层状软岩隧道开挖稳定性及锚杆非对称支护方式研究

层状软岩地层中,隧道开挖后围岩的非对称破坏特征与支护结构的非对称受力特征显著,围岩的稳定性控制面临着较大的挑战。基于该背景,建立了层状岩体各向异性本构模型,并采用该模型分析了层理面的倾向与倾角对隧道破坏模式的影响,最终提出了围岩形变控制的锚杆非对称支护模式。研究结果表明:①当岩层倾角为0°,倾向为0°～180°或倾向为0°,倾角为0°～90°时,不同组合下围岩的塑性破坏区及形变显著区域均沿着隧道竖向轴线对称分布;倾角在0°～90°之间时,围岩的塑性区及形变显著区域呈现明显的非对称分布特征;倾角为90°,倾向为90°时,围岩塑性区及形变显著区域沿着隧道竖向轴线对称分布,其余倾向条件下,围岩的塑性区及形变显著区域沿着隧道竖向轴线非对称分布;②对于层状岩体而言,层理面特征是影响围岩破坏模式的最关键因素,而地应力场的方向是次要因素;③锚杆非对称支护方案,即首先加强围岩塑性破坏较大区域内的锚杆支护,其次加强围岩位移较大区域内的锚杆支护,可以有效的控制围岩的大变形与塑性区的发展。     

斜穿过砂卵石层地质构造隧道开挖的三维数值模拟分析

以某地铁隧道浅埋暗挖法为研究对象,建立了斜穿过砂卵石地质构造隧道开挖的三维有限模型.通过模拟隧道开挖,分析了隧道在不同支护工况下的围岩应力、位移、塑性区.分析结果表明,在第一步开挖后围岩位移较小,第二步开挖后在砂卵石层最厚处的围岩位移急剧增大并在后续开挖过程中趋于稳定;开挖过程中砂卵石结构本身的性质使其承载力小,因此在其地质层处出现了塑性区;锚杆的支护作用提高了围岩的整体性能,减小了拱顶上部围岩的内应力;隧道开挖后的卸载作用使钢拱架承受上部围岩荷载且主要承受压应力.为防止隧道产生塌方开挖后应及时施做初期支护和二期衬砌.     

地铁浅埋小净距隧道施工技术

青岛地铁五江区隧道中岩柱最小距离1.495～3.0m,埋深10m,Ⅳ级围岩,为浅埋小净距隧道;隧道围岩塑性区在中岩柱处易贯通,中岩柱很容易造成失稳坍塌。经过反复讨论,确定对中岩柱采用中空注浆锚杆加固,洞身初支采用格栅、拱部径向砂浆锚杆支护,先施工右洞设临时钢支撑,再施工左洞,边开挖边支护。采用提前加固与控制爆破技术,保证了施工安全,平稳地过渡至大断面施工。     

铁路隧道软弱围岩破坏模式离散元分析

以贵广高速某铁路隧道为依托,采用离散元UDEC建立数值计算模型,对软弱破碎围岩的破坏模式和系统锚杆支护效果进行分析,可知：隧道开挖产生临空面,易引发节理结构面的破坏,拱部岩体首先出现破坏;系统锚杆能使洞周竖向、水平位移与塑性区得到有效控制;注浆加固不但使锚杆的销钉和组合梁作用更为显著,而且还有效提高了围岩的自承能力。通过分析建议取消拱部系统锚杆,加强侧墙锁脚锚杆。     

水平泥砂互层隧道围岩稳定性研究

以大梁峁特长公路隧道为依托,针对水平层状岩体隧道,采用ANSYS数值分析软件将水平泥岩砂岩互层岩体等效为正交各向异性的方式,对隧道开挖过程中围岩稳定性进行了数值试验分析,通过分析围岩塑性区、围岩应力、隧道变形、锚杆轴力、初支及二衬内力,得出施工采用支护参数的合理性和水平泥岩砂岩互层隧道围岩变形和初支、二衬应力的分布特征.     

