High Concrete Gravity Dam Research Articles

Engineering geological investigations for the foundations of large structures-examples of a concrete dam and a long bridge in Portugal

The safety of large structures requires adequate foundations, which implies a good knowledge of the geological and geotechnical conditions of the respective ground. In general, that is only possible through engineering geological studies which include proper site investigation techniques, adapted to the nature of the ground (rock mass or soil) and to the associated engineering problems. The paper illustrates the studies carried out for the design of the foundations of Ribeiradio 76 m high concrete gravity dam in a difficult rock mass and of Vasco da Gama Bridge, 13 km long, crossing the Tagus River in Lisbon, Portugal, through piles 75 m deep.

Failure analysis of high-concrete gravity dam based on strength reserve factor method

Maintaining stability against the sliding of a high-concrete gravity dam built on a rock mass of complex geology is a key problem. In this paper an anisotropic laminar layer element with thickness is used to simulate mechanical deformation properties of weak-bed intercalations at a dam’s foundation as well as a contact friction interface element without thickness to simulate joints and fissures of the rock mass at the dam’s foundation. Nonlinear finite element method (FEM) analysis was used to calculate the resistance to sliding of a high-concrete gravity dam at the dam’s foundation. The strength reserve factor (SRF) method was adopted to simulate progressive failure and possible unstable modes of the dam’s foundation system, and the method for determining the ultimate bearing resistance of this system. The strength analysis method of the connection of the plastic yield zone was used to obtain the ultimate bearing resistance of the dam’s foundation while it was undergoing failure. Finally, nonlinear finite element analysis was performed to find a solution for the sliding of this dam, the high-concrete gravity dam of Xiangjiaba Hydropower Station on Jinshajiang River in Yunnan Province, China, while it was under construction. The calculation shows that the failure of the dam is related to the strength (or weakness) of the silt-laden layer at the dam’s foundation, and the strength reserve factor of final failure was 2.6.

A stepwise damping‐solvent extraction method for large‐scale dynamic soil–structure interaction analysis in time domain

AbstractTime‐domain analysis of dynamic soil–structure interaction based on the substructure method plays an increasing role in practical applications as compared with the frequency‐domain analysis. Efficient and accurate modelling of the unbounded soil or rock medium has been a key issue in such an analysis. This paper presents a subregional stepwise damping‐solvent extraction formulation for solving large‐scale dynamic soil–structure problems in the time domain. Accuracy and efficiency of the formulation are evaluated in detail for a classical problem involving a rigid strip foundation embedded in a half‐space. A practical large‐scale soil–structure interaction problem, which represents a high concrete gravity dam subjected to seismic load, is then analysed using the proposed method. Various responses of the dam, including time histories of the crest displacement and acceleration and contours of the peak principal stresses within the dam body, are presented. Comparisons are also made between these results with those obtained using other models for the unbounded medium. Copyright © 2007 John Wiley & Sons, Ltd.

Dynamic response of a concrete dam impounding an ice-covered reservoir: Part I. Mathematical modelling

This paper examines the dynamic response of a concrete dam impounding an ice-covered reservoir and subjected to forced-vibration testing. The analytical research presented is a follow-up to an extensive dynamic testing program carried out on a 84-m high concrete gravity dam located in northeastern Quebec, Canada, under harsh winter conditions, including a 1.0- to 1.5-m-thick ice sheet covering the reservoir. One of the major challenges encountered when analyzing ice-dam-reservoir-foundation interaction is modelling the complex nature of the ice and the boundary conditions governing reservoir motion. The problem is further complicated because there are little or no appropriate experimental data and observational evidence relevant to ice-dam interaction processes. Some of these challenges are addressed herein using a two-dimensional analytical approach, which investigates the effects due to ice cover, water compressibility, and reservoir bottom absorption. A frequency-domain substructure method technique is used and a new boundary condition along the ice-cover-reservoir interface is proposed. The technique developed is implemented in a finite element code specialized in the seismic analysis of concrete dams. Numerical results are discussed in the companion paper in this issue. Key words: gravity dams, concrete dams, ice, reservoirs, mathematical models, ice-structure interaction, fluid-structure interaction, forced-vibration testing, finite elements modelling.

