Evaluation of Subgrade Modulus and Bearing Capacity with Large Scale Field Tests on Geogrid-Reinforced Granular Fill over Clay Soil

This study aims at experimentally explaining the potential benefits of geogrid reinforcedsoil foundations using large scale field tests. A total of 8 large scale field tests were carriedout to evaluate the effects of replacing natural clay soil with stronger granular fill layer andsingle-multiple layers of geogrid reinforcement placed into granular fill below circularfootings. The large scale field tests were performed using two different sizes of the circularfooting diameters which have 0.30 and 0.90m. The results of testing program are presented interms of subgrade modulus and bearing capacity. Subgrade modulus and bearing capacityvalues were calculated for each test at settlements of 10, 20 and 30mm.It has been seen that based on the test results, the use of granular fill and geogrid forreinforced soil foundations (RSF) have considerable effects on the subgrade modulus andbearing capacity

Prediction of bearing capacity of circular footings on soft clay stabilized with granular soil

AbstractThe shortage of available and suitable construction sites in city centres has led to the increased use of problematic areas, where the bearing capacity of the underlying deposits is very low. The reinforcement of these problematic soils with granular fill layers is one of the soil improvement techniques that are widely used. Problematic soil behaviour can be improved by totally or partially replacing the inadequate soils with layers of compacted granular fill. The study presented herein describes the use of artificial neural networks (ANNs), and the multi-linear regression model (MLR) to predict the bearing capacity of circular shallow footings supported by layers of compacted granular fill over natural clay soil. The data used in running the network models have been obtained from an extensive series of field tests, including large-scale footing diameters. The field tests were performed using seven different footing diameters, up to 0.90m, and three different granular fill layer thicknesses. The results indicate that the use of granular fill layers over natural clay soil has a considerable effect on the bearing capacity characteristics and that the ANN model serves as a simple and reliable tool for predicting the bearing capacity of circular footings in stabilized natural clay soil

Dynamic Response of a Single Pile Embedded in Sand Including the Effect of Resonance

In this paper, responses of a single pile embedded in sand soil (loose and dense) under dynamic loading (sinusoidal dynamic vibrations of 0.1 g to 0.5 g) have been investigated by two-dimensional analysis using the finite element method (FEM). Viscous (dashpot) boundaries have been used for taking the boundary effects of far-field into account. The applicability and accuracy of site responses of two-dimensional analysis due to the FEM modelling have been well verified with one-dimensional site responses. The results indicate that the relative density of sand (loose, dense) becomes prominent for the displacements of the pile, specifically under the frequency effects of resonance. While the pile in loose sand causes the displacements of 0.1 m to 0.5 m, the pile in dense sand leads to the displacements of 0.05 m to 0.25 m, proportionally with the dynamic loads from 0.1 g to 0.5 g. Moreover, the displacements reach their peak value at the frequency ratio of the resonance case. Viscous boundaries are found sufficient for modelling excessive displacements due to dynamic loading. However, the displacements reveal that high vibrations (> 0.1 g for loose sand, > 0.2 g for dense sand) influencing the pile deformations are critical for the issues of settlements. This is more significant for the resonance case in order for ensuring sufficient design. Consequently, the findings from the study are promising good contributions for pile design under the dynamic effect

3D Numerical Modeling of a Single Pipe Pile Under Axial Compression Embedded in Organic Soil

The objective of this paper is to numerically study the behavior pipe pile under axial compression embedded in organic soil has been numerically predicted. The pipe pile used in the study has been produced by steel and it has outer and inner diameters of 20 mm and 15 mm, respectively. The pile embedded in organic soil, which has the pile length ratios of 10, 20 and 30 (L/D), has been exposed to the axial load for different diameter ratios (d/D = 0, 0.25, 0.50 and 0.75). Numerical analyses have been performed by using Plaxis 3D computer program which is based on finite element method. The capability of the numerical analysis in the prediction of the load capacity of pipe pile has been studied. It has been understood that the results obtained from numerical analysis and experiment are in a good agreement, and then it has been observed in the parametric study that the load capacity of single pipe pile increases with the increase of the pile length and the wall thickness. © 2020, Springer Nature Switzerland AG

