loading is an important issue in geotechnical engineering, which is related to the design and stability analysis of foundations such as gravity dams, retaining walls, and ground anchorages of bridges. Herein, a new model for predicting the bearing capacity of large strip foundations under combined loading was proposed. First, a series of numerical simulation analyses of a large strip foundation resting on the surface of the soil were conducted to investigate the shape of the failure envelope in the V–M–H (vertical load, overturning moment, and horizontal load) loading space, and an improved form of failure equation was proposed. Second, the main factors influencing Vmax (the vertical ultimate bearing capacity) and the shape of the failure envelope were determined. Last, an applicable empirical equation of the failure envelope in the V–M–H loading space was presented. The results show that the deflection angle of the ellipse (θ), which is considered as a certain constant by previous studies, varies with the vertical load (V); the width of the foundation (B), the depth of the foundation (D), the cohesion of the soil (c), and the internal friction angle of the soil (φ) are the main factors influencing Vmax and the shape of the failure envelope; only parameters B, D, c, φ, and γ are needed to determine, in a unique way, the empirical equation of the failure envelope in the V–M–H loading space. The proposed model provides a convenient means of calculating the bearing capacity of large strip foundations on soil under combined loading. [ABSTRACT FROM AUTHOR]

Durations are defined as an essential component of the three primary characteristics of strong earthquakes, which exhibit a remarkable influence on the damage characteristics of a concrete dam body. However, when considering the distinctive definitions of a strong motion duration, the influence of several durations on the seismic analysis of gravity dams remains unclear. In addition, there is no specific conclusion on the optimal choice for the duration of a strong ground motion. The endurance time analysis (ETA) method, which is a high-efficiency seismic performance method, is widely used, because of the high precision and low computation effort when calculating the dynamic responses of structures. However, when using this method it is almost impossible to account for any one type of duration contribution. Therefore, a modified ETA algorithm to correct duration effects will be proposed in this paper based on the three existing types of durations, such as bracketed (Tb), uniform (Tu), and significant (Ts) durations. The dynamic response will be further corrected using a modified ETA method in the numerical application to the Koyna concrete gravity dam, which is one of the largest dams in Maharashtra state, India. A group of 20 endurance time acceleration functions (ETAFs) and 10 sets of two-dimensional (2D) artificial waves with three total durations will be synthesized through the same site design acceleration spectrum. Three types of indices that include the dissipation energy, damage, and deformation indices will be used to measure the seismic performance. The nonlinear analysis results will be compared with those from the ETA and quantitative analysis methods, which show that the modified ETA method could provide an effective estimation to monitor earthquake resistance and structural seismic performance with a certain safety margin. The influence of the duration of a strong ground motion could be considered in the modified ETA method, which could be further applied in practical engineering. [ABSTRACT FROM AUTHOR]

Seismic performance of gravity dams has been widely concerned due to their importance in hydraulic engineering. In recent years, the influence of the incident angle of seismic waves and the inhomogeneity of complex foundation on the soil–structure interaction (SSI) system has become a focus. However, the foundation is often simplified to homogeneous elastomer when simulating nonuniform excitation seismic wave propagation due to the complex theoretical formulations. Therefore, this paper considers the stratification of foundation and analyzes the dynamic response of a gravity dam under obliquely incident seismic waves. First, the gravity dam–layered foundation interaction system is established in the finite-element software, and the concrete damage plasticity (CDP) model is adopted of the dam. Then, the displacements of the foundation under seismic P or SV waves with arbitrary incident angles are calculated by combining the one-dimensional time-domain method and the free wave field calculation method. Finally, adopting the wave input method based on the substructure of artificial boundaries, the seismic waves are converted to equivalent nodal forces on the viscous-spring boundaries of the layered foundation. Furthermore, the dynamic response of the dam on the homogeneous foundation is also simulated for comparison in this paper. The calculation results confirm that the impact of arbitrary incident angle of earthquakes and the parameters of foundation on the dam response is significant, and both should be considered comprehensively. [ABSTRACT FROM AUTHOR]

