中文摘要：

双向八车道的方兴湖隧道是迄今为止国内跨度最大的框架式明挖暗埋湖底隧道,跨度最大值达38.5m,现场测试了垫层下孔隙水压力、抗拔桩桩顶应力和框架结构应力。伴随隧道左右侧回填土,垫层下孔隙水压力急剧增高,底板局部应力有较大的降低,左右边墙外侧应力整体上增加,而其他部位应力波动性比较明显。在顶部回填土过程中,除了左右边墙内侧应力无较大变化外,其他结构部位主要呈现一定的应力增量。恢复湖水后,垫层下土体基本上是承受静止水压力,只有左右洞室跨中桩体发挥抗拔作用而承受一定拉应力,建议今后类似工程优化抗拔桩设计。结构底板和左右边墙下部相对于隧道结构其他部位承受较大内力,但隧道安全性满足规范要求。

英文摘要：

Since its maximum span is 38.5m, Fangxing Lake tunnel with two-way eight lanes in total is a cut-and-cover framed tunnel and has the largest span in China so far. In the present work, the pore water pressure right below the tunnel cushion, stresses at the top of anti-uplift piles and stresses in the tunnel structure were measured on site. With the back-filling process of soils to tunnel side walls, a sharp increase in the pore water pressure right below the tunnel cushion and an obvious decrease in the local stresses of tunnel floor could be observed. In the meanwhile, the stresses in the external sides of left and right walls generally increased, while the stress fluctuation in other locations was not obvious. During the back-filling process of soil to the tunnel roof, an adequate increase in stresses in other structural locations can be monitored except for no obvious changes in stresses at the internal sides of the tunnel walls. Once the water was recovered to the lake, only the hydrostatic pressure was observed in the soil below the tunnel cushion, and only the mid-span piles of left and right tunnels might resist a part of tensile stresses, and as a result, it is recommended that the improved design should be given for the anti-uplift piles in the future identical projects. Compared to the other structural locations, the structural floor and left and right side walls may resist higher structural stresses, but with the tunnel structure satisfying the safety specifications.