GEOTECHNICAL INVESTIGATION FOR SUBSOIL HAZARD DURING EARTH FILL DAM CONSTRUCTION

Abstract

The purpose of this investigation was to assess the suitability of the underlying soils for constructing an earth fill dam for irrigation purposes. Eight soil samples were collected from four trial pits and four borrow pits, and were subjected to physical, mechanical and strength performance tests which are natural moisture content, specific gravity, Atterberg limits, grain size analysis, compaction, consolidation, permeability, and triaxial shear strength. The liquid limit, plastic limit, and plasticity index (Atterberg limits) of the soil samples ranged from 33-46%, 22-32.5%, and 6.5-22.2%, respectively. The percentage of fines and coarse contents from the grain size analysis ranged from 7.1% to 52.4% and 44.4% to 91.4%, respectively. The maximum dry density (MDD) values of the soils ranged from 1630 to 2015 Kg/m3, while the optimum moisture content ranged from 9.9% to 27%. The coefficient of permeability (K) ranged from 1.452× 10-6 to 2.196950× 10-3 cm/s. The coefficient of volume compressibility (Cv) and consolidation (Mv) ranged from 0.00020 to 0.88 mm/yr and 0.18 to 144 MPa-1, respectively, and the angle of internal friction ranged from 24.30 to 35.40°. The results indicate that the underlying soils contain a significant amount of moisture due to climatic conditions. They are well-graded soils with low to intermediate plasticity. Clay minerals, specifically Kaolinite, are present and contribute to the low to medium swelling potential of the soils. The low hydraulic conductivity makes the soils suitable for the construction of an earth fill dam, and they exhibit good strength with low settlement potential for the engineering structure.