Ultimate Lateral Pressure Research Articles

Finite-element analysis of ultimate lateral pressure of snowflake pile in undrained clay

The finite element method is used to investigate the ultimate lateral pressure of a snowflake pile in undrained clay in this paper. The effects of section geometry, lateral loading direction and pile–soil adhesion coefficient on the ultimate lateral pressure of snowflake pile are investigated by parametric analysis. The analysis results show that the normalised ultimate lateral pressure of the snowflake pile gradually decreases as the flange length–thickness ratio λ increases, the normalised ultimate lateral pressure is linearly related to the pile–soil adhesion coefficient α, the normalised ultimate lateral pressure shows the trend of first decreasing and then increases with the increasing of lateral loading angle β. On this basis, the closed-form formula of the ultimate lateral pressure coefficient of a snowflake pile is proposed. The research results can provide the basis for the design of snowflake piles in future.

Ultimate Lateral Pressure of Circular Pile in Undrained Clay Considering the Strength Reduction Induced by Pile Installation

Ultimate Lateral Pressure of Circular Pile in Undrained Clay Considering the Strength Reduction Induced by Pile Installation

Analytical Solution to Ultimate Lateral Pressure on a Vertical Plate in Undrained Soil

For a vertical plate emerging on the surface of undrained cohesive soil, the adhesion between the plate and soil considerably impacts the lateral soil pressure on it. However, very few closed-form solutions have been published to address this seemingly simple problem; they either are restricted to certain conditions or overpredict the ultimate lateral pressure. This paper applies both the lower-bound and upper-bound methods of plasticity to develop a rigorous analytical solution to the ultimate lateral pressure, allowing for the undrained shear strength of soil to increase linearly with depth and a general adhesion on the interface. A method is presented to extend the static stress field throughout the soil mass to validate the lower-bound values. The developed solution is found to be an exact solution for homogeneous soil; the predicted results for nonhomogeneous soil fall within a narrow range bounded by the lower and upper limit values, with the range of errors mostly being within 1%. The solution reduces to the classic Bell’s relationship in the undrained condition if ignoring the adhesion on the interface. When the full active pressure behind the plate is mobilized, the upper-bound solution is rigorous but the lower-bound one is not unless examining a smooth surface. However, the predicted results are close enough to more rigorous ones to be used in engineering practice.

Influence of spudcan-pile interaction on laterally loaded piles

Jack-up rigs are often operated near a permanent jacket platform for offshore gas and petroleum exploitation. A reduction in the lateral bearing capacity of adjacent platform piles could occur due to the disturbance of the soil around the footprint created by spudcan penetration and extraction. Centrifuge model tests were conducted in soft clay to investigate the lateral behaviour of piles, including a base pile and spudcan-affected adjacent piles, subjected to monotonic lateral loading. The results show that the lateral static capacity of an adjacent pile (L/D = 0.5) is reduced by 10.5% compared with that of the base pile. Obvious decreases in the soil reaction stiffness and ultimate lateral pressure occurred due to the spudcan-pile interaction and are related to the clearance and burial depth. Finally, based on the proposed modified p-y curves, which were proven to be reasonable, an engineering analysis approach is presented for evaluating the lateral bearing capacity of adjacent platform piles.

Finite element limit analysis of ultimate lateral pressure of XCC pile in undrained clay

X-section Cast in place Concrete (XCC) pile is a non-cylindrical pile that the cross section not obeying plane rotationally symmetric. In this case, the geometry of cross section as well as the lateral load direction may have influence on the ultimate lateral pressure of XCC pile. This paper presents rigorous upper and lower bound solutions for the ultimate lateral pressure of X-section Cast in place Concrete (XCC) pile in clay through two dimensional plane strain finite element limit analysis (FELA). The geometric effect, lateral load direction and the adhesion factor at the pile-soil interface are selected for parametric study. Subsequently, an empirical closed-form equation of the ultimate lateral pressure factor is proposed for predicting the lateral force acting on a XCC pile in undrained clay. It is found that the XCC pile with relatively small ratio of b/a has larger ultimate lateral pressure than the conventional circular pile under the condition of the same area of cross section.

Ultimate lateral bearing capacity of tetrapod jacket foundation in clay

The tetrapod jacket foundations that are always used to support offshore wind turbines have been investigated primarily in laboratory experiments. In this study, the ultimate lateral soil resistance on this type of foundation was investigated using the finite element method and the analytical upper bound plasticity method. The numerical results show good agreement with the theoretical upper bound solutions under the same pile spacings (S) and soil-pile adhesion factors (α). Three distinct failure mechanisms (mechanisms A, B and C) were established in terms of different pile spacings. The ultimate lateral pressure was subsequently determined using numerical analyses with consideration of the loading direction. The most critical loading direction angles (θ) vary with the soil-pile adhesion factors, and are θ=0 for α=1 and θ=π/4 for α=0. Selected empirical equations were proposed to predict the ultimate lateral bearing capacity for engineering practice, considering the pile spacing, soil-pile adhesion and loading direction.

