EPB Shield Research Articles

Development of simulation equipment system on EPB shield TBM hood operation

본 논문은 토압식 쉴드TBM(EPB shield TBM)의 후드부에 대한 시뮬레이션 시스템 개발에 대한 연구결과이다. 최근 토압식 쉴드TBM은 터널굴착에 많이 활용되고 있다. 토압식 쉴드TBM의 후드부 시스템은 터널굴착에서 매우 중요하기 때문에 후드부 시스템의 설계 및 operation parameter의 평가를 위하여서는 시공전에 사전 시뮬레이션이 요구된다. 본 연구를 위하여 모형 시뮬레이션 장비 시스템을 설계 개발하였다. 개발된 시스템의 검증을 위하여 모형실험을 실시하였으며, 개발된 시스템을 이용하여 얻은 결과는 현장에서 얻을 수 있는 토압식 쉴드TBM의 거동과 유사한 결과를 보여주었다. 이 결과로부터 토압식 쉴드TBM 굴진시 지반 loss는 후드부 챔버에 발생되는 토압의 변화에 많이 의존되는 것으로 나타났다. 따라서 본 연구에서 개발된 시뮬레이션 장비 시스템은 토압식 쉴드TBM공사 전 operation parameter를 평가하는데 매우 유용하게 활용될 수 있을 것으로 기대된다. 또한 다양한 지반조건에서의 TBM operation에 관한 정보를 제공할 것이다. This paper presents the development of simulation system on EPB shield TBM Hood operation. In recent, EPB shield TBM is widely used in the tunnel construction. Since the hood system of the EPB shield TBM is most important to excavate the tunnel, it is necessary to perform the simulation of hood system to investigate the design and operation parameters prior to tunnel construction. In order to carry out this study, the scaled simulation system was designed and developed. The model tests were performed to verify the developed system. During the simulation, the earth pressures developed in the chamber during tunnelling were measured to evaluate the operation technique. The test results obtained by the developed simulation system show clearly the similar behaviour of TBM hood compared with the field data. It was also found that the ground loss during tunnelling is dependent on the change of earth pressure in chamber. Therefore, the simulation system developed in this study will be very useful to evaluate the operation technique of the TBM hood prior to tunnel construction. In addition, this system will be applied in a various condition of ground to get the operating information.

Study on Synchronized Grouting Pressure to Segments of Shallow EPB Shield Tunnel

Based on Terzaghi's theory on loosening earth pressure, two failure modes of soil upon shallow EPB shield tunnel caused by synchronous grouting are analyzed, and the theoretical equations of synchronous grouting pressure is built to calculate the maximum and minimum grouting pressure which correspond to the limit states of subsidence and upheaval failure. Combined with a shield tunnel construction practice, the theoretical and measured values are compared. The results show that the theoretical equations are valid and can provide a theoretical approach for the parameters of shield synchronous grouting.

Evaluation of the Heading Confinement Pressure Effect on Ground Settlement for EPBTBM Using Full 3D Numerical Analysis

Ground settlement is often the most serious concern when tunneling under an old city with numerous historic monuments. A successful engineering design under these conditions would require getting the most out of the ground strength parameters and avoiding any weakening maneuver throughout the operation. Knowing that surface settlement is highly affected by tunneling parameters in EPB shield tunneling lead us to estimate the optimum values for the machine heading pressure with the lower amount of the ground settlement in fragile structure of the old city for the Esfahan Subway Project. Tunnels were dug underneath some of the most prominent historical sites along the path of the project. To improve precision and efficiency in tunneling operation, at the first step, tunnel heading confinement pressure is calculated by using an advanced 3D mathematical approach based on the limit equilibrium theory. Then, a promoted 3D finite element model is developed, taking into account the tunneling procedures and the designed heading confinement pressure from the first step. Settlements were pre-calculated and the surface displacement was checked at all sensitive locations. At the third step, settlement is estimated by exerting executed face supporting pressure to the tunnel face and the concluded amounts for displacement are compared with the outputs of extensometers. This comparison leads us to check the reliability of calculated settlements and the accuracy of the designed tunnel heading confinement pressure. Furthermore, evaluating the relation between extensometer outputs and executed tunnel face pressure at the points of extensometers stations validates the assumption that the safe face supporting pressure causes least surface displacement. Although the minimum pressure occurred in short term fluctuations, this approach confirms the sensibility of settlement with the least executed face supporting pressure.. It is also found that higher executed face supporting pressures could reduce the tunnel face stability. Therefore, documentation of appropriate software facilitates design procedures. Yet a further achievement of this study concerns effective decision implementations under strictly limited.

