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Simulation of Cracking in Large Arch Dam: Part I
Abstract
A complete fracture mechanics investigation of the cracking of the Kolnbrein arch dam is presented in two parts. In Part I, the history of cracking of this dam and theories attempting to explain it are described. The fundamental principles of mixed-mode, linear elastic fracture mechanics are then elucidated and used to study cracking observed near the toe of the dam. The stability, trajectory, and opening of two cracks are computed and favorably compared to observations. In Part II, cracking which occurred in the heel region of the dam is investigated next using computer simulation and fracture mechanics in an attempt to reproduce observed trajectory and load history before cracking. Four models for the cause of this cracking are described. All four models are shown to be viable mechanisms within the constraints of available cracking data. The necessity for combining simulation with accurate data of various types, and the insufficiency of two-dimensional analysis are discussed. The significant implication of this study is that classical fracture mechanics theory, implemented through modern computer simulation techniques, can be used to explain cracking events in concrete arch dams. This capability can prove valuable in designing against such events, and in specifying effective repair procedures.
... In the late 1970s and early 1980s, cracks were observed on the upstream side when the reservoir reached a level of 1860 m (approximately 40 m below the top level), which led to the increase of leakage from an unusual 35 L/s to an unacceptable 200 L/s. 12 Several repair works have been implemented with a buttress finally attached to the arch dam and the repairs totally cost up to $190 million. 13 Over the last decade, a series of national key hydropower projects including the Goupitan, Xiaowan and Xiluodu arch dams have been built in Southwest China and been the typical cases for study on cracking of high arch dams. ...
... Worst of all, the macrocracks will occur, and some of them will continue to expand and eventually form the penetrating cracks when the stress exceeds the tensile strength of concrete. And these penetrating cracks destroy the integrity of concrete structures and even become the potential hazards of the concrete constructions [3]. e changes of concrete temperature must be paid great attention in the design and construction process [4][5][6][7][8][9][10][11]. ...
The thermal model and the relevant parameters of concrete are the most important issues to study the space-time characteristics of temperature field, which are also the theoretical foundation of temperature control and crack prevention for the mass concrete structures. In this research, the improved adiabatic temperature rise test is carried out, and the temperature variation of fly ash concrete is analyzed. Furthermore, a thermal model of concrete considering the hydration degree is established based on the existing achievements. Meanwhile, the thermal conductivity and specific heat of concrete are measured via three approaches: by treating the parameters as constant values, by computing the parameters as variables of the degree of hydration, and by back-analyzing the parameters through BP neural network. Finally, the thermal parameters determined by different methodologies are substituted into the thermal model, respectively, and the finite element analysis of the concrete specimen is performed. By comparing simulated temperatures with various measured results, it can be found that the numerical analysis results of parameters calculated by BP neural network are closest to the measured values in the whole curing ages. Therefore, BP neural network method is an effective way to calculate the thermal parameters, and BP inversion algorithm provides a new way for accurately study the temperature profile of mass concrete structures.
... However, most of the simulation works consider concrete arch dam to behave elastically, and consequently the cracking behavior and failure 2 Mathematical Problems in Engineering mode of concrete arch dam cannot be captured. Limited studies on the cracking behavior of concrete arch dam can be found in [9,10] in which the rock foundation is assumed to be rigid and in [11,12] in which the concrete arch dam is treated as a crown cantilever and is analyzed using the linear elastic fracture mechanics method. Moreover, to the best of our knowledge, the study on the influence of the ratio of mechanical properties of weak abutment and those of strong abutment on the cracking behavior and failure mode, which can provide an extensive knowledge of the structural failure of the concrete arch dam with nonuniform abutment in a general sense, has been rarely detailed in past research works. ...
The cracking behavior and failure mode of a 78 m high concrete double-curvature arch dam with weak upper abutment are investigated through performing cracking analysis. The mechanical behavior of concrete is simulated using a smeared crack model, in which a combination of the compression yield surface and the crack detection surface with a damaged elasticity concept is employed to describe the failure of concrete. The arch dam with practical mechanical properties of the upper and lower abutments is firstly studied with emphasis on its cracking behavior during overloading. Then, a comprehensive sensitivity analysis is carried out to investigate the influence of the ratio of the mechanical properties of upper abutment to those of lower abutment on dam failure with prime attention placed on the failure mode. Simulation results indicate the adopted smeared crack model is well-suited to the crack analysis of concrete arch dam. It is shown that cracking is localized around the interface between upper and lower abutments, which leads to a fast crack growth in the through-thickness direction of dam and finally causes the dam failure. Furthermore, the sensitivity analysis presents three types of failure modes corresponding to different ratio value, wherein Modes II and III should be avoided since the weak upper abutment plays a predominant role in the cracking and failure of concrete arch dam.
... In many circumstances, incomplete joints or notch-like incomplete cuts are adopted such that the structural integrity can be better maintained whilst the tensile stress concentration can be effectively reduced. Take concrete arch dam as an instance, many arch dams around the world suffered from dam heel cracking failure under self-weight and hydrostatic pressure loads, such as the Kölnbrein arch dam in Austria [1,2] and the Zeuzier arch dam in Switzerland [3]. A common remedy for such a problem in practice is to apply an artificial joint near the dam-foundation interface, either in the form of perimetrical joints or upstream base joints ( Fig. 1(a and b)). ...
Concrete structures are intentionally built with notches or incomplete joints in many engineering practices to deal with complex loading conditions. It is of great significance to improve the crack resistance and the installation of a channel steel plate ahead of the purpose-built notch (or joint) tip may serve such a purpose. This paper presents an investigation into the strengthening mechanism of installing a channel steel plate at the head of a notch for concrete beams against opening mode fracture failure. Both test and numerical studies have been undertaken and particular attention is given to the effects of key factors on the load carrying capacity and the failure pattern. Two types of three-point bending tests were conducted on concrete beams with or without channel steel plate reinforcement for a comparison study. The test results demonstrated the capability of channel steel plate measure for increasing the beam load capacity, and the interface debonding and matrix cracking were responsible for the eventual failure of reinforced concrete beams. Correspondingly, finite element based numerical models were established to investigate the progressive cracking in test beams and the strengthening mechanism by the installation of a steel plate. A damage-plasticity material model was used for simulating the cracking development in concrete, whilst two different approaches were adopted for the steel-concrete interface modelling: one assumed a perfect bond while the other incorporated a discrete thin layer of interface to allow for potential debonding and slippage. A comparison between the numerical and test results was given, and the effects of key factors on the performance of beams with steel plate measure were investigated through parametric numerical studies. The paper ends with some discussions on the strengthening mechanism and conclusions.
