Research on the design method for uniform wear of shield cutters in sand-pebble strata

During shield tunneling in highly abrasive formations such as sand–pebble strata,nonuniform wear of shield cutters is inevitable due to the different cutting distances.Frequent downtimes and cutter replacements have become major obstacles to long-distance shield driving in sand–pebble strata.Based on the cutter wear characteristics in sand–pebble strata in Beijing,a design methodology for the cutterhead and cutters was established in this study to achieve uniform wear of all cutters by the principle of frictional wear.The applicability of the design method was verified through three-dimensional simulations using the engineering discrete element method.The results show that uniform wear of all cutters on the cutterhead could be achieved by installing different numbers of cutters on each trajectory radius and designing a curved spoke with a certain arch height according to the shield diameter.Under the uniform wear scheme,the cutter wear coefficient is greatly reduced,and the largest shield driving distance is increased by approximately 47%over the engineering scheme.The research results indicate that the problem of nonuniform cutter wear in shield excavation could be overcome,thereby providing guiding significance for theoretical innovation and construction of long-distance shield excavation in highly abrasive strata.

Failure mechanism of large-diameter shield tunnels and its effects on ground surface settlements

A new technique for the analysis of the three-dimensional collapse failure mechanism and the ground surface settlements for the large-diameter shield tunnels were presented.The technique is based on a velocity field model using more different truncated solid conical blocks to clarify the multiblock failure mechanism.Furthermore,the shape of blocks between the failure surface and the tunnel face was considered as an entire circle,and the supporting pressure was assumed as non-uniform distribution on the tunnel face and increased with the tunnel embedded depth.The ground surface settlements and failure mechanism above large-diameter shield tunnels were also investigated under different supporting pressures by the finite difference method.

Parameter identification and pressure control of dynamic system in shield tunneling using least squares method

An estimation approach using least squares method was presented for identificationof model parameters of pressure control in shield tunneling.The state equation ofthe pressure control system for shield tunneling was analytically derived based on themass equilibrium principle that the entry mass of the pressure chamber from cutting headwas equal to excluding mass from the screw conveyor.The randomly observed noise wasnumerically simulated and mixed to simulated observation values of system responses.The numerical simulation shows that the state equation of the pressure control system forshield tunneling is reasonable and the proposed estimation approach is effective even ifthe random observation noise exists.The robustness of the controlling procedure is validatedby numerical simulation results.

Impact of shield tunneling on adjacent spread foundation on sandy cobble strata

The section of shield tunnel of the Chengdu Metro line passes primarily through sandy cobble strata. There are many buildings with spread foundations along the lines. Shield tunnel construction will disturb the ground, causing displacement or stress to adjacent spread foundations. Based on the similarity theory, a laboratory model test of shield tunnel driving was carried out to study the influence of shield tunnel excavation on the displace ment of adjacent spread foundation. The results show that foundation closer to the tunnel has greater displacement or settlement than that further away. The horizontal dis placement is small and is influenced greatly by the cutting face. The displacement along the machine driving direction is bigger and is significantly affected by the thrust force. Settlement occurs primarily when shield machine passes close to the foundation and is the greatest at that time. Uneven settlement at the bottom of the spread foundation reaches a maximum after the excavation ends. In a numerical simulation, a particle flow model was con structed to study the impact of shield tunnel excavation on the stresses in the ground. The model showed stress con centration at the bottom of the spread foundation. With the increasing ground loss ratio, a loose area appears in the tunnel dome where the contact force dropped. Above the loose area, the contact force increases, forming an arch shaped soil area which prevents the loose area from expanding to the ground surface. The excavation also changed the pressure distribution around spread foundation.

