基于形貌全覆盖的岩石结构面抗剪强度尺寸效应试验研究

Experimental study on size effect of shear strength of rock joints

岩石结构面抗剪强度具有尺寸效应已成为学术与工程界共识,但现有理论和数值研究表明岩石结构面抗剪强度可能具有正尺寸效应、负尺寸效应或无尺寸效应的变化规律,由于结构面抗剪强度尺寸效应试验的难度大、费用高、周期长,造成系列尺寸结构面直剪试验较少,特别是对于起伏形貌全覆盖的系列尺寸(100~600 mm)结构面直剪试验研究还未见报道。基于Barton典型形貌曲线,采用多尺寸结构面一体化模具制作16组系列多尺寸结构面试样,通过自主研发的岩体结构面抗剪强度尺寸效应试验系统开展起伏形貌全覆盖的系列多尺寸结构面直剪试验,并采用三维全场应变测量系统(DIC)开展试验全过程非接触动态变形测量。研究结果表明:(1)形貌全覆盖系列尺寸结构面峰值抗剪强度上渐近线呈现负尺寸效应规律,下渐近线呈现正尺寸效应规律,尺寸效应呈现的具体规律与取样位置及起伏形貌特征相关。(2)不同尺寸试样同一形貌特征结构面会产生剪断、爬坡、耦合等不同剪切破坏模式;相同尺寸试样不同形貌特征结构面的剪切破坏模式也有差异,且表面形貌起伏程度越大其应变增长越快。(3)尺寸越大,具有较大起伏形貌特征的结构面剪应力与剪位移曲线峰值特征越明显;尺寸越小,具有较大起伏形貌特征的结构面峰值抗剪强度离散性越大。(4)基于等权重系数法开展了大尺寸结构面峰值抗剪强度评价,Grasselli公式计算峰值抗剪强度加权评价值与实测值相比误差较大。

Size effect of shear strength of rock joints has become the consensus of academic and engineering circles,but the existing theoretical and numerical studies show that the shear strength of rock joints may have positive size effect,negative size effect or no size effect.Due to the difficulty,high cost and long period of size effect test of shear strength of rock joints,there are few direct shear tests of joints with series size,especially for full-coverage direct shear test of rock joints with fluctuation morphology in a series of sizes(100-600 mm).In this paper,based on Barton's typical morphology curves,16 sets of multi-scale joint samples were made by multi-scale joint integration mold.The direct shear test of a series of multi-scale joints with full coverage of fluctuation morphology was carried out through the self-developed shear strength size effect test system of rock joints,and non-contact dynamic deformation measurement of the whole test process was carried out by DIC.The results show that:(1)Upper asymptote of peak shear strength of rock joint exhibits a negative size effect law,and lower asymptote exhibits a positive size effect law.The specific pattern of size effect is related to the sampling position and fluctuation morphology characteristics.(2)Different shear failure modes such as shear,climbing and coupling will occur in the same morphology of rock joints with different sizes.The shear failure modes of joints with different morphology characteristics of the same size samples are also different,and the larger the fluctuation degree of surface morphology,the faster the strain growth.(3)The larger the size,the more obvious the peak characteristics of shear stress and shear displacement curves of rock joint with large fluctuation morphology;the smaller the size,the larger the discreteness of peak shear strength of rock joint with large fluctuation morphology.(4)Based on the equal weight coefficient method,peak shear strength evaluation of large-scale rock joint is carried out.The weighted evaluation value of peak shear strength calculated by Grasselli formula has a large error compared with the measured value.