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.

Toe drain size and slope stability of homogeneous embankment dam under rapid drawdown.

The slope stability of an embankment dam has been always a serious concern of any design team. Unfortunately, the information on the potential influence of a toe drain size on the slope stability of an embankment dam under rapid drawdown conditions is still scarce. This study investigated the potential effect of a toe drain size on the slope stability of a homogeneous embankment dam under rapid drawdown conditions. Three different sizes (5m, 10m, and 15m) of the toe drain were investigated under instantaneous (worst scenario) and 5 days (more realistic) drawdown rates with the help of numerical modeling in GeoStudio. From the results, it was observed that the pore-water pressures at the upstream face of the embankment decreased with the increase in the toe drain size, while the pore-water pressures at the downstream toe were increasing with the increase in the toe drain size. The factor of safety values were also observed to be affected by the changes in the toe drain size.

Monitoring of Water Level Change in a Dam from High-Resolution SAR Data

Accurate measurement of water levels and variations in lakes and reservoirs is crucial for water management. The retrieval of the accurate variations in water levels in lakes and reservoirs with small widths from high-resolution synthetic aperture radar (SAR) images such as the TerraSAR add-on for Digital Elevation Measurements (TanDEM-X) and COnstellation of small Satellites for the Mediterranean basin Observation (COSMO-SkyMed) are presented here. A detailed digital surface model (DSM) for the upstream face of the dam was constructed using SAR interferometry with TanDEM-X data to estimate the water level. The elevation of the waterline below that of the interferometric SAR (InSAR) DSM was estimated based on upstream face modeling. The waterline boundary detected using the SAR Edge Detection Hough Transform algorithm was applied to the restored DSM. The SAR-derived water level variations showed a high correlation coefficient of 0.99 and a gradient of 1.08 with the gauged data. The difference between the gauged data and SAR-derived data was within ±1 m, and the standard deviation of the residual was 0.60 m. These results suggest that water level estimation can be used as an operational supplement for traditional gauged data at remote sites.

Discharge coefficients for ogee weirs including the effects of a sloping upstream face

Discharge coefficients (C0) for ogee weirs are essential factors for predicting the discharge-head relationship. The present study investigates three influences on the C0: effect of approach depth, weir upstream face slope, and the actual head, which may differ from the design head. This study uses experimental data with multiple non-linear regression techniques and Gene Expression Programming (GEP) models that are applied to introduce practical equations that can be used for design. Results show that the GEP method is superior to the regression analysis for predicting the discharge coefficient. Performance criteria for GEP are R2 = 0.995, RMSE = 0.021 and MAE = 0.015. Design examples are presented that show that the proposed GEP equation correlates well with the data and eliminates linear interpolation using existing graphs.

Dynamic Stress and Displacement Fields on Concrete Gravity Dams due to Harmonic Ground Motion

The partial differential equations (PDE) of equilibrium governing the natural vibrations of concrete gravity dams were derived in this work such that the fluid structure interactions were accounted for. The displacement formulation is a system of two coupled PDE in two unknown displacement components. For seismic ground motion assumed to be horizontal harmonic motion whose amplitude and period are known, the system of two coupled PDEs were solved subject to the boundary conditions using the method of undetermined parameters. In applying the method of undetermined parameters to the PDE, displacement shape functions constructed to satisfy the displacement boundary conditions were used in assuming the trial dynamic displacement fields in terms of two unknown parameters that were determined by substitution into the governing equations. Conditions for the trial dynamic displacement fields to be solutions to the governing PDE were sought by solving the resulting system of equations. The problem reduced to an algebraic eigenvalue eigenvector problem which was solved for nontrivial cases to obtain the characteristic frequency equation and the eigenvalues. Modal superposition technique was employed to obtain the general solution for the displacement fields. The use of the displacement boundary conditions at the upstream face and Fourier series theory yielded the dynamic displacement field components, and the dynamic stress fields. The maximum value of the hydrodynamic pressure distribution on the upstream face is found to occur at the bottom of the dam and is found mathematically to be a convergent series of infinite terms. The maximum hydrodynamic force was calculated by integration of the hydrodynamic pressure distribution over the upstream face of the dam, and found to be a convergent series. Values of the maximum hydrodynamic force computed in this work agree with solutions from the technical literature.

