Search

Background: Hazardous chemicals are essential for modern society but the use and transportation of them bears the risk of major incidents. Past incidents have revealed the importance of preparation and training of emergency medical service (EMS) personnel when responding to these incidents. However, studies have shown the level of preparedness to be insufficient. There is a lack of knowledge as to how EMS personnel perceive their preparedness and response when facing chemical incidents. Aim: The aim of this study was to qualitative investigate working procedures regarding chemical incidents among a cohort of EMS personnel. Method: Seventeen ambulance nurses from rural and urban areas were individually interviewed using four different realistic scenarios (vignettes). The transcribed text from the interviews was analyzed using qualitative content analysis. Result: The results were derived into two categories with underlying sub-categories: a struggle to organize the onsite work situation (insufficient managerial support, limited resources, trust in rescue services, difficult decision making, stressful responsibilities); and decontamination—a demanding and risky situation (risk management, work in protective gear, aggravating circumstances). Participants often lack real life experience in facing a chemical incident and training that improves preparedness and the ability to respond adequately. Conclusion: Chemical incidents pose many challenges for EMS personnel, but with proper training efforts many of these challenges could be solved. This study has shown the need for more accessible chemical incident training targeting EMS personnel: especially focusing on risk assessment; managerial support; resource management; equipment; and decontamination, including stress management and decision-making. Research in the area of chemical incidents is sparse and there remains much to understand concerning work procedures during chemical incidents.

Concrete dams in cold regions are designed to resist static loads from the ice sheet forming on the reservoir. Current guidelines suggest design ice loads of 50-250 kN/m based solely on geographical location, overlooking site-specific conditions. For many dams, this constitutes a considerable part of the total horizontal load and could theoretically cause problems with stability, especially for lower dams. However, the knowledge about the actual magnitude of ice loads remains limited, and no stability failure initiated by ice loads has been reported. This paper presents results from ice load measurements using a 1 X 3 m2 load panel installed at two dams in Sweden. The results from ice load measurements are presented alongside external factors such as water level, ambient temperatures, precipitation, and ice thickness, offering a more comprehensive understanding of the variables affecting ice loads on concrete dams., QC 20241211, Forecasting of ice-loads on concrete dams

Extrusion-based 3D concrete printing (3DCP) is a promising technique for fabricating complex concrete elements without formwork, offering advantages like cost reduction and enhanced design flexibility by decoupling manufacturing costs from part complexity. However, this extended formal freedom is still constrained by the fabrication process and material properties. This paper presents a novel method for applying topology optimisation internally i.e. preserving the external boundaries of the concrete element while reducing material use and weight. This method adapts the extrusion thickness along the part according to the expected stresses, reducing the material use while enhancing structural performance. To validate this method, three different unreinforced 3DCP beams are tested in three-point bending. Results show that beams with optimised material distributions presented a higher strength-to-weight ratio, averaging 47% and 63% compared with the conventional 3D printed beam. This paper demonstrates the potential of internal topology optimisation for improving the efficiency and sustainability of 3DCP., QC 20240515This project has received support from Hesselmanska Foundation, the Development Fund of the Swedish Construction Industry (SBUF) 13791, and the strategic innovation program Smart Built Environment (2020-00257), which is part of the strategic innovation areas initiative funded by Vinnova — the Swedish Innovation Agency, Formas — a Swedish Research Council for Sustainable Development and the Swedish Energy Agency. Printable material for 3DCP experiments was supplied by Sika (Sika Sverige AB).

Today, the world is facing an enormous challenge where the emissions of greenhouse gases mustbe reduced significantly to stop the increasing mean temperature. For the construction industry,this challenge means that structures must be designed more carefully, and materials must be usedand produced more efficiently. Concrete is one of the most widely used materials, and cementproduction alone contributes to around 8 % of the world's total CO2 emissions. This paper presentsa pilot study in which part of the cement clinker content in accelerated shotcrete is replaced withground granulated blast furnace slag (GGBS). Shotcrete is widely used as part of the rock supportfor tunnels in hard rock and has a large cement content. Thus, the environmental impact must bereduced significantly to meet future demands. However, introducing GGBS will slow downstrength development, which is a crucial part of shotcrete. Thus, this paper aims to investigate theearly strength development, i.e., after one and seven days. The results show that an averagecompressive strength of 18 MPa can be reached after 24 hours when 35 % of the cement clinkercontent is replaced with GGBS. Finally, some important topics for further studies are pointed out., QC 20240108

