EROSIVE RESISTANCE OF CORE MATERIALS.

Abstract

Differential settlements in embankments of earth dams can cause transverse cracks at the crest, if the embankments material lacks the necessary flexibility. The transverse cracks in earth dams can be potentially dangerous due to the fact that piping through cracks may occur and then progressive erosion can develop in the cracks leading to complete failure of the dams.. Different types of core materials differ consider-ably in the resistance that they offer to erosion. The resistance to erosion for different soils varies, i.e., the embankment of core material with low erosion resistance may develop progressive erosion in cracks or in other seepage paths, much more rapidly than a core material of high resistance. A survey of available information indicates that there is need for further work and understanding of the erosion resistance of cohesive soils for core material in embankment of dams. This work has been taken up in the W.R.D.T.C. for the past two years, the present disserta-tion being the third in the series. Experimental study has been conducted in the labora-tory by forcing water through a cylindrical hole in soil specimens after saturation in a 10.16 cm. (4 inches) diameter and a 11,70 cm (4.5 inches) high of mould and (iv) measuring the critical head, i.e. Head at which (7 erosion commences, as indicated by a continuous erosion, which can be seen in a white porcelain dish. The rate of erosion was also measured, as well as the diameter of the hole and other properties of the soil. Three types of soils have been tested as used in this study, i.e. clayey sand (Roorkee clay), Dhanauri clay and Kota's black cotton soil. Roorkee clay and Dhanauri clay have been tested as such, and then also with admixtures of bentonite and stone chips of 2 mm to 4 mm in grading in different percentages. In the present tests most of the samples have been tested in a horizontal position, and it is found that this makes a difference to development of erosion. Another new feature of these tests was the admixture of stone chips. An effort has been made to correlate the erosion resistance of the soil to the index soil properties a e the plasticity index, grain-size distribution and unconfined compressive strength. The effect of the two admixtures used has also been discussed.