高温盐溶液浸泡作用下石膏岩力学特性试验研究

EXPERIMENTAL STUDY OF MECHANICAL PROPERTY OF GYPSUM ROCK SOAKED IN HOT SATURATED BRINE

为研究盐矿水溶开采或盐岩溶腔储库建造过程中,石膏岩夹层在温度与含Cl-盐溶液长时间共同作用下的力学特性,进行主要内容包括石膏岩在40℃,70℃半饱和、饱和盐溶液浸泡作用之后的单轴抗压强度、抗拉强度、抗剪强度试验,通过对比分析揭示石膏岩在这一特殊条件下的力学特性。主要结论如下:随温度升高、盐溶液浓度增大、浸泡时间的延长,石膏岩强度呈降低弱化趋势。浸泡60 d后石膏岩单轴抗压强度弱化系数为0.10～0.73;弹性模量随温度与浓度变化也呈线性规律降低,从40℃半饱和溶液中的5.92 GPa降至70℃饱和溶液中的0.21 GPa。相同条件下,抗拉强度也从在40℃环境下的0.64～0.66 MPa,降至70℃环境下的0.27～0.47 MPa。在70℃饱和盐溶液中浸泡60 d之后,石膏岩莫尔–库仑剪切强度拟合方程为τ=0.4+σtan38.9°,而相同条件下浸泡30,80 d之后的剪切强度拟合线性方程分别为τ=1.24+σtan41.3°,τ=0.65+σtan39.3°。随浸泡时间的延长,石膏岩的黏聚力与内摩擦角均呈降低趋势。为区分石膏岩在不同条件下的破坏方式及其差异,定义岩石变形破坏脆性指标——破坏刚度,将其近似为岩石单轴压缩应力–应变曲线峰后破坏段斜率。实测结果表明,在干燥、40℃半饱和到70℃饱和溶液几种条件下,石膏岩的破坏刚度分别为704.4,690.1,218.9,255.2,19.5 GPa。相应破坏方式也由脆性向脆延性、延性转变。本研究对深入揭示石膏岩水力学特性及指导层状盐岩矿床储库溶腔控制溶解建造具有重要理论意义与应用价值。

Gypsum rock is commonly found as an interlayer in bedded salt deposits which are solution mined for the purpose of salt mining or oil and gas storage construction. To investigate the related mechanical properties of gypsum rock under the situation, series tests of uniaxial compression, tensile and shear strength are carried out in the laboratory with gypsum specimens soaked in brine of different temperatures and concentrations. It is demonstrated that the strength of gypsum rock is weakened to different extents with brine temperature and concentration increasing and soaking time lasting. The strength softening coefficient can be as low as 0.10 to 0.73 after being soaked in hot and concentrated brine for 60 d. The elastic modulus of the gypsum rock is also linearly decreased with the temperature and concentration of brine increasing. The elastic modulus of gypsum rock is 5.92 GPa after being soaked in half saturated brine of 40 ℃ for 60 days, however it suddenly decreases to 0.21 GPa when being soaked in saturated brine of 70℃ for the same time. Similarly, the tensile strength also decreases from 0.64--0.66 MPa soaked in brine of 40℃ to 0.27--0.47 MPa of 70 ℃. After being soaked in saturated brine of 70 ℃ for 60 d, a regressed equation for Mohr-Coulomb shear strength of the gypsum rock is obtained as τ = 0.4 ＋ δ tan 38.9° . Two similar strength equations are also regressed as τ = 1.24 ＋ δ tan 41.3° , τ = 0.65 ＋ δ tan39.3° when the soaked time is 30 and 80 d respectively. It demonstrates that both the cohesion and inner friction coefficient of gypsum rock decrease with soaking time lasting. A parameter of failure rigidity is defined to illustrate the difference of gypsum failure at different situations. According to the calculated results and the geometry of stress-strain curves of the gypsum rock under uniaxial compression, the failure style of gypsum rock changes from brittle to ductile damage obviously with increase of the temperature and the concentration of soaked brine. The study is significant not only for the investigation of hydromechanical property of gypsum rock, but also for guidance for solution mining or storage cavern construction in bedded salt deposits.