劈裂拉伸条件下大红山铜矿矿岩变形特性的试验研究

Experimental investigation on the tensile deformation as a result of the brazilian test for the rocks of Dahongshan copper mine

对大红山铜矿的3种岩石的试样进行了劈裂拉伸(巴西法)试验和单轴压缩试验,研究了岩石的变形特性。劈裂试验中在试样中部相互垂直的方向上粘贴了电阻应变计测量试样的变形。结果表明,在劈裂试验条件下,两种岩石均出现垂直于加载轴线方向所获得的拉伸弹模小于平行于加载轴线方向所获得的压缩弹模的现象。与单轴压缩下试样出现破裂、扩容的破坏特征相比,劈裂拉伸下试样的变形特征为接近峰值时变形曲线斜率会逐渐降低,达到峰值应力后则很快出现数值很大的拉伸变形,直至试样破坏。劈裂拉伸循环加卸载试验发现,大多数试样的拉伸卸载变形大于加载变形,致使残余变形的数值为负值,称之为反向残余变形。此现象与连续介质变形行为的预期不符,至今未见类似报道。反向残余变形是否具有普遍性及其影响,应该开展更多研究。

The goal of this paper is to study the deformation features of the rocks under the condition of the splitting tensile and the single axial compression pressure tests.For this purpose,we have conducted split tensile tests in the underground mine,whose stress state of the top and the side parts of the stope should be close or similar to the stress state of the case sample.We have also done the deformation measurements by installing the resistance strain gages in the center of the sampling section of the mine.Test results of our investigation and measurements show that the Young＇s Modulus of the tension of the compression pressure obtained from the strain gages perpendicular to the loading axis turns out to be smaller than that of the compression parallel to the loading axis.And,the ratios between the Young＇s modulus at 50% of the peak stress from the uniaxial compression,EC50,and those of the tension from Brazilian test,ET50,for the rock sample are equal to 1.63,2.10 and 2.08,respectively.What is more,we have also found that one of the causes that accounts for the fact that Young＇s modulus of tension is smaller than that of compression stress comes from the nonlinearity of the stress-strain curves under the tension.Such a difference between the secant Young＇s modulus obtained at the half value of the tensile failure stress,ET50,and that at the half compressive stress,ET50,has been made smaller than the ratio of ECA/ECA.To verify the deduction we have made,we have also conducted a recycling series of loading-unloading Brazilian tests with the same rock samples,which indicates that the unloading deformation proves to be greater than that of loading in the tensile deformation for most of the samples chosen,though the residual deformation gives out negative value,a phenomenon different from the expected ones of continuum,not yet been well explained and therefore not reported.Therefore,further investigations are needed to verify if the negative residual deformation is popular or more believable as its effects.