Page - 512 - in Book of Full Papers - Symposium Hydro Engineering

from flooding. However, it is not just a question of making the platform at a high level, because the platform is being constructed on unimproved soils. The weight of the platform and equipment must be supported by the unimproved soils before the deep mixing soil improvement can be executed to make the suitable foundation for the closure dike. There is a delicate balance between making the platform high enough for safety against flash floods and low enough such that the total weight of the platform and equipment can be supported by the unimproved soils. In the case of the Wonogiri reservoir that delicate balance resulted in a platform consisting of two parts. First, primary embankment (varying thickness but approximately 1 m) is placed up to Elevation 132. Second, the primary embankment is overtopped with a constant 1 m thick layer of soil cement up to Elevation 133. The DMSI columns will to be drilled thought the soil cement. This layer of soil cement not only formed a firm platform but also acts to tie the columns together to limit their horizontal displacements at the tops of the columns. Figure 7. Typical Section of Primary Embankment and Soil Cement The average existing ground elevation of the soft reservoir deposits was around Elevation 131 and the construction window was assumed to start when reservoir levels fell below that level. Therefore, the first year construction was to consist of the following steps: Step 1: After the reservoir level drops the soft deposits were left to dry sufficiently enough to support equipment. Fortunately the construction window corresponds to the normal dry season with strong warm dry winds occur across the reservoir to aid in the drying. While waiting for the drying, clearing and grubbing of the soils was manually executed. When the soils had dried sufficiently to support the load of swamp-track bulldozers the area was then stripped. Since the reservoir deposits were not entirely even, the area was treated by zones corresponding to vary general levels. For the main Closure Dike the area was divided into 7 zones as shown below: 512