... The first numerical simulations of concrete dams using discrete crack models were conducted assuming linear elastic fracture mechanics (LEFM), which is convenient for large structures such as the case of the Fontana gravity dam (Elices et al. 1985;Sloan and Abraham 1978) and others (Linsbauer et al. 1989). Another example of discrete crack models applied to dams was presented by Shi et al. (2003). ...
Expansions 2 3 in concrete dams may be caused by chemical or physical sources; however, in certain occasions the evidences ob-6 served in the dam may not be attributed to a single cause. Mequinenza is an example of a concrete dam affected by expansions and high 7 nonrecoverable displacements that cannot be explained by the most frequent pathologies. This paper presents new hypotheses that could 8 justify such behavior by assuming the superposition of a global phenomenon of water induced expansion in concrete in the entire dam and a 9 localized effect consisting in the opening of cracks in the construction joints located in one of the blocks. This is validated by conducting 10 numerical analyses through 2D finite element models that consider the nonlinear behavior of the construction joints and use zero-thickness 11 interface elements to simulate the potential cracking planes in the dam. The results confirmed the diagnosis proposed and the capability of the 12 model to reproduce the behavior of the dam, revealing the significant contribution of the opening of the cracks to the non-recoverable 13 displacements in the dam.
... However, for concrete arch dams, the fractures are popular in the construction and operation periods [1]. For example, Kolnbrein and Er-tan arch dams cracked after several years' service [2,3]. Xiaowan arch dam, shown in Figure 1, the highest one built in the world, had temperature fractures within the dam body during the construction period [4]. ...
It is important to estimate the probability of fracture extension and its impact on the safety of arch dams with fractures. Numerical simulation and geomechanical model test were combined to evaluate the overall stability and the extension probability of fractures. Numerical simulation forecasted the dam displacement and the operating behavior based on the parameters obtained from the back analysis. Geomechanical model test was based on small block masonry and the models with or without fractures were both tested. The results show that the deformation of dams is in line with general rules at a normal water load and the extension probability of the existing fractures is very small, which has no significant impact on the global stability of dams. Moreover, the failure process of arch dams with the existing fractures in dams at overload scenarios is similar to the one without the embedded fractures, i.e., the failure crack which is not caused by the existing fractures inside comes into being on the surface of dams itself.
... Performance and various limit-states of the structure, thus, can be determined through the IDA. It has been shown that the concrete arch dams should be analyzed in three-dimensional space because of important effects of the arch and cantilever actions in their responses [45,46]. They have been normally analyzed under three components of earthquakes, i.e. stream, cross-stream and vertical components. ...
... Field measurements of many arch dams, such as Buffalo Bill dam in America [2], Kolnbrein dam in Austria [3][4][5], Dragan arch dam [6] and Glen Canyou arch dam [7] in Romania, Cabril dam in Portugal [8], and Xiangshui arch dam [9] in China, demonstrate that the heel and toe regions along a cross-section, as well as the downstream middle part and both ends of an arch layer from a plan view, are most vulnerable to cracks under actual working conditions. The occurrences of these cracks indicate that the development of new configurations in arch is necessary and of great importance, which will definitely lower the risk of cracks and potential failures by water pressure and thermal loads in the operations of arch dams. ...
This paper presents a retrospective investigation into the performance of a new type of flexible-arch configurations in Shimenzi arch dam based on the past ten-year-long field measurements. The flexible-arch configurations are mainly comprised of artificial short joints at the middle downstream surface and a middle
contraction joint with hinged well and enlarged arch ends with bending joints. Fundamental design considerations of these components are provided, and their
contributions to the performance of Shimenzi arch dam are discussed in detail using the monitoring data from joint meters, strain gauges, and thermometers. Some elementary numerical studies have been conducted on a typical arch structure with different arrangements of artificial joints. Both the field data and numerical results
prove well the effectiveness of the purposely built short joints and the middle contraction joint on the relaxation of tensile stress mobilization. Field survey data also
clearly demonstrate the significance of the hinged well at the upstream side of the middle joint for a continuous arch force transfer.
... The accuracy of FRANC have been shown in several studies (e.g., Linsbauer et al., 1989;Ingraffea, 1990;Bittencourt et al., 1992;Fischer et al., 1995;Bittencourt et al., 1996). A complete evaluation of the accuracy in computing stress intensity factors is given by Bittencourt et al. (1992). ...
Opening-mode fractures developed from a free surface in a layered material often terminate at the interface that divides the fractured layer and the underlying layer. They also display regular spacing that is of the same order of magnitude as the thickness of the fractured layer. We have investigated the stress distribution between two adjacent edge fractures as a function of the ratio of fracture spacing to thickness of the fractured layer using a two-layer elastic model with a fractured top layer. The results show that when the ratio of fracture spacing to the layer thickness changes from greater than to less than a critical value the normal stress acting perpendicular to the fractures near the free surface changes from tensile to compressive. This stress state transition precludes further infilling of fractures unless they are driven by mechanisms other than a pure extension, or there are flaws that significantly perturb the local stress field between the fractures. Hence, the critical fracture spacing to layer thickness ratio defines a lower limit for fractures driven by extension, which also defines the condition of fracture saturation. The critical value of the fracture spacing to layer thickness ratio is independent of the average strain of the fractured layer, and it increases with increasing ratio of Young's modulus of the fractured layer to that of the underlying layer. The critical value increases with increasing Poisson's ratio of the fractured layer, but it decreases with increasing Poisson's ratio of the underlying layer. For the case with the same elastic constants for the fractured layer and the underlying layer, the critical spacing to layer thickness ratio is about 3.1. Delamination between the fractured layer and the underlying layer makes the critical spacing to layer thickness ratio much greater. Infilling fractures grow more easily from flaws located near the bottom of the fractured layer than from those located near the free surface when the spacing to layer thickness ratio is less than the critical value. The propagation of an edge flaw between adjacent edge fractures is unstable, but for the flaw to propagate to the interface, its height has to be greater than a critical size, that decreases with increasing fracture spacing to layer thickness ratio. The propagation behavior of an internal flaw with its lower tip at the interface depends on the edge fracture spacing to layer thickness ratio. The propagation is unstable, when the fracture spacing to layer thickness ratio is greater than a critical value; stable, when the fracture spacing to layer thickness ratio is less than another critical value; and first unstable, then stable, and/or unstable again, when the fracture spacing to layer thickness ratio is between these two critical values.
