Tunnel Work Research Articles

Development of holistic prognosis models using exploration techniques and seismic prediction

AbstractAs part of the Brenner Base Tunnel project, the currently running Tulfes‐Pfons construction lot includes a stretch of the exploratory tunnel (ET), which has a length of 15 km and is being bored by a gripper TBM. During this tunnelling work, a diverse and broad set of exploration techniques is being used. Although it is an exploratory tunnel, the tunnel is subject to the same constraints as a performance heading. The choice of exploration techniques was made with regard of the capability to smoothly integrate them into regular tunnelling in order to not create further downtime. The exploration techniques are useful for the current ET but also to produce a forecast for the subsequent main tunnels (MT). The geological investigation is undertaken by face and peripheral mapping as well as by percussion drilling ahead of the machine. The geotechnical exploration is carried out by analysing the TBM parameters and the system behaviour, and analysing the percussion drilling. The exploration concept is completed with the geophysical reflection seismic method. All these exploration methods have different sensitivities, exploration ranges and directions, strengths and weaknesses, so they complement one another. This paper assesses the exploration techniques based on the experience until now. A case study of one fault zone is presented to show how the different exploration methods interact and contribute to a holistic prognosis model.

Cover Picture: Geomechanics and Tunnelling 6/2017

AbstractDSI is supplying numerous supporting measures for the 9 km long NorthConnex Tunnel, one of Australia's longest road tunnels. The tight project schedule and continuous operation of the tunnelling work require an optimal supply chain, product management, planning and cooperation between the project teams and DSI Underground, Australia (see page 788–789)

Gloggnitz contract after completion of the intermediate access at Göstritz

AbstractThe intermediate construction access at Göstritz was planned based on the results of a comprehensive geological investigation programme. The intermediate access minimises the risk of the excavation of the Semmering Base Tunnel through the Grassberg‐Schlagl fault system, which is located in the Otterstock area in Lower Austria. The site consists of an approx. 1000 m long access tunnel, a complex system of shaft head caverns, two shafts with a depth of about 250 m down to the level of the tunnel as well as a system of shaft bottom caverns for the four tunnel drives in the directions of Gloggnitz and Mürzzuschlag. During the construction of the access tunnel, a new shaft head layout was proposed by the contractor in form of value engineering to optimize further construction operation, and the optimized layout was adopted to the contract. At the end of the access tunnel, it turned out that the shaft head cavern system could neither be constructed in the original layout as tendered nor in the newly revised layout due to a geological fault zone, which had not been predicted despite extensive geological investigation in advance. Consequently, ÖBB, designer and contractor worked intensively to find a new feasible design to enable further construction of the cavern system, avoid a standstill of tunnelling works and comply with all approvals.

Investigation of a large ground collapse and countermeasures during mountain tunnelling in Hangzhou: a case study

This paper presents a case study of ground collapse (30 m wide and 16 m deep) during tunnelling under a water channel in the city of Hangzhou, China. The ground collapse damaged the constructed tunnel locally, and remedial measures had to be taken to resume the tunnelling works. In this paper, a forensic geotechnical and geological study was undertaken in which the geological condition at the collapsed site was reviewed, the causes for the collapse were investigated, and the development of the soil failure mechanism was evaluated. Remediation measures undertaken at the project site are also discussed. During this forensic investigation study, the strata over the tunnel was found to be of low strength and furthermore erodible to groundwater seepage. Groundwater seepage was detected, which was attributed to be the triggering force that contributed to the collapse. Tunnelling construction using explosives for blasting rocks was attributed to be one of the causes of the failure. A four-step rapid remediation measure was proposed on site, which included filling of the collapsed crater, reinforcement of collapsed debris in the tunnel, grouting and dewatering, and removal of debris and tunnelling. Tunnelling was resumed soon thereafter. The field monitoring data validated effectiveness of the proposed rapid remediation.

