In-situ modulus detector for subgrade characterization

Resilient moduli are widely used in mechanistic analyses to predict distresses in pavement structures. The objective of this study is to develop an in-situ modulus detector (IMD) to evaluate the resilient moduli of subgrades based on various influencing factors. The IMD consists of a tip module, a driving rod, and a hammer-drop system. In the tip module, a load cell and an accelerometer are installed to measure the dynamic responses of force and acceleration. The resilient modulus is calculated from the deviator stress and the recoverable strain determined using the IMD. A weathered soil is prepared for the compacted specimens that are used in the dynamic penetration tests. These dynamic penetration tests are conducted with the IMD on four compacted specimens with different water contents under seven different hammer-drop heights. The experimental results demonstrate that the maximum amplitudes of the force and displacement depend on the drop height of the hammer and the water content of the compacted specimens. The resilient modulus profiles obtained from using the IMD can be influenced by the hammer energy, water content, and dry density of soils. The IMD may be a promising field-testing device to evaluate the in-situ resilient moduli of subgrades.