Shaft Resistance During Driving in Clay from Laboratory Tests

Géotechnique, 1982

Most design procedures for estimating pile capacities are empirical in nature, and the mechanism of load transfer from a pile to the soil is not well understood. In this Paper the mobilization of shear stress along a rough pile shaft in normally consolidated clay is considered in terms of the effective stresses acting in the clay. Theoretical predictions of the stress changes which occur in the soil adjacent to the pile shaft on loading are presented and shown to be in good agreement with some experimental results. For drained loading conditions reductions in radial effective stress generally occur, and the peak mobilized angle of shaft friction is shown to be independent of initial soil stresses before pile loading. The validity of the theoretical model is shown and the loading behaviour, drained and undrained, of driven piles is examined. Comparison between these predictions and field data suggests that fabric disturbance caused by pile installation may seriously affect pile capac...

Abstract: In this paper, a pile foundation with 0.6 m diameter and 12 m length is embedded in fully saturated and partially saturated Iraqi soils, within Baghdad city. The analysis was carried out using finite element method. The partially saturated parameters were calculated using laboratory methods (i.e. filter paper method), such as the H-Modulus function based on the soil water characteristic curve (SWCC) which was obtained through the program (Soil Vision), after identifying the basic properties of the soils. Then, the SWCC is converted to relation correlating the void ratio and matric suction. The slope of the latter relation can be used to define the H Modulus function. The finite element programs SIGMA/W and SEEP/W were then used in the analysis. Eight noded axisymmetric isoparametric quadrilateral elements are used for modeling both soils skeleton and pore water pressure. A parametric study is carried out and different parameters are changed to study their effects on the behavior of partially saturated clay. These parameters include the degree of saturation, depth of water table, shear strength of clay, negative pressure head, soil density, permeability function, volumetric water content function, and the unsaturated soil modulus (H). This study included the effect of partial soil saturation on the ultimate shaft resistance, and the adhesion factor (α) in piles for each depth of water table and degree of saturation. The study revealed that when the soil becomes partially saturated by dropping water table at different depths with different degrees of saturation, the pile capacity increases. It was concluded that a great effect of partial soil saturation on the values of skin friction due to lowering of water table and degree of saturation for the three soils. The maximum shear force along the pile shaft increases with dropping of water table. A rapid increase in the shear force takes place when the water table is lowered to 2 m and 4 m and becomes smaller for larger depths of water table level. An increase in the shear force of the three soils is found with increasing matric suction to specific value and a decrease in shear force for greater values of matric suction. Keywords: Pile, unsaturated soil, clay, shaft resistance

Journal of Geotechnical Engineering, 1993

Comprehensive measurements of the effective stresses developed during the installation, equalization, and load testing of displacement piles in a loose to medium dense quartz sand are presented. The results shed new light on the mechanisms that control shaft friction in sand. First, it is demonstrated directly that the stresses developed at any given soil horizon depend strongly on both the distance of that horizon from the pile tip and the soil's initial state. Second, pile loading is shown to induce radial effective stress changes associated with the soil fabric set up by installation and dilation phenomena at pile-soil interface. Thirdly, the operational angles of interface friction are found to be constant volume values that correlate well with the results from laboratory interface shear tests.

Canadian Geotechnical Journal, 2020

Although there are several studies indicating that heating increases the long-term shaft resistance of energy piles, the mechanisms by which heating causes this increase have not been adequately evaluated yet. This article presents a comprehensive analysis and discussion to assess the important factors contributing to this increase by integrating the findings from three recently published papers studying the thermo-mechanical behavior of clay and the clay–pile interface. In these three studies, reconstituted kaolin clay was used, and cyclic and monotonic heat ranging between 24 and 34 °C were applied to the clay and interface. The interface was sheared under two stiffness boundary conditions: constant normal stiffness (CNS) and constant normal load (CNL), where normal stresses varied between 100 and 300 kPa. The analysis presented in this article reveals that the increase in strength of the interface under the CNL condition is primarily attributed to clay stiffening at the interface...