Study on Knowledge-Based Cutter Head Design Theory of Shield Tunneling

A knowledge-based cutter head design theory of shield tunneling is proposed because of lacking integrated cutter head design theory in China. A three-dimensional theory system is structured by the Hall three-dimensional theory. The basic concepts of the mentioned theory and connotations of knowledge model which takes cutter head of EPB shield tunneling as an example are also expounded in detail. The application in practice shows that the knowledge-based cutter head design theory is feasible. It is important to improve design quality, efficiency and reduce cost in cutter head design.

쉴드 TBM 터널에 적용 가능한 리스크 관리: II. 리스크 분석 방법

본 논문에서는 쉴드 TBM 터널에서 적용 가능한 리스크 분석 방법을 연구하였다. FTA 방법을 통해 리스크 아이템과 각각의 발생확률을 확인하고 AHP 방법을 통해 각각의 리스크 아이템의 영향도를 구하였다. 마지막으로 각각의 리스크 아이템의 리스크 레벨을 평가할 수 있었다. 개발된 방법을 EPB 쉴드 터널이 사용된 서울 지하철 현장에 적용하여 리스크 분석 결과가 현장 데이터에 부합하는 합리적 결과임을 검증하였다. In this paper, a risk analysis methodology applicable to shield TBM tunnels was studied. Fault Tree Analysis (FTA) was utilized to identify all risk items and to calculate the probability of failure of each item and Analytic Hierarchy Process (AHP) was used to obtain the impact of each risk item. Finally, a risk level of each risk item can be assessed. Developed methodology is applied to a Seoul subway site in which EPB shield tunnel method was utilized and it was found that risk analysis results matched reasonably well with field data.

Effect of EPB Shield Tunneling on Adjacent High Speed Railway Viaduct

Based on a project of subway constructed near elevated high speed railway, FEM method is adopted to analyze the effect of shield tunneling on the horizontal and vertical displacement of pile foundation of the viaduct as well as the pile caps on the condition that the nearest clear distance is 5m. The results show that with appropriate parameter control of shield tunneling, the effect of EPB shield tunneling on the displacement of piles in the three directions, i.e. horizontal displacement along and perpendicular to the longitudinal direction of the rail line and vertical displacement, is little. The same goes for the differential settlement between pile caps.

Design and Analysis for EPB Shield Bracket Based on Ansys

According to the structural characteristics of EPB shield bracket, the author establishes 3D solid model by Solidworks and corresponding finite element model of the bracket portion which is connected to the cutterhead by ANSYS WORKBENCH software. Through the static analysis of bracket’s stress characteristics under extreme conditions, we get its stress, deformation and safety coefficient distribution law under the maximum constraint conditions. After getting the maximum equivalent stress, the analysis of the calculation results shows that this kind of bracket with good static characteristics can meet the design strength requirement. This paper points out the weak position of bracket’s strength, and provides some reference data for the structural optimization design, as well as some basic data for both the structural design of bracket and the construction maintenance. Moreover, the structure analysis in the process of the grid selection and the key technology of the post-processing method are discussed in detail. The design example shows the effectiveness of the method.

Ground movements in EPB shield tunneling of Bangkok subway project and impacts on adjacent buildings

Monitoring data of the first Bangkok subway project excavated by 8 EPB shields were analyzed to evaluate the ground movement characteristics and responses of adjacent buildings. Mostly the maximum ground surface settlements were in the range of 20–40mm, corresponding to 0.5–2.0% of tunnel volume loss, although few sections experienced larger settlements reaching 100mm. Larger ground losses tended to occur while excavating in sand or mixed soil layers and at locations of long duration stoppage. There was only a slight trend of relationship between the settlement and shield pressure. The predominant factor controlling the movement was the human related factor in shield operating which was not easy to predict. Obstructions from piled foundations and other known and unknown buried utilities and objects, resulted in non-conformance of ground surface settlement troughs to the Gaussian function, thus they could not be predicted by any empirical and analytical methods. Shield face pressures often caused outward ground displacements that complicated the final ground movements, particularly the lateral displacement which could not be predicted by available analytical methods. Long term consolidation settlements mainly occurred in the soft clay layer, but the amount and rate did not seem significant. On impacts to buildings, buildings on deep piles showed the least induced settlements. But for buildings on short piles, the settlements may be larger or smaller than ground surface settlements, depending on the distance from tunnel center line and pile tip depth.

