High Rockfill Dam Research Articles

An Optimization Model for Construction Stage and Zone Plans of Rockfill Dams Based on the Enhanced Whale Optimization Algorithm

Rockfill dams are among the most complex, significant, and costly infrastructure projects of great national importance. A key issue in their design is the construction stage and zone optimization. However, a detailed flow shop construction scheme that considers the opinions of decision makers cannot be obtained using the current rock-fill dam construction stage and zone optimization methods, and the robustness and efficiency of existing construction stage and zone optimization approaches are not sufficient. This research presents a construction stage and zone optimization model based on a data-driven analytical hierarchy process extended by D numbers (D-AHP) and an enhanced whale optimization algorithm (EWOA). The flow shop construction scheme is optimized by presenting an automatic flow shop construction scheme multi-criteria decision making (MCDM) method, which integrates the data-driven D-AHP with an improved construction simulation of a high rockfill dam (CSHRD). The EWOA, which uses Levy flight to improve the robustness and efficiency of the whale optimization algorithm (WOA), is adopted for optimization. This proposed model is implemented to optimize the construction stages and zones while obtaining a preferable flow shop construction scheme. The effectiveness and advantages of the model are proven by an example of a large-scale rockfill dam.

Laboratory experiments on the improvement of rockfill materials with composite grout

Dam deformation should be strictly controlled for the construction of 300m-high rockfill dams, so the rockfill materials need to have low porosity. A method of using composite grout is proposed to reduce the porosity of rockfill materials for the construction of high rockfill dams. The composite grout is a mixture of fly ash, cement and sand with the properties of easy flow and post-hardening. During the process of rolling compaction, the grout admixture sprinkled on the rockfill surface will gradually infiltrate into the inter-granular voids of rockfill by the exciting force of vibratory roller to reduce the porosity of rockfill. A visible flowing test was firstly designed to explore the flow characteristics of composite grout in porous media. Then, the compressibility, shear strength, permeability and suffusion susceptibility properties of composite grout-modified rockfill are studied by a series of laboratory tests. Experimental results show that the flow characteristics of composite grout are closely related to the fly ash content, the water-to-binder ratio, the maximum sand size and the content of composite grout. The filling of composite grout can effectively reduce the porosity of rockfill materials, as well as increase the compression modulus of rockfill materials, especially for loose and gap-graded rockfill materials. Composite grout-modified rockfill tends to have greater shear strength, larger suffusion erosion resistance, and smaller permeability coefficient. The composite grout mainly plays the roles of filling, lubrication and cementation in rockfill materials.

Different Deformation Patterns in High Core Wall Rockfill Dams: A Case Study of the Maoergai and Qiaoqi Dams

The time‐dependent behaviour of high rockfill dams is complex and not easy to accurately predict. Many discrepancies were revealed by the comparison of the observed deformation histories of different dams, and the deformation of some high rockfill dams did not correspond to the general deformation law. Field monitoring is therefore an effective method for understanding complex dam deformation behaviour. In this paper, actual measured deformation data resulting from continuous monitoring of the Maoergai and Qiaoqi dams are analysed. These two dams have similar heights, crest lengths, and alluvium overburden thicknesses. Our aim is to explain the actual deformation histories on the basis of the mechanical behaviours of these dams in order to warn engineers about potential problems that cannot be predicted. The results indicate that the deformation patterns of the two dams are completely different. The dam construction and water impoundment schedule is the major reason for the different horizontal displacement patterns. The reservoir filling rates and rainfall are the main reasons for the different settlement patterns. The case histories are useful for understanding the wide range of possible postconstruction deformation in a dam.

Stress and Deformation Property of Geomembrane Surface Barrier for High Rock-fill Dam

Based on the direct shear test results of interface between a composite geomembrane and cushion material, nonlinear elastic, perfectly plastic model was used to describe the interface behaviors. The interface model was incorporated into the Geogrid element of a fast Lagrange analysis of continua in three dimensions (FLAC3D) procedure through a user-defined program in the FISH. Then a geomembrane surfaced rock-fill dam on thick pervious foundation was numerically analyzed using the incorporated model. The numerical results showed that only small tension deformation can be found in the most area of geomembrane on the dam surface. However, large tension deformation of geomembrane appeared close to the anchorage in the peripheral zone of the barrier. The anchorage structure of geomembrane in this area should be carefully designed to avoid tension failure of geomembrane.

