High Rockfill Dam Research Articles

Elastic-plastic-creep behavior of high rockfill dams: a case study on Lianghekou CRFD

The instantaneous loading and time-dependent creep deformations occur simultaneously during the lifetime of rockfill dams, but their proportions in monitoring records are still unclear. In previous works, loading and creep were generally simulated independently in turn. This uncoupled method may induce misleading conclusions in interpreting dam behaviors. In this paper, an advanced elastic-plastic-creep model is applied to capture the interaction of loading and creep under complex conditions with varying loading rates based on a benchmark example of 295m-high Lianghekou core wall rockfill dam (CRFD). The instantaneous elastic-plastic parameters of rockfills are calibrated by large-scale triaxial tests (including 300mm and 800mm in diameter) and the time-dependent creep parameters are obtained by back analyses on monitoring records. A series of numerical analyses on the dam are conducted. The loading-creep coupling process of rockfills is successfully captured and the instantaneous and time-dependent creep deformations are explicitly separated. The 800mm-diameter triaxial test weakens the size effect and provides an acceptable representation for the instantaneous behaviors of prototype rockfills. The good agreement between the calculations of the elastic-plastic-creep coupling analysis and measurements indicates creep contributes about 8~15% to total construction deformation. The work provides guides for properly interpreting and evaluating actual dam behaviors.

A Methodology for Modeling a Multi-Dimensional Joint Distribution of Parameters Based on Small-Sample Data, and Its Application in High Rockfill Dams

A Methodology for Modeling a Multi-Dimensional Joint Distribution of Parameters Based on Small-Sample Data, and Its Application in High Rockfill Dams

A novel finite element limit equilibrium method and its application in instability analysis for 3-D high core rockfill dams

The safe operation of high rockfill dams is an important issue related to human life and property safety. However, the stability analysis of high core rockfill dams with complex spatial morphology is mostly confined to two-dimensional, and appropriate stability analysis methods are scarce. Therefore, it is necessary to develop the three-dimensional stability analysis method for high core rockfill dams and study the spatial stability mechanism after impoundment. Firstly, a finite element limit equilibrium framework suitable for stability analysis of high rockfill dams is introduced, and the horn-shaped three-dimensional failure mechanism is presented for optimization. Then, according to the statistical results of the actual core rockfill dam above 100 m, 15 high dam models with actual Duncan-Chang parameters between 100 m and 300 m are established to study the three-dimensional instability mechanism. Meanwhile, grey relation analysis (GRA) is used for quantitative analysis of stability sensitive factors. Finally, the stability analysis of the Quxue core rockfill dam (173.2 m) was completed within the established stability framework. The results show that the combined failure mechanism with the horn-shaped is suitable for dam stability analysis, and with the increase of height and slope ratio of dam, the most dangerous sliding surface evolves to shallow layer. In addition, GRA results show that slope ratio is the most sensitive parameter compared to dam height and material parameters. The practical engineering stability results of Quxue show that the research results can provide a reliable reference for the stability of the high core rockfill dam.

A New Method for the Compaction Quality Inspection of High Rockfill Dams Based on 3D Laser Scanning Technology

The compaction quality is directly related to the deformation and stability of the rockfill dam. Measuring the test pit volume efficiently and accurately is the most critical step during the compaction quality inspection. A new method for calculating the test pit volume based on point cloud data is proposed. An auxiliary device that can change the scanning distance and angle of the handheld 3D laser scanner is developed to collect the initial point cloud. The segmentation method of the initial point cloud data including the test pit and the compaction surface outside the pit is to divide the data into two parts according to the order number of the segmentation point, after slicing and sorting point clouds, which is the key to ensuring the computational precision. The segmentation points are the adjacent two points with the greatest order number difference in these point clouds whose distance from the line connecting the end points of the slicing point clouds is less than dz. The compaction surface point clouds are used to construct a plane by the least-squares algorithm so that the closed three-dimensional model is formed by registering it with the test pit point clouds. After converting the test pit surface to the horizontal plane by the Rodrigues formula, the test pit point clouds are divided into n2 parts with equal projection areas on the horizontal plane, and n2 prisms are constructed using them and their projection areas. The test pit volume is the sum of the intersection space volumes of all prisms and the test pit model, and the intersection space is determined by comparing the Z-values of point clouds. The new method was programmed in MATLAB and applied to the Shuangjiangkou rockfill dam with a height of 315 m. The relative error of volume results between the new method and the old water-filling method is 0.14–2.31%. The cause of the error is analyzed, and it is proved that the results of the new method are closer to the real volume of the test pit in theory. This method reduces the inspection cost but greatly improves the level of precision, efficiency, and intelligence for compaction quality inspection.

