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In any underground excavation project, choosing the best excavation technique and careful preliminary assessments of wear costs and production rates are crucial aspects to consider. The production rate and costs of tools, as well as the frequency of tool replacement, deeply affect the duration and cost‐effectiveness of the whole project. Among the rock‐specific characteristics affecting tool wear, Cerchar abrasivity index (CAI) and uniaxial compressive strength (UCS) play an important role. In this article, the relationship between these two parameters was examined by regression analyses for 237 different rocks with the aim to define a preliminary and expected wear potential of three groups of rocks: sedimentary, metamorphic and igneous rocks. The analysis of the results showed that 86 % of the igneous rocks analysed have a CAI > 2, which is a medium or high level of abrasiveness. In sedimentary rocks, over 70 % of the samples are characterised by low abrasiveness behaviour (CAI < 2). Results obtained for these rocks can represent an instrument for predicting the abrasiveness potential of a rock when the UCS is known associating it with an expected range value of CAI. Metamorphic rocks, on the other hand, cannot be classified in specific ranges of UCS and CAI. For this rock group, therefore, a univocal tool for forecasting could not have been obtained, but analyses of rock type and quartz content show that the mineralogical content cannot be considered the only parameter for a wear analysis. [ABSTRACT FROM AUTHOR]

In the tunnelling industry, a large share of the market is occupied by EPB (Earth Pressure Balance) machines. To operate this kind of machine, a radical change in the rheological behaviour of the excavated soil must be performed, and this is achieved by adding water, foam, and, eventually, polymers. The stability of the foam is assessed through a half-life test. The main limitation of this test is that only one value is used in the characterization of the foam degradation process, which is insufficient to describe the whole evolution of the phenomenon. The results of more than 270 tests were modelled through a five-parameter mathematical formulation that suited the experimental data. The results show that the influence of concentration on the stability of the foam is not always present and that the flow rate used during production bears an influence on the characteristics of the foam. [ABSTRACT FROM AUTHOR]

Two‐component grout is nowadays the most popular backfilling technique, used widely in rock or soil thanks to its versatility and the undoubted advantages for operatives compared to other backfilling technologies. Despite its intensive adoption in shielded tunnelling projects, very poor and often fragmented information is available, especially on the engineering properties used for the mix design calibration (design phase) and secondly on construction sites as the acceptance protocol (operative phase). In this work, starting from real construction sites data, an analysis has been performed in order to determine the intrinsic characteristics of the two‐component grout technology. Moreover, the most frequently used engineering parameters have been identified to characterise both component A and the hardened grout, correlated with their usage frequency. The outcomes illustrate that although at the current time different choices are made at different construction sites, a pattern of tests has been recognised, that can be considered as a significant cornerstone for the characterisation of two‐component grout. [ABSTRACT FROM AUTHOR]

• Comparison approach for highlighting the bentonite role. • Mechanical performances improved by using the bentonite. • Bentonite not as grout stabiliser: a key ingredient for the grout properties. • Surface compression strength as valid mechanical parameter at short curing time. • Impossible to predict the grout performance for a certain bentonite without testing. Two-component grout is the most used backfilling technology in shielded mechanised tunnelling. Bentonite is an important ingredient in the production of component A, since it plays a key role in the mortar stabilisation. Furthermore, recent studies have highlighted its involvement in the mechanical and elastic performance of the hardened grout after short curing times, while no information is available for long curing times. This study proposes an innovative test campaign, based on a comparison between a standard two-component grout mix design (reproduced with 5 different bentonites) and a special mix design, produced without using the bentonite. This interesting comparison highlights the important role of the bentonite and its activation time in properties related to fresh grout (component A) and hardened grout. Assessments of bleeding, viscosity, unit weight, gel time, surface compression strength (SCS), uniaxial compression strength (UCS) and tensile strength (T 0) have permitted a deep quantitative analysis that, undoubtedly, highlights the importance of bentonite in this widespread backfilling grout technology. [ABSTRACT FROM AUTHOR]

The wear phenomenon evaluation in EPB shield tunneling machines is not a simple issue, as a large number of parameters are involved, such as soil and tool material properties, soil conditioning and pressure in the bulk chamber. The evaluation of the influence of these parameters and predicting this influence is a complex task and the research has proposed different test procedures and approaches. In this paper a new procedure for testing wear of tools with an innovative concept and design is presented. The experimental results obtained using conventional steel and hard material tools, tested with natural and conditioned soils, are discussed. The outcomes show the feasibility of the proposed procedure and the quality of the measurements that can be obtained using the proposed wear tool shape. [ABSTRACT FROM AUTHOR]

