循环荷载条件下岩石变形损伤及能量演化的实验研究
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摘要
在岩土工程施工及运营阶段,经常会遇到周期性荷载的作用,岩体在周期性荷载作用下的力学性能是影响岩土工程长期稳定性的重要因素之一。因此,深入系统开展周期性荷载作用下岩石的变形损伤的演化规律具有十分重要的理论研究价值和工程实际指导意义。
本文以重庆三峡库区三叠系上统须家河组(T3xj)的砂岩为研究对象,利用MTS815岩石力学测试系统和RLW-2000M煤岩三轴流变试验机对岩石分别进行了单轴循环荷载(包括不同含水状态、不同应力水平)、三轴循环荷载(包括轴向应力循环、围压循环)和孔隙水压力循环荷载(包括不同上限循环幅值、不同下限循环幅值)实验。论文分析了循环荷载作用下岩石滞回环曲线的演化规律,并从能量的角度探讨了循环荷载作用过程中岩石能量吸收与释放的演化规律,研究结果表明:
岩石在单轴和三轴循环荷载作用下,随着循环次数的增加,岩石应力-应变滞回环曲线呈现由疏变密的特征,且残余应变量逐渐减小并趋于稳定。孔隙水压力循环荷载作用下,岩石的每个轴向有效应力-轴向应变滞回环和横向有效应力-横向应变滞回环曲线均为顺时针发展且可分为4个阶段。
另外从能量的角度分析可知,在单轴和三轴循环荷载作用下,每次循环完成后的单位体积耗散能均随着循环次数的增加而减小并逐渐趋于稳定,即单个循环荷载完成后岩石耗散掉的能量在逐渐减小。而在孔隙水压力循环荷载作用下,单位体积耗散能随着循环次数的增加而增大并逐渐趋于稳定,在循环的初始阶段,单位体积耗散能为负值,说明岩石试件向外释放能量,而随着循环次数的增加,单位体积耗散能有趋向于零并有向正值演化的规律,说明岩石试件开始从外界吸收能量。
In the construction and service stage of geotechnical engineering, rock mass often encounter the effect of cyclic loading and mechanical property of rock mass under cyclic loading is one of important influencing factors of long-term stability of geotechnical engineering. Therefore, it is of great significance to systematically study the evolution of deformation and damage of rock under periodic loading.
In this paper, sandstone obtained from the Three Gorges Reservoir (T3xj) are studied on the characteristic of deformation and damage under cyclic loading (including uniaxial cyclic loading, triaxial cyclic loading and cyclic pore water pressure) by rock mechanics test system MTS815 and RLW-2000M triaxial creep testing machine. Based on analysis of evolution of hysteresis loop curves of sandstone under cyclic loading, the energy evolution of dissipation and release of rock specimens are also discussed. The conclusions are as below:
In uniaxial and triaxial cyclic loading, with the increase of cycle number, stress– strain hysteresis loop curves show the characteristic of sparse to dense and the residual strain is gradually decreasing and become stabilized. In cyclic pore water pressure, the development of each axial effective stress– train hysteresis loop and horizontal effective tress– transverse strain hysteresis loop are clockwise and show a law of four stages.
On the other hand, energy dissipation and release of sandstone specimen has been described though the use of theory of energy principle. It has been found that in uniaxial and triaxial cyclic loading, dissipated energy per unit volume of the completion of every cycle is gradually decreasing with the increase of cycle number, which means that the dissipate energy in rock specimen after the completion of each cyclic loading. However, in the cyclic pore water pressure, dissipated energy per unit volume of the completion of every cycle is gradually increasing with the increase of cycle number. In the initial stage of cyclic pore water pressure, dissipated energy per unit volume is negative, which shows that sandstone specimen releases energy to outside. While with the increase of cycle number, dissipated energy per unit volume are gradually moving to zero and has the trend to be positive, which means that sandstone specimen dissipates energy.
