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Metro (subway) is an advanced public transport infrastructure system in urban areas with high capacity. The traffic operation of a metro is not affected by other vehicle traffic thanks to underground tunnels. With these benefits metro lines are preferred to solve the traffic problem in urbanized cities such as Istanbul, which is the focus of this study. Metro projects require huge amounts of budgets to be built. Putting these projects into service in targeted time is of great importance. The objective of this study is to minimize total metro construction project time by utilizing fiber reinforcement in tunnel linings. In this research, using fiber reinforcement to construct primary (initial) tunnel linings and secondary (final) tunnel linings of the metro projects are analyzed in terms of project duration. After comparison of two railway tunnel projects, evaluations and observations of a completed metro project revealed that using fiber reinforcement for either the primary lining or the final lining of tunnels reduces construction time of metro station tunnels by 25%. In addition, using fiber reinforcement to construct both the final lining and the primary lining of tunnels reduces construction time of the metro station tunnels and the whole metro project by 47% and 22%, respectively. The results of this study can be useful for completing challenging metro projects and putting it into service within the targeted time.

Earth has been used worldwide as a building material for centuries and it is still one of the most used construction materials. In many countries the excavated soil is becoming one of the largest construction waste and its disposal is costly and problematic. For this reason, there is a rising interest in employing the excavated soil directly in field, possibly as an added value construction material. In this paper a new type of rammed earth is presented. This new material is based on the shotcrete technology and has been named shot-earth. A mix of stabilized soil, aggregates and water is consolidated by high speed projection rather than by mechanical compaction to obtain both structural and non-structural elements. The first characterization of the physical properties of this material has shown the great potential of this technology.

This paper presents the design and testing of a scale proof-of-concept prototype robotic end-effector system for autonomous robotic shotcrete application and radiation surveying in underground uranium mining environments. The system presented consists of two functionally distinct prototype tools that achieve the independent tasks of autonomous robotic spray pattern control and surface radiation surveying. The first prototype tool presented is a novel, robotic shotcrete spraying tool that is capable of autonomously maintaining and adjusting its circular spray pattern diameter on target surfaces in response to changes in target surface distance. Control algorithms are presented that give the robotic shotcrete spraying tool the capability to produce advanced figure eight and spiral spraying patterns for surface preparation applications that involve spot filling deep surface cracks and pockets. Physical testing of the prototype tool empirically verified its ability to maintain circular spray pattern diameters at various target distances and demonstrated the application potential of the advanced figure eight and spiral spraying patterns. The second prototype tool presented is a Geiger–Müller tube-based radiation detection tool that uses lead shielding and a single-hole collimator in combination with precise robotic positioning to capture localized radiation measurements of surfaces within radiation-rich environments. Physical testing of the prototype tool demonstrated its ability to create radiation survey profiles that distinctly characterized the radiological profile of test target surfaces embedded with various radioactive sources.

The Tunnel Oberau, with a length of 2.9 km, forms the core of the local bypass of Oberau. Between the two massifs Kirchbichl and Muhlberg, the tunnel is situated in the valley of the Giesenbach in alluvial gravel with only a small overlap underneath settlement-sensitive buildings. In this paper, the measures in the tunnel to minimize the settlements of the buildings during the shotcrete excavations are described. Basis for this planning were extensive 3D-FE-calculations. Furthermore, under two buildings a compensation grouting measure was carried out, in order to compensate the occurring settlements. This paper describes how the required time and the amount of injection material (grout) could be reduced during the compensation grouting in highly permeable gravel.

