Abstract
Field tests and numerical analyses conducted to establish the feasibility of reinforcing soft, loose, or otherwise inadequate subgrade soils with a grid of small-diameter, stabilized, vertical granular columns to support traditional pavement systems are described. This technique may prove to be cost-effective if it is used to improve subgrade soils so that the sub-base or base courses can be reduced in thickness or eliminated. Field plate bearing tests were carried out on unreinforced cohesionless silty sand and on the same soil reinforced with vertical reinforcing columns constructed of four materials: crushed granitic gneiss, silica sand, cement-stabilized native soil, and cement-stabilized silica sand. The field tests indicated that the columns made of the two cement-stabilized materials substantially increased the subgrade modulus of the native soil. In contrast, the two unstabilized columnar reinforcing materials produced no substantial improvement in stiffness. The field tests were modeled by using an axisymmetric finite-element (FE) program and hyperbolic constitutive relationships for the native soil and the columnar reinforcing materials. Triaxial tests were performed on reconstituted specimens of the native soil and compacted specimens of cement-stabilized native soil to determine the stress–strain–strength parameters required for the FE analyses. The FE analyses modeled the plate bearing tests on the reinforced soil to a reasonable degree, indicating that the FE method used has the potential to simulate a complete pavement system (including a wearing surface) in which the subgrade soil is reinforced with columns of stabilized granular materials.
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