Earth-fill dams are the most common types of dam and the most economical choice. However, they are more vulnerable to internal erosion and piping due to seepage problems that are the main causes of dam failure. In this study, the seepage through earth-fill dams was investigated using physical, mathematical, and numerical models. Results from the three methods revealed that both mathematical calculations using L. Casagrande solutions and the SEEP/W numerical model have a plotted seepage line compatible with the observed seepage line in the physical model. However, when the seepage flow intersected the downstream slope and when piping took place, the use of SEEP/W to calculate the flow rate became useless as it was unable to calculate the volume of water flow in pipes. This was revealed by the big difference in results between physical and numerical models in the first physical model, while the results were compatible in the second physical model when the seepage line stayed within the body of the dam and low compacted soil was adopted. Seepage analysis for seven different configurations of an earth-fill dam was conducted using the SEEP/W model at normal and maximum water levels to find the most appropriate configuration among them. The seven dam configurations consisted of four homogenous dams and three zoned dams. Seepage analysis revealed that if sufficient quantity of silty sand soil is available around the proposed dam location, a homogenous earth-fill dam with a medium drain length of 0.5 m thickness is the best design configuration. Otherwise, a zoned earth-fill dam with a central core and 1:0.5 Horizontal to Vertical ratio (H:V) is preferred.

https://www.mdpi.com/2071-1050/12/6/2490/pdf

Experimental and Numerical Analysis for Earth-Fill Dam Seepage

A method is presented for the approximate estimation of the time for progression of internal erosion and piping, and development of a breach leading to failure in embankment dams and their foundations. The method accounts for the nature of the soils in the dam core, the foundation, and the materials in the downstream zone of the dam. Guidance is also provided on the detectability of internal erosion and piping, taking account of the mechanism of initiation, continuation, and progression to form a breach, for internal erosion and piping in the embankment, the foundation and from the embankment to foundation. It is shown that in many dams which have poor internal erosion and seepage control and are constructed mainly of earthfill, the time for potential development of piping is short, and for these dams continuous monitoring of seepage or surveillance would be needed to detect the piping in time to give warning of possible failure, and to give time to attempt intervention to prevent the failure.

Closure of "Time for Development of Internal Erosion and Piping in Embankment Dams"

A new type of collar, the hooked-collar, was studied through experiments and numerical methods Tests were conducted using a hooked collar of a width of 125b and a height of 025b, where b is the bridge-pier width The hooked-collar efficiency was evaluated by testing different hooked-collar placements within the bridge-pier, which were compared to the bridge-pier without any collar A double hooked-collar configuration, one placed at the bed level and the other buried 025b, was the most efficient at reducing the scour hole In other cases, a hooked-collar positioned 025b above the bed slightly reduced the scour hole and had similar scour patterns when compared to the pier without the hooked-collar The flow fields along the vertical symmetrical plane in the experiments are also presented Laboratory experiments and numerical tests show that maximal downflow is highly reduced along with a corresponding decrease in horseshoe vortex strength for the experiments with the hooked-collar, compared to cases without the hooked-collar The flow fields reveal that the maximum turbulent kinetic energy decreases with the installation of the hooked-collar

A Hooked-Collar for Bridge Piers Protection: Flow Fields and Scour

Previous experimental research on utilizing pier modifications as countermeasures against local scour has focused primarily on circular pier. It is of utmost importance to further investigate the most suitable pier shape for pier modification countermeasure separately and in combination. This experimental study aims to reduce the stagnation of the flow and vortex formation in front of the bridge pier by providing a collar, a hooked collar, a cable, and openings separately and in combination around a suitable pier shape. Therefore, six different pier shapes were utilized to find out the influence of pier shape on local scouring for a length–width ratio smaller than or equal to 3. A plain octagonal shape was shown as having more satisfactory results in reducing scour compared to other pier shapes. Furthermore, the efficiency of pier modification was then evaluated by testing different combinations of collar, hooked collar, cable, and openings within the octagonal bridge pier, which was compared to an unprotected octagonal pier without any modification. The results show that by applying such modifications, the scour depth reduced significantly. The best combination was found to be a hooked collar with cable and openings around an octagonal pier. It was revealed that the best combination reduced almost 53% of scour depth, as compared to an unprotected octagonal pier.

