Numerical Modeling of Reinforced Soil Segmental Wall Under Surcharge Loading (original) (raw)
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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.
Influence of Parameters the Wall on Reinforced Soil Segmental Walls
The behaviour of retaining walls in geosynthetic reinforced soil is complex and requires studies and research to understand the mechanisms of rupture, the behaviour of the reinforcements in the soil and the behaviour of the main elements of the system: reinforcement-wall-soil. Several researches have been done on the use of geosynthetics as backfill massive reinforcement material (experimental studies, numerical analysis, reduced models ...). This parametric study was conducted to investigate the influence of numerical parameters of the wall which confront us in the projects, on the behaviour of walls on reinforced soil segmental walls. A 3.6 m high wall is composed of modular blocks of earth sand reinforced with four geogrids layers was modelled. The properties of materials, the wall geometry, and the boundary conditions will be explained later. The finite difference computer program FLAC3D was used in this study. The results of this numerical study allowed to deduce the importance of each parameter of the wall selected for the behaviour of retaining walls in soil reinforced by geogrid. The inclination of wall "W" is of great importance for the calculation of retaining walls in modular blocks and can provide an important contribution to the horizontal balance of this type walls. The value of lateral displacements of the facing tends to continuously decrease with the increase of "W". More the wall is inclined plus the horizontal stresses behind the wall and values of the tensile stress in the layers of geogrid "T" decrease in an expressive manner. The dimensions of modular blocks (types) and the mechanical characteristics of modular blocks (category) have a remarkable effect on the calculation of retaining walls in modular blocks reinforced with layers of geogrid.
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.
Parametric analysis of reinforced soil walls with different backfill material properties
NAGS'2006 Conference, Las Vegas, …, 2006
The influence of backfill type and material properties on the performance of reinforced soil segmental retaining walls under working stress conditions (end of construction) is investigated using a numerical model. The numerical model has been validated against the measured data from several 3.6 m-high test walls in a previous investigation and is now used in this study to investigate the response of idealized 6 m-high wall models at the end of construction. Four different backfill types representing a select granular fill, a backfill with low friction angle, and backfill types with significant fines content (i.e. a cohesive strength component) were used in the numerical simulations. The numerical results demonstrate that for the case of a granular backfill, a small amount of soil cohesion can significantly reduce wall lateral displacements provided that the relative displacement between reinforcement and backfill (i.e. backfill-reinforcement interface compliance) is negligibly small.
Prediction of reinforcement loads in reinforced soil walls
Proper estimation of soil reinforcement loads and strains is key to accurate design of the internal stability of geosynthetic and steel reinforced soil structures. Current design methodologies use limit equilibrium concepts to estimate reinforcement loads for internal stability design, with empirical modifications to match the prediction to observed reinforcement loads at working stresses. This approach has worked reasonably well for steel reinforced walls but appears to seriously overestimate loads for geosynthetic walls. A large database of full-scale geosynthetic walls (16 fully instrumented, full-scale geosynthetic walls and 14 walls with limited measurements) and 24 fully instrumented, full-scale steel reinforced wall sections was utilized to develop a new design methodology based on working stress principles, termed the K-Stiffness Method. This new methodology considers the stiffness of the various wall components and their influence on reinforcement loads. Results of simple statistical analyses to evaluate the ratio of predicted to measured peak reinforcement loads in geosynthetic walls were telling: the AASHTO Simplified Method results in an average ratio of measured to predicted loads of 0.45 with a coefficient of variation (COV) of 91 percent, whereas the proposed method results in an average of 0.99 and a COV of 36 percent. The proposed method remains accurate up until the point at which the soil begins to fail (approximately 3 to 5 percent strain). For steel reinforced MSE walls the improvement was more modest: AASHTO's Simplified Method results in an average ratio of predicted to measured loads of 1.12 with a (COV) of 45 percent, whereas the new K-Stiffness Method results in an average of 0.95 and a COV of 32 percent. The objective of the method is to design the wall reinforcement so that the soil within the wall backfill will not reach a state of failure consistent with the notion of working stress conditions. This soil failure limit state is not considered in the design methods currently available, yet, given the research results presented herein, is likely to be a controlling limit state for geosynthetic structures. The fruit of this research is a more accurate method for estimating reinforcement loads, thereby reducing reinforcement needs and improving the economy of reinforced soil walls. The scope of this research was limited to reinforced soil walls that utilize granular (non-cohesive, relatively low silt content) backfill.
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.
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.
Factors affecting the design and performance of slender reinforced soil walls
EUROGEO5 – Proc. 5th European Geosynthetics Congress,, 2012
The paper summarizes the results of numerical analyses performed in order to model the performance of slender reinforced walls, adopted in practical applications as a solution when the appearance of a concrete wall is not accepted and should therefore be masked. The geometry and slenderness of this kind of rein-forced structure have been considered as pre-eminent factors. Limit equilibrium analyses as well as finite element analyses have been carried out in order to explore stability and deformation issues that have to be considered for the design of the masking reinforced wall
Behaviour of Two-Tiered Geosynthetic-Reinforced Soil Walls
INAE Letters, 2019
The literature studies and current design methodologies of reinforced soil wall show increases in tensile stresses in reinforcement with increase in height of wall. This results in decrease of spacing between reinforcement and ultimately increases in cost of construction. Alternatively, the reinforced soil wall can be constructed in tiered fashion to improve aesthetic and reduce cost of construction. This paper focuses on the performance of two-tiered-reinforced soil-retaining walls with different offset lengths. A numerical model of geosynthetic-reinforced soil-retaining wall with a concrete-block facing reported in literature is simulated using commercial finite element software ANSYS. The backfill soil is modelled using the Drucker-Prager plasticity model. The concrete facing is simulated as elastic material and reinforcement with non-linear material properties. The results obtained from numerical model are validated with those from physical model studies reported in literature. Using validated model parameters, two-tiered-reinforced soil walls with different offset lengths are simulated. Four models of 0 offset, 1.2-m offset, 2.0-m offset and 3.0-m offset are developed to study the effects of tiered wall. The offset lengths are determined as intermediate offset distance and large setback distance as per FHWA (2010). The walls are studied for horizontal displacement of facing, strain developed in backfill soil and in reinforcement layers. The maximum horizontal displacements of reinforced soil wall decrease with increase in offset length of tiered wall. By considering the strain variation in soil, two deformation zones-shear deformation zone near the facing and compaction zone below the upper tier facing-are identified. The strains in compaction zone of lower tier increase with increase in offset length. The reinforcement strains in top reinforcement layer of lower tier decrease with increase in offset length. Keywords Multi-tiered-reinforced soil wall • Backfill strain • Numerical model • ANSYS