The Influence Of Increase In Fines Content On The Engineering Properties A Sandy Soil Deposit In Nsukka, Enugu State, Nigeria.

ABSTRACT

This project addresses the effects of increase in fines contents on the geotechnical properties

of sandy soils and the roles the fines play in slope instability in Nsukka, Enugu state in

Nigeria. Field investigation revealed that the major landslides and gully erosion sites in south

eastern Nigeria are localized within areas where these sandy soils are present. Geotechnical

investigation of these sandy soils was carried out to assess their importance in the numerous

geohazards in the area. Particle size analysis show that the soil is uniform-medium grained

sandy soil; with large amount of fines matrix .The value of the sandy soil's coefficient of

uniformity (Cu) is 6.The sandy soil sample collected was sieved and the fine and coarse grain

matrix separated. Particle size analysis, compaction test and shear tests was conducted on

samples with mix ratios of 10%, 20%, 30% fines content. The coefficient of permeability (K)

for the mixed soil sample was calculated using the Allen Hazen's empirical method. It was

found that as the fines content increased from 8.85% fines content to 30% fines content the

values of K decreased from 4.26 X 10-4-5.0 X 10-6 (cm/s). The reduction in permeability

values shows that the soils drainage properties reduced with increase in fines content of the

soil. The compaction test result shows that, as the fines content increased from 8.85%-30%,

the maximum dry density decreased from 1.84Kg/m3 to 1.494Kg/m3. However the optimum

moisture content increased from 10% to 18%.The soils were tested under a 300 KN/m2 total

normal stress in unconsolidated undrained (UU) Triaxial test and 517 KN/m2 normal stress in

direct shear testing conditions. It was found that; the internal friction angle decreased with

increase in normal stress and fines content while the value of cohesion increased with

increase in fines content and normal stress under triaxial and direct shear testing conditions.

From the results of the study it was concluded that the susceptibility of sandy soils within the

region to landslides is enhanced by the large amount of fine grain matrix.