Lime stabilization of highly plastic clayey soil for the impervious core of embankment dam
The case of Gidabo dam, Ethiopia
The stability of different part of zoned embankment dam including the core has to be guaranteed during design and construction to ensure the overall stability of the structure. Selection of appropriate material is a very crucial step. Important material properties of the core are low permeability, erosion resistance and cracking resistance. Impervious clayey soils are a widely available and used materials for the construction of core of zoned embankment dams in Ethiopia. However, such soil is characterized by high compressibility, poor shear strength when compacted and saturated, difficult in moisture control during construction (poor workability) and requires slow rate of construction to allow dissipation of excess pore water pressure. Despite their undesirable characteristics, the use of locally found material is becoming more necessary for sustainability reasons. The present study has been, thus, conducted with intention to alter some of the undesirable characteristics of clayey soil using chemical additives. Six soil samples from Gidabo dam area were collected and different laboratory tests were conducted (i.e. Atterberg limits, permeability, compaction, 1D-consolidation, and undrained-unconsolidated (UU) triaxial) tests) on raw samples and after treatment with different percentage of hydrated lime. Seven days curing time and the lime addition ratios of 0 %, 2 %, 4 %, and 6 % by dry weight were considered. After lime treatment, the liquid limit, plasticity index and swelling potential decreased. The permeability also decreased by more than one order of magnitude from 4.47 * 10-6 to 3.63 * 10-7. The stiffness and compressibility of the soil increased and reduced, respectively. Lime content of 6% has been found to be the minimum lime percentage required to make soils of the study area desirable core fill material.