The poor sealing
effect of gas extraction boreholes causes low
efficiency of gas extraction. As a consequence, the requirements of
coal mine safety production are often not attained. The sealing effect
of boreholes depends not only on the sealing material itself but also
on the combination degree between the material and the hole wall and
the structural change characteristics of the material during operation.
Our theoretical analysis shows that the amount of liquid leakage increases
with the gap width Δ
h
in a cubic law, decreases
with the sealing hole viscosity in a hyperbolic form, increases linearly
with the diameter of the borehole, and increases with the eccentricity
in a quadratic function. We have developed a PD sealing material that
has good compactness and sealing effects, excellent water retention
performance, and an expansion rate of 1.29. The material can generate
secondary expansion through microscopic development, which is beneficial
to improve the quality of the sealing hole. HV-CMC has good stability
in plugging mucus. In addition, the manual pump has been redeveloped
to be portable and also to overcome the blockage of the suction valve
of the original device. In addition, the auxiliary device for drilling
and sealing has been invented. The field application demonstrates
that the gas concentration and flow pressure difference of the new
sealing borehole can be maintained at a high level in a short period
of time and then decrease slowly with time. The resulting improved
sealing effect demonstrates that our new approach has important theoretical
and practical significance for mine gas drainage.
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