جستجوی مقالات مرتبط با کلیدواژه « grout curtain » در نشریات گروه « زمین شناسی »

A grout curtain is constructed beneath the dam foundation to control water seepage. Cement is used to execute the grout curtain and to extend until it reaches impermeable bedrock. Grout curtain will mostly reach groundwater, too. The reaction between cement and water caused the cement compound to enter groundwater and changes its quality. The extent of change and its continuity is important so that it needs to be studied and investigated over time. In this research, the change of water quality has been studied by comparison of water test analysis during 4 years. For this purpose, four phases of water samples including site springs samples before any disturbance (first phase, 1392), after cement grout and before impoundment (second phase,1394), and also two phases samples after impoundment (third phase,1395 and fourth phase,1396) with one-year interval were examined. Samples of the second, third and fourth phases were taken from observation wells which are located downstream of the grout curtain. Therefore, it is expected to see the effects of cement entry in the groundwater flow through the curtain to the observation wells. In this study after categorizing the achieved data, using SURFER and GIS software, different parameters were interpolated in different periods and compared by the production of zoned maps, and the degree of variation of different elements was investigated. Diagrams and maps show that pH, SiO2, Na, K, Fe, CaCO3, SO4 and EC have been significantly changed which indicates that cement compounds have been entered into the groundwater and have decreased the water quality.

Karst regions have been considered unsuitable for dam construction because of complex hydrogeological characteristics. The most frequent problem at the karst dam sites is water leakage from the reservoirs. The Shah Ghasem Dam with a reservoir capacity of 9 million cubic meters, was constructed at the south of Yasouj City to regulate water flow of Shah Ghasem Spring. The dam is located on the northern limb of Shah Ghasem Anticline, a fold which is mainly composed of the marlstone layers of the Pabdeh-Gurpi Formation, alternative marlstone and limestone layers of Transition Zone and karst limestone belonging to the Asmari-Jahrom Formation. The reservoir water is in direct contact with the impermeable Pabdeh-Gurpi Formation, karstic Asmari Formations and their transition zone. By starting of dam operation in 1996, leakage occurred from the reservoir through the limestone layers of the Asmari Formation and Transition Zone. To reduce leakage, ten boreholes were drilled and grouted, but no effect on leakage amount was observed. The main object of this study is to determine leakage paths at the Shah Ghasem Dam reservoir, by considering the geological and hydrogeological settings, water pressure tests, cement consumption, and time series of water table in the reservoir and downstream boreholes. Results indicated that an extensive treatment work was needed to reduce the water leakage amount, but performing a benefit cost analysis was required to make a proper decision. Moreover, the karst aquifer at the northern limb of the anticline was recharging by the reservoir leakage water, supplying downstream drinking water.

Salman Farsi is located in 180 kilometers of the southeast of Shiraz on the Ghareh-Agai River with the arch-gravity concrete dam of 125m height from the foundation. The grout curtain is situated entirely within the karstic limestone environment in the Asmari formation. To evaluate the quality of the curtain after grouting operation, some boreholes were drilled and water pressure tests were performed on them. In this research, according to the results of water pressure tests on the controlled boreholes, the secondary permeability index was calculated and through the classification of the rock masses, their quality were determined after the grouting operation. Results indicate that although the right bank of grout curtain has better quality than the left bank, however the quality of the grout curtain has been in the range of good to excellent.