不同试验方法下岩石抗拉强度及破裂特性

Tensile strength and damage characteristics of rock under different test methods

岩石抗拉强度为岩石力学性质的主要指标之一,拉伸破坏也为岩石破坏的主要形式之一,同时也是岩体工程设计与稳定性评价中的重点控制参数。岩石的抗拉强度和变形特性与试验方法密切相关,目前主要方法包括直接拉伸、巴西劈裂和三点弯曲等。该文选用几种较具代表性的岩石试样(花岗岩、大理岩、辉绿岩),通过对比试样在不同试验方法下的试验结果,同时结合数值模拟方式对不同方法下的试验过程进行理论模拟分析,得出不同试验方法下的岩石抗拉强度和变形特性的变化规律:①巴西劈裂法得出的抗拉强度明显高于直接拉伸法,而三点弯曲得出的强度为抗折强度,其强度数值最高,岩石变形模量则反之。②三点弯曲得出的虽为抗折强度,但岩石实质上也为拉伸破坏造成,故其强度可作为岩石抗拉强度的重要参考,约为直接拉伸和巴西劈裂强度的2.5倍,变形模量介于两者之间。③巴西劈裂方法下岩石的变形破坏为中间起裂,并向两端发展,直接拉伸方法由于受中部切缝的影响,其变形首先会在切缝两端产生并向中间发展,而三点弯曲方法下岩石的变形破坏由底部表面起裂并向中间发展。

Tensile strength of rock is one of the main strength indexes of rock and one of the key parameters for design and stability evaluation of rock mass engineering.Accordingly,tensile failure is one of the major failure modes.The accurate obtaining of tensile strength and deformation characteristics of rock is closely related to the test methods.At present,the main methods for rock tensile testing are direct stretching test,Brazilian test and three-point bending test.Several types of rock samples such as granite,marble and diabase are involved,and results of different test methods are compared.Numerical and analytical methods are carried out for the analysis of tests.The results can be concluded that:First,the tensile strength result from Brazilian test is significantly higher than ones from direct stretching test,the strength obtained by the three-point bending is the bending strength with the highest value,and deformation modulus are reversed.Second,although the strength obtained by the three-point bending is bending strength,the rock failure is also caused by tensile stress,so the value could be termed as an important reference for the tensile strength of rock,which is about 2.5 times of the direct tensile and Brazilian splitting strength,and deformation modulus is between direct tensile and Brazilian splitting.Third,the deformation and failure mode of rock under the Brazilian splitting method is central generation of cracks with developing to both ends.Due to the influence of the central slit,the deformation of rock under the direct tensile method will firstly develop at the two ends of the slit and then to the centre.The deformation and failure of rock under the three-point bending method is cracked from the bottom surface and develops to the centre.