The fronts of tunnels excavated under particularly difficult ground conditions by employing conventional tunnelling methods are commonly supported: the stabilization is usually achieved either by improving the mechanical properties of the soil (injections, jet grouting, soil freezing, etc.) or by introducing linear inclusions. This last technique, consisting in the introduction of pipes (usually made of fibreglass reinforced polymers) in the front, is particularly popular since it is very simple to adapt the reinforcement geometry, length and number to the different conditions encountered during the excavation. The design of this reinforcement technique is nowadays based on very simplified approaches: on either empirical formula or the limit equilibrium method. In a previous paper, the authors numerically studied the mechanical response of unreinforced fronts in cohesive soils and defined a non-dimensional front characteristic curve. In this paper, the authors intend to take into consideration the role of reinforcements by following the same approach. A procedure allowing the definition of the reinforced non-dimensional front characteristic curve, once the reinforcement pattern is assigned, is introduced. The practical use of this curve is described.
The Maastrichtian–Paleocene El Haria formation was studied and defined in Tunisia on the basis of outcrops and borehole data; few studies were interested in its three-dimensional extent. In this paper, the El Haria formation is reviewed in the context of a tectono-stratigraphic interval using an integrated seismic stratigraphic analysis based on borehole lithology logs, electrical well logging, well shots, vertical seismic profiles and post-stack surface data. Seismic analysis benefits from appropriate calibration with borehole data, conventional interpretation, velocity mapping, seismic attributes and post-stack model-based inversion. The applied methodology proved to be powerful for charactering the marly Maastrichtian–Paleocene interval of the El Haria formation. Migrated seismic sections together with borehole measurements are used to detail the three-dimensional changes in thickness, facies and depositional environment in the Cap Bon and Gulf of Hammamet regions during the Maastrichtian–Paleocene time. Furthermore, dating based on their microfossil content divulges local and multiple internal hiatuses within the El Haria formation which are related to the geodynamic evolution of the depositional floor since the Campanian stage. Interpreted seismic sections display concordance, unconformities, pinchouts, sedimentary gaps, incised valleys and syn-sedimentary normal faulting. Based on the seismic reflection geometry and terminations, seven sequences are delineated. These sequences are related to base-level changes as the combination of depositional floor paleo-topography, tectonic forces, subsidence and the developed accommodation space. These factors controlled the occurrence of the various parts of the Maastrichtian–Paleocene interval. Detailed examinations of these deposits together with the analysis of the structural deformation at different time periods allowed us to obtain a better understanding of the sediment architecture in depth and the delineation of the geodynamic evolution of the region. 相似文献
The Hammam Lif coast (North-East of Tunisia) suffered from erosion mainly after the storm that damaged the zone in 1981. To protect it, eight shore-parallel breakwaters were built. The present study is interested in presenting the effect of the protection works on the coastline behavior by using aerial photographs geo-referenced by the digital photogrammetric method and empirical relationships. The successive breakwaters made a general accretion with formation of seven tombolos and salient. The response of the coast to these structures was related to the characteristics of these latter (length, distance to coast, and spacing). The effectiveness of such protection works is shown by the evaluation of the accretion areas formed behind them. The breakwaters which are the longest, less distant from the shoreline, and less spaced formed well-developed tombolos. Whereas, the structures which are short, very far from the coastline, and far from each other caused very small tombolos and even a salient. 相似文献
Riassunto Si segnala la notevole regressione subita dalla linea di spiaggia di Belvedere Marittimo nel periodo 1913–1938 e se ne discutono i possibili fattori, specie l'effetto del vento sull'erosione del fondo marino, accennando alle indagini intraprese dal R. Istituto Geofisico e Geodetico di Messina. 相似文献