Rockfall protection net fences are key protection systems in mountainous areas worldwide to ensure the safety of infrastructures, roads and urban areas. Maintenance of these products is fundamental for public administrations in order to guarantee risk mitigation. This paper deals with the assessment of the installation problems and damages induced by ageing of rockfall protection net fences, using numerical modelling in order to evaluate the influence of these issues on their behavior. A percentage of the residual efficiency is assessed as a useful tool for risk analysis and maintenance planning. [ABSTRACT FROM AUTHOR]

• Bentonite in component A influences the elastic parameters of the grout. • Velocity of the shear wave is the main parameter for elastic properties computation. • The bentonite's influence on the Poisson's ratio is less than on the elastic moduli. Two-component grout is nowadays the material most used for the backfilling phase in tunnelling with a shield machine. The operative simplicity of the technology and the fast hardening reaction between the two components are the main reasons that have contributed to the intensive spread of the use of this backfilling technique all around the world. Although bentonite is one of the basic ingredients for the grout production, its effect on the elastic properties of the grout has not been completely investigated so far. In this work, six different two-component grouts and their elastic properties have been studied by means of geophysical measurements. The six grouts were characterised by the same mix design and five different bentonites, while one grout had no bentonite. The variation of the dynamic parameters over time was analysed at short curing times (up to 24 h). In detail, the shear wave velocity, the dynamic moduli and Poisson's ratio were determined by means of the ultrasonic pulse velocity technique. The results show that the grouts with the bentonites have higher dynamic moduli than the grout without the bentonite. Moreover, a final analysis of the experimental data provided an analytical relationship to calculate the shear-wave velocity for each of the six grouts at any curing times. [ABSTRACT FROM AUTHOR]

• By using the UPV method, two-components grouts can be studied at short curing time. • Elastic Modulus, shear modulus, and Poisson ratio have been computed at short time. • Two-component grouts stop to increase performance after 1 month. • Two-component grouts mechanical parameters have been computed at short curing time. The use of shield machines and instantaneous segment linings for tunnel construction is one of the most used tunnelling methods today. Despite a large number of applications in different tunnelling projects all around the world, knowledge of the behaviour of two-component grout is quite limited, mainly due to the fast hardening process that inhibits using the classic approach for concrete characterization. In the present work, an innovative approach based on ultrasonic measurements is introduced, aimed to characterize the elastic properties of this innovative backfilling material. Specifically, ultrasonic pulse velocity was applied to two-component grout samples to describe the interesting and fast evolution of the material from the mixing phase until 6 months of curing using geophysics parameters. The dynamic Young's modulus (E) and the dynamic shear modulus (G) exhibited a clear increasing trend, starting from values of a few tens of MPa to final values equal to 1000 MPa and 340 MPa, respectively. The Poisson's ratio (ν), close to the value of incompressible materials (0.5) at the short curing time, exhibited a decreasing trend, reaching roughly 0.445 after 3 months of curing. [ABSTRACT FROM AUTHOR]

The soil conditioning is a process of fundamental importance during the excavation of tunnels with Earth Pressure Balance full face machine. The soil conditioning is achieved through the addition of foam at the excavation face and in the bulk chamber that modifies the natural soil properties from solid-like to fluid-like with a pulpy behavior. Clearly, a material with a pulpy or fluid-like consistency is not suitable for the construction of embankments of landfill or for other civil purposes. It is therefore important to have a procedure able to identify how long it is necessary before the conditioned soil recovers its geo-mechanical properties, since this knowledge is needed at the design stages from a logistic point of view. The paper proposes and discusses a procedure to find out whether and when the conditioned soil gets back to its original properties. The procedure foresees direct shear tests, vane tests, Proctor tests, and rotational mixer tests at different time schedules from the production of the conditioned soil in the laboratory. The conditioned soil samples have been cured in a controlled environment up to 60 days from the conditioning. Thanks to these tests, it is possible to assess if and when the soil recovers its natural behavior or if a permanent alteration is induced. The proposed procedure has been applied to a standard alluvial soil showing that most of the original properties of the soil are recovered already after seven days from the conditioning. The carried-out tests have shown that the procedure is feasible and easy to apply. [ABSTRACT FROM AUTHOR]