Ultimate lateral capacity of timber poles embedded in clay

This paper presents results of field testing to evaluate the lateral capacity of timber poles embedded in Auckland residual clay. The work was undertaken because a relationship proposed by Broms in 1964 predicts lateral capacities for embedded poles used in construction of pole retaining walls that are frequently too conservative because of assuming zero lateral resistance over the upper 1·5 embedment diameters. In all, 16 poles were installed in residual clay at a site in Albany (north of the city of Auckland, New Zealand), 12 of them were concreted into 0·45 m bored holes and four of them were driven. In total, 14 poles were tested. The paper describes the test method and the interpretation of the results. The main conclusion is that an ultimate lateral pressure distribution starting from about 2su at the ground surface and increasing linearly to 9su at a depth of about nine embedment diameters gives satisfactory modelling of the measured pole capacities. For the limited range of embedment depths and loading geometries covered in the field testing, an equation based on a constant ultimate lateral pressure with depth of 3su gives a reasonable prediction of the lateral capacity of the timber poles.

Ultimate lateral pressure of two side-by-side piles in clay

The ultimate earth resistance for a group of two side-by-side piles that are laterally loaded in clay is investigated using four different methods of analysis: three numerical (the displacement finite-element method, and the upper- and lower-bound finite-element limit analysis methods) and one analytical (an analytical upper-bound plasticity method developed in this paper). The results of the three numerical methods are shown to be in excellent agreement, while the analytical solution presents a theoretical upper bound that is very close to the numerical results. The results of the analyses are used to identify the predominant failure mechanisms for different pile spacings and pile–soil adhesions. They are also used to develop a design chart and design equations for determination of the ultimate lateral bearing capacity factor.

Limiting pressure on a laterally loaded pile in a frictional soil

This letter investigates, by means of finite-difference analyses, the ultimate lateral pressure developed on a pile moving relative to a soil whose strength is characterised by an effective angle of shearing resistance φ′. Analyses were carried out to determine the distribution of ultimate pressure with depth, with particular attention paid to near-surface effects, for a value of φ′ representative of a clay soil. The model results are compared with common empirical distributions of ultimate lateral pressure, obtained generally from full-scale and model tests in sand. It was found that the depth to which the unconfined ground surface affects the ultimate lateral pressure developed is consistently about five pile diameters. Below the zone influenced by surface effects, limiting lateral pressures were found to increase linearly with depth. Commonly used empirical distributions for the limiting pressure were found to bracket the numerical results for a frictionless pile–soil interface and underestimate the numerical results for a full-strength pile–soil interface.

Analysis of pile behaviour in liquefying sloping ground

Abstract 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.

Interpretation from large-scale shake table tests on piles undergoing lateral spreading in liquefied soils

Results from a benchmark test on full-scale piles are used to investigate the response of piles to lateral spreading. In the experiment, two single piles, a relatively flexible pile that moves together with the surrounding soil and a relatively stiff pile that does not follow the ground movement have been subjected to large post-liquefaction ground displacement simulating piles in laterally spreading soils. The observed response of the piles is first presented and then the results are used to examine the lateral loads on the pile from a non-liquefied soil at the ground surface and to evaluate the stiffness characteristics of the spreading soils. The measured ultimate lateral pressure from the crust soil on the stiff pile was about 4.5 times the Rankine passive pressure. The back-calculated stiffness of the liquefied soil was found to be in the range between 1/30 and 1/80 of the initial stiffness of the soil showing gradual decrease in the course of lateral spreading.

The Effects of Soil Yielding on Seismic Response of Single Piles

ABSTRACT In the seismic analysis of pile foundations the soil is often assumed to be an elastic material and the pressure at the soil pile interface is not limited during the analysis. This may result in a considerable error, as the computed pressure from an elastic analysis may go well beyond the ultimate lateral pressure of real soil. In fact, significant yielding at the soil-pile interface has been observed during real earthquakes, and also in laboratory tests. The yield zone is usually near the ground surface where the effect of inertial force due to the superstructure is higher. This yielding redefines the pile response, and in general cannot be ignored. In order to examine the effects of soil yielding on the internal pile response during earthquakes an approximate analysis is described in this paper which is an extension of a static method developed by the second author (1982) for the analysis of piles subjected to lateral soil movement. This method is then used to investigate the effects of soil yielding on the internal response of piles through a comparative study in which real earthquakes are used. It is shown that for strong earthquakes and heavily loaded piles the soil yielding may considerably increase the amount of maximum pile moment developed in the pile. A marked difference in the effects of yielding on the pile moment and shear is observed and discussed.

Earth Pressures on Piles in a Row Due to Lateral Soil Movements

ABSTRACT One of the most important points to be solved on passive piles may be to accurately estimate the lateral pressure acting on piles due to soil movements. The authors have already presented a theoretical equation to estimate the lateral pressure on piles in the previous paper, considering the pile interval as accurately as possible. In this paper, to check the validity of the theoretical equation presented, a series of model tests are carried out for various conditions of the pile and the soil. First, based on the experimental results, the validity of an assumption on the plastic state of soil made in the theoretical derivation and the significance of the presented theoretical equation are clarified. Then, both the experimental and theoretical values of the lateral pressure on piles are compared for both clay and sand specimens, followed by their very good agreements for various kinds of soil strength, pile diameters and intervals between piles. Consequently, it is concluded that the theoretical equation due to the authors’ theory can estimate the lateral pressure on passive piles in a row when the soil just around piles becomes a plastic state, with a sufficient reliability over a wide range of the interval between piles. Finally, a method to approximately estimate the ultimate lateral pressure is also shown.