Behavior of Walls and Piles in Cohesive Soils Under Cyclic Loads
Abstract
The nonlinear cyclic behavior of a soil-structure system has a significant influence on the
mechanical response of this system. The cyclic response of soil-structure system has been
studied experimentally and analytically. However, the results of these studies are not yet
reproducing the applicability of key aspects of soil-structure behavior concepts in practice. A key
prerequisite is to model the cyclic response in a facilitative and realistic way. There are several
constitutive models in the literature that are available for cumulative responses, but they need
many soil tests for calibration and they can be used under specific numerical codes and can be
only executed by specialists. To overcome these difficulties, this research develops a simplified
constitutive model (a kinematic hardening constitutive model with Von Mises failure criterion)
for analyzing nonlinear plastic response of a soil-structure system subjected to cyclic loading.
In addition, cumulative deformations are an essential aspect of the performance of walls
and piles/caissons under cyclic loading. Therefore, reasonable estimates of the cumulative plastic
displacements of structures in cohesive soils are necessary, particularly for soils which the cyclic
influence may be significant. For example, the cumulative wall displacements that increase over
time as the system is subjected to repeated live loading from trains passing near wall, in addition
to the vertical settlements under the train track. Studying the effects of cyclic loading of railroads
on the soil-wall system is necessary to improve train safety when a soil-wall system is near the
tracks. As a second example, while pile and caisson anchors and foundations for offshore
structures, such as wind turbines and the oil/gas exploration and production facilities have been
the focus of considerable attention with respect to monotonic load capacity, much less attention
has been given to cumulative displacements under cyclic loading. This issue is particularly
crucial for inclined loading, since cumulative displacements can lead to loss of embedment of the
caisson or pile.
Since stress-strain behavior of soils is inelastic even at small strains, analyses based on
linear elasticity, or on elastoplastic models that assume purely elastic behavior beneath the
ultimate yield surface, cannot predict the cumulative soil deformations. Hence, an analysis that
takes inelastic soil behavior at low stress levels into account, such as a bounding surface
plasticity model, is required to predict cumulative displacements under cyclic loading.
A cyclic nonlinear elastoplastic soil spring model has been applied to predict the
monotonic and cyclic nonlinear p-y curve of piles in soft clay during the cyclic loading.
Predictions of pile performance based on the kinematic hardening constitutive model used in this
research are shown to match the centrifuge test results better than predictions based on the
widely used API soil springs. This proposed spring model can overcome the limitations of the
API clay model and can be implemented with either MATLAB or as UEL (User-defined
elements) subroutine in ABAQUS/Standard. Predictions based on the spring model developed in
this research shows good agreement with the measurements of cumulative displacement and soil
stiffness from centrifuge tests involving cyclic loading of a single pile in soft clay.
Subject
PlasticityKinematic hardening model
Bounding surface model
Cyclic loading
Inclined loading
Lateral loading
Offshore structures
Wind turbines
Caisson
Pile
Anchor
Mooring line
Single-line
Multiline
Sheet pile wall
Retaining wall
Railroads
Cumulative displacements
Wall displacements
P-y curve
Cyclic backbone
Soil spring
Lateral soil pressure
Finite element analysis
Asymmetric Fourier elements
ABAQUS
UEL subroutine
MATLAB
Cohesive soil
Nonlinear cyclic behavior
Soil-structure system
Von Mises failure criterion.
Citation
Al-Ramthan, Ahmed Qasim Obaid (2019). Behavior of Walls and Piles in Cohesive Soils Under Cyclic Loads. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /185013.