ABSTRACT:

The Zapotillo Dam is a 130m high roller compacted concrete dam constructed in Mexico. In connection with the excavation of a recent slide at the left abutment of the dam, a slide of the adjacent slope was activated. The lower part of the sliding surface is located at the elevation of the dam's crest. The article describes the measured sliding movements, the inmediate stabilizing measures, the FE back-analyses as well as the long-term support and measurement results during and after stabilization of the slope. At the right abutment above the stilling basin, there is a rock slope which tends to toppling failure as well as a large deposit of talus material. The article reports on the FE stability analyses as well as the excavation and stabilization measures foreseen in the design.

1 PROJECT

The Zapotillo dam is currently constructed in the area of the major city Guadalajara, Jalisco, Mexico (Fig. 1). It is planned to be a 130 m high roller compacted concrete dam, which will create a drinking water reservoir with a volume of aprox. 1 billion m3. In plan view, the dam has a curved geometry with a crown length of around 390 m and a centric spillway (Fig. 2). The dam is designed as a gravity dam.

The sliding slope, which will be dealt with in chapter 3 of the given publication, is located at the left abutment of the dam (see red circle in fig. 2). The toppling zone and debris of talus material, which are discussed in chapter 4, are located at the right hand side of the stilling basin (see red circle in Fig. 2).

2 GEOLOGICAL AND GEOTECHNICAL CONDITIONS

At the dam site an alternating sequence of volcanic rocks, mainly tuffs and ignimbrites, is encountered (Fig. 3). The ignimbrites are strongly jointed and tend to form rock columns (Fig. 4). Uniaxial compressive strength amounts to aprox. 10 to 50 MN/m2. With values in the order of 2,000 to 5,000 MN/m2, they have a rather small deformability modulus. The Tuff layers have an even smaller deformability modulus, which ranges in the order of magnitude of 500–3,000 MN/m2. Their uniaxial compressive strength ranges between 2 and 15 MN/m2. They are also jointed (Fig. 5).

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