Risk identification and risk mitigation during metro station construction by enlarging shield tunnel combined with cut-and-cover method

Constructing a metro station by enlarging shield tunnels combined with a mining/cut-and-cover method provides a new method to solve the contradictions of construction time limits of shield tunnels and stations. As a new-style construction method, there are several specific risks involved in the construction process. Based on the test section of Sanyuanqiao station on Beijing metro line 10, and combined with the existing methods of risk identification at present, including a review of world-wide operational experience of similar projects, the study of generic guidance on hazards associated with the type of work being undertaken, and discussions with qualified and experienced staff from the project team, etc., the specific risks during the construction process of the metro station constructed by enlarging shield tunnels combined with the cut-and-cover method are identified. The results show that the specific risks mainly come from three construction processes which include constructing upper enclosure structures, excavating the soil between shield tunnels and demolishing shield segments. Then relevant risk mitigation measures are put forward. The results can provide references for scheme improvement and a comprehensive risk assessment of the new-style construction method.

Seismic reliability analysis of shield tunnel faces under multiple failure modes by pseudo-dynamic method and response surface method

In order to investigate the stability problem of shield tunnel faces subjected to seismic loading,the pseudodynamic method(P-DM)was employed to analyze the seismic effect on the face.Two kinds of failure mechanisms of active collapse and passive extrusion were considered,and a seismic reliability model of shield tunnel faces under multifailure mode was established.The limit analysis method and the response surface method(RSM)were used together to solve the reliability of shield tunnel faces subjected to seismic action.Comparing with existing results,the results of this work are effective.The effects of seismic load and rock mass strength on the collapse pressure,extrusion pressure and reliability index were discussed,and reasonable ranges of support pressure of shield tunnel faces under seismic action were presented.This method can provide a new idea for solving the shield thrust parameter under the seismic loading.

Tunnel face stability and ground settlement in pressurized shield tunnelling

An analysis of the stability of large-diameter circular tunnels and ground settlement during tunnelling by a pressurized shield was presented. An innovative three-dimensional translational multi-block failure mechanism was proposed to determine the face support pressure of large-shield tunnelling. Compared with the currently available mechanisms, the proposed mechanism has two unique features:(1) the supporting pressure applied to the tunnel face is assumed to have a non-uniform rather than uniform distribution, and(2) the method takes into account the entire circular excavation face instead of merely an inscribed ellipse. Based on the discrete element method, a numerical simulation of the Shanghai Yangtze River Tunnel was carried out using the Particle Flow Code in two dimensions. The immediate ground movement during excavation, as well as the behaviour of the excavation face, the shield movement, and the excavated area, was considered before modelling the excavation process.

盾构隧道下穿高铁路基变形影响规律及加固优化研究

为研究盾构隧道下穿高铁路基施工时对路基的影响规律,探究在隧道开挖过程中运用不同加固措施对既有高铁路基的影响程度。以西安市某地铁工程为依托,利用室内模型试验对比分析盾构隧道下穿高铁CFG桩复合路基过程中,无加固、超前管幕工法加固与地表袖阀管注浆加固3种隧道施工条件下,地表沉降值和沉降槽的空间分布规律;采用数值模拟分析验证超前管幕工法加固工况下盾构隧道下穿时,高铁路基、道床的位移变化规律。室内模型试验结果表明:盾构隧道施工中采用管幕工法加固后复合地基正上方的地表沉降最大值减小28.6%,采用袖阀管注浆加固后减小18.0%,并且采用两种加固措施后的CFG桩最大附加轴力均减小20%以上。因此,在隧道掘进过程中采用一定加固措施,可改善围岩稳定性,其中管幕工法加固效果更为显著。数值模拟分析表明:采取管幕工法加固施工与不采取加固措施相比,路基最大沉降量减少33.78%,道床最大沉降量减少45.08%。因此,管幕工法加固能够有效减小对既有高铁路基的影响。