Safety criteria for slope stability of high rockfill dams based on the generalized reliability ratio of safety margin

Safety criteria for slope stability of high rockfill dams based on the generalized reliability ratio of safety margin

Late-stage diversion risk assessment for high dams considering early initial impoundment: a case study of Lianghekou Station, China

Early initial impoundment can generate additional revenue but bring more flood risk in late-stage construction diversion. In view of the possible flood risk and catastrophic consequences caused by high dam failures induced by early impoundment, a comprehensive assessment is proposed. Taking the Lianghekou high rockfill dam on the Yalong River, southwest China, as an example, this study established the late-stage diversion risk model and predicted the failure probabilities for the original, 15 days ahead, and 30 days ahead schemes varied with the initial impoundment time using the Monte Carlo method. Then, considering overtopping-induced gradual breaking of rockfill dams, the NWS dam-break flood forecasting model (DAMBRK) was used to estimate the break development and the outflow hydrograph. Due to no significant differences being found in the outflow hydrographs of the three schemes, life loss was used an index for the consequences of inundation. Combining the failure probability, life loss, and early impoundment revenues brought by earlier power generation, a satisfied initial impoundment scheme was acquired using the multi-objective decision model. The results revealed this method can find a reasonable initial impoundment time in view of the late-stage diversion risk assessment.

The Use of Shape Accel Array for Deformation Monitoring and Parameter Inversion of a 300 m Ultrahigh Rockfill Dam

The global construction of rockfill dams has now surpassed the 300 m height level. Despite great achievements in dam design and construction, monitoring techniques have lagged behind the development of high rockfill dams. Existing deformation monitoring techniques are ill-suited to the high earth and water pressures, and extended monitoring periods are required for ultrahigh rockfill dams. This study introduces, for the first time, the use of a shape accel array (SAA) to monitor internal displacement in a 300 m high earth core rockfill dam. The SAA employs a rope-like array of capacitive MEMS accelerometers for deformation measurement. Compared to conventional monitoring techniques, SAA is a data-intensive monitoring technique. Based on the intensive data obtained from SAA, we employed a parameter inversion method, utilizing multiobjective optimization algorithm, the nondominated sorting genetic algorithm-III (NSGA-III), to inverse the constitutive model parameters of the rockfill dam. The multiobjective parameter inversion method maximizes the use of multisource monitoring data for predicting rockfill dam deformation.

Analysis of the behavior of a high earth-core rockfill dam considering particle breakage

This paper presents a finite element analysis for the behavior of the Lianghekou high earth-core rockfill dam, which was just completed in construction in China. An elastoplastic constitutive model that can account for the degradation of rockfills due to particle breakage (hhu-SH-breakage model) was applied to simulate the mechanical behavior of the rockfills. The earth-core wall was analyzed by using the modified Cam-clay model combined with the Biot’s consolidation theory. Numerical results are in good agreement with in-situ measurements during construction, indicating the reasonability of the numerical analysis. Based on the breakage-packing concept, which is able to extract the breakage-induced deformation from the total deformation, numerical analysis showed that the breakage-induced settlement for the extra high rockfill dam is not negligible. Inspired by the sensitivity analysis using the hhu-SH-breakage model, engineering advices were proposed to reduce the settlement of high rockfill dams.

