ABSTRACT
Sands, clays, and shales (Ti) of Illaro formation from the Tertiary era are of A-7-5 classification. Shales and round stone (Kro) of Nkporo shale group formed from cretaceous era have A-7-5, A-2- 7 and A-6 classification; Shales, and limestone (Kwn) of Agwu-Ndeaboh shale group formed from cretaceous era are classified as A-6, A-2-7, and A-7-5; while black shale and siltstone (Kea) of Eze Aku shale group formed from cretaceous era have A-2-6, and A-7-6 classifications. Granitoids (Pcg) of older granites series in basement complex formed from Pan Africa era are mainly A-7-6, A-7-5 with few A-6, and A-2-6 classifications; Gneiss migmatate complex (Pcb) of Migmatate Gneiss schist complex formed from Basement complex of Precambrian era have A-2-4, A-2-6, A-2-7, A-7-5, and A-7-6 classifications; Meta-sediments/Volcanics Gneiss formed from Migmatate Gneiss schist complex of Basement era have A-4, A-6, A-7-5 and A-7-6. Generally, it is observed that the lower the Atterberg limits, the better the materials. The sub grade materials in the North central zone have the percentage passing BS No 200 sieve from 7 to 94, while the liquid limit value ranged from non plastic (NP) to 72 % and 7 plasticity index ranged from non plastic (NP) to 46 %. The soils used for sub-grade are suitable except in few locations where the specification was not met. The sub grade materials in the North east zone have the percentage passing BS No 200 sieve from 10 to 93, while the liquid limit value ranged from NP to 61 % and plasticity index ranged from NP to 33 %. Suitable materials were met except in few locations where the specifications were not met. The sub grade materials in the North west zone have the percentage passing BS No 200 sieve from 2 to 89, while the liquid limit value ranged from NP to 77 and plasticity index ranged from NP to 45. The soils are of good qualities in most locations except in few areas with very fine soil where percentage passing BS No 200 sieve is greater than 35, with high value of liquid limit These make the soils to be susceptible to high volume changes upon contact or withdrawal of moisture. The sub grade materials in the South west zone have the percentage passing BS No 200 sieve from 9 to 56, while the liquid limit value ranged from NP to 65 % and plasticity index ranged from NP to 28 %. The percentage passing BS No 200 sieve for sub grade materials in the South east zone have ranged from 7 to 94, while the liquid limit ranged from NP to 72 % and plasticity index ranged from NP to 46 %. The material was very fine and this region had stone base and soil-cement in their base course. The percentage passing BS No 200 sieve for sub grade materials in the South south zone ranged from 15 to 60, while the liquid limit value ranged from NP to 70 % and 8 plasticity index ranged from NP to 44 %. The material is very fine. This region has stone base and soil cement in their base course.