On the Feasibility of Pressure Profile Measurements With Time-Domain Reflectometry

Many applications in geotechnical engineering require knowledge of total pressure distributions. So far, only measurements at single points at individual locations of interest can be carried out with conventional geotechnical measurement devices. Time-domain reflectometry (TDR) has already been used to assess the amount of shearing at multiple distinct locations along coaxial cables grouted in a rock or soil mass. However, pressure profile determination has not been investigated up to now. A novel approach has been investigated to determine pressure profiles from the time-domain reflection data of transmission lines. Mechanical forces change the distance between rubber-insulated conductors of transmission lines and, therefore, affect the spatial distribution of capacitance and inductance. These variations lead to partial reflections of an incident step pulse from which physical parameter distributions along the inhomogeneous transmission line are reconstructed. A reconstruction algorithm that was originally developed for soil moisture profile determination (Spatial-TDR), was adopted and applied in laboratory experiments. A further experiment illustrates TDR signals that can be expected in actual applications under different load conditions.