Volume 30, Issue 4 (July 2007)
Design of a Miniature Piezoprobe for High
The stratigraphic features present in all natural deposits, which reflect their deposition environment, can significantly influence the response of these deposits to engineered construction. This paper presents the development of a miniature piezoprobe optimized for the continuous detection of stratigraphic features within a varved soil deposit where individual layers are less than one centimetre in thickness. The study uses previous research to identify parameters in the design of a field-deployable miniature piezoprobe and to present a framework that enables stratigraphic detection from pore pressure measurements. Laboratory experiments on the ability of fluids to saturate the filter and the influence of the fluid-filter system on piezoprobe sensitivity reveal that low to moderate viscosity immiscible fluids (e.g., 100 cS silicone oil) provide optimal performance considering practical implementation aspects. Laboratory and field studies that examine the soil deformation characteristics within the vicinity of such probes indicate that an apex filter location is preferable for stratigraphic detection and that soil deformations around the probe are primarily limited to less than one probe radii. Proof of concept results from an in situ profile obtained with the miniature piezoprobe compares well with measurements from a continuous core sample from a Connecticut Valley varved clay deposit.