Methodology for Calculation of Rigidity in Earth Dam Slope Protection under Conditions of Wave Impact
Various types of protection are used in order to ensure rigidity in earth dam slopes and dumped rip-rap and precast and cast-in-situ reinforced plates are the most commonly used for this purpose. Durability and reliability of the protections mainly depend on the fact whether protection parameters have been correctly calculated and correspondingly observed during the process of protection creation, the main protection parameters are material diameter of dumped rip-rap and thickness of reinforced plates. Values of protection parameters calculated in accordance to the existing formulae significantly differ among themselves. Some of these formulae are acceptable for small water reservoirs in Belarus and provide actual results only for large water reservoirs where a wave height reaches two metres and even more. A new calculation methodology which is suitable for Belarusian water reservoirs of various size is proposed with the purpose to determine diameter of dumped rip-rap material and thickness of plates for earth dam slope protection in the zone of active wave impact. The methodology has been developed on the basis of the theory pertaining to limit equilibrium of slope shearing and holding forces. While calculating diameter of dumped rip-rap material the following shearing forces have been taken into account: uplift wave pressure depending on wave height; drag force which is formed on the slope due to back sweep of wave; shearing component of protection material gravity force which is dependent on preselected slope ratio. Holding forces are determined with due account of main physical and mechanical properties of dumped rip-rap material: density of particles in water suspension, porosity, internal friction and holding component of protection material gravity force. While developing methodology for calculation of reinforced concrete plate thickness a drag force has not been taken into account because the flow which is formed on the plate surface does not exert an influence on their equilibrium. Bottom slope zone where hydrodynamic pressure is created by bottom velocity has usually a reduced-weight protection in the form of broken stone, gravel and finely broken stone rip-rap. Dependences for determination of dumped rip-rap fineness have been obtained as a result of slope rigidity criterion conversion. The proposed formulae for calculation of earth dam slope protection parameters can be recommended for application in design organizations.