Effects of core characteristics on seepage through earth dams

In this research, SEEP2D and SEEP/W numerical models are used to simulate seepage through earth dams with internal cores. In order to evaluate the two models' performance, they were compared in cases with no, vertical, and wedge-shaped cores. SEEP/W was then used to study further cases due to its accuracy in drawing the phreatic line within the core zone. The effect of the core's characteristics on the amount of discharge, and the phreatic line's levels at the core's upstream and downstream faces were investigated. Four core types – vertical, wedge-shaped, upstream inclined, and downstream inclined – were considered. Different hydraulic conductivities, upper widths, and core slopes were also evaluated. The wedge-shaped core is the most effective of those investigated in reducing seepage discharge and the phreatic line's level at the core's downstream face, the vertical core came second. Design equations are provided for all the core shapes considered in the study.

Analysis and Estimation of Seepage Through Earth Dams with Internal Cut Off

The study of seepage through earth-fill dams is very important for the constructed dams to ensure that the control of seepage is sufficient for the safe and sustainable operation of the dam. It is also important in the design and construction of new dams to ensure that the seepage through and under the dam will be well controlled. Construction horizontal, inclined, trapezoidal or pipe filters one of the dam protection methods. Cut off also can be constructed to minimize seepage discharge directed to the downstream face of the dam. Seepage through an earth dam with internal cut off is experimentally studied in the laboratory of Irrigation Engineering and Hydraulics Department, Faculty of Engineering, Alexandria University, Egypt on a Hele-Shaw model. Also, using computer program SEEP/W (which is a sub-program of Geo-Studio). The experimental and numerical analyses of seepage through earth-fill dam with internal cut off is conducted. Results from solutions are compared with each other.

Free Flow and Discharge Characteristics of Trapezoidal-Shaped Weirs

A number of studies have considered the effects of weir design variations on the free- and submerged-flow characteristics of trapezoidal broad-crested weirs. It appears that the hydraulics of short-crested weir flows have received little attention; thus, the current knowledge is incomplete. By systematically analyzing a large set of experimental data, the present study aims to fill in this knowledge gap and to provide a complete description of the discharge characteristics of trapezoidal-shaped weirs, including the salient features of two-dimensional weir flows. The analysis of the axial free-surface profiles for short-crested weir flows attested that the location of the nearest station for the correct measurement of the overflow depth under free-flow conditions is at η0 from the heel of the weir, where η0 is the upstream free-surface elevation. Additionally, an empirical equation for the free-flow discharge coefficient is proposed as being valid for a trapezoidal-shaped weir with varying upstream- and downstream-face slopes. The results of this investigation reveal that the streamline curvature and the slopes of the upstream and downstream weir faces significantly affect the streamwise flow patterns and, hence, the free-flow discharge.

Experimental Tests on a Small-Scale Model of a Mine Stope to Study the Behavior of Waste Rock Barricades during Backfilling

This paper presents a reduced-scale physical model of a mine stope used to reproduce the underground stope backfilling practiced in some Canadian mines. The objective is to study the geomechanical behavior of the waste rock barricades in interaction with the mine backfill. The instrumentations, along with visual observations and preliminary results, are presented. The main results demonstrated that: (i) the stability of the barricade depends on its physical properties (e.g., size, location, particles gradation and compaction) and the frictional behavior at the barricade/drift walls interface, and (ii) for two backfill formulations, cemented and uncemented, prepared with 70% of solid mass concentration, the volumetric strain due to self-weight consolidation of the backfilled room was higher for uncemented backfill (16%) than for the cemented one (4.5%). In addition, the results highlighted the importance of using shotcrete around the downstream face of the barricade, mostly at the top, to close the gaps and bind the barricade particles, which improves its stability.

