Simple formulas for the dynamic stiffness of pile groups     

Reza Taherzadeh  Didier Clouteau  Régis Cottereau 《地震工程与结构动力学》2009,38(15):1665-1685

Simple formulas are derived for the dynamic stiffness of pile group foundations subjected to horizontal and rocking dynamic loads. The formulations are based on the construction of a general model of impedance matrices as the condensation of matrices of mass, damping, and stiffness, and on the identification of the values of these matrices on an extensive database of numerical experiments computed using coupled finite element–boundary element models. The formulations obtained can be readily used for the design of both floating piles on homogeneous half‐space and end‐bearing piles and are applicable for a wide range of mechanical and geometrical parameters of the soil and piles, in particular for large pile groups. For the seismic design of a building, the use of the simple formulas rather than a full computational model is shown to induce little error on the evaluation of the response spectra and time histories. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Probabilistic impedance of foundation: Impact of the seismic design on uncertain soils     

Régis Cottereau  Didier Clouteau  Christian Soize 《地震工程与结构动力学》2008,37(6):899-918

In the linear seismic design of buildings, the (deterministic) substructure method is a customary and efficient approach. However, the existence of spatial variability in the parameters of the mechanical model of the soil, as well as parametric errors, calls for the use of probabilistic approaches in order to provide a reliable design of the structure. The construction of probabilistic models of the soil impedance matrix provides a natural path to such approaches within the context of the substructure method. Two main techniques are described in this paper: a parametric one, typically using the stochastic finite element method, and a nonparametric one, which was introduced more recently. The latter is explored more specifically, and the possibilities it offers in terms of seismic design are presented. In particular, it is shown that it allows for the estimation of quantiles of the quantities of interest, rather than confidence intervals, which lead to highly conservative design. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Dating carbonate rocks with in-situ produced cosmogenic Be: Why it often fails     

Silke Merchel  Rgis Braucher  Lucilla Benedetti  Olivier Grauby  Didier L. Bourls 《Quaternary Geochronology》2008,3(4):299-307

Surface exposure dating of carbonate rocks using cosmogenic ¹⁰Be is problematic. We have performed step-wise leaching of calcite-rich samples in order to investigate the reasons for this. Results on different grain size fractions clearly indicate the source of atmospheric ¹⁰Be is clay. We demonstrate that partial-leaching procedures, which result in moderate pH levels will not release ¹⁰Be (in-situ produced or atmospheric) due to the instant re-absorption on grain surfaces. By contrast, under strongly acidic conditions, all absorbed ¹⁰Be is leached from aluminosilicates giving abnormally high ¹⁰Be concentrations and consequently exposure ages that are too old. Dating is only possible if samples do not contain any clay minerals or if they can be removed prior to carbonate dissolution.  相似文献   

Can sediment supply variations create sequences? Insights from stratigraphic forward modelling     

Jinyu Zhang  Peter M. Burgess  Didier Granjeon  Ronald Steel 《Basin Research》2019,31(2):274-289

Classic sequence stratigraphy suggests depositional sequences can form due to changes in accommodation and due to changes in sediment supply. Accommodation‐dominated sequences are problematic to define rigorously, but are commonly interpreted from outcrop and subsurface data. In contrast, supply‐dominated sequences are much less commonly identified. We employ numerical stratigraphic forward modelling to compare stratal geometries forced by cyclic changes in relative sea level with stratal geometries forced by sediment discharge and water discharge changes. Our quantitative results suggest that both relative sea‐level oscillations and variations in sediment/water discharge ratio are able to form sequence‐bounding unconformities independently, confirming previous qualitative sequences definitions. In some of the experiments, the two types of sequence share several characteristics, such as an absence of coastal‐plain topset deposits and stratal offlap, something typically interpreted as the result of falling relative sea level. However, the stratal geometries differ when variations in amplitude and frequency of relative sea‐level change, sediment/water discharge ratio, transport diffusion coefficient and initial bathymetry are applied. We propose that the supply‐dominated sequences could be recognised in outcrop or in the subsurface if the observations of stratal offlap and the absence of coastal‐plain topset can be made without any strong evidence of relative sea‐level fall (e.g. descending shoreline trajectory). These quantitative results suggest that both supply‐dominated and accommodation‐dominated sequences are likely to occur in the ancient record, as a consequence of multiple, possibly complex, controls.  相似文献   

Geological and geophysical studies of the Agoudal impact structure (Central High Atlas,Morocco): New evidence for crater size and age     

Houda El Kerni  Hasnaa Chennaoui Aoudjehane  David Baratoux  Mohammed Aoudjehane  Andr Charrire  Hassan Ibouh  Pierre Rochette  Yoann Quesnel  Minoru Uehara  Thomas Kenkmann  Gerwin Wulf  Michael Poelchau  Van Binh Nguyen  Maria Aboulahris  Samira Makhoukhi  Georges Aumaître  Didier Bourls  Karim Keddadouche 《Meteoritics & planetary science》2019,54(10):2483-2509

