Investigation of earth dikes built on “zasukhas” of Lake Sivash

Conclusions

• 1. The actual foundation settlement along the axis of the dikes investigated ranged from 0.24 to 0.61 m (averaging 0.38 m), or 20% of that provided in the design. This is explained by the presence of “shrinkage crusts” and the considerable content of crystallized salts in the silt layer, which increase their bearing capacity in the water area of zasukhas of Lake Sivash.

• 2. The maximum settlement moduli recorded at individual points ranged from 262 to 363 mm/m, and averaged about 300 mm/m. Based on these data, in future designs of earth dams and dikes on the “zasukhas” of Lake Sivash with heights of 4–6 m and the same thickness of silts, the settlement moduli adopted should be within the range 250–300 mm/m along the structure's axis, and 200–250 mm/m over the whole width of their bases.

• 3. The preliminary construction of an initial fill 1–1.2 m thick is the most expedient method of construction of dikes on a layer of silts in the water area of zasukhas. In placing these initial fills a heaving of the silts out of the dike foundation material is observed, caused mainly by the dynamic forces generated by heavy equipment delivering and spreading the soil.

• 4. With the relatively high permeability of the layer of silts with a thickness of 4–6 m (k=1.10⁻⁶ cm/sec), settlement of the dike foundations, according to calculations, occurs during a period of 15–20 days. On this basis, after placing the initial fills, the subsequent layer-by-layer construction of the dikes, with moistening and compaction of the soil, can be carried out without any special interruptions; however, the rate of fill rise should be limited to 1 m/month.

• 5. The side slopes of earth dams founded on silts should be limited to 4∶1 to 6∶1 (H:SS) to ensure their stability and also to enable rock to be hauled to its final placement location directly.