Dynamic Response of Shallow-Buried Tunnels Traversing High Loess Slopes

Considering the existence of numerous shallow-buried tunnels traversing high slopes in the loess area in western China and the fact of high seismic intensity there,we investigate the dynamic response rules of a shallow-buried loess tunnel and its slope under the action of seismic waves with different intensities.Through large-scale shaking table model tests,we successfully analyze the characteristics and process of the destabilization of tunnels and slopes,and propose valuable suggestions regarding the reinforcement parts of a tunnel for reducing seismic damage.The results show that the main seismic damage on a slope include the failure of the sliding surface between the top and foot and the stripping of the soil around the tunnel entrance,while the damage on a tunnel is mainly manifested as the seismic-induced subsidence at the portal section and the cracking deformation at the joint areas.Finally,we propose that the“staggered peak distribution”phenomenon of the maximum acceleration values at the vault and inverted arch area can be considered as a criterion indicating that the tunnel enters into the threshold of dynamic failure.

Key Techniques for the Construction of High-Speed Railway Large-Section Loess Tunnels

The successful completion of the Zhengzhou-Xi＇an high-speed railway project has greatly improved the construction level of China＇s large-section loess tunnels, and has resulted in significant progress being made in both design theory and construction technology. This paper systematically summarizes the tech- nical characteristics and main problems of the large-section loess tunnels on China＇s high-speed railway, including classification of the surrounding rock, design of the supporting structure, surface settlement and cracking control, and safe and rapid construction methods. On this basis, the key construction tech- niques of loess tunnels with large sections for high-speed railway are expounded from the aspects of design and construction. The research results show that the classification of loess strata surrounding large tunnels should be based on the geological age of the loess, and be determined by combining the plastic index and the water content. In addition, the influence of the buried depth should be considered. During tunnel excavation disturbance, if the tensile stress exceeds the soil tensile or shear strength, the surface part of the sliding trend plane can be damaged, and visible cracks can form. The pressure of the surrounding rock of a large-section loess tunnel should be calculated according to the buried depth, using the corresponding formula. A three-bench seven-step excavation method of construction was used as the core technology system to ensure the safe and rapid construction of a large-section loess tunnel, following a field test to optimize the construction parameters and determine the engineering measures to stabilize the tunnel face. The conclusions and methods presented here are of great significance in revealing the strata and supporting mechanics of large-section loess tunnels, and in optimizing the supporting structure design and the technical parameters for construction.

Finite element analyses of Wanjiazhai water transmission tunnel excavation and service

This paper is devoted to the nonlinear stress and strain analysis oftunneling and working conditions of Wanjiazhai Division Project No.7 Tunnel in Shanxi province ofChina. The initial geological stress of loess was simulated by grading fill; the theory of unloadingproposed by Duncan and boundary stress of elasticity were used to calculate the excavation of thetunnel; Goodman joint elements were applied to simulate the joints of the liners; both loading andunloading tests have been performed to determine the parameters of Duncan-Chang's model and thecalculated results were compared; Terzaghi' s theory on loosening earth pressure was applied. Manyworking conditions were analyzed and some reasonable results were obtained. Based on the analyses,reparative measures were proposed and completed. The tunnel has functioned well since October, 2001.

黄土地区铁路隧道围岩支护参数多目标优化探讨

提出基于变异算子优化粒子群的黄土地区铁路工程隧道围岩支护参数多目标优化,以围岩压力作为外部荷载,将受力施加于梁单元,建立荷载结构模型,根据计算模型与优化约束条件,构建支护优化参数模型,调整搜索最优参数,基于变异算子优化粒子群,将粒子分为基础群与综合群;引入变异算子,对惯性权重参数进行调整,对围岩支护压力、二次衬砌厚度、喷层厚度等参数进行迭代计算,得到优化后的围岩支护参数。优化后围岩喷层厚度最高由26 cm减少到12 cm,支护压力最高由65 kPa增加到253 kPa,二次衬砌厚度最高由58 cm减小到30 cm,优化效果较好。