Dammhaverier är mycket ovanliga och därför är kunskapen om brottförloppet vid ett potentiellt dammbrott begränsad. Uppstår brottet utan förvarning, eller finns tidiga tecken på allvarliga problem? Hur utvecklas brottsbräschen under brottförloppet? Detta är frågor som blivit än mer aktuella efter tre internationella dammhaverier under 2023. För att söka svar har en serie skalmodellförsök utförts där haverier av betongdammar simuleras. En viktig parameter vid säkerhetsbedömningen av en betongdamm består i att utvärdera dess stabilitet. Förenklat görs dettag enom att jämföra om dammkroppens vikt är tillräcklig för att stå emot lasten från vattnets tryck. Traditionellt beaktas enbart en mindre del av en betongdamm när dess stabilitet utvärderas men de nya försöken indikerar att det vore eftersträvansvärt att undersöka hela dammen samtidigt eftersom lasten fördelas mellan konstruktionsdelarna. Många betongdammars tillstånd övervakas idag genom automatiska mätningarav till exempel vattenstånd, förskjutningar och grundvattentryck. Dock finns det ingen standardiserad metod för att definiera larmgränser,vilket detta projekt syftar till att utveckla i framtiden., QC 20240118

The infrastructure is in many countries aging and continuous maintenance is required to ensure the safety of the structures. For concrete structures, cracks are a part of the structure's life cycle. However, assessing the structural impact of cracks in reinforced concrete is a complex task. The purpose of this paper is to present a dataset that can be used to verify and compare results of the measured crack propagation in concrete with the well-known Digital Image Correlation (DIC) technique and with Crack Monitoring from Motion (CMfM), a novel photogrammetric algorithm that enables high accurate measurements with a non-fixed camera. Moreover, the data can be used to investigate how existing cracks in reinforced concrete could be implemented in a numerical model. The first potential area to use this dataset is structural engineering. The data can be used to verify non-linear material models used in a finite element (FE) software to simulate the structural response of reinforced concrete. In particular, the data can be used to investigate how existing cracks should be modelled in a FE model. The second potential area is within image processing techniques with a focus on DIC. Until recently, DIC suffered from one major disadvantage; the camera must be fixed during the entire period of data collection. Naturally, this decreases the flexibility and potential of using DIC outside the laboratory. In a recently published paper [1], an innovative photogrammetric algorithm (CMfM) that enables the use of a moving camera, i.e. a camera that is not fixed during data acquisition, was presented. The imagery of this dataset [2] was used to verify the potential of this algorithm and could be used to validate other approach for non-fixed cameras. The dataset presented in this paper includes data collected from a three-point bending test performed in a laboratory environment on uncracked and pre-cracked reinforced concrete beams. Structural testing was performed using a displacement, QC 20231101, TACK - Tunnel Automatic CracK Detection

This dataset contains data from three-point bending test of uncracked and cracked reinforced concrete in a laboratory environment.First, uncracked beams were tested to a load level close to the maximum capacity. The cracks were thereafter mapped before the beams were tested until failure. During the second test, the crack propagation was monitored using four fixed cameras and one non-fixed camera. The data contains measured force and displacement from the test, imagery from the fixed and non-fixed cameras as well as documentation of initial cracks and structural testing of reinforcement. A full description of the dataset is provided in the paper "Experimental dataset to assess the structural performance of cracked reinforced concrete using Digital Image Correlation techniques with fixed and moving cameras" published in Data in Brief., QC 20240102, TACK -Tunnel Automatic CracK Detection

Large volumes of steel fibre reinforced shotcrete (sprayed concrete) and steel bolts are commonly used to support tunnels in hard rock. This generates a high CO2-footprint which must be reduced in order to decelerate the continuously increasing average temperature worldwide caused by the emissions of greenhouse gases. Thus, alternative design methods and the possibility to use other materials than steel are currently investigated. Work is ongoing on testing the load-bearing capacity of shotcrete reinforced with fibres of steel, basalt and synthetic materials. This also includes a comparison between tests using Round Determinate Panels (RDP) and four-point bending of beams. Moreover, the practical use of RDP testing as a quality control methodology is also investigated in situ. Here, the goal is to identify several shotcrete mixes suitable for use in tunnelling so that the right material and fibre volume can be used in the right place., QC 20231023