An approach for the real-time slip deformation coupled with strain softening of a high rockfill dam subjected to pulse-like ground motions

The dynamic stability of a dam is a major engineering problem, especially since many high dams have been built or designed in near-fault zones. However, few studies have been focused on the dynamic stability of dams subjected to near-fault pulse-like ground motions. The stability analysis of high rockfill dam subjected to pulse-like ground motions is a meaningful topic. In the traditional computing methods for slope stability, the position of potential sliding surfaces can’t be accurate determined. In order to get more accurate results, the finite element method of sliding calculation is proposed to calculate variation process of the dynamic stress of the element. Meanwhile, the strain softening of rockfill materials under low confining pressure is obvious. Hence, the dam stability considering the strain softening of rockfill materials is an urgent problem that must be investigated. In this study, the peak strength and residual strength were obtained, and the normalized residual strength curve considering strain softening was put forward by analyzing consolidated drained triaxial test data that were derived from real projects. The soil slope stability procedure (FEMSTABLE 3.0) was developed by the first author and used to perform a seismic stability analysis of a core-wall dam in the near-fault area. In addition, the more reasonable approach was proposed to calculate the real-time slip of the dam under pulse-like ground motions, and the method was coupled real-time slip deformation and strain softening. The proposed method of sliding calculation may spend much time on computing safety factors and accumulated displacements of a large number of sliding surfaces, therefore the multicore parallel computing technique was used to improve the calculation speed. Moreover, the sliding displacement responses of the dam subjected to pulse-like and non-pulse ground motions were compared. Furthermore, the effects of pulse-like ground motions on the dynamic stability of 300 m core-wall dam considering strain softening were investigated. The results show that the pulse-like ground motion has a considerable effect on sliding displacement and strain softening of the rockfill, ignoring this factor may lead to inaccurate result.

Review of macro- and mesoscopic analysis on rockfill materials in high dams

With the quick development of the hydrolic engineering in China, the height of the rockfill dams reaches the level of 200– 300 m. High rockfill dams over 200 m behave differently in deformation mode compared to previous lower dams. Due to the particular features of rockfill materials in macroscopic and mesoscopic scales, such as continuity, discrete and crushability, the constitutive models and the deformation mechanisms for rockfills are not yet clear. It is necessary to investigate the mechanical behaviors of rockfill materials from macro- to meso-scale. This paper makes a review on macro- and mesoscopic analysis of rockfill dams and rockfill materials in recent years. The constituitive modeling and the parameter calibration of rockfill dams, the mesoscopic method, deformation mechanisms and the scale effect for rockfill materials are discussed. Besides, the further investigation trends of deformation analysis and control methods in rockfill dams are shown.

Strain Analysis of the Nuozhadu High Rockfill Dam during Initial Impoundment

The safety of rockfill dams during initial impoundment has always been an issue of interest for regulatory agencies. Specifically, it is necessary to identify potential tensile strain zones and shear strain concentration zones in which cracks may form. In this paper, a meshless smoothing method is proposed to construct the strain field of a prototype dam based on monitoring displacement data. For verification, this method is applied to calculate the strain field of the Nuozhadu core wall rockfill dam. The results show that the proposed method can provide regulatory agencies with an effective tool for dam inspection during initial impoundment.

The Deformation Mechanism of a High Rockfill Dam during the Construction and First Impoundin

The Masjed-e-Soleyman dam is a high rockfill dam with clay core, located in Iran. During construction and first impounding, a considerably high excess pore water pressure has been developed inside the core and has been being dissipated with a very slow rate, so the consolidation deformations have been insignificant. However, there have been reports of noticeable internal deformations in the dam, the crest has also exhibited quick settlements during the first impounding. The main objective of this paper was to identify the deformation mechanism of this dam. For this purpose, the data recorded by its instruments were carefully studied and then a three-dimensional numerical model of the dam was developed. The mechanical behavior of materials was idealized by a hardening strain constitutive model. A numerical method was proposed, based on this constitutive model and Rowe’s stress–dilatancy theory, to simulate the deformation behavior of coarse-grained materials, like rockfills, due to particle size distribution, particle breakage, rotation, and rearrangement under shearing. The results show that significant development of pore pressure in the core and its insignificant dissipation, plastic shear deformations inside the core and extensive collapse settlements of the upstream shell are the main causes influencing the deformation mechanism.

