Rate-dependence of the compressive and tensile strength of granites
Rate-dependence of the compressive and tensile strength of granites
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DOI：
10.5194/adgeo-62-11-2023
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发表时间：
2023-10
影响因子：
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通讯作者：
J. Kendrick;A. Lamur;Julien Mouli-Castillo;A. Fraser-Harris;A. Lightbody;K. Edlmann;Christopher McDermott-Christ
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作者：
J. Kendrick;A. Lamur;Julien Mouli-Castillo;A. Fraser-Harris;A. Lightbody;K. Edlmann;Christopher McDermott-Christ
抽象的。岩土材料的强度和断裂对于地下工程实践是不可或缺的，例如优化地热能开采所需的工程实践。特别重要的是材料强度的时间和应变率依赖关系，它决定了破坏时释放的能量，并影响诱发地震活动的大小、裂缝结构，从而影响水力传导性和系统渗透性。在这里，我们进行了一系列在不同变形速率下的单轴压缩和巴西拉伸强度测量，以限制应变率对G603花岗岩强度的影响。对致密、低渗透、中粒花岗岩进行了从10−5到10−2 S−1的4种应变率(在巴西试验中为直径等效应变率)的力学试验，其破坏范围从拉伸速度最快的1s以下到压缩速度最慢的1000s以上。适用的费率包括ISRM和ASTM材料压缩试验和巴西拉伸试验标准所建议的费率。我们发现了显著的速率强化效应，在测试的4个数量级的应变率中，压缩和拉伸强度都增加了大约35%。我们发现，在这个变形速率范围内，静态杨氏模数保持相对恒定，然而，由于系统平衡施加应力的时间缩短，变异性在较快的速率下减小。在较慢的应变率下强度较低会导致较小的应力降，这表明岩石以较慢的速率被驱动到压缩和拉伸破坏时，在破坏时释放的能量较少。与工程地质应用中常规使用的标准化材料特性相比，材料强度的应变率依赖性的这种限制将被证明是有用的，因为我们将开发越来越复杂的策略，如循环软刺激，以使用更少的能源来获取资源，同时降低环境风险和产生更少的废物。
Abstract. The strength and rupture of geomaterials are integral to subsurface engineering practices, such as those required to optimise geothermal energy extraction. Of particular importance is the time- and strain-rate-dependence of material strength, which dictates the energy released upon failure, and impacts the magnitude of induced seismicity, fracture architecture and thus hydraulic conductivity and system permeability. Here, we performed a series of uniaxial compression and Brazilian tensile strength measurements at a range of deformation rates in order to constrain the impact of strain rate on the strength of G603 granite. The dense, low permeability, medium-grained granites were mechanically tested at 4 strain rates (or diametric equivalent strain rates in the case of Brazilian tests) from 10−5 to 10−2 s−1, such that sample failure was achieved in anything from below 1s at the fastest rate in tension, to over 1000s at the slowest rate in compression. The applied rates encompassed those recommended by ISRM and ASTM material testing standards for compressive and Brazilian tensile testing. We found a significant rate strengthening effect, whereby compressive and tensile strength both increased by approximately 35 % across the 4 orders of magnitude of strain rate tested. We found that the static Young's modulus remained relatively constant across this range of deformation rates, however variability was reduced at faster rates, owing to the reduced time for equilibration of the system to imposed stresses. The lower strength at slower strain rates causes smaller stress drops, indicating that rocks driven to compressive and tensile failure at slower rates release less energy upon failure. Such constraints of the strain-rate-dependence of material strength, in contrast to the use of standardised material characteristics conventionally used in Engineering Geology applications, will prove useful as we develop increasingly sophisticated strategies such as cyclic soft stimulation to access resources using less energy, whilst reducing environmental risk and producing less waste.