Influence of thickness of a vertical core on the slope stability of earth and rockfill dams

An analytical study was undertaken to identify the zone within which the thickness of a vertical core has no influence on the stability of upstream and downstream slopes of earth and rockfill dams. Stability analysis was carried out for a 180 m high earth and rockfill dam on strong foundation. Dam sections having different core thicknesses were analysed, to identify the critical thickness beyond which the factor of safety of upstream and downstream slopes exhibited reduction for end-of-construction, steady-state-seepage and rapid-drawdown conditions. The influence of four parameters on critical core thickness was identified: dam height, relative strength of core to shell, pore pressure ratio r_u and drawdown level. The study shows that the core does not influence the stability of outer slopes, if it is positioned such that its thickness is within 50% of the height of the dam. On the other hand, if the thickness of the core is above 150% of dam height, it causes a reduction in the stability of the outer slopes. In the intermediate cases, the magnitude of the critical thickness of the core depends upon the relative strength of the core to shell and the pore water pressure parameter r_u.