Thierry Verdel

Modeling Uncertainties in Mining Pillar Stability Analysis

Many countries are now facing problems related to their past mining activities. One of the greatest problems concerns the potential surface instability. In areas where a room-and-pillar extraction method was used, deterministic methodologies are generally used to assess the hazard of surface collapses. However, those methodologies suffer from not being able to take into account all the uncertainties inherent in any hazard analysis. Through the practical example of the assessment of a single pillar stability in a very simple mining layout, this article introduces a logical framework that can be used to incorporate the different kinds of uncertainties related to data and models, as well as to specific experts choices in the hazard or risk analysis process. Practical recommendations and efficient tools are also provided to help engineers and experts in their daily work.

Vulnerability Assessment of Mining Subsidence Hazards

Between 1996 and 1999, five mining subsidence events occurred in the iron-ore field in Lorraine, France, and damaged several hundred buildings. Because of the thousand hectares of undermined areas, an assessment of the vulnerability of buildings and land is necessary for risk management. Risk assessment methods changed from initial risk management decisions that took place immediately after the mining subsidence to the risk assessment studies that are currently under consideration. These changes reveal much about the complexity of the vulnerability concept and about difficulties in developing simple and relevant methods for its assessment. The objective of this article is to present this process, suggest improvements on the basis of theoretical definitions of the vulnerability, and give an operational example of vulnerability assessment in the seismic field. The vulnerability is divided into three components: weakness, stakes value, and resilience. Final improvements take into account these three components and constitute an original method of assessing the vulnerability of a city to subsidence.

Comparison of building damage assessment methods for risk analysis in mining subsidence regions

The occurrence of subsidence phenomena in urban regions may induce small to severe damage to buildings. Many methods are provided in the literature to assess buildings damage. Most of these methods are empirical and use the horizontal ground strain as a subsidence intensity in the vicinity of a building. Application and comparison of these methods with a case study is the main objective of this paper. This comparison requires some harmonization of the existing methods and the development of a software, which combines the subsidence hazard prediction, the damage evaluation methods and a database of buildings with structural parameters as well as the geographical coordinates of the buildings An additional results is the development of a method for the prediction of the horizontal ground strain in the vicinity of each building. Results are given as a map of damaged buildings for the case study and the different existing methods with some statistical calculations such as the mean and the standard deviation of damage in the city. Comparison of these results allows identification of the “safer” method that give the higher mean of damage. The comparison of the calculated results and observed damage in Lorrain region show that, the Dzegeniuk et al. methods is more realistic in comparison of the other empirical methods.

Velocity survey of an excavation damaged zone: influence of excavation and reloading

Abstract During gallery excavation, regardless of the method chosen, the surrounding rock is mechanically disturbed in the case of underground disposal of chemical or radioactive wastes, and such mechanical changes to the rock state can create preferential pathways for the release of material from the waste inside the excavation (e.g. chemical waste gases, brine or dissolved radionuclide) up to the biosphere. The mechanical characterization of this disturbed zone is thus essential in assessing the rock capacity necessary to form an impermeable geological rock barrier. The key to this effort lies in determining the nature, extent and change to this disturbed zone. A survey by ultrasonic wave analysis is particularly appropriate for these purposes, as it provides information on the zone left undisturbed by the boreholes. The main aim of this paper is to describe a recent in situ experiment (called EZ-A) conducted in Opalinus clay at the Mont Terri Rock Laboratory in Switzerland. This experimental campaign successfully studied the possibility of improving the properties of rocks forming the excavation damaged zone (EDZ). The experiments consisted of three stages: the first entailed locating the EDZ caused by the construction of gallery EZ-A at the Mont Terri laboratory; the second traced the evolution of the EDZ arising from a 20 cm thick and 150 cm deep slot excavation in the EZ-A gallery floor; and the third stage focused on the P-wave velocity evolution surrounding the slot during a pressure loading at the slot walls, which serves to characterize the EDZ evolution in the slot. These three stages were carried out using seismic tomography and then recording the wave propagations during the excavation and reloading stages. The measurement of velocity before and after slot excavation reloading, together with the survey during slot excavation, showed a decrease in P-wave velocity underneath the slot floor down to a 0.2 m depth. Reloading clearly improves P-wave propagation along the sidewall and slightly decreases it under the slot.