Effect of anisotropy and destructuration on behavior of Haarajoki test embankment

This paper investigates the influence of anisotropy and destructuration on the behavior of Haarajoki test embankment, which was built by the Finnish National Road Administration as a noise barrier in 1997 on a soft clay deposit. Half of the embankment is constructed on an area improved with prefabricated vertical drains, while the other half is constructed on the natural deposit without any ground improvement. The construction and consolidation of the embankment is analyzed with the finite-element method using three different constitutive models to represent the soft clay. Two recently proposed constitutive models, namely S-CLAY1 which accounts for initial and plastic strain induced anisotropy, and its extension, called S-CLAY1S which accounts, additionally, for interparticle bonding and degradation of bonds, were used in the analysis. For comparison, the problem is also analyzed with the isotropic modified cam clay model. The results of the numerical analyses are compared with the field measurements. The simulations reveal the influence that anisotropy and destructuration have on the behavior of an embankment on soft clay

Numerična analiza okroglega temelja na naravni glini, stabilizirani z zrnatim polnilom

In this study, numerical predictions of the scale effect for circular footings supported by partially replaced, compacted, layers on natural clay deposits are presented. The scale- effect phenomenon was analyzed according to the footing sizes. Numerical analyses were carried out using an axisymmetric, two-dimensional, finite-element program. Before conducting the analysis, the validity of the constitutive model was validated using field tests performed by authors with seven different footing diameters up to 0.90 m and with three different partial replacement thicknesses. It is shown that the behavior of the circular footings on natural clay soil and the partial replacement system can be reasonably well represented by the Mohr Coulomb model. The Mohr-Coulomb model parameters were derived from the results of conventional laboratory and field tests. After achieving a good consistency between the results of the test and the numerical analysis, the numerical analyses were continued by increasing the footing diameter up to 25 m, considering the partial replacement thickness up to two times the footing diameter. The results of this parametric study showed that the stabilization had a considerable effect on the bearing capacity of the circular footings and for a given value of H/D the magnitude of the ultimate bearing capacity increases in a nonlinear manner with the footing diameter. The Bearing Capacity Ratio (BCR) was defined to evaluate the improved performance of the reinforced system. It was found, based on numerical and field-test results that the BCR of the partially replaced, natural clay deposits increased with an increase in the footing diameter and there was no significant scale effect of the circular footing resting on natural clay deposits.V tej študiji so predstavljene numerične napovedi obsega učinka na okrogle temelje, podprtih z delno zamenjanimi in zgoščenimi plastmi na usedlinah naravne gline. Pojav obsega učinka je analiziran glede na velikost temelja. Numerične analize so bile izvedene z uporabo osno simetričnega, dvodimenzionalnega programa s končnimi elementi. Pred izvedbo analize je bila potrjena veljavnost osnovnega modela z uporabo terenskih testov s sedmimi različnimi premeri temeljev do 0,90 m in s tremi različnimi delno zamenjanimi debelinami. Izkazalo se je, da lahko obnašanje okroglih temeljev na tleh iz naravne gline in delno zamenjanim sistemom dovolj primerno prikažemo z Mohr-Coulombovim modelom. Parametri Mohr Coulombovega modela so izpeljani iz rezultatov z običajnimi laboratorijskimi in s terenskimi testi. Z doseženo dobro složnostjo med rezultati testa in numeričnimi analizami, so bile nadaljevane numerične analize s povečevanjem premera temeljev do 25m in upoštevanjem z delno zamenjavo debeline do dvakratnega premera temeljev. Rezultati te parametrične študije so pokazale, da ima stabilizacija precejšen učinek na nosilno kapaciteto okroglih temeljev in da se pri dani vrednosti H/D magnituda mejne nosilne kapacitete poveča s premerom temelja na nelinearni način. Določen je količnik nosilne kapacitete (BCR) za določitev izboljšanega učinka ojačenega sistema. Na podlagi rezultatov numeričnih in terenskih testov je ugotovljeno, da se BCR delno zamenjanih odloženih naravnih glin poveča s povečanjem premera temeljev in da ni pomembnega obsega učinka okroglega temelja ležečega na usedlini z naravno glino