In the longwall exploitation system, the main gates are subject of the
most intensive movements of the rock mass, where the proximity of the
excavation front is a key factor. The paper presents the results of a
research on the constants *mb* and s of Hoek-Brown failure
criterion for the rocks surrounding the gallery: shale, sandy shale,
coal and medium-grained sandstone, in relation to the distance to
longwall face. The research comprised numerical modeling based on
convergence monitoring records. The convergence measurements were
carried out on three stations in a selected maingate in a coal mine from
Upper Silesia Coal Basin near Jastrzębie-Zdrój, concurrently with
changing distance to the longwall face. The measured were the width, the
height and the heave of the floor of the gate. The measurements showed
that the convergence at the longwall-maingate crossing was 1.5-3 times
greater than in the locations much further from the longwall face. It
was demonstrated that this effect was due to continuously changing
properties of the rock-mass surrounding the gallery that can be
expressed as decreasing empirical parameters mb i s of Hoek-Brown’s
criterion. These parameters are decreasing exponentially together with
the distance to the longwall face The consistency between the
theoretical and factual curve varies between 70% to 98%. The change of
each of the parameters can be described by general equation P = a·
exp(–b·d), where a, *b* are constants, and *d* is
the distance to the excavation face. The authors highlight that during
the measurements period the horizontal stress was 1.45 to 1.61 times
greater than the concurrent vertical stress. The so high horizontal
stress causes heave of unsupported gallery floor which is commonly
observed in the mines in Silesia.