Effects Of Reinforcement Stiffness Research Articles

Determination of shear stress-shear strain behavior of polymeric geostrip reinforced MSE wall

In this paper, the shear strain-dependent dynamic response properties of a retaining wall model made of mechanically stabilized earth (MSE) with polymeric geostrip material are investigated in a 1-g shaking table test. The values of lateral displacements and accelerations measured at different points along the MSE wall surface were used to evaluate the equivalent hysteris loops. The effect of reinforcement stiffness and backfill slope angle on the equivalent shear stiffness modulus (Ge) and damping ratio (D) were investigated. The experimental results show that the variation of shear stiffness modulus and damping ratio as a function of shear strain (γ) is affected by vertical pressure (σv), but the effect of the stiffness of the polymeric geostrip on the damping ratio is negligible. The variations of the Ge, Ge/σv, Ge/Gmax, and D as a function of γ are expressed in exponential equations with high least squares values in this study.

Seismic coefficients for pseudo-static analysis of wrap-faced GRS walls with nonlinear soil fills

Pseudo-static seismic design procedure for Geosynthetic Reinforced Soil (GRS) walls includes the selection of a suitable horizontal seismic coefficient for external and internal stability analysis. The present guidelines for the seismic design of GRS walls have been mostly adopted from studies performed on conventional retaining walls. Hence, it is required to study the seismic response of GRS walls. In the present study, a finite element (FE) model of a wrap-faced GRS wall was developed in OpenSees. It was analysed for multiple earthquake time histories to study the variability in earthquake characteristics. The shaking level was also varied from 0.12g to 0.48g to consider the nonlinear response of backfill soil. The acceleration response and dynamic earth pressure increment in the wall were observed to increase with the shaking level but at a lower rate for higher shaking levels. The reinforcement force increments under seismic loading also showed a similar response. The internal failure plane in the GRS wall was slightly inclined, although not completely aligned with Rankine's active failure plane. Seismic coefficients are recommended for wrap-faced GRS walls as a function of PHA. The coefficients were calibrated using the maximum earth pressure and reinforcement forces obtained from FE analysis. The effect of reinforcement stiffness is also incorporated in the recommendation for internal stability analysis. A seismic coefficient greater than PHA is suggested at low shaking levels. It is in direct contrast to many previous studies as the coefficients are calibrated considering the maximum force demand in the GRS wall. Force-based designs need to consider the applicability of maximum earth pressure and reinforcement forces in the GRS wall, which can cause either external or internal instability in the wall. While at higher PHAs, the seismic coefficient should be almost constant to provide reliable estimates of earth pressure and reinforcement forces.

Effect of reinforcement stiffness on response of back-to-back MSE wall upon infiltration

Back-to-back mechanically stabilized earth (MSE) walls are being widely utilized as bridge abutments and highway ramps, considering their cost effectiveness and ease of construction. Though high quality well-graded granular fill is the most appropriate backfill material, owing to its scarcity, locally available low-quality soils are often used as backfill. Nevertheless, numerous failure cases of such walls with low-quality soil are reported, especially subsequent to rainwater infiltration. The stiffness of reinforcement is a key parameter affecting the overall behaviour of MSE walls. The present study investigates the influence of reinforcement stiffness on the response of select fill, marginal fill, and hybrid-fill back-to-back MSE walls using a finite element (FE) based approach. Results show that stiffness of reinforcement has a significant effect on the overall performance of marginal fill wall upon rainfall infiltration. Specifically, with the increase of reinforcement stiffness, the infiltration-induced facing displacement decreases and reinforcement tension increases. However, the performance of select fill and hybrid-fill walls following rainfall infiltration was found to be satisfactory even with low stiffness reinforcements, and further improvement with increase of reinforcement stiffness was insignificant. The reduction of safety factors during infiltration was shown to be independent of reinforcement stiffness for all wall types.

Performance Analysis of Geosynthetic Reinforced Earth Wall by Analytical Experimental and Finite Element Methods

Ease of construction and performance under earthquake loads causes interest in construction of reinforced earth walls worldwide. In this study, reinforced earth walls with sand and clay backfill at a height of 450 mm are constructed and tested under bridge abutment loading conditions. A finite element analysis is performed and results are compared with experiment results. In the parametric study made by conducting finite element method, effect of reinforcement stiffness and reinforcement density on the horizontal displacements along the retaining wall face, the maximum tensile force, total maximum tensile force, and slope stability are investigated.

Experimental and numerical study on the bearing capacity of encased stone columns

Stone columns have attracted considerable attention as a ground improvement techniques recently. Performance of stone columns, however, depends on confining pressure offered by the surrounding soils. In the case of very soft soils, the lateral confining pressure may be insufficient and this may lead to column bulging failure. Encapsulating the individual stone column enhances the lateral resistance against bulging by additional confining pressure. In this study, the influences of the length of encasement and type of aggregate materials on the bearing capacity of a single stone column in both dry sand and clay bed were investigated. The results indicated a clear improvement by encasing the half-length of the column. The numerical study also showed the effect of reinforcement stiffness reduces with increase in the cohesion of the clay. Parametric study showed that the effect of encasement stiffness is insignificant for clay bed with high values of cohesion.

