Study on effect of segments erection tolerance and wedge-shaped segment on segment ring in shield tunnel

INTRODUCTION Shield tunnel method has become the most pre- ferred method in city tunnel construction because of its excellent attributes: little effect on surrounding environment, fast and safe construction, outstanding performance in earthquake resistance, etc. (Zhang et al., 2004). In different shield tunnels, the arrangement and number of segments are different, but the whole assembling process is generally the same. The as- sembling process begins with A2P, then A1P, A3P, BP, CP, …     

盾构施工参数对地层变形的影响

以南宁地铁一号线南湖段下穿隧道为工程背景,建立隧道开挖的三维有限元模型,通过数值分析,得到盾构施工过程中地层变形的分布规律,讨论盾构施工过程中注浆压力对地表沉降、水平位移及拱顶位移的影响,分析掌子面压力对地表隆起的影响规律。研究结果表明,注浆压力对地表变形会产生明显的影响,随着注浆压力的增大,地表沉降及水平位移明显减小。当掌子面压力大于0.1 MPa时,会引起掌子面前方土体产生向上的位移,地表隆起量随掌子面压力的增加而增大。     

基于ANSYS程序的钢筋混凝土梁非线性数值模拟

采用商用程序ANSYS对不同配筋率的钢筋混凝土梁进行非线性数值分析，以考察不同配筋率对钢筋混凝土梁受弯性能的影响。结合数值模拟分析过程，详细介绍了基于ANSYS程序的钢筋混凝土构件非线性数值分析的关键技术，分析了对不同配筋率的钢筋混凝土粱的刚度变化、破坏特征、截面应力分布、裂缝发展和钢筋、混凝土应力及应变发展过程。     

Model test and numerical analysis on long-term mechanical properties of stepped reinforced retaining wall

Model tests and numerical analyses of stepped reinforced retaining wall were performed to investigate the effects of rheology of backfill and creep of geogrids on the long-term performance of the structure.The geogrid tensions,soil pressures,wall deformations and foundation pressure were measured during model construction and loading.A visco-elasto-plastic model and an empirical nonlinear visco-elastic model were utilized to simulate the stresses and deformations of geogrid-reinforced earth-retaining wall under long-term loads.By comparing test data with numerical results,it is shown that the foundation pressure distribution is nonlinear,and the lateral constraint of geogrids for backfill can cause a redistribution of foundation pressure.The curve of soil pressure is outside convex at each step initially,and it is close to the distribution for the case of vertical wall subsequently.The variation trend of geogrid tensions at different heights is obtained.Moreover,the failure mechanism and development mode of potential slip surface in retaining wall are proposed.     

3D finite element simulation of tunnel boring machine construction processes in deep water conveyance tunnel

Applying stiffness migration method, a 3D finite element mechanical model is established to simulate the excavation and advance processes. By using 3D nonlinear finite element method, the tunnel boring machine (TBM) excavation process is dynamically simulated to analyze the stress and strain field status of surrounding rock and segment. The maximum tensile stress of segment ring caused by tunnel construction mainly lies in arch bottom and presents zonal distribution. The stress increases slightly and limitedly in the course of excavation. The maxi-mum and minimum displacements of segment, manifesting as zonal distribution, distribute in arch bottom and vault respectively. The displacements slightly increase with the advance of TBM and gradually tend to stability.     

钢筋混凝土屋面悬挑屋檐结构的有限元分析

结合工程实际,在钢筋混凝土屋面飘板结构设计中,对其悬挑屋檐方案安全问题采用有限元方法进行计算和分析,结果显示,悬挑屋檐板的最大跨度应取4.8m,梁按变截面设计并不增加悬挑屋檐板的最大位移,在悬挑屋檐板端部内增设几道钢筋,可使悬挑屋檐板的端部位移和应力均匀.     

Mechanical behavior of segment rebar of shield tunnel in construction stage

In this paper, a 3D finite element （FE） program ADINA was applied to analyzing a tunnel with 9 segment tings. The loads acting on these segment tings included the squeezing action of tail brush of shield machine under attitude deflection, the jacking forces, the grouting pressure and the soil pressure. The analyses focused on the rebar stress in two statuses： （1） normal construction status without shield machine squeezing; （2） squeezing action induced by shield machine under attitude deflection. The analyses indicated that the rebar stress was evidently affected by the construction loads. In different construction status, the rebar stress ranges from -80 MPa to 50 MPa, and the rebar is in elastic status. Even some cracks appear on segments, the stress of segment rebar is still at a low level. It is helpful to incorporate a certain quantity of steel fiber to improve the anti-crack and shock resistance performance.     

