ABSTRACT: Based on the results of in-situ observations and physical model analysis, a computer simulation method, FEAEBP, has been developed to predict the behaviors of main roof breakage in longwall mining by considering it as a Kirchhoff plate on Winkler elastic foundation. This method is used to investigate the initiation, and development of the breaking process of main roof and its displacement field before and after its breakage. In this paper the simulation method is introduced, characteristics of the displacement field of the main roof is discussed and monitoring variation of the displacement field of the main roof in a Chinese longwall face is demonstrated.
It is well known that the main roof should be induced to break in longwall mining. Without it the main roof will cause roof weighting which may endanger the miners and mining operations.
Normally, in China a longwall face is about 100-200 m wide and the thickness of the main roof is usually 2-8 m. Thus, the main roof in this case can be considered as an elastic plate, or a Kirchhoff plate, when it is separated from the upper strata or when the friction force between them is very small. On the other hand, the immediate roof and coal seam around the plate, being served as supporting abutments for the main roof, can be considered as an elastic medium ix) conform with the assumption for the Winkler elastic foundation.
Based on these assumptions, the theoretical model of main roof can be simplified as a Kirchhoff plate on Winkler elastic foundation (Fig. 1), and a computer simulation method, FEAEBP, has been developed. This model is capable of simulating a moving face under different boundary conditions.
FEAEBP has demonstrated that it can effectively simulate the breaking process of the main roof (1,2). Using this model the displacement fields of the main roof before and after its breakage were obtained, and some new concepts found which are introduced in this paper.
2 DISPLACEMENT FIELD OF MAIN ROOF BEFORE ITS FIRST BREAKAGE
In the middle of a longwall face, the mode] can be simplified as a beam on Winkler's elastic foundation (Fig. 2(a)), the displacement, y, of the main roof over the seam is derived by the following equation
(1) EIy(4) + ky = q
and boundary conditions
(2) EIy(2) = M x = 0
(3) EIy(3) = Q x = 0
(4) y = q/k x = 8
where M ---- Internal bending moment of the main roof at x = 0,
Q ---- Internal shearing force of the main roof at x = 0,
K ---- Composite elastic coefficient of the immediate roof and the seam.
Solving for Eqs. 1 - 4,
(available in full paper)
where ß = 4vk/4EI --- calculation parameter,
Fig. 2(b) is the displacement curve of main roof in Yunggong Mine by substituting into Eq. 5 the following parameters obtained through field observations and laboratory testings: