Influence of toe restraint on reinforced soil segmental walls (original) (raw)
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The performance of a metallic reinforced soil segmental retaining wall is examined in a systematic manner using two numerical modelling approaches. Finite element modelling was carried out using the commercial program PLAXIS and finite difference modelling using the commercial program FLAC. Numerical model results using both approaches were compared against measurements recorded for a well-instrumented full-scale 3.6-m high wall constructed with a sand backfill, modular-block facing, and steel reinforcement (welded wire mesh). This paper presents measured and predicted toe loads, facing displacements, and reinforcement connection loads at end of construction and during subsequent staged surcharge loading approaching failure. Both numerical models have been verified against recorded measurements. The sensitivity of the assigned backfill soil friction angle on the magnitude and distribution of reinforcement connection loads is also examined. The paper concludes with a summary of lessons learned to achieve satisfactory agreement between predicted performance and wall measurements using both modelling approaches.
Canadian geotechnical journal, 2005
The paper describes a numerical model that was developed to simulate the response of three instrumented, full-scale, geosynthetic-reinforced soil walls under working stress conditions. The walls were constructed with a fascia column of solid modular concrete units and clean, uniform sand backfill on a rigid foundation. The soil reinforcement comprised different arrangements of a weak biaxial polypropylene geogrid reinforcement material. The properties of backfill material, the method of construction, the wall geometry, and the boundary conditions were otherwise nominally the same for each structure. The performance of the test walls up to the end of construction was simulated with the finite-difference-based Fast Lagrangian Analysis of Continua (FLAC) program. The paper describes FLAC program implementation, material properties, constitutive models for component materials, and predicted results for the model walls. The results predicted with the use of nonlinear elastic-plastic models for the backfill soil and reinforcement layers are shown to be in good agreement with measured toe boundary forces, vertical foundation pressures, facing displacements, connection loads, and reinforcement strains. Numerical results using a linear elastic-plastic model for the soil also gave good agreement with measured wall displacements and boundary toe forces but gave a poorer prediction of the distribution of strain in the reinforcement layers.
Numerical Model for Reinforced Soil Segmental Walls under Surcharge Loading
Journal of Geotechnical and Geoenvironmental Engineering, 2006
The construction and surcharge loading response of four full-scale reinforced-soil segmental retaining walls is simulated using the program FLAC. The numerical model implementation is described and constitutive models for the component materials ͑i.e., modular block facing units, backfill, and four different reinforcement materials͒ are presented. The influence of backfill compaction and reinforcement type on end-of-construction and surcharge loading response is investigated. Predicted response features of each test wall are compared against measured boundary loads, wall displacements, and reinforcement strain values. Physical test measurements are unique in the literature because they include a careful estimate of the reliability of measured data. Predictions capture important qualitative features of each of the four walls and in many instances the quantitative predictions are within measurement accuracy. Where predictions are poor, explanations are provided. The comprehensive and high quality physical data reported in this paper and the lessons learned by the writers are of value to researchers engaged in the development of numerical models to extend the limited available database of physical data for reinforced soil wall response.
NUMERICAL MODELING OF REINFORCED SOIL SEGMENTAL WALL UNDER SURCHARGE LOADING
iaeme
This paper outlines the finite element procedure for simulating the performance of a reinforced soil segmental (modular blocks) wall. Analyses were performed using a software code which is developed in FORTRAN and validated for reported case histories in the literature. The material properties of the wall like backfill, foundation, modular concrete fascia blocks and reinforcement were expressed using linear elastic models. A series of parametric studies was conducted to identify effects of reinforcement, stiffness and Poison’s ratio of backfill and foundation strata on the performance of the wall. Increased stiffness of backfill and foundation improves the performance of the wall by restraining the front face deformation. The design charts for deflections at top and bottom and also, height of rotation are developed in the current work by varying the stiffness of backfill and foundation. These charts are useful to the designer to choose appropriate backfill and also, to ascertain the suitability of available foundation for the construction of wall, considering codal provisions regarding deformation limits at the front face of the wall.
Numerical Study of Reinforced Soil Segmental Walls Using Three Different Constitutive Soil Models
Journal of Geotechnical and Geoenvironmental Engineering, 2009
A numerical finite-difference method ͑FLAC͒ model was used to investigate the influence of constitutive soil model on predicted response of two full-scale reinforced soil walls during construction and surcharge loading. One wall was reinforced with a relatively extensible polymeric geogrid and the other with a relatively stiff welded wire mesh. The backfill sand was modeled using three different constitutive soil models varying as follows with respect to increasing complexity: linear elastic-plastic Mohr-Coulomb, modified Duncan-Chang hyperbolic model, and Lade's single hardening model. Calculated results were compared against toe footing loads, foundation pressures, facing displacements, connection loads, and reinforcement strains. In general, predictions were within measurement accuracy for the end-of-construction and surcharge load levels corresponding to working stress conditions. However, the modified Duncan-Chang model which explicitly considers plane strain boundary conditions is a good compromise between prediction accuracy and availability of parameters from conventional triaxial compression testing. The results of this investigation give confidence that numerical FLAC models using this simple soil constitutive model are adequate to predict the performance of reinforced soil walls under typical operational conditions provided that the soil reinforcement, interfaces, boundaries, construction sequence, and soil compaction are modeled correctly. Further improvement of predictions using more sophisticated soil models is not guaranteed.
