1. O.T. Omogbehin 1 & E.J. Ajidahun 1 University of Benin, Department of Geology, Benin City, Nigeria. The Physico-chemical Parameters responsible for road failures in Southern Nigeria. Geotechnical tests were carried out, these include, Atterberg test, particle size, compaction test and plasticity index. Sieve analysis showed that the soils from this zone are within the medium to coarse grain range with low percentages of silt/clay, therefore the soil is non plastic. The compaction tests also showed that the optimum moisture content ranges from 13.50% to 15.20% while the maximum dry density ranges from 1.75mg/m 3 to 1.98mg/m 3. The plasticity index revealed that the soils are non-cohesive and non-plastic because it ranged from 1.2% to 5- 2%. The maximum dry density values are generally low which indicated that the soil is not compact but loose. There were presences of pockets of smectitic clay with high montmorillonite content. This has the most swelling potentials and accounts for the most of the damages resulting from expansive clays. UNIVERSITY OF BENIN, NIGERIA RESEARCH BACKGROUND: Loose sands are prone to a number of geological/environmental problems like erosion and mass wasting. Road failure in the southern part of Nigeria is a phenomenon that scientists have shown much interest on. Diagenetic fabrics of compaction, dissolution, alteration and corrosion were common features. The reaction rims around grain margins indicating severe alteration and corrosion were seen growing from grain margins inward, leaving the sandstone, which many have been indurated with little or no cementing material, thus leading to the friability of the sandstone and its susceptibility to erosion. Apart from the friability of the soil in this area, mineralogical compositions of the underlying soil have made the area prone to some hazards. AIMS: This study aims at investigation of the physico-chemical parameters that are responsible for the road failures in southern part of Nigeria which is majorly overlay by the loose sand particularly the Nanka and Ajali Formations in Nigeria with view to using the results to state the remediations that will be used to reduce the menace of raod failures and erosion in the area. Thus, there is need to understand the physical, chemical and mineralogical composition of the soil in this environment PROCEDURE: Grain Size Analysis was carried out with the use of Camsizer and Sedigraph. So also, Atterberg limit test, Compaction and plasticity Index tests were carried out, while mineralogical constituents were determined using X-Ray Diffraction (XRD). Figure showing failedroad in Anambra State Failed Road in Asaba, Delta State Figure showing the loose sand in Auchi ( Failed Road in Benin, Edo State Failed Road in Port-Harcourt, River State Mineral Liberation Analyser (MLA) and x-ray mapping with the GXMAP (Ford analysis or grain-based X-ray mapping) method.Ford analysis or grain-based X-ray mapping Use ITRAX to monitinor the hardpan formation along the column Particle Sise Distribution SUMMARY OF THE SOIL TEST IN THE STUDY AREA S/NO SAMPLE LOCATION DEPTH (m) SMECTITE CLAY (%) PLASTIC LIMIT LIQUID LIMIT PLASTIC INDEX MDD (kg/m3) OMC (%)CBR (%) 1Asaba2.051525.033.58.51.7514.920.3 2Auchi0.951325.733.09.31.9713.524.2 3Ahoda1.501327.335.05.71.9614.418.4 4Asaba1.901425.028.18.51.9815.223.1 5Asaba 11.901220.625.67.21.9714.393.8 6Anambra1.021215.723.59.91.9714.4123.3 7Benin2.401317.333.55.51.9714.1110.67 8Benin 22.501417.3529.011.661.9614.04114.27 TOTAL14.22106179.95241.266.2515.53114.84528.04 MEAN1.78813.2521.74430.158.2811.94114.3566.005