Although the failure of a concrete dam is a complex and highly dynamic process, the current safety assessments of concrete gravity and buttress dams rely on a simplified 2D stability analysis, which neglects the load redistribution due to 3D monolith interactions and the valley shape. In addition, the estimation of breach parameters in concrete dams is based on assumptions rather than analyses, and better prediction methods are needed. Model tests have been conducted to increase the understanding of the failure behavior of concrete dams. A scale model buttress dam, with a scale of 1:15, consisting of 5 monoliths that were 1.2 m in height and 4 m in width, was constructed and loaded to failure using water pressure. The model dam had detachable abutment supports and shear keys to permit variations in the 3D behavior. The results showed that the shear transfer was large between the monoliths and that the failure of a single dam monolith is unlikely. A greater lateral restraint gives not only a higher failure load but also a better indication of impending failure. These findings suggest that the entire dam, including its boundary conditions, should be considered during a stability assessment. The results also suggest that the common assumption in dam safety codes that a single monolith fails during flooding analysis is not conservative. The dataset obtained provides a foundation for the future development of dam-monitoring alarm limits and for predictive models of dam-breaching processes., QC 20231017

Dam failures may have catastrophic consequences, including the release of largeamounts of water, significant property damage, and loss of life. However, safety assessments ofconcrete gravity and buttress dams often rely on simplified methods that do not consider the interactionbetween monoliths, the shape of the foundation or the presence of stiff abutments. Numericalmodeling can be a valuable tool for analyzing the stability of these dams, but it can bedifficult to validate these models due to a lack of documented dam failures. This paper presentsthe results of a numerical study examining the ability of dynamic finite element analyses to simulatedam failures. The study used the results from a series of physical model tests as a case studyfor validation. It was found that the numerical model was able to accurately reproduce the failuremode and breach development observed in the physical model tests and capture the effect of theloading rate on the failure mode and time for the failure to develop. Simulations were also performedin prototype scale to verify that the model tests were representative of a real dam failure.Further research is needed to determine the reliability of the numerical models under differentloading conditions and in realistic geological settings. However, these findings suggest that numericalmodeling can be a valuable tool for analyzing the stability of concrete gravity and buttressdams and predicting the development of failures., QC 20231017

Fibre-reinforced shotcrete (sprayed concrete) is one of the major components in the support system for tunnels in hard rock. Several empirical design methodologies have been developed over the years due to the complexity and many uncertainties involved in rock support design. Therefore, this paper aims to highlight how the choice of design methodology and fibre type impacts the structural capacity of the lining and the emission of greenhouse gases (GHG). The paper starts with a review of different design methods. Then, an experimental campaign is presented in which the structural performance of shotcrete reinforced with various dosages of fibres made of steel, synthetic and basalt was compared. A case study is presented in which the permanent rock support is designed based on the presented design methods. Here, only the structural requirements were considered, and suitable dosages of fibres were selected based on the experimental results. The emission of GHG was calculated for all design options based on environmental product declarations for each fibre type. The result in this paper indicates that synthetic fibres have the greatest potential to lower the emissions of GHG in the design phase. Moreover, the choice of design method has a significant impact on the required dosage of fibres., QC 20230307

Fibre-reinforced shotcrete is an essential part of the support of hard rock tunnels. Due to the complexity of the design, a combination of empirical and numerical analysis is commonly used in the design. The required dosage of fibres for structural purposes is determined based on minimum energy absorption or residual flexural strength. The latter is derived from tests on beams, while energy absorption is tested on panels. It is widely known that tests on beams suffer from a large scatter in results due to the short fracture zone in combination with the natural variation in the number and orientation of fibres which bridge the crack. This impacts the characteristic strength derived from these tests negatively. This paper presents a numerical study to investigate how the test method affects the required dosage of fibres. First, a non-linear model for shotcrete based on continuum damage mechanics is presented. Thereafter, the model is tuned against test results for beams and panels. A model tuned on beams is then used to simulate the response of a panel and vice versa. The results indicate that the size of the fracture zone has a significant effect on the post-cracking behaviour and that the required dosage of fibres could be decreased if specimens with longer fracture zones, i.e., panels or slabs, are used., QC 20231122

