Productivity and working costs of modern trench-cutters for the construction of concrete diaphragms in an urban environment

In the excavation of shallow underground works in an urban environment using the ‘cut and cover' method, the choice is often made to use concrete diaphragms in order to support the side walls, before proceeding with the excavation of the ground. When these diaphragms exceed a depth of about 20 m, trench-cutters are generally used to excavate the panels, using a supply of bentonite mud. A remarkable development of trench-cutters has taken place over the last 30 years and these machines today allow panels to be excavated in any type of ground whatsoever, even when it is highly cemented. The experience that has been gained in Turin (Italy) in recent years can be considered interesting, because of the huge number of diaphragms that have been completed and the varying characteristics of the ground in the urban area, which ranges from loose sand and gravel to highly cemented ones. On the basis of detailed analysis of the in situ behaviour of trench-cutters in Turin and of laboratory investigations on the effects of wear on the tools, it has been possible to make a preliminary estimation of the construction costs and the productive times of the concrete diaphragms for the different types of geolog

A review of the benefits of electronic detonators

Computerized drilling and the electronic timing of detonations are two technological breakthroughs which have had an important role in updating drilling and blasting excavation methods, although the electronic timing of detonators is still a comparatively infrequent technical solution to precision blasting problems. On the basis of an extensive collection of published cases, this paper reviews the successes achieved and the main expected advantages from the electronic ignition devices. After describing the primary characteristics of these detonators, some elements will be considered, in order to better understand their applications in different conditions, both in open pit and underground sites: extension of the time delay number, freedom in the choice of time intervals between detonations, timing accuracy, reduction of vibrations, control of back-break and fragmentation. The results are compared to those obtained by pyrotechnical timing devices, and summarized in the concluding remarks

Experiences from Experimental Mining in Brazil

The Experimental Mine (EM) of the Research Center of Responsible Mining of the University of São Paulo became the subject of investigation in a few years after its development ; it is an open-pit quarry currently exploiting marble and gneiss , used to produce industrial limestone and construction aggregates. It is a developing enterprise, dealing with the challenges of a technological upgrade from a small -scale operation to the characteristics of a medium -sized company. The Experimental Mine Project (EMP) was born to attend a double demand: to provide research and development (R&D ) support to a growing company and to provide experimental opportunity for a field of knowledge such as mining engineering that requires a large scale for its experiments. The main challenges of the EMP are related with the remaining small -scale mining features, such as large variety of equipment available, high level of operational flexibility, scarcity or absence of mine planning, being focused on daily operations. In such an environment, the first role of the EMP was to evaluate in a quantitative way the effects of unit operations over the whole mining process. The current excavation technique is by drilling and blasting. Many experimental campaigns have been conducted on site, with different purposes. One of the main research lines was to increase the productivity of the quarry by lowering production costs and improving the quality of the product, then optimizing the entire production cycle; the relationship between the unit costs of drilling and explosives were evaluated, as well as the link between the blast design and some factors affecting the downstream processing of the product. The paper describes the methods employed to conduct the research and the improvements to be pursued, with the due consideration to the influence and interference of the many parameters involved, from the rock-mass characteristics to the final products

Analysis of predictor equations for determining the blast-induced vibration in rock blasting

The paper proposes a new empirical correlation designed to complement the "site laws" currently used to evaluate the attenuation in the rock masses of vibrations induced by rock blasting. The formula contains a deformed exponential known as the K-exponential, which seems to well represent a large number of both natural and artificial phenomena ranging from astrophysics to quantum mechanics, with some extension in the field of economics and finance. Experimental validation of the formula was performed via the analysis of vibration data covering a number of case studies, which differed in terms of both operation and rock type. A total of 12 experimental cases were analysed and the proposed formulation exhibited a good performance in 11 of them. In particular, the proposed law, which was built using blast test data, produced very good approximations of the points representing the vibration measurements and would thus be useful in organising production blasts. However, the developed formula was found to work less well when a correlation obtained for a given site was applied to another presenting similar types of rocks and operations, and thus should not be employed in the absence of measurements from test data. Keywords: Rock blasting, Vibrations, Predictor equation, Site law, K-statistics, K-exponentia

The Music of Blasting

A common adage in the Explosives Industry goes by saying that "Blasting is not bombing". One of the key differences between the two employs of explosive energy lays in the same gap existing between the application of acoustic energy that differentiates noise from music: timing and the distribution of energization in time. While timing in blasting is widely accepted to influence blast induced vibrations, it is still not completely investigated when related to rock fragmentation and downstream benefits. This paper shows a research about this topic, developedon two phases: 1) test blasts at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo; 2) development project for large-scale production blasts in an open-cast mine. The first phase of the research was performed attempting to increase the productivity of the experimental mine, by lowering production costs and improving the quality of the product. Some Key Performance Indicators (KPIs) were established to monitor the results. A new blast design method and a more appropriate initiation sequence were designed according to the principles of: i) decomposition of the blast; ii) taking advantage of the free surfaces to favor the movement of the blasted material; iii) simultaneous holes firing as far away as possible, to avoid undesired cooperation of charges that may induce the explosive energy to work with shear effect instead of producing fragmentation. The results show that the proper selection of delay timing leads to significant benefits for rock fragmentation, downstream processes and the quality of final walls. The second phase of the study was a research and development (R&D) project in an open-cast mine with the goal to achieve an average P80 of 300 mm (11,8”) in the run-of-mine (ROM) product without altering the existing budget. The project included several variables in the blast design that were not previously taken into account, such as the orientation of natural joint sets in the rock mass, specific energy of the explosive and firing sequence. The new blast design method considered the directions of natural joint sets and determined the drilling pattern and the firing sequence accordingly to favor the movement of the blasted rock along its preferential direction, to reduce its confinement. At the end of the project, it was achieved an average P80 of 304 mm (12”) in the ROM, 50% lower than the one at the beginning of the project. The final blast of the project showed a reduction of 3% of the drill and blast cost, employing the same powder factor and the same drill pattern size used at the beginning of the project. The results of this study show how blast performance is related to variables that are not contemplated in the most common design methods or fragmentation models: the firing sequence, the degree of freedom and the direction of movement in the blast

