Mixed Face Conditions Research Articles

An evaluation of cutting head design of current tunnel Boring machines and suggestions to improve machine Performance

ABSTRACT This paper evaluates cutterhead design of current tunnel boring machines (TBMs) in considerations with the actual cutting action of discs observed on the most common cutter heads. The discs on the current TBM cutter heads were found to predominantly perform asymmetrical cutting action, which generates excessive sideway forces impairing steering action of the machine. The effective s/p ratios related to actual cutting action of discs emerge to be significantly higher than those of the laboratory-determined values, and this consequently leads to adverse cyclic deepening effect. The gross lateral loads arising from excessive side forces were stated to be minimised if the adjacent discs are arranged to cut in symmetrical position by adopting appropriate cutterhead design methods suggested in this paper. Furthermore, a dynamic analysis was carried out in terms of reaction forces on cutter heads of different geometries, and it was indicated that flat face cutter heads have better steering abilities than conical or domed types, in mixed face conditions. Similar analysis on disc angular spacing also inferred that scattered type disc arrangements with equal angular spacing are preferable to cutterheads with spoke or star type lacing, in terms of cutterhead balance.

Influence analysis and relationship evolution between construction parameters and ground settlements induced by shield tunneling under soil-rock mixed-face conditions

This study investigates the influences of the key shield parameters on tunneling-induced ground settlements considering the dynamic excavation process. The advanced machine learning method in conjunction with principal component analysis is applied to evaluate the nonlinear relationships between ground settlements and the multi-parameters in the soil-rock composite ground. Considering the interaction among multi-factor, the nonlinear relationships of excavation characteristic parameters are developed by the correlation analysis to quantify shield machine performance in the mixed ground. Predictions on ground settlements in the soil-rock mixed-face are conducted in good agreement with the in-site measured data from the Nanjing Metro Line No. S7 tunnel. The implementation effects of the Light-GBM based model are evaluated by RMSE and R2. Subsequently, the influence weights of the most important influencing factors are ranked to control the parameters, which will be beneficial to optimize the excavation scheme during the dynamic construction process. Finally, the empirical formulas are proposed according to the high-correlation parameters as well as the measured datasets by the nonlinear multiple regression process, which can provide guidance for shield tunnel operation in the soil-rock composite ground.

Laboratory Test of EPB Shield Tunneling in Mixed-Face Conditions

Field measurements and laboratory tests were carried out to study the mechanical behaviors of soil in response to earth pressure balance (EPB) shield tunneling in mixed-face conditions, i.e., layers of granite and sand. Specifically, an experimental investigation was carried out using a laboratory-scale model to replicate the EPB tunneling operations in such ground conditions. The effects of the ratio of rock/sand at the tunnel face (Tr/Ts) and the cover-to-diameter ratio (C/D) on the soil pressure in the chamber, ground displacement, and volume loss were examined. The results show that the soil's response to the mixed-face conditions differs significantly from that in the homogenous ground and highly depends on the ratio of rock/sand, especially for relatively shallow tunnels. As the ratio of rock/sand at the tunnel face increased, the pressure gradient in the chamber became more inconsistent. The translated cumulative curve does not always provide a good fit in the mixed-face conditions, particularly in cases when the rock/sand ratios are high. A smaller width of settlement trough has been observed for cases with a large rock/sand ratio compared to that in clay and cohesionless soil.

The use of TBM process data as a normative basis of the contractual advance classification for TBM advances in hard rock

AbstractIn April 2016 a newly formed working group began with the revision of the Austrian standard ÖNORM B 2203‐2. The goal of the group was the establishment of a practicable advance classification scheme, which would be applicable both for the design and for the construction phase. In addition, a clear separation should be established between a regular advance, which is clearly described and can be calculated by the bidding contractor, and a ”hindered advance“, which cannot clearly be described and calculated. The contractual framework is used to compensate for the regular advance, and hindering occurrences such as water ingress or increased wear are compensated by additional contractual time‐dependent costs. Fair compensation regulations for hindered advance (such as an advance through blocky rock mass, mixed face conditions, swelling, squeezing ground, major face instabilities, increased adhesion and stickiness of muck, obstacles and suspension losses) are to be defined as well. The method presented in this paper and based on systematic TBM data evaluation achieves both the goal of contractual advance classification and the goal of establishing a simple threshold differentiating regular advance and hindered advance.

