考虑隧道围岩蠕变的复合式衬砌受力规律

Force rule of composite lining considering creep of tunnel surrounding rock

将锚杆作用力视为体力作用于围岩内,将初期支护与锚杆锚固范围内的围岩视为围岩加固体,建立了围岩力学模型,基于统一强度理论分析了隧道蠕变条件下的围岩应力与变形规律,推导了复合衬砌应力与变形表达式,分析了隧道围岩蠕变过程中支护结构受力特点及不同初期支护强度下二次衬砌受力变化规律。分析结果表明:当初期支护按照"初期支护应与围岩共同受力且能保证施工阶段安全"的原则进行设计时,在围岩蠕变作用下,锚杆与喷射混凝土最大受力分别为48、286kPa,与开挖阶段相比分别增大了57.5%、13.7%,且超过支护结构最大承载力,说明在进行初期支护设计时,仅满足隧道开挖过程中围岩稳定而不考虑蠕变产生的附加应力影响,可能造成隧道运营过程中初期支护结构破坏,不利于隧道稳定;当二次衬砌厚度由300mm增大至500mm时,二次衬砌最大受力增大了40.5%,荷载分担比由25.2%增大至36.2%,而增大初期支护强度后,二次衬砌受力减小了14.5%,荷载分担比由25.2%减小至22.3%,说明二次衬砌荷载随初期支护强度增大而减小,而随自身强度增大而增大,应重视初期支护与二次衬砌支护强度的协调配置,实现围岩压力的合理分配;在软岩地质条件下,应保证隧道施工过程中围岩稳定并避免围岩蠕变过程中发生结构破坏,以实现初期支护与二次衬砌共同承担蠕变引起的附加应力。

Anchor force was regarded as the physical force acting on the surrounding rock, the initial support and the surrounding rock in the anchorage zone were regarded as reinforced surrounding rock, and the mechanical model of surrounding rock was established. Based on the unified strength theory, the stress and deformation laws of surrounding rock of tunnel in the creep process were analyzed, the expressions of stress and deformation of composite lining were derived, and the stress characteristics of supporting structure in the creep process of tunnel surrounding rock and the change laws of secondary lining stresses under different initial support strengths were analyzed. Analysis result shows that compared with the excavation stage, the maximum forces of bolt and shotcrete are 48 kPa and 286 kPa in the creep process of surrounding rock, respectively, and increase by 57.5% and 13.7%, respectively, which exceeds the maximum bearing capacity of supporting structure when the initial support is designed in accordance with the principle of ＂the initial support should be based on the joint force with the surrounding rock to ensure the safety of construction phase＂. So it can cause the failure of initial support structure during tunnel operation if only to meet the stability of surrounding rock during tunnel excavation without considering the additional stress caused by the creep during designing the initial support, which is not conducive to tunnel stability. When the thickness of secondary lining increases from 300 mm to 500 ram, its maximum load increases by 40.5 %, and the load sharing ratio increases from 25.2% to 36.2%. When the initial support strength increases, the load of secondary lining reduces by 14.5%, and the load sharing ratio reduces from 25.2% to 22.3~. So the load of secondary lining decreases with the increase of initial supporting strength, but increases with the increase of itself strength, and it is important to rationally allocate the strengths of initial support and secondary lining support to realize the reasonable distribution of surrounding rock pressure. In order to realize the effect that the primary support and the secondary lining jointly bear the additional stress caused by the creep under the condition of soft rock geology, the primary support not only ensures the stability of surrounding rock during tunnel construction, but also avoids the structural damage in the process of rock creep.1 tab,5 figs, 25 refs.