Stone-concrete – material for rockfill dam face zone

The main limitation of the construction of high rockfill dams with a reinforced concrete face is the inevitability of high tensile stresses in the face due to deformations of the dumped rockfill. Modern means of "struggle" consist in face reinforcement, in the face cut by deformation seams, in placing of the "sliding seam" on the border of the screen with the sub-screen zone, but all of them are associated with a significant increase in the cost of the dam. The article presents the results of experimental work on the creation of a special material based on a quarry stone, called stone-concrete, which makes it possible to create a harder, in comparison with the stone outline, base for a reinforced concrete face. The technology of creating such material in the construction of dams consists of watering a layer of crush-stone or gravel-pebbly with a height of up to 0.6 m with a cement-sand mix of a specially selected composition in order to create a uniform conglomerate with predetermined properties.

The impact of active faulting on the geotechnical properties of the Upper Gotvand Dam, southwest Iran

Fault movement in dam foundations is an earthquake hazard feature that may lead to severe structural distortions. Such movements may manifest as rock failures, crushing and displacements of rock masses. Faults with surface breaking and potential block movements are also of considerable interest in the issue of dam safety. The Upper Gotvand Dam is the highest rock fill dam in Iran which was constructed over the Karun River in the Khuzestan Province, southwest Iran. Its location in the Zagros active belt, the most active seismotectonic zone of the country, makes it prone to abutment instability and potential seepage through the foundation and abutments. The dam foundation is on the sandstones of the Agha-Jari Formation while the abutments are composed of rock mass of the Bakhtyari Formation. The right abutment of the dam is highly fractured and displaced due to action of the Pir-Ahmad active fault.. Geotechnical sections along the dam axis and across the right abutment indicate four strike faults near the right bank as well as sharp changes in the dip of bedding along the dam axis. The Agha-Jari layers are tightly folded beneath the dam axis with a 30° inter-limb angle forming a chevron fold. The geomechanical classification of the outcropped rocks is in the range of weak to very weak. The whole region is affected by an N-S basement tectonic lineament introduced in this research as the Lali-Ahvaz trend. Variations in the geotechnical properties of the dam site are mostly due to the movement of the Pir-Ahmad Fault. The activity of the fault should be re-assessed for future operations and producing dam maintenance plans as fault activity could diminish future dam safety.

Integration of creep into a modified hardening soil model for time-dependent analysis of a high rockfill dam

This paper proposes an approach to extend a modified hardening soil model into the time-dependent analysis of high rockfill dams. The key feature of the extended model is the integration of a creep model and the double yield surface elasto-plastic model, via modifying the hardening functions. The integrated model is validated by a laboratory multistage creep test. Results from three-dimensional analyses including the without creep and with creep considerations of the Nam Ngum 2dam have been compared with the in-situ measurements. The prediction of dam deformation can be significantly enhanced by the proposed model.

Influence of core thickness on stability of downstream slope of earth and rockfill dams under end-of-construction and steady-state-seepage: a comparison

The steepness of the slopes of earth and rockfill dam is governed by stability considerations which in turn are influenced by the strength of the core and shell materials as well as their geometry. An analytical study has been undertaken to evaluate and compare the variation in the factor of safety of the downstream slope of a dam on account of variation in the thickness of vertical core for the two conditions, namely, steady-state seepage condition and end-of-construction condition. A 180-m high earth and rockfill dam section, founded on strong base, having section and slopes similar to a high dam in the northern India was used as a base section for analysis. The study shows that as core thickness increases beyond a critical value, it causes a progressive decrease in the stability of downstream slope. This critical core thickness is observed to lie in the range of 50–150% of dam height for both conditions and a core within this zone does not influence stability of downstream slope. The rate of decrease in factor of safety is also observed to be similar in both conditions. The influence of relative strength of shell to core, height of dam and pore water parameter on critical core thickness is highlighted.