Wavenet ability assessment in comparison to ANN for predicting the maximum surface settlement caused by tunneling

An alternative method of maximum ground surface settlement prediction, which is based on integration between wavelet theory and Artificial Neural Network (ANN), or wavelet network (wavenet), is presented. In order to minimize the risk of tunneling, a tunnel engineer needs to be able to make reliable prediction of ground deformations induced by tunneling. Any prediction from numerical analysis was highly dependent on the model adopted for modeling the soil behavior. However, setting up a realistic model that would be able to calculate tunneling-induced settlement profiles is rather difficult. Most of the researches show that the capability (i.e. pattern recognition and memorization) of an ANN is suitable for inherent uncertainties and imperfections found in geotechnical engineering problems considering its successful application without any restriction. Wavenet is a single hidden layer feedforward neural network, which uses wavelets as its activation functions. In this study different wavelets are applied as activation functions to predict the maximum surface settlement due to tunneling. Wavenet parameters such as dilation and translation are fixed and only the weights of the network are optimized during its learning process, which is performed by a back-propagation algorithm. The efficacy of this type of network in function learning and estimation is demonstrated through measurements extracted from EPB shield tunneling. The simulation results indicate decrease in estimation error values that depicts its ability to enhance the function approximation capability and consequently exhibits excellent learning ability compared to the conventional back-propagation neural network with sigmoid or other activation functions.

Transportation Matching Design of Earth Pressure Balance Shield in Medium Distance Tunnel

Aiming at medium distance transportation of excavated spoil and constructional components in the tunnelling process, this paper combines with a water-conveyance tunnel engineering and analyzes the influence factors that affect the construction efficiency of earth pressure balance shield(EPB shield), and then works out an available scheme based on that the transport link should well match with shield tunnelling. The field condition indicates that the equipment lectotype, marshaling and transport organization in this scheme guarantee the transport capacity and continuity for tunnelling, which ensures construction progress. The idea in this design can provide similar engineering with reference.

Response of a double-decked metro tunnel to shield driving of twin closely under-crossing tunnels

Twin tunnels on Shenzhen metro Shekou Line were driven by EPB shields through weathered granite gneiss closely under-crossing a double-decked tunnel embedded in strongly weathered granite gneiss on Luobao Line. The performance of the existing tunnel as affected by under-crossing tunnels was continuously monitored by means of an automatic high-performance total station measuring system. Displacements of the existing tunnel caused by under-crossing tunnels in different under-crossing stages were measured. The measured data were timely processed and fed-back to related operators to realize an information-oriented project. Based on the measured data discussions and analyses were carried out in terms of the impact of the under-crossing shield tunnelling on the existing tunnel, effect of rainfall infiltration on the performance of the existing tunnel, allowable deformations of the existing tunnel, possibility of reducing the number of measuring points in a monitoring cross section and the influence on the existing tunnel caused by twin tunnels. Thanks to the staggered single tunnel under-crossing and other favorable factors, the measured deformations of the existing tunnel were well below the predefined allowable values. Under the guidance of monitoring, the under-crossing project was smoothly completed without interruption of metro traffic. This is a valuable example for evaluating the shield tunnelling induced effects on adjacent existing tunnels and establishing criteria to guide shield tunnelling under similar conditions.

Research on Ground Settlement due to EPB Shield

The surface settlement is affected by many factors due to EPB shield. This paper takes the shield construction of Guangzhou Metro Line 5 as an example, carries out three dimensional numerical experiments on the ground settlement rule. The result indicates that soil warehouse pressure and the efficiency of grouting is important factors of the surface displacement. To increase grouting pressure and shorten the grouting time can reduced the ground settlement in effective. With the increase the soil warehouse pressure, the settlement behind the working face is reduced and the front working face is increased. When the soil warehouse pressure is at the over balance condition, the raising ground is increased and the settlement is reduced. The value of settlement is much larger than the value of raising. So to increase the soil warehouse pressure is another effective method to reduced the ground settlement on the premise that the front soil body of shield does not be destroy.

The Efficiency Analysis on Cutting Power of EPB Shield Cutter

There are two basic types of EPB shield cutter: panel type and spoke type. The efficiency and process of the driving work will be directly related to the chose of the cutter type. Torque model of the shield cutter can be established by analyzing the load under working conditions. Methods to analyze the efficiency of two different types of cutters under working conditions can be explored, through analysis with specific examples of projects in this paper. Thus, theoretical basis can be provided for analyzing and studying the efficiency of shield cutter.