Can Geotech J, 2007
In this paper the K-stiffness method is extended to the case of c-soils using data obtained from a total of nine new case studies -six from Japan and three from the USA. A common feature in this new data set is that the walls were all constructed with a vertical face using backfill soils with a range of fines content. The walls varied widely with respect to facing type. This new data set together with previously published data for vertical walls is now used to isolate the effect of soil cohesion on reinforcement loads within the framework of the original K-stiffness method. The new data set is used to calibrate a modified K-stiffness method equation that includes a cohesion influence factor. The modified K-stiffness method is demonstrated to quantitatively improve the estimate of the magnitude and distribution of reinforcement loads for internal stability design of vertical-faced geosynthetic reinforced soil walls with c-soil backfills when compared to the current American Association of State Highway and Transportation Officials simplified method.
Seismic Analysis of Segmental Retaining Walls. I: Model Verification
Journal of Geotechnical and Geoenvironmental Engineering, 2001
Block-faced geosynthetic reinforced soil retaining walls, referred to as ''segmental'' retaining walls, have been extensively used in recent years as permanent civil engineering structures. The disjointed concrete facing blocks are held together through interface friction and concrete keys or mechanical connectors. Because of the disjointed nature of the facing blocks, the design of the segmental wall must consider the available shear resistance between these blocks. Connection capacity must also be considered. Of concern also is the permanent deformation of the segmental wall face following an earthquake. This paper describes a finite-element analysis of a model segmental wall subjected to earthquakelike loading generated by a shake table. The finiteelement analysis used the computer program DYNA3D. Results from DYNA3D, using a simple model-Ramberg-Osgood model-to simulate the nonlinear hysteretic behavior of soil, are consistent with observed results from laboratory shake table tests on segmental walls.
Influence of foundation compressibility on reinforced soil retaining wall behaviour
The influence of compressible foundations on the mechanical behaviour of geosynthetic reinforced soil walls is very complex. This paper presents the results of two 1/6-scale reinforced soil wall tests that were carried out to isolate the influence of vertical foundation compressibility on wall behaviour. These tests are a continuation of a research program that initially investigated the influence of horizontal and vertical toe compliance on wall performance. The results of these physical model tests have been published in the proceedings of the two previous CGS conferences (Ezzein and Bathurst 2006, 2007). A control wall (Wall 16) was constructed using a high quality sand backfill, a rigid foundation and a rigid horizontal support at the toe of the facing. A second wall (Wall 17) was nominally the same but was constructed over compressible layers of rubber and foam. The paper presents measured results for wall deformations, reinforcement strains and soil settlement at end of construction and during staged uniform surcharge loading. These results have important implications to current design of reinforced soil walls that do not consider the influence of foundation compliance on the magnitude of reinforcement loads and their distribution. RÉSUMÉ L'influence des fondations compressibles sur le comportement mécanique des massifs de sols renforcés de géosynthétiques, est très complexe. Cet article présente les résultats de deux essais à une échelle de 1/6 sur massifs renforcés, réalisés pour isoler l'influence de la compression verticale de la fondation sur le comportement du massif. Ces essais sont une continuation d'un programme de recherche qui initiallement étudiait l'influence de la souplesse verticale et horizontale en pied de mur sur le comportement du massif. Les résultats de ces essais sur modèles physiques ont été publiés dans les compte-rendus de deux congrès antérieurs de la SCG (Ezzein et Bathurst 2006, 2007). Un mur contrôle (Mur 16) a été construit avec un remblais de sable de haute qualité, une fondation rigide et un soutient horizontal rigide au pie du mur. Un second mur (Mur 17) était essentiellement identique sauf qu'il a été construit sur des couches compressibles de caoutchouc-mousse. L'article présente les résultats mesurés pour les déformations du mur, les déformations des renforcements et le tassement du sol après construction et pendant l'application par palier de surcharges uniformes. Ces résultats ont des implications pour le design actuel des massifs de sols renforcés, qui ignore l'influence de la souplesse de la fondation sur l'intensité et la distribution des efforts dans les renforcements.
Influence of Horizontal Toe Restraint on Reinforced Soil Retaining Wall Behaviour
2006
The research program described in this paper investigates the influence of magnitude of horizontal toe compliance on the performance of 1/6-scale reinforced soil retaining walls at end of construction and during subsequent staged surcharge loading. The walls were 1.2 m high and were constructed with a very stiff horizontal toe support, a free support and with two different spring arrangements resulting in horizontal reaction stiffness values falling between these two limiting conditions. The data showed that the wall performance was sensitive to the range of toe boundary stiffness conditions investigated. As horizontal toe stiffness increased the following observations were made: a) wall deformations decreased but the displacement mode changed from uniform translation to rotation about the toe; b) the toe carried progressively more of the total horizontal earth force acting at the back of the facing column, and; c) strains in the reinforcement layers were attenuated, particularly at...
Reinforced Soil Retaining Wall Testing, Modeling and Design
2007
This paper presents an overview of a program of physical and numerical modeling of reinforced soil walls conducted by the writer and co-workers, and the development of a new design approach for these systems. The physical testing described in the paper was carried out in a full-scale test facility at RMC and involved a series of wall models designed to isolate the contribution of facing type, reinforcement type and reinforcement arrangement on wall behaviour under serviceability conditions and surcharge loading approaching wall collapse. The numerical modeling was carried out using the program FLAC and the results verified against selected physical tests carried out at RMC. The results of physical tests carried out at RMC and data collected from instrumented structures reported in the literature has led to the development of an empirical-based design methodology (K-stiffness Method). This new approach to reinforced soil wall design has been quantitatively and qualitatively demonstrated to be much more accurate than the current limit equilibrium-based tie-back wedge design method currently used in North America.