Crossing the East River of New York in the Era of Mixed Face Tunneling

Research Article| May 23, 2018 Crossing the East River of New York in the Era of Mixed Face Tunneling David M. Cregger David M. Cregger 1 AECOM Technology, 250 Apollo Drive, Chelmsford, MA 01824 1Corresponding author email: david.cregger@aecom.com Search for other works by this author on: GSW Google Scholar Author and Article Information David M. Cregger 1 AECOM Technology, 250 Apollo Drive, Chelmsford, MA 01824 1Corresponding author email: david.cregger@aecom.com Publisher: Association of Environmental & Engineering Geologists First Online: 30 Nov 2017 Online Issn: 1558-9161 Print Issn: 1078-7275 © 2018 Association of Environmental & Engineering Geologists Environmental & Engineering Geoscience (2018) 24 (2): 137–141. https://doi.org/10.2113/EEG-1982 Article history First Online: 30 Nov 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David M. Cregger; Crossing the East River of New York in the Era of Mixed Face Tunneling. Environmental & Engineering Geoscience 2018;; 24 (2): 137–141. doi: https://doi.org/10.2113/EEG-1982 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Engineering geology and case history experience have been relied upon as predictors for several historical East River tunnel crossings, as shown in Figure 1. Differing rock types were crossed, consisting of gneisses, schist, and limestone or dolomite nearly vertical in orientation and part of a complex tightly folded sequence, but deeply weathered along faults parallel to the river. Each crossing had vertical grade requirements, forcing the alignment through known geologic hazards of poor-quality rock and mixed face. The presence of decomposed and highly crushed zones at depth and glacial or man-made deposits further complicated the mixed face conditions for... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Estimation of the cutterhead torque for earth pressure balance TBM under mixed-face conditions

In this paper, the cutterhead torque of the modified earth pressure balance (EPB) tunnel-boring machine (TBM) in mixed-face ground is analyzed. The theoretical model of the cutterhead torque of EPB TBM in single soft ground is generalized to the mixed-face ground. To determine cutting torque, a theoretical model for drag bits and disc cutters, which are suitable for mixed-face ground and nonhomogeneous distribution of drag bits on cutterhead, is established and the force formulas are derived. The components of cutterhead torque are investigated in detail. It is found from the results that the friction torques acting on the frontal surface, circumference and back surface of cutterhead, cutting torque, shearing torque acting on opening and agitating torque are important torque components and occupy a fairly large proportion. Moreover, in mixed-face ground, cutting torque induced by disc cutters is an important part, especially when hard rock has a greater proportion.

Sydney Metro – ground characterisation and TBM selection for the Sydney Harbour crossing

AbstractThe Sydney Harbour crossing is a key element of Sydney Metro City & Southwest, which includes 15.5 km of twin tube running tunnels extending from Chatswood at the north through to Sydenham, south of the Central Buisness District (CBD). One of the key features is the 1 % length of the alignment that passes under Sydney Harbour. The rest of the alignment is through rock, but the harbour crossing is designed to pass through harbour sediments and mixed face conditions undersea. An in depth study and analysis was required to confirm the feasibility of the safe construction of this short length of the tunnel in sub‐aqueous, soft ground conditions. It was necessary to carry out detailed, targeted investigation of the ground to enable the selection of an appropriate tunnelling technique for constructing the tunnels.

