Estimation of Stiffness of Non-Cohesive Soil in Natural State and Improved by Fiber and/or Cement Addition under Different Load Conditions

The aim of this study was to compare the stiffness of gravelly sand under various load conditions—static conditions using the CBR test and cyclic conditions using the resilient modulus test. The tests were conducted on natural soil and soil improved by the addition of polypropylene fibers and/or 1.5% cement. The impacts of the compaction and curing time of the stabilized samples were also determined. The soil was sheared during the [Formula: see text] tests, even after fiber reinforcement, so the resilient modulus value for the unbound sand could not be obtained. The cement addition improved [Formula: see text] , and the curing time also had an impact on this parameter. The fiber addition increased the value of the resilient modulus. The CBR value of the compacted gravelly sand was relatively high. It increased after adding 0.1% fibers in the case of the standard compacted samples. The greater fiber addition lowered the CBR value. For the modified compacted samples, each addition of fibers reduced the CBR value reduced the CBR value. The addition of cement influenced the CBR increase, which was also affected by the compaction method and the curing time. The addition of fibers to the stabilized sample improved the CBR value. The relationship [Formula: see text] obtained for all data sets was statistically significant but characterized by a large error of estimate.