Research on underground structure has been carried out by many researchers from around the world in order to create an underground space that can ensure the safety of its users. One thing that must be considered in the underground structure is the support system which has objective to control the deformation of rock mass caused by stress distribution during or after the underground construction process. This literature review describes the distinction of supporting elements according to their characteristics and functions in a support system. The selection of supporting elements by empirical approach and finite element method will also be discussed in this paper. Grout injection and grout bolt are support elements that function as reinforcement. Friction bolt and mechanical point anchor serve to hold whilst mesh, straps, steel set, shotcrete and concrete lining serve to retain loose rock from falling. Both empirical approach and finite element method have its own strengths and weaknesses in determining the support system and therefore must be used together to produce a safe design according to the geological conditions of the project site. This article tries to help the contractors, engineers and designer in selecting appropriate support system in order to ensure safety of its users.

The authors express their sincere gratitude to engineering and technical personnel of Orlovskaia mine of Vostoktsvetmet ltd for assistance in organizing and conducting observations in mines.

For the first time in Pakistan, Steel Fibre-Reinforced Shotcrete (SFRS) is used as the final lining for the Diversion Tunnels of Gulpur Hydropower Project. The project’s diversion tunnels were open...

Shotcrete is often used for the construction and stabilization of tunnels and other underground structures, where it is susceptible to different forms of physical and chemical attacks affecting its durability. An advanced understanding of the factors that limit the durability of shotcrete is crucial to develop tailored strategies for enhancing its service life. The main focus of this contribution is to shed light on the durability of shotcrete by revising the literature, highlighting what is missing and needs to be addressed, assessing how the knowledge about concrete durability can be transferred to shotcrete, and providing recommendations for durable shotcrete structures.

The safety and stability of roadways is greatly influenced by the complex geological conditions present in the Sanmenxia Bauxite Mine, Henan Province, China. In this study, based on data from field survey, advanced detection methods, numerical studies, and monitoring studies, we have adopted the method of steel fiber-reinforced shotcrete to improve the excavation rate of roadways and guarantee the safety of the tunnel when it passes through unfavorable geological bodies, such as shale rocks and broken argillaceous limestone. Field surveys showed that the stability of roof rocks is the major problem faced by engineers; however, tunnel construction using cast-in-situ concrete, which is the method currently applied, costs too much time, resulting in an excavation rate that is too slow to meet the requirements of the Sanmenxia Bauxite Mine. Here, we propose an optimized scheme which, when combined with numerical simulations and data from advanced detection techniques and field monitoring surveys, can improve the efficiency of roadway roof support. During the implementation of the new scheme, the geological anomalies ahead of the working face were detected in advance. It is assumed that the supporting effect of the steel fiber-reinforced shotcrete is equivalent to that of the cast-in-situ concrete as long as a certain thickness is reached. Moreover, the steel fiber-reinforced shotcrete has better mechanical properties than cast-in-situ concrete and achieves a better combination effect with surrounding rock masses. Based on geological conditions and numerical results, the shotcrete should be thickest in the middle area along the roadway axis passing through the unfavorable geological bodies, and gradually become less thick from the middle to both ends. Field tests were carried out to verify the effectiveness of the scheme. The monitoring results show that the roadway passing through broken argillaceous limestone was stable after being supported by shotcrete (at least 80 mm); its thickness should reach at least about 120 mm when passing through shale rock mass. The results indicate that the use of steel fiber-reinforced shotcrete can considerably shorten the construction time compared with cast-in-situ concrete support. The scheme has proved to be a feasible, economical, and time-saving method for underground excavation in the Sanmenxia Bauxite Mine.

The reduction of clinker use is mandatory to lower the negative environmental impact of concrete. In shotcrete mixes, similarly to the case of conventional concrete, the use of supplementary cementitious materials (SCMs) and proper mix design allow for the substitution of clinker without compromising the mechanical properties. However, the impact of the substitution on the durability of shotcrete needs to be further assessed and understood. The results from the present study, obtained from real-scale sprayed concrete applications, show a reduction of the Ca2+ leaching and sintering potential of clinker-reduced shotcrete mixes due to the presence of SCMs. This positive effect, crucial for low maintenance costs of tunnels, is mainly related to a reduced portlandite content, which on the other hand negatively affects the carbonation resistance of shotcrete. Additionally, the hydration of SCMs positively influences the chloride penetration resistance presumably due to a combination of microstructural changes and changes in the chloride binding capacity. Differences found in the pore size distribution of the various mixes have low impact on the determined durability parameters, in particular compared to the effect of inhomogeneities produced during shotcrete application.

