ABSTRACT:
Shahriar dam is a double-curvature concrete arch dam which is under construction near the town of Mianeh in northwest of Iran. The alluvial sediments in the riverbed of the dam are underlain by lowstrength clay and therefore are likely to cause slope stability failures. In this paper, effort has been made to focus on the effect of jet grouting to avoid slope failure during excavation and construction of a retaining structure. Finally, the paper concludes with presenting the differences between strength properties of the riverbed''s clay before and after jet grouting and operation of jet grouting on slope stability.
1 INTRODUCTION
The foundation of the Main Dam requires excavation of the alluvial deposits down to competent bedrock. The average ground elevation of the alluvial plain is about 975 masl. The elevation of the bedrock at its deepest point is about Elev. 920 masl. Hence, about 55 m of alluvium have to be excavated at the deepest section of the valley. Excavation of approximately 55 m deep alluvium is not possible without some strengthening and support measures (Fig.1). The reasons for these measures are the presence of a basal clay layer with relatively low shear strength and the limited space between the upstream cofferdam and the Main Dam requiring relatively steep excavation slopes. There are two approaches to ensure the stability of an excavation pit, namely: 1. Strengthening the soil either by mixing it with some material (lime, cement) to increase its shear strength (mainly its cohesion component) or reinforce it with some mechanical device (e.g. net, grid, strips, etc.), mainly to increase the friction angle. 2. Supporting the potentially unstable mass of earth materials by engineered structures, such as retaining walls with or without anchoring. Often a combination of these two approaches is used to reach the most economic solution.
