Olivier Deck

Taking the soil–structure interaction into account in assessing the loading of a structure in a mining subsidence area

Underground mining of raw materials is often the cause of ground movements at the surface. Whether planned or accidental, such movements can cause considerable damage to structures located within the area of influence of underground mining works. Examples are the recent subsidences that took place at the end of the 1990s in the Lorraine iron mining field. A better understanding is necessary of how ground surface movements can be imparted to the supported structure and damage it. Indeed, it is too often considered that damage depends only on ground strain and no account has been taken of soil-structure interaction phenomena, which may affect considerably the structural behaviour. The stiffness of a structure is quantified in comparison to that of the ground as regards the various movements of the ground surface. This investigation highlights situations in which ground movements are integrally imparted to a structure. When this is not the case, the resulting complex soil-structure interaction phenomena is analysed. For this purpose, a finite-element software is used to generate models incorporating the ground material and a supported rigid structure. The ground movements are broken down into two basic movements in order to highlight the impact and the relative importance of one of these movements: ground curvature and horizontal strain. Structural stresses are quantified for different mechanical properties of the ground and the structure, as well as for different amplitudes of ground movement. This investigation made it possible to devise a methodology for analyzing structures in mining subsidence areas in order to determine cases in which soil-structure interaction phenomena must be considered. The investigation made it possible to hierarchically organize the ground and structure parameters, the variability of which has a significant effect on the behaviour of the structure affected by mining subsidence.

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.

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.

Analytical model to predict building deflections induced by ground movements

The building relative deflection is a parameter used to assess the level of the damage of the building when influenced by ground movements due to tunnelling or subsidence. The goal of this paper is to improve an analytical model that can predict the building-relevant relative deflection, induced by ground movements, by considering the soil–structure interaction phenomena. The Pasternak model is investigated to take into account the influence of the shear strain in the ground. The building is modelled with a Euler–Bernoulli beam placed on an initially deflected ground equivalent to the free-field ground movements. The static and the cinematic equilibrium of both the ground and the building are calculated to assess the transmitted building deflection. Mechanical parameters of the soil of the analytical models are discussed, and a methodology is developed to determine their values. Final results are compared with numerical finite element models (CESAR-LCPC) with a good agreement. They show the importance of the shear deformation of the soil that must be taken into account for a more confident prediction of the transmitted building deflection. To facilitate the operational use of the results, an abacus, relating the deflection ratio to the relative stiffness, is plotted.

Influence of differential settlements on masonry structures

The paper presents a contribution to the development of a numerical method to assess and classify the consequences of differential settlements on masonry structures. The main objective is to compare different criteria of damage assessment. The work consists to study a masonry wall, using numerical modelling, subjected to a differential settlement with a distinct element method (UDEC). Due to the distinct element method, the displacement requires to impose an optimal numerical velocity during a given period. The influence of vertical displacement on the wall has been studied by analyzing several criteria of damage assessment based on joints behavior in shear or tension. Based on the comparison with threshold values of the admissible differential settlement, the cumulative length of separate joints has been considered to satisfy an adequate criterion. The classification of damage level could be based on this criterion.

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.