• Plasticizer loss is the main phenomenon affecting the durability of PVC membranes. • A device for accelerated ageing tests on PVC membranes has been developed. • Mechanical tests are performed to study the time-dependent properties of membranes. • Plasticizer loss with time has been modelled from plasticizer absorption tests data. • The end-of-life time of the two commercial PVC membranes is evaluated. Waterproofing heavily influences the operation and maintenance costs of underground structures. Currently, the most commonly used technology for tunnel waterproofing is plasticized polyvinyl chloride (PVC-P) geomembranes. However, not much is known about the long-term durability of these geomembranes, especially in relation to the long expected lifespan of new tunnels (i.e. 100–150 years). Therefore, in this paper, the durability of two commercially available PVC-P geomembranes is studied with the help of a specifically designed accelerated ageing device in addition to mechanical and absorption tests. The degradation resulting from plasticizer loss is extrapolated to the long term, and a threshold value for the end-of-life of the PVC-P geomembrane is estimated from the mechanical tests. [ABSTRACT FROM AUTHOR]

• Foams differently generated lead to different stability of conditioned soil. • Higher liquid generator flow rate in the production of foam leads to more stable foam. • Higher flow rates in the production of foam leads to less stable conditioned soil. • Soils conditioned through foams with lower FER have more stability over time. In tunneling technology, Earth Pressure Balance-Tunnel Boring Machine (EPB-TBM) technology operations require altering excavated soil rheology through soil conditioning, a vital aspect for optimal counterpressure control and soil extraction. This transformation is achieved by introducing additives like foam, and inherits its time-dependent behavior. Having observed a discrepancy in the stability of two foams generated with different flow rates, the core objective of research is exploring the influence of this parameter on time-dependency of mechanical properties of conditioned soil. This aspect is then studied also through a semi-quantitative analysis aimed to investigate correlations between the generation flow rates, the Foam Expansion Ratio, and used Foam Injection Ratio with the time-stability of conditioned soil properties. [ABSTRACT FROM AUTHOR]

The application of full‐face mechanized tunnelling, mainly with EPB shielded machines, has widely increased in the last years and today it can be considered the key technology when tunnelling in soils above and below the water table. The applicability range of EPB machines has widened thanks on one side to the technological and mechanical progresses and on the other side to the quality and effectiveness of the conditioning products. No recognized standards are available for laboratory testing of conditioned soil and each research centre has developed its own procedures and methods. In this paper, an overview of the most frequently used procedures is presented and discussed briefly. [ABSTRACT FROM AUTHOR]

Utilizing the earth pressure balancing technique on hard rock tunnel boring machines (TBMs) is an efficient way to overcome engineering geological hazards that disrupt the application of these machines. Considering that geomechanical and engineering geological conditions of soil and rock are dramatically different, proposing a suitable conditioning design for earth pressure balance (EPB) hard rock TBMs requires particular attention to the characteristics of the excavated material and ground conditions. In this paper, foam application providing a favourable support medium for EPB hard rock TBMs is evaluated based on the experience of the Tehran metro line 6 southern expansion sector project, using laboratory and actual data. TBM muck, with different water contents, was used as the test specimen after granulometry correction. The trend of changes in the workability of foam conditioned mix was obtained by performing 350 slump tests. The pressurized permeability cell test (PPCT), a testing device capable of applying high water pressures to the conditioned material, was used to evaluate the impermeability of workable mixes. Results indicate that although foam can efficiently increase the workability of dry and moistened specimens, the presence of a separated liquid phase in the test specimen disrupts its application; moreover, foam conditioned mix is permeable even against low water pressures. [ABSTRACT FROM AUTHOR]

• EPB conditioning is critical in high-cobble content soils. • Cobble segregation in bulk chamber may lead to major problems. • Slump test is suitable for soils with maximum particle diameter of 40 mm. • The interaction between the conditioned matrix and cobbles is important. • Tilt Slidind Test evaluates the interaxtion of cobbles with the matrix. Many cities are built on alluvial soils and the excavation for services and tunnels become more important as the surface becomes more congested. Today EPB shields excavation is the leading technology for tunnel excavation in urban context due to the limited space on the surface, the noise, vibration and safety requirements. In cases with high cobbles content optimization of the conditioning is necessary in order to allow a homogeneous flow of cobbles in the pressure chamber and along the screw conveyor. This should be assessed through a test that evaluates the reduction of the gravitational separation of the larger elements in the chamber and the risks of face instability, tool breakage and water inflow through the screw conveyor. This paper presents a new test to evaluate the homogeneity of flow of cobbles in the excavated mass. The development of the test is described along two test campaigns and the improvements achieved in the second campaign are explained. Two indexes are proposed to assess the suitability of conditioning. [ABSTRACT FROM AUTHOR]