Some design and performance considerations of diaphragm type pressure cells using strain gauges

Abstract

The two basic types of earth pressure cells that are commonly used are the piston type, which has a very rigid active face (where a change in pressure is reflected by the movement of the whole of this face), and the diaphragm type, which consists of a fairly flexible diaphragm clamped to a rigid edge. One of the intrinsic disadvantages of the diaphragm type of earth pressure cell is that it is most vulnerable to non-uniform stress distribution across its diaphragm. To overcome this problem special attention is paid to providing a uniform stress distribution during calibration and also trying to attain a fairly uniform distribution in the field by placing the cells with extreme care. However, it must be realized that a non-uniform distribution of earth pressure is the norm rather than the exception in nature. Even the most carefully placed earth pressure cell cannot avoid some degree of minor non-uniformity in pressure distribution. It is the purpose of this note to investigate this effect of non-uniform stress distribution on a diaphragm type earth pressure cell which uses strain gauges on the active diaphragm. From these studies, it is intended to find some means of minimizing the effect of this non-uniform pressure distribution in the initial design stage and of detecting the degree of this non-uniformity in pressure distribution so as to be able to assess the acceptability of the earth pressure cell readings during the final operation stage. /TRRL/