Although carbon textile reinforcement widely used to replace the steel reinforcing bars but the bonding strength of carbon textile is generally much smaller than that of common steel bars. This study examines the strengthening effect of concrete slab-type elements strengthened in flexure by carbon textile reinforcement according to the surface coating of textile and the amount of reinforcement. The effect of the surface coating of textile on the bond strength was evaluated through a direct pullout test with four different sizes of coating material. The surface coated specimens developed bond strength approximately twice that of the uncoated specimen. The flexural strengthening effect with respect to the amount of reinforcement was investigated by a series of flexural failure tests on full-scale reinforced concrete (RC) slab specimens strengthened by textile reinforced concrete (TRC) system. The flexural failure test results revealed that the TRC system-strengthened specimens develop load-carrying capacity that is improved to at least 150% compared to the non-strengthened specimen. The strengthening performance was not significantly influenced by the textile coating and was not proportional to the amount of reinforcement when this amount was increased, owing to the change in the failure mode. The outstanding constructability afforded by TRC strengthening was verified through field applications executing TRC strengthening by shotcreting on a concrete box culvert.

Investment in underground mining is coming down all over the world, but deep reserves are available for extraction. Conventional sinking and lining of mine shaft projets or pits for winding men and materials from deep underground mines are getting very costly and being deferred. We found Polish technology of Shaft sinking with monolithic mining very efficient in Sudamdih, Monidih and Satgram projects in India. Russian collaboration for Jhanjra for shaft sinking and mine construction for large mine has been successful. Underground production is declining world over, while remaining reserves are at greater depths. Designing and coding original model programs by collecting actual field data to run the programs to determine cost benefit at different depths with standard diameters has been done. Most companies are avoiding deep mining projects, because of exorbitant cost of shaft sinking. As per experience of the researcher, pre-split blasting and shotcrete lining can be much faster and cheaper. So model programs have been designed and run with practical field cost and technical data, as exemplified in this paper. Future of deep pit mining will be assured with successful adoption of the method in projects, especially through hard rock strata

This paper presents the results of investigation of properties of fine-grained concrete on expansive cement for fiber-reinforced shotcretes used for metro tunneling. Basic factors affecting material expansion after mixing with water are described. The influence of expansive components on the values of strength indices and volumetric deformations of shotcrete is studied. Improvement of process, physical and mechanical, and operational characteristics of obtained shotcrete is proven.

A criteria for how close, in time and distance, to young shotcrete blasting can take place would be an important tool in planning for safe and economical tunnelling projects. As a first step, field tests with shotcrete at ages of 1 to 25 hours, sprayed on tunnel walls, have been conducted in a Swedish mine. The shotcreted areas were subjected to vibrations from explosive charges detonated inside the rock. The acceleration measurements showed that the shotcrete had withstood high particle velocity vibrations without being seriously damaged. Drumminess of shotcrete appeared, indicating that the major failure mechanism was sudden loss of adhesion to the rock. Elastic wave propagation theory has been implemented numerically to further study the failure mechanism. Due to the changes in shotcrete-rock impedance ratio as the shotcrete cures, the stresses at the interface between shotcrete and rock experience a maximum during a short period within the first 24 hours of shotcrete age.

Rock bolts are commonly used in conjunction with Fibre Reinforced Shotcrete (FRS) linings to stabilise ground around excavations. A steel cover plate is often placed over the protruding end of a rock bolt to dissipate load from the bolt into the FRS lining. The process of drilling and installing rock bolts takes place after the lining is sprayed, so a hole must be made through the lining to insert the bolt. To examine the effect of this on lining behaviour, an investigation has been carried out to determine the influence of a central hole on the punching capacity of a FRC panel. Grout or concrete is commonly placed between the cover plate and lining to distribute the load more evenly, so the effect of this aspect of rock bolting practice on punching behaviour has also been examined.

