三维动静组合加载含水煤样强度特征试验研究

Experimental study of strength characteristics of water-saturated coal specimens under 3D coupled static-dynamic loadings

为探讨含水煤样动静组合加载下的力学特征,利用改进split Hopkinson pressure bar(SHPB)和RMT–150试验系统对自然和饱水7 d煤样进行了三维动静组合加载、三维静载对比试验。结果表明:三维静载试验中,自然煤样峰值强度变化幅度为10.49%,饱水7 d煤样峰值强度变化幅度为59.98%,饱水强度软化系数为0.81;三维动静组合加载试验中,轴压强度低于单轴静载煤样强度的55%时,饱水7 d煤样的动态强度高于自然煤样动态强度,饱水7 d煤样比自然煤样动态强度分别提高了7.85%~18.44%(围压4 MPa)和8.71%~19.84%(围压8 MPa);不同围压相同轴压试验中,自然和饱水7 d煤样的动态强度随着围压增大均呈增大趋势,饱水7 d煤样动态强度增加幅度比自然煤样动态强度增加幅度大,表明饱水煤样对围压变化的响应较强。揭示饱水对煤样的强度影响较显著,但应变率起到控制作用,中或高应变率条件下裂隙水与裂隙耦合形成较大刚度,三维动静组合加载饱水煤样动态强度呈增高特征。

In order to study the mechanical properties of water-saturated coal specimens under coupled static-dynamic loadings,contrast experiments between 3D coupled static-dynamic loadings and 3D static loadings on both water-saturated coal specimens and natural coal specimens were conducted by using the improved split Hopkinson pressure bar（SHPB） and the RMT–150 test systems. Results shows that,under 3D static loadings,the variation of peak strength of natural coal specimens is 10.49%,while the variation of peak strength of 7 d saturated specimen is 59.98%,with a softening coefficient of 0.81. Under 3D coupled static-dynamic loadings,when the axial pressure is less than 55% of the uniaxial compression strength,the dynamic strengths of the 7 d saturated coal specimens are higher than those of the natural coal specimens,the increased strength of 7 d saturated coal specimens are 7.85%–18.44%（confining pressure 4 MPa） or 8.71%–19.84%（confining pressure 4 MPa） compared to the natural coal specimens. In the case of different confining pressures with the same axial pressure,with the increase of confining pressure,the dynamic strengths of the 7 d saturated and the natural specimens are both increased. Moreover,the increment of dynamic intensity of 7 d saturated coal specimens is larger than that under the natural state,indicating that water-saturated coal specimens are more sensitive to confining pressure. Experimental results show that the effect of water-saturation to the strength of coal specimen is significant,but the strain rate plays a controlling role. The coupling effect between the water and coal fissure causes the larger stiffness under the conditions of medium or high strain rate. The dynamic strength of water-saturated coal specimens increases under 3D static-dynamic loadings.