Failure precursor of surrounding rock mass around cross tunnel in high-steep rock slope

The stability of the surrounding rock mass around cross tunnel in the right bank slope of Dagangshan hydropower station, in the southwestern China, was analyzed by microseismic monitoring as well as numerical simulations. The realistic failure process analysis code (abbreviated as RFPA3D ) was employed to reproduce the initiation, propagation, coalescence and interactions of micro-fractures, the evolution of associated stress fields and acoustic emission (AE) activities during the whole failure processes of the surrounding rock mass around cross tunnel. Combined with microseismic activities by microseismic monitoring on the right bank slope, the spatial-temporal evolution and the micro-fracture precursor characteristics during the complete process of progressive failure of the surrounding rock mass around cross tunnel were discussed and the energy release law of the surrounding rock mass around the cross tunnel was obtained. The result shows that the precursor characteristic of microfractures occurring in rock mass is an effective approach to early warn catastrophic damage of rock mass around cross tunnel. Moreover, the heterogeneity of rock mass is the source and internal cause of the failure precursor of rock mass.

A Simplified Method for the Stress Analysis of Underground Transfer Structures Crossing Multiple Subway Tunnels

According to the design specifications,the construction of extended piles involves traversing the tunnel’s upper region and extending to the underlying rock layer.To address this challenge,a subterranean transfer structure spanning multiple subway tunnels was proposed.Deliberating on the function of piles in the transfer structure as springs with axial and bending stiffness,and taking into account the force balance and deformation coordination conditions of beams and plates within the transfer structure,we established a simplified mechanical model that incorporates soil stratification by combining it with the Winkler elastic foundation beam model.The resolved established simplifiedmechanicalmodel employed finite difference technology and the Newton-Simpsonmethod,elucidating the mechanical mechanism of the transfer structure.The research findings suggest that the load carried by the upper structural columns can be transferred to the pile foundation beneath the beams through the transfer structure,subsequently reaching the deep soil layer and ensuring minimal impact on adjacent tunnels.The established simplified analysis method can be used for stress analysis of the transfer structure,concurrently considering soil stratification,pile foundation behavior,and plate action.The pile length,pile section size,and beam section size within the transfer structure should account for the characteristics of the upper load,ensuring an even distribution of the beam bending moment.

Load compensation research on twicetension for loop anchor cable of inner lining in Yellow River-crossing tunnel

The load compensation equipment for anchor cable named low retraction prestressed anchorage system with twice-tension(referred to as twice-tension anchorage system) is proposed in the paper. Calculation results of loop anchorage prestressing loss(PL) values of inner lining(IL)in Yellow River-crossing tunnel under two anchorage systems,including twice- tension anchorage system and HM(Chinese transliteration is huanmao)anchorage system,are introduced. The software ANSYS is selected to realize the three-dimensional(3D) finite element modeling to accomplish simulation and calculation works under the two anchorage systems,respectively. Stress processes of IL under the two working conditions,of which one is completed cable tensioning(CCT) and the other is water in the tunnel with the designed water pressure(DWP),are contrasted and analyzed. Impacts of prestressing forces of anchor cables on structural safety under the two anchorage systems are contrasted. The calculation results show that the twice-tension anchorage system can reduce PL effectively and then increase prestresses of wall concrete(WC). Meanwhile,the anchorage system has the advantages of improving security and stability of tunnel structure,reducing project costs and saving steel consumption. The research work is available to related design and construction of anchor cable,and is worthy of promotion and application.

Tunneling between double wells of atom in crossed electromagnetic fields

The tunneling between double wells of atom in crossed electromagnetic fields is investigated by a one-dimensional Hamiltonian model. The crossed fields induced outer well is apart from the nuclear origin and it is very difficult to access by means of spectroscopy but it will be possible if there exists the tunneling of the electron between the outer well and the Coulomb potential predominated well at the nuclear origin. A one-dimensional quantum calculation with B-spline basis has been performed for hydrogen atom in crossed fields accessible in our laboratory, at B = 0.8 T and F = -220 V.cm^-1. The calculation shows that the wavefunctions of some excited states close to the Stark saddle point in the outer well extend over to the Coulomb potential well, making it possible to penetrate the quantum information of the outer well. However, the tunneling rate is very small and the spectral measurement of the transitions from the ground state should be of a high resolution and high sensitivity.

