桥下采沙对桥梁受力及安全影响研究

Study on Bridge Bearing Capacity and Safety Affected by Sand Mining under Bridge

近年来河道无序采沙对桥梁结构安全带来了很大隐患,针对桥下乱挖乱采河沙情况,以采用摩擦桩基础的某高速公路连接线特大桥梁为研究对象,通过理论分析、数值模拟和现场试验,开展桥下采沙对桥梁承载能力及安全的影响研究。研究结果表明:桥下挖沙导致了桩端土处承载力和单桩承载力显著降低,而对墩柱下沉量、主梁跨中挠度和墩柱弯矩影响较小;试验车辆在桥上行驶时,采沙桥墩墩顶竖向动位移和纵向动位移较未采沙桥墩有所增大,刹车则引起两个方向动位移显著增大,远大于跑车试验数据;过路汽车试验数据远大于试验车数据,过路车超载严重;试验车辆和过路车作用下主梁跨中动挠度变化不明显;车辆重量是影响墩顶竖向位移的主要因素,车辆刹车时的纵向制动力是影响墩顶纵向位移的主要因素;桥上刹车和超载具有较大危害,需尽快采取限速、限重、加固等措施,避免桥上紧急制动和水流冲刷,保证桥梁结构安全。

In recent years, sand excavation optionally at river bed has brought trouble to the safety of some bridges. Taking a huge bridge using friction pile foundation on expressway connecting line as the research object, considering the phenomenon of excessive digging river sand under bridge, the influence of such sand mining on bridge bearing capacity and safety is studied by theoretical analysis, numerical simulation and field test. The research result shows that （ 1 ） under-bridge dredging has led to the obvious reduction of the bearing capacity of pile tip soil and .bearing capacity of single pile, but it has less effect on the deflection of pier stud, the mid-span deflection of the girder, and bending moment Of pier stud ; （2） when test vehicle is running on the bridge, there has been an increase in the sand excavation bridge pier top vertical dynamic displacement and longitudinal dynamic displacement than the sand bridge pier without surrounding sand mining, braking will cause the 2 kinds of dynamic displacement increase significantly which are much higher than vehicle running test data; （3） passing cars＇ experimental data are much larger than test vehicle＇s data and passing cars are seriously overloaded; （4） under the action of test vehicles and passing cars, the girder mid-span dynamic deflection has no evident change; （5） vehicle weight is the main factor that influencing the vertical displacement of the pier top, when the vehicle brakes, the longitudinal braking force is the main factor of influencing longitudinal displacement of the pier top; （6） braking and overloaded vehicle running on the bridge has a greater detriment, it is needed to take measures such as speed limit, weight limit, reinforce and so on to avoid emergency braking on bridge and water scouring and ensure the safety of bridge structure.