Différentes déclinaisons de l'aléa liquéfaction: de la cartographie préventive au projet

As part of its Public Service, Applied Research, and Client Service activities, BRGM's Thematic Centre for Natural Geological Risks (NGR) has recently undertaken studies in order to characterize "liquefaction hazard". The paper considers definitions and presents several approaches to liquefaction hazard assessment, demonstrated by several examples. The first approach is a naturalistic one: Hazard assessment is considered in a structured manner by undertaking: – a regional inventory of historic events – mapping of formations susceptible to liquefaction in homogeneous risk areas subject to seimic activity – preventive mapping of the phenomena at local scale The second approach is a semi-deterministic one: It allows to produce a seismic microzonation, considering parametric calculations and charts (Seed's reverse method). This approach can be used also to recommend soil improvements when liquefaction hazard does exist. The third approach is a deterministic approach: It takes into account a 3D geotechnical model of the analysed area, as well as specific charts to produce a liquefaction hazard assessment of soils and an advanced seismic microzonation. This method was used in Guadeloupe and Martinique districts (French Lesser Antilles) ad for the design of a new TGV railway track in the south of France. The proposed methodology relies on the French Association for Earthquake Engineering recommendations and brings some innovative aspects: combined naturalistic and geotechnical analyses for liquefaction hazard assessment, combined chart use and 3D geotechnical modelling for liquefaction hazard microzonation. Apart from the complete analysis of the liquefaction hazard not always being useful, it also demands major resources, and is consequently sometimes broken down into several less-detailed stages. The various examples considered thus form a continuum and are simply variations of a same definition of the liquefaction hazard: where: X, Y and Z=coordinates t=time Δu=interstitial over-pressure σ'_vo=initial effective stress I_L=Iwasaki's liquefaction index     

Seismic evaluation of the destress blasting efficiency

In this paper, selected methods of destress blasting efficiency assessment are presented, and novel quantitative methods based on in situ seismic measurements are proposed. The newly formulated solution combines two different approaches. The first, which is useful mostly for the near-field seismic analyses, is based on the analysis of seismic amplitude characteristics, and the second, relevant for far-field evaluation, is extended by the duration and frequency of the seismic wave. Both approaches are based on the seismic analyses of the waveforms generated by blasting recorded by the local seismic network. The proposed solutions are tested and validated in deep underground mines in Poland in which the room-and-pillar mining method is applied. Based on performed analysis, it is shown that both methods may be used as a rockburst hazard control in underground mines. However, developed methods may also be successfully implemented in other engineering practices, including the assessment of seismic vibrations in open pits and quarries.     

A new method for assessing the application of deterministic or stochastic modelling approach in evacuation scenarios

The utilisation and importance of evacuation simulation models have grown due to their capabilities in the prevention, management and subsequent analysis of emergencies, and their contribution to protecting human life. Although several evacuation models for different types of scenarios exist in the field of fire safety engineering, it should be noted that most of these employ a deterministic approach. However, the evacuation process is a highly random phenomenon that is subject to the variability of human behaviours and other risk factors pertaining to an emergency.This paper studies the effect of using a deterministic instead of a stochastic approach in evacuation modelling. In this sense, two methods are proposed: (1) an exact method, which analyses the relative error when a deterministic approach is used and also offers acceptance or rejection criteria and (2) an a priori method, which predicts when a deterministic approach can be accepted or rejected by considering the independent variable characteristics of the corresponding model. Both methods are applied to two evacuation scenarios: 1) passenger trains and 2) road tunnels. These application cases show the usefulness of these two methods. Furthermore, this paper shows the necessity of continuing to study the influence of diverse factors in deterministic or stochastic modelling for evacuation analysis.     

Landslide hazard and risk zonation—why is it still so difficult?

The quantification of risk has gained importance in many disciplines, including landslide studies. The literature on landslide risk assessment illustrates the developments which have taken place in the last decade and that quantitative risk assessment is feasible for geotechnical engineering on a site investigation scale and the evaluation of linear features (e.g., pipelines, roads). However, the generation of quantitative risk zonation maps for regulatory and development planning by local authorities still seems a step too far, especially at medium scales (1:10,000–1:50,000). This paper reviews the problem of attempting to quantify landslide risk over larger areas, discussing a number of difficulties related to the generation of landslide inventory maps including information on date, type and volume of the landslide, the determination of its spatial and temporal probability, the modelling of runout and the assessment of landslide vulnerability. An overview of recent developments in the different approaches to landslide hazard and risk zonation at medium scales is given. The paper concludes with a number of new advances and challenges for the future, such as the use of very detailed topographic data, the generation of event-based landslide inventory maps, the use of these maps in spatial-temporal probabilistic modelling and the use of land use and climatic change scenarios in deterministic modelling.     

Evaluation of molecular methods used for establishing the interactions and functions of microorganisms in anaerobic bioreactors

Molecular techniques have unveiled the complexity of the microbial consortium in anaerobic bioreactors and revealed the presence of several uncultivated species. This paper presents a review of the panoply of classical and recent molecular approaches and multivariate analyses that have been, or might be used to establish the interactions and functions of these anaerobic microorganisms. Most of the molecular approaches used so far are based on the analysis of small subunit ribosomal RNA but recent studies also use quantification of functional gene expressions. There are now several studies that have developed quantitative real-time PCR assays to investigate methanogens. With a view to improving the stability and performance of bioreactors, monitoring with molecular methods is also discussed. Advances in metagenomics and proteomics will lead to the development of promising lab-on chip technologies for cost-effective monitoring.     