Train crossing modeling based on measurements and best numerical approximation in subway tunnels

Communication based train control systems(CBTC) must work even in the worst situation—train crossing.This paper models the propagation characteristics in one of the most common and pivotal scenarios—train crossing in subway tunnels which is rarely mentioned in previous publications.Firsdy,measurements for train crossing scenario at 2.4 GHz in a real subway line in Madrid have been made.The field measurement is the most reliable way to reveal the propagation characteristics involving shadowing effect and fast fading.Moreover,to precisely describe the fast fading distribution and eliminate the inevitable weak points of traditional fitting way,a best numerical approximation method using Legendre orthogonal polynomials has been proposed.Comparisons show that this method works better and is of greater physical significance.Finally,a complete statistical model is given and all the coefficients can be applied by system designers for the link and system level simulations.

Hyperstatic reaction method for calculations of tunnels with horseshoe-shaped cross-section under the impact of earthquakes

Tunnels are now an integral part of the infrastructure in major cities around the world. For many reasons, these tunnels have horseshoe-shaped cross-sections with round top and flat bottom. This paper presents some improvements to the use of the Hyperstatic Reaction Method-HRM for analysing tunnels with horseshoe-shaped cross-sections when these tunnels operate under the influence of earthquakes, particularly in cases when the tunnel lining is a continuous lining. The analysis used parameters of a tunnel from the Hanoi metro system, as well as parameters of the strongest earthquake that may occur in the central Hanoi area in the improved HRM and 2 D numerical methods using the ABAQUS software. On the basis of the results obtained, the paper gives conclusions about the HRM methodology when it is used to calculate tunnels that have horseshoe cross-sections operating under the influence of earthquakes.

Horizontal freezing study for cross passage of river-crossing tunnel

To determine the appropriate soft foundation treatment for a river-crossing tunnel, freezing reinforcement design and technology were introduced based on the channel tunnel design and construction practice. Through finite element analysis and engineering practices, two rows of horizontal perforated freezing pipes were designed and installed on both sides of a passage for tunnel rein- forcement, which produced the thickness and strength of frozen crust that satisfied the design requirements. These information are valuable for guiding the design and construction of river-crossing tunnels in coastal areas.

Does the ratio of the carpal tunnel inlet and outlet cross-sectional areas in the median nerve reflect carpal tunnel syndrome severity?

Although ultrasound measurements have been used in previous studies on carpal tunnel syndrome to visualize injury to the median nerve, whether such ultrasound data can indicate the severity of carpal tunnel syndrome remains controversial. The cross-sectional areas of the median nerve at the tunnel inlet and outlet can show swelling and compression of the nerve at the carpal. We hypothesized that the ratio of the cross-sectional areas of the median nerve at the carpal tunnel inlet to outlet accurately reflects the severity of carpal tunnel syndrome. To test this, high-resolution ultrasound with a linear array transducer at 5–17 MHz was used to assess 77 patients with carpal tunnel syndrome. The results showed that the cut-off point for the inlet-to-outlet ratio was 1.14. Significant differences in the inlet-to-outlet ratio were found among patients with mild, moderate, and severe carpal tunnel syndrome. The cut-off point in the ratio of cross-sectional areas of the median nerve was 1.29 between mild and more severe（moderate and severe） carpal tunnel syndrome patients with 64.7% sensitivity and 72.7% specificity. The cut-off point in the ratio of cross-sectional areas of the median nerve was 1.52 between the moderate and severe carpal tunnel syndrome patients with 80.0% sensitivity and 64.7% specificity. These results suggest that the inlet-to-outlet ratio reflected the severity of carpal tunnel syndrome.

新建隧道近接上穿对既有盾构隧道纵向变形的影响

新建隧道近接上穿将诱发下卧盾构隧道隆起变形,预测既有盾构隧道位移发展对近接上穿施工控制和既有盾构隧道保护具有重要意义。基于两阶段法,提出新建隧道近接上穿引发既有盾构隧道纵向位移解析解;通过可考虑环间接头弱化的非连续盾构隧道模型模拟既有盾构隧道,采用Riftin地基考虑盾构隧道-土层相互作用,同时通过Mindlin经典解得到新建隧道开挖卸载应力,并作用于既有盾构隧道之上,建立新建隧道上穿作用下既有盾构隧道纵向变形解答;通过将杭州圆形顶管隧道上穿既有地铁1号线、上海地铁8号线隧道上穿既有地铁2号线两个工程案例实测值与本文方法和常用Euler-Bernoulli(EB)等效连续梁模型计算结果进行对比,验证本文方法的合理性。研究结果表明:本文方法和EB连续梁模型预测的隧道纵向位移均接近实测值;本文方法预测的隧道弯矩和接头张开量均大于EB连续梁模型;但EB等效连续梁模型预测的纵向位移曲线整体呈现为光滑连续,而本文方法预测的位移曲线是由一系列短直线连接而成,在接头处存在“尖点”。

