This paper describes a detailed field study in which multiple in-situ test methods were used to characterize the subsurface material at 3 selected sites. The test methods included: the pressuremeter test (PMT), standard penetration test (SPT), Texas cone penetration test (TCP), dynamic cone penetration test (DCP) and falling weight deflectometer (FWD) test. The data collected were used to determine the soil stiffness parameters; modulus of subgrade reaction and the modulus of elasticity. These soil parameters were then used in appropriate soil-structure interaction models to calculate moments, shear and axial thrusts at critical sections of three instrumented concrete box culverts located at these sites. The calculated moment and load demands were then compared with those determined from measured strains. The results from these comparisons were used to draw conclusions regarding the validity of demand predictions made using different model-soil stiffness parameter combinations.