A newly built roller-compacted concrete gravity dam is located on the Yalongjiang River in southwest China. Complex geological conditions greatly puzzled the designers of the project. There are abundant joints within the riverbed that form the double- inclined wedge foundation. This is a typical mode of instability of concrete gravity dams. The equal-K method, which falls into the category of conventional limit-equilibrium methods, is provided in the design codes of gravity dams to evaluate the stability of a dam against sliding along deep failure surfaces. The factor of safety calculated by the equal-K method is determined by the angle of the force acting on the interface of the two inclined wedges, denoted by φ, which is unspecified in the design codes. On the basis of Sarma's assumption, this study proposes an algorithm for the determination of ∅, which needs only slight improvement of the algorithm in the existing codes. The justification of the proposed procedure is demonstrated by showing that the results from the proposed procedure are very close to those from a rigorous limit-equilibrium method in which all equilibrium conditions are satisfied. [ABSTRACT FROM AUTHOR]

The rock foundation of a gravity dam is usually cut into slide blocks by the structural surfaces. Its stability is controlled by the characteristics and the combining action of these structural surfaces. The failure of a gravity dam can be caused by the destruction or large deformation of local rocks under the condition of certain loads. The coupling of continuous-discontinuous deformation is a typical characteristic of the process. As a new design idea, the powerhouse and dam are combined into an integer with one structural pattern to improve the antisliding stability of the gravity dam. The external loads are undertaken together by the powerhouse and dam. The loads acting on the dam can be transferred partly to the powerhouse, and the powerhouse weight and tail water pressure can increase the dam's stability. The optimal design of a gravity dam section can be implemented, decreasing the project quantity, and reducing construction costs. This design idea has been adopted by the Yangtze Three Gorges Project in China. The coupling methods of discontinuous deformation analysis (DDA) and FEM are used to implement the deep antisliding stability evaluation for a gravity dam under the combining action of both the powerhouse and dam. The blocks are subdivided into the finite element meshes; the displacement field and stress field in the blocks are solved by FEM, and the contacts between the deformable blocks are simulated and analyzed with the DDA method. The description ability for the block deformation can be increased, the calculation precision for the stress field in block can be improved, and the ability of DDA in solving the large deformation of a multiblock system can be inherited. Therefore, the destructive form determined by this coupling method is closer to the actual situation. As an example, the coupling methods of DDA and FEM are used to analyze and assess the deep antisliding stability of the No. 3 left powerhouse-dam section of one dam when the upstream loads are taken together by the high gravity dam and the combined powerhouse located behind dam. The effect of combining the action of the powerhouse and dam is appraised by the numerical analysis for the mechanism transferring force between the dam and powerhouse, the influence on the deformation and stress of dam and powerhouse under the combining action of powerhouse and dam, the interaction of structural planes, etc. The entire instability process of the dam is simulated and analyzed by means of reducing the mechanical parameters. Last, the qualitative and quantitative analyses are implemented to evaluate the local and the whole stability of the gravity dam under the combining action of the powerhouse and dam. [ABSTRACT FROM AUTHOR]

Cataclastic rocks and fault gouge present highly variable properties, from those of soil-like materials to those of competent rock mass. In most cases, the entire rock mass, or internal major shear zones, can be represented as a block-in-matrix rock (bimrock), i.e., rock fragments of different shape and size, embedded in a finer matrix. In this paper, a tectonized metamorphic rock mass at the site of a planned gravity dam is investigated. The dam foundation is crossed by numerous major discontinuities, often grouped to form wider shear zones and characterized by high persistency, waviness, and abundant cataclastic filling. Systematic measurements of local orientation and filling thickness along the discontinuity traces made a detailed morphological analysis possible. The most frequent type of filling is a lightly cemented matrix-supported gouge. Undisturbed sampling of filling materials was successful only in some special cases. Laboratory tests, as well as in-situ mechanical tests, were therefore difficult and not exhaustive. Micromechanical distinct-element method (DEM) modeling was instrumental in obtaining a more comprehensive framework of deformation and failure mechanisms of cataclastic materials. The mechanical properties of the particulate model were first analyzed by numerical simulation of biaxial and direct shear tests. The relationship between the overall constitutive parameters and micromechanical properties, such as interparticle friction, contact stiffness, cement bond strength, volumetric block proportion, and block shape, was determined. The complex interplay between the geometric features of a major discontinuity (joint-wall roughness and waviness) and the properties of the infilling bimrock was then investigated, and finally, the overall strength of the infilled discontinuity was analyzed. [ABSTRACT FROM AUTHOR]