Coupling model for assessing anti-seepage behavior of curtain under dam foundation

The seepage under a dam foundation is mainly controlled by the performance of the curtain.Its anti-seepage behavior may be weakened by the long term physic-chemical actions from groundwater.According to seepage hydraulics and geochemistry theory,a coupling model for assessing the behavior of the curtain under a dam foundation is set up,which consists of seepage module,solute transport module,geochemistry module and curtain erosion module,solved by FEM.A case study was carried out.The result shows that the curtain efficiency is weakened all the time.Aqueous calcium from the curtain is always in dissolution during the stress period for simulation,which leads to the increasing amount in groundwater reaching 846.35-865.312 g/m3.Within the domain,reaction extent differs in different parts of the curtain.The dissolution of Ca(OH)2 accounts to 877.884 g/m3 near the bottom and is much higher than that of the other parts.The erosion is much more serious near the bottom of the curtain than the other parts,which is the same to the upstream and downstream.Calcium dissolution is mainly controlled by hydraulic condition and dispersion,and it varies in a non-linear way within the domain.

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 III1and III2as 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 fi nite 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.

Application of strength reduction method to dynamic anti-sliding stability analysis of high gravity dam with complex dam foundation

Considering that there are some limitations in analyzing the anti-sliding seismic stability of dam-foundation systems with the traditional pseudo-static method and response spectrum method, the dynamic strength reduction method was used to study the deep anti-sliding stability of a high gravity dam with a complex dam foundation in response to strong earthquake-induced ground action. Based on static anti-sliding stability analysis of the dam foundation undertaken by decreasing the shear strength parameters of the rock mass in equal proportion, the seismic time history analysis was carried out. The proposed instability criterion for the dynamic strength reduction method was that the peak values of dynamic displacements and plastic strain energy change suddenly with the increase of the strength reduction factor. The elasto-plastic behavior of the dam foundation was idealized using the Drucker-Prager yield criterion based on the associated flow rule assumption. The result of elasto-plastic time history analysis of an overflow dam monolith based on the dynamic strength reduction method was compared with that of the dynamic linear elastic analysis, and the reliability of elasto-plastic time history analysis was confirmed. The results also show that the safety factors of the dam-foundation system in the static and dynamic cases are 3.25 and 3.0, respectively, and that the F2 fault has a significant influence on the anti-sliding stability of the high gravity dam. It is also concluded that the proposed instability criterion for the dynamic strength reduction method is feasible.

Feasibility of columnar jointed basalt used for high-arch dam foundation

Columnar jointed basalt, with a lot of small-spacing structural planes and poor integrity, is a kind of fractured rock mass. Through comprehensive study of columnar joints shape, roughness of fracture surface and chemical composition of basalt, it is known that columnar joints of Baihetan dam area were formed as a result of cooling and shrinkage effects of magma. The columnar jointed basalt is mainly formed through chemical reaction of chlorite, kaolinite, epidote and tremolite, and the columnar joints mainly consist of chlorite according to slice identification and chemical analysis. Test results show that the columnar jointed basalt has high uniaxial compressive strength, low friction coefficient, and high cohesion, shear strength and deformation index. Meanwhile, the columnar jointed basalt is closely locked, and joint surfaces are well closed. The permeability of the rock is quite weak, and the P-wave velocity in the rock could get up to 5 000 m/s. All these show good rock properties. The columnar joints develop regularly, different from the general fractured rock masses. In summary, the columnar jointed basalt can be used directly as a foundation of dam.

Dam foundation excavation techniques in China:A review

A protective layer(PL) is commonly reserved above foundation surface to protect the underlying rock mass during dam foundation excavation. In China, the PL of dam foundation is conventionally subdivided into two or three thin layers and excavated with the shallow-hole blasting method, even by pneumatic pick method in case of soft rock mass. The aforementioned layered excavation of the PL delays the construction of the whole project. After nearly 30-year practices, several safe and effcient methods for the PL excavation of dam foundation are gradually developed. They include shallow-hole bench blasting with cushion material(SBC) at the bottom of the hole, and horizontal smooth blasting(HSB). The PL is even cancelled on the condition that horizontal pre-split technique is employed during dam foundation excavation. This paper introduces the aforementioned two PL excavation methods(shallow-hole blasting and bench blasting) and horizontal pre-split technique of dam foundation without protective layer(HPP). The basic principles of blasting method, blasting geometry, charge structure, drill-and-blast parameters of typical projects are examined. Meanwhile, the merits and limitations of each method are compared. Engineering practices in China show that HSB is basically the optimal method for dam foundation PL excavation in terms of foundation damage control and rapid construction. Some new problems for dam foundation PL excavation arising, such as strong unloading and relaxation phenomenon that encountered in the gorge region of southwest China, are needed to be addressed; and the corresponding countermeasures are discussed as well.

