Evaluation and prediction of earth pressure balance shield performance in complex rock strata:A case study in Dalian,China

This research explores the potential for the evaluation and prediction of earth pressure balance shield performance based on a gray system model.The research focuses on a shield tunnel excavated for Metro Line 2 in Dalian,China.Due to the large error between the initial geological exploration data and real strata,the project construction is extremely difficult.In view of the current situation regarding the project,a quantitative method for evaluating the tunneling efficiency was proposed using cutterhead rotation(R),advance speed(S),total thrust(F)and torque(T).A total of 80 datasets with three input parameters and one output variable(F or T)were collected from this project,and a prediction framework based gray system model was established.Based on the prediction model,five prediction schemes were set up.Through error analysis,the optimal prediction scheme was obtained from the five schemes.The parametric investigation performed indicates that the relationships between F and the three input variables in the gray system model harmonize with the theoretical explanation.The case shows that the shield tunneling performance and efficiency are improved by the tunneling parameter prediction model based on the gray system model.

Discrete element simulation of mechanical characteristic of conditioned sands in earth pressure balance shield tunneling

The discrete element method (DEM) was used to simulate the flow characteristic and strength characteristic of the conditioned sands in the earth pressure balance (EPB) tunneling. In the laboratory the conditioned sands were reproduced and the slump test and the direct shear test of the conditioned sands were implemented. A DEM equivalent model that can simulate the macro mechanical characteristic of the conditioned sands was proposed,and the corresponding numerical models of the slump test and the shear test were established. By selecting proper DEM model parameters,the errors of the slump values between the simulation results and the test results are in the range of 10.3%-14.3%,and the error of the curves between the shear displacement and the shear stress calculated with the DEM simulation is 4.68%-16.5% compared with that of the laboratory direct shear test. This illustrates that the proposed DEM equivalent model can approximately simulate the mechanical characteristics of the conditioned sands,which provides the basis for further simulation of the interaction between the conditioned soil and the chamber pressure system of the EPB machine.

Feasibility study of tar sands conditioning for earth pressure balance tunnelling

This paper presents the results of laboratory test on the feasibility of soil conditioning for earth pressurebalance （EPB） excavation in a tar sand, which is a natural material never studied in this respect. Thelaboratory test performed is based on a procedure and methods used in previous studies with differenttypes of soils, but for this special complex material, additional tests are also conducted to verify particularproperties of the tar sands, such as the tilt test and vane shear test usually used in cohesive materials, anda direct shear test. The laboratory test proves that the test procedure is applicable also to this type of soiland the conditioned material can be considered suitable for EPB excavations, although it is necessary touse a certain percentage of fine elements （filler） to create a material suitable to be mixed with foam. Thetest results show that the conditioned material fulfils the required standard for an EPB application.

Optimal arrangement for pressure measurement points in working chamber of earth pressure balance shield

In order to exactly provide scientific basis for pressure dynamic balance control of working chamber of earth pressure balance shield (EPBS),study on optimal arrangement of pressure measurement points in working chamber was conducted. Based on mathematical description of optimal arrangement for pressure measurement points,fuzzy clustering analysis and discriminant analysis were used to divide pressure regions of nodes on bulkhead. Finally,the selection method of optimal measurement points was proposed,and by selecting d6.28 m EPBS as study object,the case study was conducted. By contrast,based on optimal arrangement scheme of pressure measurement points,through adopting weighted algorithm,the absolute error mean of equivalent pressure of working chamber is the smallest. In addition,pressure curve of optimal arrangement points presents parabola,and it can show the state of pressure distribution on bulkhead truly. It is concluded that the optimal arrangement method of pressure measurement points in working chamber is effective and feasible,and the method can provide basis for realizing high precision pressure control of EPBS.