Influence of Soil Reinforcement on Horizontal Displacement of MSE Wall

Mechanically stabilized earth (MSE) walls offer simple construction techniques, pleasing aesthetics, and cost-effective solutions as an alternative to conventional gravity walls. However, design and construction should be carefully evaluated to achieve satisfactory performance of the wall. A case study is presented on a MSE wall located on State Highway 342 in Lancaster, Texas. The horizontal movement of the MSE wall was between 300 and 450 mm within 5 years of construction. A forensic investigation was performed to determine the causes of the excessive movement. It was identified that inadequate reinforcement length was one of the contributing factors that caused horizontal displacement of the MSE wall. The objective of this study was to determine the effects of soil reinforcement on excessive movement of the MSE wall. As a part of the forensic investigation, two inclinometers were installed at the site to monitor any additional movement of the MSE wall. The inclinometer results suggested that the wall continued to move at an average rate of 4.5 mm/month during the investigation period. A finite-element (FE) program was used to simulate horizontal displacement and stability of the MSE wall. It was observed that the numerical modeling results were in good agreement with inclinometer results. A parametric study was conducted to identify the effects of soil reinforcement on horizontal movement at varied wall heights and backfill conditions. Numerical analyses results indicated that the effect of reinforcement stiffness was not significant at a wall height of 4 m compared with 8 and 12 m. The wall movement varied from 74 to 29 mm for an increase in reinforcement stiffness from 250 to 42,000 kN/m at 1.0H reinforcement length. The variations in displacement with reinforcement lengths suggested that substantial reduction in displacement occurred for an increase in length-height (L/H) ratio from 0.5 to 0.7. FE modeling results were used for sensitivity analysis employing a statistical analysis program. Based on the analyses, reinforcement length and stiffness were identified as influential factors for the horizontal displacement of MSE walls at a specific height.

ANALYSIS OF STEEL BRIDGES WITH RECTANGULAR WEB OPENINGS: FINITE ELEMENT INVESTIGATION

This study is concerned with parametric study of the effect of rectangular web openings on the response of steel bridges with cross frames and bottom lateral bracings. The study includes studying the deflections of steel bridges as an important factor of static response and the frequencies of steel bridges as an important factor of dynamic response. The influence of rectangular web openings of various sizes and numbers on the response of steel bridges is investigated with and without horizontal stiffeners (reinforcements). Buckling and instability failures of the steel beams are not considered in the present analysis. Based on the analysis results of steel bridges with cross frames and bottom lateral bracings, it is shown that existence of only one rectangular (square) web opening at mid span has almost negligible effect on the maximum deflections at mid span and small effect on the frequencies of bridge models. However, existence of more than one square or rectangular web opening leads to great increase in the deflection at mid span and considerable decrease in frequencies. Also, an increase in the ratio of web opening height to web height leads to great increase in the maximum deflection of bridge model. On the other hand, horizontal stiffeners (reinforcements) above and below web openings improves both static and dynamic response of steel bridge models especially, for multiple web openings. However, the effect of reinforcement stiffness is more pronounced for static response.

Combined effect of PVDs and reinforcement on embankments over rate-sensitive soils

A numerical study of the behavior of geosynthetic-reinforced embankments constructed on soft rate-sensitive soil with and without prefabricated vertical drains (PVDs) is described. The time-dependent stress–strain-strength characteristic of rate-sensitive soil is taken into account using an elasto-viscoplastic constitutive model. The effects of reinforcement stiffness, construction rate, soil viscosity as well as PVD spacing are examined both during and following construction. A sensitivity analysis shows the effect of construction rate and PVD spacing on the short-term and long-term stability of reinforced embankments and the mobilized reinforcement strain. For rate-sensitive soils, the critical period with respect to the stability of the embankment occurs after the end of the construction due to a delayed, creep-induced, build-up of excess pore pressure in the viscous foundation soil. PVDs substantially reduce the effect of creep-induced excess pore pressure, and hence not only allow a faster rate of consolidation but also improve the long-term stability of the reinforced embankment. Furthermore, PVDs work together with geosynthetic reinforcement to minimize the differential settlement and lateral deformation of the foundation. The combined use of the geosynthetic reinforcement and PVDs enhances embankment performance substantially more than the use of either method of soil improvement alone.

Reinforced embankments over soft foundations under undrained and partially drained conditions

The behaviour of geosynthetic reinforced embankments constructed on soft cohesive foundations under undrained and partially drained conditions is examined using an elliptical cap soil model. Consolidation is modelled using Biot theory. The effects of reinforcement stiffness, partial consolidation of the foundation soil during embankment construction and foundation soils with different initial undrained strength profiles are examined. Particular attention is focused on the strains in the geosynthetic reinforcement at working conditions and at embankment failure. The effect of reinforcement on the deformation of the foundation soil is evaluated. It is shown that reinforcement can significantly reduce the maximum lateral deformations, vertical deformation and foundation soil heave during embankment construction. For the conditions examined, partial drainage during construction provides an 11–38% increase in the factor of safety against failure of reinforced embankments relative to that expected under perfectly undrained conditions.