Search

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]

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]

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]

Featured Application: This paper presents a laboratory test campaign focused on the reduction of the wear phenomenon related to a material extracted from a marble quarry. The aim of the work is to propose a potential solution for the wear reduction pertaining to chainsaw cutting machine tools. The use of ornamental stones has a historical value that makes them strategically precious in Italy; marble can offer high performance in architectural applications, even though the variability of the rock mass requires detailed studies to optimize the exploitation techniques and reduce waste. Italy is world famous for its marble, which is extracted mainly through chainsaw cutting machines, which are currently used intensively due to their high-safety working conditions compared to alternative techniques and for their great versatility, especially in underground applications. Although this cutting technique is well-rooted, an uncommon problem of tool wear was found in the quarry under study, which strongly affected productivity. A series of laboratory test were carried out to estimate the wear potential of the rock and the suitability of the tools. The Cerchar abrasivity test highlighted a mean wear potential for the marble of 2.77, while microhardness outcomes pointed out the presence of quartz veins in the tested material (values over 10,000 MPa). Finally, additives typically used in the conditioning process of EPB machines in tunneling were tested with the purpose of reducing the extent of wear. A reduction of about 50% in the wear (in terms of weight lost) was obtained for a moisture content of 9%. [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]

The study takes into account different classes of tunnel boring machines (TBM), with the aim of identifying correlation models which are meant to estimate, at a preliminary design phase, the construction time of a tunnel and to evaluate the mechanical and operational parameters of the TBMs, starting from the knowledge of the tunnel length and the excavation diameter. To achieve this goal, first of all a database was created, thanks to the collection of the most meaningful technical parameters from a large number of tunnels; afterwards, it was statistically analyzed through Microsoft Excel. In a first phase, forecasting models were identified for the three types of machines investigated, separately for compact rocks (open TBM) and fractured rocks (single and double shield TBM). Then, the mechanical parameters collected through the database were analyzed, with the aim of obtaining models that take into account, in addition to the type of TBM, the geological aspect and the type of rock characterizing the rock mass. Finally, the validation of the study was proposed in a real case, represented by the Moncenisio base tunnel, a work included in the new Turin–Lyon connection line. The estimated values were compared with the real ones, in order to verify the accuracy of the experimental models identified. [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]

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]

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]