Earth pressure balance control for EPB shield

This paper mainly deals with the critical technology of earth pressure balance (EPB) control in shield tunneling. On the assumption that the conditioned soil in the working chamber of the shield is plasticized, a theoretical principle for EPB control is proposed. Dynamic equilibrium of intake volume and discharge volume generated by thrust and discharge is modeled theoretically to simulate the earth pressure variation during excavating. The thrust system and the screw conveyor system for earth pressure control are developed based on the electro-hydraulic technique. The control models of the thrust speed regulation of the cylinders and the rotating speed adjustment of the screw conveyor are also presented. Simulation for earth pressure control is conducted with software AMESim and MATLAB/Simulink to verify the models. Experiments are carried out with intake control in clay soil and discharge control in sandy gravel section, respectively. The experimental results show that the earth pressure variations in the working chamber can be kept at the expected value with a practically acceptable precision by means of real-time tuning the thrust speed or the revolving speed of discharge system.

Deviation correction strategy for the earth pressure balance shield based on shield–soil interactions

The control system presently used in shield posture rectification is based on driver experience,which is marginally reliable.The study of the related theory is flawed.Therefore,a decision-making approach for the deviation correction trajectory and posture rectification load for an earth pressure balance(EPB)shield is proposed.A calculation model of posture rectification load of an EPB shield is developed by considering the interactions among the cutter head,shield shell,and ground.The additional position change during the shield attitude correction is highlighted.The posture rectification loads and shield behaviors results can be solved by the proposed method.The influences of the stratum distribution(i.e.,bedrock height in the upper-soft and lower-hard strata)on shield behaviors and posture rectification loads are analyzed.Results indicated that the increase of pitch angle in the upper-soft and lower-hard strata causes a sharp rise in vertical displacement.The bedrock height increases the magnitudes of the required posture rectification moments when hr/D>0.5.For a tunnel with hr/D≤0.5,the variation of hr/D has little effect on the posture rectification moments.Finally,the posture rectifying curves based on the theoretical model are compared with the target ones based on the double circular arc interpolation method.The required results can be obtained regardless of the soil–rock compound stratum distribution.The maximum rectification moment in the rock layer is almost 12.6 times that in the soil layer.Overall,this study provides a valuable reference for moment determination and the trajectory prediction of posture rectification in compound strata.

Soft ground tunnel lithology classification using clustering-guided light gradient boosting machine

During tunnel boring machine(TBM)excavation,lithology identification is an important issue to understand tunnelling performance and avoid time-consuming excavation.However,site investigation generally lacks ground samples and the information is subjective,heterogeneous,and imbalanced due to mixed ground conditions.In this study,an unsupervised(K-means)and synthetic minority oversampling technique(SMOTE)-guided light-gradient boosting machine(LightGBM)classifier is proposed to identify the soft ground tunnel classification and determine the imbalanced issue of tunnelling data.During the tunnel excavation,an earth pressure balance(EPB)TBM recorded 18 different operational parameters along with the three main tunnel lithologies.The proposed model is applied using Python low-code PyCaret library.Next,four decision tree-based classifiers were obtained in a short time period with automatic hyperparameter tuning to determine the best model for clustering-guided SMOTE application.In addition,the Shapley additive explanation(SHAP)was implemented to avoid the model black box problem.The proposed model was evaluated using different metrics such as accuracy,F1 score,precision,recall,and receiver operating characteristics(ROC)curve to obtain a reasonable outcome for the minority class.It shows that the proposed model can provide significant tunnel lithology identification based on the operational parameters of EPB-TBM.The proposed method can be applied to heterogeneous tunnel formations with several TBM operational parameters to describe the tunnel lithologies for efficient tunnelling.

联络通道施工盾构机接收对已建盾构隧道影响试验研究

联络通道机械法施工中盾构机接收对已建盾构隧道受荷变形影响机制暂不明确问题,通过设计1∶10的缩尺模型试验,开展了联络通道机械法施工中盾构机接收对已建盾构隧道影响试验研究。试验结果分析表明:联络通道机械法施工时,盾构机开挖面附加水平土压力将导致接收端已建盾构隧道对侧的土压力在中部有显著的增大,而两端则减小,即导致顶推对侧发生了水平被动土拱现象;在中间附加水平土压力作用下,隧道在中间发生了显著的竖椭圆变形,而在两端则发生了一定的横椭圆变形;隧道中间发生竖椭圆变形对上下地层形成挤压,在竖向上同样形成了被动土拱现象;隧道纵向挠曲变形时出现了一定的反弯现象。盾构隧道作为地层中的管状结构物,在地层中纵向变形分析时需要考虑横断面变形的影响。

