预防锤击预制桩挤土效应的措施与效果

对沉桩施工过程中所产生的问题及其对周围建筑物等设施造成影响做了初步分析。以上海海怡花园预制桩工程为例，介绍几种预防和减少预制桩施工挤土效应的方法，并对几种方法的实践成果作了论述。     

Mise en évidence et analyse d'une structure atlasique ennoyée au front de la Chaîne alpine tunisienne

The eastern Tunisian Atlas shows major subsurface faults: the Kairouan–Sousse Fault (FKS), to the north, and the El Hdadja fault (FEH), to the south. The FKS is an inherited structural trend active since Late Cretaceous times. This fault is an eastern splay of the Chérichira–Labeïd fault. It separates a large northern diapiric structure (Ktifa Diapir) from a subsident domain (the Kairouan–El Hdadja rim-syncline), with a pull-apart configuration to the south. The latter area, which appears to be an inherited weakness zone at the range border, has recorded a series of tectonic events that characterizes the Alpine structural development in Tunisia. To cite this article: S. Khomsi et al., C. R. Geoscience 336 (2004).     

Magmatic character and geotectonic setting of some tertiary-quaternary Italian volcanic rocks: Orogenic,anorogenic and «Transitional» association — A review

Discrimination functions based on major element distribution (Pearce, 1976) can be used to define the different basalt types of the Tyrrhenian and Perityrrhenian areas in an attempt to clarify their geodynamic significance.The future Tyrrhenian and Perityrrhenian areas have been affected since Oligocene by either compressional (subduction related) or transitional processes which produced well-defined orogenic and anorogenic magmas. A local development of «transitional» magma types, characteristic of «anomalous» volcanic arcs, also occurred with geochemical features that are intermediate between within-plate and orogenic magmas.The eruption of orogenic rock suites (calcalkaline, shoshonitic and leucite-bearing rocks) took place along the Apennine border on the east and southeast of the Tyrrhenian basin from Upper Miocene to Quaternary (Aeolian and neighbouring seamounts; Campania; Latium; Capraia Island). Absence of spatial zonation and interlayering of products with a various potassic character are the peculiar features of these rocks that appear to be originated from a heterogeneous and variously metasomatized mantle source by the influx of fluids (H₂O andLile enrichment) from the subduction zone affecting the Apennine-Maghrebides collisional front during Tertiary times.In the central Tyrrhenian area oceanic tholeiitic magmatism and creation of a new oceanic crust occurred from Upper Miocene. This activity was probably accomplished by Lower Pliocene when a within-plate volcanism produced the seamounts of the Batial Plain (Magnaghi, Vavilov, base of the Marsili Smts.).Etna and Ustica volcanisms occurring along the Perityrrhenian border on the south and west the Aeolian volcanism respectively, show geochemical characteristics that are transitional between anorogenic and orogenic magmas which could indicate some influence of fluids subduction-related to their mantle sources.The complex magmatic situation of the Tyrrhenian and Perityrrhenian areas may be caused by magma-producing events either from unmodified (anorogenic) or variously modified mantle sources (transitional to orogenic) depending on their proximity to and influenced by the Cainozoic subduction zone which developed along the Apennines-Maghrebides collisional front.     

Caractérisation géométrique et cinématique des structures liées aux phases compressives de l'Éocène au Quaternaire inférieur en Tunisie : exemple de la Tunisie nord-orientale

During Eocene to Early Quaternary period, three compressive tectonic phases are recognized in Northeast Tunisia: a NW–SE to north–south phase during the Late Eocene, a N120-to-N140 phase in the Late Miocene, and a NW–SE to north–south phase in the Plio-Early Quaternary. The first Eocene phase has built NE–SW folds and remobilised east–west-to-N120 and NE–SW faults with a reverse component. The second Miocene phase is characterized by east–west-to-N120 faults with a normal component and NE–SW folds. The third phase occurred during the Plio-Early Quaternary has edified NE–SW folds associated with east–west-to-N120 dextral reverse strike-slip faults and NE–SW faults with a reverse component. To cite this article: H. Mzali, H. Zouari, C. R. Geoscience 338 (2006).     