未确知测度理论在盾构下穿既有隧道安全风险评价中的应用

盾构下穿既有隧道工程施工通常存在较大风险,为了对风险等级做出准确有效的评价,提出了基于未确知测度理论的盾构下穿既有隧道安全风险评价模型。首先,通过对相关规范和现有文献的研究,并结合盾构下穿隧道施工的特点,构建了盾构下穿既有隧道安全风险评价指标体系,包括盾构掘进参数、新建隧道条件、既有隧道条件、地质条件和施工管理条件5个一级指标,以及掘进速度、掘进推力、注浆压力等19个二级指标;其次,将综合安全风险划分为5个等级,并明确了各指标的等级划分标准;然后基于熵权-未确知测度理论构建盾构下穿既有隧道安全风险评价模型,采用熵权法确定指标权重,根据未确知测度理论构建各指标的单指标未确知测度函数,将各指标数据值代入单指标未确知测度函数中得到单指标测度评价矩阵,结合指标权重和单指标测度评价矩阵计算得到多指标测度评价向量,依照置信度准则确定安全风险等级;最后,将提出的模型应用于实际盾构下穿既有隧道工程中,对其进行安全风险等级评价。结果表明,模型评价结果与实际风险等级一致,并通过与模糊层析分析法对比验证了所提模型应用于工程实践的有效性,研究结果可为实际施工安全管理提供决策支持。

富水环境下盾构隧道最小覆盖层厚度设计与计算方法综述

覆盖层厚度设计是建设水下盾构隧道的关键环节之一。覆盖层厚度过小,围岩在施工扰动下易发生失稳,引起塌方、突水等灾害;覆盖层厚度过大,则会对工程预算与工期提出更高的要求。通过文献调研,结合已有实际水下盾构隧道工程案例,对现有合理覆盖层厚度设计和计算方法进行研究与总结。得出:1)水下盾构隧道设计方法主要分为理论分析法和数值模拟法;2)根据隧道结构稳定分析侧重点不同,理论分析法可分为考虑抗浮稳定性设计方法和考虑掌子面稳定性设计方法;3)现阶段水下盾构隧道合理覆盖层厚度的设计方法多基于数值模拟和理论分析,对实际工程工况进行一定程度的简化,且未能全面考虑复杂建(构)筑物环境、施工工艺以及隧道自身结构特性的影响,覆盖层厚度的研究深度和设计方法的适用性仍需进一步提高;4)目前,富水环境下盾构隧道最小覆盖层厚度的研究内容已较为丰富,但与实际工程的结合较为困难。未来的研究应进一步考虑施工的经济性、施工流程、复杂环境条件、结构寿命及智慧建造平台等方面。

反拉式顶管法施工联络通道对地铁盾构隧道力学性能影响

为探究采用反拉式顶管法施工盾构隧道联络通道过程中主隧道的力学响应机制,依托北京地铁某盾构区间,建立模拟联络通道施工过程的有限元模型,通过与现场监测数据对比验证模型的准确性。继而研究联络通道施工对主隧道管片间错台位移、特殊管片应力及变形、螺栓受力的影响,并分析反力模式对主隧道管片力学特性的影响。结果表明:1)始发管片破除对主隧道力学性能影响较大,随着联络通道进一步开挖,主隧道受力和变形缓慢增大。2)管片间最大错台位移为1.17 mm,发生在特殊管片与普通管片接缝底部。特殊管片最大拉应力为18.6 MPa,出现在开口的顶、底部;最大压应力为27.0 MPa,出现在开口的腰部;最大横向扩张位移和竖向收敛位移分别为2.13 mm和4.56 mm。主隧道管片环间螺栓最大拉应力为213 MPa。3)背推式反力模式更利于控制开口处的横、竖向位移,反拉式反力模式更利于控制开口对面管片应力变形及其接缝处错动位移。

盾构隧道缓和曲线段管片组合轴线拟合计算方法

盾构隧道在缓和曲线部分存在管片拼装问题,因缓和曲线线型复杂,管片拼装点位多变,一直是施工过程中的一个难题。基于错缝拼装要求与楔形管片特点,提出一种在平面范围内,利用循环计算与误差控制的条件判定,综合比选标准环与楔形环组合,完成每环管片拼装施工,最终拟合出既满足规范与控制指标,又可保证线型较为均匀的管片拼装轴线的管片施工设计方法与验证方法。并根据实际工程需要,提出最大允许偏差控制方法和缓圆点附近的管片拼装优化措施,结合珠海市珠机线湾仔北站—湾仔站区间盾构隧道实例,证明了此方法的准确性与适用性,为缓和曲线上控制管片拼装质量提供理论依据。