... The main reasons are the temperature excursions between the internal and the external sides of the dam, dilatation of concrete when exposed to environmental conditions, as well as foundation settlements. LEFM theories were then applied to several case studies, including the analysis of cracking in the Fontana dam in North Carolina (USA) [4,5], in the Koyna dam in India [6,7,8], and in the Köhlbrein dam in Austria [9,10,11]. Recently, LEFM has also been applied to the interpretation of the reasons for collapse of the Malpasset dam in France [12]. ...
In this article, the problem of cracking in concrete gravity dams subjected to seismic loadings is examined under a multiscale perspective. Preliminarily, the size-scale effects on the mechanical parameters entering the nonlinear constitutive models of the interface crack are discussed. From a wide review of existing experimental results, it is shown that the material tensile strength, the fracture energy, the friction coefficient and the concrete compressive strength are strongly size-scale dependent. This evidence pinpoints the necessity of performing experimental testing on large scale specimens to assess the value of the parameters to be used in nonlinear fracture mechanics simulations. Moreover, the size-scale dependency of the interface constitutive properties implies the necessity of updating their values during crack propagation simulations. To do so, interface properties are not given in input a priori, but they are selected at each step of the simulation according to the specified scaling laws. The numerical simulations, based on the finite element method and a generalized interface constitutive law for contact and decohesion implemented in the node-to-segment contact strategy, show the high sensitivity of the phenomenon of crack propagation by the parameters of the damage law used to degrade the cohesive zone properties in case of repeated cycles.
... The safety and stability of such a large-scale structure is very important in the process of construction and service. Among the problems with technique that hydraulic engineers face, concrete cracks can be one of the toughest, especially the temperature cracks on the surface or through the dam body (Bazant and Xian 1997; Linsbauer et al. 1989). In addition to the damage and fracture mechanism of concrete material, the temperature load during construction is very complicated and should be treated carefully and adequately. ...
The meshfree edge-based smoothed point interpolation method (ES-PIM) is extended to the simulation of transient heat transfer problems for concrete dams in the construction process. The present ES-PIM consists of the following ingredients: (1) a novel cell death and birth technique is proposed to deal with the existence or nonexistence of the concrete layers, and hence the construction process of dams can be easily simulated; (2) a lumped diagonalization procedure for specific heat matrix is implemented to improve the stability and efficiency of transient computations; and (3) the triangular background cells are used to construct the nonoverlapping smoothing integral subdomains, and the cell-based T3- and T6/3-schemes are adopted for the node selection in the formation of PIM shape functions. On the basis of the weakened weak formulation, the ES-PIM is spatially stable and convergent to the exact solution. The ES-PIM can achieve better results in accuracy and convergence rate, in comparison with the finite element method using the same meshes. DOI: 10.1061/(ASCE)EM.1943-7889.0000312. (C) 2012 American Society of Civil Engineers.
... Several attempts have been made in recent years to investigate the fracture response of concrete dams. Simulation of crack profile in concrete dams under static and thermal load effects has attracted substantial attention of several investigators (Ayari 1988; Ingraffea 1990; Linsbauer 1986; Linsbauer et al. 1989a Linsbauer et al. , 1989b). Unlike the static response, the nonlinear dynamic response of concrete gravity dams under seismic loads is a little-understood phenomenon due t o limitations in the previous studies. ...
The seismic safety of concrete dams is a matter of serious concern around the world. During severe ground motions, the dams are likely to experience cracking due to low tensile resistance of concrete. Several analytical methods have been proposed in the literature for finite element crack propagation analysis of concrete structures. Due to lack of consistent results, and virtually impossible verification because of limited field experience in seismic cracking of concrete dams, the choice of a reliable constitutive model has become a complex task. A review of concrete constitutive models for nonlinear seismic analysis of gravity dams is presented herein. The relative merits of the proposed models have been critically examined. Comparing the theoretical soundness, and the advantages and inconveniences of the different analytical procedures, the nonlinear fracture mechanics model applied with a smeared crack analysis technique appears to be very promising. The present state of knowledge on material fracture parameters under transient conditions has been found to be limited. Review of the past finite element seismic fracture analyses of concrete gravity dams reveals that reliable numerical models for safety evaluation of the structures during severe ground motions have not yet been satisfactorily developed. Key words: gravity dams, constitutive models, fracture mechanics, seismic response, nonlinear analysis, finite element, crack propagation.
... Two examples of well-established and extensively applied damage models for ductile solids are the phenomenological Lemaitre and Chaboche's (1988) model and the micromechanics-based Gurson's (1977) model. For microcracked brittle or quasi-brittle materials such as concrete and rocks, some of the much simplified phenomenological models have also been adopted in the analysis of such important engineering structures as dams (Linsbauer et al., 1989; Yang et al., 2003). In comparison of ductile damage associated with nucleation, growth, and coalescence of microvoids, microcracking damage has some distinctly different features. ...
