Loading and Unloading Mechanical Properties and Energy Evolution Mechanism of Red-Bed Mudstone
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摘要:
为研究红层泥岩的力学特性和能量演化规律，基于5种不同围压梯度（200、250、300、350、400 kPa）及轴压与围压不等速率的应力路径，以四川遂宁地区红层泥岩为例开展了室内循环加卸载试验，得到围压效应对红层泥岩力学特性、总应变能密度、弹性应变能密度、耗散能密度的影响，以及应力-应变与能量之间的演化规律. 研究结果表明：从初始加卸载至试验结束，轴向应力输入的总能量密度、弹性应变能密度以及耗散能密度总体呈先增大后减小的“正态分布”形式；在峰前阶段，弹性应变能密度与耗散能密度间的差值会随着循环加卸载次数的增加而增大；围压的侧限作用提高了试样承载能力，总能量密度、弹性应变能密度以及耗散能密度随着围压的增大而增大；在峰后阶段，当围压≤300 kPa时，耗散能密度低于弹性应变能密度，而围压＞300 kPa时，耗散能密度高于弹性应变能密度，围压增大会进一步抑制试样破坏后弹性应变能密度的释放；相同围压下，随着干湿循环次数的增加，干燥、饱和状态下的抗压强度和弹性应变能密度均呈负相关关系；相同干湿循环次数，干燥状态的抗压强度和弹性应变能密度比饱和状态高，呈正相关关系.
Abstract:To study the mechanical properties and energy evolution law of red-bed mudstone, five different confining pressure gradients (200, 250, 300, 350, and 400 kPa) and different rate stress paths between the axial and confining pressures are used to perform indoor cyclic loading and unloading tests, taking red-bed mudstone in the Suining area, Sichuan Province, as an example. The effects of the confining pressure on the mechanical properties, total strain energy density, elastic strain energy density, and dissipated energy density of the red-bedded mudstone and the evolution law between the stress-strain and energy are obtained. The results show that the total energy density, elastic strain energy density, and dissipated energy density of the axial stress input generally increase first and then decrease in a normal distribution from the initial loading and unloading to the end of the test. During the pre-peak stage, the difference between the elastic strain energy density and the dissipated energy density increases with increasing number of loading and unloading cycles. The confining effect of the confining pressure improves the bearing capacity of the samples, and the total energy density, elastic strain energy density, and dissipated energy density increase with increasing confining pressure. During the post-peak stage, when the confining pressure ≤ 300 kPa, the dissipated energy density is lower than the elastic strain energy density; meanwhile, when the confining pressure > 300 kPa, the dissipated energy density is higher than the elastic strain energy density, indicating that increasing the confining pressure further inhibits the release of elastic strain energy density after failure. Under the same confining pressure, the compressive strength and elastic strain energy density in the dry and saturated states are negatively correlated with the increase in the number of wet-dry cycles. For the same number of dry and wet cycles, the compressive strength and elastic strain energy density in the dry state are higher than those in the saturated state, showing a positive correlation.
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Key words:
- cyclic loading and unloading /
- energy density /
- energy evolution /
- dissipation energy /
- red-bed mudstone
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图 3 三轴加卸载试验的应力路径
Figure 3. Schematic diagram of stress path of triaxial loading and unloading test
图 6 三轴循环加卸载全过程应力-应变曲线
Figure 6. Stress-strain curves of triaxial cyclic loading and unloading
图 8 加卸载应力-应变包络曲线示意
Figure 8. Schematic diagram of the stress-strain envelope curve of loading and unloading
图 10 加卸载应力-应变包络曲线示意
Figure 10. Schematic diagram of the stress-strain envelope curve of loading and unloading
图 11 循环加卸载岩样能量密度计算
Figure 11. Calculation of energy density of cyclic loading and unloading rock samples
图 13 干燥状态应力-应变与能量密度关系
Figure 13. Relationships between stress-strain and energy density in the dry state
图 14 饱和状态应力-应变与能量密度关系
Figure 14. Relationships between stress-strain and energy density in saturated state
表 1 岩样基本物理性质
Table 1. Basic physical properties of rock samples
试样编号 天然含
水率/%黏聚力/
kPa内摩擦
角/（°）天然密度/
（g·cm−3）E1 11.4 642 40.6 2.12 E2 12.3 636 39.1 2.04 E3 13.2 618 37.7 1.98 
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表 2 不同围压卸荷试验结果
Table 2. Results of different confining pressure unloading tests
试样
编号平均初
始围压/
kPa平均破
坏围压/
kPa平均抗
剪强度/
kPa平均泊
松比平均剪
切模量/
kPaE4、E5 200 75.0 634 0.31 238 E6、E7 250 62.5 702 0.33 265 E8、E9 300 88.0 834 0.33 315 E10、E11 350 134.0 871 0.31 326 E12、E13 400 174.0 983 0.32 382
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