Numerical Simulation Study on Root Stones Loss in Dam Buttress Engineering

In order to study the loss of root stones under action of water flow in dam buttress, based on Flow-3D, a mathematical model was established. At first, the physical experiment was carried out about water drag force on a 0.04 m×0.04 m×0.04 m cubic block. And then a numerical flume model about this experiment was established in Flow-3D software. The values of drag force were compared between the numerical and experimental results, and the percentage of error was less than 5%. Thus, the numerical model in Flow-3D was accurate and available. Then, a numerical simulation on root stones loss in an actual dam buttress project was carried out. Since the actual flow is turbulent, the RNGk-εturbulence model was used. And VOF method, FAVOR technology, and GMO model were also used in this simulation. The numerical results showed flow depth, pressure, velocity, turbulent energy, and root stones loss. Because water level of the inflow increased with time continuously, flow depth and velocity also increased, and the root stones would be lost. The increase in flow velocity was the fastest in the dam head, and the start time of root stones loss was also the earliest. The most serious area of root stones loss is the dam head, and the serious second area is the upper cross corner. Those root stones would have the farthest lost distance in the dam head. The root stones loss was also serous in the upstream face. However, the root stones in the upstream face and the down cross corner were less affected by water flow, so there were no root stones loss phenomena. Thus, in the actual project, the dam head, the upper cross corner, and the upstream face should get more attention.

Numerical Modeling of Flow Over a Rectangular Broad-Crested Weir with a Sloped Upstream Face

The objective of this study was to evaluate the effect of the upstream angle on flow over a trapezoidal broad-crested weir based on numerical simulations using the open-source toolbox OpenFOAM. Eight trapezoidal broad-crested weir configurations with different upstream face angles (θ = 10°, 15°, 22.5°, 30°, 45°, 60°, 75°, 90°) were investigated under free-flow conditions. The volume-of-fluid (VOF) method and two turbulence models (the standard k-ε model and the SST k-w model) were employed in the numerical simulations. The numerical results were compared with the experimental results obtained from published papers. The root mean square error (RMSE) and the mean absolute percent error (MAPE) were used to evaluate the accuracy of the numerical results. The statistical results show that RMSE and MAPE values of the standard k-ε model are 0.35–0.67% and 0.50–1.48%, respectively; the RMSE and MAPE values of the SST k-w model are 0.25–0.66% and 0.55–1.41%, respectively. Additionally, the effects of the upstream face angle on the flow features, including the discharge coefficient and the flow separation zone, were also discussed in the present study.

Analytical Expressions of Hydro-Seismic Forces on Dams

Analytical expressions for the determination of hydro-seismic forces acting on a rigid dam with irregular upstream face geometry in presence of a compressible viscous fluid are derived through a linear combination of the natural modes of water in the reservoir based on a boundary method making use of complete sets of complex T-functions.Analytical expressions for the determination of hydro-seismic forces acting on a rigid dam with irregular upstream face geometry in presence of a compressible viscous fluid are derived through a linear combination of the natural modes of water in the reservoir based on a boundary method making use of complete sets of complex T-functions. The formulas obtained for distributions of both shear forces and overturning moments are simple, computationally effective and useful for the preliminary design of dams. They show clearly the separate and combined effects of compressibility and viscosity of water. They also have the advantage of being able to cover a wide range of excitation frequencies even beyond the cut-off frequencies of the natural modes of the reservoir. Key results obtained using the proposed analytical expressions of the hydrodynamic forces are validated using numerical and experimental solutions published for some particular cases available in the specialized literature.