Geotechnical Investigations of Road Failures Along Benin Technical School Road, Benin City, Edo State

Abstract

The study evaluated the possible causes of pavement failures in Benin
Technical School Road, Benin City, Edo State. Disturbed soil
samples were collected from three (3) Sampling points in the study
area at a depth of 1m each. Soil samples were kept inside a
polyethene bag and taken to the laboratory and their geotechnical
characteristics was analysed according to ASTM. Sieve analysis,
natural moisture content, specific gravity, Atterberg limits,
Compaction and California Bearing Ratio (CBR). The results of the
test showed that the soil samples were mainly silty /clay with little
amount of fine sand. The percentage of soil passing the 75 mm sieve
size ranges from 20% - 33.1% for sampling points 1, 2 and 3. The
liquid limits was determined to be 31.94%, 23.38% and 21.03%,
while the plasticity index ranges from 11.95% - 17.67% for the three
sampling points. The specific gravity ranges from 2.48-2.51. The
maximum dry density values (MDD) are 1.83g/cm3
, 1.84g/3and
1.81g/cm3
, while the optimum moisture content values were 12.87%,
12.0% and 11.19% respectively for the three sampling points. The
California Bearing Ratio, (CBR) ranged from 3.46% to 21.70% for
soaked and 16.10 –37.59 for unsoaked samples in the three sampling
points. From the CBR result it can deduced that none of the soil
samples met the criteria for road sub-grade as CBR values for all the
soil samples were above the required 10%.Findings indicates that
failure along the study area were due to the unsuitability of the soils
as sub grade material and effect of ground water intrusion.As a
consequence may be responsible for the road instability; ultimately
leading to failed portions.The soil was classified as A-2-4 soil based
on AASHTO soil classification system. Also, the results of this
research will add to existing literatures in the in design and
construction of roads that can stand the test time.