ABSTRACT

Due to strong impacts of rockbursts in Ostrava – Karvina coalfield which affect especially roadways and cross-cuts of longwall panels it is necessary to strengthen standard steel breakthroughs support. Using of reinforcing complementary bolts seems to be very effective. Different varieties of a number and location of such rockbolts have been analysed and compared from the viewepoint of the stability under dynamic events on the base of 3D mathematic modelling. The instrument of computer modelling has been FEM applied by ANSYS code. It deals with shape and nature of deformation of steel support, strain and deformation of reinforcing bolts, critical energy by which a permanent strain is caused, influence of interaction of adjacent rock on the above mentioned characterisics. Recommendation for number and location of reinforcing complementary bolts is also contained.

1 INTRODUCTION

Break-throughs as starting space of longwall faces play an important role in application of new mining technologies. Installation of efficient longwall equipments needs large width of the cross cuts which reflects in demands on their support. Contemporary in rockburst prone areas the high proportion of rockbursts in breakthroughs is significant. According to the statistics 19 % of all rockbursts in Ostrava Karvina coal basin in the period 1993 – 2003 occurred in break-throughs in spite the fact that their total length is less than 10 % of the total summary of developed roadways. (Šnuparek 2005) In the contribution we deal with strenghtening of cross cut supports against dynamic loading due to rockbursts.

2 SUPPORT OF BREAK-THROUGHS

Cross entries are mostly driven under the roof of a seam in two steps: in basic width 5 – 6,5 m with successive extending to final width 9,5 – 10 m. The steel support consists of the straight roof beams, side arches and corner segments. Common steel support of breakthrough width 6,5 m which was modeled is shown on the fig. 1.

(Figure in full paper)

Support from steel rolled profile weight 28 kg/m contains yielding friction connections (fig. 2, 3,). Steel bolts which anchored support to the roof were modeled as amplifying elements (fig. 4, 5,).

(Figure in full paper)

3 MODELING OF DYNAMIC RESISTANCE OF SUPPORT

Design of effective strenghtening measures for higher resistance of break-through supports against rockbursts effects is based on knowledge of support behavior. Recent efficient programme packs make it possible to model complicated and quick processes. However it demands high skilled staff, efficient computing equipment and verification of model results on the base of in situ measurments.

The instrument of computer modeling is a finite element method which is applied in ANSYS program pack. Decisive parameters which determine shape and range of plastic strain of support construction are investigated due to changes and variations of the computer model.

The most important parameters are:

  • oboundary conditions including a contact of support with surrounding environment

  • oinitial conditions induced by loading impulse

  • omaterial properties of support.

The aim of computer modeling is detection of behavior of steel support during the course of dynamic response provoked by rockburst.

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