The aim and objective of this research project was to develop and investigate a rapid method of strengthening the Unreinforced Masonry walls (URM) for out-of-plane action. A total of 12 URM walls, built inside a precast fiber reinforced concrete boundary frame, were strengthened with a cement based concrete mix with or without steel reinforcement. The concrete mixes included Fiber Reinforced Concrete (FRC) (two dosage of fibers (4.6 & 6.0 kg/m3)), Engineered Cementitious Composite (ECC), and plain concrete shotcrete (PLS). Two out of 12 walls were strengthened with steel mesh reinforced shotcrete (MRS) such that a steel mesh was attached to the surface of the walls prior to spraying with concrete. In addition, one wall was plastered only with conventional cement mortar (RF) to serve as a reference. The strengthening materials were applied to both sides of URM walls using shotcrete technology. The walls were exposed to the air pressure of an actual blast from 10 kg of TNT explosive at a 1 m stand of distance. It was found that strengthening the walls with the proposed method significantly improved the out-of-plane behaviour of the URM walls. The results showed that the walls strengthened with ECCS exhibited the least damage followed by FRS-6, FRS-4.6, MRS, and PLS. Whereas, the reference wall (RF) did not survive the blast induced pressure and fully shattered into small pieces.

Limited knowledge on safe vibration levels near newly sprayed concrete (shotcrete) often leads to over-conservative limits in underground construction and tunnelling, with additional costs and plan ...

It is well known fact that masonry structures suffers extensive loss during earthquakes, leading to notable damage of lives. Majority of structures in India are Un-Reinforced masonry (URM) which are not strong and vulnerable under moderate earthquakes. Masonry construction remains vulnerable to seismic force due to many reasons like lack of integral action between brick and mortar, low shear strength of masonry, heavy mass and varying construction practices. Therefore, it is essential to increase seismic resistance of masonry structures utilizing dissimilar retrofitting measures. Past earthquakes in India and other countries reveals low seismic resistance of URM structure and extensive damage caused. Reconstruction of damaged structure may be very costly and time consuming therefore retrofitting is the best alternative to enhance the seismic performance of damaged structures. Many conventional and non-conventional techniques like, using ferrocement, shotcrete, steel elements application, grout injection, FRP, post-tensioning are available around the world for restoring the structures. This paper provides analytical work and finite element simulation of unreinforced masonry dome retrofitted using carbon fiber reinforced polymer (CFRP) or steel plate jacketing. The behavior of retrofitted structure is studied numerically. Dome structure have been analysed using commercial software SAP 2000. The structures have been analysed for gravity and earthquake loadings. Dome models have been analysed numerically using the time history data of 1999 Kocaeli earthquake while R.C. C frame is analysed by response spectrum method. Dome structure is retrofitted using steel plates and CFRP at the support level as well as tension zone. Analysis reveals that shell stresses are significantly reduced which may range from 10 percent to even 50 percent depending upon arrangement of retrofitting material for dome structure. Stress reduction can be observed significantly at the support level of the dome models.

This contribution is a study of the durability and transport properties of sprayed concrete used in an actual construction site. It considers whether concrete spraying can generate different porosities as the thickness of the sprayed layer increases. The work consisted of a study of the properties of the interior and exterior concrete layers with a particular focus on chloride penetration. A few of the methodologies and techniques used are compressive strength at 28 days, depth of penetration of water under pressure UNE EN 12390-8, boiled absorption and volume of permeable voids ASTM C642, and accelerate chloride penetration NT BUILD 443. Calculated transport property values included absorption (A) and volume of permeable voids (VPV), porosity interconnection, and chloride diffusion coefficient (De). The conclusion obtained is that there are no significant differences between the physical microstructural properties of the interior and exterior sprayed concrete layers, they present a similar porosity, and behave in the same way under a chloride attack when test tubes are completely saturated. The authors gratefully acknowledge to the competitive project BIA2016-78740-R: “Materiales proyectados ligeros para refuerzo y la rehabilitación del patrimonio urbano” funded by the Ministry of Economy and Competitiveness, within the 2016 Call for projects “Excelencia y Retos”. General Directorate of Scientific and Technical Research. Subdirectorate General for Research Projects.

