【作者】 朱磊；

【导师】 凌贤长；

【作者基本信息】 哈尔滨工业大学 ， 土木水利（专业学位）， 2022， 硕士

【摘要】 随着交通强国战略的统筹推进,铁路建设飞速发展,城市内深基坑工程的数量也迅速增加。预应力桩锚围护体系可显著提升土体稳定性、改善土体应力状态,已被广泛应用于大型建筑、地铁车站等的深基坑工程中。在高寒冻融区,春融期气温常在负温与正温间循环变化,基坑土体经受周期性的冻融循环作用,土体中的水分体积变化频率加快,而基坑土体融化水无法有效排出,导致预应力桩锚体系受到的反复冻胀力异常剧烈,给深基坑工程稳定性带来了极为恶劣的影响。然而,国内外针对高寒冻融区的深基坑工程预应力桩锚围护体系在春融期的可靠性研究近似空白。鉴于上述,针对高寒冻融区的冻融环境,依托于长春市某地铁车站深基坑工程,聚焦于我国高寒冻融区深基坑工程常见的预应力桩锚围护体系,注重于春融期基坑土体的冻融循环作用,结合现场监测与数值模拟,考虑冻融循环作用下基坑土体水-热-力三场耦合作用,开展高寒冻融区深基坑预应力桩锚体系围护性能及其变化规律的研究工作。本文主要研究内容如下:(1)针对长春市某地铁车站明挖段基坑工程及其预应力桩锚围护体系,开展了基于现场监测的春融期基坑地表沉降、桩顶水平位移及预应力锚索轴力变化规律的分析研究,发现地表沉降变化主要集中在春融后期且春融期间无明显融沉现象,大部分围护桩桩顶位移在春融期间保持较为稳定的波动状态,锚索轴力在春融初期逐渐减小、前期骤增后回落、中期与后期缓慢减小。(2)基于水热力耦合模型基础理论,建立深基坑预应力桩锚体系水-热-力三场耦合三维数值模型,利用相关监测数据对数值模型进行可靠性验证,最后对春融期温度场、地表沉降、锚索轴力、桩后压力、桩身弯矩和桩身变形的变化规律进行探究,发现围护性能评价指标均在春融前期第二阶段(平均气温升至0℃以上)发生较大变化,围护桩桩身弯矩及桩身变形的变化较桩后压力有一定滞后性,锚索轴力变化规律与监测数据基本一致。(3)以桩长、桩间距和锚索入射角为重要影响参数,以基坑底桩后压力、最大桩身应力、桩顶水平位移及预应力锚索轴力为围护性能评价指标,基于正交试验理论,开展预应力桩锚体系围护性能影响因素分析及影响程度、显著性研究,发现桩间距相对影响程度最大、锚索入射角次之、桩长最小,且桩长、桩间距和锚索入射角对各围护性能评价指标的影响基本均为高度显著。更多还原

【Abstract】 With the overall promotion of the transportation power strategy,the highway and railway construction have developed rapidly,and the number of deep foundation pit projects in the city has also increased rapidly.Prestressed pile anchor retaining system can significantly improve the stability of soil and improve the stress state of soil.It has been widely used in large-scale buildings,subway stations and other deep foundation pit projects.In the high cold freeze-thaw area,the temperature often changes between negative temperature and positive temperature in the spring thaw period.The soil mass of the foundation pit is subjected to periodic freeze-thaw cycle,and the change frequency of water volume in the soil mass is accelerated.However,the thawed water of the soil mass of the foundation pit can not be effectively discharged,resulting in the extreme reverse frost heaving force of the prestressed pile anchor system,which has a very bad impact on the stability of the deep foundation pit project.However,the research on the reliability of prestressed pile anchor retaining system for deep foundation pit in the freezing and thawing zone in spring is almost blank at home and abroad.In view of the above,in view of the freezing and Thawing Environment in the freezing and thawing area,relying on the deep foundation pit project of a metro station in Changchun,focusing on the prestressed pile anchor retaining system commonly used in the deep foundation pit project in the freezing and thawing area in China,focusing on the freezing and thawing cycle of the foundation pit soil during the spring thawing period,combined with on-site monitoring and numerical simulation,considering the three field coupling effects of water,heat and force of the foundation pit soil under the freezing and thawing cycle,The study on the retaining performance and evolution law of prestressed pile anchor system for deep foundation pit in freezing and thawing zone is carried out.The main contents of this paper are as follows:(1)In view of the foundation pit project of an open cut section of a metro station in Changchun and its prestressed pile anchor retaining system,the analysis and Research on the evolution law of foundation pit surface settlement,pile top horizontal displacement and Prestressed Anchor Cable axial force during spring thaw based on field monitoring data are carried out.It is found that the change of surface settlement is mainly concentrated in the late spring thaw and there is no obvious thaw settlement during spring thaw,The displacement of the pile top of most retaining piles remains relatively stable during the spring thaw period.The axial force of the anchor cable gradually decreases in the early spring thaw period,decreases after the sudden increase of the axial force in the early spring thaw period,and slowly decreases in the middle and late spring thaw period.(2)Based on the basic theory of hydro thermal coupling model,a three-dimensional numerical model of hydro thermal mechanical coupling of prestressed pile anchor system in deep foundation pit is established,and the reliability of the numerical model is verified by using the relevant monitoring data.Finally,the change laws of temperature field,surface settlement,Anchor Cable axial force,post pile pressure,pile bending moment and pile deformation during spring thaw are explored,It is found that the evaluation indexes of enclosure performance basically change greatly in the second stage of early spring thaw(March 15 ～ April 1).The changes of pile bending moment and pile deformation of enclosure pile lag behind the pressure behind the pile.The change law of Anchor Cable axial force is basically consistent with the monitoring data.(3)Taking the pile length,pile spacing and incident angle of anchor cable as important influence parameters,taking the back pressure of foundation pit bottom pile,the maximum pile stress,the horizontal displacement of pile top and the axial force of prestressed anchor cable as the evaluation indexes of retaining performance,and based on the orthogonal test theory,the influencing factors of the retaining performance of prestressed pile anchor system are analyzed and the influence degree and significance are studied.It is found that the relative influence degree is pile spacing > incident angle of anchor cable > pile length,And the influence of the above factors on the enclosure performance is basically highly significant.更多还原