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鉴于薄层岩体在实际地下工程中经常发生弯折破坏,利用三点弯曲试验对单层灰岩及含弱面灰岩试样进行抗弯性能测试,探究岩层受弯作用时的变形及破坏特征。试验结果表明,薄层灰岩的抗弯性能与层厚密切相关,单宽峰值弯矩及峰值力对应的岩梁挠度随层厚变化规律基本符合材料力学理论公式计算结果。薄层灰岩弯折破裂模式呈现多样化,既有垂直切穿层理的I型裂纹,也有在弱面处发生转折并沿弱面扩展的断续裂纹,以及与层理斜交的复合型裂纹等。理论分析表明,薄层岩体中的裂纹扩展路径主要受层面拉、剪强度(或断裂韧度)与岩石抗拉强度(或断裂韧度)的相对大小控制。利用双模量理论结合弯曲试验求解岩石拉伸模量需要进行迭代计算,拉压模量相差越大,迭代次数越多,收敛值越偏离初值。试验所得规律有助于深入理解薄层岩体弯曲变形特征及弯折破坏机制,并可作为对薄层岩体受弯作用理论及数值计算的有益补充。
In view of the frequent failure of thin rock mass in the actual underground engineering, the three-point bending test is used to test the flexural properties of single-layer limestone and weak-surface limestone samples to explore the deformation and failure characteristics of rock mass under bending . The test results show that the bending resistance of thin limestone is closely related to the thickness of the layer, and the law of beam deflection corresponding to the single-peak peak moment and peak force is basically in accordance with the theoretical formula of material mechanics. The bending and fracture modes of thin-bedded limestone are diversified. They are not only the I-type cracks that cut vertically through the bedding, but also the intermittent cracks which propagate along the weak face at the weak face and the complex type that obliquely intersect with the bedding Cracks and so on. Theoretical analysis shows that the propagation path of cracks in thin rock mass is mainly controlled by the relative size of tensile strength, shear strength (or fracture toughness) and rock tensile strength (or fracture toughness). Using bimodal theory and bending test to solve the tensile modulus of rock needs to be iteratively calculated. The greater the difference between tensile and compressive modulus, the greater the number of iterations, and the more the convergence value deviates from the initial value. The experimental results are helpful to deeply understand the bending deformation characteristics and bending failure mechanism of thin rock mass, and can be used as a useful supplement to the theory and numerical calculation of thin rock mass bending.