基于现场直剪试验和强度软化的围岩压力解析

高地应力、强挤压软岩隧道在开挖前,隧道设计线路范围内的原岩就已处在塑性状态,隧道开挖后对支护有影响的围岩处于不同的塑性区范围内.就此,考虑到岩体的力学性能通过现场试验能较为全面地反映,对两座隧道高地应力软岩段的现场直剪试验曲线进行分析,并进行室内常规三轴压缩试验,得到了适用于塑性软岩隧道的简化本构关系曲线和应变软化模型.在此基础上对圆形塑性软岩隧道支护后的围岩应力状态和位移状态进行分析,在考虑围岩强度参数■、■随应变软化的情况下,推导出了塑性软岩隧道的扰动区半径r_d和支护力p_i解析表达式,并建立了动态支护力p_i与动态隧道壁径向位移u之间的关系,研究成果可为高地应力、强挤压塑性软岩隧道的支护设计提供一定的参考.     

某二元结构高边坡加固效果对比分析研究

在分析原始边坡天然和暴雨状态下的边坡稳定性和塑性区分布的基础上,利用Midas有限元分析软件分析了锚杆支护和抗滑桩方案对边坡稳定性的支护效果。研究结果表明,锚杆支护下边坡的安全系数由原来的1.137提高到了2.084,抗滑桩支护下的边坡天然工况下的安全系数为1.627,比边坡的原始安全系数提高了41.2%;最后从施工和工程经济性等角度对两种支护方案进行了对比,提出了主动支护措施与被动支护措施结合的支护建议。     

山岭公路隧道系统锚杆支护作用及其施工质量问题分析

锚杆是新奥法隧道施工的主要支护手段,对围岩的稳定能发挥重要的支护作用.通过对锚杆支护作用的阐述,结合公路隧道施工当中锚杆出现的常见质量问题,对这些问题的后果进行了分析,指出今后山岭公路隧道施工中,需重视锚杆的支护作用并加强监管措施,确保锚杆的施工质量.     

超浅埋隧道下穿冲沟边坡塌方分析与处治

某铁路隧道在下穿冲沟边坡时出现冒顶。针对该隧道工程的实际情况,建立数值分析模型,采用FLAC3D程序模拟隧道施工力学行为,考虑暴雨积水对围岩的影响,从围岩塑性区分布、位移以及锚杆和超前大管棚内力分布情况分析隧道变形和冒顶发生的原因。结果表明：隧道超浅埋、持续降水积水、围岩力学性质差及施工支护不当导致坍方。结合工程实际提出洞内加固、冲沟边坡加固及开挖控制的综合处治方法,取得了理想的效果,为日后类似工程提供借鉴与参考。     

数值分析在隧道支护中的应用

通过对某一隧道的施工形式及其所采用的支护方进行了数值分析,分析不同的支护参数对隧道周边应力和位移的影响,得出了有关塑性区分布与支护方式之间的关系,并对各类支护方式进行了比较与分析.     

双线性强化隧道和桩孔三剪弹塑性解

将隧道和桩孔简化为厚壁圆筒, 基于三剪强度准则和双线性强化模型, 考虑材料的应变强化和中间主应力效应, 推导了厚壁圆筒在均匀内外压作用下的弹塑性极限解, 并给出恒定外压条件下塑性区半径与内压的关系式, 分析了强化模量系数、半径比、中间主应力与材料强度拉压异性对厚壁圆筒弹塑性极限解的影响规律。研究结果表明: 所得弹塑性极限解克服了Tresca屈服准则与Mises屈服准则未考虑拉压异性, Tresca屈服准则与Mohr-Coulomb屈服准则未考虑中间主应力与双剪强度理论极限解存在滑移面突变现象的不足; 弹塑性极限解均随半径比与中间主应力影响系数的增大而增大, 随拉压强度比的增大而减小, 外压对极限内压的影响程度随着拉压强度比的增大而减小; 当强化模量系数为0.1、半径比为2时, 考虑强化效应的塑性极限内压比不考虑时相对增大10%以上, 随着半径比增大到4, 塑性极限内压比不考虑强化效应时相对增大38%以上, 强化效应影响更加明显, 故对于存在应变强化效应的材料, 采用双线性强化模型的分析结果更接近工程实际; 当不考虑中间主应力与应变强化时, 土体的极限扩孔压力弹塑性极限解与Vesic解相差在0.02%以内, 当考虑了土体的中间主应力和应变强化效应后, 塑性区半径与内半径比为10时, 弹塑性极限解分别是Vesic解的1.06、1.81倍, 因此, 基于Vesic解的极限扩孔压力过于保守。      

