Coefficient of wall friction pm for the determination of pressures

B7.2.1 Principle of the test

A sample of the particulate material is sheared along a surface representing the silo wall (a sample with corrugation in the case of corrugated steel silos) and the friction force at the sheared surface is measured.

B7.2.2 Apparatus

The test apparatus is shown in Figure B1. The diameter of the box shall be at least 40 times the maximum particle size and the compacted height H of the sample shall be between 0,15D and 0,20D. In the case of wall samples with irregularities such as corrugations the box size shall be selected accordingly.

B7.2.3 Procedure

1) The reference stress shall be equal to the horizontal silo pressure.

2) Sample preparation shall be carried out according to the guidelines given in B6.

3) Shearing of the sample shall be carried out at a constant rate of approximately 0,04mm/sec.

4) The friction force F1 attained at large deformations shall be used in the calculation of the coefficient of friction (Figure B1).

Coefficient Friction Test Method
Figure B1 — Test method for determination of wall friction coefficient
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