既有双洞扩挖隧道抗震性能分析

以某隧道扩挖工程为背景,建立三维有限元模型并进行动力时程分析,探讨扩挖隧道衬砌结构在地震荷载作用下的位移和内力变化规律,同时与扩挖前对应规律进行对比分析,研究扩挖隧道对相邻隧道结构抗震性能的影响,为扩挖隧道的抗震性能设计提供参考。     

地铁隧道下穿既有高速铁路桥影响分析与施工对策研究

地铁隧道施工引起铁路轨道沉降和变形可能影响正常运营,为控制盾构隧道施工引起的轨道沉降和变形,保护铁路运营安全,对盾构隧道下穿铁路段的区间线位及工程风险进行研究。文章以某市地铁1号线下穿既有高速铁路桥为依托,采用计算软件对隧道下穿既有高速铁路桥进行了数值模拟分析,得到了最大沉降量为11mm,超过了6mm的容许沉降量;通过分析施工过程中沉降情况,提出了施工建议。可为同类工程提供参考。     

高强混凝土墙耐火性能的有限元分析

确定了钢材和混凝土热工参数和热一力本构关系,采用ABAQUS软件建立了火灾下高强混凝土墙温度分布和受力性能分析的有限元模型,计算结果得到以往实验结果的验证.在此基础上,对高强混凝土墙高温下的应力分布、混凝土裂缝以及重要影响因素进行了分析,初步了解了火灾下高强混凝土墙的力学性能,为进一步确定科学合理的抗火设计方法创造了条件.     

洞内桩基托换施工有限元模拟

北京地铁五号线左线隧道穿越南护城河桥下,首次采用扩大断面四层支护的结构,洞内桩基托换方案,截断护城河桥三排共4根桩。采用有限元软件Ansys平面动态模拟洞内桩基托换,研究洞内桩基托换对地面、桥梁的影响,并提出安全托换的建议。     

洞内桩基托换施工有限元模拟

北京地铁五号线左线隧道穿越南护城河桥下,首次采用扩大断面四层支护的结构,洞内桩基托换方案,截断护城河桥三排共4根桩。采用有限元软件Ansys平面动态模拟洞内桩基托换,研究洞内桩基托换对地面、桥梁的影响,并提出安全托换的建议。     

数值分析中数值积分法的教学实践研究

数值积分法是数值分析中的最基本方法之一.在数值积分法的教学过程中采用问题教学法,即通过提出问题—分析问题—解决问题—巩固问题的解决的教学设计,不仅能使学生深刻理解各种数值积分公式,而且能培养学生的科研能力和创新能力.     

真空预压法加固软基的流固耦合数值分析

利用数值分析方法建立了软土地基模型,采用比奥固结理论,计算分析了真空预压下的软土地基流固耦合作用;并进一步分析了真空度损耗率、密封墙、塑料排水板打设深度等因素对软基加固效果的影响。分析结果表明:在抽真空早期,地表沉降增长很快,达到一定天数后,沉降值逐渐趋于稳定;真空负压沿深度、水平方向上损耗,在加固软土外围形成一个零孔隙水压力面;真空度损耗率、塑料排水板打设深度对真空预压加固软土的效果影响很大;侧向密封墙对加固区内土体影响不大,但其限制了真空负压的侧向传递,使影响区的地基沉降大幅减小。     

列车荷载对下穿盾构隧道影响的模型试验

为研究地面线路运营对下穿盾构隧道结构的影响规律,基于相似比理论建立室内大型试验模型,模拟上部列车荷载作用下土层及其内部盾构隧道结构的受力变形过程,总结变形规律。结果表明,模型试验能够较好地反映外部荷载影响下土层以及内部盾构隧道结构的受力和变形特性;地表列车荷载在土层传递过程中,同一层面上沿地面线路方向的土压力大于两侧土压力,远离线路的地层受列车荷载影响相对较小,同一竖向截面土压力变化量由上至下逐渐减小,即外部荷载对浅层土的影响明显大于深层土;盾构隧道在地表列车行驶过程中,环向出现背车面受拉迎车面受压的受力特性,呈斜向压扁,纵向应变从中间交叉点向盾构隧道两侧逐渐减小,呈下凹压弯;盾构隧道埋深越小,受地表荷载影响越显著,增大一倍埋深对应纵向应变最大值减小约44.5%。     

钢筋增强ECC梁受弯性能的试验及数值研究(英文)