This article addresses several issues in damage micromechanics for microcracked brittle or quasi-brittle solids, with major attention paid on summarizing some recent works of the present authors. First, we discuss the methods for characterizing evolutionary damage of microcracks and introduce the concept of orientation domain of microcrack growth. Second, we describe how to calculate the macroscopically effective constitutive relation of microcracking solids under complex loading. Third, the effective medium or effective field methods for estimating the effective elastic moduli of microcracked solids are formulated into a universal framework. Fourth, a subregion method is suggested to calculate the effective elastic moduli, fracture strength, and failure process of solids containing a large number and/or a high density of microcracks. Additionally, this method is combined with the finite element method to simulate the damage evolution and failure process of engineering structures.
... Several attempts have been made in recent years to investigate the fracture response of concrete dams. Simulation of crack profile in concrete dams under static and thermal load effects has attracted substantial attention of several investigators (Ayari 1988;Ingraffea 1990;Linsbauer 1986;Linsbauer et al. 1989aLinsbauer et al. , 1989b. Unlike the static response, the nonlinear dynamic response of concrete gravity dams under seismic loads is a little-understood phenomenon due t o limitations in the previous studies. ...
A finite element method for seismic fracture analysis of concrete gravity dams is presented. The proposed smeared crack analysis model is based on the non-linear fracture behaviour of concrete. The following features have been considered in the development of the model: (i) the strain softening of concrete due to microcracking; (ii) the rotation of the fracture band with the progressive evolution of microcrack damage in finite elements; (iii) the conservation of fracture energy; (iv) the strain-rate sensitivity of concrete fracture parameters; (v) the softening initiation criterion under biaxial loading conditions; (vi) the closing-reopening of cracks under cyclic loading conditions. The seismic fracture and energy response of dams and the significance of viscous damping models to take account of non-cracking structural energy dissipation mechanisms are discussed. The influences of global or local degradation of the material fracture resistance on the seismic cracking response of concrete dams were also studied. Two-dimensional seismic response analyses of Koyna Dam were performed to demonstrate the application of the proposed non-linear fracture mechanics model.
... The theoretical basis, accuracy and friendly user interface of FRANC have been introduced by a number of authors (e.g. Wawrzynek and Ingraea, 1987;Linsbauer et al., 1989;Ingraea, 1990;Bittencourt et al., 1992;Fischer et al., 1995;Bittencourt et al., 1996;. For the purposes of stress intensity factor calculation in this paper, we use three cycles of re®nement of the mesh in the crack tip area. ...
Spacings of opening-mode fractures (joints and veins) in layered sedimentary rocks often scale with the layer thickness. Field observations reveal that the ratio of fracture spacing to the thickness of the fractured layer, S/Tf, ranges from less than 0.1 to greater than 10. There is a critical spacing to layer thickness ratio that defines the condition of fracture saturation, and explains the observed spacing ratios between 0.8 and 1.2. Values of S/Tf>1.2 are explained as the results of the fracturing process having not reached the saturation level. To explain ratios of S/Tf<0.8, we study the possibility for further fracture infilling, by considering flaw distributions between adjacent fractures loaded by extension of the layer. Results show that infilling fractures grow more easily from flaws located near the interface than from those in the middle of the fractured layer. The propagation of a flaw located in the middle of the fractured layer is unstable, but for the flaw to propagate toward the interfaces, its height has to be greater than a critical size. This critical size decreases with increasing S/Tf. The propagation behavior of a flaw with one of its tips at the interface depends on S/Tf. The propagation is unstable when S/Tf is greater than a critical value. When S/Tf is less than this critical value, the propagation is first unstable, then stable, and then unstable again. An infilling fracture can cut through the fractured layer only if S/Tf is greater than another critical value, otherwise the infilling fracture can only partially cut the fractured layer. For models with the same elastic constants for the fractured layer and the neighboring layers, this critical value is 0.546, and the minimum spacing to layer thickness ratio of fractures formed by the in filling process under extension is 0.273.
Three‐point bending tests of the full‐graded concrete under different loading rates were carried out. The cracks were quantitatively analyzed by digital image correlation (DIC). The toughening mechanism during the crack development process was observed, and there are obvious crack branching and aggregate interlocking during the crack propagation. At the same load level, the crack opening width increases with the increase of the loading rate. DIC detects a decrease in the tortuosity of the fracture morphology. And at the same time, the damage of the dam concrete was evaluated by the frequency analysis and the damage type analysis from acoustic emission (AE) signals. The signal strength increases at a higher loading rate as well as the tensile type cracks. The results show that the monitoring results of DIC and AE technique are in agreement with each other, which is very effective for determining the fracture behaviour of concrete materials.
Highlights
• The aggregate interlocking and crack branching form the toughening mechanism after peak
• The interlocking and crack branching decrease with the increase of the loading rate.
• Signals with different frequency content correspond to different fracture scale.
• The development type of crack tends to direct tension with the increase of the rate.
Concrete arch dam exhibits remarkable spatial-time characteristics because its working state might be evolved dramatically attributable to the dynamic construction process and operation environment. To overcome the limitations of routine design and analysis approaches for the high arch dam due to predetermined modes and assumptions, further advanced study is demanded to demonstrate the adequacy of structural analysis theories and calibration standards, as well as to evaluate its safety credibly. In this chapter, the systematic study on Xiaowan Arch Dam at a height of 294.5 m is exhibited, which covers the whole process from the back analysis of in situ geo-stress to the excavation/reinforcement of abutment/foundation, followed with the concrete placement/cooling/grouting operation until the reservoir impoundment/service. This study is supported by a toolkit termed as the “Digitized System of Xiaowan Arch Dam” (DSXAD) which is the combination of the instrumentation system, the FEM system towards the fields of permeability/temperature/deformation, and the decision making system towards engineering judgment. The evolution of the real working state of the arch dam has been thoroughly revealed, and a series of difficult technical issues such as the foundation rock EDZ and dam concrete cracks emerged during its construction, are successfully solved under the guidance of the DSXAD.