Evaluation of groundwater flow through a high rockfill dam foundation in karst area in response to reservoir impoundment

Constructing high dams in karst valleys remains a challenging issue as karst conduits provide preferential channels for flow through the foundations. The uncertainty of the karst system drastically increases the risk of leakage and hence the difficulty in seepage control at the foundations. This study examined the transient flow behaviors through a karst foundation on which a rockfill dam with a height of 219 m had been constructed. During reservoir filling, an abnormal pressure rise occurred in the foundation downstream the grout curtains, typically with a magnitude of 53∼69 m higher than the pore pressure head at the neighboring positions. This phenomenon was comprehensively investigated by site characterization, inverse modelling, numerical simulation and cross-correlation analysis, demonstrating that the abnormal pressure rise is locally induced by eroded fault (left bank) or contact zones between karst formations (right bank). These conduits have an effective permeability value one order of magnitude higher than that of the karst formations, which quickly transmit the reservoir pressure pulse across the grout curtains, as evidenced by a higher cross-correlation and a smaller lag between pool level and piezometer measurements. The grout curtains have sufficiently low permeability in limiting the amount of leakage through the foundation, and hence ensure the safety of the reservoir operation in spite of the pressure rise. This study confirms the applicability of the equivalent continuum model in addressing groundwater flow problems in karst formations, as long as the site conditions are properly characterized.

An improved generalized plasticity model for rockfill materials and its experimental and numerical verification

PurposeThe stress–strain behaviors of rockfill materials in dams are significantly affected by the anisotropy and grain crushing. However, these factors are rarely considered in numerical simulations of high rockfill dams. This study intends to develop a reasonable and practical constitutive model for rockfill materials to overcome the above problems.Design/methodology/approachThe effects of anisotropy and grain crushing are comprehensively considered by the spatial position of the reference state line. After the improved generalized plasticity model for rockfill materials (referred to as the PZR model) is developed and verified by laboratory tests, it is used with the finite element method to simulate the stress–strain behaviors of the Nuozhadu high core rockfill dam.FindingsThe simulated results agree well with the laboratory tests data and the situ monitoring data, verifying the reliability and practicability of the developed PZR model.Originality/valueA new anisotropic state parameter is proposed to reflect the nonmonotonic variation in the strength as the major principal stress direction angle varies. This advantage is verified by the simulation of a set of conventional triaxial tests with different inclination angles of the compaction plane. 2) This is the first time that the elastoplastic model is verified by the situ monitoring data of high core rockfill dams. The numerical simulation results show that the PZR model can well reflect the stress–strain characteristics of rockfill materials in high core rockfill dams and is better than the traditional EB model.

Effect of size and strain rate on particle strength and stress–strain properties of rockfill materials

The stress-strain properties of the rockfill materials under cyclic loading conditions are critical for the seismic safety analysis of dams. However, due to the effect of size and strain rate, the parameters obtained from the scaled laboratory tests may not accurately calculate the earthquake response. In the presented study, a novel approach has been developed to infer the prototype parameters based on the single particle strength. Firstly, a series of particle crushing tests with different sizes and loading rates were conducted. The results show that as the strain rate increases, the particle strength enhances and the size effect on particle strength gradually weakens. According to the established particle strength model, it is assumed that two specimens have homothetic particle size distributions and the same compaction, and is geometrically similar, then the size effect relations on macroscopic stress and strain tensors can be derived, a set of monotonic and cyclic triaxial tests are used to validate the approach. Furthermore, the effect of particle size and strain rate on the equivalent linear model is determined, the small-strain modulus parameter K obtained from the laboratory test should be modified. This study provides a reference to the engineering design and seismic safety evaluation of high rockfill dams.

Large-scale shaking table model tests and numerical simulation for composite reinforcement aseismic measure of high earth rockfill dam

<p indent="0mm">The aseismic safety of high earth rockfill dams is an important problem in engineering construction in the intensive earthquake area of West China. A composite reinforcement aseismic measure (CRAM) for high earth rockfill dams was developed. The CRAM’s effectiveness and reliability were validated using comparative model tests on a large-scale shaking table. Numerical simulation was used to examine the CRAM’s reinforcement mechanism. The results demonstrated that the CRAM had an inhibiting effect on the acceleration response; the CRAM can effectively inhibit the loosening and slipping of rockfill at the crest and reduce earthquake-induced permanent deformation. The numerical simulation also revealed that the shear strain amplitude and distribution were significantly altered. A slightly larger shear strain appeared at the front of the CRAM’s internal reinforcement materials, and the dam slope’s potential sliding surface was transformed from shallow sliding to deep sliding. As a result, the CRAM can improve the high earth rockfill dam’s seismic safety. The research results can provide a reference for the seismic design of the high rockfill dam in the intensive earthquake area.