Numerical analysis of wetting-induced instabilities in partially saturated soils under plane strain conditions

This paper concerns the hydromechanical stability of partially saturated soils during wetting. The response of a loose silty sand is numerically/theoretically investigated with the main aim of identifying both triggering mechanisms and predisposing factors to instability. This latter is testified by both a rapid increase in the pore water pressure and an unexpected loss of numerical convergence. The study has been conducted at different scales from laboratory tests to boundary value problems, and in both cases, the controllability theory has been employed to both interpret and justify the numerical results.     

A stability criterion for elasto‐viscoplastic constitutive relationships

In this paper, the onset of mechanical instability in time‐sensitive elasto‐viscoplastic solids is theoretically analyzed at the constitutive level and associated with the occurrence of ‘spontaneous accelerations’ under stationary external perturbations. For this purpose, a second‐order form of Perzyna's constitutive equations is first derived by time differentiation, and a sufficient stability condition is identified for general mixed loading programs. These loading conditions are in fact the most general in both laboratory tests and real boundary value problems, where a combination of certain stress and strain components is known/prescribed. The theoretical analysis leads to find precise stability limits in terms of material hardening modulus. In the case of constitutive relationships with isotropic strain‐hardening, no instabilities are possible while the hardening modulus is larger than the so‐called ‘controllability modulus’ defined for (inviscid) elasto‐plastic materials. It is also shown that the current stress/strain rate may also directly influence the occurrence of elasto‐viscoplastic instability, which is at variance with elasto‐plastic inviscid media. Copyright © 2015 John Wiley & Sons, Ltd.     

Optical‐NIR spectra of quasars close to reionization (z ∼ 6)

X‐shooter, with its characteristics of resolution, spectral coverage and efficiency, provides a unique opportunity to obtain spectra of the highest‐redshift quasars (z ∼ 6) that will allow us to carry out successful investigations on key cosmological issues, from the details of the re‐ionization process, to the evolution of the first galaxies and AGNs. In this paper, we present the spectra of three z ∼ 6 quasars: one obtained during the commissioning of X‐shooter and two in the context of our ongoing GTO programme. Combining this sample with data in the literature, we update the value of the C IV cosmic mass density in the range 4.5 ≤ z ≤ 5, confirming the constant trend with redshift between 2.5 and 5 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Analysis of Summer Ozone Observations at a High Mountain Site in Central Italy (Campo Imperatore, 2388 m a.s.l.)

Tropospheric ozone (O₃) is an important atmospheric pollutant and climate forcer. The Mediterranean basin is a hot-spot region in terms of short-term O₃ distribution, with frequent episodes of high tropospheric O₃, especially during summer. To improve the characterisation of summer O₃ variability in the Mediterranean area, during the period 6–27 August 2009 an experimental campaign was conducted at Campo Imperatore, Mt Portella (CMP), a high mountain site (2,388 m a.s.l.) located in the central Italian Apennines. As deduced from analysis of atmospheric circulation, the measurement site was significantly affected by air masses originating over the Mediterranean basin, which affected the measurement site for 32 % of the time. Analysis of average values and diurnal and day-to-day variability revealed that CMP O₃ observations (average value 60.0 ± 5.1 ppbv) were comparable with measurements at other European mountain stations, indicating a prevalent effect of meteorological conditions and atmospheric transport on the synoptic scale. In fact, only a small “reverse” diurnal variation typically characterises diurnal O₃ variability because of local thermal wind circulation, which sporadically favours transport of air masses rich in O₃ from the foothill regions. Statistical analysis of five-day back-trajectory ensembles indicates that synoptic-scale air-mass transport from the Mediterranean Sea usually results in decreasing O₃ concentrations at CMP, whereas the highest hourly O₃ values are mostly associated with air masses from central continental Europe, eastern Europe, and northern Italy. High O₃ concentrations are also related to downward air-mass transport from higher altitudes. Comparison of in-situ O₃ variability with tropospheric O₃ satellite-based measurements reveals similar features of the two data sets. Together with the results from back-trajectory analysis, this indicates that CMP measurements might usefully improve characterisation of broad-scale O₃ variability over the central Mediterranean basin.