Grout curtain in the foundation of the Nurek dam and evaluation of its effectiveness

Abstract

The Nurek hydro development with a 300-m-high earth-rock damconstructed in a region of high seismic activity is a unique hydraulic structure.The on-site observations, which are the tool of monitoring the state of the dam, include a study of the seepage regime along with geodetic and seismometric investigations. The observations began at the time of constructing the dam in 1971. During this time a considerable body of data has been accumulated, making it possible to reveal the characteristics of the seepage regime and to evaluate the effectiveness of the cutoff elements. General problems of seepage in the body and foundation of the Nurek dam were examined earlier [I, 2]. We will analyze the effectiveness of the grout curtain, which is the main cutoff element in the foundation of the dam.Design of the Grout Curtain (Fig. i). The engineering-geological conditions, which to a considerable extent determine the design of the grout curtain, are rather complex. The alluvial and deluvial deposits as well as weathered rocks were completely removed to a depth of as much as 40 m under the entire area of the foundation of the core of the dam. The depth of excavation was determined, along with removal of the weak rocks, by the requirements imposed on the shape of the foundation pit of the core, which should have a cup-shaped form for facilitating uniform settlements of the core. The entire foundation under the core of the dam was covered with shotcrete with a thickness up to 15 cm to level the asperities of the rock surface. In the foundation of the core area grouting was carried out to a depth of I0 m to ensure a reliable contact of the core with the foundation; in its lower part area grouting is connected to the grout curtain.The grout curtain, which is intended for reliable damming of concentrated seepage paths in the foundation of the dam, is made to the entire depth of that part of the foundation where zones with increased unit water absorption q ~ 0.01 liter/min'm: were found, regardless of the head acting on this stretch of the foundation, as a consequence of which its depth varies within 40-140 m. At the upper elevations of the canyon walls the curtain is extended 120 m into each wall. The maximum depth of the curtain in the left wall reaches 140 m; in the right wall its depth is less, the maximum value here is 105 m (Fig. i).The number of rows (width) of the grout curtain was determined by the head and seepage properties of the foundation rocks. In the right wall on stretches with a head up to 60 m, composed of well-groutable rocks, the curtain was made single-row with a hole spacing of 4 m in the row. On stretches with a large heat, where poorly groutable rocks occur, the curtain is double-row to the entire depth with a distance between rows of about 2.5 m with respect to the tops of the holes and with a spacing of the holes in each row of 4 m. In the left wall above elevation 800 m, where the rocks are most weathered and jointed, a triple-row curtain was made. Lower the curtain is double-row along the entire wall.Fo...

A Review of Test Methods for the Determination of the Permeability Coefficient of Gravelly Soils Used for Embankment Dams

“…Embankment dam with earth core wall (core wall dam) originates from the homogeneous earth dam and its derivative earth dam [1] and has gradually become the most common type of embankment dam, especially high embankment dam. Some 300-meter-high embankment dam under planning, design, and construction such as Nurek Dam (300 m), Nuozhadu Dam (261.5 m), Lianghekou Dam (295 m), Shuangjiangkou dam (312 m), and RM Dam (315 m) are all core wall dams [2][3][4][5][6][7][8][9].…”