Critical State of Lateritic Soils Taken from Varied Burrow Pit Depth

Abstract

The study aimed to investigate the behaviour of Lateritic soil at a critical state. Four undisturbed samples were taken at 1.5 m and 3.0 m respectively. Laterite materials were sourced from Janguza Burrow Pit. The samples were collected by manual digging to a depth of 1.5m and 3.0 m and inserted in polyethene bags. To classify the material, the tests conducted on the soil samples included natural moisture content, Atterberg limits, specific gravity and particle size distribution. Furthermore, Undrained Triaxial test was conducted on the soil samples with the measurement of pore pressure to determine the critical state condition of the Lateritic soil. The average moisture content value for 1.5 m depth was 3.83%, and that for 3.0 m depth was 5.57%. Atterberg limits at 1.5m depth are as follows: Liquid limit (LL) =22.9%, Plastic limit (PL) =12.6% and Plasticity Index (PI) =10.3% and for 3.0 m depth the values are Liquid limit (LL) =22.1%, Plastic limit (PL) =9.48% and Plasticity Index (PI) =12.7%. The average specific gravity is 2.67 and 2.71 for 1.5m and 3.0m depth respectively. Samples at 1.5m are found to be Well–Graded (GW) gravel-sand mixtures from sieve analysis result, while samples at 3m depth were found to be Well-Graded except sample A and D which showed poorly graded sand (GP) and gravel-sand mixtures. The samples were found to be overconsolidated and at dry side of critical. The state of stress and void ratio ranges from 30.55 kN/m2to 60.47 kN/m2 and 0.12 to 0.18 respectively. Pore pressure was stable at a range of 0.006%- 0.045% for 1.5m depth and 3.0m depth was stable at 0.005%- 0.004%. The sample reached critical state condition at deviator stress ranges 229.74 kN/m2 to 274.31 kN/m2 for 1.5 m and 3.0 m depth. The average values of the critical state soil parameters at 1.5m and 3.0 depth are ⋋=0.174, Γ=2.07 and M = 0.885 and ⋋=0.299, Γ=2.839 and M = 0.813, respectively. The results indicated that both samples were heavily overconsolidated. Overconsolidated soils heave when used in road construction, thus presenting maintenance challenges to road authorities. It is important to carry out periodic checks on the state of consolidation of soils to avoid the use of overconsolidated soils in construction. Similarly, to ensure that soils from burrow pits performed satisfactorily an oversight function should be exercised by the appropriate ministry.