Velocity rate of screw streams in the site of submerged vanes

Introduction. The formation mechanism of longitudinal screw streams (LSS) along the upstream and downstream face of submerged vanes (SV) is considered. Acting along with the artificial transversal circulation (ATC), these streams protect the water intake from the channel sediments. The intensities and directions of LSS and ATC depend on the regime of flow, the planned-geometric characteristics of the vanes. Recommendations concerning the purpose of SV’s rational characteristics in the aspect of steady formation of all three protective streams in the flow for river damless intakes are contradictory and require clarification. The purpose of the study is to analyze the velocity rate of the LSS in SV site at various planned-geometric characteristics of the vane and hydraulic modes of its operation based on a physical model with an erosion-resistant channel (without water separation), as well as to determine an efficient range of setting angles of the SV’s to the tray board in terms of formation of steady and intensive LSS along the upstream and downstream face of the vane. Materials and methods. Model physical hydraulic studies and theoretical calculations were used. Five hydraulic modes of SV’s operation were studied, with various planned-geometric characteristics, using the physical model with an erosion-resistant channel (without water separation). The obtained experimental data were summarized and analyzed. Results. Results of laboratory hydraulic studies of LSS velocity rate in LSS site were presented. Experimental graphic dependence diagrams were plotted characterizing the intensity and direction of the LSS along upstream and downstream faces of the vane. Conclusions. A determining influence of the setting angle of the vane to the tray board (bank line) on the intensity and direction of the LSS in SV’s site was found out. Experimentally, an efficient SV setting angle was determined in terms of the formation of steady and intensive LSS along the upstream and the downstream vane face with practically usable direction.

Experimental evidence dynamic pressures reduction on plunge pool floors downstream flip bucket for increasing downstream face slopes

In this research, the ejecting jet from a flip bucket downstream of a chute spillway was simulated using physical modeling. The effects of influencing parameters upon fluctuations and extreme values of dynamic pressure were investigated. The angles of 0°, 30°, 45°, and 60° were adopted for the mobile bottom wall. The discharges were set as 67, 86, 161, and 184 litre/s and the depths of water cushion on the mobile bottom wall were set as 0, 15, 30, and 45 cm. The method suggested by Castillo for computation of fluctuating coefficient of dynamic pressure (see Castillo (2007) Pressure characterization of undeveloped and developed jets in shallow and deep pool. Proceedings of the Congress-International Association for Hydraulic Research32 (2), 645) was validated via the laboratory data. The results showed that the increase in water cushion depth downstream has led to a decrease in mean pressure and in pressure fluctuations. The analyses showed that the fluctuating pressure coefficient was a function of water cushion depth, and its maximum value was taken when there was a water cushion on the mobile bottom wall. With an increase in discharge and mobile bottom wall angle, the maximum value of the fluctuating coefficient occurred in less water cushion depth. Moreover, with the growth of discharge, the maximum positive and negative fluctuations of the pressure increased first and then decreased.

Application of GPR in assessing of concrete dam structures health

<p>In this paper an application of GPR in the analysis of concrete structure is presented. Scanning is done as a part of preparation for mitigation works of dam ’Grančarevo’. The goal was to inspect existing small cracks and leakages. The dam is arc-shaped concrete dam with double curvatures. It is operational since 1968, and is situated 18km downstream from the wellspring of Trebišnjica river and 17km upstream from the town Trebinje, in Bosnia and Herzegovina. Relative height of the dam is 123m, while its width along the crown is 439m. Continuous monitoring of dam’s construction and surrounding terrain is conducted at over 800 measuring points. In order to determine precise position, geometry and propagation of cracks, this was the first time GPR was used.</p><p>GPR scanning was done on several important locations: on the crown, downstream face, internal galleries, down- and upstream walls, using antennas with 900 and 400MHz central frequencies. Based on scanning results, position and geometry of cracks within the concrete are successfully determined. Lateral scanning (on downstream face of the dam) are correlated with the results obtained on the crown. Also, at several locations, zones with higher humidity are noticed. These zones are significant since they present areas of higher priority during mitigation and they are often found in the vicinity of junctions between two concrete segments of the dam.</p><p>Obtained results indicate that GPR technology is rather useful tool for structure health monitoring which provides information that are significant in planning mitigation measures and extending a lifetime of a concrete object.</p><p> </p>