In recent decades, many cities have become densely populated due to increased urbanization, and the transportation infrastructure system has been heavily used. The downtime of important parts of the infrastructure, such as tunnels and bridges, seriously affects the transportation system’s efficiency. For this reason, a safe and reliable infrastructure network is necessary for the economic growth and functionality of cities. At the same time, the infrastructure is ageing in many countries, and continuous inspection and maintenance are necessary. Nowadays, detailed inspections of large infrastructure are almost exclusively performed by inspectors on site, which is both time-consuming and subject to human errors. However, the recent technological advancements in computer vision, artificial intelligence (AI), and robotics have opened up the possibilities of automated inspections. Today, semiautomatic systems such as drones and other mobile mapping systems are available to collect data and reconstruct 3D digital models of infrastructure. This significantly decreases the downtime of the infrastructure, but both damage detection and assessments of the structural condition are still manually performed, with a high impact on the efficiency and accuracy of the procedure. Ongoing research has shown that deep-learning methods, especially convolutional neural networks (CNNs) combined with other image processing techniques, can automatically detect cracks on concrete surfaces and measure their metrics (e.g., length and width). However, these techniques are still under investigation. Additionally, to use these data for automatically assessing the structure, a clear link between the metrics of the cracks and the structural condition must be established. This paper presents a review of the damage of tunnel concrete lining that is detectable with optical instruments. Thereafter, state-of-the-art autonomous tunnel inspection methods are presented with a focus on innovative mobile mapp, QC 20230426, TACK -Tunnel Automatic CracK Detection

Tunnels in hard rock are typically supported with a thin layer of fibre-reinforced shotcrete in combination with rock bolts. Cracks in the shotcrete could lead to corrosion of the fibres, which reduces the residual strength and could lead to downfall of shotcrete. Therefore, routine inspections are carried out to maintain a safe tunnel. Today, visual inspections are mainly performed, which is timeconsuming and prone to human errors. TACK (Tunnel Automatic CracK Detection) is a research project that aims to develop an autonomous tunnel inspection method based on a hybrid approach of photogrammetry and deep-learning. Data from the tunnel is collected with a mobilemapping system equipped with LiDAR sensors and high-resolution cameras. LiDAR data is used to create a 3D model of the tunnel. Then, a deep-learning approach is used to automatically detect cracks in the acquired images. Once the cracks are detected, a novel photogrammetric algorithm is used to calculate the geometric features of the cracks, i.e. length and width. Finally, the risk associated with the cracks is assessed, and critical sections in need of repair or visual inspections can be pointed out. This paper presents a case-study based on data collected from one tunnel., QC 20220912, TACK -Tunnel Automatic CracK Detection

The structural behaviour of fibre reinforced shotcrete (sprayed concrete) as support in hard rock tunnels are complex and depends on the interaction between shotcrete, bolts and rock. It is here studied how variations in shotcrete thickness and bond strength affect the behaviour of this type of rock support system. Numerical models are used to simulate bond failure, shotcrete cracking and pull-out of grouted rock bolts. It is shown that local variations in shotcrete thickness affects possible shrinkage crack patterns and when subjected to the load from a loose block, the force is transferred to the surrounding rock through bond stresses distributed over a narrow band in the shotcrete. Moreover, it is shown how the structural capacity with respect to bond failure depends on the shotcrete thickness., QC 20220919

In this dataset, data from experimental testing of fibre-reinforced shotcrete is presented. The dataset contains five different fibres made of steel (Dramix 3D, Dramix 4D and Dramix5D), synthetic (BarChip R54) and basalt (MiniBar). Preparation of specimens and testing were performed by Vattenfall R&D in Älvkarleby, Sweden. This first version of the dataset contains the results for shotcrete specimens prepared through casting. The same shotcrete mix was used for all specimens, and three different dosages were used for each of the fibres except for Dramix 5D, for which only two dosages were tested. The dataset contains the shotcrete mix and standard output for the test of compressive strength according to EN 12390-3, residual flexural strength according to EN 14488-3 and energy absorption according to ASTM C1550. This dataset can be used to study how the structural toughness of fibre-reinforced shotcrete is affected by the dosage of fibre. Moreover, the data can be used to compare the structural performance of fibres of different materials. The data also provide a foundation to select a reasonable dosage of fibres to fulfil the structural requirements put on shotcrete in the design phase., QC 20230404

