打桩施工对既有隧道及地表振动的影响

Impact of Pile Driving on the Vibrations of Existing Tunnels and Ground Surface

打桩施工产生的振动荷载可通过土体传导到地表和邻近隧道衬砌,分析该振动荷载传播规律,可为监测打桩施工侵限提供参考。建立了桩-土-隧道相互作用的三维有限元模型,并与实测数据对比验证了模型的可靠性。考虑不同打桩深度和桩与隧道水平距离,研究了打桩对既有隧道和地表的振动效应。结果表明:地表振动随着打桩深度的增加呈先增加后递减的趋势;当桩入土深度超过一定值,打桩深度与水平距离对衬砌振动速度有显著的影响。监测打桩施工入侵地铁隧道的衬砌振动速度预警值可采用12.5 mm·s^(-1),但对于隧道正上方打桩,超过该值时基本可以判断桩底距离衬砌小于一个隧道直径的范围,若要在更早阶段监测到邻近打桩,应结合地表振动监测进行综合判断。

The vibration load generated by the pile driving can be transmitted to the ground surface and the adjacent tunnel through the soil.The analysis of the propagation of the vibration is useful for the monitoring of possible pile driving that threatens the surrounding infrastructures.A three-dimensional finite element model of pile-soil-tunnel interaction was established.The reliability of the model was verified by a comparison with measured data.Considering various pile driving depths and different horizontal distances between the pile and tunnel,the impact of pile driving on existing tunnels and ground was studied.The results show that:with the increase of the pile driving depth,the vibration of the ground surface first increases and then decreases.When the pile tip depth exceeds a certain value,the influences of the pile driving depth and horizontal distance on the lining vibration is significant.It is recommended to use 12.5 mm·s^(-1)as the warning value of the vibration velocity of the tunnel lining for the intruding of piling construction into the tunnel.However,if the pile driving is conducted directly above the tunnel,the lining vibration exceeding the warning value indicates that the distance between the bottom of the pile and the lining is already less than one diameter of the tunnel.A warning system combined with surface vibration monitoring is necessary if the pile driving needs to be detected at an earlier stage.