Consulting: Civil Engineering

Dam and Spillway Analysis

Spillway of Miskog Dam in Sweden

Itasca has provided analysis for several large earthfill and rockfill dams, including Bennett Dam in northern British Columbia, the world's largest rockfill dam. For Bennett Dam, Itasca developed two- and three-dimensional models to study the response during construction and reservoir filling to determine the cause of sinkholes, which appeared in the crest in two locations. A special constitutive model was used to represent the fill material behavior.

Frequently, a key to understanding dam behavior is the effective stress acting in various materials. Therefore, an important feature of dam analysis is the ability to predict accurately the water pressures and flow within the dam components and its foundation. Itasca's FLAC code is used to study the water flow within dams and granular foundations assuming porous media flow. If the foundation is rock, as is the case for nearly all dams in Sweden, flow through jointed rock is studied using Itasca's UDEC code.

In many places, such as Chile, the dynamic behavior of the dams during earthquakes is an important consideration. Itasca performs fully non-linear analysis of dam behavior in the time domain. The starting point for all dynamic analyses is the static condition of the dam that is obtained through modeling of the construction sequence and reservoir filling. Earthquake histories are applied at the base of the model and are propagated through the foundation and dam. Hydrodynamic interaction between the dam and reservoir is also represented using a method developed by Westergaard. The behavior of the dam in real time allows weaknesses in the design to be identified and corrected. In some cases, the design can be optimized by increasing the slope angles without adversely affecting performance.

Itasca has performed dam analysis for nearly all types of dams including arch dams (Saint Maria), concrete-faced rockfill dams (El Bato), earthfill dams (Convento Viejo), rockfill dams (Bennett) and concrete gravity dams (Sweden). In addition, although not strictly civil engineering, Itasca has performed numerous analyses of tailings dams. The key element in tailings dam analysis is the study of the potential effects of liquefaction. Empirical relations, backed up by laboratory testing, are used to represent the build-up in water pressure that occurs prior to liquefaction.

Dam spillways have also been studied by Itasca. In the case of the F. E. Walter Dam, Itasca performed analyses to recommend a reduced foundation-reinforcement pattern that potentially saved the U.S. Army Corps of Engineers over $100,000. Itasca worked with Vattenfall in Sweden to study spillway erosion affecting the Midskog dam: Itasca examined the mechanism involved in the erosion, developed a simple model to explain the mechanism and presented results from two-dimensional discontinuum analyses that showed the erosion potential of past, present and future spillway conditions. Data regarding water pressure fluctuations at specific locations, flow velocities, etc. used in the analysis were based on a 1:50 scale physical model run at Vattenfall's Älvkarleby laboratory.