Monitoring Cityringen Metro project in Copenhagen, Denmark

Due to open in 2019, Cityringen Metro in Copenhagen, Denmark, consists of 17 underground stations, five shafts and 15·57 km of twin tunnels. Construction is in dense urban areas and much of the tunnelling was in soft ground or mixed-face conditions. Continuous monitoring of the ground, structures, groundwater, noise and vibration has been critical to successful completion of the 8 year project. Monitoring data were also used to justify design changes to avoid intrusive mitigation measures. Illustrated with case studies, this paper describes the scope of the monitoring and how the extensive amount of data was managed.

The mechanism of hysteretic ground settlement caused by shield tunneling in mixed-face conditions

Shield is used more and more widely, such as coal mine roadway, hydropower tunnel, traffic tunnel and so on. But Tunneling with a tunnel boring machine (TBM) may cause inevitable ground subsidence. Though over the world numerous researches have been conducted for surface settlement induced by TBM in soft ground, the researches of surface settlement induced by TBM in a sandy cobble stratum are limited and a comprehensive study of the mechanism of delayed settlement induced by TBM in a sandy cobble stratum is unavailable. A ground stable state or surface settlement can be determined based on real-time monitoring data for surface dynamic subsidence. Subsequently, TBM tunneling parameters can be adjusted to accommodate various geological conditions. A sand-pebble-soil matrix is a typical heterogeneous material. The macro-mechanical performance of this matrix significantly differs from any material. In a general situation with a low water level and minimal disturbance, a stratum can stabilize by itself for a long period of time. Considering the characteristics of the stratum, ground loss can be divided into two phases: immediate settlement, which tends to stabilize, and delayed settlement, which tends to occur in sand-cobble strata, where settlement develops at a much slower rate than in single-medium strata. Monitoring data is not sufficient to guide the construction in the case of delayed settlement. Cobble-soil matrix can be treated as a spatial structural system that is constituted by single granular soil, aggregates of granular soil and pebble grains. Based on Particle Flow Code in 2 Dimensions (PFC2D), the mechanical characteristics of the matrix and the TBM tunneling process were numerically simulated. Movements of the pebble grains were traced and recorded in real time. The model addressed the mechanism of surface collapse from the perspective of mesomechanics. According to the model, a matrix formed self-stabilizing arch that overlies an underground cavity seems gradually wear out with expanding the cavity and eventually penetrating to the ground surface. The law of ground movement and the formation mechanism of ground subsidence in TBM advancement were investigated. The main factors that affect surface subsidence are the speed of advancement, the underground water level and the supporting period. In the numerical analysis, the surface-loss lag was reproduced and the field monitoring data were verified. The findings of this study provide a new method for investigating ground subsidence in similar strata.

Prediction of TBM performance in mixed-face ground conditions

A significant number of TBM performance prediction models in full-face soil or rock conditions are available in literature. However, very few prediction models exist for tunnels excavated in mixed-face ground conditions, mainly due to the complexity of the ground.Tunnelling in areas where two or more materials with significantly different geotechnical properties are simultaneously encountered on the tunnel face has often been described as one of the most challenging tunnelling scenarios. In such cases tunnel face instabilities are common and a thorough geotechnical assessment is necessary in order to select the most appropriate tunnelling technique.TBM performance for tunnels in mixed-face conditions was studied, based on the analysis of data from a tunnel project in Singapore excavated into Bukit Timah Granite. The areas considered are located within granite characterised by different weathering grades, which frequently results in mixed-face ground conditions represented by varying percentages of rock and soil simultaneously present at the tunnel face.A new TBM performance prediction index was proposed for mixed-face ground conditions, named as Mixed-face Penetration Index (MFPI). MFPI accounts for the total thrust force exerted by the TBM on the tunnel face (MN) and for the penetration rate (mm/rev). The index was correlated with: (a) the percentage of rock on the tunnel face, (b) the uniaxial compressive strength (UCS) of intact rock and (c) the rock quality designation (RQD) of rock mass, by using a weighted rock mass rating of the tunnel face (RMRm). Although no correlation was determined between MFPI and the geotechnical properties of the soil, its presence was considered in the TBM performance prediction model by assigning an RMR value to the soil portion equal to zero.MFPI and RMRm were correlated using regression analysis tools. The proposed relationship between these two indexes has been validated based on the recorded data of TBM performance in mixed-face ground along the excavated tunnel in Bukit Timah granite.