Block Limit Analysis Method for Stability of Slopes During Earthquakes

Based on the limit analysis upper bound method, a new mechanism of soil slope failure has been proposed which was consisted of plastic shear zone and rigid block zone. The different zones interface were regarded as discontinuity lines. Two sliding blocks of the slope were also incorporated horizontal seismic force and vertical gravity force. The velocities and forces were analyzed in two blocks, and the expression of velocity discontinuities was derived according to the principle of incompressibility. The external force done work for the blocks and the internal energy dissipated of the plastic shear zone and the velocity discontinuous were solved. The stability ratios were derived for the height of two-level slope with different rates to involve seismic and no seismic. The present stability ratios were compared to the previous study, which showed the superiority of the mechanism and the rationality of the analysis. The critical height of the slope can provide a theoretical basis for slope support and design.     

Study on the squeezing effect of open-ended pipe piles

During the installation of a pipe pile, the soil around the pile will be squeezed out. This paper deals with this squeezing effect of open-ended pipe piles using the cylindrical cavity expansion theory. The characteristics of soil with different tension and compression modnli and dilation are involved by applying the elastic theory with different moduli and logarithmic strain. The closed-form solutions of the radius of the plastic region, the displacement of the boundary between the plastic region and the elastic region and the expansion pressure on the external surface of the pipe piles are obtained. When obtaining these solutions, the soil ping in the open-ended pipe pile is considered by employing an incremental filling ratio to quantify the degree of soil plugging. Moreover, the effects of the ratio of tension and compression moduli, angle of dilation and incremental filling ratio on the radius of the plastic region and the expansion pressure on the external surface of the pipe pile are investigated. The parametric analyses show that it is necessary and important to consider the difference between the tension modulus and compression modulus, dilation angle and incremental filling ratio for studying the squeezing effect of open-ended pipe pile installation. It is concluded that the analytical solutions presented in this paper are suitable for studying the squeezing effect of open-ended pipe piles.     

基于区内出行比例的城市交通小区半径计算方法

针对国内城市交通小区划分多靠定性分析的情况,分析了国内外交通小区划分方法,提出了基于区内出行比例的交通小区半径定量计算方法。基于交通小区半径和出行距离的三种不同组合,推导出了相应的区内出行比例计算模型,利用Excel软件的VBA编程功能,进行了三者之间的数量关系计算,通过对区内出行比例的控制,得出交通小区半径的合理范围。实例计算结果表明:当区内出行比例范围为5%～10%时,西安中心市区交通小区的合理半径在0.7～1.1km之间,而实际调查区内出行比例为9.28%,交通小区半径为0.9km,调查值与计算值接近,小区半径定量计算方法可行。     

桥梁结构钢裂纹塑性区的研究及应用

为了研究裂纹塑性对裂纹扩展的影响,利用工程简化算法、应力函数法、扩展有限元法对桥梁钢裂尖塑性区的尺寸和形状分别进行了计算;由于平面应力和平面应变情况下尾迹场循环塑性的特性不同,利用不连续扩展有限元对两种情况下尾迹场的循环塑性和塑性累积进行了模拟分析,探讨了裂尖塑性区、循环塑性区的形成和尾迹场产生压应力的机理.研究结果表明:裂尖塑性区尺寸与应力水平（名义应力与屈服极限的比值）的平方成正比,当应力水平大于0.4时,裂尖塑性区尺寸需要考虑应力水平的影响;裂尖塑性区的形状以蝶形向前伸展,使裂纹尾迹场免受裂尖高应力场的拉伸作用,有利于裂纹闭合;裂尖塑性区存在材料的逆向流动,在循环塑性区裂纹表面的塑性累积产生压应力效应有利于裂纹提前闭合,这种塑性诱发的裂纹提前闭合对研究变幅加载、过载引起的裂纹扩展滞后有重要意义.      