Predicting anomalous zone ahead of tunnel face utilizing electrical resistivity: II. Field tests

In our companion paper (Park et al., 2016), a method was developed to predict the characteristics (i.e., location, thickness, permittivity ratio, and conductivity) of the anomalous zone ahead of a tunnel face by utilizing the electrical resistivity of the ground (hereafter referred to as the Ground Prediction Method). The prediction accuracy of the developed Ground Prediction Method is investigated via laboratory tests using artificially created anomalies. This paper is part two in the series of companion papers; it attempts to examine the prediction accuracy of the developed Ground Prediction Method via field testing. The field tests are performed at railway and highway construction sites, at which conventional tunneling methodology is employed for tunnel construction, as well as at a subway tunnel construction site, at which an earth pressure-balanced shield tunnel boring machine is used for tunneling work. At tunneling job sites using the conventional tunneling method, a relatively stronger and weaker zone are predicted ahead of the tunnel face at the railway and highway construction sites, respectively. On the other hand, a relatively stronger zone exhibiting lower permittivity than that of the rock adjacent to the tunnel face is predicted at the tunneling site employing the mechanized tunneling method. In conclusion, assessing the ground condition ahead of the tunnel face via the newly developed Ground Prediction Method proves to be effective; prediction results of ground conditions show good agreement with those characterized via direct observation of the excavated face taken during tunneling work using conventional tunneling methods, in addition to those predicted from daily observations of muck conditions carried out in the process of tunnel construction using the mechanized tunneling method.

Diesel Exhaust Exposure Assessment Among Tunnel Construction Workers-Correlations Between Nitrogen Dioxide, Respirable Elemental Carbon, and Particle Number.

Occupational exposure to diesel exhaust is common due the widespread use of diesel-powered combustion engines. Diesel exhaust is chemically complex and consists of thousands of compounds present as gases and particulate matter. Both nitrogen dioxide (NO2) and elemental carbon (EC) have been used as markers for diesel exhaust exposure. Currently EC is regarded as the best surrogate of diesel exhaust. The objective was to quantify the occupational exposure to diesel exhaust in underground tunnel construction work using a multi-metric approach, and to investigate the correlations between NO2, respirable EC, respirable organic carbon (OC), respirable total carbon (TC), respirable dust (RD), and particle number. Also, the use of NO2 as a proxy for diesel exhaust was evaluated, how much of the variability in the diesel exhaust exposure was attributed to within and between individual factors and if there was a difference between expert and self-administered measurements of NO2. The personal exposure to diesel exhaust was assessed by expert supervised measurements of NO2, EC, OC, TC, RD and particle number in the breathing zones of underground tunnel workers. Stationary sampling of NO2, EC, OC, TC, RD, size-fractioned mass concentration, and particle number were conducted. The personal and stationary measurements were conducted on three occasions simultaneously. The workers measured their exposure by repeated self-administered measurements of NO2. The self-administered measurements were performed twice for each worker with at least one month lag between the samplings. In the simultaneous sampling of diesel exhaust, the geometric mean (GM) concentration of NO2 and respirable EC were 72 µg m-3 (10th-90th percentile 34-140 µg m-3) and 2.6 µg m-3 (10th-90th percentile 1.6-7.3 µg m-3), respectively. The GM for OC and TC was 28 µg m-3 (10th-90th percentile 20-42 µg m-3) and 31 µg m-3 (10th-90th percentile 20-50 µg m-3), respectively. The GM for RD and particle number was 180 µg m-3 (10th-90th percentile 20-530 µg m-3) and 47 900 cm-3 (10th-90th percentile 27500-94100 cm-3), respectively. A significant correlation was found between NO2 and respirable EC [Spearman's correlation r = 0.53 (P = 0.05)]. The within-worker variability of NO2 was 45.5% and the between-worker variability was 54.5%. The self-administered measured concentrations of NO2 (GM 70 µg m-3) did not statistically differ from the NO2 concentrations measured by an expert (P > 0.35). The diesel exhaust exposure in tunnel construction work was low. A significant correlation between NO2 and EC was observed. This indicates that NO2 could be used as a proxy for diesel exhaust in tunnel work if diesel exhaust is the only source of NO2 and if the ratio between EC and NO2 is known and constant. Passive sampling of NO2 is much easier and cheaper to perform compared with active sampling of EC. It is possible to utilize self-administered NO2 measurements in extreme and inaccessible work environments. This study adds support to continued use of NO2 as an exposure marker in combination with EC for diesel exhaust exposure. In tunnel construction work, the variability in the diesel exhaust exposure was high both between- and within-workers.

