深厚软土地区河道开挖高铁桥墩围护方案研究

Study of Excavation Enclosure Solutions for Construction of High-Speed Railway Bridge Piers in Soft Ground

在建湖杭高铁余杭特大桥39~45号墩、宁杭高铁京杭运河特大桥37~42号墩建设占用了德清县曹家横港处部分河道,需在高铁间及高铁桥梁下原位恢复河道。桥址为深厚软土地区,为降低河道开挖对高铁桥梁的影响,提出宁杭高铁桥梁与河道间采用钻孔灌注桩进行隔离、湖杭高铁桥梁两侧及桥下河床底采用水泥搅拌桩置换加固、增加河床铺砌,以维持挖方荷载平衡并提升河床底承载力的方案。采用PLAXIS 3D软件建立有限元模型,分析河道开挖时高铁桥墩围护方案对高铁桥墩变形的影响,并在施工中进行监测。结果表明:采用该高铁桥墩围护方案,河道开挖到河床底且施工河床铺砌的最不利工况下,高铁桥墩位移计算最大值为1.61 mm(竖向)、实测最大值仅0.8 mm(横向),小于规范规定的2 mm限值,该方案可行。

The construction of the piers No.39 to 45 of Yuhang Bridge carrying a section of the Huzhou-Hangzhou High-speed Railway and the piers No.37 to 42 of Beijing-Hangzhou Canal Bridge carrying a section of the Nanjing-Hangzhou High-speed Railway occupied part of the channel of the canal in the Caojiagang village,Deqing County,there was a need to restore the channel of the canal between the two high-speed railways and below the high-speed railway bridges.Given that the bridge sites are located in deep soft ground,measures should be taken to reduce the impact of excavation on the canal channel and improve the load bearing capacity of the pile foundation.Bored pile foundation was determined for the piers of Nangjing-Hangzhou high-speed railway bridge,with the purpose of isolating the bridge and the canal channel.The zones besides the Huzhou-Hangzhou High-speed Railway and the riverbed below the bridge were strengthened by the soil-cement mixing piles and paving the riverbed.A finite element model was developed in PLAXIS 3D software to analyze the excavation enclosure on the deformation of the high-speed railway bridge pier,and the excavation process was under control.As per the analysis,when enclosed for protection,the maximum calculated vertical displacement of high-speed railway bridge pier is 1.61 mm under the most unfavorable conditions(when the excavation proceeded to the riverbed and the paving of the riverbed was underway),but the maximum measured transverse displacement was only 0.8 mm,less than the limit value of 2 mm stipulated in the code,proving that the measures proposed were feasible.