Fibre-reinforced shotcrete is the most common support method for hard rock tunnels in the Nordic countries. The design of shotcrete is often based on empirical methods or simplified analytical equations, which neglect variations in mechanical properties and shotcrete thickness. Data collected from the field shows that significant variations in shotcrete thickness and bond strength should be expected during tunnel construction. However, how this affects the structural behaviour and capacity of the shotcrete lining is unknown. Moreover, the design philosophy for shotcrete assumes that the primary failure modes of shotcrete, i.e. bond and flexural failure, can be treated separately. This was derived based on observations of experiments in a laboratory environment. Therefore, the focus of a finalized doctoral project was to develop a numerical framework to simulate the structural behaviour of fibre-reinforced shotcrete in interaction with hard rock and rock bolts. The effect of variations in shotcrete thickness and bond strength was studied through numerical simulations to increase the understanding of its effect on the failure load of the lining. The results indicate that the most important parameter is the mean value of the shotcrete thickness and bond strength around a narrow perimeter of the block., QC 20230307

Världen står inför en enorm utmaning där utsläppen av växthusgaser måste minskas för att bromsa den ständigt ökande globala medeltemperaturen. Samtidigt har en lång urbaniseringstrend lett till att transportinfrastrukturen i många tätbefolkade städer måste byggas ut för att bibehålla ett fungerande transportnät. I många fall är tunnlar det mest fördelaktiga alternativet eftersom de inte stör den befintliga stadsbilden. För att minska klimatpåverkan från byggandet av nya tunnlar har Trafikverket initierat ett forskningsprojekt som ska undersöka potentialen för alternativa fibrer och detta drivs av avdelningen för Betongbyggnad på KTH., QC 20221227

Reducing the environmental impact from tunnel construction put focus on finding alternative designs for rock support based on fibre reinforced shotcrete (sprayed concrete). Different types and materials for fibres for use in shotcrete are developed and new methods for control of the load-bearing capacity and new techniques for material investigation in laboratory environments are tested. In an ongoing project the behaviours under flexural loading for shotcrete with some fibres of typical geometries and materials are compared through testing of Round Determinate Panels. For the tested dosages of fibres, the highest energy absorption capacity was for steel fibres, with macro synthetic and basalt fibres showing similar but lower results. The efficiency of fibres depends on the numbers crossings a crack and how these are oriented vs tensile stresses. Computed tomography (CT) X-ray scanning is now used in the laboratory for visualization of the interior of shotcrete samples. Examples from examination of steel fibre orientation in test cores are given., Part of proceedings ISBN 978-294064315-8QC 20221025

QC 20221025

Crack detection and measurement are standard procedures during infrastructure inspections all over the world. Traditionally, infrastructures are only visually inspected. To accomplish this, tunnels must be closed and inspections are carried out during the night to minimize infrastructure downtime. Also, the limited time and the length of the system make it impossible to accurately inspect tunnels which increases the risk that cracks are not detected. Recently, inspections have been carried out using semi-automatic methods where a mobile mapping equipment is used to capture the scene and reconstruct the 3D model (the socalled digital twin) of tunnels using geomatics sensors (visible and infrared cameras, LiDAR, IMU). Then, the digital twin and the images are manually analysed to find cracks and mark their extent. Due to the large amount of data, the method is time-consuming, inefficient and affected by errors. The aim of this work is to improve efficiency and accuracy of inspections., QC 20220928, TACK - Tunnel Automatic CracK Detection

Fibre-reinforced shotcrete is the most common support method for hard rock tunnels in the Nordic countries. Data collected from the field shows that significant variations in shotcrete thickness and bond strength should be expected during the construction of a tunnel. However, how this affects the structural behaviour and capacity of the shotcrete lining is unknown. Therefore, this was the focus of a recently finalized research project at KTH Royal Institute of Technology, in which numerical simulations were used to study the structural behaviour of fibre-reinforced shotcrete in interaction with hard rock and rock bolts., QC 20220908

