Marilena Cardu

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.

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 geology.

Technical–operational comparison between trench-cutters and clam excavators for concrete diaphragm construction in underground works at shallow depths

The most common excavation methods for the construction of tunnels in urban areas are the ‘cut and cover’ method and the traditional method of excavation at the tunnel face. The first method is usually used for works at shallow depths, even though it frequently involves burdensome deviations and shifting of the existing underground plants and networks. It has been used to realise the Underground Railway Link in Turin (Italy), where excavation was made using trench-cutters and clam excavators. The results of a technical–operational comparison between the two techniques are presented in this work, from which the advantages concerning the use of trench-cutters compared to the use of clamshell bucket excavators have been determined.

Surface Miners: Evaluation of the Production Rate and Cutting Performance Based on Rock Properties and Specific Energy

The purpose of this research was to evaluate the production rate (PR) and cutting performance of surface miners (SM) based on rock properties and specific energy (SE). We use data from equipment manufacturers and experimental data in this study and propose a new method and equations to determine both the PR and the cutting speed of SM. The unconfined compressive strength (UCS) of the rock, its abrasivity, and the machine’s engine power are the three most important factors influencing the PR. Moreover, the cutting depth, UCS, and engine power have a significant impact on the cutting speed. We propose a new method and equations to determine the energy required to cut a volume unit and a surface unit, i.e., specific energy, and establish the relationship between SE, UCS, and PR. The results of this study can be used by surface miner operators to evaluate the applicability of the machines to a specific mine site.

Rock Excavation by Drilling & Blasting: Evaluation of the Performance of the Equipment in an Open Pit Limestone Quarry

The paper deals with a research carried out at an open pit quarry, to optimize the production through the analysis of the equipment. The discussion was focused on the currently available machines: excavators, dump trucks and drills. The objective was to optimize some aspects of the exploitation, making it possible to complain with the desired productivity.

Italian regulations on Explosives Use and Marketing: an Undergoing Evolution

Abstract The paper reviews the legislative activity presently underway in Italy, in order to comply with the EC recommendations and guidelines on the subject of the explosives use in civil and mining applications and of the explosives marketing. The following points are dealt with in particular: a critical comment to the safety and environment protection regulations concerning explosives use; the problems posed by the lack of flexibility of the regulation system; practical aspects not adequately considered by the regulations; amongst them, the explosives transportation in the working sites, the explosives bulk charging practices, the qualification of the explosives operators and the checks needed to ascertain their technical skill. In the concluding remarks the actual status of Italy and of other Countries are compared, on the basis of the regulation system coverage with special reference to the safety problems.

Determining the Particle Size of Debris from a Tunnel Boring Machine Through Photographic Analysis and Comparison Between Excavation Performance and Rock Mass Properties

This paper presents the results of a study carried out on a 6.3-m-diameter exploratory tunnel excavated in hard rock by an open tunnel boring machine (TBM). The study provides a methodology, based on photographic analysis, for the evaluation of the particle size distribution of debris produced by the TBM. A number of tests were carried out on the debris collected during the TBM advancement. In order to produce a parameter indicative of the particle size of the debris, the coarseness index (CI) was defined and compared with some parameters representative of the TBM performance [i.e. the excavation specific energy (SE) and field penetration index (FPI)] and rock mass features, such as RMR, GSI, uniaxial compression strength and joint spacing. The results obtained showed a clear trend between the CI and some TBM performance parameters, such as SE and FPI. On the contrary, due to the rock mass fracturing, a clear relationship between the CI and rock mass characteristics was not found.

Evidences of the influence of the detonation sequence in rock fragmentation by blasting – Part II

This paper shows the work conducted at the Experimental Mine of the Research Center of Responsible Mining of the University of Sao Paulo, taking into account the theoretical issues presented in the first part of the article. The research was performed without changing the production cycle and without resorting to investments in new types of equipment: it has attempted to increase the productivity of the quarry, 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, a more appropriate initiation sequence and some simple, inexpensive and effective solutions were identified and applied. The results show that the proper selection of delay timing can be of significant benefit to downstream processes as well as enhanced fragmentation itself.