Estimation of environmental load of geotechnical structure using multiple regression analysis

With the increased global interest in greenhouse gas reduction, many countries around the world have been making a range of efforts to reduce greenhouse gas emissions. The Ministry of Environment suggested a goal of 37% reduction relative to the expected greenhouse gas ‘business as usual’ (BAU) for all industries; thus, greenhouse gas reduction in the construction industry is also inevitable. To reduce greenhouse gas, the effects of a construction project on the environment need to be minimized, and an integrated evaluation that involves various kinds of environmental pollution (e.g., resource usage, water, air, and soil) as well as greenhouse gas is required. Therefore, in this study, for a reasonable and objectively valid evaluation of the environment-friendliness of a tunnel facility (a geotechnical structure), a life cycle assessment was performed based on existing cases following the ISO 14040 series standard. The purpose of this study is to suggest an environmental load evaluation technique that statistically analyzes the effects of work processes, input materials, and energy sources during tunnel work by suggesting the estimation equation for 8 impact categories that affect environmental load.

INCREASE IN EFFICIENCY OF THE CYCLIC DRIVING OF WELLS IN SOIL

Processing methods of a cyclic driving of wells with a diameter over 300 mm by methods of vibro-impact pushing and combined with partial consolidation and excavation of soil on the basis of use of pneumo-percussive mashines (pneumatic bore-hole driver) are given in work. The results of researches received with use of the ground intake devices physical models have allowed to establish characteristics of change of force of resistance to the return transportation of the equipment with the taken soil core in process of his removal from a face. Analytical expressions for engineering calculation of the winch tractive force are received. Technical characteristics of the created number of the winches of scraper type working at the uniform energy carrier with shock cars – compressed air are given.The schematic diagram winch with hybrid pneumatic drive, the having variable traction and high-speed characteristic is offered at a limited expense of the energy carrier which realization of a design at vibroshock breakdown and a combined method allows to reduce time of a production cycle of formation of wells and to increase productivity of driving works. A schematic diagram of a winch with a hybrid pneumatic drive is proposed, which has variable traction and speed characteristics with a limited energy carrier consumption, the implementation of the design which in vibro-impact pushing and combined method allows to reduce time of process of formation of wells and improve the performance of the tunneling works.

Geological aspects on the sustainability of ancient aqueducts of Athens

Geological aspects of the ancient aqueducts of Athens are examined with particular emphasis on the hydrogeological and geotechnical conditions which made possible their continuous function throughout the centuries up today. In particular, the sustainability of the Hymettos and the Hadrianic aqueducts is investigated and attributed to the capture of underground water and the skillful construction of the tunnels. The geometry of the Hadrianic aqueduct and the situation in the ancient tunnel are presented based on data obtained during the resumption of the ancient work in the 19th and 20th centuries. The up to forty meters deep wells along the tunnel continue to collect underground water at many places along the twenty kilometers long path of the Hadrianic aqueduct. Similarly, the Hymettos aqueduct still irrigates the National Garden with a daily rate of about one thousand cubic meters. The stability of the ancient tunnels is correlated with the surrounding geological formations; it turns out that the stability problems of the ancient tunnels are comparable to those met in the tunneling works of the Metro lines, particularly in the Athenian Schists. A new part of an ancient aqueduct was crossed during the Metro works which is considered to belong to the Hymettos aqueduct.

