加卸荷应力路径下巷帮煤体力学特性与损伤破坏研究

Study on mechanical characteristics and damage failure of coal mass from roadway side wall under loading and unloading stress path

为探究煤巷开挖卸荷帮部破坏机理,开展巷帮煤体常规三轴压缩及峰前卸围压2种应力路径下实验室试验,分析其力学特性与损伤破坏规律。结果表明:常规三轴压缩试验中,破坏特征表现出由低围压下的脆性向高围压下的塑形转变;峰前卸围压应力路径下,破坏更易发生,且全部为脆性破坏;煤体强度对围压变化较敏感,卸荷条件下其峰值更低;变形模量随围压被卸除而降低,开始阶段变化平缓,随后下降趋势不断加剧;泊松比随围压减小而增大,其变化趋势同变形模量基本一致;卸荷应力路径下,煤体破坏是一种以剪切破坏为主,但仍存在部分劈裂破坏的复合状态;破断角以抛物线趋势随初始围压的提高而增加,但卸荷应力路径下其值明显更小;卸荷条件下损伤因子与围压之间的变化关系及趋势同泊松比一致;随初始围压的增加,卸荷条件下围压差比λ逐渐降低。

To explore side wall breakage mechanism of coal roadway for excavation unloading,laboratory tests of coal mass in roadway side wall under loading and unloading stress paths were conducted,and its mechanical properties and damage failure were analyzed.The results indicated that in conventional triaxial compression test,with the raise of confining pressure,failure characteristics of coal mass would be changed from brittleness to ductility.Under stress path of confining pressure reduction,failures were more likely to happen and all of them were brittle failure.Coal mass strength was very sensitive to confining pressure variations and its peak value was lower under unloading stress path.Deformation modulus decreased with the reduction of confining pressure,change was gentle in the initial stage,but the downtrend was aggravated continuously by later.Poisson ratio increased as confining pressure conduction and its variation trend agreed with modulos of deformation.Under unloading stress path,coal mass failure was a composite state,in which shear failure was the chief form,but splitting failure also might appear.Fracture angle increased with the raise of initial confining pressure along a parabolic curve,but its value was obviously smaller under unloading stress path.Under unloading stress path,the relationship and variation trend between damage factor and confining pressure agreed with poisson ratio.Confining pressure difference ratio decreased with the raise of initial confining pressure under unloading stress path.