Control Parameters of EPB Shield Tunneling in Weathered Granite Ground and Below Existing Tunnels

The choice of reasonable parameters of EPB shield tunneling in weathered granite ground is of great importance to reduce tunneling-induced effects on existing tunnels. Combined with the practice of the EPB shield tunneling below existing interval tunnels from Kexueguan station to Dajuyuan station of Shenzhen metro line No.1, the method of design and regulation of main parameters including the earth pressure in excavation chamber, the ground conditioning, the volume of the discharged soil, the grouting control and the advance speed, of the EPB shield tunneling are studied. The practice of the below-crossing shows in the weathered granite ground, it is reasonable that the earth pressure in excavation chamber is taken as 0.15-0.2 mpa, and that FER, FIR and CF of foam are taken as 8-15, 30-50% and 3-5% respectively, and that the amount of synchronization grouting is 8-10 m3 per ring along with the injecting pressure of 0.3-0.4 mpa, and that the second phase injection is employed to control the further settlement of existing tunnels when necessary, and that the advance speed is taken as 8-10 mm/min, and as steady as possible. Meanwhile, adjustments according measured data must be performed when necessary. Moreover, the real-time monitoring and a collaborative-work environment among the Parties involved in project are also very crucial to facilitate the risk management of the below-crossing.

Research on characteristics of deformation in thrust system for EPB shield machines

The purpose of the research is to investigate into characteristics of deformation in thrust system which reduces the stiffness with the increase of displacement for piston in hydraulic cylinder. Firstly, based on the hyperstatic compatibility, the spatial deforming ellipse for the driving system has been discovered. Then the characteristics for the deforming ellipse of even and non-uniform arrangement systems have been analyzed in detail. Finally, applying deforming ellipse to the thrust systems of a shield machine in engineering applications, the characteristics of the deforming ellipse affected the behavior of the thrust system have been discussed. The result could provide a theoretical foundation and support for the design of thrust systems in shield tunneling machines.

Model Reference Control for Bulkhead Pressure of EPB Shield in Tunneling

The supporting pressure is achieved through control of the incoming and outgoing materials in the head chamber in shield tunneling, i.e., through regulation of the screw conveyor rotation, thrust force of jacks and the excavation advance rate. The discrete state equation of controlling system is derived based on mechanical equilibrium principle. The objective function of model reference control for bulkhead pressure is proposed. Optimal controlled variables are determined by using weighted least square method. The numerical simulation results show that bulkhead pressure of shield machine can be controlled by individually adjusting speed of screw conveyor in most cases, and the regulation of thrust force of jacks plays a secondary role for controlling bulkhead pressure.

Torino metro line 1: Use of three TBM-EPBs in very coarse grained soil conditions

Earth Pressure Balance type Tunnel Boring Machines (TBM - EPB) were introduced in the tunneling industry about 30 years ago with the aim of facilitating mechanized excavation in ground containing a significant proportion of fine grained soils, which were problematic for the existing slurry shield machines (TBM - SS). Until recently, TBM-EPB applications have continued to be limited to ground containing fine grained soil and low water permeability because of the difficulty, in coarse grained soil, of controlling the earth pressure transferred to the tunnel face. However, the addition of fines in the excavation chamber has permitted efficient and economical TBM - EPB employment in coarse grained soils of mainly sand and gravel. Therefore, these machines are gradually increasing their market. One example of successful TBM - EPB exacavation in highly permeable coarse grained soils is Turin's first subway line, which includes 9 km of tunnels, 15 stations, a train depot and control centre, building protection measures and other secondary structures. Construction began in November 2000 and the metro line shall be operational at the end of 2005. Tunneling was completed between October 2002 and March 2005 with three earth pressure balance tunnel boring machines (EPB-TBMs) in Turin's fluvial and glacial deposits of gravel, sand and cobbles in a silty matrix, with a grain-size curve falling outside the typical normally recognised limits of application of EPB shields. Soil improvement by grouting was undertaken to limit risk of damage to pre-existing structures potentially influenced by tunnel excavation. Ground conditioning in the excavation chamber took place with injection of a mix of a calcium carbonate filler in water, to compensate the natural grain-size curve and integrate use of traditional ground conditioning foams. A monitoring system with over three thousand instruments, based on a Web-GIS architecture, was installed to control safety during construction. The Turin experience is a clear demonstration that, taking correct measures, it is possible, even in an urban context which requires careful control of ground settlements, to economically employ EPB shields in very coarse and highly permeable soils, traditionally considered unsuitable for these machines. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

