摘要
针对土岩结合二元地层深基坑工程中“吊脚桩”围护结构存在的问题,提出了灌注桩内接微型钢管桩围护结构。考虑微型钢管桩与桩间岩土的“纽结效应”和开挖后桩间岩石与带裂缝混凝土相似性,将该结构等效为上部灌注桩+下部带裂缝的钢筋混凝土无腹筋等效梁阶梯变截面桩(梁)模型,下部等效梁中微型钢管为纵向钢筋,桩间岩石为带裂缝混凝土。用侧向刚度折减来定量表征围护结构截面减少和岩体裂缝对围护结构刚度影响,提出基于侧向刚度折减的弹性支点法来计算围护结构内力,并考虑纵筋销栓作用计算等效梁抗剪承载力。工程实例计算表明,侧向刚度折减系数β由0.85减至0.12,上部灌注桩弯矩增大55.8%,下部等效梁弯矩减少48.7%,上部灌注桩剪力减少13.6%,下部等效梁剪力减少22.0%,桩顶水平位移增加39.5%。开挖至土岩结合面处该结构相对于“吊脚桩”围护结构,桩顶水平位移、竖向沉降没有明显突增,桩顶最终水平位移、竖向沉降仅为“吊脚桩”围护结构的43%、69%。桩顶水平位移监测值为5.5mm,仅为计算包络值的35%,说明刚度折减系数可适当提高。本研究可为土岩结合二元地层深基坑支护提供参考。
This study focuses on addressing the issues associated with the“end-suspended pile”structure in deep foundation pits within soil-rock composite strata by implementing an enclosure structure called“micro-steel tube pile internally connected into concrete pile”.The structure is analyzed considering the“knot effect”between the micro steel pipe pile and the rock,as well as the similar mechanical characteristics between excavated rocks and cracked concrete.The structure is modeled as a stepped variable section pile(beam),consisting of an upper concrete pile and a lower equivalent cracked beam without stirrups.The micro steel pipes serve as axial reinforcements for the equivalent beam,while the rocks represent the cracked concrete of the equivalent beam.The reduction in lateral stiffness is used to quantitatively assess the impact of section reduction and rock mass fractures.An elastic subgrade method based on lateral stiffness reduction is employed,taking into account the dowel action of axial reinforcement to calculate the shear bearing capacity of the equivalent beam.The analysis of a case study demonstrates that the lateral stiffness reduction coefficient β ranges from 0.85 to 0.12,the bending moment of the upper concrete pile increases by 55.8%,the bending moment of the lower equivalent beam decreases by 48.7%,the shear force of the upper concrete pile decreases by 13.6%,the shear force of the lower equivalent beam decreases by 22.0%,and the horizontal displacement of the concrete pile top increases by 39.5%.Comparing this structure with the“end-suspended pile”structure,it is observed that the horizontal displacement and vertical settlement of the concrete pile top do not significantly increase.The final horizontal displacement and vertical settlement of the concrete pile top are only 43%and 69%,respectively,compared to the“end-suspended pile”structure.The measured horizontal displacement at the concrete pile top is 5.5 mm,which is only 35% of the calculated results,suggesting that the lateral stiffness reduction coefficient can be appropriately adjusted.This study provides valuable insights for the design and protection of deep foundation pits in soil-rock composite strata.
作者
张军舰
张勇
隋倩倩
ZHANG Jun-jian;ZHANG Yong;SUI Qian-qian(Geotechnical Technology Co.,Ltd.,Hangzhou,Zhejiang 311401,China;Geotechnical Investigation and Surveying Research Institute,Qingdao,Shandong 266032,China;Qingdao Geotechnical Foundation Engineering Company,Qingdao,Shandong 266032,China)
出处
《岩土力学》
EI
CAS
CSCD
北大核心
2024年第3期867-877,共11页
Rock and Soil Mechanics
关键词
土岩组合二元地层
灌注桩内接钢管桩
纽结效应
纵筋销栓作用
带裂缝混凝土
侧向刚度折减
soil-rock composite stratum
micro-steel pipe pile internally connected into concrete pile
knot effect
dowel action
cracked concrete
bending stiffness reduction
