综采工作面基本顶厚跨比对其初次断裂失稳影响规律

综采工作面基本顶初次断裂失稳机理对工作面支架选型及采场围岩稳定性控制至关重要。通过建立顶板力学模型分析得出:综采工作面基本顶初次断裂前，基本顶厚跨比从初始状态减小趋近极限状态时，其内部最大主应力σ1与最大剪应力τmax均逐渐增加;当厚跨比接近02时，σ1与τmax均出现陡增，但σ1增加速率大于τmax，易在基本顶两端顶部发生断裂，且基本顶初次断裂时极限厚跨比n1一般大于02。在不发生滑落失稳条件下，基本顶极限厚跨比n1随回转角θ的增大近似呈线性增加;证明了基本顶铰接结构回转初期(θ为0°～3°)易发生滑落失稳。在仅考虑厚跨比影响的条件下，基本顶铰接结构发生回转失稳的临界条件为极限厚跨比n1=0624。然而，当n1<0624时，回转极限平衡角大于岩块回转平衡角所允许的最小值时，亦会造成铰接结构回转失稳。同时，在考虑支架弹性变形的基础上，建立了基本顶铰接结构滑落失稳对工作面支架动载系数计算方法，当直接顶与基本顶离层量Δh为0时，动载系数Fsd取最小值;Δh不为0时，Fsd随Δh增加而增大，但随直接顶与支架刚度之比、直接顶自重与基本顶传递载荷之比增加而减少。最后，通过对不同综采工作面初次来压时支架工作阻力与动载系数进行计算，验证了理论分析的有效性。

Influence of main roof thickness span ratio on the initial cracking induced instability in fully mechanized longwall face

The mechanism of the initial fracture instability of main roof in a fully mechanized longwall face is critical to the selection of hydraulic support and the control of surrounding rock.The fracture process and structural instability mechanism of main roof were analyzed by establishing the roof fracture mechanical model.The results show that the internal maximum principal stress σ1 and the maximum shear stress τmax increase gradually,with the decrease of the thickness span ratio of main roof from the initial state to the limit state.When the thickness span ratio is close to 0.2,both σ1 and τmax increase sharply,but the increase rate of σ1 is greater than that of τmax,and the main roof is thus easy to break at the top of both ends.The limit thickness span ratio n1 of main roof is normally greater than 0.2 when the initial fracture appears at the main roof.The n1 of hinge structure of main roof that does not appear sliding instability increases linearly with the increase of the rotation angle θ.The hinge structure is easy to occur sliding instability at the beginning of the initial rotation when the rotation angle is 0°~3°.The critical value of the rotation instability of the hinge structure is n1 equals to 0.624 on a condition that only the roof thickness span ratio dominates.When the n1 is less than 0.624,however,the rotation limit balance angle βj becomes larger than the minimum value β1 allowed by the swing balance angle,and the hinge structure occurs rotation instability.In addition,the method for determining the dynamic load factor of the longwall face when the main roof structure appears slipping instability was obtained.When the separation layer Δh between immediate roof and main roof is 0,the minimum value of the dynamic load factor Fsd should be applied.When Δh is non zero,Fsd increases with the increase of Δh,but also can be reduced with the increase of the ratio of immediate roof to support stiffness ks,the ratio of immediate roof weight to main roof transfer load m.Finally,the liability of the theoretical analysis was verified by the analytical calculations for the initial weighting of different fully mechanized longwall faces.