岩石平面应变状态辨识特征与精度控制

Identification Characteristics and Accuracy Control of Rock Plane Strain Compression Test

水工隧洞等地下工程围岩可视为处于平面应变状态,为了认识岩石平面应变状态辨识特征,开展了系列离散元岩石力学试验。首先,阐述岩石平面应变试验的意义及问题;然后,通过实验室单轴结果标定一类花岗岩参数,从“数据”和“损伤”两方面分析了岩石平面应变状态的辨识特征;最后,探索了岩石平面应变试验侧限装置的精度控制阈值。结果表明:(1)通过分析平面应变压缩下岩样轴向应力、侧限墙应力、裂纹发育趋势,给出了3个特征数据点,揭示了岩石从损伤到破裂的阶段性变化过程;(2)平面应变压缩过程中的3个特征点界定了试样裂纹发育的演化规律;裂纹从零星分散发育到局部化发育,然后开始深化连通直到试样破裂;(3)建议岩石平面应变试验的侧限装置的位移允许值取单轴峰值点对应的单向侧应变,在该阈值控制下获得的“半平面应变状态”的特征点与“完全平面应变状态”的特征点基本吻合。

The surrounding rock of underground engineering such as hydraulic tunnels is in a plane strain state.In order to identify the characteristics of rock plane strain state,a series of rock mechanic tests are conducted based on discrete element method(DEM).Firstly,the significance and problems of rock plane strain compression test(PSCT)are described;Secondly,parameters of a granite are calibrated by the lab uniaxial test results,and then the characteristics of the rock plane strain state are analyzed from the data and microcrack development;Finally,the threshold for strain confining device of the rock PSCT are further explored.The results show that:(1)3 characteristic data points are given by analyzing the axial stress,confining wall stress and crack development trend of rock samples under PSCT,and the staged process of rock from damage to fracture is revealed;(2)The 3 characteristic points of PSCT define the stage process of the crack development:the cracks develop from scattered to localized,and then deepen the connection until the samples breaks;(3)It is suggested that the control threshold of the confine device should be the unidirectional strain corresponding to the stress peak point under uniaxial compression.The characteristic points coordinates of the half plane strain state obtained under the control of this threshold can basically coincide with the characteristic points of the complete plane strain state.