Role of smectite-rich shales in frequent foundation failures in southeast Nigeria

Abstract

This paper investigated the geotechnical properties of smectite-rich shale, and its implications as foundation material. Ten expansive shale samples were collected from foundation materials at Akpugo in Nkanu West L.G.A. of Enugu State, southeast Nigeria. Samples were subjected to grading, Atterberg limitscum-compaction tests, slake durability, specific gravity, permeability, undrained triaxial tests and x-ray diffraction scan. Fines and sand contents of the soil samples range from 51-97% and 3-49% respectively. Liquid limit, plastic limit and plasticity index have average values of 60.7, 19.1 and 43.3% respectively. Linear shrinkage and free swell showed average of 16.3% and 76%. These results are indicative of predominant clay soil with high plasticity, compressibility and water holding capacity. XRD scan established presence of smectite and illite clay minerals, confirming soil high plasticity, capable of causing instability in foundation soil. The shale achieved maximum dry density range between 1.79 and 1.94 kg/m 3 at optimum moisture content range of 6.9-12.8%, indicating poor to fair foundation materials. The shale cohesion ranges from 15 to 30 kPa while the angle of friction ranges between 10 • and 18 • , signifying an average strength soil material. Samples slake durability index and specific gravity fall within 24-55% and 2.50-2.58 respectively, suggesting non-durable and weak soil. Permeability of the samples ranges between 7.36×10 −6 and 4.77×10 −8 cm/s which suggested low drainage capable of causing water-log at sites. Therefore, the shale could be generally classified as poor to fair foundation material, which on moisture influx experience reduction in strength due to deterioration of its constituent minerals, especially clay and cement materials during the lifespan of engineering structures. Authors therefore recommend modification of foundation soil, appropriate foundation design and good drainage control as ways of improving stability of engineering structures underlain by expansive shale.

Evaluation of the mechanical properties and critical slope parameters of mine tailings at Enyigba, South eastern, Nigeria

“…These values are suggestive of slope material with average OMC and moderate MDD. The curves represent that of low to medium plastic clays described by Maduka et al [39], thus assenting with the consistency limits. Arora [3] noted that heavy clays of very high plasticity have very low-moderate dry density and high optimum water content, which is consistent with the view that high OMC and low-moderate MDD is suggestive of moderate materials.…”

“…These values implied low to moderate values of cohesion and low values of internal friction angle. The low shear strength parameter values could be the consequence of presence of expansive minerals [38,39]. The strength of a soil has been observed to drop whenever permeability inhibits drainage from the material voids owing to upsurge in hydrostatic pore pressure within the soil [9].…”

Integrated Geotechnical and Mineralogical Evaluation of the Subgrade of some failed Pavements along Enugu-Onitsha Expressway Southeastern Nigeria

“…The study area experiences a very heavy downpour of rain which originates from the tropics of the rain forest region's climates, accompanied by a stubborn high-intensity storm that ranges annually between 1850 and 2500mm. There are two prevalent seasons the study area experiences which include the wet and dry season respectively Maduka et al (2016). The wet season begins in April and gradually increases in intensity through May and June with a dramatic drop in August (commonly referred to as the August break).…”

Integrated geotechnical and mineralogical evaluation of the subgrade of some failed pavements along Enugu-Onitsha expressway Southeastern Nigeria

“…The study area experiences a very heavy downpour of rainfall which originates from the tropical rain forest region’s climates, accompanied by a stubborn high-intensity storm that ranges annually between 1850 and 2500 mm. There are two prevalent seasons the study area experiences which include the wet and dry season respectively 9 . The wet season begins in April and gradually increases in intensity through May and June with a dramatic drop in August (commonly referred to as the August break).…”