Soil stiffness as a function of dry density and the degree of saturation for compaction control

A data set of the coefficient of vertical subgrade reaction for a plate diameter of 30 cm, K-P.FWD, measured by Portable Falling Weight Deflectometer tests in full-scale compaction tests on sandy soil using various types of compaction machines was analysed. Based on this analysis and the previous analysis of a CBR data set from another full-scale compaction test series, a set of conclusions could be drawn. The soil stiffness indexes (SSIs), CBR and K-P.FWD, can be expressed by, respectively, an empirical equation multiplying a function of rho(d) and another of S-r, where CBR and K-P.FWD decrease significantly as S-r increases. As such, rho(d) values cannot be estimated from SSI alone. By fixing the field rho(d) - w compaction curve by keeping the soil type and the field compaction energy level, CELf, to those in the field compaction tests in which the SSI - rho(d) - S-r correlation has been calibrated, field compacted rho(d) & w states can be estimated by measuring the SSI values. Then, by the upper-bound and lower-bound control of SSI, the field compacted states approach the specified target, where, typically, rho(d) = the maximum dry density for CELf and S-r = the optimum degree of saturation, (S-r)(opt). A method to incorporate this indirect but fast SSI-based compaction control into the conventional rho(d) & w-based compaction control is proposed. (C) 2021 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.