Feasibility of PSO–ANFIS model to estimate rock fragmentation produced by mine blasting

Desired rock fragmentation is the main goal of the blasting operation in surface mines, civil and tunneling works. Therefore, precise prediction of rock fragmentation is very important to achieve an economically successful outcome. The primary objective of this article is to propose a new model for forecasting the rock fragmentation using adaptive neuro-fuzzy inference system (ANFIS) in combination with particle swarm optimization (PSO). The proposed PSO–ANFIS model has been compared with support vector machines (SVM), ANFIS and nonlinear multiple regression (MR) models. To construct the predictive models, 72 blasting events were investigated, and the values of rock fragmentation as well as five effective parameters on rock fragmentation, i.e., specific charge, stemming, spacing, burden and maximum charge used per delay were measured. Based on several statistical functions [e.g., coefficient of correlation (R 2) and root-mean-square error (RMSE)], it was found that the PSO–ANFIS (with R 2 = 0.89 and RMSE = 1.31) performs better than the SVM (with R 2 = 0.83 and RMSE = 1.66), ANFIS (with R 2 = 0.81 and RMSE = 1.78) and nonlinear MR (with R 2 = 0.57 and RMSE = 3.93) models. Finally, the sensitivity analysis shows that the burden and maximum charge used per delay have the least and the most effects on the rock fragmentation, respectively.

Oxidative potential of subway PM2.5

Air quality in subway systems is of interest not only because particulate matter (PM) concentrations can be high, but also because of the peculiarly metalliferous chemical character of the particles, most of which differ radically from those of outdoor ambient air. We report on the oxidative potential (OP) of PM2.5 samples collected in the Barcelona subway system in different types of stations. The PM chemical composition of these samples showed typically high concentrations of Fe, Total Carbon, Ba, Cu, Mn, Zn and Cr sourced from rail tracks, wheels, catenaries, brake pads and pantographs. Two toxicological indicators of oxidative activity, ascorbic acid (AA) oxidation (expressed as OPAA μg−1 or OPAA m−3) and glutathione (GSH) oxidation (expressed as OPGSH μg−1 or OPGSH m−3), showed low OP for all samples (compared with outdoor air) but considerable variation between stations (0.9–2.4 OPAA μg−1; 0.4–1.9 OPGSH μg−1). Results indicate that subway PM toxicity is not related to variations in PM2.5 concentrations produced by ventilation changes, tunnel works, or station design, but may be affected more by the presence of metallic trace elements such as Cu and Sb sourced from brakes and pantographs. The OP assays employed do not reveal toxic effects from the highly ferruginous component present in subway dust.

Relative displacement of the tendon and subsynovial connective tissue using ultrasound captures different phenomena than mechanical tendon shear

The most common finding in carpal tunnel syndrome is fibrosis and thickening of the subsynovial connective tissue (SSCT). While the SSCT mediates tendon gliding in the carpal tunnel, this histopathology suggests excessive shear forces are involved in injury development. Ultrasound is often used to quantify relative motion between the finger flexor tendons and SSCT as an indirect measure of “shear-strain”; however, the underlying mechanical implications of using ultrasound are not well understood. The middle flexor digitorum superficialis (FDS) tendon of 8 cadavers was moved in a combination of 2 wrist postures (neutral, flexed), 3 velocities (5, 10, 15cm/s), and 3 forces (10, 20, 30N) to assess ultrasound-based FDS-SSCT relative displacement while simultaneously quantifying tendon frictional work in the carpal tunnel. We found independent velocity effects for both constructs (relative displacement, ηp2=0.862, p<0.05; frictional work, ηp2=0.937, p<0.05), indicating ultrasound captured viscous gliding resistance owing to the gel-like inter-fibrillar matrix of the SSCT. FDS-SSCT relative displacement also increased independently in a flexed wrist posture (p=0.010) and with greater tendon force (p=0.036), likely representing strain dependant changes with tendon position. Alternatively, we found a significant posture×force interaction on tendon frictional work (p<0.01), due to, in part, greater surface friction against the transverse carpal ligament with a flexed wrist and high force. While ultrasound provided a different interpretation compared to direct measurement of mechanical shear, FDS-SSCT relative displacement successfully localized viscoelastic shear-strain, which may help elucidate the role of hand motion in SSCT pathology and CTS.

