Subgrade Resilence Modulus Rapid Examination

Subgrade resilient modulus is mainly mechanical parameter to indicate subgrade bearing capacity in the evaluation of pavement design, construction quality and pavement performance. The subgrade modulus influenced the design thicknesses of pavement directly. So, the study of subgrade resilient modulus is significant. Now, some shortcomings are complicated in testing, long in test time, more in tester, expensive in equipments and difficult to remote place in the testing methods of subgrade resilient modulus in the specifications of pavement design and construction. The results with the different testing methods are different. At the same time, there is not uniform between subgrade design index (subgrade resilient modulus) and construction control index (compaction degree). Therefore it will be urgent to research a kind of method with practice, rapidness and convenience to test subgrade resilient modulus and to control construction quality of subgrade reasonably.Through a great deal of indoor and outdoor testing, a rapid method with Portable Falling Weight Deflectometer (PFWD) to test subgrade resilient modulus is studied. The method has some advantages with short test time, few tester, light equipment and wide test site. The researches show that the testing data with PFWD is precision and reliable. So the correlations of PFWD and bearing plate, CBR, deflection, FWD are established according to many testing results. The analyses indicate that the correlations are good in double logarithm.There are many factors to influence subgrade resilient modulus, and the main 3 factors are soil type, compaction degree and moisture content. Soil type belongs to physical character of soil including 2 soil character parameters of particle size and limit of moisture. According to the 4 aspects of compaction degree, moisture content, particle size and liquid plastic limit, the paper analyzes the influences each parameter on subgrade resilient modulus. The correlations of single factor and multi factors are created respectively between subgrade resilient modulus and each factor. The results show that there are good correlations between subgrade resilience modulus and each factor. Through the above analyses, a reasonable method to decide subgrade resilient modulus is obtained which can provide the scientific design parameters.