Estimation of nonlinear pile settlement can be simplified using one-dimensional "t-z" curves that conveniently divide the soil into multiple horizontal "slices." This simplification reduces the continuum analysis to a two-point... more
Estimation of nonlinear pile settlement can be simplified using one-dimensional "t-z" curves that conveniently divide the soil into multiple horizontal "slices." This simplification reduces the continuum analysis to a two-point boundary-value problem of the Winkler type, which can be tackled by standard numerical procedures. Theoretical "t-z" curves can be established using the "shearing-of-concentric cylinders" theory of Cooke and Randolph-Wroth, which involves two main elements: (1) a constitutive model cast in flexibility form, γ =γ(τ); and (2) an attenuation function of shear stress with radial distance from the pile, τ =τ(r). Soil settlement can then be determined by integrating shear strains over the radial coordinate, which often leads to closed-form solutions. Despite the simplicity and physical appeal of the method, only a few theoretical "t-z" curves are available in the literature. This paper introduces three novel attenuation functions for shear stresses, inspired by continuum solutions, which are employed in conjunction with eight soil constitutive models leading to a set of 32 "t-z" curves. Illustrative examples of pile settlement calculation in two soil types are presented to demonstrate application of the method.
An appropriate constitutive model embedded in a finite element engine is the key to the successful prediction of the observed behaviour of geotechnical structures. However, to capture the behaviour of geomaterials accurately, the... more
An appropriate constitutive model embedded in a finite element engine is the key to the successful prediction of the observed behaviour of geotechnical structures. However, to capture the behaviour of geomaterials accurately, the constitutive models have to be complex involving a large number of material parameters and constants. This paper presents a methodology for converting or recasting complex constitutive models for geomaterials developed based on any constitutive theory into a fully trained Artificial Neural Network (ANN), which is then embedded in an appropriate finite element solution code. The length of strain trajectory traced by a material point, also called ‘intrinsic time’ is used as an additional input parameter in training. For the purpose of illustration, two constitutive models viz. Hardening Soil Model available in the commercial software, PLAXIS and a two-surface deviatoric hardening model in the multilaminate framework have been cast in the form of an ANN. Computational efficiency is perceived to be the main advantage of this methodology.
The Leaning Tower of Pisa was built between 1173 and 1360 and began to lean at the beginning of its construction. Extensive investigations to reveal the causes of the tilting only began in the early 20th century. Although few earthquakes... more
The Leaning Tower of Pisa was built between 1173 and 1360 and began to lean at the beginning of its construction. Extensive investigations to reveal the causes of the tilting only began in the early 20th century. Although few earthquakes have been recorded, there is a renewed interest in the seismic behavior of the tower triggered by the availability of new data and technologies. This paper highlights the influence of using new strength-controlled constitutive models in case of 1D nonlinear response analysis. This is an aspect that has been poorly investigated. Most of the computer codes currently available for nonlinear seismic response analysis (SRA) of soil use constitutive models able to capture small-strain behavior, but the large-strain shear strength is left uncontrolled. This can significantly affect the assessment of a 1-D response analysis and the Leaning Tower's subsoil can be useful for this study as it represents a well-documented and well-characterized site. After a geological and geotechnical description of the subsoil profile and a synthesis of available data, the seismic input is defined. One-dimensional SRAs were carried out by means of a computer code which considers an equivalent-linear soil modelling and two codes which assume nonlinear soil response and permit to use strength-controlled constitutive models. All the parameters were calibrated on the basis of the same soil data, therefore allowing for a direct comparison of the results.
Seven teams took part in a benchmarking exercise on selection of parameter values for the Barcelona BasicModel (BBM) from experimental data on an unsaturated soil. All teams were provided with experimental results from tests performed on... more
Seven teams took part in a benchmarking exercise on selection of parameter values for the Barcelona BasicModel (BBM) from experimental data on an unsaturated soil. All teams were provided with experimental results from tests performed on a compacted soil in order to determine values for the ten BBM soil constants and an initial value for the hardening parameter. The coordinating team then performed simulations (at stress point level) with the 7 different sets of parameter values, in order to explore the implications of the differences in parameter values and hence to investigate the robustness of existing BBM parameter value selection procedures. The major challenge was found to be selection of values for the constants λ(0), r, β, N(0) and pc and an initial value for the hardening parameter p0(0), with the various teams proposing significantly different values for some of these key parameters. A key lesson emerging from the exercise is the importance of choosing a method for selecting values for the parameters β and pc which places the main emphasis on attempting to optimise the match to the experimental spacing of normal compression lines at different values of suction.