Since the discovery of shatter cones (SCs) near the village of Agoudal (Morocco, Central High Atlas Mountains) in 2013, the absence of one or several associated circular structures led to speculation about the age of the impact event, the number, and the size of the impact crater or craters. Additional constraints on the crater size, age, and erosion rates are obtained here from geological, structural, and geophysical mapping and from cosmogenic nuclide data. Our geological maps of the Agoudal impact site at the scales of 1:30,000 (6 km²) and 1:15,000 (2.25 km²) include all known occurrences of SCs in target rocks, breccias, and vertical to overturned strata. Considering that strata surrounding the impact site are subhorizontal, we argue that disturbed strata are related to the impact event. Three types of breccias have been observed. Two of them (br1‐2 and br2) could be produced by erosion–sedimentation–consolidation processes, with no evidence for impact breccias, while breccia (br1) might be impact related. The most probable center of the structure is estimated at 31°59′13.73?N, 5°30′55.14?W using the concentric deviation method applied to the orientation of strata over the disturbed area. Despite the absence of a morphological expression, the ground magnetic and electromagnetic surveys reveal anomalies spatially associated with disturbed strata and SC occurrences. The geophysical data, the structural observations, and the area of occurrence of SCs in target rocks are all consistent with an original size of 1.4–4.2 km in diameter. Cosmogenic nuclide data (³⁶Cl) constrain the local erosion rates between 220 ± 22 m Ma^?1 and 430 ± 43 m Ma^?1. These erosion rates may remove the topographic expression of such a crater and its ejecta in a time period of about 0.3–1.9 Ma. This age is older than the Agoudal iron meteorite age (105 ± 40 kyr). This new age constraint excludes the possibility of a genetic relationship between the Agoudal iron meteorite fall and the formation of the Agoudal impact site. A chronolgy chart including the Atlas orogeny, the alternation of sedimentation and erosion periods, and the meteoritic impacts is presented based on all obtained and combined data.  相似文献   

Are flawed MPAs any good or just a new way of making old mistakes?     

Le Quesne  Will J. F. 《ICES Journal of Marine Science》2009,66(1):132-136

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A luminescence‐based chronology for the Harletz loess sequence,Bulgaria     

Johanna Lomax  Markus Fuchs  Pierre Antoine  Denis‐Didier Rousseau  France Lagroix  Christine Hatt  Samuel N. Taylor  Jessica L. Till  Maxime Debret  Olivier Moine  Diana Jordanova 《Boreas: An International Journal of Quaternary Research》2019,48(1):179-194

The Harletz loess‐palaeosol sequence is located in northwestern Bulgaria and represents an important link between well‐studied loess sequences in eastern Romania and further sites to the west of the Carpathians (e.g. Serbia and Hungary). The aim of this study was to establish a chronostratigraphy of the deposits, using various methods of luminescence dating, together with basic stratigraphical field observations as well as magnetic properties. Luminescence dating was carried out using the quartz fine grain fraction and a SAR protocol, and the feldspar coarse grain fraction, applying the MET‐pIRIR protocol. Due to underestimation of the quartz fine grain fraction in the lower parts of the sequence, the resulting chronology is mainly based on the feldspar ages, which are derived from the stimulation temperature at 150 °C. A comparison with nearby sequences from Serbia, Hungary and Romania, and interpretations obtained through the stratigraphical and sedimentological signature of the sequence, supports the established chronology. Our data suggest that the prominent palaeosol (soil complex) in the upper quarter of the sequence was formed during MIS 5. It would follow that large parts of the Last Glacial loess overlying this palaeosol were probably eroded, and that the thick loess accumulation underlying this soil complex can be allocated to the penultimate glacial (MIS 6). A prominent MIS 6 tephra, which has been reported from other sequences in the area, is also present at Harletz.  相似文献   

Coupling of VAMPERS within iLOVECLIM: experiments during the LGM and Last Deglaciation     

Danielle C. Kitover  Hans Renssen  Ronald van Balen  Jef Vandenberghe  Didier M. Roche 《第四纪科学杂志》2019,34(3):215-227

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Relocation optimization of electric cars in one-way car-sharing systems: modeling,exact solving and heuristics algorithms     

Amine Ait-Ouahmed  Didier Josselin  Fen Zhou 《International journal of geographical information science》2018,32(2):367-398

Car-sharing system with electric cars is a very convenient service for urban transportation: it allows users to pick up a vehicle at a station and rent it during a short time. To manage this kind of system in the best way, it is necessary to solve the critical problem of vehicle stock imbalance across the stations. Several decision levels must be considered to balance the car distribution by taking into account the quality of service and the system operation cost. To this end, a linear programming model is proposed to formalize the problem in a mathematical framework, which allows the computation of optimal vehicle distribution strategies. To make our solution time efficient and usable for solving large problems, a greedy algorithm and a tabu search algorithm are proposed. These two algorithms are applied to the Auto Bleue network in Nice and its surrounding (France) using extensive simulations. Besides, an integrated mapping method is provided within the Geographical Information System QGIS to estimate flows and their locations. Numerical results demonstrate that the tabu search algorithm is able to find near-optimal solutions and good compromises between client satisfaction, number of staff agents and vehicles used, and computing time.  相似文献   

Personalized sightseeing tours: a model for visits in art museums     

Mayeul Mathias  Fen Zhou  Juan-Manuel Torres-Moreno  Didier Josselin  Marie-Sylvie Poli  Andréa Carneiro Linhares 《International journal of geographical information science》2017,31(3):591-616

This article describes a method to provide adapted visit tours in art museums according to the preferences expressed by the visitor and exhibits prestige. It is based on a dual approach with, on the one hand an automatic textual analysis of the official information available online (labels of exhibits) that allows to rank the exhibit attractiveness for a standard museum visitor. On the other hand, individual preferences are also taken into account to adapt the visit according to the personal cultural awareness of the visitor. We use operations research to solve a routing optimization problem, aiming at finding a visit tour with time constraints and maximization of the visitor satisfaction. Depending on the instance size and the problem scale, an integer linear programming (ILP) model and a greedy algorithm are proposed to recommend personalized visit tours and applied on two museums: ‘Musée de l’Orangerie’ in Paris and ‘National Gallery’ in London. The obtained results show that it is possible to recommend a good tour to visitors of an art museum by taking into account the common prestige of the exhibits and the individual interests, joining automatic text summarization and routing optimization in a limited geographical space.  相似文献