基于泥水平衡盾构掘进参数的PSO-BP神经网络掘进地层识别模型研究

为解决泥水平衡盾构机在掘进时无法准确地实时识别掘进地层的问题,以珠三角水资源配置工程为例,研究泥水平衡盾构机的盾构推力、掘进速度、刀盘转速、刀盘扭矩在不同地层下的变化规律,提出基于掘进参数的PSO-BP神经网络掘进地层识别方法,建立盾构推力、掘进速度、刀盘转速、刀盘扭矩4种掘进参数为输入集,地层编码为输出集的地层识别模型。工程数据的验证结果表明,该模型在珠三角水资源配置工程数据集上的掘进地层的识别准确率达99.07%,PSO-BP神经网络算法的识别准确率明显高于BP、RF、RBF、CNN等机械学习算法。

考虑推进过程的土压平衡盾构渗流场解析解及喷涌判别

考虑推进过程中盾构正面附加推力产生的超孔隙水压力,用解析的方法分析了盾构喷涌问题。将土舱渗流场划分成两个区域,利用叠加原理和分离变量法得到土舱水头显式级数解,将螺旋输送机内流场视为一维渗流,通过土舱与螺旋输送机交界面的连续条件确定盾构渗流场解析解。通过数值模拟结果验证了解的正确性,并进行了参数分析。参数分析表明:正常掘进状态下的盾构推力波动频率与渣土固结系数比值近似为0.1~10 m^(-2),可对应于渗透系数10^(-3)~10^(-5)cm/s,当比值大于20 m^(-2),可以忽略超孔隙水压力的影响,比值小于0.01 m^(-2)时,水压力分布近似稳态渗流状态,但比值在1 m^(-2)附近时,超孔隙水压力将存在显著的影响。结合已有的喷涌研究,给出了典型盾构在不同推力波动频率与土体固结系数比值下的临界渗透系数。通过对盾构喷涌实例进行对比,证明了解析解的喷涌判别是有效的。

土压盾构非满舱掘进时压缩空气与地层适应性分析

针对气压辅助工法应用越来越多工程实践,基于Geostudio Air/w建立的气-水-固耦合数值计算模型,探讨了不同盾构隧道顶部埋深、上覆闭气层厚度、地层性质以及盾构压力舱空舱高度对开挖面渗气量的影响。结果表明:分析广州地铁21号线某区间土压盾构气压辅助工法的应用案例,压缩空气渗气量控制在1.2 m^(3)·min^(-1)内,在开挖面建立稳定的支护压力,确保盾构掘进达到微扰动控制水平;闭气能力强的粉质黏土和黏土地层土压盾构掘进时,通过向压力舱注入少量压缩空气可以更好的保持开挖面支护压力的稳定;渗透系数较大、地质分布不均的砂卵石、上软下硬地层,难以进行满舱掘进时,可根据隧道埋深和上覆闭气层厚度来选择合适的空舱高度,确保压缩空气逃逸量小于产气量;土压盾构穿越渗透性地层,上覆闭气层厚度在10.0 m以上、或埋深大于28.0 m时,压缩空气逃逸量较少,也不易发生压缩空气逃逸冒顶。

滇中引水隧洞砾质土地层盾构渣土饼化控制技术

砾质土地层盾构掘进时,容易发生盾构刀盘结泥饼现象,须对渣土改良参数进行合理优化,以降低结泥饼风险。依托滇中引水龙泉倒虹吸盾构隧洞工程,首先分析砾质土地层盾构结泥饼风险以及分散型泡沫剂发泡性能,然后结合坍落度试验和界限含水率试验探究分散型泡沫改良渣土的塑流性特征,提出砾质土地层盾构渣土饼化风险控制技术,并通过现场跟踪试验对饼化控制技术进行验证。研究结果表明:(1)分散型泡沫剂发泡倍率随着浓度增加而增长,随发泡压力增加呈先增后减趋势,在发泡压力为0.3 MPa时获得最佳发泡倍率;(2)分散型泡沫剂能有效改善砾质土渣土塑流性,降低砾质土渣土液塑限,进而降低渣土饼化风险;(3)提出砾质土渣土改良参数建议值并应用于实际工程,应用后盾构总推力、扭矩明显降低且离散程度减小,盾构推进速度明显提升,验证了砾质土地层盾构渣土饼化控制技术的合理性。

