Soil Constitutive Laws Research Articles

Effects of axial loading on dynamic response of laterally loaded single piles in liquefiable layered soil of Kolkata city considering nonlinearity of soil

In the present study, an advanced nonlinear finite-element based 3D numerical study has been carried out to investigate the effects of axial loading on dynamic response of soil-pile system in liquefiable layered soil deposits of Kolkata city. An advanced soil constitutive law based on multi-yield surface plasticity model implemented in fully-coupled u-p formulation is adopted for soil-fluid interaction and pore water pressure development reasonably. The present model is validated with the past experimental results. Then, a detailed systematic parametric study is performed for numerical simulation of pile failures in layered soil deposit under axial loading by taking into account various soil conditions, pile and ground motion parameters. It is seen that the depth of liquefaction (DL) is decreased from 11.5 to 1.5 m adjacent to the pile when the axial load on pile increases from 0 to 1327 kN. Parametric studies also reveal that the bending moment response of pile under axial loading can be higher in non-liquefiable condition, with reference to the liquefiable condition. The peak lateral displacement decreases by 83.2% in non-liquefiable condition and 60.71% in liquefiable condition due to decrease of axial load from 1327 to 0 kN. Also, peak bending moment developed in the pile decreases by 97.2% in non-liquefiable condition and 82.7% in liquefiable condition when the axial load reduces from 1327 to 0 kN. So, the designer should be considered both extreme scenarios for safe and economical design. Also, it is noticed that the buckling capacity of pile is improved significantly by using larger diameter pile and the bending capacity is increased by selecting higher grade of concrete. It is concluded that the bending and buckling failure mode may be avoided by selecting a suitable combination of material strength and pile geometry.

Numerical Simulation of Tieback Excavations with Soldier Piles Using a New Unified Soil Model Considering at Rest Condition

The present research aims to understand the behavior of tieback retaining walls during the excavation. Employing the finite difference method (FDM), a 3D model was developed in this study to obtain the earth pressure diagram and horizontal movement of tieback walls during and after construction. A rigorous non-linear analysis of tieback retaining walls requires an efficient solving algorithm of the governing equations as well as a nonlinear soil constitutive law that could capture different stress paths including at rest condition during the sequences of construction. A newly proposed unified two-surface elasto–plastic model based on the critical-state soil mechanics is employed to simulate different stress paths of the matrix soil during the excavation. The model describes strain-softening and stress-dilatancy using non-associated flow rule and implements dilatancy parameter. This model is capable of adopting the proper function for the yield surface, simulating drained and undrained responses of soil under triaxial conditions as well as soil response under drained laterally confined (K0) conditions. Using the presented unified soil constitutive model, the effect of soil plasticity was incorporated into the finite difference method. In the numerical model of the tie-back retaining walls, cable structural elements are used to simulate the tendon anchors, while the shotcrete facing and soldier piles are modeled using shell and beam structural elements, respectively. Effects of different crucial factors were monitored during a comprehensive parametric study. The results gave information on the influence of the following factors on tieback walls behavior: the magnitude of anchors pre-tensioning load, the length of anchors bonded zone, the vertical position of the first anchor, and the stiffness of the soldier piles.

Numerical analysis of the installation effects on the behaviour of soft clay improved by stone columns

ABSTRACTThis paper addresses the installation effects of stone columns in soft soils. Focus is made on the lateral expansion of stone material using the vibro displacement and substitution techniques by means of numerical simulations. The behaviour of reinforced soil after stone column installation is investigated to show how the properties of soft soils can be improved prior to final loading. The effect of such an improvement on the prediction of reinforced soil settlement is evaluated. The axisymmetric unit cell model (UCM) served for the comparison between numerical predictions made by the Mohr-Coulomb and hardening soil constitutive laws adopted for the soft soil. An equivalent group of end bearing columns model was investigated in the axisymmetric condition to predict the settlement of reinforced soil by adopting the Mohr-Coulomb constitutive model for soft clay. The reduction of settlements predicted by the unit cell and group of columns models, due the improvement of the Young’s modulus of soft clay, were compared. It is concluded that a significant reduction of settlement is expected when the group of columns model is considered.

Selection of load–transfer functions for passive lateral loading of pile groups

Abstract A finite element study has been carried out to determine the pile–soil–pile interaction behaviour for closely spaced pile rows and groups under passive lateral loading from soil movement. A horizontal section close to the piles was studied to determine the effects of pile spacing and soil constitutive law on the load–transfer relationships of the piles. The study has revealed links between the soil stress–strain law, the soil deformation mechanism and the pile load–transfer curves. Interaction behaviour was seen to depend on the prevailing deformation mechanism which in turn was governed by the soil constitutive law. Elastic-plastic and power law soil models were applied. Interaction factors suitable for design use to account for increasing lateral pressure on piles during passive lateral loading have been produced for a range of pile spacings and power law soil exponents. Interaction between piles increased both with reduction of pile spacing and with increase of soil exponent—the less soil stiffness degradation with shear strain, the greater the interaction between piles at a given spacing. This suggests that the passive interaction factors calculated using elastic methods are likely to overestimate the effects of pile–soil–pile interaction.

Elastoplastic soil constitutive laws generalized to partially saturated states

This paper deals with the plastic behaviour of partially saturated soils by modifying an existing model for fully saturated soils. The saturated soil model, formulated in the framework of generalized plasticity, considers volumetric as well as deviatoric strain hardening and takes account of the memory of past stress history and possible limit states. The generalization of the existing model to simulate the experimentally observed behaviour of partially saturated soils has been obtained by introducing Bishop's stress and suction as independent stress parameters and by modifying the hardening parameter and the yield condition to take into account the role of suction. Le comportement plastique des sols pardellement saturés a été étudié en modifant un modèle initialement développé pour les sole saturés. Le modèle des sols saturés, con¸u dans un cadre de plasdcité généralisée, étudle l'écrouissage des déformations volumétriques et déviatoriques et dent compte de la mémoire du matériau concernant l'historique des contraintes et des éats limites auquels il aurait pu avoir étésoumis. La généralisation de cc modèle aux sole pardellement saturés testés se fait par introduction de la contrainte de Bishop et de la succion, en tant que paramètres de contrainte indépendants, et par modification des parametres d'écrouissage et des conditions aux limites, permettant ainsi de prendre en compte le rôle de la succion.