Subsoils for support of roadway, airfield, and parking area pavements are being improved and reinforced by the incorporation of a grid of small diameter, short, stabilized, vertical, granular columns. The method is a smaller-scale variation of a patented process to reinforce bearing soils beneath building foundations. The columnar material can consist of soil, soil with chemical agents, soil with special synthetic inclusions, artificial soil, or stone. The grid of columns is constructed simultaneously using a single apparatus. The improvement of subsoils in this manner is rapid and economical in many applications. To determine qualitatively and quantitatively the degree of improvement which can be obtained, a finite element analytical study and laboratory and field experimental research programs are being conducted on a variety of soils using the stabilization method. Laboratory tests include one-dimensional compression, triaxial, and large-scale plate bearing tests. A series of plate bearing tests, as well as borehole shear, KO-blade, and dynamic penetrometer tests are being conducted in the field on in-situ soil reinforced with full-scale elements. In addition, a prototypical apparatus for constructing a single granular column in-situ is being produced and used to construct the granular columns for the field experiments. The finite element analyses are being conducted to model the results from the laboratory and field tests, and to perform a parametric study of the important factors influencing the degree of improvement which can be obtained from incorporation of granular columns constructed of a variety of materials within different subgrade soils. The results from the laboratory and field tests can be extrapolated to subgrade soils and conditions not tested in the experimental research program. Evaluation of the results from the analytical and experimental studies will establish the feasibility of the proposed method for stabilizing subsoils to support pavements.The potential commercial application as described by the awardee: Small-scale granular columns will produce low-cost, reliable, pavement system reinforcement by use of special, patented compaction equipment. Potential commercial applications are international in scope and include roadway, airfield, and parking area pavement systems.