A Design for Vortex Suppression Downstream of a Submerged Gate

Interaction of recirculating and mean flow downstream of a submerged gate may form significant vortex structures, which may affect the stability of the gate. Although these flow structures that appear in submerged hydraulic jumps received considerable attention in the literature, relatively less work was devoted to the analysis and suppression of the vortex structures downstream of a submerged gate. In this work, internal flow structure and vortex dynamics around a submerged gate were investigated through laboratory tests and large-eddy simulation (LES) using computational fluid dynamics (CFD). It is shown that numerical results obtained for mean velocity field are in good agreement with the experimental measurements. A helical vortex pair connected with a horseshoe vortex system was identified within the roller region using high-resolution numerical simulations. Damping performance of different types of anti-vortex elements placed on the downstream face of the gate are evaluated based on numerical studies. It is shown that the horizontal porous baffle mounted at an elevation below the free surface reduced the vortex magnitudes in the roller region by 26.8%. With the implementation of the proposed vortex breaker, lift forces acting on the gate lip were reduced by 9.4% and drag forces acting on the downstream face of the gate were reduced by 8.6%. Finally, in this study, we assess the performance of the vortex breaker under different flow conditions.

The Effect of Inception Point on Dissipation Energy in Stepped Spillways Modeling

Stepped spillway is generally a modification on the downstream face of a standard ogee spillway. The steps increase significantly the rate of energy dissipation taking place along the chute and reduce the size of the need for a large energy dissipate at the toe of the spillway. In skimming flow conditions, the steps act as roughness factor which is great because most of the energy is lost to maintain horizontal vortices that develop beneath the pseudo bottom. This study aimed to investigate the effect of the inception point against the value of the relative energy loss on the stepped spillway in skimming flow regime. In this research, the models test of stepped spillway carried out with twelve configuration and variations of ratio (dc/h). The slope of stepped spillway (θ) is used 30˚ and 45˚, the number of steps (N) are 40 and 20, and two type of steps: flat steps and pooled steps. The critical depth to the height of steps (dc/h) is ranging from 0.700 < dc/h < 3.00 with the discharge per unit width 69.13 cm2/s < q < 707.65 cm2/s. The results showed that the relative energy loss can be analyzed to be a function of the inception points, the number of steps, and the slope of spillway, in the equation form of (ΔH/Hmax) = a (Li/ks)bNc(sin θ)d. The discharge which function of the Froude number and height of the step already include to the length of inception point parameters.

Slope Stability of an Earth Dam during Drawdown Conditions (KHASA-CHAI Dam) as a Case Study

Aiming in this research was to have a clear view about the behavior of Khasa-Chai Dam during the draw down action taking into consideration the newly built of this dam which was filling during the time of this article, the upstream slope was investigated by taking drawdown of the water from the reservoir. This dam is consists of the zoned embankment with a total length of (2.36 km) with an upstream slope (1v:3h) and downstream slope (1v:2h). Slope stability was investigated during the drawdown of the water from the reservoir by considering the water in the reservoir to be at maximum water level and by taking two cases during the rapid and slow drawdown. SLOPE/W which is a sub program from Geo-Slope software was used in association with SEEP/W software to find the factor of safety of the upstream slip surface during the drawdown conditions. It was noticed from the drawdown conditions that the phreatic line falls almost at the same position for both cases. Also for both cases the factor of safety of the upstream slip surface falls above the value of (1.0) and that is mean the upstream slope is in a safe condition when the water drawdown. The exit gradient and the rate of flow at the downstream face decrease with time as the water in the reservoir drawdown which means the factor of safety against boiling increases with time.