Feasibility of ICA in approximating ground vibration resulting from mine blasting

Precise prediction of blast-induced ground vibration is an essential task to reduce the environmental effects in the surface mines, civil and tunneling works. This research investigates the potential of imperialist competitive algorithm (ICA) in approximating ground vibration as a result of blasting at three quarry sites, namely Ulu Tiram, Pengerang and Masai in Malaysia. In ICA modeling, two forms of equations, namely power and quadratic, were developed. For comparison aims, several empirical models were also used. In order to develop the ICA and empirical models, maximum charge weight used per delay (W) and the distance between blasting sites and monitoring stations (D) were utilized as the independent variables, while, peak particle velocity (PPV), as a blast-induced ground vibration descriptor, was utilized as the dependent variable. Totally, 73 blasting events were monitored, and the values of W, D and PPV were carefully measured. Two statistical functions, i.e., root mean square error and coefficient of multiple determination (R2) were used to compare the performance capability of those prediction models. Simulation results show that the proposed ICA quadratic form can get more accurate predicting results than the ICA power form and empirical models.

Interaction of Zr with oxidized and partially reduced ceria thin films

The growth and electronic properties of Zr on the ceria thin films were studied by X-ray photoelectron spectroscopy, low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and work function measurements. Metallic zirconium was vapor-deposited on the well-ordered fully oxidized CeO2(111) and partially reduced CeO2-x(111) (0<x<0.5) thin films, which were epitaxially grown on a Ru(0001) substrate, under ultrahigh vacuum (UHV) conditions. The results show that the deposition of Zr on both ceria surfaces leads to electron transfer from Zr to ceria, accompanied by partial reduction of Ce from Ce4+ to Ce3+ states and oxidation of metallic Zr to Zr4+. Moreover, with increasing the Zr coverage, the reduction degree of ceria films increases and eventually only Ce3+ is observed at a high coverage of Zr. The STM results suggest that Zr grows two-dimensionally (2D) on the CeO2(111) thin film at low coverages due to the strong interaction between Zr and CeO2(111).

Forecasting and prevention of water inrush during the excavation process of a diversion tunnel at the Jinping II Hydropower Station, China.

IntroductionEstimating groundwater inflow into a tunnel before and during the excavation process is an important task to ensure the safety and schedule during the underground construction process.Case descriptionHere we report a case of the forecasting and prevention of water inrush at the Jinping II Hydropower Station diversion tunnel groups during the excavation process. The diversion tunnel groups are located in mountains and valleys, and with high water pressure head. Three forecasting methods are used to predict the total water inflow of the #2 diversion tunnel. Furthermore, based on the accurate estimation of the water inrush around the tunnel working area, a theoretical method is presented to forecast the water inflow at the working area during the excavation process.Discussion and evaluationThe simulated results show that the total water flow is 1586.9, 1309.4 and 2070.2 m3/h using the Qshima method, Kostyakov method and Ochiai method, respectively. The Qshima method is the best one because it most closely matches the monitoring result. According to the huge water inflow into the #2 diversion tunnel, reasonable drainage measures are arranged to prevent the potential disaster of water inrush. The groundwater pressure head can be determined using the water flow velocity from the advancing holes; then, the groundwater pressure head can be used to predict the possible water inflow. The simulated results show that the groundwater pressure head and water inflow re stable and relatively small around the region of the intact rock mass, but there is a sudden change around the fault region with a large water inflow and groundwater pressure head. Different countermeasures are adopted to prevent water inrush disasters during the tunnel excavation process.ConclusionReasonable forecasting the characteristic parameters of water inrush is very useful for the formation of prevention and mitigation schemes during the tunnel excavation process.