地震作用下大断面偏压双线黄土隧道初期支护内力及变形响应研究

为研究西北黄土高原地区大断面偏压双线黄土隧道的初期支护结构在地震作用下的内力和变形响应特征,依托宁夏境内某大断面偏压双线黄土隧道,以工程地质勘察报告和设计资料为基础,选取Kobe波作为地震动输入,利用有限差分程序FLAC 3D建立三维数值分析模型,通过分析初期支护结构的内力和变形以研究其地震动力响应特征。研究结果表明:地震过程中左线和右线隧道拱肩位置的受拉侧会发生变化,左线隧道拱腰和右线隧道拱肩、拱脚和仰拱位置的轴力会发生拉压变化。地震作用下左右线隧道峰值弯矩和峰值轴力的最大值均在拱脚,应加强此位置的抗震设计。静载作用下左、右线隧道边墙弯矩分布不对称,且左线隧道更明显。地震作用下,左线和右线隧道的最大弯矩和最大轴力分别出现在左拱脚和右拱脚,且左线隧道(偏压侧隧道)动力响应更为剧烈;右线隧道整体变形明显大于左线隧道,地震作用下左右线隧道变形均增大且整体向右倾斜,左线和右线隧道的最大位移分别在右拱肩和右拱腰处,位移值分别为34.98 mm和39.11 mm。综合结构内力和变形响应分析,地震作用下左线和右线隧道的拱脚位置易出现结构损伤,且左线(偏压侧)隧道拱脚位置更易损伤。

大断面黄土隧道下穿地表建筑物沉降分析及对策

依托西延高铁某黄土隧道下穿地表建筑物工程实例,采用理论分析、数值模拟等手段,对大断面黄土隧道下穿地表建筑物施工中地表沉降范围及对策进行研究。结果表明:基于随机介质理论,隧道两侧的地表沉降范围可划分为强、弱、无影响区,隧道施工对地表强影响区范围约等于隧道埋深,弱影响区范围约为隧道埋深的2倍;在开挖面到达办公楼正下方时办公楼沉降值约占总沉降值的70%;穿过办公楼后,沉降速率趋于收敛,隧道施工中接近地表建筑物要加强施工质量,保证地表结构安全;隧道通过地表建筑物后,地表沉降趋于收敛,但沉降值仍不断增大,隧道穿越地表建筑物后,应持续开展建筑物沉降变形监测,掌子面二衬紧跟,保证地表建筑物结构安全;大断面黄土隧道下穿地表建筑物时,采用三台阶临时仰拱(腰梁)法、锁脚加强、初支加强等措施后,可保证隧道施工安全,相关措施可为相类似工程的施工提供借鉴意义。

Mechanical response of Q_(2)loess stratum surrounding a hydraulic tunnel under dry-wet cycles

Understanding the mechanical response of Q2 loess subjected to dry-wet cycles(DWCs)is the premise for the rational design of a hydraulic tunnel.Taking the Hanjiang-to-Weihe south line project in China as the research background,the microstructure evolution,strength degradation and compression characteristics of Q2 loess under different DWCs were investigated,and the fluid-solid coupling analysis of the hydraulic tunnel was carried out using the FLAC3D software.The amplification effect of tunnel surrounding soil pressure(SSP)and its influence on the long-term stability of the tunnel under different DWCs were obtained.The results showed that the pore microstructure parameters of the undisturbed and remolded loess basically tend to be stable after the number of DWCs exceeds 3.The porosity of Q2 loess is increased by 26%.The internal friction angle and cohesion of Q2 loess are decreased by 35%and 31%,respectively.The vertical strain of Q2 loess is increased by 55%after considering the DWCs.After the DWCs stabilized,the SSP ratio is increased between 10%and 25%.With the increase in buried depth of the tunnel,the SSP ratio is increased by 8%e10%.The SSP is reduced from 8%to 16%by the rise in groundwater level.As the number of DWCs increases and the burial depth of the tunnel decreases,the distribution of SSP becomes progressively more non-uniform.Based on the amplification factor and the modified compressive arch theory,the SSP distribution model of loess tunnel was proposed,which can be preliminarily applied to the design of supporting structures considering DWCs.