考虑衬砌截面协调变形约束的既有隧道受盾构下穿施工影响的Fourier能量变分解

目前关于新建盾构开挖诱发既有地铁隧道变形的理论研究,大多将既有隧道简化为不含接头的Euler-Bernoulli梁,而忽视了衬砌截面的剪切变形与管片接头的局部刚度削弱。此外,既有地基模型理论较少考虑衬砌管片与接触土体的协调变形约束。首先,采用Loganathan-Polous公式计算盾构开挖诱发的土体自由位移场,并将既有隧道视为考虑剪切变形的Timoshenko梁,基于沿轴线变化的抗弯与剪切刚度函数来描述管片接头的局部削弱作用;然后,结合能量变分原理与连续弹性体Mindlin解,建立考虑衬砌截面协同变形约束的隧道位移控制方程,将盾构开挖诱发的附加荷载施加于既有隧道,并使用Fourier级数方法求解既有隧道纵向变形;最后,将Fourier能量变分解与3组工程实测数据进行对比验证,取得了较好的一致性。此外,考虑隧道抗弯刚度、剪切刚度、接头刚度削弱作用、土体参数与隧道空间位置等因素的共同影响,使用抗弯系数、剪切系数及接头系数进行敏感性分析。结果表明,考虑截面变形协调约束的理论解更为符合实际,不考虑变形协调约束所得隧道位移结果偏大;衬砌接头局部刚度的削弱作用将造成隧道弯矩沿轴线在接头处发生明显锯齿状突变;抗弯系数与剪切系数的增长均导致隧道结构所受弯矩降低;剪切系数由低到高的增长将导致隧道变形模式发生“弯曲控制-弯剪混合-剪切控制”三阶段变化;隧道变形模式进入“剪切控制”阶段的过程中,抗弯刚度的变化对隧道内力影响逐渐降低;接头系数的增长将造成隧道所受弯矩降低,但隧道抗弯刚度较大时其影响逐渐减弱。

既有交叉隧道和站台下新建地铁盾构隧道施工变形预测模型研究

在地铁建设过程中,盾构施工对既有结构的影响一直是工程施工安全和效率的关键考量因素。文章运用有限元数值模拟方法,研究广州地铁隧道A盾构施工对相邻隧道B、C和站台D的变形影响,旨在揭示新建隧道下穿既有结构时的变形规律,并预测其影响范围。研究结果表明,变形最大值位于施工轴线最近点,随着与施工位置距离的增加而减小,变形主要发生在施工平行经过期间。地表沉降呈对称分布,最大值位于隧道中部,既有隧道连接处的von-Mises应力受新建隧道开挖影响较小,应力峰值随盾构施工推进而移动,但变化幅度有限。现场监测数据与数值模拟结果高度一致,可验证该模拟方法的有效性和可靠性。文章相关研究可为地铁工程施工提供重要参考,有助于优化施工方案,提高工程的安全性和效率。

水下高速公路盾构隧道联络通道冻结施工模拟分析

公路盾构隧道联络通道建设面临较大的不确定性和风险,通常采用人工地层冻结法进行施工。以孟加拉吉大港卡纳普里河底盾构隧道联络通道为研究对象,分析联络通道施工过程中冻土帷幕和结构衬砌受力情况,研究采用双圈管冻结施工过程中冻土帷幕发展规律。针对施工期和运营期衬砌受力的最不利工况进行验算,分析积极冻结和维护冻结阶段温度场的变化,并研究部分不确定参数的敏感性。分析结果表明,该联络通道设计施工方案合理可行。

