Evaluation of Damsites Groutability Using Secondary Permeability Index, Rock Classification (Case Studies)

Abstract

Problem statement: The dam body and foundation seepage is one of the important points in design parameters. This index is related to the permeability. There fore permeability is one of the basic parameter in design grout curtain, prevent water escape from foundation and avoid negative seepage pressure in borrow materials, so grouting is used. Grouting means injected materials like cement or chemical materials under pressure to rock or soil layers. Approach: Purpose of grouting is treatment fractures, fissures, increase strength and decrease seepage. Grout curtain is used for sealing beneath dam body and other structure to obtain above aspects. Results: The present research dealing to study the geotechnical characteristics and conditions of two damsites (Kavar and Sheshpir dam) regarding to their permeability and groutability. Permeability in rock mass is controlled by jointing and their characteristics. The Kavar dam may be constructed on Gareh Aghaj river. This site is located in 40 km southwest of Fars province, Iran. The river flow direction is parallel to the local syncline axis. The main geological features of damsite are faults, fractures and gypsum lenses that they may lead to water escape from reservoir. The rocks in the right abutment of the dam are heavily crushed with low strength. Therefore it is expected that water escape from this zone and some parts of dam axis may happen. This is approved from boreholes logs analysis and Water Pressure Tests (WPT). The other dam which called Sheshpir is located in west of Shiraz, Iran. Regarding to structural geology of this site, two large anticlines are extended in general direction of Zagros mountain range (northeast- southwest). The geology index features are karstic and jointed rock with faults. In general, regarding the grout-curtain design for each case, it is necessary to evaluate the volume of grout and injection system. Because of complexity of local structural geology especially rock foundation, it is difficult to estimate above-mentioned parameters. Conclusion/Recommendations: Therefore, through a number of WPT in both sites, the Permeability and hydro fracture tests results were used in the foundation for the design of the grouting program. using SPI rock classification systems, it is possible to identify the karstic features of the formation and the relationships between the permeability and groutability. This method that first expressed by foyo identify the special classification for grouting. In this system use results of Water Pressure Test (WPT) and Rock Quality Design (RQD) simultaneously. With the help of these two parameters rock class and grout complex is identified.