齿轮新标准下检测中心距公差带和功能齿厚测量

说明了最大、最小检测半径的计算,推证了双面啮合下节圆压力角(节点展角)的计算公式;解释了检测中心距公差带(径向综合测试公差带)的形成和作用,对个别代号的含义提出了看法;列举了保证功能齿厚测量精度的主要要求,给出了部分因素对测量精度影响的比率。     

Stresses and Shear Fracture Zone of Jinshazhou Tunnel Surrounding Rock in Rich Water Region

Field evidence has shown that large-scale and unstable discontinuous planes in the rock mass surrounding tunnels in rich water region are probably generated after excavation. The tunnel surrounding rock was divided into three zones, including elastic zone, plastic damage zone and shear fracture zone fof assessing the stability of the tunnel surrounding rock. By local hydrogeology, the stresses of surrounding rock of Jinshazhou circular tunnel was analyzed and the stress solutions on the elastic and plastic damage zones were obtained by applying the theories of fluid-solid coupling and elasto-plastic damage mechanics. The shear fracture zone generated by joints was studied and its range was determined by using Mohr-Coulomb strength criterion. Finally, the correctness of the theoretical results was validated by comparing the scopes of shear fracture zones calculated in this paper with those from literature.     

Ⅰ型裂纹稳定扩展裂尖塑性区研究

运用FRANC2D/L软件分别对6.35 mm和2 mm两种厚度Arcan试件的Ⅰ型裂纹稳定扩展进行数值计算,研究了该软件的网格划分技术对计算结果的影响,发现该软件的计算精度主要受裂纹区的网格密度影响（当裂纹面单元与裂纹每步扩展单元尺寸一致时,计算精度好）.通过分析有效应力,研究了材料、裂纹扩展长度及试件厚度对裂纹尖端塑性区尺寸的影响.研究结果表明,材料的屈服应力越大,其裂尖塑性区尺寸越小;塑性区尺寸随裂纹扩展长度的增加,先增大后趋于不变;塑性区的形状与板厚或边界有关,6.35 mm厚的母材及3种焊接板材塑性区成扩散型,2 mm厚的母材成Dugdale模型,25.4 mm以上厚度母材成平面应变模型;裂纹启裂时,塑性区随着厚度的增加而减小,最终不变.     

Study on toughening on crack prevention of jointed rock masses with different pre-stress anchor cables

The major reason of the failure of jointed rock-mass is the formation of the plastic zone near the crack tip of I-II mixed crack which leads to the growth, propagation of the branched crack under load condition. In the paper, the failure judgment of mini-plastic zone??s displacement is derived by the Mises yielding rule. The anchor cable is simulated by the different link elements and inflicting pre-strains according to the difference of mechanism of the consolidated segment and free segment. The stress and strain fields near crack tip of twain collinear cracks of different angles and consolidated conditions are simulated by iso-parametric element with eight nodes. The iso-parametric element with eight nodes is degenerated to singular element at crick tip to simulate crack. It is shown that the mini plastic zone??s displacement near the crack tip begins to increase, then decreases with the increase of the angle of the crack. The better consolidated condition is, the smaller the angle of crack tip is when the mini plastic zone??s displacement near the crack tip arrives at the biggest value. The mini plastic zone??s displacement near the crack Tip 2 is bigger than that near the crack Tip 3. The crack is easier to failure with the increase of load.     

组合效应对腹板削弱型梁柱节点的影响

采用数值模拟方法分析了混凝土楼板组合效应对钢框架腹板开圆孔削弱型梁柱节点的影响,着重讨论了节点承栽力、弹塑性阶段的应变分布、梁塑性区的产生和扩展情况,并与未考虑组合效应此类节点的性能进行了对比．削弱截面与柱的距离和削弱半径是重要的削弱参数,决定了腹板削弱型节点塑性区的扩展特征．研究结果表明,组合效应对腹板开圆孔削弱型梁柱节点区域的应变分布和塑性区扩展影响显著,其削弱参数的确定须充分考虑楼板组合效应．