Matric suction measurements of compacted subgrade soils

The mechanical response of compacted subgrade soils is highly influenced by matric suction. This paper proposes a detailed procedure for matric suction determination, using the filter paper technique, in samples compacted in the laboratory using the standard Proctor procedure (ASTM D698-12). Special attention is paid to the quantification of errors associated with the measurement of matric suction in compacted soils using the filter paper technique. The procedure is illustrated through suction measurements made for two fine-grained soils obtained from Indiana road sites. Soil samples were compacted at the optimum water content (OWC) and also both wet and dry of optimum. Test results indicated that the matric suction was substantially different for soils compacted on the dry side of the OWC and at the OWC. Matric suction measurements approached zero for soils compacted at water contents greater than the OWC + 2%. At the OWC, the soil with the lowest plasticity index but highest clay content developed higher matric suction than the soil with the highest plasticity index. The proposed test procedure facilitates the estimation of matric suction of subgrade soils in the laboratory.