This paper presents the recent advances in the development of a novel 3D concrete printing technology called Shotcrete 3D Printing (SC3DP). In order to demonstrate the unique assets of this technique a design and fabrication strategy for fully reinforced, double curved concrete demonstrator featuring high surface quality was developed, and is described in detail in this paper. In particular, two topics were highlighted in this demonstrator, firstly the integration of structural reinforcement in both principal directions and secondly an automated surface finishing process for a high-quality concrete surface. This combination of additive fabrication and formative and subtractive postprocessing was demonstrated at the unique large-scale Digital Building Fabrication Laboratory (DBFL) of Technische Universitat Braunschweig. The result of this fabrication experiment, a 2.5 * 2.3 * 0.18 m concrete wall element, is finally discussed in relation to the state of the art in 3D concrete printing.

3D concrete printing is of great potential to replace shotcrete for hard rock tunnel linings with the advantages of high surface quality and the avoidance of rebound. However, without spraying fresh concrete onto the excavated surface at a high speed, 3D printable concrete still faces challenges of achieving strong adhesion, which closely depends on the substrate surface properties. In this work, the influence of the substrate surface roughness and moisture content on the tensile adhesion of 3D printed concrete in the fresh and hardened state was studied. A tack test and a 3D concrete printing test were used to evaluate the tensile adhesion in the fresh state. Further, the tensile adhesion of 3D printed concrete in the hardened state was measured by a pull-off test and compared with that of mold cast samples. Results showed that the printed material could not completely fill macro rough textures due to the limited pressure at the nozzle. As a result, less contact at the interface was formed when the substrate surface roughness level increased, which subsequently compromised the tensile adhesion in the fresh and hardened state. Fortunately, the tensile adhesion in the fresh and hardened state can be improved by applying a coating onto the substrate beforehand. On the other hand, an increased moisture content enhanced the tensile adhesion in the fresh state due to surface tension, while it reduced the tensile adhesion in the hardened state in the context of 3D concrete printing which can be attributed to a higher water-to-cement ratio at the contact zone.

Salt lake is widely distributed in Western China. The high concentrations of chlorine salt, sulfate, and magnesium salt in soil and underground water are the leading causes to the deteriorated performance of lining shotcrete and corrosion of reinforcement. This study aims to investigate the durability performance and deteriorated rules and mechanism of shotcrete lining in salt lake corrosion environment by using dry-wet (DW acid-soluble sulfate ion; and pH value of pore solution are tested using X-ray diffraction, thermogravimetric-differential scanning calorimetry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, RapidAir 457, and electrochemical method. Acid solubility sulfate content clearly increased with the D&W cycle, and water-soluble chloride and sodium content slowly increased. Meanwhile, water-soluble calcium and concrete pH value decreased. The combination of the expansion stress and crystallization pressure from thaumasite, brucite, gypsum, ettringite, and crystallized salt enlarged the air-void number and air content in shotcrete. Moreover, web crack formation caused deterioration of the physical and mechanical properties of shotcrete. Meanwhile, normal concrete was damaged by macrocracks connected with air void and microcracks, thereby creating crystallization pressure. Drawing stress between steel fiber and shotcrete could evidently absorb the expansion stress and crystallization pressure. Consequently, steel fiber could improve shotcrete corrosion resistance.

