Intruder penetration into granular matter studied by Lock-in   Accelerometry
  Understanding the penetration dynamics of intruders in granular beds is relevant not only for fundamental physics, but also for geophysical processes and construction on sediments or granular soils in areas potentially affected by earthquakes. In this work, we use Lock-in accelerometry to study the penetration of intruders into quasi-2D granular matter fluidized by lateral shaking. We observed that there are two well-defined stages in the penetration dynamics as the intruder sinks into the granular material. 
L. Alonso-Llanes, G. S\'anchez-Colina, E. Mart\'inez, A. J.   Batista-Leyva, R. Toussaint and E. Altshuler
cond-mat.soft