Description of pore pressure and alarm thresholds

One of the main loads acting on a concrete dam is uplift pressure. Although recognized in the beginning of the twentieth century, there is still great uncertainty in the estimates of uplift pressure. In this project researchers will identify how uplift pressure should be described and accounted for in reliability based stability calculations under different geological conditions, and develop methods for improved evaluation of uplift pressure.

Uplift pressure is produced in a dam rock foundation by water in fractures or pores in the foundation rock. It is usually assumed that at the upstream side the pressure equals the reservoir head, and at the downstream side it equals the tail water head. Between these points, the uplift pressure varies depending on the loads acting on the dam, the temperature in the surroundings, the geology of the foundation rock, type and extent of foundation treatment and efficiency of foundation drainage system.

Due to the many factors that influence the uplift pressure under concrete dams the question is complex. A simplified linear or bi-linear assumption of the acting uplift pressure described with a deterministic value, which is assumed stationary over time and only affected by the reservoir level is an oversimplification. A statistical distribution of the pore pressure representing prevailing uncertainties is more representative and is therefore a key question in order to determine the probability of failure and the safety for the dam and its associated risk.