Research on the Seepage Safety Monitoring Indexes of the High Core Rockfill Dam

The study on developing the reasonable safety monitoring indexes plays a most importantly role in the health monitoring of high core rockfill dams. However, researches on this topic are relatively scarce both at home and abroad. In this paper, the characteristics and failure modes of seepage in high core rockfill dam are analyzed firstly. Then, a safety monitoring index based on seepage quantity, which reflects the overall seepage behavior, is developed, using the real-time monitoring data and its safety monitoring model. Moreover, another safety monitoring index based on seepage gradient, reflecting the local seepage behavior, is proposed, combining the spatial layout of osmo- meters and local failure mechanisms of core wall. Additionally, one more safety monitoring index based on permeability coefficient, which considers the overall and local seepage behaviors, is developed, on the basis of establishing the finite element analysis model and real-time seepage coefficient inversion analysis model of high core rockfill dam. A case study on these indexes of Nuozhadu high core rockfill dam is developed, which improves the reliability of seepage safety evaluation of the dam.

Seepage Control in a High Concrete Face-Rock Fill Dam Based on the Node Virtual Flow Method

The seepage control system of a high Concrete Face Rock-Fill Dam (CFRD) may have anti-seepage deficiencies during both construction and operation. In order to solve these, the three-dimensional Finite Element Method (FEM) model was built based on dam body filling, anti-seepage system, defect location and bedrock distribution. The seepage field simulation and computation were carried out using an improved node virtual flux method and the zero-thickness crack model theory. The water head distribution, seepage lines and dam leakage field were obtained by simulation under different conditions, and the seepage characteristics during construction and operation were analyzed systematically. Taking a high CFRD as an example, the results showed that during the flood-control construction period, the incomplete nature of the dam face slab can lead to seepage damage near the second seepage control line. Moreover, during operation period; the seepage control system was still effective when the dam face slab was incomplete.

Performance of the reinforced right abutment slope of Zipingpu Dam during magnitude 8.0 earthquake, Wenchuan, China

On 12 May 2008, an earthquake of magnitude 8.0 on the Richter scale occurred at Wenchuan in China. Zipingpu dam also experienced the earthquake. The maximum ground acceleration near the top of the 156 m high rockfill dam exceeded 2 g . The right dam abutment slope, which accommodates all the discharge facilities, remained intact after this severe earthquake. However, the natural slopes on the opposite side of the reservoir were severely damaged. It has been found that the reinforcement provided by more than 1000 prestressed cables in the right abutment slope helped to stabilize it. Measurements from multipoint extensometers and load cells installed in the slope showed that there were sudden changes in displacement and stress during the earthquake. This is clear evidence that reinforcement with anchored cables can be successfully used to stabilize a slope.

A modified dynamic shear modulus model for rockfill materials under a wide range of shear strain amplitudes

High rockfill dams experience a wide range of shear strain amplitudes during earthquakes. To provide more reliable material property descriptions for earthquake response analysis of high rockfill dams, this study investigates the dynamic properties of rockfill materials in a wide strain range by large-scale cyclic triaxial testing with a high-sensitivity laser sensor. The results reveal the considerable increase of shear modulus and decrease of damping ratio with increasing confining pressure for a given initial stress ratio and the significant effect of the initial stress ratio on the small-strain shear modulus and normalized shear modulus. Previously proposed equations were found to imprecisely depict the variation of the dynamic shear modulus of rockfill materials for a wide strain range. Furthermore, the dynamic shear modulus is dependent on the Initial stress ratio in the anisotropic stress condition. Based on the existing hyperbolic model, a modified model for rockfill materials is suggested to accurately estimate the nonlinear behavior. The applicability of the modified model and previous studies for rockfill materials are assessed in the estimation of the normalized shear modulus. The results provide a reference for evaluating the accurate shear modulus in a wide strain range for strong earthquake motions.

