超欠挖状态下支护结构的力学特性研究

Mechanical analysis of support structure based on over-under-excavated tunnels

在传统的喷射混凝土支护结构设计中,通常假设支护结构层是一个薄壁等厚层。钻爆法开挖的隧道围岩表面由于受爆破的影响存在不同程度的超欠挖,导致初期支护喷射混凝土结构层厚度不均匀。充分考虑超欠挖情况下隧道围岩表面的不平整性,根据喷射混凝土支护厚度将支护后的隧道表面不规则形状依据实际喷层情况归结为未完全填充、局部填充和完全填充三类。基于弹性力学厚壁圆筒理论,建立了单一喷射混凝土支护结构和喷射混凝土+钢格栅联合支护结构的等效刚度与最大支护力的理论公式。基于上述原理,结合收敛-约束法对某隧道开挖工程的稳定性进行了分析,得到了隧道支护结构的安全系数。结果表明,所提出的方法对超欠挖隧道的稳定性分析具有较好的适用性,验证了该方法的可行性。

Conventionally,the traditional design of shotcrete support structure has assumed that support structure is a prismatic layer with uniform thickness.Due to the influence of blasting,the surrounding rock surface of the tunnel with drilling and blasting method has different degrees of over-under-excavation,which results in the uneven thickness of the initial support structure layer.In the consideration of the possibility of rock surface irregularities caused by overunder-excavation,this paper,according to the shotcrete thickness,divides the irregular surface of the tunnel after supporting into three categories：not fully filled,partially filled,and fully filled.With utilizing the thick-wall cylinder theory of elastic mechanics,the theoretical formula of the parameters,such as equivalent support stiffness and maximum support pressure,are established under the support of shotcrete or shotcrete ＋steel grid.Based on the research findings mentioned above,this work analyzes the stability of a tunnel excavation project with the aid of the convergence-confinement method and calculates the safety factor of the support structure.The results show that the proposed method has a preferable applicability to the stability study of over-under-excavated tunnel,and the availability is verified preliminarily.