The underlying mechanisms governing the behaviour of displacement piles in sand are not well understood, leading to unreliability in design methods. A series of plane-strain calibration chamber tes...

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Displacement and strain paths during plane-strain model pile installation in sand

A small-scale physical modelling method was developed to study the movement of clay during pile installation The clay was simulated using a mixture of amorphous silica and mineral oil, which becomes almost transparent when the refractive indices of the oil and the silica are well matched After adding reflective particles and consolidating the mixture in a transparent container, cylindrical model piles were driven vertically at the centre A vertical section aligned with the pile centreline was illuminated by a laser light sheet, and a sequence of digital images was recorded These were analysed using particle image velocimetry, and the complete displacement distribution during the pile installation was obtained Notwithstanding some discrepancies at shallow depths, the observed displacements generally showed fairly good agreement with the theoretical predictions of the shallow strain path method (SSPM) once the effect of some soil trapped beneath the flat pile tip was taken into account Normalisation of the horizontal and vertical components of movement employing both the pile length and radius, based on SSPM theory, was shown to be valid The normalised vertical displacement contours were similar to those published by previous researchers The results of this study could be used to assess the impact of disturbance due to pile installation on, for example, buried services or archaeology

Physical modelling of pile penetration in clay using transparent soil and particle image velocimetry

In this paper, a novel finite-element procedure is used to analyze steady cone penetration in soils. Although the procedure is, in principle, applicable to clay and sand with any plasticity model, this paper is only concerned with steady cone penetration in undrained clay. The steady-state finite-element analysis focuses on the total displacements experienced by soil particles at a particular instant in time during the cone penetration test. This is possible because, with the steady-state assumption, the time dependence of stresses and strains can be expressed as a space dependence in the penetration direction. As a result, the finite-element solution of steady cone penetration can be obtained in one step. When compared with the strain path method, the present finite-element procedure offers the following advantages: (1) all equations of soil equilibrium are fully accounted for; (2) cone and shaft roughness can be taken into account in a more rigorous manner and, as a result, the sleeve friction ratio can be properly predicted; and (3) the finite-element procedure can be more easily adapted to analyze cone penetration in dilatant soils.

Analysis of steady cone penetration in clay

The shortage of field measurements to examine existing predictive methods for pipe piles in clay prompted an experimental programme in Shanghai, China, in which displacements and stresses were measured in the vicinity of two pipe piles during their installation in a soft lightly overconsolidated clay. The test programme was also conducted to assist assessment of the installation effects associated with a recently patented cast-in-place concrete pipe pile, referred to as the PCC pile. The field measurements are compared with existing predictive methods such as the shallow strain path and cavity expansion methods (SSPM and CEM). The SSPM is shown to be the most suitable for the prediction of ground displacements, although the more straightforward CEM can provide realistic predictions of radial movements when calculations are performed using a solid pile with an area equivalent to that of the annulus of the pipe pile. Installation-induced excess pore pressures remote from pipe piles are also shown to be well...

Pipe pile installation effects in soft clay

This paper evaluates theoretical predictions of ground movements caused by the installation of driven (or jacked) piles in clay The predictions are based on an approximate analysis framework referred to as the shallow strain path method (SSPM) that simulates undrained pile penetration from the stress-free ground surface Large strain conditions close to the pile are solved numerically, and closed-form analytical expressions are obtained from small strain approximations at points further away These results show that, for closed-ended cylindrical piles of radius R and embedment L, the normalized displacements are functions of their dimensionless position x/L In contrast, for a planar sheet pile or unplugged open-ended pile, the far-field soil displacements at x/L depend only on the wall thickness The proposed analyses show favorable agreement with data from a variety of available sources including field measurements of building movements caused by installation of large pile groups; uplift of a pile caused by driving of an adjacent pile within a group; and spatial distributions of ground movements caused by installation of a single pile (both cylindrical closed-ended and sheet pile wall), including a particularly detailed set of measurements in a large laboratory calibration chamber The comparisons show that the proposed analysis is capable of reliably predicting the deformations within the soil mass but generally underestimates the vertical heave measured at the ground surface Further investigation suggests that this discrepancy may be related to the occurrence of radial cracks observed at the ground surface during pile installation and is consistent with tensile horizontal strains computed in the SSPM analyses

Prediction of ground movements due to pile driving in clay

A new method of analysis is described for estimating the deformations and strains caused by shallow undrained penetration of piles and caissons in clay. The formulation combines previous analyses for steady, deep penetration, with methods used to compute soil deformations due to near-surface ground loss, and is referred to as the Shallow Strain Path Method (SSPM). Complete analytical solutions for the velocity and strain rates are given for a planar wall, an axisymmetric, closed-ended pile and unplugged, open-ended pile geometries. In these examples, the analyses consider a single source penetrating through the soil at a constant rate, generating a family of penetrometers with rounded tips, referred to as simple wall, pile and tube geometries. Soil deformations and strains are obtained by integrating the velocity and strain rates along the particle paths.

The transition from shallow to deep penetration is analysed in detail. Shallow penetration causes heave at the ground surface, while settlements occur only in a thin veneer of material adjacent to the shaft and in a bulb-shaped region around the tip. The size of this region increases with the embedment depth. Deformations inside an open-ended pile/caisson are affected significantly by details of the simple tube wall geometry. © 1997 by John Wiley & Sons, Ltd.

M. Santagata

Papers

Deformation analysis of shallow penetration in clay