深厚软基区海堤填筑下穿对既有桥梁桩基的影响

Influence of Sea Embankment Underpass on the Pile Foundation of Existed Expressway Bridge in Deep Soft Soil Area

以某深厚软土区海堤填筑下穿含匝道高速公路桥的复杂工程为研究案例,通过精细化3维有限差分数值模拟,分析采用工程加固措施后,大面积填筑对既有端承型桥梁桩基的影响程度及机理。研究表明:1)通过CAD+CAE动态设计优化,选定了钻孔灌注桩+框架梁+高压旋喷的加固方案,框架结构具有较好的整体刚度和协同受力特性,高压旋喷在上部软土层形成硬壳,可减小固结变形量。2)附加荷载在框架梁中充分形成压力拱,可显著降低对桥梁横向的挤压,有效控制两侧匝道下桩基的附加水平位移,在沿桥向将大面积堆载转化为灌注桩和框架梁内力,避免桩基产生过大附加弯矩;经计算,工后桩顶水平位移最大值4.38 mm,基桩最大压应力增量小于0.9 MPa,均能较好地满足控制要求。3)钻孔灌注桩+框架梁整体结构的有效性还体现在其可对桥桩产生类似套管的隔离保护,配合分层对称填筑工艺,可降低桥桩-桩周土相对变形,对控制基桩轴力增量作用显著。综上可知:精细化数值模拟可有效克服相关行业规范在评价复杂桩-土相互作用时的局限性,为研究工程方案的适用性及效果评价提供必要的技术支撑。

Taking a complex practical project that the sea embankment undercrossing an existed expressway bridge in deep soft soil region as research case,utilizing the 3D finite difference numerical simulation as research method,and considering the special reinforcement design,a detail engineering influence analysis for the existed end-bearing pile foundation induced by filling was conducted.The results showed that:1)Based on the dynamic design optimization by CAD&CAE,the optimized reinforcement scheme,i.e.,bored pile+frame connection beam+high pressure jet grouting,was determined,the frame structure showed good integrity and synergistic force characteristics,and the high-pressure jet grouting would effectively improve the engineering properties of soft soil,the“hard crust layer”effectively reduced the consolidation deformation of overlying soft soil;2)Under the action of additional loading,pressure arch was formed in the frame structure,extrusion induced from transverse direction could be reduced effectively,the additional horizontal displacement of piles under both ramps would be effectively controlled,and in the direction along bridge axis,large area additional loading was transferred to additional bending moment of bored piles and axial force of connecting beams,so the additional bending moment increment of piles could be effectively controlled,after filling,the maximum horizontal displacement on pile top was 4.38 mm,and the maximum increase of compressive stress was less than 0.9 MPa,which met the control requirements well;3)The whole supporting structure could be regarded as the sleeve around bridge piles,accompanying with symmetrical thin-layer filling of embankment,it would effectively reduce the relative deformation between bridge piles and surrounding soil,and played a significant role in controlling the axial force increment of piles.To sum up,finely numerical simulation effectively overcame the limitations of technical specifications method in complex engineering applications,and provided a necessary technical support in evaluation applicability of project scheme and effect.