Settlement of a Pile under Cyclic Lateral Loads in Dry Sand

It is found through centrifuge model tests that the cyclic lateral load on a pile reduces the shaft friction and induces additional pile settlement. A theoretical model using the load-transfer method was proposed for the settlement prediction of cyclic laterally loaded piles in dry sand. A simple formula was established to quickly predict the pile settlement in practical engineering. The theoretical model provided a reasonable estimate of the pile settlement, while the predictions from the proposed quick prediction formula were relatively conservative. A new concept of “settlement-controlled design” was proposed to advance the methodology for the design of a pile by considering potential settlement after many cycles of lateral loads. According to the design plane derived from this study, the design-state points were suggested to be limited in the convergent zone.

Interaction between a long pile and the multilayered soil body with account for elastic and rheological properties as well as soil stabilization

Introduction. When the footing is embedded in loose clayey soils, buildings may settle down for a long period of time. The projected settlement period is of great importance for the design of foundations designated for such soils. Therefore, the approach to describing the process of foundation settlement must be considered as rheological. This article addresses the setting of and a solution to the problem of interaction between a long pile and surrounding multilayered and underlying soils with account taken of the rheological properties of the surrounding soil body. The creep process is considered with account taken of stabilization. Materials and methods. Linear problem setting is considered. The analytical method is employed to present a solution. The rheological stabilization parameter is used to describe the creep process. Results. An expression is derived to determine the reduced shear modulus for the multilayered soil body. The relationship between the value of the force applied to the pile toe and the time is derived with regard for the rheological stabilization parameter. Analytical solutions are enforced by graphs in the article. Graphs describing the relationship between pile settlement, the force applied to the toe of the pile, passing through alternating soil layers, and the time are provided for various values of viscosity and the variable parameter of stabilization. Conclusion. Solutions, obtained by the co-authors, are used to perform the preliminary identification of displacement of long piles and surrounding multilayered underlying soils. The rate of stress changing underneath the pile toe depends on soil viscosity. The rheological coefficient of stabilization has a major effect on the time of pressure stabilization underneath the pile toe, as well as the time of the pile settlement stabilization. Dependencies, derived in this article, make it possible to project the future settlement pattern.

Improvement of methods for pile foundations design on settlement

Introduction. The paper describes a new approach for pile foundations design. The system of mechanical impacts is described in a new way for the pile foundation design based on the foundation settlement taking into account the distribution of elastic deformation of the pile material in a soil base. Materials and methods. In contrast to the existing approaches to determining the pile settlement due to elastic deformations of the pile material, all impacts in the form of load from the pile cap, friction forces on the pile lateral surface and the actual reaction at the pile tip are taken into account differentially according to the principle of forces independence. The new design equation is proposed to describe the distribution of friction forces on the lateral surface of the pile. The friction forces in a homogeneous soil of the base are represented as a parabolic distribution function, and not as a linearly increasing one, as established in the standards. Results. As a result, the equation is obtained for a pile settlement design due to the elastic strain of pile material. An example of calculating the pile settlement according to the proposed method and comparing the results with existing methods is given. Negative friction forces from the reaction of the soil under the lower end of the pile increase the value of the elastic deformation of the pile shaft. Conclusions. The refined equation for calculating the elastic component of the pile settlement makes it possible to obtain a lower value of the settlement in comparison with the standard approach by taking into account the influence of friction forces of the soil along the pile lateral surface. The proposed method for pile foundations design based on the settlement can serve as a justification for the reserve of the load-bearing capacity of the pile foundation according to the settlement criterion which will allows obtaining a certain economic effect.

Seismic reliability of axially loaded vertical piles

The reliability of single vertical pile foundations subjected to seismic loads is assessed and compared with the minimum acceptable reliability level for static load conditions mandated by the Canadian codes. The analysis is executed for a site with a mean shear-wave velocity of the top 30 m of the ground equal to 250 m/s subjected to the ground motion hazard of five Canadian cities. Using both a full probabilistic analysis and simplified probabilistic model, the results seem to indicate that the current design practice is unable to achieve the reliability target of the codes. The shortfall is particularly significant when the limiting pile settlement is relatively small. The calculated reliability level of small limiting settlements is impacted by the geotechnical variability, whereas the seismic hazard variability affects large pile limiting settlements. Finally, the simplified probabilistic model produces the same results as the full probabilistic model for large pile settlement and is a convenient tool to execute code calibration.

Theoretical "t-z" Curves for Piles in Radially Inhomogeneous Soil

Accurate estimates of pile settlement are key for efficient design of axially loaded piles. Calculations of pile settlement can be simplified using one-dimensional “t-z” curves describing pile settlement at a certain depth as a function of side friction. In the realm of this simplified framework, theoretical “t-z” curves can be derived by substituting an attenuation function describing the variation of shear stress with distance from the pile, into a soil constitutive model relating shear strain to shear stress, then integrating with respect to distance to get the settlement at the pile circumference due to an applied shear stress. A handful of analytical “t-z” curves are available in the literature using the concentric cylinder model to define an attenuation function; these include solutions for linear-elastic, power-law and hyperbolic constitutive models. However, radially homogeneous soil has often been assumed, ignoring the effect of the pile installation resulting in unconservative calculations of pile settlement. This paper considers the installation of the pile, resulting in a radially variable shear modulus distribution in the surrounding soil. A radial inhomogeneity correction factor has been developed for selected constitutive models based on two simplified functions for the soil inhomogeneity, which can be applied to the previously derived “t-z” curves produced assuming radially homogeneous soil. The performance of this simplified method is investigated.

PILE SETTLEMENT INDUCED FROM SOIL MOVEMENT DUE TO BREAKDOWN OF RETAINING WALL

Very few studies measured the settlement of retaining wall supported piles foundation under a soil movement. This study explores the pile settlement induced from the sudden breakdown of a closely located retaining wall using a small-scale experimental model. Various factors affect the pile settlement, but the influence of the embedment ratio of the pile and collapsed height of the retaining wall is relatively more visible. The induced settlement decreases with pile embedment depth and increases with the collapsed height of the retaining wall. The pile settlement initially increases at a higher rate with an increase in the collapsed height to a certain extent, beyond which, becomes relatively less observable. Pile group settlement reduces with the increase in spacing and the number of piles in longer piles. However, opposite trends have been observed in piles with a smaller embedment ratio. The settlement reduces logarithmically with the increase in the distance between piles and the retaining wall. Pile groups with small embedment ratio are severely more affected by the breakdown of the retaining wall than the piles of a large embedment ratio. Pile groups placed parallel to the retaining wall are more affected than those placed orthogonally.