Analysis of mechanical behaviors of big pipe roof for shallow buried large-span tunnel

A series of researches on mechanical behaviors of big pipe roof for shallow large-span loess tunnel were carried out based on the Wenxiang tunnel in Zhengzhou—Xi'an Special Passenger Railway. The longitudinal deformations of the pipe roofs were monitored and the mechanical behaviors of the pipe roofs were analyzed at the test section. A new double-parameter elastic foundation beam model for pipe roof in shallow tunnels was put forward in Wenxiang tunnel. The measured values and the calculation results agreed well with each other,revealing the force-deformation law of big pipe roof in loess tunnel:At about 15 m in front of the excavating face,the pipe roof starts to bear the load;at about 15 m behind the excavating face,the force of the pipe roof tends to be stabilized;the longitudinal deformation of the whole pipe roofs is groove-shaped distribution,and the largest force of pipe roofs is at the excavating face. Simultaneously,the results also indicate that mechanical behaviors of pipe roof closely relate to the location of the excavation face,the footage of the tunnelling cycle and the mechanics parameters of pipe roof and rock. The conclusions can be reference for the design parameter optimization and the construction scheme selection of pipe roofs,and have been verified by the result of numerical analysis software FLAC3Dand deformation monitoring.

深埋老黄土隧道支护限阻器力学特性及其应用研究

为深入探究基于限阻器的隧道让压支护,即限阻支护的受力特征,基于室内试验结果,采用数值计算和数据拟合的方法,系统阐明了限阻器的力学性能和本构关系,提出限阻支护的数值模拟方法;并结合工程应用,分析不同参数下限阻支护的变形和受力特征。结果表明:限阻器的力学性能与竖板的高度和厚度相关,引入预制弯弧可使限阻器性能可控;限阻器采用应变软化/硬化实体单元和弹性正交异性膜单元模拟;限阻器较小的恒阻值降低了限阻支护的轴力但同时也增大了弯矩,有利于小偏心受压破坏防治但增加了大偏心受压破坏风险;限阻器的合理压缩量为7~12 cm,建议在工程应用中对限阻器做降高、增厚和弯弧优化,可进一步增效降本。

湿陷性黄土区输水隧洞盾构施工风险评估

为了提高针对湿陷性黄土区输水隧洞盾构法施工安全评估的可靠性,从人员管理、机械材料、施工技术、施工环境4个方面构建较为完善的施工安全风险评估指标体系;利用灰色-DEMATEL方法对中心度进行处理得到风险指标权重;以风险发生概率和风险损失程度两个维度为基础构建二维云评估模型,其中发生概率由主、客观方法相结合来确定,损失程度通过改进雷达图法从人员伤亡、经济损失、工期延误、功能缺陷和环境影响5个方面来综合确定。将该评估模型运用到引汉济渭工程X输水隧洞盾构法施工项目的安全评估中。结果表明:该项目施工风险评估等级为Ⅱ级,施工安全风险程度较小,评价结果符合工程实际,验证了该评估模型的可行性和有效性。研究成果可为湿陷性黄土区类似输水隧洞盾构法施工安全风险评估提供借鉴和参考。