为了研究钢筋增强ECC梁受弯性能,进行了钢筋增强ECC梁和普通钢筋混凝土梁受弯的对比研究.结果表明,相比普通钢筋混凝土梁,钢筋增强ECC梁的受弯承载力和延性分别提高了24.8%和187.76%,并且在梁中用ECC代替混凝土可有效延缓裂缝的发展.此外,采用简化的ECC本构模型对钢筋增强ECC及混凝土梁的受弯性能进行了非线性有限元分析,模拟结果与试验结果吻合较好,在服役期间钢筋增强ECC梁的裂缝可以控制在0.4 mm以下.ECC材料的使用可明显提高梁的抗弯承载力、变形能力、延性等受弯性能.     

T形配钢型钢混凝土偏压构件力学性能研究

建立了T形配钢型钢混凝土偏压构件力学性能分析的有限元模型,计算结果得到以往实验结果的验证。在此基础上,分析了不同阶段材料应力状态和各参数对偏压构件力学性能的影响。结果表明:T形配钢型钢混凝土构件在不同加载角下的性能有所不同,加载角为180°时极限承载力大于其他角度情况;混凝土抗压强度、型钢含钢率、配筋率、荷载偏心率、长细比对构件荷载-变形曲线的影响较大,随着混凝土强度、型钢含钢率、配筋率的增加,极限承载力和刚度增加;随着荷载偏心率的增加,极限承载力和刚度下降;随着构件长细比的增加,构件承载力总体呈现线性下降趋势,刚度下降明显。     

盾构开挖顶推力对下平行隧道影响的数值分析

以滨海软土地层中盾构隧道平行上穿既有隧道为背景,通过数值仿真软件对开挖动态过程进行了精细化模拟,研究盾构隧道施工顶推力对周边地层及其内部既有隧道受力变形的影响。结果表明,在新建隧道上穿施工过程中,开挖扰动对地层的影响范围主要集中在距离开挖面-1.0~1.5D区域内(D为盾构隧道外径),扰动效果以新建隧道轴线为中心呈环状向外扩散,盾构顶推力从0.1MPa增至0.4MPa时,地表变形及1.0D范围内地层压力均增大20%以上;新建隧道平行上穿既有隧道过程中,既有隧道断面变形从横向鼓曲变为竖向拉伸,且整体出现上浮现象,顶推力达0.3MPa后,既有隧道拱底和拱顶隆起速度增加,以拱底为基准,顶推力自0.1MPa增加至0.4MPa时,隧道上浮量增大34.2%;施工过程中除保证常规地表变形监测外,对于近接平行上穿施工还需加强对既有隧道竖向变形的监控,必要时采取结构加固措施和施工参数综合调整办法,以降低开挖扰动对周边地层和结构物的影响。     

Determination of wind pressure coefficients for arc-shaped canopy roof with numerical wind tunnel method

In this paper, the wind load on an arc-shaped canopy roof was studied with numerical wind tunnel method (NWTM). Three-dimensional models were set up for the canopy roof with opened or closed skylights. The air flow around the roof under wind action from three directions was analysed respectively. Wind pressure coefficients on the canopy roof were determined by NWTM. The results of NWTM agreed well with those of wind tunnel test for the roof with opened skylights, which verified the applicability and rationality of NWTM. The effect of the closure of skylights was then investigated with NWTM. It was concluded that the closure of the skylights may increase the wind suction on the top surface of the roof greatly and should be considered in the structure design of the canopy roof.     

超长钻孔灌注群桩承载特性的实验研究和数值分析

采用离心机模型试验和三维有限元模型对天兴洲大桥的超长嵌岩钻孔灌注群桩进行了分析.离心机试验中,根据相似理论,不同的原型材料用不同的指标进行模拟,细砂、桩身、承台分别以天然密度、抗压刚度、抗弯刚度作为指标进行模拟.对土体未开挖阶段、钻孔阶段、混凝土灌注阶段和养护阶段的应力场进行了详细的讨论,并应用ANSYS进行了分析.根据2种方法得到的结果,从荷载沉降曲线、桩身轴力分布和侧向摩阻分布等方面,对比分析了加载和卸载条件下超长钻孔群桩的承载特性.结果表明,有限元计算模型与离心机试验模型沉降观测的结果吻合得很好;桩顶反力的分布规律复杂,与承台的自身刚度、相应的假定和分析方法有关;轴力随着深度先稍微增加,后逐渐减少,并且在岩层中减少的速度远比砂土中快.