盾构施工引起上部既有桥梁病害及处理案例分析

Case Analysis of Damage and Treatment of Existing Upper Bridges Caused by Shield Tunnel Construction

以中南地区某区间隧道及出入段线隧道下穿既有桥梁为背景案例,分析了四条盾构隧道施工引起桥梁桩基沉降变形及桥梁病害的特征及机理。根据桩基沉降变形及桥梁病害特征,提出采用桩基后压浆、桥面板UHPC增大截面、盖梁自密实混凝土增大截面进行加固。通过注浆前后钻孔取芯进行室内试验,分析后压浆增强土体强度的效果。结果表明:1)区间隧道比出入段线隧道埋深更大,与桩基距离更小,区间隧道两侧桩基沉降最大;2)受桩基差异沉降影响,相比于铰接墩,固结墩的受力增量更大,出现环向裂缝;3)后压浆引起桩基周边土体含水率、孔隙比减小,压缩模量、粘聚力、内摩擦角、标贯击数增大,且淤泥的强度提高最大,其中淤泥的标贯击数增大100%。土体强度的提高可有效增大桩基的承载能力。

Based on the background of the shield tunnelingunder existing bridges in a entrance/exitsection tunnel in the central and southern regions,the characteristics and mechanisms of settlement deformation of bridge pile foundation and bridge diseases caused by the construction of 4-line shield tunnel are analyzed.In terms of the characteristics of pile foundation settlement and bridge diseases,it is proposed to use post grouting for pile foundation,UHPC for bridge deck to increase the section,and self compacting concrete for capping beams to increase the section.Laboratory tests were carried out by drilling the core before and after grouting,analyzing the effect of post-grouting on strengthening soil strength.The results show that:1)Compared with the access segment tunnel,the buried depth of the section tunnel is larger,and the distance between the piles and the section tunnel is smaller,so the pile settlement on both sides of the section tunnel is larger.2)Due to the differential settlement of pile foundation,compared with the articulated pier,the load increment of the consolidated pier is larger and the circumferential cracks appear in the consolidated pier.3)Post grouting causes a decrease in the water content and void ratio of the soil around the pile,while increasing the compression modulus,cohesion,internal friction angle,and standard penetration blow count.The maximum increase in strength of silt is achieved,with a 100%increase in the number of standard penetrationtests for silt.The improvementof soil strength can effectively increase the bearing capacity of pile foundations.