Dams are constructed to control the surface runoff. One of the important points involved in grouting operation and cut off curtain design is the geological and hydrogeological investigation of the site and evaluation of its groutability. The commonly method used for determination of permeability coefficient is water pressure test (WPT). The test includes measurement of water pressure (P) and discharge (Q) pumped in the drilled boreholes and its graphical representation as (P-Q) diagrams which can be interpreted to give rock mass hydromechanical behaviour. Based on the test designation, in Ostur dam site, 400 water pressure tests were conducted and analyzed. Results of these tests are used to determine the type of hydrogeomechanical behaviour. In the other hand, the test grouting was also conducted in continuation of the (WPT) operation and the results have shown that the bedrock of this dam is impermeable, with very low groutability potential. However, the shallow part of rock mass is partly affected due to weathering. The type of flow in these parts is identified as turbulent. From the other side, the rock mass is also intersected in deep parts by hydrothermal veins. The flow type in these parts is different from the shallow parts.
Recognition of the mass rock specifications and the foundations as a part of investigation of the dam site is one of the main purposes of dam study. So the permeability is a main factor in design of cut off grout curtain for preventing the escape of water through foundation and preventing the negative effect of seepage from the foundation materials. In this paper, Ostur dam is studied which is an arch concrete located at E: 48° 2′ 11" and N: 37° 30' 8", 6 km east of Ostur village, 39 km northeast of Mianeh city, East Azarbaijan Province, northwest of Iran to be built across Ghezel Owzan river.
Due to tectonic activity in the region, diorite mass rock which has shaped the most litology of the dam axis has been intersected by a set of the joints and fractures. In order to determine the joint sets and study their trend change, surface sampling and measurement of the discontinuities has been done in both right and left abutments of the dam axis (Figure 1). Totally around 2500 discontinuities were surveyed out of which 1400 belong to the right abutment and 1200 are from the left abutment. In order to statistically analyze and show the joints, the lower hemisphere presentation of these discontinuities were drawn by Dips software (5.1 versions). From the results, 5 joint sets were identified in each abutment which their streonets and contour diagrams have been shown in the Figure 1 for left abutment and Figure 2 for right abutment.