Today, Digital Image Correlation (DIC) has become a standardized method to track displacements and crack-propagation of civil engineering structures in a laboratory environment. The benefit of using DIC over other standard methods is that it is contact-free and only requires a standard DSLR camera. Moreover, the displacement can be tracked over the entire image, which is a great advantage compared to the limitations of standard sensors that only measure the deformation at a specific point. In standard DIC, the displacements are directly extracted from the images. Hence, the position of the camera must be fixed during the entire test. Therefore, DIC is commonly used in a laboratory environment to measure displacement during short-term testing, e.g. testing of the structural capacity of a reinforced concrete beam. The data presented in this paper was used to verify a newly developed and innovative photogrammetric algorithm, Deformation from Motion (DfM). This algorithm overcomes the standard limitation of traditional DIC and enables high-accuracy measurements to be performed using a camera with no fixed position. As a reference, the crack propagation was on one side monitored with a LVDT and on the other side with a camera with a fixed position. During testing, a moving camera also captured imagery on both sides., QC 20230913, TACK -Tunnel Automatic CracK Detection

Fibre reinforced shotcrete (sprayed concrete) is often used to support tunnels in hard rock. The shotcrete should be designed to carry the load from a loose block, which is assumed to be transferred to the surrounding rock mass over a narrow band. It is commonly accepted that the width of this band is constant, and independent of the shotcrete thickness. In this paper, numerical simulations are used to show that the width of this band and the load capacity is strongly correlated to the mean shotcrete thickness around the perimeter of the block. Furthermore, it is also shown that a strong linear correlation exists between the mean bond strength and the rock support capacity. Based on this, a lower bound function to estimate the structural capacity for the lining is suggested. No correlation was found between the structural capacity and the minimum or maximum shotcrete thickness or bond strength. This indicates that, under certain conditions, local areas with low thickness and bond strength can exist around the block perimeter without having any significant effect on the rock support capacity., QC 20210910

Civil infrastructures, such as tunnels and bridges, are directly related to the overall economic and demographic growth of countries. The aging of these infrastructures increases the probability of catastrophic failures that results in loss of lives and high repair costs; all over the world, these factors drive the need for advanced infrastructure monitoring systems. For these reasons, in the last years, different types of devices and innovative infrastructure monitoring techniques have been investigated to automate the process and overcome the main limitation of standard visual inspections that are used nowadays. This paper presents some preliminary findings of an ongoing research project, named TACK, that combines advanced deep learning techniques and innovative photogrammetric algorithms to develop a monitoring system. Specifically, the project focuses on the development of an automatic procedure for crack detection and measurement using images of tunnels and bridges acquired with a mobile mapping system. In this paper, some preliminary results are shown to investigate the potential of a deep learning algorithm in detecting cracks occurred in concrete material. The model is a CNN (Convolutional Neural Network) based on the U-Net architecture; in this study, we tested the transferability of the model that has been trained on a small available labeled dataset and tested on a large set of images acquired using a customized mobile mapping system. The results have shown that it is possible to effectively detect cracks in unseen imagery and that the primary source of errors is the false positive detection of crack-like objects (i.e., contact wires, cables and tile borders)., QC 20201001

Vilka brottmekanismer är det som styr bärförmågan för en bultförankrad sprutbetongförstärkning och hur påverkas förstärkningens bärförmåga av att enskilda prover ej uppfyller ställda krav avseende tjocklek eller vidhäftningshållfasthet? Dessa frågor har studerats och besvarats i ett nyligen avslutat doktorandprojekt genomfört på avdelningen för Betongbyggnad på Kungliga Tekniska Högskolan. Ett ramverk för numeriska simuleringarna har utvecklats för att studera sprutbetongens bärförmåga och särskild fokus har lagts på att studera hur vanligt förekommande variationer i sprutbetongtjocklek och vidhäftningshållfasthet påverkar förstärkningens bärförmåga och strukturella beteende., QC 20210910