本文以重庆三峡库区三叠系上统须家河组(T3xj)的砂岩为研究对象,利用MTS815岩石力学测试系统和RLW-2000M煤岩三轴流变试验机对岩石分别进行了单轴循环荷载(包括不同含水状态、不同应力水平)、三轴循环荷载(包括轴向应力循环、围压循环)和孔隙水压力循环荷载(包括不同上限循环幅值、不同下限循环幅值)实验。论文分析了循环荷载作用下岩石滞回环曲线的演化规律,并从能量的角度探讨了循环荷载作用过程中岩石能量吸收与释放的演化规律,研究结果表明:
岩石在单轴和三轴循环荷载作用下,随着循环次数的增加,岩石应力-应变滞回环曲线呈现由疏变密的特征,且残余应变量逐渐减小并趋于稳定。孔隙水压力循环荷载作用下,岩石的每个轴向有效应力-轴向应变滞回环和横向有效应力-横向应变滞回环曲线均为顺时针发展且可分为4个阶段。
另外从能量的角度分析可知,在单轴和三轴循环荷载作用下,每次循环完成后的单位体积耗散能均随着循环次数的增加而减小并逐渐趋于稳定,即单个循环荷载完成后岩石耗散掉的能量在逐渐减小。而在孔隙水压力循环荷载作用下,单位体积耗散能随着循环次数的增加而增大并逐渐趋于稳定,在循环的初始阶段,单位体积耗散能为负值,说明岩石试件向外释放能量,而随着循环次数的增加,单位体积耗散能有趋向于零并有向正值演化的规律,说明岩石试件开始从外界吸收能量。
In the construction and service stage of geotechnical engineering, rock mass often encounter the effect of cyclic loading and mechanical property of rock mass under cyclic loading is one of important influencing factors of long-term stability of geotechnical engineering. Therefore, it is of great significance to systematically study the evolution of deformation and damage of rock under periodic loading.
In this paper, sandstone obtained from the Three Gorges Reservoir (T3xj) are studied on the characteristic of deformation and damage under cyclic loading (including uniaxial cyclic loading, triaxial cyclic loading and cyclic pore water pressure) by rock mechanics test system MTS815 and RLW-2000M triaxial creep testing machine. Based on analysis of evolution of hysteresis loop curves of sandstone under cyclic loading, the energy evolution of dissipation and release of rock specimens are also discussed. The conclusions are as below:
In uniaxial and triaxial cyclic loading, with the increase of cycle number, stress– strain hysteresis loop curves show the characteristic of sparse to dense and the residual strain is gradually decreasing and become stabilized. In cyclic pore water pressure, the development of each axial effective stress– train hysteresis loop and horizontal effective tress– transverse strain hysteresis loop are clockwise and show a law of four stages.
On the other hand, energy dissipation and release of sandstone specimen has been described though the use of theory of energy principle. It has been found that in uniaxial and triaxial cyclic loading, dissipated energy per unit volume of the completion of every cycle is gradually decreasing with the increase of cycle number, which means that the dissipate energy in rock specimen after the completion of each cyclic loading. However, in the cyclic pore water pressure, dissipated energy per unit volume of the completion of every cycle is gradually increasing with the increase of cycle number. In the initial stage of cyclic pore water pressure, dissipated energy per unit volume is negative, which shows that sandstone specimen releases energy to outside. While with the increase of cycle number, dissipated energy per unit volume are gradually moving to zero and has the trend to be positive, which means that sandstone specimen dissipates energy.
引文
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[2] Jager J C, Cook N GW.岩石力学基础[M ].北京:科学出版社, 1983. 952105
[3]葛修润.周期荷载下岩石大型试件的变形和强度特性研究[J].岩土力学,1987,8(2):11-19.
[4]葛修润,卢应发.循环荷载作用下岩石疲劳破坏和不可逆变形问题的探讨[J].岩土工程学报,1992,14(3):56~60.
[5]章清叙,葛修润,黄铭,等.周期荷载作用下红砂岩三轴疲劳变形特性试验研究[J].岩石力学与工程学报,2006,25(3):473~478.
[6]章清叙.周期荷载作用下岩石三轴疲劳特性实验研究[学位论文].上海交通大学. 2005,2-23.
[7]葛修润,蒋宇,卢允德,等.周期荷载作用下岩石疲劳变形特性试验研究[J].岩石力学与工程学报,2003,22(10):1581~1585.
[8]蒋宇,葛修润,任建喜.岩石疲劳破坏过程中的应变规律及声发射特性[J].岩石力学与过程学报. 2004,23(11):1810-1814.
[9]席道瑛,王少刚,刘小燕,等.岩石的非线性弹塑性响应[J].岩石力学与工程学报,2002,21(6):772-777.
[10]陈运平,席道瑛,薛彦伟.循环荷载下饱和岩石的应力–应变动态响应[J].石油地球物理勘探,2003,38(4):409–413.
[11]席道瑛,薛彦伟,宛新林.循环荷载下饱和砂岩的疲劳损伤[J].物探化探计算技术. 2004,26(3):193-198.
[12]陈运平,席道瑛,薛彦伟.循环荷载下饱和岩石的滞后和衰减[J].地球物理学报. 2004,47(4):672-679.
[13]许江,杨红伟,李树春,等.循环加、卸载孔隙水压力对砂岩变形特性影响实验研究[J].岩石力学与工程学报,2009,28(5):892~899.
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