A highway embankment founded on a sloping tectonised marly-sandstone flysch formation located in the Apennines chain (Italy) has been affected for about 30 years by continuous slow movements. Given ...the strategic importance of the involved infrastructure, different investigation and monitoring campaigns have been carried out to get information about the properties of the involved soils and collect data about the displacements and piezometric regime. Field monitoring, in particular, reveals that the observed displacements result from a failure mechanism involving both the embankment and the foundation soils. However, significant gaps in monitoring jeopardize the possibility to assess the long-term trends in the displacements and piezometric regime and the significance of weather forcing in regulating the phenomena. To address such research questions, a procedure, easily transferable in different contexts, is proposed and applied to the test case: a simple hydrological proxy indeed permits evaluating the rate of movement featured by weatherinduced seasonal variability. Such a mechanical response has been confirmed by the results of a simplified numerical model aimed at finding out the main features of the observed kinematics accounting for a hydrological balance of the involved area.
In the Mediterranean area, several alluvial coastal plains, developed after the Holocene transgression, are affected by subsidence. The Volturno alluvial-coastal plain, along the eastern Tyrrhenian ...Sea (southern Italy) is characterized by subsidence rates determined through InSAR data analysis and ranging between 0 and <−20 mm/year in an area of about 750 kmq across the Volturno River. Inside this area, the pattern of subsidence shows sites with apparently anomalous localized subsidence. To understand the driving mechanisms of this process, a lithostratigraphic reconstruction was provided focusing on the spatial distribution of the horizons considered weak by a geotechnical point of view; then, the subsidence map was overlain spatially with geological data in a Geographic Information System (GIS) environment. The spatial analysis highlighted the major ground deformation occurring within the outer boundary of the incised paleo-valley, corresponding to the Holocene alluvial/transitional filling that overlies a compaction-free Pleistocene basement. Inside this general trend, differential compaction was detected corresponding to the thick occurrence of clay and peat deposits, suggesting that the subsidence rate registered in the plain are due in part to the consolidation of primary settlements of soft and compressible soils that characterize the subsoil of these areas, and in large part to the secondary consolidation settlements.
The conventional design of a piled foundation is based on a bearing capacity approach, and neglects the contribution of the raft. As a consequence, piled foundations are usually designed by ...overconservative criteria. With respect to the conventional approach, a more rational and economical solution could be obtained by accounting for the contribution of the raft toward the overall bearing capacity, but this potential is not exploited due to the lack of theoretical and experimental research on the behavior of piled rafts at failure. Based on both experimental evidence and three-dimensional finite element analyses, a simple criterion is proposed to evaluate the ultimate vertical load of a piled raft as a function of its component capacities, which can be simply evaluated by the conventional bearing capacity theories. The results presented in the paper thus provide a guide to assess the safety factor of a vertically loaded piled raft.
Celotno besedilo
Dostopno za:
DOBA, FGGLJ, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Energy piles are foundation elements having the double scope of transferring structural loads from the structure to the ground and of exchanging heat with the surrounding soil. It follows that pile ...state of stress and settlement are altered by the time-dependent temperature change in both pile and soil. This work is aimed at investigating the effect of thermal cycles on the behaviour of a single energy pile. To this end, fully coupled thermo-hydro-mechanical analyses have been carried out using the Finite Element code ABAQUS. The single pile is installed in a normally consolidated clay behaving according to different constitutive models involving Mohr-Coulomb, Modified Cam Clay and Hypoplastic. The latter is employed with and without the thermal formulation capable of accounting for the thermal collapse of NC clays during heating. A single free-head pile is considered and the results are presented in terms of pile axial force and settlement developed cycle by cycle.
The work at hand attempts to propose a local pile design method based on pile load test results for a reference site. Such LPDM is simply based on the identification of three dimensionless ...quantities, such as the capacity ratio CR, the stiffness ratio SR, and the group settlement ratio Rs. To prove the LPDM reliability, experimental data collected during years in the Neapolitan area (Italy) have been used to obtain the abovementioned coefficients. Then, LPDM has been applied, as a preliminary design method, to three well-documented case histories applying capacity and settlement-based design (CBD and SBD) approaches. The satisfactory agreement between the geometry in the original design of piles and the one obtained by applying the LPDM proves that the proposed methodology may be very helpful for preliminary design, allowing for reasonable accuracy while requiring few hand calculations.
The behaviour of a kinematically stressed pile in layered soil under the passage of vertically-propagating seismic S waves is investigated by means of rigorous three-dimensional Finite-Element (FE) ...analyses. Both pile and soil are idealized as linearly viscoelastic materials, modelled by solid elements and pertinent interpolation functions in the realm of classical elastodynamic theory. The system is analyzed by a time-Fourier approach in conjunction with a modal expansion in space. Constant viscous damping is considered for each natural mode, and a FFT algorithm is employed to switch from frequency to time domain and vice versa in natural or generalized coordinates. The scope of the paper is to: (a) provide some rigorous elastodynamic results in both frequency and time domains that can be used as reference cases; (b) elucidate the role of a number of key phenomena and salient dimensionless parameters for the amplitude of pile bending at an interface separating two soil layers of different stiffness; (c) propose a simplified semi-analytical formula for evaluating such moments; (d) provide some remarks about the role of kinematic bending in seismic design of pile foundations, with emphasis on the long-standing issue of establishing an optimal pile diameter to resist such bending. The results of the study offer a new interpretation of kinematic pile bending in terms of the interplay between pile and soil, expressed through dimensionless layer thickness, pile-to-soil stiffness ratio and impedance contrast at the layer interface. A case study from Japan is presented.
► A zero moment condition exists for infinite combinations of problem parameters. ► An analogous condition exists to ensure equal bending at pile head and interface. ► Small interface depths and layer stiffness contrasts reduce interface pile bending. ► Deep interfaces and sharp layer stiffness contrasts increase interface bending. ► A variation in pile diameter does not have a clear effect on seismic performance.
The work at hand proposes a method for assessing, under reasonable hypotheses from an engineering perspective, the failure envelope of a pile group subjected to generalized loading conditions ...involving a vertical and a lateral force along with a moment. Following different assumptions of increasing complexity, a simple closed-form expression, which is however capable of considering also the strong dependence of sectional yielding moment on the axial force, is derived. The use of such formula, which allows a practical hand calculation of the interaction diagrams at failure, returns conservative yet very accurate results. As a follow up, with reference to reinforced concrete piles, design considerations involving both structural and geotechnical failure under lateral load are reported. It is found that for most cases, if steel reinforcement is established to resist the design bending moment, the geotechnical Ultimate Limit State checks are automatically satisfied.
AbstractThis work aimed at providing analytical closed-form solutions for the design of thermal piles. To this end, a model in which a cylindrical pile is attached along the shaft to a series of ...distributed vertical springs representing soil stiffness is proposed. The pile has constant section and elastic properties; the restraints provided by the superstructure and base stiffness are represented through concentrated springs. The model allows derivation of exact solutions for homogeneous, two-layer soil and soil with linearly increasing stiffness with depth. In addition, approximate energy solutions are derived via the principle of virtual work for more general subsoil conditions with spring stiffness calibrated through finite element results. Expressions for the axial force and shear stress at the pile–soil interface are provided for typical soil stiffness distributions. A successful comparison to literature studies, involving complex transient-coupled numerical analyses and two field tests, corroborate model reliability. The proposed analytical solutions provide insight into the behavior of thermally loaded piles and can be used as a simple tool for ultimate limit state design.
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