含水率影响下黄土盾构隧道壁后注浆浆液扩散特性试验研究

为了揭示黄土盾构隧道壁后注浆浆液在地层中的扩散形式和规律,考虑盾构隧道盾尾间隙特征,建立含水率、渗流压力、土压力可实时监测以及扩散过程可视的模型试验系统。考虑黄土不同含水率,通过试验研究浆液扩散形式以及注浆过程中的含水率、渗流压力和土压力变化规律。研究结果表明:在相同干密度下,不同含水率对壁后注浆浆液扩散形式影响显著;含水率为10%时,浆液未发生明显扩散,浆-土形成了明显的分界面,仅分界面处的含水率发生显著变化,各分层土体土压力较大;含水率为20%和30%时,浆液扩散范围增大,各分层土体含水率均有变化,土压力和渗流压力出现了阶跃曲线,土体中形成了明显的浆脉。黄土盾构隧道壁后注浆中浆液的扩散形式主要为压密扩散、压滤扩散和劈裂扩散。

黄土盾构隧道围岩强度指标结构性参数表征与荷载计算

为了考虑黄土地层特征,获取合理的围岩压力以指导黄土盾构隧道结构设计,通过对比盾构隧道与新奥法隧道围岩压力现场测试数据,结合黄土盾构施工实践,验证形变围岩压力计算黄土盾构隧道围岩荷载的合理性;考虑黄土地层的强度参数,通过芬纳公式构建黄土盾构隧道形变围岩压力的计算方法;采用三轴剪切实验,探究原状黄土的应力应变关系以及应力结构性参数的变化规律,构建应力结构性参数下黄土强度指标的计算方法;结合盾构隧道开挖支护下围岩的应力应变变化规律,建立深埋黄土盾构隧道围岩结构性参数场的计算框架,结合结构性参数修正的黄土强度准则,给出深埋黄土盾构隧道围岩压力的计算方法。研究发现,使用形变压力理论计算黄土盾构隧道围岩荷载具有合理性;原状黄土相比重塑黄土有明显的应力峰值及应变软化现象;黄土应力结构性参数与粘聚力存在较好的拟合关系,与内摩擦角相关性低;当仅考虑地层浸水造成黄土结构性演变引起的围岩压力变化时,当含水率由1%增加到25%,塑性圈半径由4.6 m增加为5 m,围岩压力由587 kPa增加到622 kPa。

银西高铁黄土含水层隧道群井降水模拟研究

研究目的:银西高铁上阁村隧道穿越董志塬黄土含水层施工中出现的渗涌水,受地下水渗流影响,引起了洞身黄土含水率增加、围岩自稳性变差等问题。为解决上阁村富水黄土隧道施工难题,论文首先分析了上阁村隧道黄土含水层分布特征,其次介绍了地表降水施工辅助措施及其效果,最后应用MIDAS/GTS建立隧道工程群井降水模型,实现了不同流量以及渗透系数工况下的隧道开挖渗流模拟计算。研究结论:(1)上阁村隧道长大段落通过软塑黄土含水层,通过地表降水梳干隧道洞身范围内地下水,提高了隧道洞身黄土围岩稳定性,确保了隧道施工的安全和进度;(2)不同单井流量(80 m^(3)/d、90 m^(3)/d、100 m^(3)/d)的群井数值模拟结果表明,地下水位降深在短时间内达到了设计要求,验证了降水设计参数及效果;(3)本研究可为黄土等低渗透岩体富水隧道工程施工处置及设计提供依据。

黄土盾构隧道开挖围岩扰动特性模型试验研究

为了探究不同含水率和埋深等工况下的黄土盾构隧道开挖对围岩的扰动作用特征,采用相似模型试验,首先通过三轴试验测定了不同含水率下原状黄土物理参数及强度指标,通过大量试配得到了不同含水率下与原状黄土强度指标参数相似的试验用土。其后,考虑盾构隧道盾尾间隙特征,开展不同含水率及埋深等组合工况下盾构开挖模拟试验,通过微型土压力传感器、百分表等监测元件以及数字图像技术等手段,分析了不同工况下地层变形、地表沉降和围岩应力的变化规律。研究发现:含水率较低时,围岩的自稳能力强;含水率越高,埋深越大,开挖对地层的扰动作用也越大;地表最大沉降值与含水率呈正相关,与埋深呈负相关;围岩剩余应力随含水率和埋深的增大而增大,但当含水率增大至一定值(26.6%)时,围岩剩余应力骤减;基于不同含水率下的围岩应力及变形发展规律,可将黄土含水率分为自稳、形变以及松动含水率,基于含水率和埋深引起的围岩松动情况,可将不同工况下的黄土盾构隧道围岩压力作用模式按照形变压力和松动压力计算,以更加适应黄土地层的特性。