NATM터널의 공종별 환경부하 특성 분석

국내 외 기후변화 대응 체제의 강화에 따라 전 세계적으로 온실가스 감축을 위한 노력을 기울이고 있다. 건설 분야에서는 건축물을 중심으로 온실가스 저감을 위한 연구가 활발히 이루어지고 있으나, 온실가스 이외에 지구환경에 영향을 미치는 각종 오염물질을 고려한 종합적인 환경부하 저감을 위한 연구는 다소 부족하다. 이에 본 연구에서는 NATM터널을 대상으로 LCA (Life Cycle Assessment, 전과정 평가) 방법론을 이용하여 공종별 환경부하 특성을 분석하였다. 분석 결과, 라이닝콘크리트공, 숏크리트공, 갱문 및 개착터널 등 7대 공종이 NATM터널의 주요 환경부하 공종으로 나타났으며 전체 환경부하량의 89.22%를 차지하는 것으로 나타났다. 또한 대표공종들의 연장(m)당 환경부하량을 산정하여 비교 분석한 결과 개착구간에 해당하는 갱문 및 개착터널 공종의 환경부하량이 가장 큰 것으로 나타났으며, 전체 터널 구간을 대상으로 할 경우 라이닝콘크리트공과 숏크리트공에서 환경부하량이 많이 발생하는 것으로 분석되었다. 본 연구의 결과는 설계초기단계에서 환경부하 대표공종의 물량을 개략적으로 산출하여 전체 환경부하량을 추정하는 모델 개발 시 활용할 수 있을 것으로 판단되며, 향후 친환경 SOC건설을 위한 환경부하 관리방안을 수립하는데 큰 역할을 할 것으로 기대된다. Many countries are trying to reduce a greenhouse gas to step up their fight against climate change. There are many studies related to building only for reducing a greenhouse gas in construction area but studies related to reducing a comprehensive environmental load including various pollutants that affects the global environment are lacking. This study aims to analyse the characteristics of environmental load by work type for tunnel projects. Analysis showed that seven work types, including lining concrete, shotcrete, tunnel portal and open-cut tunnel work, etc., are representative works generated environmental load. These seven works represent 89.22 percent of total environmental load. In addition, comparison results of environmental load per tunnel's length by work type showed that a major factor of environmental load is caused by a tunnel portal and open-cut tunnel work with relatively short length (excavation length). And lining concrete and shotcrete work are larger than any other environmental load with tunnel's total length. It is expected that the result of this study will be used to make a estimation model for environmental load using approximate quantity survey of representative work types in the early stage of tunnel design. And it will be play a considerable role in establishing of environment management plan for sustainable infrastructure construction.

Numerical simulation of ventilation and dust suppression system for open-type TBM tunneling work area

In order to study the characteristics of the ventilation and dust suppression system for open-type TBM tunneling work area in a Ø8.53 diversion project, the numerical simulation method is adopted, and a three-dimensional steady airflow model, a dust flow model as well as other related flow characteristic equation models are established by considering the dust production mechanism of TBM construction. Besides, corresponding simulation models validated by experiment are established using CFD software, and the impacts of the main vent location, the air baffle length in the main beam and the exhausting air flow quantity on flow field distribution and dust flow behavior in open-type TBM tunneling work area are investigated. The results show: when the main vent is located 70–80m away from the working face, the ventilation in TBM tunneling work area is optimal; when the air baffle is as long as the main beam, the dust collection efficiency is the highest, reaching 89.4%; under the condition that the exhausting air flow quantity is less than half of the ventilation air flow quantity required by energy consumption and the minimum backflow velocity, the best dust suppression effect can be achieved when the exhausting air flow quantity is 40% of the ventilation air flow quantity.