Seismic Resistant Effects of Composite Reinforcement on Rockfill Dams Based on Shaking Table Tests

In this article, the seismic resistant effect of a new reinforcement measure on rockfill dams, the Composite Reinforcement, is investigated based on 1-g large-scale shaking table tests. A 1 m high rockfill dam, which is scaled from the Yele rockfill dam in China, is tested by inputting a series of motions designed from a realistic Wenchuan earthquake record. The model dam is divided into two sections, with one section representing a normal rockfill dam (RD) while the other section employing the Composite Reinforcement (composite reinforced rockfill dam (CRRD)). The seismic-resistant effect of the Composite Reinforcement is investigated by comparing the recorded dynamic response of the two dams, in terms of the peak acceleration amplification factor distribution along the dam core, the crest settlement, and the visualized failure pattern. Results show that the application of the Composite Reinforcement can effectively mitigate the seismically induced deformation of the rockfill dam by reducing the peak crest acceleration and residual crest settlement by 18% and 55%, respectively, when subjected to a 0.5 g input motion. The investigation of the captured failure pattern on the two dams further indicates the effective reinforcing effect of the Composite Reinforcement on preventing the sliding failures of rockfill materials in the top 20% height of the dam body.

A modified elasto-plastic model with double yield surfaces and considering particle breakage for the settlement analysis of high rockfill dams

This paper improves the elasto-plastic model with double yield surfaces in the context of the hardening soil model for the simulation of the settlement behavior of high rockfill dams. The stress-dependent stiffness values (E50 and Eoed control the shear hardening and the cap yield surfaces, respectively) are modified to exhibit different degrees of evolution with changes in the stress state. A modification of Rowe's stress-dilatancy theory is proposed to account for the influence of particle breakage. Good quantitative agreement between simulated and measured stress-strain relationships can be achieved; in particular, the volumetric strain is much improved from the original model. The developed model is applied to predict the settlement of Nam Ngum 2, a 182 m high rockfill dam, during the construction stage, in conjunction with a three-Dimensional (3D) Finite Element (FE) analysis. The findings show that a good agreement between computed settlements and dam field monitoring data can be achieved.

Parameters inversion of high central core rockfill dams based on a novel genetic algorithm

Parameters identification of rockfill materials is a crucial issue for high rockfill dams. Because of the scale effect, random sampling and sample disturbance, it is difficult to obtain the actual mechanical properties of rockfill from laboratory tests. Parameters inversion based on in situ monitoring data has been proven to be an efficient method for identifying the exact parameters of the rockfill. In this paper, we propose a modified genetic algorithm to solve the high-dimension multimodal and nonlinear optimal parameters inversion problem. A novel crossover operator based on the sum of differences in gene fragments (SoDX) is proposed, inspired by the cloning of superior genes in genetic engineering. The crossover points are selected according to the difference in the gene fragments, defining the adaptive length. The crossover operator increases the speed and accuracy of algorithm convergence by reducing the inbreeding and enhancing the global search capability of the genetic algorithm. This algorithm is compared with two existing crossover operators. The modified genetic algorithm is then used in combination with radial basis function neural networks (RBFNN) to perform the parameters back analysis of a high central earth core rockfill dam. The settlements simulated using the identified parameters show good agreement with the monitoring data, illustrating that the back analysis is reasonable and accurate. The proposed genetic algorithm has considerable superiority for nonlinear multimodal parameter identification problems.

An algorithm in generalized coordinate system and its application to reliability analysis of seismic slope stability of high rockfill dams

This paper introduced generalized coordinate system into reliability analysis involving correlated random variables. Correlation between two random variables is reflected by rotation of the corresponding coordinate axes and correlation coefficient between the two variables is identical to cosine of angle between the axes. The equivalent matrix formulation for the Hasofer–Lind reliability index represents the shortest distance from the failure surface to the origin in the generalized coordinate system of standardized normal variables. A simple optimization algorithm for reliability computing was established based on the perspective of reliability index and the gradient of limit state function in generalized coordinate system. Based on the algorithm and the Ordinary method of slices, a probabilistic approach for evaluating the seismic slope stability of high rockfill dams was developed and was applied to the slope reliability analysis of an actual high rockfill dam under seismic loading. The results of the slope reliability analysis are discussed and conclusions are presented in this paper.