Evaluation of ground movements in EPB-shield tunnelling for Bangkok MRT by 3D-numerical analysis

This paper presents results of 3D numerical analysis using FLAC3D to evaluate characteristics of ground movements associated with MRT subway tunnelling using EPB shields in Bangkok subsoils. Effects of influencing factors i.e. face pressure, soil layering, piezometric drawndown of groundwater, tail void grouting, and input values of initial horizontal ground stress were investigated. A comparison was made between the prediction by the analysis and monitoring data. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

Shield tunneling database management for ground movement evaluation

Tunneling in urban environments is very challenging and ground movements induced by tunneling are major concerns during excavation. Based on many case histories, one realizes that many factors such as geological conditions, shield operation, and tunnel geometry affect ground movements. Therefore, to understand the complicated behavior of ground-shield interaction, all geological data, instrumentation records, tunneling data, surveying records, and daily activity updates have to be systematically collected and managed. During the excavation of the Bangkok MRTA project, a 22 km twin-tunnel, observation and data collection were extensively conducted at the subway project while eight EPB shields were excavating the tunnel. In this context, a computerized database system was assembled using all information collected from the MRTA project which records on a ring-by-ring (1.2 m interval) basis. The database contains monitoring results that include all shield operational records, field instrumentation readings, and geological information. The database system consists of different hierarchic levels. The main database provides linkages to sub databases (e.g., second and third levels), and within main databases. Input data were associated with the lining ring number along the tunnel alignment. The main advantage of this computerized database is that it does not only serve as a data management tool, but can also be used for studying of the ground-shield interaction by providing: (1) records of operational parameters (i.e., face pressure, penetration rate, thrust force, grouting pressure, time and shield position) along the tunnel alignment; (2) instrumentation readings (i.e., surface settlements, sub-surface settlement, lateral deformation and pore pressure); (3) tunnel alignment coordinates; (4) instrumentation layouts; and (5) geological conditions. Hence, this computerized database is useful for the study of the EPB shield tunneling method and ground deformations. Moreover, the database was used as an evaluation system to identify which ground- and EPB-characteristic have the greatest influence on ground movements and to show correlations between parameters. Therefore, this developed database can help tunnel engineers and shield operators to evaluate ground deformations caused by the shields during the tunnel excavation. (A) Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Comparison of face pressurized shield methods in various soil conditions

Up to the present time the Wayss & Freytag Ingenieurbau AG has completed more than 127 km of tunnelling using different tunnelling methods. Shielded tunnels, tunnels using conventional methods as well as immersed tunnels were constructed in different countries nearly all over the world. Over the last 30 years most of the important developments concerning the machine technology for EPB- and Slurry-Shields have taken place. Since the first application of a hydroshield for the Wilhemsburg Collector project in Hamburg in the early seventies, several steps of development have led to the current state-of-the-art in mechanised tunnelling. The continuous improvement of TBM techniques allows the execution of high quality tunnelling particularly with regard to maximum safety and efficiency. The practical experience of the construction companies are an essential basis for continued development. After all, the performance risk of tunnelling is usually borne by the contractors. The first application of a hydroshield was in the early seventies on the project Wilhelmsburg interceptor sewer in Hamburg. The hydroshield was an evolutionary concept in shield design which blazed new trails in the difficult field of tunnelling in sub aqueous or water bearing soils. The essential features of the hydroshield method were sensitive control of the pressure of the supporting fluid by means of a compressed air cushion, high capacity hydraulic transport of the excavated soil and recycling of the supporting fluid and, above all, no use of compressed air behind the sealed bulkhead of the cutter chamber within the tunnel. Since this first use of a hydroshield, several steps of development have taken place and led to the current state-of-the-art. At present a lot of TBMs are equipped with integrated stone crushers, horizontally movable supporting plates and a centre cutter. Each application of mechanised shield tunnelling requires an individual solution in order to reach the best result and highest quality. In many cases these solutions cannot be found in a conventional application of common techniques but very often in additional improvements of details. The pros and cons of Slurry and EPB tunnelling have to be compared and evaluated. Under certain mixed face conditions the application of a hydroshield can have decisive advantages compared to an EPB shield and its application is preferred. One such situation can be the occurrence of mixed ground conditions at the working face in terms of hard rock at the bottom and soft soil at the top of the face. With an EPB shield these conditions can lead to insufficient face support. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.