基坑开挖引起地铁结构隆起的堆载控制研究

Loading control for the uplift of subway structures induced by adjacent excavation

基坑开挖引起邻近的地铁车站及区间隧道产生附加变形。为有效控制地铁结构的隆起,以天津地区已运营地铁结构两侧贴建的某基坑项目为依托,通过对基坑开挖过程中的实测数据进行整理,分析地铁站体及区间隧道的竖向变形规律,在此基础上利用数值模拟方法对工程实测进行拟合,进而评估地铁结构上方不同堆载强度、不均匀堆载、不同堆载时机以及不同堆载分级等方案对于地铁结构的隆起控制效果及规律。研究结果表明:两侧基坑开挖引起地铁结构的最大隆起变形发生在车站与隧道连接位置附近;随着堆载强度增加,地铁结构的隆起量随之减小,当超过一定强度后区间隧道部分区段将产生沉降;堆载对区间隧道的控制效果比地铁站体更好,但需要提前评估堆载引起隧道变形的安全性;基坑深度增加对相邻隧道变形的限制能力减弱,导致相同堆载强度下隧道的变形幅度更大;不均匀堆载方案可以更精确控制地铁结构变形,有效减缓地铁结构之间的差异变形,但与均匀堆载相比需适当提高加载曲线的最大强度值;在总堆载强度不变情况下,提前进行堆载反压,并且采用分级加载的方式,可以更有效地控制地铁结构的隆起变形。在此基础上提出一些施工建议,使研究成果为今后类似工程的地铁结构隆起变形控制措施提供参考与借鉴。

Excavation of a foundation pit could induce additional deformation of nearby subway stations and tunnels.To effectively control the uplift of the subway structure,a foundation pit project adjacent to the operating subway structure in Tianjin was selected as the example.The vertical deformation of the subway station and tunnel during the excavation process was analyzed by organizing the measured data during the excavation process.Base on this analysis,a numerical simulation method was employed to fit the field monitoring data.The effectiveness of loading in controlling the uplift of the subway structure was evaluated,including load intensity,uneven loading,loading time,and step loading.The results indicate that the maximum uplift deformation of the subway structure caused by the excavation on both sides occurs near the connection between the subway station and the tunnel.The uplift of the subway structure decreases with increasing load intensity.Settlement can occur in some tunnel sections once the load intensity surpasses a certain threshold.Loading has a better control effect on deformation of the uplift of the tunnel compared to that of subway station,but the safety of tunnel deformation caused by loading needs to be evaluated in advance.The deformation constraint on adjacent tunnels weakens as the excavation depth increases,resulting in greater deformations caused by the same loading.Uneven loading can accurately control the deformation of the subway structure and effectively mitigate differential deformations between subway structures.Nevertheless,compared to uniform loading,it is necessary to appropriately increase the maximum load intensity.With the total load intensity remaining constant,the methods of preloading and step loading can be more effective in controlling the uplift deformation of the subway structure.Based on these findings,several construction recommendations were proposed.The proposed construction recommendations can provide a reference and guidance for the uplift deformation control of subway structures in the future.