First fracture characteristics of main roof plate structure with goaf (coal pillar) on both sides and elastic-plastic foundation boundary

Abstract

In order to study the fracture position and engineering significance of the main roof plate structure under the condition of goaf on both sides (coal pillars), the double plasticized foundation boundary mechanical model of the main roof plate structure considering the elastic-plastic deformation of coal and the width and support capacity weakening of coal pillar on both sides is constructed. Based on the finite difference algorithm and the principal moment breaking criterion, the shape characteristics, location attributes and overall position characteristics of the main roof fault line above the asymmetric coal pillars area and the long side solid coal area are systematically calculated, and the new conclusions and important engineering significance of the new model are clarified by comparing with the traditional models from seven levels and four pairs of areas in transverse and longitudinal directions. The conclusions are as follows: ① The asymmetric coal pillars parameters on both sides have little influence on the main roof principal bending moment and fracture position above the long side solid coal area, but significantly affect the principal bending moment, position and fracture shape of the main roof above the coal pillar areas respectively. There are three types of evolution patterns of the main roof fracture line above the coal pillar areas on both sides (strong/wide coal pillar area + weak/narrow coal pillar area). With the increase of main roof thickness and elastic modulus, while coal pillars width, coal pillar bearing capacity and working face span decrease, its evolution law is as follows: asymmetric “continuous single arc + continuous single arc”→ “continuous single arc + open discontinuous double short arc”→ asymmetric “open discontinuous double short arc + open discontinuous double short arc”. ② The fracture line of the main roof above the long side solid coal area mainly has three types of location attributes. With the increase of main roof thickness and elastic modulus, while the plastic zone width and plasticization degree of solid coal and working face span decrease, its evolution law is as follows: the fracture line is above the plastic coal area (C-S type) → elastoplastic coal boundary area (C-TS type) → elastic coal area (C-T type). ③ With the increase of coal pillars width, coal pillar bearing capacity and working face span decrease, and considering the location attribute of the fracture line, the fracture mode and evolution law of the whole area of the main roof are as follows: the mode of C-S ()→the mode of C-TS ()→the mode of C-T ()→ mode of C-T ()→the mode of C-T (). Aiming at the three kinds of mechanical models for studying the fracture of the main roof plate structure with goaf (coal pillar) on both sides, the important differences of the three kinds of models are compared from seven levels, and its important engineering role is expounded from four transverse areas (front and rear of the mining area, coal pillar areas on both sides) and four longitudinal areas (asymmetric left coal pillar underlying and underlying mining space output/input coal pillar/body).

Keywords

• leftover coal pillar
• main roof
• goaf on both sides
• elastic-plastic foundation
• plate structure