礁灰岩嵌岩桩的模型试验

援建马尔代夫的马累－机场岛跨海大桥项目作为我国“一带一路”的经济建设规划之一,桥梁桩基坐落于与我国南海珊瑚礁岩土体结构极为相似的珊瑚礁中。由于国内外开展珊瑚礁嵌岩桩的设计经验不足,故需要通过试验方法获取珊瑚礁嵌岩桩的承载特性和相关数据。对取自马累岛和机场岛桥基位置的礁灰岩岩芯开展室内桩基承载特性试验研究。测得礁灰岩的密度、相对密度、饱和单轴抗压强度、三轴剪切强度等基本物理力学指标,结合礁灰岩中嵌岩桩模型试验结果,获得模型桩承载力随桩端位移的变化规律。试验结果表明：桩岩界面先后经历弹性剪切、剪应力跌落和摩擦剪切3个阶段。在弹性剪切阶段,界面剪切变形以弹性变形为主,极限弹性位移 呈现出随弹性模量E增大而递减的趋势。在剪应力跌落阶段,应力软化急剧,并很快过渡到界面的摩擦剪切。通过试验发现,在低围压下,礁灰岩的残余侧摩阻力与饱和单轴抗压强度呈正相关关系。随着围压增大,残余侧摩阻力受围压影响较大。     

Numerical Investigation of the Dynamic Compressive Behaviour of Rock Materials at High Strain Rate

The dynamic compressive strength of rock materials increases with the strain rate. They are usually obtained by conducting laboratory tests such as split Hopkinson pressure bar (SHPB) test or drop-weight test. It is commonly agreed now that the dynamic increase factor (DIF) obtained from impact test is affected by lateral inertia confinement, friction confinement between the specimen and impact materials and the specimen sizes and geometries. Therefore, those derived directly from testing data do not necessarily reflect the true dynamic material properties. The influences of these parameters, however, are not straightforward to be quantified in laboratory tests. Therefore, the empirical DIF relations of rock materials obtained directly from impact tests consist of contributions from lateral inertia and end friction confinements, which need be eliminated to reflect the true dynamic material properties. Moreover, different rocks, such as granite, limestone and tuff have different material parameters, e.g., equation of state (EOS) and strength, which may also affect the DIF of materials but are not explicitly studied in the open literature. In the present study, numerical models of granite, limestone and tuff materials with different EOS and strength under impact loads are developed to simulate SHPB tests and to study the influences of EOS and strength, lateral inertia confinement and end friction confinement effects on their respective DIFs in the strain rate range between 1 and 1,000 s^?1. The commercial software AUTODYN with user-provided subroutines is used to perform the numerical simulations of SHPB tests. Numerical simulation results indicate that the lateral inertia confinement, friction confinement and specimen aspect (L/D) ratio significantly influence DIF obtained from impact tests and the inertia confinement effect is different for different rocks. Based on the numerical results, quantifications on the relative contributions from the lateral inertia confinement and the material strain rate effect on DIF of granite, limestone and tuff material compressive strength are made. The effects of friction coefficient, L/D ratio and rock type on DIF are discussed. Empirical relations of DIF with strain rate for the three rock materials representing the true material strain rate effect are also proposed.     

不同结构类型珊瑚礁灰岩弹性波特性研究

基于岩石弹性波特性的地震方法是目前地球物理勘探中最主要的方法,岩石中弹性波传播速度是联系岩石物理力学特性与地质学的有效桥梁。对于海相生物成因的珊瑚礁灰岩而言,其弹性波特性研究是了解珊瑚礁体内部整体性质的有效途径。研究表明,珊瑚礁灰岩的弹性纵波速度与干密度、回弹值呈线性正相关关系,与孔隙度呈线性负相关关系。不同结构类型珊瑚礁灰岩弹性波特性表现出显著的差异性,珊瑚骨架灰岩和珊瑚砾块灰岩均匀性较好,珊瑚砾屑灰岩和珊瑚砂屑灰岩离散性较大。基于珊瑚礁灰岩纵波速度与干密度、孔隙度以及回弹值之间的关系,结合某珊瑚礁体钻孔岩芯沿深度变化的回弹值信息以及岩芯薄片光学检测结果,提出一个基于纵波速度的珊瑚礁灰岩质量等级的划分标准,具有一定的可靠度和适用性。运用岩石二相体模型基本原理,建立了修正的时间平均公式,而不同结构类型珊瑚礁灰岩弹性波特性均符合雷莫亨特-加德纳方程。     

