基于应力-应变曲线的礁灰岩脆性特征评价

Brittleness evaluation of coral reef limestone base on stress-strain curve

脆性是岩石类材料的重要性质。针对南海某岛礁在某深度范围内的珊瑚格架灰岩、砾块灰岩、砾屑灰岩及砂屑灰岩的钻孔芯样,开展室内物理性质测试及压缩试验。研究表明,礁灰岩的物理力学性质与其沉积组构和成岩作用密切相关;基于峰后应力降的相对大小和绝对速率的脆性指标计算方法能够反映礁灰岩的破坏特征;围压对礁灰岩的脆性指标影响显著,随着围压的增大,试样的脆性指标呈现趋势性降低;单轴压缩条件下,低孔隙率的砂屑灰岩脆性指标与水泥砂浆类似,同时高于格架灰岩及砾块灰岩;随着孔隙率的增大,砂屑灰岩和砾屑灰岩的脆性指标减小,饱和单轴抗压强度也与孔隙率呈负相关关系。

This project planed to investigate the brittleness index of coral reef limestone which is an important property of rock materials.For this purpose,physical property test,uniaxial and triaxial compression tests were performed on four types of reef limestone core samples(framestone,bindstone,rudstone and bioclastic limestone)which were sampled in a certain depth from a certain coral reef in South China Sea.The test results show that the physical and mechanical properties of reef limestone are strongly influenced by the fabric and diagenesis.The failure characteristics of reef limestone can be accurately described by the brittleness index which is calculated based on the relative magnitude and the absolute velocity of post peak stress dropping.The investigation also suggests that the brittleness index is sensitive to the confining pressure and decreases with the increase of confining pressure.Meanwhile,under uniaxial compression,the brittleness index of bioclastic limestone with low-porosity is similar to that of cement mortar,and higher than that of framestone and bindstone.Furthermore,with the increase of porosity,the brittleness indexes of rudstone and bioclastic limestone decrease,and the saturated uniaxial compressive strength is negatively correlated with porosity.