The structural response of box culverts to variable soil compressibility condition was studied in this paper. This was made possible by modelling the soil as springs, and varying the spring stiffness which was represented by the modulus of subgrade reaction of the soil. The results showed that the values of maximum bending moments for gravity actions on box culverts increased linearly with modulus of subgrade reaction, but remained within close values. The results also showed good agreement with results from literature for highly compressible soils. However, for incompressible soil condition, results from standard tables in literature were more conservative with about 10% difference for gravity actions, and 21% difference for lateral actions. The term ‘highly compressible’ that was used in literature for manual analysis was discovered to be more valid for lateral load cases than for gravity load cases. Subsequently, the variations of other action effects such as shear force, axial force, torsion, and soil spring settlement with modulus of subgrade reaction were also studied.
Keywords: Box Culvert, Modulus of Subgrade Reaction, Soil Settlement, Staad Pro.
Proctor method), West African Standard (WAS), and British Standard Heavy (BSH) (equivalent of modified Proctor method). These methods are laborious, time-consuming and material-consuming (Jayan & Sankar, 2015). The shortcomings outlined above together with proof by some earlier authors Ring et al. (1962), Ramiah et al. (1970), Benson et al. (1998) and most recently Anjita et al. ( 2017) that soil type, its grain size distribution, index properties, and specific gravity influence the MDUW and OMC of soils led researchers to develop empirical relationships between MDUW/OMC and index properties of soils. Such index properties as liquid limit (LL), plastic limit (PL), plasticity index (PI), fines content (FC), sand content (S d C) etc. have previously been used.
In this study, the optimum stabilizer content for a poor lateritic soil intended as subgrade material for a pavement was sought. The natural soil was first characterized and classified and the soil fall into the class of A-6 based on Nigeria General Specifications for Roads and Bridges (NGSRB) AASHTO soil class for pavement construction. The soil was stabilized at three binder points of 4%, 8% and 12% which coincided with specification limits for cement based on NGSRB with the range of 7-11% recommended for soils in the class A-6. The results from the compaction tests and unconfined compressive strength (UCS) tests show that the suitable stabilizer falls within the specified range of 7 – 11%. Binder contents/proportions of 4% RHA, 8% RHA, 8% (50R + 50O), 4% (60C/L + 40R/O), 8% (70C/L + 30R/O), 8% (0C/L + 100R/O), 8% (50C/L + 50R/O) gave the most promising results of MDUW and UCS. In other to carry out a comprehensive investigation of the properties of the soil to determine which of the promising binder contents/proportions would be most suitable as stabilizer for the soil, it was recommended that other qualifying tests of specific gravity, Atterberg limits, CBR, UCS, durability and permeability tests be carried out for these recommended binder contents/proportions.
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