珊瑚骨架灰岩三轴压缩声发射特性研究

通过对珊瑚骨架灰岩在不同围压条件下的声发射监测试验,获取珊瑚骨架灰岩三轴压缩力学特性及其声发射（AE）基本特征。研究表明,珊瑚骨架灰岩强度特性符合Mohr-Coulomb强度准则。珊瑚骨架灰岩在三轴压缩作用下的宏观破坏特征表现出较明显的围压效应,即单轴压缩表现为劈裂式张拉断裂面;随着围压的增大,由两级台阶式宏观断口逐渐过渡呈现为单斜面剪切带。珊瑚骨架灰岩在三轴压缩作用下的AE时序演化规律与其应力-应变曲线特征基本吻合,等效破坏时间所对应的累计振铃计数、累计能量计数与围压之间呈良好的对数函数关系。峰前累计振铃计数、累计能量计数在长期强度?cd之前表现出稳定的平缓现象,符合岩石的线弹性变形特征,并在约90%处呈现剧增现象,即为岩石内部微裂纹快速不稳定扩展的开始。珊瑚骨架灰岩在单轴压缩作用下的峰前能量演化规律与其应力?应变曲线特征基本吻合,峰前弹性能、峰前耗散能同样在约90%处出现转折现象。     

Mechanical behaviors of conjugate-flawed rocks subjected to coupled static–dynamic compression

Conjugate flaws widely exist in rock masses and play a significant role in their deformation and strength properties. Understanding the mechanical behaviors of rock masses containing conjugate flaws is conducive to rock engineering stability assessment and the related supporting design. This study experimentally investigates the mechanical properties of conjugate-flawed sandstone specimens under coupled static–dynamic compression, thereby providing insight into how conjugate fractures interact to produce tracing tensional joints. Results indicate that the coupled compressive strength and the dynamic elastic modulus of conjugate-flawed rock specimens show remarkable loading rate dependence. For a fixed strain rate, the specimen with a static pre-stress equal to 60% of its uniaxial compressive strength has the highest coupled strength. Besides, both higher static pre-stress and strain rate can induce smaller mean fragment size and greater fractal dimension of the specimen, corresponding to a more uniform distribution of the broken fragments with smaller sizes. When the static pre-stress is lower than 80%UCS, the flawed specimen under a higher strain rate is characterized by higher absorbed energy. However, when the pre-stress equals 80%UCS, the value of the energy absorbed by the specimen in the dynamic loading process is negative due to the release of the preexisting considerable elastic strain energy input from the static pre-loading. As for the failure modes, cracks always penetrate the preexisting ipsilateral flaw tips to form anti-wing cracks. Under dynamic loading, the conjugate-flawed specimen generally shows tensile failure at a low strain rate, while the shear failure dominates at a high strain rate. In addition, based on progressive failure processes of the conjugate-flawed rock specimens, the evolution of tracing tensional joints in the field is discussed.

