尺寸效应对岩石单轴压缩试验影响研究

Study on the influence of size effect on rock uniaxial compression test

为探究尺寸效应对小尺寸岩样单轴压缩试验的影响规律,通过在室内伺服试验机上对直径25 mm,不同长度的花岗岩岩样进行单轴压缩试验,研究尺寸效应对小尺寸花岗岩岩石力学参数以及破坏形式的影响规律。试验结果表明,随着长径比增加,岩样表现出抗压强度和泊松比逐渐减小,弹性模量增加的趋势。其中,多项式模型较为适合小尺寸岩样尺寸效应强度模型;不同长径比岩样的单轴压缩试验应力应变曲线加载趋势不同,其峰值应变随着长径比的增加而减小;随着长径比的增加,岩石破坏形式从脆性剪切破坏转变为剪切破坏,最后逐步变为脆性破坏,岩样破坏面数量与角度出现规律性变化。当长径比在1.1~2.2时,岩样破坏形式遵循相同的破坏准则,通过拟合公式推导不同长径比岩样的力学参数存在可行性;岩石单轴试验破坏过程中的能量与长径比呈负相关,且当长径比在1.9~2.2时,各能量变化幅度趋于平缓,岩样破坏形式较为统一,其强度在数值上表现的差异性较小,可作为小尺寸岩样单轴试验的最佳长径比。

In order to explore the influence of size effect on the uniaxial compression test of small-size rock samples,the uniaxial compression test of granite rock samples with diameter of 25 mm and different lengths was carried out on the indoor servo testing machine to study the influence of size effect on the mechanical parameters and failure modes of small-size granite rock.The test results show that with the increase of length-diameter ratio,the compressive strength and Poisson’s ratio of rock samples decrease gradually,and the elastic modulus increases.Among them,the polynomial model is more suitable for the size effect strength model of small size rock samples;the stress-strain curves of uniaxial compression tests of rock samples with different aspect ratios have different loading trends,and the peak strain decreases with the increase of aspect ratio.With the increase of aspect ratio,the failure mode of rock changes from brittle shear failure to shear failure,and finally gradually becomes brittle failure.The number and angle of failure surfaces of rock samples change regularly.When the aspect ratio is between 1.1 and 2.2,the failure mode of rock samples follows the same failure criterion,and it is feasible to derive the mechanical parameters of rock samples with different aspect ratios by fitting formula.The energy in the failure process of rock uniaxial test is negatively correlated with the aspect ratio,and when the aspect ratio is between 1.9 and 2.2,the change range of each energy tends to be gentle,the failure form of rock sample is relatively uniform,and the difference of its strength in value is small,which can be used as the best aspect ratio of small size rock sample uniaxial test.