3-D fracture network dynamic simulation based on error analysis in rock mass of dam foundation

Accurate 3-D fracture network model for rock mass in dam foundation is of vital importance for stability,grouting and seepage analysis of dam foundation.With the aim of reducing deviation between fracture network model and measured data,a 3-D fracture network dynamic modeling method based on error analysis was proposed.Firstly,errors of four fracture volume density estimation methods(proposed by ODA,KULATILAKE,MAULDON,and SONG)and that of four fracture size estimation methods(proposed by EINSTEIN,SONG and TONON)were respectively compared,and the optimal methods were determined.Additionally,error index representing the deviation between fracture network model and measured data was established with integrated use of fractal dimension and relative absolute error(RAE).On this basis,the downhill simplex method was used to build the dynamic modeling method,which takes the minimum of error index as objective function and dynamically adjusts the fracture density and size parameters to correct the error index.Finally,the 3-D fracture network model could be obtained which meets the requirements.The proposed method was applied for 3-D fractures simulation in Miao Wei hydropower project in China for feasibility verification and the error index reduced from 2.618 to 0.337.

The Effect of Alluvial Foundation on the Earth Dams Settlement

Careful monitoring in the earth dams, to measure deformation caused by settlement and movement has always been a concern for engineers in the field. In order to measure settlement and deformation of earth dams, usually the precision instruments of settlement set and combined Inclinometer that is commonly referred to IS instrument, will be used. In some dams, because the thickness of alluvium is high and there is no possibility of alluvium removal (technically and economically and in terms of performance), there is no possibility to place the end of IS instrument (precision instruments of Inclinometer-settlement set) in the rock foundation. Inevitably, have to accept installing pipes in the weak and the deformable alluvial foundation that this leads to errors in the calculation of the actual settlement (absolute settlement) in different parts of the dam body. The purpose of this paper is to present new and refine criteria for predicting settlement and deformation in earth dams. The study is based on conditions in three dams with a deformation quite alluvial (Agh Chai, Narmashir and Gilan-e Gharb) to provide settlement criteria affected by alluvial foundation. To achieve this goal, the settlement of dams was simulated by using finite difference method with FLAC3D software and then the modeling results were compared with reading IS instrument. In the end, the caliber of the model and validate the results, by using regression analysis techniques and scrutinized modeling parameters with real situations and then by using MATLAB software and Curve Fitting Toolbox, a new criteria for the settlement based on elasticity modulus, cohesion, friction angle, density of earth dam and alluvial foundation was obtained. The results of these studies show that, by using the new criteria measures, the amount of settlement and deformation for the dams with alluvial foundation can be corrected after instrument readings and the error rate in reading IS instrument can be greatly reduced.

Control of Seepage through Earth Dams Based on Pervious Foundation Using Toe Drainage Systems

Many dangerous effects arise from seepage through earth dams based on pervious layer. Therefore, the dam embankment must be provided with seepage control measures to avoid such effects. In the present work, different control methods were used such as flat slopes, toe drainage systems, and a catch drain in the tail water. The hydraulic performance of each control measure was evaluated using the analytical solutions, previously developed, to estimate the seepage quantity (q), the height of seepage surface (h3), and the coordinates of the free surface (hx). Study was conducted on a physical model for a dam embankment having a top width (b) = 10.0 meter, height (Hd) = 30.0 meter, and slope factor (m) = 1.5. The obtained results were analyzed and presented in dimensionless charts. Results showed that, the used control measures possess a great effect on the characteristics of seepage through earth dams based on pervious foundations. A comparative study was conducted between the studied toe drainage systems to enable the designers the better choice for design purposes.

Seismic response analysis of arch dam-water-rock foundation systems

The effect of water compressibility on the seismic responses of arch dams is not well understood.In this paper,a numerical model is developed with rigorous representation of the dynamic interaction between arch dam-water- rock foundation.The model is applied to the seismic response analysis of an arch dam with a height of 292m designed to a seismic intensity of IX.It is shown that consideration of the water compressibility clearly decreases the stress responses at key positions of the dam,while the added mass model gives a conservative estimate.