New model for predicting Instantaneous Cutting Rate of axial-type roadheaders

Roadheaders are mechanical excavators which have been extensively used in tunneling, mining and civil engineering works. Performance prediction of the roadheader is major factor in determining the economy of an underground excavation project. In this study, a new model for predicting the Instantaneous Cutting Rate (ICR) has been developed. The performance of EBZ260W axialtype roadheader has been evaluated in the laboratory artificial rock cutting tests and in the tunneling field tests. Using the model, the processes of the artificial rock cutting in the laboratory tests have also been simulated. The predicted average ICRs in the laboratory tests, and in the simulations, together with the measured average ICRs in the laboratory tests and in the field tests are presented in this paper. The comparison of the predicted and measured ICRs shows that the relative error is within 5%. There are also reasonable agreements and strong correlations between the model and tests results. The new ICR prediction model is also supported by the empirical prediction formulas developed by other researchers. Hence, the model can be used to reliably predict the ICR for axial-type roadheaders.

The “penalty factors” method for the prediction of TBM performances in changing grounds

Tunnel construction by TBMs through hard rock is significantly affected by the geological and geotechnical conditions at tunnel level. Ground parameters such as uniaxial compressive strength, fracturing degree and abrasiveness, and factors such as water inflows and stress level may deeply affect the way a TBM will perform. In addition, different types of TBMs will behave differently in a given condition.This paper presents a method for TBM performance prediction in changing grounds, which has been developed in the framework of the European project “New Technologies for Tunnelling and Underground Works” (NeTTUN). The model starts from an optimum TBM performance in best conditions, i.e. when all ground parameters are in their “best state”. A stepwise reduction of the optimum advance rate is then performed, according to “reduction factors” that quantify the effect of degrading ground conditions on the TBM advance rate. By doing so, the “penalty factors” model is able to take into account a very wide range of ground conditions, from very good to very poor. Two types of TBMs commonly employed in rock tunnelling have been considered, i.e. Gripper and Shielded machines, each of them characterized by its own set of reduction factors.In order to consolidate the factor values and to validate the model, a TBM performance database, also developed in the framework of the project NeTTUN, has been used. The database includes a large number of tunnels excavated in different ground conditions with all standard TBM types. The comparison between the values given by the “penalty factors” model and the actual TBM performances observed during construction shows that the developed tool may provide a reliable estimation of the TBM performance based on simple ground parameters.The “penalty factors” model has also been interfaced with the DAT (“Decision Aids for Tunnelling”). The DAT software, co-developed by MIT and LMR-EPFL, is able to compute the probabilistic distributions of the tunnel construction time and – cost in function of the geology – and construction related uncertainties.The model is conceived to be used in its present form. However, the methodology can be easily adapted to match the expertize of the user, who is free to update the optimal performances, the ground parameters and/or the values of the reduction factors according to his/her own experience. The model can also be extended to other TBM types and to conventional excavation methods.

Rock Cracking Indices for Improved Tunnel Support Design: A Case Study for Columnar Jointed Rock Masses

Measurements indicate that the development of cracking is a key feature relating to the strength and collapse of a columnar jointed rock mass. In this context, a new support design method utilising rock cracking indices for columnar jointed rock mass under high stress is proposed to restrain the development of cracking in the surrounding rock mass. The method involves limiting the cracking evolution of the surrounding rock mass by designing the appropriate parameters and time of installation of the support system. Two indices are suggested: the allowable depth of the excavation damaged zone (EDZ); and the allowable damage extent of the rock mass in the EDZ. The method involves limiting the evolution of cracking in the surrounding rock mass by designing the parameters and time of installation of the support system. The support system should have a suitable stiffness and installation time so as to restrain the evolution of the depth and damage extent of the EDZ within the surrounding rock. Therefore, the depth and damage extent of the EDZ, as well as the axial stress in the anchor bolts, are calculated at different distances between the support location and the tunnel working face to find the appropriate stiffness and installation time of the support system. The method has been successfully adopted to determine the thickness of shotcrete, the arrangement and installation time of rockbolts, and other parameters, for five large diversion tunnels at the Baihetan hydropower station, China, which were excavated in columnar jointed rock masses.