International Journal of Civil Engineering
Volume:17 Issue: 4, Apr 2019

In embankment dams, filters/drain systems constitute a first line of defense against the phase of continuation of erosion. It is generally assumed by several authors that the continuation of internal erosion can be prevented using adequate granular filters in areas where important hydraulic gradients may develop. This paper addresses the most important purpose and functions of filters. Once the internal erosion process initiates, for a given load condition, and there are no effective filters stopping eroded particles along the erosion path, the occurrence of progression of internal erosion should be assessed. In zoned dams, upstream zones may assist in controlling the phase of progression of erosion, before flows became excessively large for the downstream zone to discharge safely. The limitation of the progression of internal erosion in zoned dams, potentially caused by an upstream zone can be assessed using a new test cell. This device and correspondent test results are presented and analyzed. Two case studies of dams with internal erosion problems are described. The first is an embankment dam, Lapão dam, where due to design and construction problems an internal erosion process was developed. The other is Crestuma dam, a gated structure type. Since the dam started operating, the river bed in the vicinity of the dam has been subject to frequent monitoring that evidenced progressive erosion of the protective layer. This paper presents the results of the studies undertaken in relation to the hydraulic stability of the alluvial foundation of the dam’s stilling basins and of the downstream rockfill, and the main features of the implemented solutions.

Concrete dams are one of the most important infrastructures in every country and the seismic safety assessment of them is a major task in dam engineering field. Dam–foundation–reservoir system analysis is a complex interaction problem because this system consists of three domains with different behaviors. For accurate analysis of this system, some important factors should be considered such as foundation mass and earthquake input mechanism. In this paper, the effect of foundation mass and earthquake input mechanism on seismic response of concrete gravity dam is investigated. For this purpose, two different methods are introduced for modeling of massed semi-infinite foundation in finite element method, namely free-field boundary condition and domain reduction method (DRM). To verify the feasibility of proposed methods for seismic analysis of dam–foundation–reservoir system, the displacement and stress outputs using proposed methods are compared with EAGD-84 results. The obtained results indicate that both methods are accurate enough for finite element modeling of massed foundation. Finally, Koyna concrete gravity dam is analyzed for rigid, massless and massed foundation cases using DRM and it is concluded that the foundation has significant effect on dam response and the common massless foundation approach overestimates the dam response.

In this paper, the constitutive framework of hypoplasticity is used to model long-term deformations and stress relaxations of weathered and moisture sensitive rockfill materials. The state of weathering of the material is represented by a so-called solid hardness in the sense of a continuum description. The time-dependent degradation of the solid hardness is a result of progressive weathering caused for instance by hydro-chemical reactions of fluid with the solid material. The degradation of the solid hardness can lead to collapse settlements and creep deformations, which are also called wetting deformations. In contrast to a previous version, a new evolution equation for a more refined modelling of the degradation of the solid hardness is proposed. With respect to a pressure-dependent relative density, the influence of the pre-compaction of the material and also the influence of the pressure level on the stiffness can be modelled in a unified manner using a single set of constants. The performance of the new model is validated by comparison of the numerical simulations with experiments data.

The failure of a large dam can be catastrophic to human life and property downstream. Therefore, the seismic safety is of particular concern for high dams in seismically active regions. This paper addresses the nonlinear seismic response analysis of high arch dams due to spatially-varying ground motions. Firstly, a comprehensive analysis model developed at Tsinghua University is presented, which takes into account radiation damping effect of semi-unbounded canyon, dynamic interaction of dam-water, opening of contraction joints, seismic damage cracking and strengthening of dam concrete, and nonlinearity of foundation rock. Subsequently, the seismic damage of Pacoima dam during the 1994 Northridge earthquake is qualitatively analyzed by the developed analysis model. The results agree with the actual damage observed after the earthquake. Most of the contraction joints opened and closed during the earthquake, and a larger residual opening occurred at the thrust block joint after the earthquake. The cracks continue from the bottom of the thrust block joint in three directions: diagonal, horizontal, and vertical. Finally, a large-scale numerical simulation of seismic ground motion from source rupture to dam canyon is introduced, which can simulate the characteristics of near-field ground motions at dam sites by considering the effect of source mechanism, propagation media, and local site.

Rock-filled concrete dam is a new type of dams constructed by RFC technology. Dozens of RFC dam have been built in China. At first, a brief introduction to RFC dams is presented in this paper. Then, some researches of RFC are introduced. The research focuses on mechanical properties and thermal–physical properties of RFC. Some data in-situ are also presented. Research results demonstrated that the RFC has good properties to be employed to build dams.

A zoned earth dam 40 m high is analysed and modelled using a numerical code able to deal with unsaturated–saturated soils and the coupled hydro-mechanical phenomena. The paper discusses the selection of the materials for the design of the dam. The dam construction was modelled at the design stage (a type “A” calculation) and results are compared with actual measurements registered during construction until the time when the dam reached two-thirds of the total final height. The limitations of the type A model are discussed and an updated model is presented taking into account compaction data and field tests performed during construction.

For the seismic design and seismic safety checks of large storage dams, dynamic analyses have to be carried in the time domain, as inelastic deformations have to be expected under the safety evaluation earthquake ground motion. As input for such analyses acceleration time histories are needed. The characteristics of these time histories are discussed. They may include features such as spectrum matching of recorded or artificial acceleration time histories, aftershocks, directivity effects, near-fault effects, extended duration of strong ground shaking, number of earthquakes, and stochastic independence of earthquake components as listed in the new guideline on the Selection of Seismic Parameters of Large Dams of the International Commission on Large Dams. These acceleration time histories used for dam design are models of earthquake ground motions but have hardly anything in common with real earthquake acceleration time histories, but using such records, the dam engineer can provide a safe design, which is the main objective of the design of any structure.