软弱破碎围岩变形特性的改进原位承压板试验研究

Experimental study on the deformation characteristics of soft broken surrounding rock mass under modified in-situ bearing plate test

原位承压板试验是获得软弱碎裂岩体变形参数的一种有效方法,但是试验受场地条件限制,且测试成果因围岩结构特征影响而具有显著的尺寸效应特征。以凉山州某在建水电站引水隧洞工程为依托,针对薄层状、软弱碎裂板岩,通过改进常规承压板试验方法,实现在建隧洞内灵活、快速的承压板试验,获得岩体的变形特征及变形模量。试验结果表明:(1)深黑色极薄层状炭质板岩完整性极差,受地下水的长期软化作用,围岩稳定性差;灰色薄层状砂质板岩,层间压密闭合,岩块强度较高,水软化作用不明显,完整性较好,开挖稳定性较好;(2)岩体受宏细观结构面的强烈切割呈显著的各向异性特征,变形参数具显著尺寸效应,实测围岩割线模量E_(0)和包络线模量E_(e)随承压板直径D的增大而减小;(3)为减小承压板尺寸效应,对改进的原位小吨位快速承压板试验,可在同一试点依次开展多尺寸加载试验,采用指数函数拟合实测变形模量值,进而获取合理的围岩变形参数,据此获得某水电站引水隧洞开挖极薄层状炭质板岩围岩的变形模量建议值为E_(0)=42.9 MPa,E_(e)=60.8 MPa,薄层状砂质板岩围岩变形模量建议值E_(0)=238.3 MPa,E_(e)=691.3 MPa。研究为软弱破碎围岩变形特征和参数的快速、高效获取提供了一种有效的方法,为今后类似在建隧洞工程围岩变形参数测试提供参考。

It is an effective method for soft and fractured rock mass to obtain the deformation parameters of surrounding rock by in-situ conventional bearing plate tests.However,it is be restricted by the site condition and the results is significantly size effective due to the structural surrounding rock mass.Relying on the diversion tunnel of a hydropower station in Liangshan Prefecture,conventional bearing plate test was modified,which can be performed with multisize bearing plates flexibly and efficiently during construction of tunnel,to reasonably determine the deformation characteristics and parameters of lamellar and fractured slate.The results show that:(1)the dark black and extremely thin carbonaceous slate was poor integrity,the stability of surrounding rock was very poor in addition with groundwater softening;due to the compaction of stratification plane,weakly water softening and relatively strong block,the gray sandy slate was better stability.(2)the rock mass was significantly anisotropic on account of the extremely fractured macro-meso structural plane,which also resulted in the significantly size effective of tested deformation parameters by conventional bearing plate tests.The secant and envelope modulus,E_(0)and E_(e),decreased with the increasing of diameter of bearing plate D.(3)in order to diminish the size effect of bearing plate,it is suggested to perform tests with multi-sized bearing plates on the same position for the modified in-situ small tonnage and efficient bearing plate test.Then exponential function can be used to fit the measured deformation modulus and further determined the more reasonable deformation parameters of surrounding rock mass.Based on it,the proposed deformation modulus of carbonaceous slate and sandy slate of the diversion tunnel were E_(0)=42.9 MPa,E_(e)=60.8 MPa and E_(0)=238.3 MPa,E_(e)=691.3 MPa,respectively.This study provides an efficient method for weak and fractured surrounding rock mass to rapidly determine the deformation parameters,and provides a reference for the similar excavating tunnel in the future.