From Exploratory Tunnel to Base Tunnel: Hard Rock {TBM} Performance Prediction by Means of a Stochastic Approach

Tunnel boring machine (TBM) performance prediction is often a critical issue in the early stage of a tunnelling project, mainly due to the unpredictable nature of some important factors affecting the machine performance. In this regard, deterministic approaches are normally employed, providing results in terms of average values expected for the TBM performance. Stochastic approaches would offer improvement over deterministic methods, taking into account the parameter variability; however, their use is limited, since the level of information required is often not available. In this study, the data provided by the excavation of the Maddalena exploratory tunnel were used to predict the net and overall TBM performance for a 2.96 km section of the Mont Cenis base tunnel by using a stochastic approach. The preliminary design of the TBM cutterhead was carried out. A prediction model based on field penetration index, machine operating level and utilization factor was adopted. The variability of the parameters involved was analysed. A procedure to take into account the correlation between the input variables was described. The probability of occurrence of the outcomes was evaluated, and the total excavation time expected for the tunnel section analysed was calculated

Investigating the effects of bench geometry and delay times on the blast induced vibrations in an open-pit quarry

The paper analyzes the results of research aimed to monitor, predict and minimize the ground vibrations induced by blasting in an open pit limestone quarry in Italy. Data on 135 vibrations taken from 18 production blasts and 2 signature blasts were examined, including the effects of the bench orientations. Blast vibrations at the quarry were monitored for approximately three months. The blast vibration magnitudes and frequencies and their effects were analysed by both the conventional PPV concept and a software that is able to predict the vibration amplitudes of a production blast at the target sites by modelling signature blast data. The results have been rated and classifi ed considering the peak particle velocities (PPV) measured in a number of critical areas near the quarry. A comparative analysis between the results predicted by the software and actual blast results was carried out. The benefi ts of the software were then highlighted, proving able to predict ground vibrations induced by blasting more reliably than the conventional site laws. Finally, based on the results, some arrangements were provided for two bench geometries employed at the quarry site

AUTOMATIC MEASUREMENT OF DRILLING PARAMETERS TO EVALUATE THE MECHANICAL PROPERTIES OF SOILS

Any underground work, carried out either to perform excavations, should be based on detailed knowledge of the geological, hydrogeological and geomechanical conditions of the underlying materials. The continuous automatic diagraphy is a test that consists in the continuous surveying of drilling parameters, with total destruction of the core, which can be used, together with geognostic probing surveys and a detailed definition of the stratigraphy of the subsoil, to evaluate the geotechnical characteristics of soils. One of the main advantages of the use of instrumented surveys is that of being able to perform a greater number of in situ tests at the same costs and times. Over the last two decades years, the use of rotating hydraulic surveys for geognostic investigations, combined with automatic acquisition systems of the main drilling parameters, have become widespread. The study presents the results obtained during an investigation campaign of the subsoil of areas in Piedmont, Italy, which was necessary to carry out important civil engineering works

The influence of rock mass fracturing on splitting and contour blasts

Splitting and contour blasting are aimed to achieve suitable profiles by cutting along a surface, while common blasting is intended to detach and to fragment relevant rock volumes by increasing the fracturing state. These techniques are adopted in both underground works (tunnels, caverns, quarries) and also for surface excavations (quarries, mines, rock slopes engineering). Contour blasts are widely used techniques in mining and civil engineering to enhance performance while maintaining the safety of personnel and infrastructure. Splitting blasts are mainly used in dimension stone mining to obtain intact blocks of valuable ornamental stone. The parameters of controlled blasting (geometry, charge, blast agent) require an accurate selection using optimised blasting patterns and explosive properties; most of the proposed methods are limited and unsatisfactory due to insufficient consideration of rock mass properties. A quick but effective comparison and analysis of the different characteristics of the rock mass and its heterogeneities is presented, as it indicates a better strategy to determine a tailored blasting design for a given site, thus significantly improving the contour blasting quality

Precision Rock Excavation: Beyond Controlled Blasting and Line Drilling

The strictness of the result of an excavation, whether mechanical or by means of explosives, is naturally conditioned by the objective, and therefore by the type of technique applied to achieve it. To attain the best results in terms of rock breakage and respect of the final profile, it’s im-portant to evaluate the excavation specific energy and its optimization. This research being a re-vision of different techniques to achieve good quality of the final walls, it focuses on evaluating the effects of those techniques on the quality of the result, both in open-pit and underground op-erations. Different geometries and configurations can be applied to both quarrying and tunnel-ling blasts. The research is aimed to push contour blasts to their limits, and the main aspects are discussed in order to improve the blast parameters in the daily practice