During the construction of a rock tunnel in Stockholm, several sections with leaching shotcrete (sprayed concrete) were found one year after the spraying was completed. An investigation was therefore conducted, and its results are presented in this paper. The amount of leaching after such a short time indicated that a one-sided water pressure existed in combination with a permeable shotcrete. The reason for the water pressure was likely a partly unsuccessful grouting that created sections with leaking water. The permeable shotcrete could be a combined result of insufficient curing and the use of accelerators, and the effect of in-situ curing was therefore investigated. A total of six slabs were sprayed and cured under different conditions in the tunnel. Test results according to standards indicated that curing has no significant effect on the development of mechanical strength or water penetration through the shotcrete. However, this is believed to be a result of the test method rather than the non-existing effect of curing. Lastly, some modifications to the test standard were proposed for future studies of in-situ curing., QC 20200123

Shotcrete is widely used as rock support and can support the load from blocks either by bonding to the rock or by bending between rock bolts. By introducing fibres, the ductility of the shotcrete will increase and the crack widths decrease. Predictions of the structural behaviour for fibre reinforced shotcrete (FRS) are however complicated due to the large scatter normally seen in test results. The reason is mainly related to the non-uniform distribution and orientation of the fibres which could lead to uncertainties regarding the quality of in-situ shot-crete. The aim with this paper is therefore to investigate if a probabilistic material model for FRS can be used to capture the scatter in the results. An isotropic damage model that combines an exponential softening curve for unreinforced shotcrete and a bi-linear curve to account for the effect of fibres were used. Suitable distributions for each of the parameters in the model have been proposed based on fitting of experimental results. Thereafter, Monte Carlo simula-tions were used to produce results for a large number of lab tests. Results show that the model together with the proposed distributions was able to capture the scatter in test results., QC 20191112

Tunnels in hard, jointed rock are commonly reinforced with shotcrete (sprayed concrete) applied directly on the irregular rock surface. The thickness for such linings can be as small as 50 mm, which result in a fast drying. The resulting shrinkage of the restrained lining is a well-known phenomenon, which leads to cracking. The installation of drainage systems also results in an end-restrained shotcrete lining that is more prone to shrinkage cracking. The drying process is a complex problem that depends on multiple factors such as cement content, porosity and ambient air conditions (i.e. temperature, relative humidity and wind speed). Two numerical models capable of capturing the structural effects of drying shrinkage were compared in this study. It was found that inclusion of non-linear drying shrinkage is important for accurately describing crack initiation in an end-restrained shotcrete slab. The best fit to the experimental data was obtained when the rate of drying was described as a non-linear decreasing function., QC 20180307

Tunnels in hard and jointed rock are normally excavated with an arch shape to enable the rock to carry itself. The arch effect depends on the stability of individual blocks and too high or too low horizontal stresses could cause blocks to be pushed out or to fall down. To prevent this, systematic rock bolting in combination with fibre reinforced sprayed concrete (FRSC) is commonly used to support the rock. To understand the failure mechanism of the lining when subjected to the load from one block is therefore important for the design. In this paper, the three main failure mechanisms for a rock support shotcrete lining has been identified as failure in the fibre reinforced concrete, bond failure between shotcrete and rock or failure of rock bolts. For each of the failure modes, a short review of numerical methods is presented followed by a selection of a preferred modelling approach. The selected methods are then verified against experimental results from the literature. The selected methods all shows good agreements with tests and demonstrates the ability to simulate each failure mode one by one., QC 20180730

Modern tunnels in hard rock are usually constructed by drill and blast with the rock reinforced by shotcrete (sprayed concrete) in combination with rock bolts. The irregular rock surface and the projection method of shotcrete leads to a tunnel lining of varying thickness with unevenly distributed stresses that affect the risk of cracking during shrinkage of the young and hardening material. Depending on water conditions, shotcrete is either sprayed directly onto the rock surface or over a drainage system, creating a fully restrained or an end-restrained structural system. In this paper, a method for non-linear numerical simulations has been demonstrated, for the study of differences in stress build up and cracking behaviour of restrained shotcrete slabs subjected to shrinkage. Special focus was given to the effects of the irregular shape and varying thickness of the shotcrete. The effects of glass fibre reinforcement and bond were implemented in the study by changing the fracture energy in bending and in the interaction between shotcrete and the substrate. The study verifies that an end-restrained shotcrete slab is prone to shrinkage induced cracking, and shows the importance of a continuous bond to avoid wide shrinkage cracks when shotcrete is sprayed directly onto the rock., QC 20170418