Several concrete dams all over the world exhibit severe cracks. It is very important to investigate the influence of cracks on the long-term behavior of dam structures to ensure safe operation. The interpretation of measured dam displacements is usually based on statistical hydrostatic-seasonal-time and hydrostatic-thermal-time models. The main purpose of this article is to present a statistical hydrostatic-thermal-crack-time model to interpret displacements of concrete arch dams with influential horizontal cracks. The hydrostatic-thermal-crack-time model is applied to analyze the Chencun dam, an arch–gravity dam with a large-scale horizontal crack on the downstream face. The crack stretches horizontally across most of the dam blocks. Its crack mouth opening displacement had been continually increasing even after reinforcement treatment, accompanied by abnormal deformation characteristics of the arch–cantilever system. A three-dimensional finite element model, containing the pre-existing crack using special gap elements, is built to reproduce the structural response, assess the contribution of the crack on the registered movements, and obtain the relationship between the crack mouth opening displacement and the dam crest displacement. Based on this, the hydrostatic-thermal-CMOD-time model considering crack mouth opening displacement is developed. Compared with the traditional models, the hydrostatic-thermal-crack-time model is expected to provide a better fit accuracy. The results also show that the crack and the corresponding reinforcement measure have a significant effect on the deformation behavior of the dam. This can provide some useful indications for concrete structures with similar problems.
As a kind of slim shell structure flexibly based on its deformable foundation, high concrete arch dam exhibits remarkable spatial–time characteristics. In this paper, the Xiaowan Hydropower Project accommodating 294.5 m high double curvature arch dam is taken as example, to which the factor of time is introduced in the whole numerical simulation procedure. The dynamic inputting of the parameters related to the structural geometry and material properties (e.g. thermal, permeability, deformation/stress) following the construction progress is realized in an intension to establish a four-dimensional (spatial–time) numerical simulation procedure. The Digitized System of Xiaowan Arch Dam (DSXAD) is further formulated by the combination of the instrumentation system, the spatial–time simulation procedure, and the engineering judgments. The DSXAD has been working well in tracing the real working status of the dam during its construction period as well as service period. A series of difficult technical issues in the construction of the Xiaowan Dam are successfully solved with the help of the DSXAD. Through this practices important theoretical insights are achieved, which founds a new landmark for the high arch dam construction in China.
This paper applies a simplified fracture model to the cracking of an arch dam as a case study. The fracture model is based on linear elastic fracture mechanics (LEFM), wherein the arch dam itself is discretized by 3-D boundary elements. The criterion for crack propagation employs the strain energy factor theory, or so-called S-theory, with certain simplifications for crack growth. The latter involve primarily the assumption of a through crack, which implies that the crack front advances as a straight line. Presented are the results for the first upstream cracking of the Kölnbrein arch dam, which occurred in 1978. In general, it is concluded that the numerical fracture model predicts adequately the observed cracking of this dam in terms of the relevant reservoir level, temperature and pattern of cracking.
The effects of cracking of Xiaowan arch dam on the possibility of cracking propagation, and on the stress, displacement and stability should be considered seriously after phased realistic impounding. The basic principle is three-dimensional nonlinear numerical computation by simulation of the construction process of Xiaowan arch dam and the cracks in the dam based on reasonable material parameters which are obtained by the multipoint displacement back analysis on the basis of the monitoring data. The result indicates that the parameters obtained by the displacement back analysis are reasonable and accurate; and the prediction of the dam displacement is of high precision, which can provide a good stability estimation of the dam. The predicting results fit well with the monitoring data and the results of geomechanical model test. The global deformation of the dam accords with the general pattern; and the possibility of crack propagation is very small under the normal water load. The effects of cracking on the global stability of the dam are very small; and the limit state of the dam is similar to that of no cracking working condition. Both of them crack from the surface to the inside, instead of cracking from the internal cracking.
In this paper, the phenomenon of interface crack propagation in concrete gravity dams under seismic loading is addressed. This problem is particularly important from the engineering point of view. In fact, besides Mixed-Mode crack growth in concrete, dam failure is often the result of crack propagation along the rock-concrete interface at the dam foundation. To analyze such a problem, the generalized interface constitutive law recently proposed by the first author is used to proper modelling the phenomenon of crack closing and reopening at the interface. A damage variable is also introduced in the cohesive zone formulation in order to predict crack propagation under repeated loadings. Numerical examples will show the capabilities of the proposed approach applied to concrete gravity dams.
A 3-D Boundary Element Method and Minimum Strain Energy Density Factor Theory (S-theory) were used to study the stability and propagation of cracks at the heel of high arch dams using a double-curved arch dam as a case study. The results demonstrate that the crack stability depends on the locations of the initial cracks and the uplift pressure on the crack surfaces plays a key role in crack propagation. The rock foundation stiffness also affects crack stability. Crack propagation will greatly weaken the effective cross section of the arch dam when the crack is very deep. The results show that the crack at the heel of the arch dam is stable for normal loads. The analytical method was then used to predict the trajectory of the crack propagation for extremely adverse condition using a multi-step extension.
Impounding deformation of slope and foundation is a noteworthy problem during construction and operation periods of high arch dams. Reservoir impoundment is accompanied with various impacts, including material degradation, effective stress decreasing and buoyancy in rock masses. These phenomena are related with some engineering concerns like landslide, dam stability and reservoir-induced earthquake. However, research on mechanism of impounding effects is still limited. By extending the strength reduction method (SRM) in slope limit analysis, a modified method named stiffness and strength reduction method (SSRM) is proposed and implemented in FEM codes to simulate material degradation. Moreover, the expression of effective stress for fractured rock mass with fluid is incorporated into the Drucker-Prager criterion. Based on monitoring data of left bank slope deformation and valley width reduction of Jinping I arch dam, the above two methods are applied in the analysis of impounding influence of slope and foundation. Results show that the dam has good capability against slope deformation, with displacement and stress fields locally changed.