The article proposed to use the specific surface area of the fibers to calculate the tensile strength of the fiber reinforced concrete and shotcrete. Graphs of the tensile strength dependences on the fiber diameter and length are plotted; the range of diameters at which smooth fibers will not be pulled out is established. Other ways of tensile strength increase of fiber reinforcement shotcrete were analyzed. It is proposed to use separate erection of shotcrete and the fibers in order to create a technology of ferrocement layers erection. There are named issues, which are needed to be solved in order to implement proposed method of reinforcement.

Studying the application of nanomaterial in cement matrixes is a new subject which has attracted the attention of researchers. Development of engineered cementitious composite has produced a solution to numerous shotcrete application challenges. In this study, mechanical tests were conducted to evaluate the strength of the concrete modified by fibers and nanomaterials in terms of comparison with conventional concrete and shotcrete. It is included in the application of Nano-Al2O3 and Nano-SiO2, which are some of the cement constituent. With proper homogenization, Nano-Al2O3 acts as filler for improving the pozzolanic reaction in the concrete. Nano-SiO2 particles also prevent the diffusion of external destructive factors into the concrete, thus improving the durability and stability of concrete. On the other hand, application of Alkali Resistant (AR) glass fibers improves the tensile and compressive strengths as well as concrete continuity and also resolves the changes created in mechanical properties of the fibers caused by alkaline concrete environment. Test results revealed that the maximum increase in compression and flexural strengths of modified concrete were 20.6 and 52%, respectively of its optimum compounds for 0.7% glass fiber with 1% Nano-Al2O3 and 1.5% Nano-SiO2, while in the modified shotcrete, these values were increased by 22.9 and 75%, respectively. In addition, application of the mentioned materials led to decrease of penetration depth and water absorption of the modified concrete by 46.78 and 2.5%, respectively, in relation to the conventional concrete. Also, addition of fibers and nanomaterials in shotcrete reduced the effect of cracking due to shrinkage and the modified shotcrete material rebound.

Most of the existing roughness estimation methods for water tunnels are related to either unlined or concrete/steel-lined tunnels. With the improvement in shotcrete technology, advancement in tunneling equipment and cost and time effectiveness, future water tunnels built for hydropower projects will consist of rock support with the extensive use of shotcrete lining in combination with systematic bolting and concrete lining in the tunnel invert. However, very little research has been performed to find out tunnel surface roughness for shotcrete-lined tunnels with invert concrete, which is important in calculating overall head loss along the waterway system to achieve an optimum and economic hydropower plant design. Hence, the main aim of this article is to review prevailing methods available to calculate tunnel wall roughness, and to use existing methods of head loss calculation to back-calculate roughness of the shotcrete-lined tunnels with invert concrete by exploiting measured head loss and actual cross-sectional profiles of two headrace tunnels from Nepal. Furthermore, the article aims to establish a link between the Manning coefficient and the physical roughness of the shotcrete-lined tunnel with invert concrete and to establish a link between over-break thickness and physical roughness. Attempts are also made to find a correlation between over-break thickness and rock mass quality described by Q-system and discussions are conducted on the potential cost savings that can be made if concrete lining is replaced by shotcrete lining with invert concrete. © 2017 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Many unreinforced masonry buildings are completely destroyed after destructive earthquakes but, their failure mechanisms cannot be precisely determined. More specifically damage to such buildings is evinced during low or moderate magnitude earthquakes. The aim of this study is to identify the failure mechanisms of existing unreinforced masonry buildings and present a reconstruction strategy or offer strengthening procedures, in order to inhibit damage to masonry structures after destructive earthquakes. For this purpose, a moderate magnitude earthquake which occurred on April 4, 2019 near the township of Sivrice in Elazig city, in the east of Turkey, was investigated. The magnitude of the studied seismic motion was expressed as M w = 5.2 by the Ministry of Interior Disaster and Emergency Management Presidency. Although this seismic effect was a moderate magnitude earthquake, significant failures occurred. Many masonry buildings and adobe dwellings in the villages of Sivrice were severely damaged by the earthquake. For field observations, ten villages located around the epicentre were visited 65 dwellings were observed and the damage patterns were assessed in detail. The observations showed that the main reasons for the damage to the dwellings were weak structural detailing of wall-to-wall and wall-to-roof connections, inhesion of earthen roofs, and a lack of bond beams in the structural walls. According to field observations, it is deduced that the performance of the undamaged masonry dwellings after earthquakes does not prove that they have adequate seismic safety. Therefore, reinforcing methods (shotcrete implementation, decreasing of space, corner reinforcing etc.) and innovative strengthening procedures (fibre reinforced polymer) are recommended for the undamaged existing unreinforced buildings at the end of the paper.

