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.

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.

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.

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。

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。

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%。

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。

大直径土压平衡盾构隧道下穿既有高速公路施工影响分析

通过对大直径土压平衡盾构隧道下穿既有高速公路的施工影响进行分析,研究了当前阶段高速公路变形沉降控制标准和采用不同加固措施情况下既有高速公路施工影响变化。研究结果表明,在未加固工况中路基变形的最大值为28.6mm,加固工况中路基的沉降变形最大值为17.3mm。对比分析表明,洞内的注浆加固对于地表的沉降变形控制效果是极为显著的,所以在盾构隧道开挖过程中对于盾构隧道洞内进行注浆加固十分必要。

地铁盾构洞内盾尾刷更换技术研究

土压平衡盾构穿越承压水、透水地层时,盾尾刷会出现严重磨损,止水效果变差,对盾构隧道的掘进质量、安全等造成严重影响。因此,盾尾刷的快速更换对施工安全和工程质量至关重要。徐州地铁6号线一期工程市紫区间右线掘进过程中,通过洞内更换盾尾刷技术进行研究,提出土压平衡盾构机掘进期间进行安全、高效的洞内盾尾刷更换技术措施。结果表明,洞内快速更换盾尾刷安全快速可行。

Experimental study on workability and permeability of sandy soils conditioned with thickened foam

Water spewing and muck plugging often occur during earth pressure balance(EPB)shield machines tunnelling in water-rich sandy strata,even though the conventional foam has been employed to condition sandy soils.In this study,a novel thickened foaming agent suitable for EPB shield tunnelling in water-rich sandy strata is developed.In contrast to conventional foam-conditioned sands,the thickened foam-conditioned sand has a low permeability due to the consistent filling of soil pores with the thickened foam,and the initial permeability coefficient decreases by approximately two orders of magnitude.It also exhibits a suitable workability,which is attributed to the enhanced capability of the thickened foam to condition sandy soils.In addition,the effect of concentration on the stability of the foam is explained by the Gibbs-Marangoni effect,and conditioning mechanisms for the thickened foam on sands are discussed from the evolution of foam bubbles.

土压平衡式盾构用主驱动密封气动压力控制系统及其控制方法

传统土压平衡式盾构机主驱动密封压力控制采用一种油气混合压力控制装置,该装置承压能力不超过0.6 MPa。在操作过程中需要技术人员实时调节,对人员操作要求较高,存在误操作等安全风险,严重时会导致掌子面塌陷、主驱动密封失效、主轴承损坏等严重后果。为解决这一问题,设计了一种土压平衡式盾构用主驱动密封气动压力控制系统及其控制方法。该系统根据土压平衡式盾构机土仓压力的变化自动调节主驱动密封腔压力,并将主驱动密封的最大承压能力提高至0.8 MPa,显著降低人员操作安全风险。该系统对需高承压盾构施工的设备制造及操作有较强的指导意义。

大直径土压盾构机下穿超浅覆土河道施工关键技术

采用土压平衡盾构机下穿既有河道是近年来土压盾构机技术研究探索的重要方向,本文通过借助宁芜铁路改造工程盾构段的工程实际,详细阐述了大直径土压平衡盾构机在下穿极浅覆土河道时遇到的技术难题,并给出了适应性的河道加固解决方案和针对性措施。研究表明:针对河道进行分批次分步围堰加固,是保证盾构安全高效穿越河道的关键技术措施;大直径土压盾构在下穿河道时有针对性地及时调整掘进参数是超浅覆土施工的必要措施,相关处理措施可为该类工程提供参考借鉴。

花岗岩基岩凸起地层盾构施工新认识

以基岩凸起为代表的软硬不均地层对盾构施工有很大影响,特别是在市区施工受环境限制无法采用常规手段进行预破碎的情况下,盾构机能不能穿越,如何安全穿越基岩凸起成为困扰工程技术人员的重大难题。以厦门地铁2号线五缘湾南站—五缘湾站区间盾构通过长80m未预破碎的极高强度花岗岩基岩凸起为背景,分析基岩凸起的地质构成及其对盾构施工带来的危害,提出了针对性的解决措施并成功实践。

富水地层土压平衡盾构施工方法及管理措施

隧道开挖是隧道施工中常见的作业之一,其施工方法对隧道施工具有重要影响。在实际作业环节中,一些地区的地质较为特殊,含有较多的水分,一定程度上影响隧道施工的落实。土压平衡盾构施工方法作为专业的施工方式,通过先进的盾构机实现掘进作业,规避富水地层对施工产生的影响。本文从富水地层入手,探讨富水地层土压平衡盾构施工方法,分析其施工难点。在此基础上,对该施工方法进行详细分析,保证施工作业的落实。

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.

Real-time analysis and prediction of shield cutterhead torque using optimized gated recurrent unit neural network

An accurate prediction of earth pressure balance(EPB)shield moving performance is important to ensure the safety tunnel excavation.A hybrid model is developed based on the particle swarm optimization(PSO)and gated recurrent unit(GRU)neural network.PSO is utilized to assign the optimal hyperparameters of GRU neural network.There are mainly four steps:data collection and processing,hybrid model establishment,model performance evaluation and correlation analysis.The developed model provides an alternative to tackle with time-series data of tunnel project.Apart from that,a novel framework about model application is performed to provide guidelines in practice.A tunnel project is utilized to evaluate the performance of proposed hybrid model.Results indicate that geological and construction variables are significant to the model performance.Correlation analysis shows that construction variables(main thrust and foam liquid volume)display the highest correlation with the cutterhead torque(CHT).This work provides a feasible and applicable alternative way to estimate the performance of shield tunneling.

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.

卵石地层土压平衡盾构撕裂刀布置模式对比研究

为研究卵石地层土压平衡盾构撕裂刀布置模式对刀具磨损的影响,结合北京地铁19号线平—积区间、牛—金区间基本相同地层条件下撕裂刀不同布置模式的盾构掘进工程案例,采用数学回归分析方法对比“大高差宽间距”和“小高差窄间距”2种撕裂刀布置模式下的刀具磨损系数。研究结果表明:1)在地质情况、掘进参数、渣土改良等条件基本一致的情况下,采取“小高差窄间距”撕裂刀布置模式的刀盘上刀具磨损量更大,其高撕裂刀、低撕裂刀、刮刀的磨损系数分别为“大高差宽间距”模式的1.5、3.2、2倍;2)“大高差宽间距”撕裂刀布置模式下,高、低撕裂刀起到了良好的分层犁松作用,有效降低了撕裂刀的磨损;3)“大高差”撕裂刀布置模式比“小高差”布置模式下的刮刀磨损系数减小了42.7%,“宽间距”布置模式比“窄间距”布置模式下的刮刀磨损系数减小了36.1%。