This paper is a preliminary attempt to clarify a cracking issue confronting a double-curvature arch dam. The cracking occurs in the immediate vicinity of the interfaces between the dam body and some of its gate piers. This study seeks to address what is the biggest factor in the occurrence of the cracks. Both an on-site examination and a finite element analysis (FEA) were performed. The on-site examination consists of crack inspection and a concrete strength test. The FEA primarily focuses on structural loads (gravity and hydraulic thrust). The most obvious finding to emerge from the on-site examination is the symmetrical distributions of the cracks in the piers. The trends of the calculated stress contours correlate fairly well with those of the observed crack propagations, regardless of whether or not the hydraulic thrust is considered in the FEA. Our work has led us to conclude that the cracks result primarily from gravity rather than the hydraulic thrust. The cracking issue is independent of the water storage of the reservoir. Long-term and regular monitoring of the cracking lengths and openings should be a priority. The present findings have important implications for further reinforcement and maintenance work on the cracking gate piers.
A procedure is presented for the analysis of the stability and propagation of cracks in arch darns based on linear elastic fracture mechanics and three-dimensional boundary element modeling. A simplified crack propagation criterion is employed and the crack trajectories are obtained by multistep extension. The first upstream cracking which occurred in the Kolnbrein arch dam is studied in detail under various conditions concerning the foundation interface, location of crack initiation, reservoir water level and load combinations. Crack trajectories close to the observed one are obtained with water level at 1,850-1,860 m, which agrees with the prototype experience. It is found that the hydrostatic load and associated uplift pressure on the crack surfaces are the key factors for causing an initial crack at the dam base to propagate to the upstream face. It is also noted that the bonded condition at the interface between the dam and the upstream elevated foundation is responsible for producing the distinctive profile of the observed crack, which daylights on the upstream face at an acute angle.
The modeling of uplift pressure within dam, on the foundation on which it was constructed, and on the interface between the dam and foundation is a critical aspect in the analysis of concrete gravity dams, i.e. crack stability in concrete dam can correctly be predicted when uplift pressures are accurately modelled. Current models consider a uniform uplift distribution, but recent experimental results show that it varies along the crack faces and the procedures for modeling uplift pressures are well established for the traditional hand-calculation methods, but this is not the case for finite element (FE) analysis. In large structures, such as dams, because of smaller size of the fracture process zone with respect to the structure size, limited errors should occur under the assumptions of linear elastic fracture mechanics (LEFM). In this paper, the fracture behaviour of concrete gravity dams mainly subjected to uplift Pressure at the crack face was studied. Triangular type, trapezoidal type and parabolic type distribution of the uplift pressure including uniform type were considered in case of evaluating stress intensity factor by surface integral method. The effects of body forces, overtopping pressures are also considered and a parametric study of gravity dams under the assumption of LEFM is performed.
In the Xiaowan arch dam there are massive temperature cracks nearly parallel to the dam axis. Obviously, whether the cracks
may spread or not during the water storage process is one of the crucial factors for the safety of a dam. In this paper, a
new type of crack element, in which the contact component is implicitly included into the concrete component, is proposed
to simulate the effects of the existing cracks. The crack element is proved by numerical example to share the merits of both
conventional contact elements and joint elements. With a finite element model of the cracked arch dam together with its rock
foundation established, the transient displacement and stress fields of the dam are obtained. The complicated rock foundation,
the construction process of the arch dam, the massive cracks, the transient temperature field, as well as the water storage
process have been taken into consideration in the simulation. In addition to the global model, several sub-models for typical
crack tips are also generated with finer elements placed around the tips. Thus, more accurate displacement and stress distribution
are obtained by simultaneous sub-model simulation. Based on the calculation of stress intensity factor for crack tips by extension
method, the temperature cracks in the Xiaowan arch dam are finally proved to be stable.
An investigation was carried out to establish a criterion for three-dimensional (3-D) mixed-mode fracture of concrete. Experiments on 3-D mixed-mode fracture were conducted to obtain the critical load Pcr. The stress intensity factor of the specimens per unit load with different combinations of KI,, KII and KIII was calculated by the mixed hybrid finite element method. Based on the stress intensity factor per unit load and the critical load, 25 groups of critical stress intensity factors were calculated, from which a criterion for the 3-D mixed-mode fracture of concrete was derived.
A rigorous analytical procedure for the crack analysis of concrete dams is established using a newly developed numerical technique for analyzing multiple discrete cracks in concrete. The theoretical aspect of the problem solution is addressed first, focusing on the cracking modes of multiple cracks, followed by a brief review on the numerical formulation of the Mode-I type crack propagation for multiple discrete cracks. Next, a simple technique for modeling curvilinear crack propagation is introduced, and the method is examined through numerical studies on the bending tests of simple plain concrete beams with multiple cracks. Then, a well-quoted scale model of a concrete gravity dam is used to study the cracking behaviors in concrete dams; the numerical modeling involves not only the original single-crack problems but also multiple-crack problems. Employing two different types of numerical models and assuming multiple initial notches of different sizes at different locations along the upstream face of the model dams, various kinds of cracking behaviors are obtained and discussed, focusing on the crack interactions.
Excessive borehole pressurization may cause damage to the borehole with a large possibility of the initiation of new cracks and/or the propagation of minute flaws appearing as surface cracks or embedded cracks in the vicinity of the borehole. When these flaws propagate under the control of the borehole pressure-induced symmetrical radially, rapidly decaying stress field and internal crack face pressure they extend along spacially curved surfaces trying to realign themselves again in a plane, the direction of which is governed by the relative magnitude of the pressures in the borehole and the crack. A 3D-crack propagation algorithm serves for the evaluation of the nucleation possibility of borehole cracks and embedded cracks as a function of the state of stress. Numerical modelling concentrates on a centrally bored cube with an inclined semi-elliptical surface starter crack and an embedded elliptical planar starter crack subjected to various boundary conditions. The distributions of the stress intensity factors K1, K2 and K3 along the crack periphery as a function of the pressures and the state of primary stress have been established. Examples for the behaviour of crack initiation and extension due to pressurization are given. An application to high pressure injection in steep boreholes extending from inspection galleries in high arch dams is presented.
