The IUCM requires four additional input parameters when analysing anisotropic rocks. These are listed at https://forum.cavroc.com/d/111-list-of-input-parameters-used-in-the-iucm. A detailed discussion on how to assign the anisotropic input parameters when using the IUCM is provided by Vakili et al. (2014).
It should be noted that anisotropic behaviour is often overlooked during data collection or in laboratory tests. Much of the well-accepted literature on rock mechanics often recommends using isotropic behaviour with an average or lower bound of the rock strength properties instead of explicitly accounting for the anisotropic behaviour. Vakili et al. (2014) demonstrated that these conventional approaches could lead to significant errors, particularly in more challenging ground conditions.
The guidelines provided by Vakili et al. (2014) should be followed when selecting and preparing core samples for laboratory testing, carrying out laboratory tests, and interpreting the results. Refer to https://forum.cavroc.com/d/110-laboratory-testing-and-validating-test-results-for-anisotropic-rock.
Ideally, the miMin parameter should be obtained from triaxial tests conducted on samples with β angles (the orientation of the anisotropic fabric element with respect to the specimen loading axis) of between 30° and 45° (direction with the lowest strength). However, without this information, the ratio of tensile strength to UCS (both at their lowest value based on the β angle) can be used to estimate the miMin. As a rule of thumb, if none of the above methods could be used, a miMin equal to half of the miMax can be assigned.
The anisotropy factor (ratio of σc max to σc min) should be obtained from the results of laboratory UCS tests on samples with varying β angles. This ratio can be estimated from the U shape graphs of UCS versus β angles. In the absence of this information, Table 3.2 can be used to assign an indicative anisotropy factor based on typical foliation intensity present in the intact rock specimens.
Table 1 Classification of Anisotropy Intensity in Various Rocks
AnisoDip and AnisoDipD parameters are the dip and dip direction of the plane of weakness (anisotropy). Unless the model explicitly represents folding, the average values of dip and dip direction from mapping or core logging should be used.
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