Geological Behavior (GBR)

The present study focuses on investigation of competence, corrosivity and plasticity of soils using geophysical and geotechnical methods in Naraguta area. Twenty (20) VES stations were occupied in the study area using Schlumberger array with current electrode separation (AB) varying from 1.5 to 125 m. The VES data acquired in the field were interpreted by curve matching using the Winresist software. Ten (10) soil samples were collected at depth of about 1.5m for geotechnical tests (Liquid limits, plastic limits, plasticity index and linear shrinkage). Resistivity value (23.4-2528.9 Ωm) was used to classify the competence of the soils into three namely: highly competent (>750 Ωm), competent area (350-750Ωm) and incompetent (<100Ω). The soil corrosivity in the area was classified into three namely: moderately corrosive (10-60 Ωm), slightly corrosive (60-180 Ωm) and practically non-corrosive (>180Ωm). The study area is underlain by four (4) geoelectric layers which comprises of Clay, Sandy clay, Clay sand and crystalline rock. The plasticity index (11-270) is classified into medium-plastic (7-17) and highly plastic (>17). The linear shrinkage (7.5-10.7) indicates medium (5-10) and poor-quality soil (10-15). Three (3) degree of expansion zones identified are low, medium and high degree of expansions. Three (3) danger of severity zones were identified namely: non-critical, marginal and critical. Based on the geophysical values the area can be classified into highly competent, competent and incompetent soil for building construction while the geotechnical values indicate medium plasticity/compressibility which suggests medium competence while high plasticity/compressibility suggest low competence.