Uniaxial compressive strength (UCS) is a critical rock mechanical parameter. Conventional UCS measurement is cumbersome and the point load test is widely used to estimate UCS. The correlations between UCS and point load index (I_s(50)) are grain size or anisotropy-dependent. To direct using I_s(50) to estimate UCS for heterogeneous rock, the effect of grain size or anisotropy on the equations of UCS-I_s(50) was respectively investigated using sandstone (fine or coarse grain size) and gneiss (0°, 45°, 90° inclined anisotropy) samples. Based on the regression analysis, power or linear functions of UCS-I_s(50) can be derived from rocks with different heterogeneous characteristics. For the samples with coarse grain size or 45° inclined anisotropy, both the UCS and I_s(50) data show high discreteness and an inferior correlated degree. No significant correlation of UCS-I_s(50) can be obtained from samples with vertical anisotropy. The accuracy of estimated UCS weakens substantially when rock contains different grain size magnitudes. Meanwhile, a similar phenomenon can be observed from the gneiss containing multidirectional anisotropy. Although the 45° inclined anisotropy deteriorates the correlated degree of UCS-I_s(50), the UCS estimated capability can be immune from this effect. Moreover, using the empirical equations ignoring grain size or anisotropy can result in considerable discrepancies of estimated UCS. It is thus suggested to present point load test on fine- and coarse-grained rocks respectively for predicting UCS. For the rocks with visible anisotropy, point load test loaded parallel to the anisotropy is invalid in the UCS estimation.

单轴抗压强度 (UCS) 是一个关键的岩石力学参数。传统的 UCS 测量比较繁琐，点载荷测试被广泛用于估计 UCS。UCS 和点载荷指数 ( I _s(50) ) 之间的相关性取决于晶粒尺寸或各向异性。为了指导使用I _{s (50)}估计非均质岩石的 UCS，分别使用砂岩（细粒度或粗粒度）和片麻岩（0° , 45°, 90° 倾斜各向异性）样品。基于回归分析，UCS - I _{s(50) 的幂函数或线性函数}可以从具有不同异质特征的岩石中提取。对于粗粒度或45°倾斜各向异性的样品，UCS和I _s(50)数据均显示出较高的离散性和较差的相关度。从具有垂直各向异性的样品中不能得到UCS-Is _{(50) 的}显着相关性。当岩石包含不同的粒度大小时，估计 UCS 的准确性会大大降低。同时，在含有多向各向异性的片麻岩中也可以观察到类似的现象。虽然 45°倾斜各向异性恶化了 UCS- I _s(50)的相关度，UCS 估计的能力可以不受这种影响。此外，使用忽略晶粒尺寸或各向异性的经验方程可能会导致估计的 UCS 存在相当大的差异。因此建议分别对细粒和粗粒岩石进行点载荷试验，以预测 UCS。对于具有可见各向异性的岩石，平行于各向异性加载的点载荷试验在UCS估计中是无效的。