Self-boring pressuremeter

Notation and abbreviations

The following abbreviations are used throughout the working instructions for Cambridge Insitu pressuremeters:-

ADM – Adiprene Membrane

BFC – Ball Foot Clamp

CDU – Cutter Drive Unit

CHL – Chinese Lantern

CI – Cambridge Insitu

DMM – Digital Multi-Meter

DVM – Digital Volt-Meter

EIU – Electronic Interface Unit

EPC – Effective Pressure Cell

FESU – Fluid-to-Electricity Separating Union

GESU – Gas-to-Electricity Separating Union

HCP – Hydraulic Control Panel

Fitting re-usable hydraulic and pneumatic couplings

The alencoflex couplings on the instrument hose, and the hydraulic couplings on the power pack are almost all of a re-usable design and are fitted in a similar manner:-

  1. Make sure that the end of the hose is cut square, with no ragged ends of steel braid protruding.

  2. In the case of hydraulic couplings it is important to match the coupling to the hose – we use 'non-skive one wire' fittings throughout.

Checking the Lift-Off performance of the arms

From time to time it is as well to check that the arms on the instrument do not show an excessive amount of movement due to the application and removal of external pressure.

This is important because exactly this takes place every time the instrument is bored into the ground and a test carried out.

Checking the instrument for straightness

We have from time to time found it necessary to straighten an instrument. The jacking forces required to penetrate stiff formations can, if the instrument is not supported by the ground over its entire length, bend the instrument.

We have a jig which holds the instrument and allows a dial gauge to plot the departure from true as the instrument is rotated – see Figure 26-1. However such an arrangement is easily contrived, and it may be equally convenient to support the instrument in a lathe between centres.

Drying out a flooded pressuremeter

Note: the procedures described refer to operation with the Strain Control Unit. The symptoms and remedies still apply when an operator is controlling the system manually using the Pressure Control Panel.

If the membrane becomes punctured during the course of a test the first indication is an increase in activity from the Strain Control Unit as it attempts to put more gas into the instrument. If the leak is severe, the UP valve light will be on continuously, and the pressure:displacement plot on the computer screen will show a sudden fall in pressure.


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