软土地层盾构掘进参数分析及掘进速度预测

依托佛山地铁3号线逢沙站—创意园站区间隧道工程,通过现场实测数据,详细分析了土压平衡盾构穿越软土地层时盾构掘进参数内在变化规律,并建立了掘进速度预测模型。首先,对盾构掘进参数进行数理统计分析,对各掘进参数的分布进行正态性检验;其次,进行Pearson相关性分析,找出线性相关性较强参数间变化规律;再次,利用基于互信息的特征选择算法,筛选与掘进速度非线性相关性较高的参数变量;最后,分别建立随机森林回归预测模型和基于遗传算法优化BP神经网络预测模型,对掘进速度进行预测。研究结果表明:在软弱地层盾构隧道工程中,通常采用较低的刀盘转速、刀盘扭矩及较高的掘进速度、贯入度、盾构总推力、土仓压力;掘进速度等参数均通过了采用K-S检验法的正态性检验;掘进速度与贯入度存在极强相关性关系;基于遗传算法优化BP神经网络预测模型的预测精度略优于随机森林回归预测模型,随机森林回归预测模型在测试集中的平均绝对误差、均方根误差、拟合优度分别为4.055、5.038、0.871,而基于遗传算法优化BP神经网络预测模型分别为0.822、1.244、0.991。

青岛地铁土压平衡盾构碎石土改良方法研究

盾构在碎石土地层掘进时经常面临着地层渗透性强、刀盘扭矩大、刀具磨损严重等诸多困难。为解决上述施工难题,以青岛地铁4号线典型的碎石土地层为研究对象,首先通过颗粒筛分、LCPC试验和渗透性试验评价了碎石土的基本特性,结合传统的砂土和黏性土改良方案设计了5组碎石土改良配比方案,对不同配比方案进行坍落度试验、渗透性试验和直剪试验,分析了不同改良指标碎石土的流塑性、渗透性及抗剪力学特性,根据实际工程中盾构刀盘扭矩的变化情况验证了泡沫与聚合物组合改良的最佳方案。研究表明:7%浓度泡沫与5%浓度聚合物配比的改良剂能够有效降低碎石土的渗透系数,同时起到降低刀盘扭矩的作用。

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。

土压平衡盾构施工引起地面变形研究的评述

[目的]土压平衡盾构施工过程中会不可避免地产生土体扰动,引起地层变形,进而对周围建筑环境产生不利影响,开展土压平衡盾构施工引起地层变形的研究具有重要意义。[方法]通过整合各类相关文献,以施工各环节的联系为中心进行研究。阐明了土压平衡盾构施工工作机理,从隧道几何因素、土层地质条件和盾构掘进参数三方面研究地面变形诱因。论述了土压平衡盾构施工引起地面变形的预测方法,并分析了各方法的适用性与优缺点。以变形诱因和变形预测为基础,列举了土压平衡盾构施工致地面变形的控制措施。指出了土压平衡盾构施工研究中存在的不足,并对土压平衡盾构施工未来发展方向进行了展望。[结果及结论]土压平衡盾构施工引起地面变形的诱因为隧道几何因素、土层地质条件和盾构掘进参数。土压平衡盾构施工引起地面变形的预测方法有经验公式法、理论解析法、有限单元与有限差分的数值模拟法,模型试验法、人工智能法。基于对地面变形的监测,不断调整施工中的盾构参数,是目前控制土压平衡盾构地面变形的有效方法。

