软土场地航道近接开挖对既有桥梁桩基稳定性的影响

Influence of Adjacent Excavation on the Pile Foundation Stability of an Existing Bridge near Channel in Soft Soil Sites

京杭大运河二通道整治工程近接穿越大量软土场地既有桥梁,工程开挖扰动不可避免会对桥梁桩基稳定性造成影响。以杭州市海宁段某既有桥梁下方航道近接开挖为例,采用饱和非饱和理论开展软土场地航道近接既有桥梁工程施工过程数值模拟,探讨航道开挖、通航对桥梁桩基周边地下水水位及桩基稳定性的影响。结果表明:航道开挖将导致桥梁桩基周围土体孔压减小,且因受主动土压力影响,桩基将产生轻微沉降,并向开挖区偏移,最大变形出现在距离桩顶约3/8桩长处;通航后桥梁桩基周围土体孔压增大,其导致桥梁桩基上浮,并向非开挖侧偏移;总体上开挖扰动对桩基稳定性的影响远大于通航水位抬升的影响,航道近接开挖施工将造成既有桥梁桩基向航道偏移。研究成果可为软土场地航道近接开挖对既有桥梁桩基稳定性控制提供借鉴。

The regulation project of the second channel of the Beijing to Hangzhou Grand Canal needs to cross many existing bridges closely in soft soil sites.The excavation disturbance of the project will inevitably significantly impact the stability of the pile foundation of the overpass bridge.Taking the channel excavation under an existing bridge in the Haining section of Hangzhou City as an example,numerical simulations on the construction process of the channel adjacent to an existing bridge project in soft soil sites were carried out based on saturated-unsaturated seepage theory.Channel excavation and navigation influences on the groundwater level and pile stability around the bridge pile foundation were analyzed and discussed.The results show that excavation of the channel would lead to a decrease in the water pressure of the soil around the bridge pile foundation.Due to the influence of active soil pressure,the pile foundation would experience a small settlement and shift towards the excavation area.The maximum deformation would occur at a distance of about 3/8 of the pile length from the top.The increase in soil water pressure around the bridge pile foundation after navigation would cause the bridge pile foundation to float upwards and shift toward the non-excavated side.The impact of excavation disturbance on the stability of pile foundations was overall more significant than that of navigation water level rise.The excavation near the waterway would cause the existing bridge pile foundations to shift toward the river.The research could provide a theoretical reference for ensuring the stability control of existing bridge pile foundations during the excavation of adjacent waterways in soft soil sites.