桥桩钢套管施工引起地铁隧道纵向变形计算研究

Computational research on longitudinal deformation of subway tunnels caused by steel casing construction of bridge piles

依托杭州某桥梁试桩邻近地铁隧道建设工程,建立桥桩钢套管施工简化力学模型,提出考虑套管分节施工特点与挤土效应影响的全套管灌注桩施工附加力的修正计算公式。同时,基于Mindlin应力解和两阶段分析法,求解桥桩施工引起的既有隧道附加应力与纵向竖向变形,并进一步分析桥桩施工全过程的动态影响规律。得出以下结论:(1)引入土塞高度折减系数和区段修正分别对桩端压力、桩侧径向压力和桩侧垂向摩阻力进行修正,更符合桥桩钢套管施工附加力的分布规律。(2)桥桩钢套管施工引起地铁隧道纵向变形的理论计算结果与实测数据对比验证较为吻合。(3)随着桥桩钢套管施工深度的不断增加,既有隧道先小幅隆起而后沉降变大,随后趋于平稳,且纵向沉降区进一步扩大。施工到达隧道埋深附近时引起隧道隆起最大,隆沉交界点位于隧道底部1.5D深度范围。(4)桩侧垂向摩阻力是引起既有隧道变形的关键性因素,并随施工深度增加而影响扩大;桩端压力在施工远离隧道埋深一定范围后影响减弱;桩侧径向压力对隧道竖向变形的影响甚微。(5)桥桩施工全过程中不仅要关注隧道最大竖向变形的发展,而且要留意随施工深度改变产生的隧道纵向隆沉变化以及管片纵向错台变形。

Relying on the construction project of a test bridge pile adjacent to a subway tunnel in Hangzhou,a simplified mechanical model of the steel casing construction of bridge piles is established,and a revised calculation formula for the additional force resulted from the construction of the full-pipe cast-in-place piles considering the construction characteristics of casing sections and the effect of soil squeezing is proposed. At the same time,based on the Mindlin stress solution and two-stage analysis method,the additional stress and longitudinal vertical deformation of the existing tunnel caused by the construction of the bridge piles are calculated,and the dynamic influence law of the whole process of construction of the bridge piles is further analyzed. The following conclusions are drawn:(1) The application of the reduction factor of the soil plug height and the section correction to respectively calculate the pile tip pressure,the pile side radial pressure and the pile side vertical friction is more in line with the distribution law of the additional force due to bridge pile steel casing construction.(2) The theoretical calculation results of the longitudinal deformation of the subway tunnel caused by the construction of the bridge pile steel casing are more consistent with the actual measurement data.(3) With continuously increasing the construction depth of the bridge pile steel casing,the existing tunnels first uplift slightly,then subside and finally tend to be stable,accompanied by the longitudinal settlement area further expanding. When the construction reaches near the buried depth of the tunnel,the tunnel reaches the maximum uplift,and the junction of uplift and settlement is located at the depth of 1.5 D at the bottom of the tunnel.(4) The pile side vertical friction is a key factor that causes the deformation of the existing tunnel,and the influence will expand with the construction depth. The influence of the pile tip pressure will weaken after the construction is far away from the tunnel buried depth for a certain range, and the pile side radial pressure has little effect on the vertical deformation of the tunnel.(5) During the whole process of construction of bridge piles,attention should be paid not only to the development of the maximum vertical deformation of the tunnel,but also to the longitudinal heave change of the tunnel and the longitudinal dislocated deformation of the segments due to changes in the construction depth.