Plane strain fracture toughness (KIc) values are determined for the modified ring (MR) test through numerical simulation of crack growth to highlight the sensitivity of MR KIc values on applied displacement or force boundary conditions, slip conditions at the specimen-platen interface, and the Poisson ratio (v) of the test material. Numerical calculation of fracture toughness in the MR test is traditionally conducted assuming a uniform force along the specimen loading surfaces and no slip between the specimen and the loading platens. Under these conditions KIc increases by 30–40% as v decreases from 0.4 to 0.1. When slip is allowed at the specimen-platen interface under a uniform force, KIc values are independent of v, and for any given v, are 5–25% less than those determined under a no-slip boundary condition. Under a uniform displacement of the specimen loading surfaces, KIc is essentially independent of v, regardless of specimen-platen interaction. Moreover, although KIc values determined under unifor displacement and no-slip boundary conditions are always higher than those determined under uniform displacement and slip-allowed boundary conditions, the average difference in KIc for these two methods is less than 5% for the two specimen geometries examined. This suggests that under uniform displacement conditions, KIc is essentially independent of specimen-platen interaction. Because KIc values determined from MR testing are strongly dependent on the modeling procedure, future reports of KIc determined from this test should be accompanied by detailed reports of the modeling procedure. Until further testing reveals the most accurate simulation technique, we advocate use of a uniform displacement formulation for KIc determination from MR testing because results from this method are insensitive to most modeling parameters. Numerical results from models conducted under uniform force, no-slip boundary conditions should be viewed as an upper bound to KIc.
Smeared crack analysis models based on a nonlinear fracture mechanics (NLFM) crack propagation criterion are considered to study the two-dimensional static fracture behavior of plain concrete structures. A coaxial rotating crack model (CRCM) and a fixed crack model with a variable shear resistance factor (FCM-VSRF), both using a secant stiffness formulation, are considered in studying the behaviors of a notched shear beam, a model concrete gravity dam, and a full-scale concrete gravity dam: all have been experimentally or numerically investigated in the past. The responses obtained from smeared crack analyses are compared with those reported in the literature by other investigators. The CRCM appears to perform better than the FCM-VSRF in alleviating the stress-locking phenomenon generally observed in smeared crack analyses. However, the crack profiles predicted by the rotating crack model are prone to the directional bias caused by finite element meshes of the elementary beam problem and the model concrete dam. The two smeared crack propagation models (CRCM and FCM-VSRF) provide reasonable responses when a full-scale concrete gravity dam is analyzed.
Automated simulation of arbitrary, non-planar, 3-D crack growth in real-life engineered structures requires two key components: crack representation and crack growth mechanics. A model environment for representing the evolving 3-D crack geometry and for testing various crack growth mechanics is presented. Reference is made to a specific implementation of the model, called FRANC3D. Computational geometry and topology are used to represent the evolution of crack growth in a structure. Current 3-D crack growth mechanics are insufficient; however, the model allows for the implementation of new mechanics. A specific numerical analysis program is not an intrinsic part of the model, i.e. finite and boundary elements are both supported. For demonstration purposes, a 3-D hypersingular boundary element code is used for two example simulations. The simulations support the conclusion that automatic propagation of a 3-D crack in a real-life structure is feasible. Automated simulation lessens the tedious and time-consuming operations that are usually associated with crack growth analyses. Specifically, modifications to the geometry of the structure due to crack growth, remeshing of the modified portion of the structure after crack growth and reapplication of boundary conditions proceeds without user intervention. Copyright © 2000 John Wiley & Sons, Ltd.
Bedding-perpendicular joints confined to individual beds in interbedded sedimentary rocks commonly exhibit spacings which are proportional to the thickness of the jointed bed, and which vary according to lithology or structural position. The mechanical explanation for this relationship is well understood when the joints are driven by far-field crack-normal tensile stresses, but poorly understood for cracks driven by elevated fluid pressures, where the crack-driving stress is the difference between the crack-normal compression and the fluid pressure in the crack. Through a series of finite-element numerical models, we investigate how various parameters influence the driving-stress distribution around pressurized cracks in layered media, and thereby identify factors influencing the spacing of fluid-driven joints. For the situation we modeled, we observe that: (1) crack-driving stress is reduced in the vicinity of pressurized joints, and that the extent of the stress reduction depends on the contrast in elastic properties between the layers; and (2) crack-driving stress distribution depends on the ambient pore pressure during jointing. These results indicate the spacing of fluid-driven joints should depend on lithology and pore pressure.
The experimental and numerical investigations presented in this paper were carried out to determine the splitting forces and crack propagation scenarios of naturally bedded layered slate rock. Splitting loads were determined by impact splitting of regular-sized slate blocks under plane strain test loading conditions, using a hydraulic actuator with a wedge-shaped indenter. The mechanical properties of slate blocks required for numerical analyses were obtained from detailed experimental testing. The velocity of dynamic crack propagation in slate blocks under indenting wedge impact loading was determined using a series of strain gauge sensors. Numerical studies were carried out using ABAQUS, a general purpose, finite element analysis (FEA) program. Mode I dynamic crack propagation was simulated numerically by the gradual releasing of the restrained node on the symmetric plane of the specimens. Mode I stress intensity factors were computed for different crack lengths and the results were compared with the plane strain material fracture toughness obtained from earlier experiments/FEA. Very good agreement was obtained between analysis results and the measured fracture toughness value of slate, for the applied impact splitting load. Using the equation derived from a parametric study, of results obtained from the numerical analysis of different sizes of slate blocks, the maximum theoretical impact splitting force was determined using the plane strain fracture toughness value obtained from FEA. The difference between the loads obtained from the experimental studies and the derived empirical equation, varied between + 4.96% and −32.34%.
It is still very difficult for researchers and engineers to implement the simulation analysis including a complete process
and a full model with the complicated arch dam and the foundation, and to evaluate the cracking potential in the construction
and service periods. To take Xiaowan project of China for an example, a practical system of simulation feedback analysis,
a specific cracking criterion, and a resolution for the conflicting requirements of temperature and stress/strain simulation
are presented, which are put into a successful practice. The simulation results of temperature, stress, and cracking are identical
well with the monitor data. A modified temperature control measure is propounded, and the significant effect is gained by
adopting the new scheme.