Seismic Behavior of Post-Tensioned Gravity Dams: Shake Table Experiments and Numerical Simulations

Displacement controlled shear tests on small concrete lift joint specimens with different surface roughnesses reinforced with an unbonded post-tension cable are conducted to study a related joint constitutive model, and to determine the failure mechanisms associated to it. To investigate the applicability of the joint model, shake table tests are conducted on a 3.4-m high plain concrete post-tensioned gravity dam that has a cold lift joint about midheight. Numerical simulations using the joint constitutive model are compared with the experimental results. From the displacement controlled shear tests, it is shown that the post-tension cable provides additional strength to the joint by applying an additional normal load on the joint, and by the shear resistance that can be mobilized (cable dowel action). The tests performed on rough surface joints have demonstrated that the dilatancy phenomenon due to asperities increases the post-tension force. Shake table tests on the 3.4-m high dam model have shown that post-tensioning largely reduces residual sliding displacements of the joint. This reduction is a function of the frequency content of the base excitation. However, a single post-tension cable placed near the upstream face increases the upstream rocking response of the upper block, which is also a function of the frequency content of the excitation. Strong seismic excitations can induce cable failure at a lower value than its uniaxial tensile strength when significant shear displacements take place. To describe this brittle failure mechanism, a cable failure criterion that considers the mobilized shear and tensile strengths was proposed and was found to be adequate. Moreover, the post-tensioned joint model proposed showed good agreement with the static and dynamic tests performed to evaluate the joint shear force.

Effective ambient vibration testing for validating numerical models of concrete dams

Ambient vibration tests were conducted on a 56 metre high concrete gravity dam to measure its modal properties for validating a finite element model of the dam–reservoir–foundation system. Excitation was provided by wind, by reservoir water cascading down the spillweir, and by the force of water released through outlet-pipes. Vibrations of the dam were measured using accelerometers, and 3-hour data records were acquired from each location. Data were processed by testing for stationarity and rejecting non-stationary portions before Fourier analysis. Power spectra with low variance were generated from which natural frequencies of the dam were identified clearly and modal damping factors estimated. Modal analysis of the frequency response spectra yielded mode shapes for the six lowest lateral modes of vibration of the dam. The finite element model for the dam was analysed using EACD-3D, and the computed mode shapes and natural frequencies compared well with the measured results. The study demonstrates that ambient vibration testing can offer a viable alternative to forced vibration testing when only the modal properties of a dam are required. Copyright © 1999 John Wiley & Sons, Ltd.

An engineering geological appraisal of the Lakhwar Dam, Garhwal Himalaya, India

A 204 m high solid concrete gravity dam is proposed across the River Yamuna in Garhwal Himalaya, India. It will be located on dolerite rocks which have been intruded into the slates of Chandpur Formation. The present study includes the evaluation of the dam foundation by means of drifts, drill holes, water pressure tests and abutment slope stability studies. The water pressure test indicate the necessity of providing a grout curtain below the dam foundation. The analysis of the dam abutments for stability using the Limit equilibrium method indicates that the right abutment slope is kinematically unstable for plane failure mode. The plane failure analysis of the right abutment slope was carried out by modifying the Hoek and Bray (1981, Rock Slope Engineering, 3rd ed., Institute of Mining and Metallurgy, London) technique of plane failure analysis. The analysis reveals that right abutment slope may become unstable during the stripping operation. Based upon the analysis a safe cut slope design for the abutments have been suggested. Subsurface exploration by means of cross drift and drill holes has indicated a sheared contact of slate and dolerite in the foundation area. To avoid the settlement of the dam along this shear zone precautionary measures are suggested.

