Experimental study on mechanics and permeability characteristics of Jurassic red sandstone under hydro-mechanical coupling
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摘要:
三峡库区广泛分布侏罗系红砂岩, 在水库运行期间红砂岩的渗流-应力耦合特性关乎库区内多数滑坡和岩质边坡的稳定性。借助岩石多场耦合三轴试验系统, 对三峡库区侏罗系红砂岩开展了不同围压、不同渗透压下的三轴压缩试验, 系统研究了红砂岩的三轴压缩力学特性和渗透率演化特征。研究结果表明: ①红砂岩的峰前应力-应变曲线可分为孔隙压密阶段、弹性变形阶段、微裂隙稳定发展阶段和非稳定发展阶段。红砂岩的力学参数与渗透压的关系呈负相关, 与围压呈正相关。②随着围压升高, 红砂岩的破坏模式由张拉破坏过渡到剪切破坏。③不同渗透压下, 渗透率曲线呈平稳发展→缓慢上升→快速上升3阶段演化规律; 不同围压下, 渗透率曲线先降低后升高。④从能量角度分析了渗透压和围压对岩石的作用, 验证了渗流对岩石的劣化效应以及围压对裂纹发展的抑制作用。本试验对鲜有报道的侏罗系红砂岩的强度、变形和渗透特性做了系统的研究, 对渗流-应力耦合课题有补充意义。其工况根据三峡库区边坡岩体的应力水平来确定, 试验结果对分析库区边坡稳定性具有指导意义。
Abstract:Jurassic red sandstone is widely distributed in the Three Gorges reservoir area. During the operation of the red sandstone reservoir, the hydro-mechanical coupling characteristics affect the stability of most landslides and rock slopes. In this paper, triaxial compression tests under different confining pressures and osmotic pressures are carried out on the Jurassic red sandstone in the Three Gorges Reservoir area by means of the multi-field coupled triaxial test system. The mechanical properties and permeability evolution characteristics of the red sandstone under triaxial compression are systematically studied. The results show that: ①The pre-peak stress-strain curve of red sandstone can be divided into pore compaction stage, elastic deformation stage, stable development stage of micro-cracks, and unsteady development stage. The mechanical parameters of red sandstone are negatively correlated with osmotic pressure and positively correlated with confining pressure. ②With the increasing of confining pressure, the failure mode of red sandstone transitions from tensile failure to shear failure.③The permeability under different osmotic pressures shows a "three-stage" evolution law of developing steadily firstly, then increasing slowly and increasing sharply lastly; the permeability under different confining pressures decreases firstly and then increases. ④The effects of osmotic pressure and confining pressure on rock are analyzed from the perspective of energy, and the degradation effect of seepage inrock and the inhibition effect of confining pressure on crack development are verified. The experimental results have guiding significance for the stability of bank slope.In this experiment, the strength, deformation and permeability characteristics of the little-reported Jurassic red sandstone were systematically studied, which is of complementary significance to the topic of seepage-stress coupling. The working conditions are determined according to the stress level of the rock mass on the slope of the Three Gorges reservoir area, and the test results have guiding significance for analyzing the stability of the slope in the reservoir area.
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图 8 渗透压、偏应力与轴应变关系曲线
a.围压3 MPa, 渗透压1 MPa; b.围压3 MPa, 渗透压1.5 MPa; c.围压3 MPa, 渗透压2 MPa; d.围压5 MPa, 渗透压2 MPa; e.围压7 MPa, 渗透压2 MPa
Figure 8. Osmotic pressure, deviatoric stress-axial strain curves
图 9 不同渗透压下红砂岩能量变化曲线
a.渗透压1 MPa, 围压3 MPa; b.渗透压1.5 MPa，围压3 MPa; c.渗透压2 MPa，围压3 MPa; d.能量大小
Figure 9. Energy evolution curves under various osmotic pressure
图 10 不同围压下红砂岩能量变化曲线
a.围压3 MPa，渗透压2 MPa; b.围压5 MPa，渗透压2 MPa; c.围压7 MPa，渗透压2 MPa; d.能量大小
Figure 10. Energy evolution curves under various confining pressure
表 1 红砂岩基本物理参数
Table 1. Physical properties of red sandstone
试样编号 直径/mm 长度/mm 天然密度/(g·cm-3) 孔隙率/% 饱和吸水率/% 压缩波波速/(m·s-1) 1# 49.36 101.89 2.643 1.62 0.66 3 453.79 2# 49.52 102.15 2.649 1.49 0.56 3 462.42 3# 49.38 101.96 2.651 1.52 0.62 3 455.87 4# 49.41 101.64 2.643 1.65 0.63 3 444.83 5# 49.67 101.43 2.651 1.47 0.56 3 447.59 
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表 2 试验方案
Table 2. Experimental scheme
试样编号 围压/MPa 渗透压/MPa 1# 3 1.0 2# 3 1.5 3# 3 2.0 4# 5 2.0 5# 7 2.0
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表 3 红砂岩试样特征应力
Table 3. Characteristic intensity of red sandstone
试样编号 闭合应力/MPa 起裂应力/MPa 损伤应力/MPa 1# 18.96% 53.24% 72.36% 2# 13.97% 34.08% 80.66% 3# 14.11% 33.87% 71.24% 4# 16.36% 38.63% 82.22% 5# 12.18% 54.55% 79.60%
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表 4 红砂岩力学参数
Table 4. Mechanical parameters of red sandstone
试样编号 围压/MPa 渗透压/MPa 峰值应力/MPa 初始弹性模量/GPa 泊松比 最大体积应变/% 1# 3.0 1.0 127.90 24.4 0.345 0.124 6 2# 3.0 1.5 121.50 21.1 0.326 0.140 4 3# 3.0 2.0 119.95 13.5 0.304 0.157 3 4# 5.0 2.0 125.27 20.1 0.364 0.091 7 5# 7.0 2.0 137.13 21.4 0.451 0.017 0
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表 5 红砂岩初始渗透率
Table 5. Initial permeability of red sandstone
岩样编号 初始渗透率/10-19 m2 1# 2.5 2# 5.1 3# 8.0 4# 1.3 5# 0.8
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