     

单轴压缩下软岩的动态力学特性试验研究

对软岩(砂浆模拟材料)进行了应变速率范围为10-5~101s-1的动单轴压缩实验。实验结果表明,试样的抗压强度随应变速率的增加有较明显的增加趋势,增加幅度大于硬岩;试样的弹性模量以及泊松比随着应变速率的增加均有增加的趋势,但幅度小于强度的增加幅度。并根据不同应变速率下试样破裂面的SEM实验结果,初步地分析了软岩动态力学特性机理。     

柴达木盆地东北缘石炭系生物礁发育特征及其地质意义

对柴达木盆地东北缘石炭系地层中生物礁的发育特征及区域展布进行了系统阐述。基于野外实地考察与室内镜下分析,采用地球化学与岩石学方法相结合,总结归纳柴达木盆地东北缘石炭系生物礁的岩石学特征、生物特征以及地层特征,分析生物礁主要产出层位及规模大小,探讨其古环境与油气地质意义。研究结果表明:柴达木盆地东北缘石炭系造礁生物主要为四射珊瑚,其次为横板珊瑚,发育锥状、盘状的单体珊瑚和管状、丛状、蜂窝状的群体珊瑚,附礁生物为腕足、等;珊瑚礁在岩层中以点状产出,呈不连续带状分布,依据其在地层中的发育规律与展布特征,分为簇状竖直丛生管状珊瑚、簇状水平延伸管状珊瑚以及簇状顶端向下倾斜管状珊瑚;根据岩石中的生物颗粒含量,生物礁灰岩储层岩石类型分为珊瑚骨架灰岩、珊瑚颗粒石灰岩、生物颗粒质石灰岩、含生物颗粒石灰岩以及泥晶灰岩。柴达木盆地东北缘早石炭世以碳酸盐台地环境为主,晚石炭世以海陆交互的潮坪环境为主。研究区石炭系生物礁主要位于下石炭统怀头他拉组三、四段,在石灰沟、旺尕秀等剖面可见厚层油砂,指示柴达木盆地东北缘石炭系具有良好的生烃潜力。     

不同应变率下砂岩动态强度准则的试验研究

分别利用RMT－150C和多功能分离式霍普金森压杆（SHPB）试验系统对砂岩进行了不同应变率下的单轴压缩、三轴压缩和拉伸试验。结果表明,在围压为0或围压一定的情况下,应变率低于102 s-1时,抗压强度的增加与应变率的量级呈正比;在应变率高于102 s-1时,岩石的抗压强度增加趋势与应变率的1/3次方呈正比。拉伸强度也存在类似规律。针对101～102 s-1应变率范围内缺少岩石动态强度准则这一现状,根据上述试验规律,结合Mohr-Coulomb准则、Hoek-Brown准则和Griffith准则的原理,给出了不同应变率范围内动态Mohr-Coulomb准则和动态Hoek-Brown准则的具体表达形式。研究结果表明,在低应变率情况下,动态Mohr-Coulomb准则和动态Hoek-Brown准则均适用,但Griffith准则判别结果误差很大。在高应变率情况下,动态Mohr-Coulomb准则比较适用,Griffith准则仅适用于评估高应变率单轴抗压强度和抗拉强度之间的关系。     

珊瑚礁岩土工程地质的探索与研究——从事珊瑚礁研究30年

珊瑚礁是一种特殊的岩土体,从工程地质角度可分为珊瑚砂屑土和珊瑚礁灰岩两大类。本文回顾了珊瑚礁研究30年的基本历程,重点对珊瑚砂屑土的静力学特性、动力学特性、颗粒强度低等特殊力学性能以及桩基工程性质的探索和研究成果进行了回顾与展望,并以南海岛礁工程建设为引,号召更多的科研学者加入到珊瑚礁的研究队伍中,共同促进珊瑚礁工程地质学科的发展。     

动态冲击下锦屏大理岩力学响应与能量特性

为了分析锦屏水电站大理岩的动力学响应和能量特性,采用分离式霍普金森压杆对岩样开展了动态压缩试验,并引入分形维数定量表征试样的破碎形态、能耗特性及其与应变率的内在关系。结果表明：动态载荷下大理岩应力-应变曲线初始压密段不明显,当应变率较低时,应力-应变曲线呈现出回弹现象;试样峰值应力随应变率的增大而增加,且动态抗压强度与...