Correlation analysis of flexible road pavement surface condition and load bearing capacity of subgrade soil

Following the continuous deterioration of flexible road pavements on Federal Highways in Northern Nigeria, which in some quarters is attributed to poor structural capacity of the subgrade soil or design and workmanship; this study examined the relationship between the instantaneous surface condition of flexible road pavement and the California Bearing Ratio (CBR) values of the corresponding subgrade soils. An investigation of road surface condition was carried out on 60 km length of the Zaria – Kaduna Federal Highway in Northern Nigeria. Experimental results on the mechanical properties of the corresponding subgrade soils of road segments measured at Chainages were obtained from the Nigeria Federal Ministry of Power, Works and Housing (FMPWH). The primary data used by the study were measured as quantities of surface area distresses along the site which included; cracks, potholes, rutting and edge failure, while secondary data from the FMPWH database included; natural moisture content, maximum dry density, specific gravity, liquid limit, plastic limit, liquidity index, optimum moisture content, California Bearing Ratio (CBR), percent of soil particles passing #200 sieve and AASHTO classification of the subgrade soil. A Pearson correlation analysis between the road pavement surface condition and the CBR value of the subgrade soil at 95% Confidence Level using a 1-tailed statistics for the test hypothesis revealed that, there was no dependency between the pavement surface condition and the corresponding CBR property of the subgrade soil

Effect of Reagent Concentration on Strength of Lateritic Soil Bio-Treated with <i>Bacillus thuringiensis</i>-Induced Calcite Precipitate Tested with Pocket Penetrometer

The strength of lateritic soil bio-treated with a Bacillus thuringiensis (Bt)-induced calcite precipitate was investigated using a pocket penetrometer (PPT). The effect of bacterial (Bt) and cementation solution concentration (Cs) on the strength of the microbial-induced calcite precipitate (MICP) worked soil was also evaluated. Soil samples were treated with Bt and Cs using three mix ratios (i.e., 25% Bt: 75% Cs, 50% Bt: 50% Cs, and 75% Bt: 25% Cs) based on the natural soil liquid limit (LL = 36.0%). Bt suspension densities of 0, 1.5 × 108, 6.0 × 108, 1.2 × 109, 1.8 × 109, and 2.4 × 109 cells/mL were applied to the soil with four varying Cs concentrations (i.e., 0.25, 0.5, 0.75, and 1 M). The prepared specimens were allowed to homogenise and equilibrate at laboratory conditions. A pocket penetrometer (PPT) was used to test the unconfined compressive strength (UCS) of the prepared specimens at 3, 5, and 7 days after bio-treatment to evaluate the strength of the MICP worked soil at different moisture contents. The results obtained show that the UCS values increased with higher Bt and Cs as well as with a reduction in moisture content as the bio-treated soil equilibrated with the environment. The recorded UCS values for the mix ratios considered were in the order: 50% Bt: 50% Cs > 25% Bt: 75% Cs > 75% Bt: 25% Cs. Therefore, a PPT can be used to determine the approximate unconfined compressive strength of treated soil