Effects of slurry on stickiness of excavated clays and clogging of equipment in fluid supported excavations

Mechanized excavation of tunnels and fabrication of deep foundation elements in soft ground often requires a fluid support of the temporarily created openings. The supporting fluids are generally mixtures of bentonite with water, enhanced by chemical additives for difficult geological conditions. The properties of the slurries are chosen to guarantee the stability of the excavation, in particular providing sufficient support to the coarse grained soil layers. When these are interlaid with clayey layers, excavation can be hindered by clogging problems, requiring time consuming cleaning works and causing construction delays. Clogging is caused by the stickiness of the excavated clay, which can be affected both by the clay mineralogy and the composition of the supporting slurry. The paper investigates these effects by means of a laboratory experimental study using novel stickiness tests: the mixing test and a model TBM cutter-head test. For bentonite slurries, the stickiness of the excavated soil was found to correlate with the shear resistance of the slurry. Therefore, increased slurry strength, while beneficial for excavations in coarse soils, may lead to increased susceptibility to clogging under mixed face conditions. In contrast, some pure polymer slurries can help to combine high slurry resistance with low clogging potential by protecting clay aggregate surface from penetration of water.

Proposed soil classification based on the experiences of soft-ground tunneling in Iran

An essential step in successful mechanized and conventional tunneling operations is a thorough characterization of ground conditions and identification of geological and geotechnical risks. In bored tunneling, this and other information is needed in order to select the appropriate tunnel boring machine (TBM) and to determine its technical specifications for proper soil conditioning and optimal TBM performance. In conventional tunneling, this information is also important for ensuring the correct choice of drilling method and minimizing drilling risk. The major geological risks in tunneling (New Austrian Tunneling Method [NATM] or mechanized) are stickiness and clogging of soils, soil abrasi veness, soils with low fine content or oversized grains, tunnel collapse and instability, groundwater fluctuation, mixed-face conditions, liquefaction, and soil movement. Experiences from both conventional and mechanized tunneling in Iran show that the potential for each geological hazard is higher in certain types of soils. As such, knowledge of the various soil types is important for predicting soil behavior and possible geological hazards. In this study, we present a simple and practical classification of soil types for the prediction of soil behavior and geological hazards in both conventional and mechanized tunneling. With this method, soils are classified based on two parameters. The first is soil grain distribution. For this purpose, tests were conducted on soil samples from the test pit and geotechnical boreholes, and the percentage of particles remaining above a no. 4 sieve and those passing through a no. 200 sieve were calculated for each sample. The second parameter is the consistency index, which is estimated from the Atterberg limits. The soils were classified into ten groups based on these two parameters, and soil behavior and geological hazards for each class were then predicted based on Iranian tunneling experiences. Finally, the real soil behavior and geological hazards in the Qom tunnel were analyzed to determine the accuracy of the predictions. The results showed that the predictions were largely comparable to actual conditions. These results were then directly used for preliminary and permanent lining design and recommendations for soil conditioning, as well as for structural design of the different stations.

Pressurised TBM tunnelling in mixed face conditions resulting from tropical weathering of igneous rock

Weathering is a process that turns rock into soil. Deep weathering is prevalent in tropical and sub-tropical areas. The resulting sub-surface conditions can be very onerous for tunnelling, with tunnel drives commonly encountering a significant proportion of mixed face conditions, comprising partly rock and partly soil. Problems that have been encountered have included: inability to maintain the face pressure, ground loss, sinkholes, slow rates of tunnelling, rapid tool wear, damage to tools, mixing arms and other parts of the TBM, very frequent and long interventions, clogging and blow-outs. The nature and extent of the problems on any particular tunnel have depended on the type and design of the TBM, the nature of the rock and the proportion of the tunnel in mixed ground. In Singapore this has resulted in a change from mainly EPB to mainly slurry tunnelling in weathered igneous rock; however, predominantly EPB TBMs have been used in weathered sedimentary rock. Information from EPB and slurry TBM drives is used to illustrate the issues involved.

