Development of In-Situ Modulus Detector for Transportation Substructure

Resilient modulus of the subgrade is used for design and evaluation of transportation substructure. However, existing testing methods, e.g., falling weight deflectometer, can only provide the profile of resilient modulus of the substructure indirectly estimated from the measured deflection on the surface. The objective of this study is to develop a new testing device, so-called in-situ modulus detector (IMD), to evaluate the stiffness of subgrade along a depth. The IMD consists of a hammer, a guide, a driving rod, and a tip. At the bottom of the driving rod, a piezoelectric accelerometer and a load cell composed of four strain gauges are installed. To investigate and compare the penetration performance, three different shaped tips of the IMD are used. For dense and loose specimens, dynamic penetration tests are carried out by using eight different falling heights. The test results demonstrate that the penetration depths of cone-shaped tip are greater than those of wedge- and plane-shaped tips, regardless of soil density. The effect of buffer on penetration performance is significant for dense specimen. Based on the dynamic response, in-situ resilient modulus profiles are estimated along the penetration depth.