Keywordsarch dam–cracking potential–construction process–finite element method–simulation feedback analysis
The current situations and growing prospects of China’s hydro-power development and high dam construction are reviewed, giving
emphasis to key issues for safety evaluation of large dams and hydro-power plants, especially those associated with application
of state-of-the-art computational mechanics. These include but are not limited to: stress and stability analysis of dam foundations
under external loads; earthquake behavior of dam-foundation-reservoir systems, mechanical properties of mass concrete for
dams, high velocity flow and energy dissipation for high dams, scientific and technical problems of hydro-power plants and
underground structures, and newly developed types of dam-Roll Compacted Concrete (RCC) dams and Concrete Face Rock-fill (CFR)
dams. Some examples demonstrating successful utilizations of computational mechanics in high dam engineering are given, including
seismic nonlinear analysis for arch dam foundations, nonlinear fracture analysis of arch dams under reservoir loads, and failure
analysis of arch dam-foundations. To make more use of the computational mechanics in high dam engineering, it is pointed out
that much research including different computational methods, numerical models and solution schemes, and verifications through
experimental tests and filed measurements is necessary in the future.
The problem of crack propagation in bi-layered structural components is addressed. Due to the presence of the bi-material interface and depending on the loading direction, a competition between different crack trajectories (failure modes) can take place. The quantification of the dominant failure mode and of the prevailing fracture mechanism is very often a challenging task, although it is crucial for design purposes. In this contribution, starting from the experimental observation of failure modes in a variety of engineering applications involving bi-layered structural components, an interpretation is proposed in the framework of the finite elements discretization and linear elastic fracture mechanics. The effect of thermo-elastic and residual stresses on the stability of crack propagation is carefully examined. Numerical results confirm the qualitative experimental observations of failure modes in bi-layered structural elements used for rock drilling applications.
The application of fracture mechanical technology to massive concrete structures, in particular dams, with special reference to linear and nonlinear methods, and in which validity-studies of material parameters are demonstrated.
Mixed-mode crack growth in a scaled-down model of a concrete gravity dam is investigated. An initial crack is assumed under equivalent hydraulic and self-weight loadings. The two-domain boundary element method (BEM) is applied in conjunction with the theory of linear elastic fracture mechanics (LEFM). The body force is included to simulate the weight effect of the dam on crack growth.The criteria of maximum tangential stress, minimum strain energy density function, maximum tangential strain and maximum energy release rate are used to predict the mixed-mode crack path. The numerical simulations are compared with the experimental results for the scaled down 1:40 model of a concrete gravity dam. Analytical results obtained from a cohesive fracture model using a finite element code are also discussed.It is found that the four foregoing LEFM criteria perform equally well for predicting crack trajectories, load versus crack tip opening displacement (CTOD), and load versus crack tip sliding displacement (CTSD) relations. This may be due to the dominance of the Mode I effect in crack growth as the contribution of Mode II is found to be negligibly small.
Two case studies of crack propagation in concrete gravity dams are described. The studies employ mixed-mode LEFM implemented within a discrete crack, automatic rezoning, finite element method. The study of the Fontana dam elucidated the mechanisms for crack initiation, accurately reproduced observed trajectory, and evaluated the effectiveness of interim repair measures. The study of a generic gravity dam had as its objective the evaluation of usefulness of LEFM for design and quality control during construction. An envelope of safe lengths, heights, and orientations of cracks potentially growing from cold lift joints on the upstream face was derived. It was also shown that, by neglect the toughness of the foundation contact, classical design methods predict a conservative factor-of-safety against sliding, and that, when toughness is set to zero, LEFM predictions are in good agreement with the classical method.
The proper fracture mechanics to be applied to crack propagation in concrete is determined by scale effects.
The Kolnbrein arch dam in Austria presented problems as soon as 80% storage elevation had been exceeded. These mainly resulted from the tensile stresses occurring at the upstream dam toe. Remedial measures are described that enabled reservoir operation to be maintained (95% full on average). An analysis is presented of the deformation behaviour of the dam structure and its foundation. Vertical tensions increase rapidly at the upstream dam toe as soon as the deformation modulus of the foundation exceeds that of the concrete. The ratio of these moduli is of decisive importance for the stress condition at the dam base, but not for the rest of dam. It is proposed that a limit value analysis should always be carried out on unfavourable assumptions for the zone near the base. (from paper)
Computer modeling of mixed-mode crack propagation has rarely been attempted. This is because of the difficulty in updating the geometrical description to represent the changing crack geometry. The development of two interactive, graphical fracture propagation systems is described here. The Finite Element Fracture Analysis Program—Graphical (FEFAP-G) is a two-dimensional fracture propagation system. The BEM3D is a three-dimensional boundary element fracture propagation system.
In addition, the implementation of the BEM3D analysis program in a configuration formed by an FPS-264 processor attached to a VAX-11/750 used as host computer is described. The results show that a realistic three-dimensional boundary element analysis of crack propagation is not only feasible with the aid of attached processors, but it can have its total time reduced by factors of the order of hundreds when compared to VAX alone statistics.
In an example problem concerning fatigue crack propagation in a stiffened wing skin, both FEFAP-G and the BEM3D are employed to illustrate the utility of the fracture propagation systems.
A fracture analysis program has been developed which incorporates the concepts of finite element analysis, fracture mechanics, computer graphics, finite element postprocessing, automatic mesh generation, and data base design. The program FRANC (FRacture ANalysis Code) is a tool which allows a practicing engineer or a researcher to perform an incremental fracture analysis at his desk. The program draws on a substantial experience base and this paper describes the philosophy of the program and the integration of its parts. Also, a number of example problems will be presented which show some results of incremental fracture analyses.
Non-linear fracture models for discrete crack propagation Application of Fracture Mechanics to Cementitious Compos-ites The Hague, The Netherlands
- A R Ingraffea
- W Gerstle
Ingraffea, A. R., and Gerstle, W. (1985). "Non-linear fracture models for discrete crack propagation." Application of Fracture Mechanics to Cementitious Compos-ites, S. P. Shah, ed., Martinus-Nijhoff Publishers, The Hague, The Netherlands, 171-209.