考虑隧道掘进过程的新建隧道下穿既有隧道力学响应研究

为有效评估新建隧道下穿施工对既有隧道的影响,确保既有隧道运营安全,将既有隧道简化为放置在Pasternak地基模型上的Euler-Bernoulli梁,基于两阶段分析法提出新建隧道下穿施工引起既有隧道力学响应的计算方法。通过与现场监测和既有方法的结果进行对比,验证了本文方法的准确性。研究结果表明:当新建隧道开挖面位于既有隧道中点时,既有隧道差异沉降达到最大值,转角曲线关于既有隧道中心线对称;在新建隧道掘进过程中,既有隧道的最大正弯矩和最大负弯矩分别出现在既有隧道长度的2/5和3/5位置附近,最大负剪力出现在既有隧道中点处;当新建隧道开挖面到达既有隧道长度的1/4和3/4位置时既有隧道产生最大正剪力;随着隧道轴线夹角和相对弯曲刚度增大,既有隧道的内力显著增大;增大隧道竖向净距有利于控制既有隧道的力学响应。本文方法考虑了新建隧道掘进过程和新建隧道与既有隧道的不同相对位置,可为类似穿越工程风险防控提供理论依据。

长江三角洲浅层气地质赋存特征及其对越江隧道工程的影响

为研究我国长江中下游沿江、沿海平原赋存的浅层气不良地质及其对工程的影响,以长江崇太隧道遭遇浅层气地质为工程背景,基于长江三角洲地理地貌、沉积历史和沉积相特征,通过专项地质勘察和地球化学分析,研究区域浅层气地质的赋存特征,分析其对工程的不利影响,并提出针对性防治措施。结果表明:长江三角洲区域地层互相叠置、层序完整明显,浅海相淤泥质黏土层既是浅层气的产气层,又是封盖层,下覆厚状砂层是气体的良好储集体。隧址区具备典型的长江三角洲沉积特征,地层中赋存的浅层气属于原生甲烷型生物成因气;喷发性气体赋存于浅海相淤泥质黏土层内部的粉土、粉砂微、薄夹层中,属于未经长距离运移的自生、自储、自盖型生物成因气;隧道越江段主要穿越的厚层河口湾相细、中砂层虽具备良好的储气条件,但未见大量气体储集。从越江隧道段浅层气的赋存特征出发,虽然分析认为其对工程的影响程度有限,但在工程建设中仍不容忽视,需采取针对性预防措施以避免浅层气地质造成工程危害。

丁字及十字交叉管廊纵向地震响应分析

提出了丁字及十字交叉管廊纵向地震响应分析的一个改进广义反应位移法.该方法采用壳单元模拟管廊结构,以体现管廊横断面非对称形式的影响和地震作用下管廊交叉节点处的局部变形;采用非线性弹簧单元模拟预制企口接头,可反映管廊接头断面的非对称形式以及预制接头的力学行为.在ABAQUS有限元平台构建了典型交叉管廊的三维壳-弹簧计算模型,采用直接刚度法求解场地地震动响应,研究了在设计地震动幅值和地震波入射角度等因素影响下,丁字及十字交叉管廊的内力及变形响应特征,并以直线形管廊的地震响应为基准,给出了两类交叉节点的影响范围及内力放大情况.结果表明,相较于直线形管廊,管廊交叉节点处的内力及变形响应均出现明显的增高,其中丁字交叉管廊的地震响应略大于十字交叉管廊.安评波小震作用下,丁字及十字交叉管廊的接头基本处于功能完好状态,中震和大震作用下超出规范限值,其中大震下达到8 mm左右,约为直线形管廊的8~9倍;两类交叉管廊的内力放大系数范围约为2~6.工程抗震设计中,可根据该结果对交叉管廊的地震响应进行初步评估.不同设计地震动幅值和地震波入射角度下,两类交叉节点对管廊地震响应的影响范围约为20~35倍预制管节段长度,在实际工程中应引起重视.相关研究结果可为交叉管廊工程的抗震设计提供参考.

新建隧洞下穿爆破对公路隧道结构的影响:以温州市瓯江引水工程为例

为了探寻爆源逐步接近既有隧道情况下衬砌受爆破振动的响应规律、爆破荷载作用下的应力分布状态,结合温州市瓯海区西山隧洞工程,根据施工现场爆破监测数据和数值模拟结果对新建隧道爆破施工时相交隧道的安全性进行研究。研究结果表明,振速主要受到爆心距和装药量的影响,爆心距越小,装药量越大,振速峰值越高;爆心距决定隧道衬砌合速度峰值发生位置;衬砌合速度峰值位置同时是最大拉应力点;随爆心距的缩进,危险点从拱腰位置移动到拱脚。

大断面斋堂隧道爆破近区围岩损伤研究

爆破荷载作用下隧道爆破近区围岩损伤特性研究较少.以斋堂隧道为工程背景,通过现场声波测试和数值模拟的方法,研究了隧道围岩损伤效应及毫秒延期爆破中不同段炮孔对围岩损伤的影响.研究结果表明:隧道围岩损伤范围约为2.4 m,隧道围岩累积损伤由爆炸冲击损伤和爆破振动损伤两部分组成.隧道保留岩体根据损伤分布特征情况可划分为4个不同区域,即严重破坏区、强扰动区、弱扰动区和未扰动区.其中,严重破坏区和强扰动区主要受崩落孔VI和周边孔影响;弱扰动区中的“带状损伤”则是各个段位炮孔综合作用的结果.