凤凰山特大断面黄土隧道五步单侧壁导坑法研究

为解决特大断面黄土隧道采用双侧壁导坑法施工进度慢、成本高的问题,以G30连霍高速公路清水驿至忠和段扩容改造工程凤凰山隧道为背景,提出五步单侧壁导坑法。通过数值模拟对比分析双侧壁导坑法、五步单侧壁导坑法、传统单侧壁导坑法和台阶法在施工过程中的围岩变形及钢拱架应力,并结合现场试验段监测数据验证特大断面凤凰山隧道采用五步单侧壁导坑法施工的可行性。结果表明:1)五步单侧壁导坑法拱顶沉降和水平收敛比传统单侧壁导坑法分别减小3.59 cm和1.31 cm,比双侧壁导坑法分别增大1.4 cm和0.59 cm;钢拱架应力除拱肩外均小于双侧壁导坑法,最大处减少了70 MPa,钢拱架应力最大值与钢材屈服强度的比值比双侧壁导坑法增大0.04,比单侧壁导坑法减小0.08。2)传统单侧壁导坑法的安全性小于五步单侧壁导坑法,改进后的五步单侧壁导坑法相比双侧壁导坑法能在控制围岩变形的同时加快施工进度,降低施工成本。3)五步单侧壁导坑法中隔壁的最优位置应结合具体工程情况进行单独优化计算,针对本工程而言,其最优位置为45%洞宽。

洛川隧道围岩变形规律模型试验研究

以洛川隧道DK194+835为研究断面,开展不同埋深下隧道模型试验研究。通过各种试验确定原型、相似材料土和衬砌的参数,利用3D打印技术研制出一套新型衬砌材料及连接方式较好的模拟了实际工程中喷射混凝土、钢架、超前小导管。利用自制多点位移计等各种监测原件采集开挖过程中围岩内部变形及地表沉降数据。试验表明:可通过拼装的方式在模型试验中模拟隧道的分布支护,可使用滑动式连接件链接相邻位置的石膏块;不同测点竖向位移均经历缓慢增长(开挖面远离监测断面)、迅速增长(开挖面接近监测断面)、逐步稳定(开挖面经过监测断面)3个阶段。随埋深增加,监测断面前期变形(开挖面远离、接近监测断面)占比减小;地表沉降经历缓慢增长、迅速增长、逐步稳定3个阶段。随埋深增加,监测断面前期地表沉降占比减小。

浅埋偏压大断面黄土隧道下穿古建筑群开挖稳定性研究

浅埋偏压大断面黄土隧道开挖极易引发地表沉降,影响地表既有建筑物的安全使用。以兰州市白塔山隧道为工程背景,通过ABAQUS有限元软件模拟了双侧壁法和中隔壁法隧道开挖支护的动态过程,分析围岩与支护结构的变形受力特征以及地表沉降对古建筑的影响。结果表明:偏压导致两种方法开挖深埋侧土体的围岩竖向变形均大于浅埋侧,地表与拱顶沉降具有同步性,危险施工段一致;双侧壁导坑法开挖地表最大沉降为10.7 mm,二次衬砌应力主要分布在拱顶和拱腰,最危险施工段为开挖中上部土体,但工序复杂,施工进度慢;中隔壁法引发围岩最大沉降为23.0 mm,地表最大沉降为13.0 mm,二次衬砌应力主要分布在拱顶、拱肩部位,最危险工况为开挖右上台阶;两种开挖方式对古建筑的影响均符合相关规范的要求,综合考虑中隔壁法更适合对该浅埋偏压段围岩以及地表变形的控制。

