Comparison of load parameters for stored materials: CA-Silo Collaborative action on

The load parameters listed in the european prestandard and those derived from the material tests conform reasonably well in many cases. There are, however, also many cases where the agreement is not satisfactory, especially due to larger variability of the measured values. This yields cretainly for coal, and perhaps also for flour. There are too few parameters determined from triaxial tests and direct K-measurements to judge if these, presumably more accurate tests, gives systematic different results. Where exactly the same material has been used in different apparatus large differences are found in several cases. The measurement of reliable and relevant wall friction coefficients is a severe problem. If the wall friction depends on if the normal load is increasing or decreasing, it is the value for increasing load which should be the relevant load parameter, but for coal and wheat it is seen that the wall friction measured in a silo might be significantly larger than the value obtained from shear tests. The load parameters depend on the load level, perhaps in a way not reflected by the internal friction angle. It is not necessarily on the safe side to determine the parameters for a high load level.