Rock mass deformation has a major impact on rock mass behavior. Different in situ experiments were carried out at various scales to determine the deformation modulus in Bakhtiary dam. These experiments are extremely costly and time-consuming so it is favorable to forecast this parameter with high accuracy and precision. In this paper the spatial structure of deformation modulus, which was obtained from plate load tests, was investigated at Bakhtiary dam and hydro electric power plant using variogram function that is the representative dispersal of variables. Then the deformation modulus was modeled and estimated using geostatistical estimator (Kriging). Also the Kriging error distribution function was calculated. The results indicated that the estimation was reliable and the forecasting accuracy and precision were acceptable.
The deformation modulus of a rock mass is an important input parameter in any analysis of rock mass behaviour that includes deformations such as dams, tunnels and etc. Field tests to determine this parameter directly are time consuming, expensive and the reliability of the results is sometimes questionable. Therefore, study on deformation modulus variations and create a model to estimate that has been considered. Geostatistics is an interpolation method developed for estimating values of a parameter of interest using a limited set of data. It assumes that a spatial relationship exists within the data set. Geostatistical methods are obtained powerful tools for studying on variability of any parameters and estimating that. These methods are more popular in mining engineering since the 1970s, and currently they are applied in many fields of earth science, particularly in the hydrologic and environmental studies. Cromer  advocated the use of geostatistics in addressing geotechnical problems specially when interpretation derived from the spatial distribution of data has impact on decision making. Harrison and Hudson  gave illustrative worked examples on the use of geostatistics and stressed the under-utilization of geostatistical methods in rock engineering. In this study, based on deformation modulus parameter and considering these as spatial data, geostatistical analysis was performed on these values with using geostatistical software (WinGslib), and then according to variograms specifications were created models for estimating the deformation modulus in various area of Bakhtiary dam site.
The site of Bakhtiary dam and powerhouse is located in Lorestan province, southwest of Iran. The project site is almost 100 km to Khorram Abad, the nearest provincial center and also to Dorud town. It is almost 300 km to Ahwaz. The dam site is located on the Bakhtiary River bank, one of the Dez River headstreams, 5 km upstream of the confluence of the Sezar and Bakhtiary rivers, amid the Zagros Mountains and almost 50 km to the upstream of the Dez dam and hydropower plant. Its catchment's area is 6495 km2 and its average height from sea level is 2200 m, with a maximum of 4080 m.a.s.l. The mean discharge value of the river is 145 m3/s.