Seismic analysis of dam-foundation-reservoir system including the effects of foundation mass and radiation damping

One of the main concerns in using commercial software for finite element analyses of dam-foundation-reservoir systems is that the simplifying assumptions of the massless foundation are unreliable. In this study, an appropriate direct finite element method is introduced for simulating the mass, radiation damping and wave propagation effect in foundations of damfoundation-reservoir systems using commercial software ABAQUS. The free-field boundary condition is used for modeling the semi-infinite foundation and radiation damping, which is not a built-in boundary condition in most of the available commercial software for finite element analysis of structures such as ANSYS or ABAQUS and thus needs to be implemented differently. The different mechanism for modeling of the foundation, earthquake input and far-field boundary condition is described. Implementation of the free-field boundary condition in finite element software is verified by comparing it with analytical results. To investigation the feasibility of the proposed method in dam-foundation-reservoir system analysis, a series of analyses is accomplished in a variety of cases and the obtained results are compared with the substructure method by using the EAGD-84 program. Finally, the massed and massless foundation results are compared and it is concluded that the massless foundation approach leads to the overestimation of the displacements and stresses within the dam body.

Tensile reliability analysis for gravity dam foundation surface based on FEM and response surface method

In this study, the limit state equation for tensile reliability analysis of the foundation surface of a gravity dam was established. The possible crack length was set as the action effect and allowable crack length was set as the resistance in the limit state. The nonlinear FEM was used to obtain the crack length of the foundation surface of the gravity dam, and the linear response surface method based on the orthogonal test design method was used to calculate the reliability, providing a reasonable and simple method for calculating the reliability of the serviceability limit state. The Longtan RCC gravity dam was chosen as an example. An orthogonal test, including eleven factors and two levels, was conducted, and the tensile reliability was calculated. The analysis shows that this method is reasonable.

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.

Real-Time Grouting Monitoring and Visualization Analysis System for Dam Foundation Curtain Grouting

A real-time monitoring and 3D visualization analysis system is proposed for dam foundation curtain grouting. Based on the real-time control technology, the optimization method and the set theory, a mathematical model of the system is established. The real-time collection and transmission technology of the grouting data provides a data foundation for the system. The real-time grouting monitoring and dynamic alarming method helps the system control the grouting quality during the grouting process, thus, the abnormalities of grouting, such as jacking and hydraulic uplift, can be effectively controlled. In addition, the 3D grouting visualization analysis technology is proposed to establish the grouting information model(GIM). The GIM provides a platform to visualize and analyze the grouting process and results. The system has been applied to a hydraulic project of China as a case study, and the application results indicate that the real-time grouting monitoring and 3D visualization analysis for the grouting process can help engineers control the grouting quality more efficiently.

The analysis for stress-strain characteristics of concrete cutoff wall built in deep cladding foundation

Combined with a proposed homogeneous earth dam in deep cladding foundation, Duncan E-B model is applied to simulate dam-filled material, apply to three-dimensional nonlinear finite element method, attain the stress-strain distribution and alteration in concrete cutoff wall in completion and water storage periods, analysis the stress state in the contact element between concrete cutoff wall and cladding foundation, provide the corresponding measures. The calculation results show that the design of concrete cutoff wall and homogeneous earth dam is reasonable.

Analysis of seismic disaster failure mechanism and dam-break simulation of high arch dam

Based on a Chinese national high arch dam located in a meizoseismal region, a nonlinear numerical analysis model of the damage and failure process of a dam-foundation system is established by employing a 3-D deformable distinct element code(3DEC) and its re-development functions. The proposed analysis model considers the dam-foundation-reservoir coupling effect, infl uence of nonlinear contact in the opening and closing of the dam seam surface and abutment rock joints during strong earthquakes, and radiation damping of far fi eld energy dissipation according to the actual workability state of an arch dam. A safety assessment method and safety evaluation criteria is developed to better understand the arch dam system disaster process from local damage to ultimate failure. The dynamic characteristics, disaster mechanism, limit bearing capacity and the entire failure process of a high arch dam under a strong earthquake are then analyzed. Further, the seismic safety of the arch dam is evaluated according to the proposed evaluation criteria and safety assessment method. As a result, some useful conclusions are obtained for some aspects of the disaster mechanism and failure process of an arch dam. The analysis method and conclusions may be useful in engineering practice.