冻融条件下不同覆盖度土壤物理结皮的风蚀特征

[目的]研究冻融条件下物理结皮的风蚀特征变化,为冻融风蚀相关研究提供理论参考。[方法]以黄土高原北部风水复合侵蚀区内神木市六道沟小流域的沙黄土为研究对象,采用室内模拟冻融、风洞试验相结合的方式,设计不同覆盖度(0%,20%,40%,60%,80%,100%)的物理结皮进行风洞吹蚀试验,探究冻融作用对不同盖度结皮的风蚀强度、输沙率和输沙高度以及摩阻风速、空气动力学粗糙度等动力学参数的影响。[结果]①风蚀强度随风速的增加显著增大(p<0.05)、随结皮盖度的增加显著减小(p<0.05),且结皮盖度越高,风蚀减蚀率越强,最高可达96.07%;冻融后物理结皮的风蚀强度较冻融前均显著增加,冻融后风蚀强度可增加0.02~1.27倍。②物理结皮覆盖显著减小了近地表的输沙率,且近地表输沙率随结皮覆盖度的增加而减小,随风速的增加而增加;冻融后近地表输沙率增加了0.7~4.3倍,输沙高度增加了2~10 cm。③摩阻风速和空气动力学粗糙度随结皮盖度变化差异不显著,冻融前摩阻风速介于0.84~1.35 m/s之间,冻融后摩阻风速在0.80~1.51 m/s内变化,冻融后物理结皮摩阻风速有所减小,但空气动力学粗糙度变化不大。[结论]黄土高原北部的冻融作用增加了土壤风蚀程度,削弱了物理结皮对风蚀的抑制作用;随着结皮盖度增加,冻融作用后风蚀强度和近地表输沙强度明显增大;物理结皮覆盖度、冻融作用对空气动力学粗糙度的影响不显著。

下穿石油管道黄土隧道变形控制技术研究

黄土具有显著各向异性,渗透性强,多具湿陷性等特点。以可乐湾黄土隧道工程为依托,通过原状黄土物理特性试验、固结压缩与湿陷性试验和原状黄土三轴抗剪试验,深入探究工程区原状黄土的各向异性及变形特征。利用数值模拟有限元软件,在不同开挖方法、不同超前小导管长度、不同锁脚锚管长度及地表注浆的条件下,对比分析了黄土隧道施工中沉降变形趋势。结果表明:1)黄土的水平和竖直方向力学指标有明显差异,水平方向天然压缩模量大于竖直方向;2)综合考虑各种因素,建议采用二台阶五步法施工,辅助4.5 m的超前小导管及5 m的锁脚锚管;3)地表注浆对隧道及石油管道的沉降变形的保护作用效果不明显。

黄土地层地铁隧道水环境变化对地表沉降影响研究

黄土地层中城市地铁隧道水环境变化主要体现在地下水位升降和盾构衬砌管片渗水,地层中水位的变化及管片渗漏会进一步影响地表沉降。以某地铁区间隧道为背景,采用修正摩尔库仑模型(MM-C模型)和DP模型来描述复杂加卸载条件下的地层隆沉问题,并深入研究水环境变化下地表沉降规律。结果表明:盾构管片渗漏比从0.1增大到10期间,地表沉降增加了24%;管片渗漏块数从1增大到6块时,地表最大沉降增大了77%;地下水位下降5 m期间,地表最大沉降增大了1.2倍,水位降深每增加1 m,地表下沉量增加约7 mm;初始水位高度抬升5 m期间,地表最大沉降减小了37%。为了控制地表不发生过量隆沉,渗漏块数不宜超过3块,并应避免拱底管片发生破坏或渗漏,地下水位的回灌抬升高度及降水深度宜分别控制在3.0 m和2.0 m以内。