青藏铁路多年冻土桥梁桩基稳定性探讨

Study on Stability of Bridge Pile Foundation in Permafrost Area along Qinghai-Tibet Railway

研究目的：多年冻土区的桩基存在着桩身强度、均质性、桩周土回冻及变形等的不确定性。为确保青藏铁路的顺利建设和安全运营,分别进行了桥梁桩基承载力试验和桥梁桩基地温及变形的长期监测。为系统评价青藏铁路桥梁桩基的稳定特性,本文基于青藏铁路清水河桥梁桩基试验段和桥梁桩基长期监测系统,研究分析试桩的均质性、静弹模、抗压强度、静载及监测桥梁桩基断面的地温和变形特性。研究结论：桩身混凝土的完整性、均质性整体上较好,无离析等大的质量缺陷;桩身的混凝土抗压强度大多数值介于28~33 MPa之间,且抗压强度变异系数仅为0.14,静弹性模量均值为2.40×104MPa,满足技术要求;桩基周围土体人为上限总体在0.08~0.2 m之间有所回荡,且多年冻土区桥梁桩基变形小于10 mm,满足有砟桥面桥梁墩台工后变形要求,青藏铁路桥梁桩基是稳定的。

Research purposes： The uncertainties in the strength,homogeneity of pile and refreezing and deformation of soil around the pile existed to the pile foundation in permafrost area.To ensuer the smooth construction and the safe operation of the Qinghai-Tibet Railway,the bearing capacity test of the bridge pile foundation was carried out and the long-term monitoring for the ground temperature and deformation were conducted.In order to evaluate the stability of the bridge foundation of Qinghai-Tibet Railway,based on the long-term monitoring system for the bridge pile in the Qingshuihe experimental section and the bridge pile foundation of Qinghai-Tibet Railway,this paper studies and analyzes the homogeneity,static elastic modulus,compressive strength,static load and the characteristics of monitored ground temperature and deformation of the bridge foundation cross-section.Research conclusions：The study results showed the integrality and homogeneity of concrete pile were rather perfect and there was no major quality defects like segregation.The majority of the compressive strength of concrete pile was between 28～33 MPa,and coefficient of variation of compressive strength was only 0.14,and the static modulus of elasticity was 2.40×104 MPa.All these met the technical requirements.The artificial upper table for soil around the pile was between 0.08～0.2 m,and deformation of pile foundation in permafrost area was less than 10 mm,which satisfied the post-construction deformation demands for the ballasted deck piers.It was concluded the bridge foundation of Qinghai-Tibet Railway was stable.