高围压卸荷条件下大理岩破碎块度分形特征及其与能量相关性研究

 高应力条件下，岩石卸荷的力学响应特征及发生机制是高地应力地区岩体工程开挖稳定性评价及控制的关键问题。基于不同卸荷速率和初始围压条件下三轴高应力大理岩卸围压试验，结合分形理论和能量原理，研究高应力卸荷条件下岩石破裂块度分布规律及其与能量耗散和释放的相关性。高应力条件下三轴卸围压大理岩试样碎块分形性质具有较强的局部性，仅在小于某一特征尺度(分形特征尺寸阈值)范围内表现出较好的分形性质，其碎块分维数均大于2，分维数随卸荷速率增大而单调减小，但初始围压对分维数的影响与卸荷速率密切相关。相对常规三轴压缩岩样，高围压下卸荷岩样虽然峰值点附近耗散和储存应变相对少得多，但其峰值前、后应变能转化速率相对大得多，特别是峰后的弹性应变能释放速率和环向膨胀消耗应变能速率。高应力卸荷条件下卸荷速率越快、初始围压越高，峰前损伤和峰后破裂贯通历时越短，峰值点处耗散应变能和储存弹性应变能越大，峰前、峰后应变能转化速率越快，破碎岩样的分形特征尺寸阈值越大，分维数越小，张性破裂程度和性质越强。

FRACTAL CHARACTERISTICS OF FRAGMENTATION AND CORRELATION WITH ENERGY OF MARBLE UNDER UNLOADING WITH HIGH CONFINING PRESSURE

The mechanical response and unloading mechanism of rock are the key issues to evaluate and control stability for rock mass engineering excavated under high geostress.Based on the unloading confining pressure tests with triaxial high stress under conditions of different unloading rates and different initial confining pressures,combining the fractal theory and energy principle,the distribution rule of rupture fragmentation of marble specimens and its correlation with strain energy transformation are investigated.The characteristics of fragment fractal of marble specimens fractured is obvious locality under unloading confining pressure with triaxial high stress;and only in the range of sizes which is smaller than a certain features scale(fractal feature sizes threshold),it presents good fractal property.The fractal dimensions of all fragmentation are greater than 2 in the test.The fractal dimension monotonously decreases with unloading rate increasing;and the influence of initial confining pressure on it closely relates to the unloading rate.Comparing with conventional triaxial compression test specimens,the dissipation and storage strain energies of rock specimens under high confining pressure near peak point are much smaller;but the rates of strain energy transformation before and after peak point under high confining pressure are much larger;especially the rates of elastic strain energy release and strain energy dissipation by confining deformation.The unloading rate is faster and the initial confining pressure is higher,the time of damage before peak and whole crack rupturing after peak are shorter;the dissipation strain energy and storage elastic energy are larger;the transformation rate of energy before and after peak is faster;the threshold of characteristics size of fractal for broken rock sample is bigger;the fractal dimension is smaller and tensile fracture is more obvious.