开挖方式对跨基覆界面浅埋偏压隧道变形的影响分析

崩坡积～灰岩交界段(土岩交界段)一部分为松散的坡积体,一部分为岩体,工程性质相差较大,不同的隧道开挖方式会对隧道的稳定产生较大的影响。基于四川省九寨沟—绵阳高速公路某隧道工程,采用模型试验和数值模拟的方法,对有挡土墙预加固措施情况下崩坡积～灰岩接触地段浅埋偏压隧道在环形开挖预留核心土法、三台阶七步开挖法、CD法和CRD法4种开挖方式下的受力和变形特性进行研究。结果表明:土岩交界段浅埋偏压隧道的地表沉降呈现出明显的不对称特征,4种开挖方式下的最大地表沉降均向左侧偏移; 4种开挖方式产生的最大围岩位移都发生在隧道的拱顶处,且右拱肩、右拱腰的沉降值小于左拱肩、左拱腰; 4种开挖方式最大主应力的最大值出现在隧道右拱腰位置处,最小主应力的最大值出现在隧道右拱脚位置处; 相较于三台阶七步开挖法,环形开挖预留核心土法、CD法及CRD法都能够最大限度地保证隧道施工的安全。

Analysis of influence of excavation methods on deformation of shallow-buried bias tunnels across base and cover interface

The colluvial deposit-limestone junction section(soil-rock junction section)is partly loose slope deposit and partly rock mass. The engineering properties are quite different. Different tunnel excavation methods can have a significant impact on the stability of the tunnel. Based on a tunnel project of Jiuzhaigou—Mianyang Expressway in Sichuan province, the model test and numerical simulation methods were used to study the stress and deformation characteristics of shallow-buried bias tunnel in the contact area of colluvial deposit-limestone with the condition of retaining wall pre-reinforcement measures under four different excavation methods, which consist reserved core earthen method for ring excavation, three-step seven-step excavation method, CD method and CRD method. The results show that the surface settlement of shallow-buried bias tunnel in soil-rock junction section shows obvious asymmetric characteristics, and the maximum surface settlement under four excavation methods all shifts to the left. The maximum displacement of surrounding rock produced by the four excavation methods occurs at the vault of the tunnel, and the settlement values of the right arch shoulder and the right arch waist are smaller than that of the left arch shoulder and the left arch waist. The maximum value of the maximum principal stress of the four excavation methods appears at the right arch waist of the tunnel, while the maximum value of the minimum principal stress appears at the right arch foot of the tunnel. Compared with the three-step seven-step excavation method, the reserved core earthen method for ring excavation, CD method and CRD method can ensure the safety of tunnel construction to the greatest extent.