Centrifuge modelling of pile-soil interaction in liquefiable slopes|
Stuart K. Haigh and S.P. Gopal Madabhushi
|Abstract; Full Text (4680K)|
Piles passing through sloping liquefiable deposits are prone to lateral loading if these deposits liquefy and flow during earthquakes. These lateral loads caused by the relative soil-pile movement will induce bending in the piles and may result in failure of the piles or excessive pile-head displacement. Whilst the weak nature of the flowing liquefied soil would suggest that only small loads would be exerted on the piles, it is known from case histories that piles do fail owing to the influence of laterally spreading soils. It will be shown, based on dynamic centrifuge test data, that dilatant behaviour of soil close to the pile is the major cause of these considerable transient lateral loads which are transferred to the pile. This paper reports the results of geotechnical centrifuge tests in which models of gently sloping liquefiable sand with pile foundations passing through them were subjected to earthquake excitation. The soil close to the pile was instrumented with pore-pressure transducers and contact stress cells in order to monitor the interaction between soil and pile and to track the soil stress state both upslope and downslope of the pile. The presence of instrumentation measuring pore-pressure and lateral stress close to the pile in the research described in this paper gives the opportunity to better study the soil stress state close to the pile and to compare the loads measured as being applied to the piles by the laterally spreading soils with those suggested by the JRA design code. This test data shows that lateral stresses much greater than one might expect from calculations based on the residual strength of liquefied soil may be applied to piles in flowing liquefied slopes owing to the dilative behaviour of the liquefied soil. It is shown at least for the particular geometry studied that the current JRA design code can be un-conservative by a factor of three for these dilation-affected transient lateral loads.
dilation; lateral spreading; pile-soil interaction; centrifuge modelling.
Stuart K. Haigh and S.P. Gopal Madabhushi: Cambridge University, Department of Engineering, Trumpington St, Cambridge, UK
Shape factors of cylindrical permeameters|
Vincenzo Silvestri, Ghassan Abou Samra and Christian Bravo-Jonard
|Abstract; Full Text (936K)|
This paper presents an analytical solution for steady state flow into a close-ended cylindrical permeameter. The soil medium is considered to be uniform, isotropic, and of infinite thickness. Laplace equation is solved by considering rotational symmetry and by using curvilinear coordinates obtained from conformal mapping. The deduced shape factors, which are compared to approximate relationships obtained from both numerical and physical modelling, and idealizations involving ellipsoidal cavities, are proposed for use in field measurements. It is shown that some of the shape factors obtained are significantly different from published values and show a much higher dependence of the rate of flow on the aspect ratio, than deduced from approximate solutions.
shape factors; cylindrical permeameters; hydraulic conductivity; analytical solution; infinite medium; constant-head test; comparisons.
Vincenzo Silvestri, Ghassan Abou Samra and Christian Bravo-Jonard: Dept. of Civil, Geological, and Mining Engineering, Ecole Polytechnique, P.O. Box 6079, Station Centre-Ville, Montréal, Québec, Canada H3L 3A7
Finite element analysis of a piled footing under horizontal loading|
Dj. Amar Bouzid
|Abstract; Full Text (2093K)|
In this paper a semi-analytical approach is proposed to study the lateral behavior of a piled footing under horizontal loading. As accurate computation of stresses is usually needed at the interface separating the footing (pile) and the soil, this important location should be appropriately modeled as zerothickness joint element. The piled footing is embedded in elastic soil with either homogeneous modulus or modulus proportional to depth (Gibson
piled footing; horizontal loading; semi-analytical approach; interface elements; homogeneous and Gibson
Dj. Amar Bouzid: Dept. of Civil Engineering, Engineering Institute, University Yahia Fares of Médéa, Quartier Ain D
Centrifuge modelling of temporary roadway systems
subject to rolling type loading|
Andrew S. Lees and David J. Richards
|Abstract; Full Text (2442K)|
Scaled centrifuge modelling techniques were used to study the soil-structure interactions and performance of a jointed rollable aluminium roadway (or trackway) system on soft clay under light truck tyre loads. The measured performance and subsequent analyses highlighted that the articulated connections significantly reduced the overall longitudinal flexural stiffness of the roadway leading to stress concentrations in the soil below the joints under tyred vehicle loadings. This resulted in rapid localised failure of the supporting soil that in turn led to excessive transverse flexure of the roadway and ultimately plastic deformations. It is shown that the performance of rollable roadway systems under tyred vehicle trafficking will be improved by eliminating joint rotation to increase longitudinal stiffness.
model tests; tyre; clay; rutting; roadway; trackway; soil-structure interaction; centrifuge modelling.
Andrew S. Lees: Frederick University, Nicosia, Cyprus and Geofem Ltd., Cyprus
David J. Richards: University of Southampton, Southampton, UK
A complement to Hoek-Brown failure criterion for strength prediction in anisotropic rock|
Mohammad Hossein Bagheripour, Reza Rahgozar, Hassan Pashnesaz and Mohsen Malekinejad
|Abstract; Full Text (3106K)|
In this paper, a complement to the Hoek-Brown criterion is proposed in order to derive the strength of anisotropic rock from strength of the corresponding truly intact rock. The complement is a decay function, which unlike other modifications or suggestions made in the past, is multiplied to the function of the original Hoek-Brown failure criterion for intact rock. This results in a combined and extended form of the criterion which describes the strength of anisotropic rock as a varying fraction of the corresponding truly intact rock strength. Statistical procedures and in particular regression analyses were conducted into data obtained in experiments conducted in the current research program and those collected from the literature in order to define the Hoek-Brown
Hoek-Brown criterion; anisotropic rock; complement; strength prediction.
Mohammad Hossein Bagheripour, Reza Rahgozar: Dept. of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran
Hassan Pashnesaz: Tadbir Kavosh Mining and Industrial Research Centre, Shiraz, Iran
Mohsen Malekinejad: Dept. of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran