复杂硐室交叉口转向挑顶施工力学行为研究

长大隧道的辅助坑道与正洞交叉段施工工序繁多,围岩易受到开挖扰动,进而产生失稳破坏。以伏牛山隧道为工程背景,借助有限元软件PLAXIS3D构建三维数值模型,模拟了辅助坑道进入正洞的施工过程,研究了小导洞转向挑顶施工及正洞反向台阶法开挖的施工力学行为与三维空间效应,分析了施工过程中围岩应力、拱顶沉降、洞周横向收敛位移及围岩塑性区演化规律。结果表明:横向通道交叉口段施工会导致交叉口附近风机房正洞围岩产生应力重分布,在正洞拱顶及右拱腰处形成拉应力,沿风机房纵向影响范围约为1倍洞径; 风机房拱顶最终沉降量为3.7～3.9 mm,在交叉口及其附近,以小导洞爬坡挑顶阶段和风机房正洞反向开挖通过时引起的拱顶沉降量最大,小导洞转向挑顶施工引起的拱顶总沉降量相对较小; 联络通道左侧进洞使得正洞左侧横向位移增加,进而导致正洞左右两侧横向位移呈现不对称分布; 交叉口处联络通道与风机房产生了连续的塑性区,塑性点主要在开挖侧壁,拱腰处最为集中,向上延伸至拱肩,拱脚处向下发展至一定深度; 针对小导洞扩挖施工过程中交叉口、上台阶侧壁、底面出现的少量受拉破坏点,施工中应对这些部位予以重点关注,及时施作初期支护,防止局部掉块。

Research on construction mechanical behavior of turning overhanging at intersection of complex chamber

The construction processes of the intersection parts of the auxiliary tunnel and the main tunnel are complex, easily causing damage to the surrounding rock mass. On the background of the Funiushan Tunnel, a three-dimensional numerical model was built, and the construction processes of the auxiliary tunnel into the main tunnel was simulated using the finite element software PLAXIS3D. The construction mechanical behavior and three-dimensional space effect of the excavation of the intersection parts of the auxiliary tunnel and the main tunnel were studied. The evolution laws surrounding rock mass status, roof settlement, displacement around the tunnel and rock plastic zone were investigated in the construction process. The results show that the construction of the intersection section of the transverse channel will affect the stress distribution of the surrounding rock mass and generate tensile stress near the intersection section. Moreover, the main influence range is about twice the diameter of the tunnel. The final settlement of the vault of the fan room is 3.7-3.9 mm. In the vicinity of the intersection section, the settlements caused by the construction stage of the small guide hole climbing and the reverse excavation of the main hole of the fan room are greater than that caused by the construction of small guide hole. The construction of the contact channel in the left side causes large lateral displacement on the left side of the main hole, resulting in asymmetrically distribution of the displacement. Continuous plastic zones are formed in the fan room and contact channel at the intersection. The plastic points are concentrated in the neighboured of the arch waist and arch foot on both sides of the main tunnel. In view of a small number of tensile failure points at the intersection, the side wall of the upper step and the bottom surface during the expansion of the small pilot tunnel, these parts should be paid attention to in the construction, and the initial support should be applied in time to prevent local falling blocks.