盾构法隧道开挖面稳定性下的多目标优化研究

盾构法隧道开挖过程中开挖面稳定性保持非常重要,开挖面稳定性下提升工程进度、保障工程质量等目标具有重要的工程意义。目前,针对开挖面稳定性下的多目标优化控制的研究不足。选择掘进效率作为工程进度的指标,选择掘进过程引起的最大地表沉降作为工程质量指标。采用分层序列法和NSGA-II多目标优化算法,将盾构开挖面稳定作为第一层优化目标,工程进度与工程质量作为第二层优化目标,研究盾构开挖面稳定下多目标优化。在一段连续穿越堤坝、空地、敏感建筑三个场景的施工隧道中应用本研究方法,结果表明,优化后的盾构推力维持在上下限区间内,提高了施工效率和减少了地表沉降。本文方法能够根据实际工况自适应的调整和优化控制策略,提高了在实际工程中的适应性和灵活性。为类似盾构隧道工程提供了参考和指导。

波流耦合影响下分层海床隧道周围砂土渗流孔压及液化分析

目前针对波浪作用下海底盾构隧道周围渗流场的既有理论研究一般将衬砌考虑为不透水介质,较少考虑隧道衬砌的渗透性,尤其是较少考虑波浪与海流共同作用对隧道的影响。此外,既有理论一般将海床视为均质且各向同性工况,忽略了实际情况下分层海床的影响。首先,基于波流共同作用下的海床表面的动力边界条件,采用传递-反射矩阵法得到波流共同作用下自由分层海床的孔压响应;其次,采用镜像法建立了由于隧道存在引起的砂土摄动压力控制方程,并利用砂土与衬砌间渗流连续条件获得了该方程的Fourier级数展开解析解;接着,采用叠加原理得到了波流共同作用下分层海床中隧道周围砂土的渗流压力响应及液化判定解答。最后,将理论解析解与数值结果及已有的试验结果进行对比,获得了较好的一致性。此外,针对海床渗透性和隧道衬砌渗透性进行了影响因素分析。结果表明:海流顺流会增大海床中的孔压和液化程度,逆流会减小海床中的孔压并抑制海床的液化,且流速相同时海床对逆流响应的相对差异总体上也大于顺流;当分层海床上层渗透系数较大时(k+s>1×10^(-2)m/s),海床整体孔压较大,且第一次分层处孔压变化明显;当隧道衬砌渗透系数较小时(k+l<1×10^(-6)m/s),隧道对超静孔隙水压在海床内传播“阻挡”效应明显。

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。

地铁盾构隧道管片安全状态评价

为准确评价地铁盾构隧道管片安全性,基于对地铁盾构隧道管片结构病害的形成机制分析,从管片变形、渗漏水、裂缝、拱顶脱落、材料劣化5个方面建立评价指标体系,划分管片结构安全状态评价等级,构建未确知测度函数,通过基于熵值改进的G2法确定权重,根据置信度识别准则判断风险等级,并将模型应用于某地铁盾构隧道,对其管片结构进行安全状态评价。研究结果表明:采用未确知测度理论能够准确评价隧道管片的安全等级,结果准确,实用性强。

基于TJS工法的盾构隧道运营变形控制

开展隧道洞内全方位微扰动高压喷射注浆(TJS)工法对运营隧道变形控制的研究.基于典型区间运营隧道实测数据,采用Plaxis 3D有限元数值模拟软件分析TJS工法横断面布置中桩长、打设角度、桩径对隧道加固效果的影响,通过在隧道底部打设局部垫层的方法优化TJS工法.结果表明,桩长越长、角度越接近40°、桩径越大,对隧道沉降的控制效果越明显. TJS工法加固后的隧道地表沉降减少16.38 mm,水平收敛变形为未加固时的42.87%.局部垫层能够显著提升TJS桩的加固效果,“两侧短中间长”的布置能够兼顾加固效果和降低施工成本.