TBM tunneling in mixed-face ground: Problems and solutions

Mixed-face ground encountered in Tunnel Boring Machine (TBM) tunneling presents great challenges and may trigger potential hazards without warning. A detailed understanding of such unfavorable conditions is therefore critical to a successful bored tunnel. In this paper, we firstly present a brief review of the definition, classification and the factors related to mixed-face conditions. Secondly, for a better understanding of this topic, we investigate the main difficulties and problems involved in TBM tunnelling under mixed-face ground with detailed cases. Thirdly, from the viewpoint of rock-machine interaction, we give some suggestions on the corresponding mitigation measurements from three categories: (i) selection of TBM type and modification of TBM, (ii) condition of ground and (iii) optimization of TBM operation.

An application of rock engineering systems for estimating TBM downtimes

TBM performance prediction is essential for estimation of project duration and costs in mechanized tunneling projects. An accurate machine prediction is dependent on rock mass and geological exploration conditions including rock strength, discontinuity conditions, hardness, underground water, poisonous gases, instability and mixed face conditions. The relative contribution of these conditions would have a significant effect in TBM downtimes and reduce the machine utilization considerably. Nonetheless, there are few documents in the literature regarding the prediction of TBM utilization factor. Utilization factor is one of the key performance parameters that links the advance rate and penetration rate, mostly affected by the type of operation, management, maintenance, and geological conditions. Rock engineering system (RES) is a valuable analytical tool for characterizing the important parameters for the interaction mechanisms among variables in rock engineering problems and other engineering practices. The main objective of this study is application of RES for calculating geology and rock mass related downtimes index (GRDi) based on predominant rock mass properties and rock mass related downtimes. This approach was applied to a database of three long mechanized tunnels. Developed database contains geological maps, detailed engineering geology information and daily site reports including length of excavated tunnel in each rock mass units, daily boring time and different rock mass related downtimes. Results of this study showed that GRDi is a robust approach for generating a better fit and producing more reliable and accurate estimation of TBM downtimes compared to conventional statistical methods (R2=0.849).

Development and validation of a 3D numerical model for TBM–EPB mechanised excavations

A 3D numerical model for mechanised excavations is presented, which is capable of simulating the overall process of excavation and construction of a tunnel when a TBM EPB (Tunnel Boring Machine–Earth Pressure Balance) is used. The main construction aspects of a mechanised excavation are modelled. Their influence on calculated ground displacements are investigated by means of a series of parametric analyses. With the aim of testing the performance of the proposed 3D numerical model, a series of 25 Class C predictions has been carried out. Case Histories related to the construction of the 1995–2003 Madrid Metro Extension Project were considered for this purpose. As a general rule, the results obtained with the Modified Cam–Clay model closely fit in situ measurements. When the Linear-Elastic or the Mohr–Coulomb models are used, it is not as easy to summarise the results obtained, as higher fluctuations are observed around in situ measured data. A good agreement is also shown when the distribution of horizontal displacements along depth is considered. For some sections, the mechanised excavation model is not capable of reproducing the high values of the surface settlements measured in situ. A closer look at the results shows that mixed face conditions are found for these cases, with the TBM excavating through layered soil formations having sharply different mechanical behaviour.