1988

The paper discusses briefly the state of art on the subject of pile dynamics including consideration of soil-pile interaction. An analytical model which gives the response of a single pile buried in a layered soil medium considering variation in soil properties in the radial direction in each layer is illustrated. The paper also presents an experimental study on a full size test pile 40 cm dia and 7 m long driven into a five layered soil stratum. The results of the analytical and experimental studies are compared and suggestions for further work are given

Canadian Geotechnical Journal, 2010

This paper presents the results of a series of field experiments performed to study the effect of installation method on the shaft resistance developed by a pile installed in soft clayey silt. Tests were performed on piles that experienced different levels of cyclic loading during installation. The test results indicate that the radial total stress, pore-water pressure, and shear stress on the pile shaft during installation were strongly affected by the installation procedure; all three were found to increase when the jacking stroke length used during installation increased (or the number of cyclic load applications decreased). However, equalized radial effective stresses that control the long-term pile shaft capacity were found to be insensitive to the installation method. A simple expression that requires the results of a cone penetration test, laboratory measurements of the interface friction angle, and the pile geometry is proposed to calculate the shaft resistance.

The precise prediction of maximum load carrying capacity of bored piles is a complex problem because it is a function of a number of factors. These factors include method of boring, method of concreting, quality of concrete, expertise of the construction staff, the ground conditions etc. besides the pile geometry. The performance of pile load tests is, therefore, of paramount importance to establish the most economical design of piles especially where bored cast-in-situ piles are to be provided to support a structure. This paper describes the experience gained from four pile load tests at a site in the North West Frontier Province of Pakistan where a new cement plant is going to be installed. Geotechnical investigations at the site were carried out to a maximum depth of 60 m. The subsoils at the site are predominantly hard clays within the investigated depth with thin layers of gravels / boulders below 40 m depth. Perched water was encountered at various horizons. Four piles of diameter varying from 660 mm to 760 mm and length ranging between 20 m and 47.5 m were subjected to axial loads. The load test data were analyzed using various state of the art techniques including intercept of two tangents, point of change of slope, 6 mm net settlement [1], 90 percent and 80 percent Hansen [7], limit value Davisson [2], and Chin [3]. Based on a comparison of pile capacities from these methods with the theoretical values, recommendations are made on the approach to estimate the pile capacity in hard clays. Using the pile load test results, back calculations were also carried out to estimate the appropriate values of pile design parameters such as undrained cohesion and adhesion factor.

Sound Geotechnical Research to Practice, 2013

Soil heave due to pile driving in clay is discussed and, in particular, its influence on adjacent piles. Finite element studies and results of model tests are presented and compared with field measurements. It is demonstrated that in the vicinity of the driven pile, the soil is displaced mainly in the lateral direction, similar to soil subjected to passive earth pressure. General rules of estimating soil heave inside and outside a pile group are examined. A method is proposed for estimating soil heave when driving a group of piles. Practical application of predicting soil heave is illustrated by an example.

Proceedings of the Institution of Civil Engineers, 2023

Géotechnique, 2008

The paper examines, using numerical modelling, the problem of the limit shaft resistance of non-displacement piles installed in sands. The modelling makes use of an advanced, two-surface-plasticity constitutive model. The constitutive model predicts the soil response in both the small-and the large-strain range, while taking into account the effects of the intermediate principal effective stress and of the inherent anisotropy of the sand. Finite element analyses of shearing along the pile shaft are performed in order to examine the development of limit unit shaft resistance and the changes in stress state around the shaft upon axial loading of the pile. Special focus is placed on the operative value of the lateral earth pressure coefficient when limit shaft resistance is reached. The analyses offer useful insights regarding the factors controlling the value of unit shaft resistance in sands. The simulations predict a significant build-up of horizontal effective stress for dense sands. Based on these simulations, we propose a relationship between the lateral earth pressure coefficient for use in the calculation of the limit shaft resistance of the pile and the initial density and stress state of the sand.