Adjusting the Influence Function Method for Subsidence Prediction

Theextraction of ore and minerals by underground mining may induce groundsubsidence phenomena. These phenomena produce several types of ground movement likehorizontal and vertical displacements, ground curvature and horizontal groundstrain at the surface, and associated building damage in urban regions. Theinfluence function is a well-known and efficient method for the prediction ofthese movements, but its application is restricted to mining configurationswith the same influence angle around the mine. However, this angle may displaydifferent values when the mine is not horizontal or when other subsidenceevents already occurred near the considered mine.In this paper a methodology and analgorithm are developed, based on the traditional influence function method inorder to take into account different influence angles. This methodology isimplemented in the Mathematicasoftware and a case study is presented with data from the Lorraine iron minefield in France. Ground movements calculated with the developed methodologyshow a fair concordance with observed data.

Glossary of Terms on Landslide Hazard and Risk

In the last decades much effort has been devoted to the development of methodologies for landslide hazard and risk assessment. Although there are a few available glossaries, a review of the literature published in international journals and conferences show that the terminologies used differ greatly or are unclear. In 2011, the Joint Technical Committee no1 of the Federation of International Geo-Engineering Societies established a working group with the objective of preparing a standard glossary of terms relevant to landslide hazard and risk. The glossary aims at an international harmonization of terms and definitions with those used in associated disciplines (i.e. seismology, hydrology, dam safety) while taking into account the specificity of landslides. The glossary takes as starting point previous glossaries prepared by the ISSMGE TC32 and UNISDR.

Feedback from a database created for reporting accidents in tunnels and galleries

Underground construction instability has been a major cause of unforeseen accidents, especially with regard to transportation. Experienced feedback is one of the more useful methods available to improve construction design. This paper first presents a database developed to record instabilities of affected tunnels and other underground construction sites around the world. Next, the paper analyzes the parameters responsible for instability phenomena and assesses their impact on the affected construction itself as well as on nearby environments. The goal is to develop a risk analysis methodology to aid engineers in considering safety issues when designing underground infrastructures.

Using plane frame structural models to assess building damage at a large scale in a mining subsidence area

Abstract In urban regions, mining subsidence induced by underground exploitation may cause damages to buildings. This paper attempts to improve a complete method and develop a fast computational tool for large-scale building damage assessment in a mining subsidence area. Two plane frame structural models are defined to analyse the mechanical behaviours of every building exposed to the subsidence phenomenon. The matrix displacement method is chosen to compute the internal forces within the structural models. In the calculation, the integrated structural models, including specific model shapes, initial loads and element properties, should be prepared for all the buildings; the subsidence is placed into the models as imposed support displacements. The influence grades of the buildings can finally be obtained by comparing the internal forces with their corresponding grading criteria. A developed code based on this research shows that approximately 1/3 of the buildings in the city of Joeuf (France) are at a high influence grade due to the subsidence expected in this city as a result of the collapse of two mined iron layers.

Uncertainties and Risk Analysis Related to Geohazards: From Practical Applications to Research Trends

Geohazards correspond to hazards that involve geological or geotechnical phenomena like earthquake, landslide, subsidence... Such hazards are generally classed into natural hazards even if their origin is not always natural, as for mining subsidences that are the consequence of industrial underground excavations. Geohazards are mostly investigated for the purpose of risk analysis. Studies first concern hazard (HAZUS®MH MR4, Romeo et al. 2000, Wahlstrom and Grunthal 2000) and vulnerability assessment (Zhai et al. 2005, McGuire 2004, Hazus 1999, Spence et al. 2005, Ronald et al. 2008), and secondly risk assessment and management (Karmakar et al. 2010, Merad et al. 2004). However, risk management must deal with many uncertainties that concern different aspects of risk assessment. This chapter aims to clarify the interactions between risk management and uncertainties within the context of geohazards.

Geotechnical Landslide Risk Analysis on Historical Monuments: Methodological Approach

During the second half of the twentieth century, and due to major advances in science and technology, industrial risk assessment studies became a must for any new/running industry. On the contrary, natural and environmental risk assessment studies lagged behind until the last two decades of the twentieth century. This chapter demonstrates a methodological approach for the assessment of natural hazards/risks (specifically landslides and block movements), with an application to the Tomb of Ramsis I at the Valley of the Kings, Egypt. The authors were able to develop this approach using different techniques of mathematical reasoning under certainty, and chose the fuzzy logic as the best applicable one. A comparison has been done with other “classical” methods of reasoning such as the probabilistic approach.