Influence of seismic input on response of Baihetan arch dam

The dynamic responses of the arch dam including dam-foundation-storage capacity of water system,using two different earthquake input models,i.e.viscous-spring artificial boundary(AB)condition and massless foundation(MF),were studied and analyzed for the 269 m high Baihetan arch dam under construction in China.By using different input models,the stress and opening of contraction joints(OCJs)of arch dam under strong shock were taken into consideration.The results show that the earthquake input models have slight influence on the responses including earthquake stresses and openings of contraction joints in different extents.

Mosul Dam: Geology and Safety Concerns

Mosul Dam is an earth fill dam located on the River Tigris northern part of Iraq. The capacity of its reservoir is 11.11 billion cubic meters which makes it the fourth biggest dam in the Middle East. From geological perspective, the dam is located on double plunging anticlines. The rocks of the site are mainly composed of highly jointed and karistified alternating beds of limestones, gysum and marls, since the impoundment of the reservoir seepage of water was recognized under the foundation of the dam. To stop or minimize the seepage, intensive grouting operations were conducted. Recent investigations and evaluation of the conditions of the dam indicate that it is in a critical situation. In this paper, consequences of the dam failure are discussed and possible solutions are given.

Earthquake safety assessment of concrete arch and gravity dams

Based on research studies currently being carried out at Dalian University of Technology, some important aspects for the earthquake safety assessmcnt of concrete dams are reviewed and discussed. First, the rate-dependent behavior of concrcte subjected to earthquake loading is examined, emphasizing the properties of concrete under cyclic and biaxial loading conditions. Second, a modified four-parameter Hsieh-Ting-Chen viscoplastic consistency model is developed to simulate the rate-dependent behavior of concrete. The earthquake response of a 278m high arch dam is analyzed, and the results show that the strain-rate effects become noticeable in the inelastic range, Third, a more accurate non-smooth Newton algorithm for the solution of three-dimensional frictional contact problems is developed to study the joint opening effects of arch dams during strong earthquakes. Such effects on two nearly 300m high arch dams have been studied. It was found that the canyon shape has great influence on the magnitude and distribution of the joint opening along the dam axis. Fourth, the scaled boundary finite element method presented by Song and Wolf is employed to study the dam-reservoir-foundation interaction effects of concrete dams. Particular emphases were placed on the variation of foundation stiffness and the anisotropic behavior of the foundation material on the dynamic response of concrete dams. Finally, nonlinear modeling of concrete to study the damage evolution of concrete dams during strong earthquakes is discussed. An elastic-damage mechanics approach for damage prediction of concrete gravity dams is described as an example. These findings are helpful in understanding the dynamic behavior of concrete dams and promoting the improvement of seismic safety assessment methods.

Seismic safety of high concrete dams

China is a country of high seismicity with many hydropower resources. Recently,a series of high arch dams have either been completed or are being constructed in seismic regions,of which most are concrete dams. The evaluation of seismic safety often becomes a critical problem in dam design. In this paper,a brief introduction to major progress in the research on seismic aspects of large concrete dams,conducted mainly at the Institute of Water Resources and Hydropower Research(IWHR) during the past 60 years,is presented. The dam site-specific ground motion input,improved response analysis,dynamic model test verification,field experiment investigations,dynamic behavior of dam concrete,and seismic monitoring and observation are described. Methods to prevent collapse of high concrete dams under maximum credible earthquakes are discussed.

Badush Dam: A Unique Case of Flood Wave Retention Dams Uncertain Future and Problematic Geology

Badush Dam is a partially completed dam and a unique case of flood retention dams. Its intended main function is to perform flood protection once in its lifetime;that is if Mosul Dam would collapse. In such a case, the Badush dam would temporarily store the whole flood wave and route it safely to the downstream. For this end, the bulk of the reservoir is left dry, while the remaining volume at the lower part which is intended for power generation does not give an economic justification for building the full height of the dam. The short duration of the intended use as a protection dam has led to relaxing many design assumptions which have raised concerns over the dam integrity. The current controversy rages now over whether to continue the construction of the dam as it was first designed or to change all that in view of the similar site geology of Mosul Dam. Mosul dam foundations suffer at the moment from the severe continuous dissolution of the soluble materials in its foundation leading to continued maintenance grouting of that foundation. This paper gives an overview of the history of Badush dam, its current design and what new requirements which are needed if it is to replace Mosul Dam itself.