考虑上浮效应的顶管施工引起下方盾构隧道响应简化分析方法

新建顶管上穿施工会引起下方既有盾构隧道纵向隆起位移,影响地铁的正常运行。大直径顶管在注浆充足或在地下水位以下顶进时上浮效应不可忽略,而目前的简化分析方法尚未考虑此效应。采用两阶段法,将既有隧道视为Pasternak地基上的Euler-Bernoulli梁,提出考虑上浮影响的土体非均匀收敛模式下,新建顶管上穿施工引起下方既有隧道响应的简化计算方法。研究表明,均匀土体收敛模式、下沉的非均匀土体收敛模式会低估顶管下方的土体自由位移、既有隧道的纵向位移响应,与工程实测数据的对比验证了所提方法的合理性。进一步参数分析表明,降低土体损失率能有效减少既有隧道竖向位移与弯矩,且土体损失率与既有隧道最大竖向位移和最大弯矩呈线性关系;既有隧道与土体的管土刚度比的增大可减小既有隧道竖向位移,但也会增大隧道管片弯矩;增大顶管与既有隧道竖向净距有利于既有隧道竖向位移与弯矩的控制,实际工程应根据既有隧道的保护要求和顶管的上覆土厚度要求选择合理的净距。

3车道瓦斯隧道通风流场及瓦斯运移规律研究

为有效进行大断面公路瓦斯隧道施工期通风降气,以古金高速公路大梁子隧道工程为依托,采用SCDM软件建立2台阶带仰拱的计算模型,使用Fluent软件进行数值模拟,揭示在不同台阶长度、风筒出风口距掌子面距离、双风筒布设形式下,隧道掌子面及附近区域的通风流场特征和瓦斯运移规律,并结合现场监测数据进行验证。研究结果表明:1)流场在通风20 min后基本稳定,上台阶和仰拱段会形成涡流阻碍瓦斯的运移、扩散和稀释,在风筒非对称布设情况下,掌子面风筒对侧的墙角处出现瓦斯积聚现象;2)隧道内通风降气效果的敏感性影响因素排序为双风筒及布设形式>风筒出风口距掌子面距离>台阶长度,建议优先采用双风筒同侧布设送风,其次调整风筒出风口距掌子面距离为20~25 m和台阶长度为15~20 m;3)采用双风筒同侧布设通风时,掌子面及附近区域风速提高、瓦斯体积分数大幅降低,且施工现场开展的送风试验与数值计算结果吻合度高,验证了双风筒同侧送风的可靠性。

穿越煤系地层隧道预留岩墙破坏力学行为与安全厚度研究

为研究穿越煤系地层隧道在瓦斯压力和地应力作用下的力学行为变化,以贵州的天成坝隧道的瓦斯煤系地层为工程案例,通过相似模型试验搭建三维试验物理模型,分别研究预留岩墙在2种不同隧道跨度下的力学行为变化,并与数值模拟相结合研究不同因素下隧道开挖岩墙厚度变化规律。结果表明:1)隧道开挖改变了围岩的原始应力状态,在隧道掌子面前方的岩墙出现应力集中,且隧道在开挖后掌子面一侧的应力卸载使竖向应力和水平应力差值最大。2)隧道所在的地质环境相同时,预留岩墙上部垂直地应力越大,隧道的开挖跨度越大,预留岩墙的厚度越小,预留岩墙发生破坏失稳的可能性越大。3)隧道开挖过程中,预留岩墙垂直应力与位移监测点竖向位移同步变化;垂直应力达到峰值时,竖向位移变形最大;随后垂直应力减小,竖向位移变形趋于稳定;垂直应力突变导致预留岩墙破坏,位移量急剧增大。4)建立不同瓦斯压力、不同围岩等级、不同隧道跨度情况下的数值计算模型,通过正交试验法,设计8种不同工况,得到不同因素组合下预留岩墙厚度的变化规律;最后通过多因素回归分析法,拟合得到最小预留岩墙厚度的计算经验公式。