考虑层间黏聚力的水平层状围岩隧道顶板力学模型计算

水平层状岩体力学性质不仅受岩层组合和结构面控制，而且与层间黏聚力密切相关。水平层状围岩隧道在施工过程中对层间黏聚力考虑不当时，极易造成设计支护参数不合理，导致拱部掉块落石、离层、弯折，甚至局部坍塌、超欠挖等工程问题，严重影响工程安全、施工质量和建设进度。目前水平层状围岩隧道顶板一般简化为锚固梁和简支梁模型，但未考虑层间黏聚力。根据水平层状围岩隧道开挖的不同阶段，将隧道顶板分别简化为开挖初始阶段的锚固梁模型和施工扰动后的简支梁模型，并利用顶板梁体模型的协调变形条件，得出梁模型的层间黏聚力计算公式。以大梁峁隧道为工程依托，分别应用考虑层间黏聚力和不考虑层间黏聚力的梁模型进行隧道临界开挖跨度计算。结果表明：考虑层间黏聚力和不考虑层间黏聚力对水平层状围岩隧道临界开挖跨度影响较大。考虑层间黏聚力时，锚固梁模型临界开挖跨度为3.36~4.75 m，简支梁模型临界开挖跨度为2.74~3.88 m；不考虑层间黏聚力时，锚固梁模型临界开挖跨度为0.14~0.30 m，简支梁模型临界开挖跨度为0.12~0.24 m。结合大梁峁隧道工程现场，隧道开挖跨度3~6 m时，拱顶会出现平顶现象，产生离层和掉块，因此考虑层间黏聚力的水平层状围岩隧道顶板力学模型更符合工程实际情况。

Mechanical Model Calculations of Tunnel Roof with Horizontal Stratified Rock Mass Tunneling Considering the Interlayer Cohesion

The mechanical properties of horizontal stratified rock mass are not only controlled by rock formations and structural planes, but are also closely related to the interlayer cohesion. During the construction process of horizontal stratified surrounding rock mass tunneling, due to improper consideration of interlayer cohesion, it is prone to cause unsuitable support parameters and lead to engineering problems such as abundant overbreaking and rock falling from the arched roof, roof separation, and even partial collapse, which seriously affect the safety of the project, construction quality, and progress. At present, the roofs of tunnels with horizontal stratified surrounding rock are generally simplified as an anchor beam and simply supported beam model, however, interlayer cohesion is not considered. In this paper, according to the different stages of excavation, the tunnel roofs are respectively simplified into the anchor beam model at the initial stage of excavation and the simply supported beam model after construction disturbance, and the coordinated deformation conditions of the roof beam model are used to obtain the formula for calculating the interlaminar cohesion. Based on the field test case in Daliangmao Tunnel, the tunnel excavation span calculations were carried out for beam models about whether to consider interlayer cohesion. The results show that considering the interlayer cohesion has a great influence on the excavation span. Considering the interlayer cohesion, the critical excavation span of the anchor beam model is 3.36-4.75 m, and for the simply beam model is 2.74-3.88 m. When the interlayer cohesion is not considered, the critical excavation span of the anchor beam model is 0.14-0.30 m, and for the simply beam model is 0.12-0.24 m. In combination with the tunnel construction site, when the excavation span is 3-6 m, the flat top phenomenon will be present in the crown, resulting in separation and rock falling. Therefore, the mechanical model of the tunnel roof considering the interlayer cohesion is more consistent with the actual situation of project.