Use of Index Gradients and Default Tailwater Depth as Aids to Hydraulic Modeling of Flow-Through Rockfill Dams

Failure of the Downstream Shoulder of Rockfill Dams Due to Overtopping or Throughflow

“…The two main causes of failure of large rockfill dams registered up to 1986, excluding dams constructed in Japan pre-1930 and in China, are overtopping (55.6% of cases corresponding to 5 failures) and piping (11.1% of cases corresponding to 1 failure) [6]. Due to the high permeability of clean rockfill, both overtopping and piping lead to the formation of a seepage profile at the base of the downstream shoulder [7][8][9][10][11][12][13][14][15][16][17][18], that finally exits the dam at the toe [5,9,[19][20][21][22]. In the toe, delimited upstream by the first emergence point [10,20], the hydraulic gradients and seepage forces are maximum and, besides that, point outward of the dam [22], making this area prone to erosion and a zone of primary engineering concern [5,19].…”

“…Due to the high permeability of clean rockfill, both overtopping and piping lead to the formation of a seepage profile at the base of the downstream shoulder [7][8][9][10][11][12][13][14][15][16][17][18], that finally exits the dam at the toe [5,9,[19][20][21][22]. In the toe, delimited upstream by the first emergence point [10,20], the hydraulic gradients and seepage forces are maximum and, besides that, point outward of the dam [22], making this area prone to erosion and a zone of primary engineering concern [5,19]. As a consequence, failure initiates at the toe for a discharge that must overcome a given threshold [3,[23][24][25][26] and may occur by slumping, internal migration of particles, or surface unraveling erosion resulting in concentrated flow paths [22,[26][27][28][29][30].…”

Structural Failure of the Cohesive Core of Rockfill Dams: An Experimental Research Using Sand-Bentonite Mixtures

“…During extreme events such as these, catastrophic failure of rockfill structures comprises two stages: (i) failure of the downstream shoulder and (ii) failure of the impervious element. Both overtopping and piping lead to the formation of a seepage profile at the base of the dam [6][7][8][9][10][11][12][13][14][15][16][17][18], which emerges from the downstream toe [1, 17,[19][20][21][22]. Here, the hydraulic gradients and seepage forces are maximum, making this section of the dam prone to failure [1,19].…”

A one-dimensional flood routing model for rockfill dams considering exit height

“…Such dumps, which are trapezoidal in shape, may be several kilometres long and composed of a wide range of material sizes (Hosseini and Joy, 2007). Rockfill structures are also used as detention dams in river engineering in order to attenuate and delay inflow hydrographs (Hansen and Roshanfekr, 2012) in which the flow can be through or over the dam (Samani et al, 2013). The ancillary advantages of this kind of structure are flexibility, durability, permeability and economy (Leu et al, 2008).…”

“…They concluded that, for a certain discharge, the upstream water level calculated by the 1D model (in which the downstream water level was considered as the boundary condition) contained significant error when compared with a 2D model and experimental data. In the exit zone, flow emergence first occurs and, to obtain the water depth at the mentioned point for various discharges, a discharge-stage relationship can be calculated, for instance upstream and downstream discharge-stage relationships (Hansen and Roshanfekr, 2012).…”