Marwan Al Heib

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.

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.

Effectiveness of a mitigation technique for buildings subjected to ground subsidence

Abstract A physical modeling has been undertaken to study the effectiveness of a mitigation technique (peripheral trench) to protect a residential house undergoing a ground surface subsidence from mining. A simple building model and a foam-material trench model are designed and implemented. Their deformations are measured by Digital Image Correlation (DIC) technique. The 3D physical model was proved very potential to qualitatively study the impact of ground movements on surface structures and the effect of soil-structure interaction. The trench technique was pointed out very effective to protect the building. The strain in the building and its surrounding ground are significantly reduced by the presence of the trench dug around the building.

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.

Une nouvelle méthode de prédiction de fontis grâce à une modélisation par poutres plastiques

ABSTRACT The increase of the subsidence towards the surface of the ground is a rather complex phenomenon, responsible for damage to the works of surface located in their influence. Many approaches were developed, but the modelling of this phenomenon encounters theoretical and practical limitations. The approach suggested in this paper makes it possible to provide a pragmatic diagnosis using the plastic theory of beam. It is a simple and frequent approach in Civil Engineering. Two points were developed: the rigidity of the layers and the taking into account the elastoplastic behaviour of the strata. An inter-comparison between the results of the new approach and those using the numerical modelling (Distinct Elements Code) made it possible to validate the method suggested. Finally the application to the study of the behaviour of the benches on the roof of an underground cavity shows the operational and practical character of this new method.