Dynamic characteristic analysis of TBM tunnelling in mixed-face conditions

In this paper, by taking into account the periodically varying mesh stiffness in multiple pinions transmission and the speed–torque characteristics of variable frequency motor drives, the dynamic model for the revolving system of tunnel boring machine (TBM) has been established. Based on the soft ground/hard rock assumption of mixed-face conditions and the analysis of cutting force on each disc cutter and each drag bit, the time-varying excavation torque on the TBM cutterhead in mixed-face tunnelling is obtained. The dynamic excavation torque and cutterhead rotation speed are discussed and compared for TBM tunnelling in several typical mixed-face conditions, which are characterized by the area percentage of soft ground on the excavation face and the uniaxial compressive strength (UCS) of rock. The results show that the excavation torque may run up to a critical value and fluctuate greatly in extremely adverse excavation environments, which may lead to an unexpected TBM stoppage and even a catastrophic failure of the drive motor. To decrease the penetration per revolution in time through applying a lower advance velocity and a higher cutterhead revolution will significantly reduce the excavation torque and effectively avoid such situations.

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.

Tunnel alignment design for Circle Line, Stage 3, Singapore: dealing with a densely built-up urban environment and challenging ground conditions

Circle Line Stage 3 (CCL3) forms part of Singapore's enhanced Rapid Transit system and probably represents the most challenging section of underground railway lines designed so far in Singapore. The overall route alignment for CCL3 does not follow the major radial road easements but instead passes through highly built up areas comprising low rise housing and apartment block estates and crosses numerous other infrastructure. As a result of this, the tunnel alignment design had to deal with the inherent engineering difficulties associated with theses constraints which also included large numbers of existing piled structures, the extent of which is novel in Singapore. Alignment design was aimed at achieving the correct balance between four principal factors. The factors were firstly, the desire to provide the required ridership, secondly optimum railway geometry for operational purposes, thirdly, the constraints on tunnelling imposed by the existing ground conditions, impacts on existing infrastructure and the desire to avoid expensive construction methods and high risk underpinning wherever feasible. The fourth factor was that the alignment design sought to provide least impact on the public in terms of nuisance, safety and private land acquisition. The balance of these factors was paramount to the successful design of this project. The challenges of this project required the Client (Land Transport Authority) and their Designer (MWH and sub-consultants) to work closely and proactively in pursuing railway alignment options that called for major modifications to the envisaged alignment from the previous feasibility designs. The final design saw the elimination of one of the six stations and the original requirement for underpinning of 20 major structures reduced to one. Adopted tunnel construction methods were principally using face pressurised Tunnel Boring Machines, with limited cut and cover structures for track cross-overs and mined tunnels for cross-passages or temporary access. Ground conditions expected at tunnel horizon comprise Bukit Timah Granite Formation rock, soil and extensive mixed face conditions, Old Alluvium and Kallang Formation soils. The alignment design process involved the assessment of alignment options by using ground characterisation through investigation, study of existing structures and foundations, identification of obstacles to tunnelling and methods of advance, analysis of tunnelling effects on structures, design of mitigation works and railway considerations. Each option was tested in terms of impact on the general public, buildability and cost. State-of-the-art geotechnical analysis methods were used to investigate the behaviour of piled structures during tunnelling and the design of piled underpinning to low and high rise structures. Significant advantage was gained by adopting a Value Engineering approach and designing the alignment to pass beneath government buildings that were scheduled for refurbishment, allowing partial demolition and the extraction of the existing piles, which would have otherwise been in the path of the Tunnel Boring Machines, from the surface. A trial of these pile removal works was made prior to adopting the preferred pile extraction method. This paper discusses the engineering challenges faced, presents a methodology for finding the optimum design alignments and describes important aspects of the adopted alignment. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Ground stabilization for tunnel construction in mixed-face conditions

A scheme for providing stability measures for a tunnel excavated in mixed-ground conditions using chemical grouting is described. Typical geotechnical problems encountered during excavation are highlighted. An analytical approach for calculating the required thickness of grouted soil was developed. Grout characteristics to achieve the required behaviour are described, along with the recommended sequence of construction. A methodology employing finite element analyses to predict the tunnel behaviour during construction is proposed. It was utilized in designing the excavation support. Predictions compared well with actual field measurements.