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/
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