An experimental investigation into earthquake‐induced failure of medium to low height concrete gravity dams

AbstractA suitable model material was developed to construct scaled models of a 30 m high prototype concrete gravity dam monolith and the experimental technique perfected for testing the models, till failure, on the EPSRC earthquake simulator at Bristol University. A series of shaking table tests was performed with the aim of assessing the possible failure mechanisms of medium to low height dams under simple motions and simulated earthquakes. Tests were conducted with and without the presence of hydrostatic pressure. The hydrodynamic pressure was simulated using Westergaard's added mass approach. Base cracking was observed to be the main failure mechanism and a tendency of the models to slide and rock after the full crack development at the interface was also observed in some cases.

Seismic fracture analysis of concrete gravity dams

Nonlinear seismic analyses of a 90 m high concrete gravity dam, assumed to be located in eastern Canada, have been conducted using a smeared crack finite element model. Reduced frequency-independent added matrices have been used to represent the hydrodynamic and foundation interaction effects. Parametric analyses have been performed to assess the effects of the initial conditions induced by severe winter temperature, and the effects of hydrodynamic and foundation interaction mechanisms, on the nonlinear seismic behaviour of the dam. Key words: gravity dams, nonlinear seismic response, finite element, crack propagation.

Hydrodynamic pressure in a dam-reservoir system

A comparison of three approaches to the solution of the dam-reservoir interaction problem is presented. A 400-ft high concrete gravity dam, its reservoir and the rigid foundation are subjected to seismic ground motion. The computer programs ADINA-5 and EAGD-84 produced analyses which compared closely. Westergaard's added mass theory in general produced conservative results for both horizontal ground motion and the combined horizontal and vertical ground motion. Westergaard's theory produced results which were not comparable for the vertical only ground motion.

A brief introduction to the Revelstoke Project

When the Revelstoke Project reservoir was filled to elevation 560 m in March of 1984, 13 m below its normal operating level, a vertical transverse crack opened in the face of the concrete dam allowing as much as 15 000 L/min (0.25 m3/s) of water to leak into the drainage gallery. Within 2 weeks remedial measures had closed the crack and stopped the leakage. Two months later the powerplant came into service and all other features of the project performed as expected. This project, with its 2700 MW powerplant and 175 m high concrete gravity dam, is one of the largest in North America. It was planned, designed, and its construction administered by BC Hydro. This paper briefly describes the project features, planning decisions, design, and construction of the $2 billion project. Key words: hydroelectric, dam, powerplant, spillway, planning, design, construction.

Measurements of Self-Aerated Flow on a Spillway

Measurements are made on the spillway on a 36-m high concrete gravity dam. The measurements include the point of inception, and the velocity distribution and air concentration distribution and bubble size in the developing region of the flow. The measurements show that there appears to be a universal velocity distribution which is independent of the mean air concentration for average air concentrations of between 0 and 0.5, and the air concentration becomes progressively more uniform with the distance downstream. However at 200 times the depth at the point on inception downstream of this point it is still growing. At 100 times the depth at the point of inception a significant air concentration has reached the spillway floor. A simplified formulae for computing the position and properties at the point of inception is also presented.

Stability and stress analyses of headrace tunnel, Upper Seti Storage Hydroelectric Project, Western Nepal

The Upper Seti (Damauli) Storage Hydroelectric Project has a capacity of 128 MW, the storage type scheme, and includes 1000 m long horse shoe headrace tunnel, 140 m high concrete gravity dam, two diversion tunnels of lengths 712 m and 881 m and an underground powerhouse. The study was carried out to identify stability and stress conditions for the headrace tunnel to suggest the required tunnel support. The project area extensively covers dolomite and minorly covers slate. The rock mass classification showed fair to good quality of dolomite and poor to fair quality of slate. The surface wedges would form in intake portal and powerhouse site. In the headrace tunnel, structural wedges would be formed due to underground excavation and would be stabilized with the help of shotcrete and rock bolting. doi: 10.3126/bdg.v10i0.1419 Bulletin of the Department of Geology, Tribhuvan University, Kathmandu, Nepal, Vol. 10, 2007, pp. 45-54