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Dear Nicholas Salt To read a hydraulic piezometer reliably the pressure in the tubing should ideally be positive everywhere. Thus the readout unit and tubing should preferably be below the piezometric level and certainly not more than about 5m above it otherwise cavitation becomes a problem and air bubbles form in the tubes. Thus hydraulic piezometers are often used in dams. Those problems do not arise with pneumatic piezometers but you need to know the level of the tip precisely. Regards David Nash On Fri, 14 May 1999 09:16:43 +0000 [log in to unmask] wrote: > Urgent query which I hope will prompt some discussion........... > > IF cost and negative pore pressures were not an issue but accurate > assessment and rapid response was, would you opt for Pnematic or Hydraulic > piezometer in Basal London Clay/W&R Beds.........In addition, it has been > suggested to me that tubing and the readout unit must remain within 5m of > the piezometric level, is this really the case? > > Am in need of advice PDQ if anyone can offer it > Regards > Nicholas Salt > ------------------------------------------------------------- David Nash Phone Office: +44 (0)117 928 7714 Dept. Civil Engineering Secretary: +44 (0)117 928 7707 University of Bristol Fax: +44 (0)117 928 7783 Bristol BS8 1TR, UK [log in to unmask] ------------------------------------------------------------- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%