Landslides qualitative hazard and risk assessment method and its reliability

Landslide hazard and risk assessment methods can be broadly characterised as site specific or area specific. Site specific assessments may be qualitative (denoted Type I) or quantitative—based on detailed investigation and data (Type III). Area specific assessments are denoted as Type II.This paper describes the University of Wollongong Type I method which analyses hazard and risk assessment for four different conditions: natural slopes, embankments and side fills, rock slopes and cuttings and soil cuttings. Field sheets have been developed for each type of slope to enable scoring of the factors contributing to hazard and to consequence and therefore to risk. These have been tested at 23 sites in New South Wales, Australia, by two independent professionals to establish consistency levels. Some Type III assessments have been made against which the Type I assessments were compared. In the three areas reported, the comparisons indicate that the qualitative approach is conservative.     

Role of slope reliability analysis in landslide risk management

Progress in the use of qualitative and quantitative methods of landslide risk assessment is briefly reviewed. The use of a hazard-consequence matrix approach is highlighted and attention is then restricted to aspects of hazard assessment in which formal reliability concepts can be used. Widely accepted geotechnical and geological models must form the basis of credible hazard assessments under different environmental conditions. However, conventional deterministic methods of geotechnical analysis need to be supplemented by studies within a probabilistic framework which takes into consideration parameter variability and other uncertainties. Suggestions are made for using the "reliability index" in preference to the "factor of safety" in comprehensive procedures for landslide risk management. Electronic Publication     

Exploring quantitative methods for project location selection

This paper aims at exploring quantitative methods that are appropriate for project location selection. One of the major considerations of whether to undertake a construction project is to determine if the location is valuable for investment. Location selection may be simply based on past experience, rudimentary, “gut-feeling”, or a combination of them. Alternatively, it may involve scientific methods. The paper introduces both deterministic and dynamic approaches and presents some of the basic quantitative methods, including data envelopment analysis model and binary integer linear program models, serving as a base for both academics and practitioners. To expand the contribution of the paper, illustrative examples are given.     

Assessment of human health risks posed by consumption of fish from the Lower Passaic River, New Jersey

The Lower Passaic River (LPR) in New Jersey has been impacted by variety of human activities over the course of the last two centuries. In this risk assessment, we assessed potential human health risks associated with consumption of fish from the LPR, the human exposure pathway of greatest concern when addressing contaminated sediments. Our risk assessment incorporates fish consumption information gathered during a year-long, intercept-style creel angler survey and representative fish tissue concentrations for 156 chemicals of potential concern (COPCs) obtained from USEPA's public database (OurPassaic website: http://www.ourpassaic.org/projectsites/premis_public/index.cfm?fuseaction=contaminants). Due to the large number of COPCs investigated, this risk assessment was divided into two phases: (1) identification of COPCs that contribute to the majority of overall excess cancer risk and hazard estimates using deterministic and probabilistic methods, and (2) probabilistic characterization of risk using distributions of chemical concentration and cooking loss for those compounds identified in Phase 1. Phase 1 relied on point estimates of COPC concentrations and demonstrated that PCDD/Fs and PCBs (dioxin-like and non-dioxin-like) are the greatest contributors to cancer risk, while non-dioxin-like PCBs are the primary contributors to non-cancer hazard estimates. Total excess cancer risks for adult and child and receptors estimated in Phase 1 were within USEPA's acceptable excess cancer risk range, with the exception of RME child (3.0 × 10^− 4 and 1.3 × 10^− 4 for deterministic and probabilistic approaches, respectively). Phase 2 focused on PCDD, PCDF, and PCBs and used distributions of chemical concentrations in fish. The results showed that all excess cancer risk estimates were within the acceptable risk range, although non-cancer hazard estimates for PCBs slightly exceeded a Hazard Index of 1. This HHRA of LPR fish ingestion represents the most comprehensive evaluation conducted to date, and demonstrates that measured concentrations of COPCs are not likely to pose a health risk to people who currently consume fish from the LPR.     

Transforming reliability limit-state constraints into deterministic limit-state constraints

This research proposes an efficient methodology that can transform a reliability limit-state constraint into a deterministic limit-state constraint. This new method may have broad applications in reliability-based design and optimization. The method is based on subset simulation and is applicable to general systems, e.g. linear or nonlinear systems and static and dynamical systems with high-dimensional uncertainties. Once the reliability constraint is transformed into a deterministic one, it is no longer necessary to conduct reliability analyses to verify the former. This can potentially save lots of computational time during the process of reliability-based design and optimization. The main idea of the new method is the introduction of the limit-state factor and nominal limit-state function, from which a deterministic nominal limit-state constraint is established. We propose two methods of establishing this nominal constraint, and they are verified with several simulated examples, showing that the established nominal constraint is indeed a satisfactory approximation of the target reliability constraint. Finally, we propose a simplified procedure requiring only two reliability analyses that can effectively transform reliability constraints into deterministic nominal constraints.