https://www.mdpi.com/2073-4441/11/9/1761/pdf

Impact Assessment of Pier Shape and Modifications on Scouring around Bridge Pier

A review on the methods used to reduce the scouring effect of bridge pier

Application of a horizontal drain in an embankment dam has been a prevalent method to lower the phreatic line and dissipate the excessive pore water pressure. The efficiency of this type of drain is often attributed to its length, while the effect of thickness is ignored. In this research, a series of tests were accomplished and different drain sizes including different thicknesses and lengths were applied to a physical model of an embankment dam. During the tests, the pore pressures were measured both in the steady and transient conditions using a number of peizometers and pressure sensors. In steady state, the increased thickness prevented the occurrence of piping and in transient state guaranteed the stability of the upstream slope. However, the thickest drain used in this research showed different efficiencies depending upon the applied length. For the maximum effective length derived from the equations, the increase in thickness could efficiently prevent the undesirable consequences of excessive pore water pressure.

/pdf/effect-of-horizontal-drain-size-on-the-stability-of-an-15worm7s0g.pdf

Effect of horizontal drain size on the stability of an embankment dam in steady and transient seepage conditions

Local scour around bridge abutments is a widespread problem that can result in structural failure. Collars can be used as a countermeasure to reduce the scour depth. In this study, the temporal scour development around a wing-wall abutment was investigated with and without collars. The tests were carried out under clear-water conditions for different abutment lengths, with collars of different sizes placed at the bed level. When no collar was used in the experiments, 70% of the maximum scour depth occurred in less than 2 h. However, when a collar with a width greater than the length of the abutment was used, no scour was observed for up to 200 min from the beginning of the experiments. The results show that an increase in the collar width not only led to a lag time for the onset of scouring but also reduced the maximum scour depth. Moreover, an increased collar width led to a better performance in mitigating scouring around smaller abutments. Generally, the scour depth decreased by 9%–37% with different collar widths.

Effect of trapezoidal collars as a scour countermeasure around wing-wall abutments

Formation of shock waves has an important role in supercritical flows studies. These waves are often occurring during passage of supercritical flow in the non-prismatic channels. In the present study, the effect of length of contraction wall of open-channel for two different geometries (1.5 m and 0.5 m) and fixed contraction ratio was investigated on hydraulic parameters of shock waves using experimental model (models 1 and 2). For achieving to this goal, values of height and instantaneous velocity were measured in various points of shock waves observed in contractions for four Froude Numbers. In general, non-uniform distribution of velocity and turbulence intensity profiles were completely clear. Comparing results of models 1 and 2, show that the height and velocity values of formed waves in the model 2 is so much more than the model 1. Also, motion of the shock waves was accompanied with longitude gradient decrease of turbulence kinetic energy. The results of the present research can be very useful for designer engineers.

http://jcarme.sru.ac.ir/article_823_b7b90052ed93b4d6c3c78df61c3865d9.pdf

Experimental analysis of shock waves turbulence in contractions with rectangular sections

Effect of intake geometry on the sediment transport and flow pattern at lateral

Shock wave formation is very important in studies of supercritical flow. Based on increasing water height more than inlet flow depth, spreading over a wide range of downstream channel and making disturbances in water surface, formation and propagation of these waves are unfavorable in engineering. The present paper is an attempt to study the supercritical flow in contraction and expansion, and wave formation patterns. In this regard, the height and instantaneous velocity at different points of shock waves in contraction and free-surface wave profiles in expansion were measured for four different Froude numbers. In order to 3D simulation, turbulence models of k-e RNG and RSM based on Fluent software were used. For calculating free-surface wave profiles using the k-e RNG and RSM models, the mean relative errors were obtained as 30.3% and 98.2% in contraction: 13% and 2.58% in expansion, respectively. Also, the mean relative errors of the k-e RNG and RSM models for wave velocity computation of contraction were calculated as 5.26% and 2.87%, respectively. The results indicated that RSM turbulence model performs better than k-e RNG in simulating velocity profiles of shock waves.

Davod Farsadizadeh

Papers

Effect of horizontal drain size on the stability of an embankment dam in steady and transient seepage conditions

Effect of trapezoidal collars as a scour countermeasure around wing-wall abutments

Experimental analysis of shock waves turbulence in contractions with rectangular sections

Effect of intake geometry on the sediment transport and flow pattern at lateral

Experimental and numerical investigation of supercritical flow in contraction and expansion of open channels