Gotvand rock fill dam is being constructed in Khoozestan province (Iran) on the Karun river. Its foundation will be founded on the Aghajary formation, which consists of interbedded siltstone and mudstone layers. It is expected that creep deformation will occur during the operation life of the dam, requiring investigation of the time dependant behavior of the foundation. These investigations will include both numerical and analytical methodologies, which in turn will require the determination of creep parameters for the rock foundation layers. For this, creep tests were carried out on the rock samples and the strain vs. time curves were obtained. Considering the Burger’s creep model, the constants of creep law were determined. Comparison between the results of numerical modeling and laboratory creep tests showed that the difference between deformations in the two methods was less than 6%. Also the time required for both rocks to enter the tertiary creep stage was determined to be 40 days for sandstone under 17.72MPa uniaxial stress and 35 days for mudstone under 7.8 MPa uniaxial stress.


One of the more important deformation characteristics of weak rock is it’s time-dependent or creep behavior. Creep is identified as irrecoverable deformation as a function of time and without fracture. This behavior is seen in the soft rocks such as rock salt and coal. Hard rocks also show creep behavior, but only over relatively long time periods (Cristescu & Hunsche 1998). As such, one of the fundamental assumptions in the design of a rock foundation is to choose the correct modeling parameters for time-dependant analysis. Different problems may be attributed to creep of rocks including differential settlement of structures, cracking of concrete linings in tunnels, and roof failure of tunnels and caverns.

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