Analysis of pile behaviour in liquefying sloping ground

In this paper, a numerical procedure based on the finite element method is outlined to investigate pile behaviour in sloping ground, which involves two main steps. First a free-field ground response analysis is carried out using an effective stress based stress path model to obtain the ground displacements, and the degraded soil stiffness and strength over the depth of the soil deposit. Next a dynamic analysis is carried out for the pile. The interaction coefficients and ultimate lateral pressure of soil at the pile–soil interface are calculated using degraded soil stiffness and strength due to build-up of pore pressures, and the soil in the far field is represented by the displacements calculated from the free-field ground response analysis. Pore pressure generation and liquefaction strength of the soil predicted by the stress path model used in the free-field ground response analysis are compared with a series of simple shear tests performed on loose sand with and without an initial static shear stress simulating sloping and level ground conditions, respectively. Also the numerical procedure utilised for the analysis of pile behaviour has been verified using centrifuge data, where soil liquefaction has been observed in laterally spreading sloping ground. It is demonstrated that the new method gives good estimate of pile behaviour, despite its relative simplicity.     

The influence of the Evros River on the recent sedimentation of the inner shelf of the NE Aegean Sea

The transboundary Evros River discharges into the Alexandroupolis Gulf, located in the inner shelf of the northeastern Aegean Sea, where it has formed an extended delta. Grain-size and mineralogical analyses of five sediment cores, collected in the subaqueous delta, provide the following information about recent sedimentation processes in the northeastern part of the Aegean shelf: (a) river mouth deposits, consisting of coarse-grained sediments, are mainly deposited in front of the active mouth, whilst some sandy material is expected to be transported alongshore by nearshore currents; (b) delta front deposits are characterised by fine-grained sediments that include evidence of human activities which have taken place, in a more intense way, since the 1950s; and (c) prodelta deposits are represented by almost uniform riverine mud that cover the pre-existed relict sands of the shelf, indicating also the limit (some 15 km to the SW) of the influence of riverine sedimentation on the seabed of the inner shelf of the Alexandroupolis Gulf.     

Use of Shear Wave Velocity for Foundation Design

Geotechnical and Geological Engineering - This paper describes an approach for utilizing in-situ measurements of shear wave velocity Vs to carry out preliminary and check design calculations for...     

Approximate pile-to-pile interaction factors between two dissimilar piles

This paper develops approximations for the settlement interaction factors between two dissimilar piles. Via an extensive parametric study using the computer program GEPAN, approximations are developed for interaction factors for piles having dissimilar diameters but equal lengths, piles having dissimilar lengths, and for piles having dissimilar ground conditions at the pile tips. Correction factors are then given to allow for the effects of piles stiffness and length-to-diameter ratio. The approximations may be employed in analyses for group settlements to allow for the case where not all piles in the group are identical.     

An approximate numerical analysis of pile–raft interaction

This paper presents an approximate method of numerical analysis of piled–raft foundations in which the raft is modelled as a thin plate and the piles as interacting springs of appropriate stiffness. Allowance is made for the development of limiting pressures below the raft and of the ultimate axial load capacity of the piles. Comparisons between this analysis and existing solutions verify that, despite the approximations involved, the analysis can provide solutions of adequate accuracy for the settlement and pile load distribution within a piled raft. Comparisons are also made with the results of a series of centrifuge tests and with measurements of the performance of a full-scale piled raft. In both cases, the analysis predicts very well the settlement and proportion of load carried by the piles.     

A numerical model for dynamic soil liquefaction analysis

This paper presents an effective stress-based numerical model, which can be used to obtain pore pressure build up and consequent loss of soil strength due to earthquake-induced shaking. The main advantage of the new method is that it needs few model parameters compared to many existing effective stress-based ground response analysis methods. The pore pressure generation is calculated using the equivalent cycle pore pressure model developed by Seed et al. [J Geotech Engng Div, ASCE 102 (1976) 323] but the equations are used in a different manner. Pore pressure generation calculated by the new method and the equivalent cycle method for different load patterns shows that the new method can predict pore pressures which are in better agreement with experimental data, irrespective of the loading pattern. The equivalent cycle method predicts results in agreement with experimental data only when the loading pattern is highly irregular, and tends to under-predict pore pressure ratios for other loading patterns. To demonstrate the ability of the new method in simulating earthquake-induced site response and liquefaction-related ground deformations, the Kobe, 1995 earthquake has been analysed. The results obtained from the new analysis agree reasonably well with recorded accelerations and lateral ground displacements at Port Island, Kobe.     

Analysis of pile-soil interaction under lateral loading using infinite and finite elements

In order to gain a better understanding of pile-soil interaction under lateral loading, this paper presents a numerical analysis which combines the infinite and finite element method. Interest is focused on the group effect on ultimate lateral soil resistance. Firstly, a single isolated pile is analysed and reasonably good agreement is found between existing analytical solutions and results obtained by the present method. A limited parametric study is also presented and some parameters influencing the ultimate lateral soil resistance are identified. The analysis of pile groups is then considered and it is shown that the group effect tends to reduce pile capacity when the spacings between piles are within the practical ranges. The extent of the reduction depends on the arrangement of piles within the group.     

Spatially explicit mapping of hurricane risk in New England, USA using ArcGIS

Hurricanes are one of the major natural disturbances affecting human livelihoods in coastal zones worldwide. Assessing hurricane risk is an important step toward mitigating the impact of tropical storms on human life and property. This study uses NOAA’s historical tropical cyclone database (HURDAT or ‘best-track’), geographic information systems, and kernel smoothing techniques to generate spatially explicit hurricane risk maps for New England. Southern New England had the highest hurricane risk across the region for all storm intensities. Long Island, western Connecticut, western Massachusetts, and southern Cape Cod, Martha’s Vineyard, and Nantucket had high storm probabilities and wind speeds. Results from this study suggest that these locations may be of central importance for focusing risk amelioration resources along the Long Island and New England coastlines. This paper presents a simple methodology for hurricane risk assessment that could be applied to other regions where long-term spatial storm track data exist.