某工程蚀变岩孔隙特征及其软弱程度研究

孔隙作为岩体的初始损伤,对岩体的强度及变形特性的影响尤为明显,而孔隙发育是研究区内一类力学性质较软弱岩石的显著特征。对蚀变岩孔隙特征的研究是了解蚀变岩的软弱程度及孔隙度对其软弱程度的影响的有效方法。针对此蚀变岩进行岩矿及铸体薄片分析得出蚀变岩孔隙有原生、浅表生及构造3种成因,其中以原生为主。从饱水蚀变岩的常规单轴压缩试验应力-应变全过程曲线上求取蚀变岩的饱和单轴抗压强度及割线模量,再与相应试样的孔隙度进行相关性分析,结果显示出蚀变岩的饱和单轴抗压强度及割线模量均随孔隙度的增加而减小,且呈幂函数关系。由于蚀变岩的饱和单轴抗压强度(R c)及割线模量(E s)作为软硬岩评判标准具有一致性,且两者与孔隙度(n)存在较好的相关性,以此将3者共同作为蚀变岩软弱程度的划分标准,并得出软硬岩分界处n为12%、R c为30 M Pa、E s为5 GPa。

STUDY ON THE PORE CHARACTERISTICS AND THE WEAKNESS OF ALTERED-ROCK FOR A PROJECT

As initial damage of rock mass,rock pore remarkably affects rock mass strength and deformation character.Altered-rock containing more pores is the relatively soft rock mass in the studying district.This paper introduces the pore characteristics of altered-rock,the weakness of altered-rock,and the influence of porosity to the weakness.According to the rock and mineral analysis,the pores of altered-rock have three causes of formation,original,epigenetic reformation,and deformation,with the original formation dominant.Through the stress-strain curve of the conventional uniaxial compression test,the uniaxial compressive strength and secant modulus of saturated alteredrock have been acquired.And then,the relationship between this results and its porosity has been analyzed.The uniaxial compressive strength and secant modulus of saturated altered-rock are all decrease along with the porosity increase,occurring as power exponent relationship.Because the uniaxial compressive strength(Rc) and secant modulus(Es) of saturated hard and soft altered-rock have the same judge criterion,and both have a better relationship with the porosity(n),this 3 parameters have been taken as criterion for determination of weakness extent.It isindicated that 12% of n,30 MPa of Rc,and 5 GPa of Es is the soft rock and hard rock borderline.The divided criterion of altered-rock soft degree will establish the evaluation foundation of altered-rock engineering suitability and evaluation long-term stability.