||The department Civil Infrastructure of TNO Building and Construction in Delft makes use of a drop weight setup. This is a tool to administer a vertical force pulse to the ground, the input. On other locations the output motion is measured by geophones or accelerometers in order to assess the parameters of shock transmission.
The problem of the setup is that the impact pulse shows a modest quality (irregular spectrum) and its transmission through the soil has a poor coherence.
The technicians sometimes modify the pulse (to add “damping”) by catching the mass on an improvised layer of rubber or wood. Similar practice is used in some shock and impact laboratories where drop tables are installed to expose objects to fragility tests. Down, at the end of the guidance rail, often a block of lead is situated as a “damper”, optimistically called a “shock programmer”.
TNO is considering the development of an advanced drop weight with a controlled brake, which not only acts as a release mechanism, but also allows for real time computer controlled deceleration. Various deceleration patterns can be designed, such as single stop, sine burst, shock, etc. The mechanical construction does not pose problems, but measurement and control obviously require more care. The contribution can comprise considerations on the input-output aspects of terrain impacting (the function) as well as the specification of control loop, feedback means, and the effect of alternative deceleration designs.