Criteria for ultimate aseismic capacity of high rockfill dam

<p indent="0mm">The ultimate aseismic capacity is important to evaluate the seismic safety of a rockfill dam. However, no specification in China explicitly stipulates the criteria for the ultimate aseismic capacity of a rockfill dam. Existing evaluation factors and their indices to represent earthquake-induced damage to rockfill dams are not unified, and there is a problem with the safety degrees obtained by the indexes of different evaluation factors not being coordinated. In this study, a large number of systematic analyses of overall elastic-plastic deformation and slip deformation of high rockfill dams (height &gt; <sc>200 m)</sc> under earthquake are performed in addition to a comparative study of measured engineering analysis. Based on the above studies, four basic principles for determining the criteria for the ultimate aseismic capacity of a high rockfill dam are proposed: strictly following the mapping relationship between the relative settlement ratio of dam crest and the damage degree of dams under earthquake, ensuring that the dam can not be a collapse in extreme earthquakes, taking the relative settlement ratio of dam crest as the key control evaluation factor, and ensuring the coordination of different evaluation factors such as the relative settlement ratio of dam crest and the slip deformation of dam slope. Finally, the criteria for the ultimate aseismic capacity of a high concrete face rockfill dam and a core-wall rockfill dam under earthquake conditions are proposed. The findings of the study could provide an important standard basis for determining the ultimate aseismic capacity of a high rockfill dam.

Packing, compressibility, and crushability of rockfill materials with polydisperse particle size distributions and implications for dam engineering

In rockfill dam engineering, particle breakage of rockfill materials is one of the major factors resulting in dam settlement. In this study, one-dimensional compression tests on a series of coarse granular materials with artificially-graded particle size distributions (PSDs) were carried out. The tests focused on understanding the role of initial PSDs in the dense packing density, compressibility and crushability of coarse granular materials. The effects of fractal dimension (D) and size polydispersity (θ) of PSDs were quantitatively analyzed. Two different loading stages were identified from the logarithms of the stress–strain relationships, with the turning point marked as the yield stress. A similar effect of initial PSDs was observed on the packing density and low-pressure modulus of coarse granular materials. The packing density and low-pressure modulus increased monotonically with θ, and their peak values were attained at a D value of approximately 2.2. However, there was no unique correspondence between the dense packing density and low-pressure modulus. The particle breakage was influenced differently by the initial PSDs, and it decreased with the values of D and θ. The emergence of the unique ultimate state was also identified from both the compression curves and PSDs of the samples after the tests. The potential implications of the test results in the design of both low and high rockfill dams were also demonstrated.

Post-construction safety assessment of a high concrete face rockfill dam

The most important issue regarding the safety and performance of concrete face rockfill dams (CFRDs) is to determine stresses and deformations. However, predictions of crest settlements of CFRDs are usually performed using empirical relationships. In recent years, CFRDs have been constructed much higher and at more complicated topographical and geological dam sites, so numerical analysis is required to evaluate the stress and deformations in the entire dam body. Also, assessing long-term rockfill behaviour and the concrete face membrane crack potential are important for post-construction dam safety. This study evaluates post-construction deformations and crest settlements of a high CFRD under two different loading cases, considering the non-linear elasto-plastic behaviour of the rockfill structure. As a constitutive model, the Duncan–Chang hyperbolic stress–strain model was applied in finite-element simulations considering the failure criterion is isotropic and hardening. Calibration of the rockfill's hyperbolic parameters was performed by comparing the calculated displacements with actual settlement measurements. Computed crest settlements were also compared with those of some CFRDs given in the literature. Calculated crest settlement and other deformations are in good agreement with the rockfill settlement measurements and in acceptable ranges, and do not threaten the dam's safety.

Operation Performance and Seepage Flow of Impervious Body in Blast-Fill Dams Using Discrete Element Method and Measured Data

As a high-efficiency and low-investment method of dam construction, blast-fill dams have been widely used in water conservancy, mining engineering, soil and water conservation, disaster prevention and other projects. Through collecting data on the main projects of the blast-fill dams, the characteristics and development trends of blast-fill dams are analyzed in detail. Meanwhile, the design requirements of impervious bodies in the initial and reinforcement stages are systematically reviewed. Subsequently, with measured data of a typical blast-fill dam, the structural characteristics of blast-fill dams after blasting and the validity of the phreatic line height after reinforcement are analyzed using the discrete element method. We conclude that an appropriate construction schedule and flexible impervious material are critical features of the impervious body for a dam with large deformation. When the dam deformation is stable, a secondary treatment should be considered for the impervious body to improve the dam safety. The design ideas for the impervious body of blast-fill dams are also applicable to other dam types with large deformation for risk reduction, such as high rockfill dams, soft-rock dams and tailings dams, and have a certain significance for reference in the treatment of landslides and confined lakes.

