干燥及饱水岩石圆盘和圆环的巴西劈裂强度

BRAZILIAN SPLITTING STRENGTHS OF DISCS AND RINGS OF ROCKS IN DRY AND SATURATED CONDITIONS

为研究饱水对岩石抗拉强度的影响,对4种岩石的外径50 mm、厚30 mm左右的完整圆盘及不同内径(0～20 mm)的圆环进行巴西劈裂试验,对完整圆盘破裂块进行点载荷试验,对标准圆柱试样进行单轴压缩试验。基于完整圆盘劈裂强度的统计分析,除大理岩之外,其余岩石进行5次重复试验即可消除离散性。饱水对岩石拉伸强度的影响主要体现在黏结力降低,而对压缩强度的影响还包括内摩擦因数及孔隙压力。因而巴西劈裂强度的软化系数Rt大于压缩强度的软化系数Rc,而两者大致成线性关系表明圆盘的巴西劈裂与加载点的压应力集中相关;圆环内径增大到20 mm,干燥与饱水岩石圆环的巴西劈裂载荷大致相同,表明压应力的影响已经减小。圆环的巴西劈裂载荷随内径大致呈指数关系降低,而弹性力学的分析结果如Hobbs公式与实际情况差别较大。

To study the effect of saturation on the tensile strength of rock,dry and saturated rings of 30 mm in thickness,50 mm in external diameter,and 0-20 mm in internal diameter were conducted by Brazilian splitting test for four rocks.The broken discs after Brazilian splitting were point loaded.Dry and saturated cylindrical specimens were uniaxial compressed.Based on the statistical analysis of Brazilian splitting results of discs,the average strength of repeated test in 5 times may eliminate the dispersion from specimens except marble.The softening coefficient of Brazilian tensile strength is higher than and linear relative to that of uniaxial compressive strength.The influence of saturation on the Brazilian tensile strength mainly results from the high compressive stress in the neighbourhood of the load point and the cohesion decrease.Correspondingly,the splitting strengths are nearly the same for dry and saturated rings with 20 mm in internal diameter,which means that the compressive stress does not influence the ring splitting greatly.An exponential equation is proposed for rings to describe the relation between Brazilian splitting force and its inner diameter;and the Hobbs＇equation based on the elastic mechanics has great difference from the experimental results.