For decades, one of the most critical considerations of civil engineers has been the construction of structures that can sufficiently resist earthquakes. However, in many parts of the globe, ancient and contemporary buildings were constructed without regard for engineering, thus, there is a rising necessity to adapt existing structures to avoid accidents and preserve historical artefacts. There are various techniques for retrofitting a masonry structure, including foundation isolations, the use of Fibre-Reinforced Plastics (FRPs), shotcrete, etc. One innovative technique is the use of Shape Memory Alloys (SMAs), which improve structures by exhibiting high strength, good re-centring capabilities, self-repair, etc. One recent disastrous earthquake that happened in the city of Bam, Iran, (with a large proportion of masonry buildings) in 2003, with over 45,000 casualties, is analysed to discover the primary causes of the structural failure of buildings and its ancient citadel. It is followed by introducing the basic properties of SMAs and their applications in retrofitting masonry buildings. The outcomes of preceding implementations of SMAs in retrofitting of masonry buildings are then employed to present two comprehensive schemes as well as an implementation algorithm for strengthening masonry structures using SMA-based devices.

Reliability-based design optimization (RBDO) is applied to a rock tunnel support system, considering the ground-support interaction and the parametric uncertainties. Both reliability index approach (RIA) and performance measure approach (PMA) are employed as the RBDO algorithms. The first-order reliability method (FORM) and the response surface method (RSM) are used to perform the reliability analysis. The shotcrete thickness and its installation position are considered as two design variables to be optimized in an illustrative example of a circular rock tunnel. The influence of the two design variables on the reliability results is first investigated with respect to three failure modes, namely, the support capacity criterion, the tunnel convergence criterion and the rockbolt length criterion. Then, the proposed RBDO procedure is used to seek for the design variables of minimum shotcrete thickness and the optimal installation position for the rock tunnel example. The computational efficiency and stability between RIA and PMA are compared. The influences of the rock mass quality, the variation of the shotcrete thickness and the target reliability requirement on the optimized results are also investigated and discussed.

An analytical solution is proposed for limiting earth pressure on pre-stressed anchor–shotcrete retaining structures. The solution is in accordance with pre-stress diffusion model assumption, wedge theory and Mohr–Coulomb theory. Centrifuge tests were performed to investigate the feasibility of the analytical solution for the earth pressure on pre-stressed anchor–shotcrete retaining structures, and these were further verified by centrifuge tests from other published works. It was found that the results of both applied centrifuge tests agreed well with the analytical solution. The tests also provided strong proof that pre-stress has little influence on the pre-stress angle of diffusion based on elastic semi-infinite space theory.

Rail tunnels in Austria have to be amortized over an economic life of 150 years, so asset allocation has to focus on project control, project support and on predictive maintenance of tunnel lining and dewatering systems. Especially in view of the increase in total tunnel length by more than 100 per cent within the next ten years, the principles of predictive maintenance have to be improved. For this purpose, the development of proofed hybrid multi-scale methods is necessary. These methods have been used in the past to evaluate stresses in shotcrete linings, and future strategies could use the same methods for stress evaluation in the whole support structure. The second major point concentrates on work on monitoring and prediction of deposits in drain pipes. We have to look closely at filling levels and the degree of hardness of the deposits.