Urban Landslides due to Increase in Fines Content on the Engineering Properties of Sandy Soil Deposits in Nsukka, Nigeria

摘要

Major landslides and gully erosions in Southeastern Nigeria are localized within the areas of Ajali and Nanka sandy soils as revealed by field investigations.Geotechnical investigations of these sandy soils were carried out to assess their importance in the numerous geohazards in the area.Particle size analysis shows that the soil is uniform-medium grained, with large amount of fine matrix.The value of coefficient of uniformity (Cu) is 6.The sandy soil samples collected were sieved and the fine matrix separated.The fines were mixed in ratios with soil samples and particle size analysis, compaction test and shear test was conducted on the soil samples with mixed ratios of 1o％, 20％ and 30％ fines content respectively.The coefficient of permeability (K) for the mixed soil samples decreased from 2.25x10-2 m/sec.to 2.5x10-3m/sec.As the fines content increased from 8.85％ to 30％.The reduction in permeability values shows that the soil drainage properties were affected by the increase in fines content of the soil.The compaction test result shows that, as the fines content increased from 8.85％ to 30％, the dry density decreased from 1.897kg/m3 to 1.494kg/m3.However, the optimum moisture content increased from 10％ to 18％.The internal friction angle decreased with increase in fines content and normal stress in triaxial and direct shear testing conditions.From the results of the study, it was concluded that the geotechnical properties of the sandy soils are affected by the amount of the fines present.It was also found that the susceptibility of the sandy soils within the region of gully and mass movement processes is enhanced by the large amount of fine grain matrix.