Experimental study on mechanical properties of core wall gravel soil of 300-m super high rockfill dam

Experimental study on mechanical properties of core wall gravel soil of 300-m super high rockfill dam

Internal deformation monitoring for earth-rockfill dam via high-precision flexible pipeline measurements

The internal deformation of high earth-rockfill dam is an important parameter that reflects its safety. There is an urgent need to have a precise and reliable internal deformation monitoring technology due to the limitation of traditional sensors. We propose a novel method to monitor internal deformation of dam through continuous measurement of flexible pipelines that embedded in the dam. A pipeline robot is invented, with one inertial measurement unit and multiple odometers, to measure the deformation of the customized pipeline system. The proposed method is verified through filed tests and real dam in suit experiments. The results show that the relative deformation measurement precision is approximately 1/100,000 the length of the pipeline and millimeter-level deformation measurement over 300 m can be realized. This technology is promising for internal deformation monitoring of high-rockfill dams. Further research will focus on the miniaturization of measurement system and reliability improvement of this technology.

Experimental Investigation on the Shear Behavior of Interface between High Plastic Clay and Concrete

The Lianghekou earth core rockfill dam to be built in China will be the third highest rockfill dam in the world. This study presents the results of a series of direct shear tests between high plastic clay and concrete to study the shear behavior of contact clay-concrete cushion interface of Lianghekou dam. Results showed that water content and normal stress are significant factors affecting the shear behavior of the interface. The higher shear strength is related to lower water content and higher normal stress, and the shear strength can be formulated by the bifold-line type Mohr–Coulomb strength criterion. It is also found that the interface exhibits mainly two kinds of shear failure modes, that is, sliding failure along the concrete surface and shear failure in the clay matrix nearby the interface. Moreover, a nonlinear elastic model is proposed to simulate the shear behavior of the interface, of which parameters can be quickly estimated by water content. The simulation of the model is compared with the experimental results, and the results show that the model is reasonable and practical.

As-Built Inventory and Deformation Analysis of a High Rockfill Dam under Construction with Terrestrial Laser Scanning.

The construction of large earth/rock fill dams, albeit its remarkable progress, still relies largely on past experiences. Therefore, a comprehensive yet dependable monitoring program is particularly beneficial for guiding the practice. However, conventional measurements can only produce limited discrete data. This paper exploits the potential of the terrestrial laser scanning (TLS) for an accurate inventory of as-built states of a concrete-faced rockfill dam under construction and for a full-field analysis of the 3D deformation pattern over its upstream face. For the former, a well-designed 3D geodetic system, with a particular consideration of the topography, promises a regulated acquisition of high-quality and blind-zone-free point cloud at field and also eases the cumbersome data registration process while maintaining its precision in house. For the latter, a problem-tailored processing pipeline is proposed for deformation extraction. Its core idea is to achieve a highly precise alignment of the point clouds with Iterative Closed Point algorithms from different epochs in datum areas that displays a featured, undeformed geometry at stable positions across epochs. Then, the alignment transformation matrix is applied to the point clouds of respective upstream face for each epoch, followed by pairwise comparisons of multiple adjusted point clouds for deformation evaluation. A processing pipeline is used to exploit the peal scene data redundancy of the GLQ dam acquired at six different epochs. Statistical analysis shows that satisfactory accuracy for deformation detection can be repeatably achieved, regardless of the scanner’s positioning uncertainties. The obtained 3D deformation patterns are characterised by three different zones: practically undeformed, outward and inward deformed zones. Their evolutions comply well with real construction stages and unique 3D valley topography. Abundant deformation results highlight the potential of TLS combined with the proposed data processing pipeline for cost-efficient monitoring of huge infrastructures compared to conventional labor-intense measurements.