ABSTRACT
Lightweight deflectometer (LWD) has been increasingly used to assess the in-situ elastic modulus of the ground because it is portable and simply operated. It can rapidly evaluate not only the mechanistic soil properties but also the effect of foundation improvement earth works when it is conducted. A typical LWD has a mass of about 20 kg which is dropped onto the ground surface. The peak value of impulse force is from 7 to 20 kN and its loading duration is from 15 to 30 ms. The commonly used method for estimating the ground modulus from LWD test results is derived from the theory of a homogeneous, isotropic, elastic half space subjected to static load applied over a circular area. At least there are two short comings in the current practice. One is that LWD test is dynamic and its loading duration is too short to consider it pseudo-static. The second is that when the ground needs to be modeled by more than two layers, the current approach not be used to estimate multiple layer moduli.
