This paper presents a method for estimating the strength and stability of
model coal pillars with bedding planes (weakness planes) inclination. The
strength of coal relative to the angular difference between the principal
stress direction and bedding planes is considered. The failure behaviour of
model coal pillars containing weakness plane inclination by using
servo-control Schenck Machine are shown. Uniaxial and triaxial
compressive strength of coal specimens are investigated, and test results
indicated that the strength of coal pillars depends on the weakness planes
inclination with respect to the principal stress direction. However, it is
shown that with increasing confining pressure, the effect of weakness
planes inclination on the strength of the coal specimens is reduced. An
empirical method is given for prediction the compressive strength of coal
containing weakness planes inclination. The results of this method are
compared with the experimental results and Jaeger theory. Finally, three
well-known empirical strength criteria were tested against the triaxial test
data for coal containing weakness planes inclination.