煤柱-顶板系统协同作用的脆性失稳与非线性演化机制

把坚硬顶板视为弹性梁,把煤柱视为应变软化介质并采用W e ibu ll分布描述它的损伤本构模型,本文对坚硬顶板和煤柱组成的力学系统,用突变理论方法研究了它的演化失稳过程。通过对建立的尖点突变模型的分析发现,系统失稳主要取决于系统的刚度比k与材料的均匀性或脆性指标m值,并给出了失稳的充要条件力学判据和失稳突跳量的表达式。考虑煤柱介质的粘性或蠕变性,建立了系统演化的非线性动力学模型———物理预报模型,并给出了根据顶板沉降观测数据反演非线性动力学模型的方法和稳定性判别准则。对木城涧矿根据观测序列进行了动力学模型的反演分析,一个重要发现是:D值在临近失稳时陡增出现峰值而后急剧下降。根据材料损伤与声发射累计计数的对应关系,建立了系统演化过程中声发射率的动力学模型,并进行了声发射模拟分析和分维分析,发现m值与系统的演化路径对系统演化的声发射活动规律及分维特征有重要影响,单纯根据声发射监测和降维现象预报冲击地压是不可靠的。

INSTABILITY LEADING TO ROCKBURSTS AND NONLINEAR EVOLUTIONARY MECHANISMS FOR COAL-PILLAR-AND-ROOF SYSTEM

This paper presents the instability mechanisms of a mechanical system that is composed of the stiff hosts(roof and floor) and the coal pillar by using catastrophe theory.It is assumed that the roof is an elastic beam and the coal pillar is a strain-softening medium which can be described by the Weibull′s distribution theory of strength.The results indicate that whether the instability can lead to a rockburst largely depends on the system′s stiffness ratio k and the homogeneity index m of the coal pillar.A nonlinear dynamical model,which is derived by considering the time-dependent property of the coal pillar,is used to study the physical prediction of rockbursts.An algorithm of inversion on the nonlinear dynamical model is adopted in the search of the precursory abnormality from the observed series of roof settlement.A case study of the Muchengjian coal mine is conducted.Its nonlinear dynamical model is established from the observation series using the algorithm of inversion.An important finding is that the catastrophic characteristic index D drastically increases to a peak value and then quickly drops close to instability.A dynamical model of acoustic emission(AE) is then established based on damage mechanics of coal pillars for modeling the AE activities in the evolutionary process of the system.It is concluded that the values of m and the evolutionary path of the system have a great impact on AE activity patterns and characteristics.