基于移动激光扫描的地铁隧道渗漏水定位及快速检测方法

渗漏水是地铁隧道最主要的病害之一,也会导致其他结构病害,开展地铁隧道渗漏水病害检测方法研究具有重要意义。本文聚焦于地铁隧道渗漏水问题,提出了一种基于移动激光扫描点云数据的渗漏水定位及检测方法。首先,结合移动激光扫描检测方法,开展了隧道精确定位方法研究。然后,对YOLOv7模型进行了改进,引入了ConvNeXt网络和CBAM模块以使模型更好地捕获多尺度、多抽象级别的特征,增强对渗漏水关键特征的关注;使用GIoU Loss损失函数,使模型能够更好地处理不完整渗漏水框;预测时使用Soft-NMS加权平均的方法,保留更多的边界框,从而提高检测精度。结合在重庆地铁获取的激光扫描数据构建的盾构法和矿山法隧道渗漏水数据集,验证了本文方法的高效性和稳健性。消融试验表明,本文方法相较于基线模型在不同数据集上均取得了显著的性能提升,在盾构法数据集中,准确率P提升了8.1%,召回率R提升了4%;在矿山法数据集中,准确率P提升了8.6%,召回率R提升了6.8%。同时,与主流目标检测算法,如Faster RCNN(Swin)、Faster RCNN(ConvNeXt)、YOLOv8对比,本文方法在精度和速度方面都表现出优势。最后,本文展示了部分隧道渗漏水的定位与检测结果,以验证本文方法的实用性。

内外水力交互下浅埋带压盾构隧道水土压力计算模型

针对浅埋有压盾构隧道内外水力交互渗流下引起的松动水土压力变化,基于修正镜像法获得了考虑内水压的地层渗流场分布与水力梯度。随后基于考虑松动区内部应力分布的修正Terzaghi公式给出了考虑隧道内水压下的松动区任意位置的水土压力解,并与数值模拟结果进行了对比验证。主要结论如下:采用圆弧拱和抛物线拱的主应力轨迹线能够有效描述隧顶松动区应力分布情况;当地层渗透系数与衬砌渗透系数比值小于1000时,内压水头大小对水土压力的影响显著;内压水头的增加将减小松动区有效应力,引起上覆土体卸载,同时引起隧顶松动区总应力增大,表明该范围内孔隙水压的增长对水土压力的变化占据主导作用;5参数正交分析结果的线性回归分析结果表明隧道埋深和半径对土压力有显著的正向影响,土体摩擦角和黏聚力均表现为负向影响。在相对低渗透地层条件下,内压水头对隧顶有效应力和总应力分别表现为显著的负向和正向影响。

上软下硬地层盾构开挖面稳定性计算模型

针对上软下硬地层失稳特点,在假定开挖面附近因土体失稳而由软硬地层分界线先向上诱发形成部分楔形体、再呈倒圆台状向地面发展的基础上,提出开挖面稳定性计算模型。先基于极限平衡法提出部分楔形体计算模型;再依据修正后的楔形体计算模型,分别计算上覆土压力和开挖面前方部分楔形体的受力;最后依托青岛地铁6号线某区间工程开展数值模拟,验证理论模型。结果表明:不同支护应力比条件下的土体变形范围有所差异,土体变形主要发生在开挖面前方和上方并呈泡状延伸;数值模拟得到的开挖面失稳形态基本符合理论计算模型的假定形状;理论计算得到该例盾构开挖面极限支护应力比为0.21,与数值模拟的误差率为5%;当开挖面支护力小于极限支护力时,上软下硬地层开挖面水平变形会突然迅速增大;开挖面附近的岩土体变形主要发生在上部软弱部分,最大水平位移出现在上部软土中心附近,开挖面上土体最大水平位移与开挖面上方地表最大竖向位移间的相关性较高,两者变形规律类似。