考虑温度效应的盾构刀盘黏附试验及堵塞防治

土压平衡盾构在黏性地层掘进时易产生刀盘结泥饼、堵塞等问题,不仅会导致排渣不畅降低掘进效率,并且频繁的开仓处理会增加工程风险,而掘进会产生大量热量影响土体黏附性。采用自主研发的刀盘旋转黏附试验系统,探究刀盘温度与含水率、黏土含量、黏土类型等因素联合作用下刀盘黏附效果,并分析了泡沫剂、抗黏剂在不同掺入比下堵塞防治效果。研究结果表明:温度升高会使得旋转扭矩与刀盘表面的土体黏附量降低,但会加速黏土硬化;土体含水率、黏土含量对于扭矩影响趋势相反,但对黏附量影响规律相同,随着土体含水率或黏土含量增加,黏附量先增加后降低,含水率在20%、黏土含量在30%时黏附性最强;膨润土比高岭土黏附性更强;土体含水率、黏土含量与黏土类型对于黏附量的影响可以使用稠度指数进行表征,随着稠度增加黏附量会出现先增加后降低的趋势,稠度指数在0.50~0.75时土体黏附性最强,低稠度指数土体对温度敏感性更强;单独添加泡沫剂会降低土体黏附量,但在注入比为70%时,仍存在大量土体黏附;使用泡沫剂+抗黏剂联合改良在注入比为50%时改良效果较好,继续增加注入比对土体改良效果影响较小。研究成果对于评估黏性地层土压平衡盾构掘进堵塞风险与黏性土渣土改良方案选择具有一定的指导意义。

复杂环境下城际铁路大直径双模盾构选型技术及应用

为研究复杂地质环境下大直径双模盾构选型技术及应用效果,以深大城际机场东站—黄麻布站区间为依托,首先分析了该区段的工程重难点和施工风险,结果表明:该区间需穿越长距离硬岩地层和部分软土地层,下穿多处重要建构筑物和穿越多条构造破碎带和节理密集带,施工风险高、难度大。因此,为兼顾盾构机在硬岩地层的掘进效率和软土及不良地质条件下的地层稳定,综合选用EPB(earth pressure balance)/TBM(tunnel boring machine)双模盾构机,并根据施工重难点对盾构机结构和功能系统进行了针对性设计。最终,对该盾构的现场工程应用进行了效果评价。结果表明:所选的EPB/TBM双模盾构能较好地满足工程需求,确保了盾构机掘进的安全性和高效性。研究成果可为其他类似条件下的双模盾构机选型提供参考和指导。

富水砂层土压平衡盾构渣土改良技术研究

富水砂层土体具有流塑性差、渗透性强的特点,土压平衡盾构施工时易造成排土困难和喷涌事故。针对西安地铁10号线穿越富水砂层的土压平衡盾构工程,采用膨润土泥浆和泡沫剂改良盾构渣土,提出了改良渣土流塑性的评价方法,基于其流塑性和渗透性确定最佳改良方案,为工程提供借鉴和参考。结果表明:(1)当改良渣土塌落后无开裂或坍塌、塌落形状为梨形、塌落度为180~210 mm、塌落渣土与地面接触角θ为0°~90°时,流塑性合适,此时改良渣土的渗透系数于90 min内稳定在10-5cm/s,满足工程要求;(2)最佳改良方案为:渣土、膨润土、水三者质量比保持在200∶1∶40~200∶1.5∶44之间,泡沫剂溶液体积比浓度为2%,泡沫注入比为6%。

土压平衡盾构掘进高瓦斯水工隧洞的HSP法超前地质预报

针对土压平衡盾构法掘进高瓦斯隧洞的超前地质预报技术难题,在讨论隧洞开挖方法与瓦斯潜在逸散的基础上,采用HSP预报方法进行高瓦斯盾构掘进施工超前地质预报。结果表明:HSP通过盾构破岩土震源可以获得较好的围岩强反射区域信号,对掌子面前向100 m、径向2倍洞径范围内的断层破碎带、溶洞、软弱夹层、孤石(规模均为等效直径≥2 m)探测准确率≥80%,异常体定位误差≤3 m;通过综合预判前方地质构造及瓦斯状态,进而确定选取常压作业开仓检查及换刀的位置,大幅降低了开仓检查和换刀作业风险,为久隆水库关门山充水隧洞奠定了安全基础,也可为今后类似工程提供借鉴。