Reinforced Soil Model Research Articles

Physical model study on failure mechanism of strip footing on reinforced granular deposit

This study proposes guidelines for predicting the failure mechanism of a shallow strip footing resting on geosynthetic-reinforced granular deposit at different stages of footing settlement. Physical model tests are performed on footings resting on unreinforced and geosynthetic-reinforced soil. The reinforcement parameters varied include the depth between consecutive reinforcements, number of layers and the depth of the reinforced zone. Additionally, contours of deformation and maximum shear strain of soil and mobilised tensile strain in reinforcement with increasing footing settlement are studied. The improvement of bearing capacity ratio and the peak tensile strain in the reinforcement was monitored for three normalised settlement ratios of 5% (low), 10% (medium) and 25% (high). The reinforced soil models were found to depict primarily a punching shear failure limited solely within the reinforced zone at s/B of 5%. This was supplemented with a well-formed triangular wedge in the underlying unreinforced soil at s/B of 10%. In addition to above mechanisms, the radial shear zones were prominent at s/B of 25%. Failure mechanisms have been proposed eventually for each s/B value investigated, including guidelines on the upper and lower bounds of the load dispersion angle in the reinforced soil and wedge angle of the underlying unreinforced soil.

Study of the reliability and efficiency of using reinforced soil models within the framework of the finite element method

Within the framework of the finite element method, the influence of the dimensions of the calculation model on the values of subsidence when using different soil models was studied.
 Numerical calculations of the soil environment based on FEM differ from analytical ones in that a necessary condition for their application is the choice of a soil model, which is characterized by a different theoretical basis, which, with the help of equations of different complexity and input parameters of a different number, describe the behaviour of the simulated soil massif.
 Given that the numerical solution of problems based on FEM involves the modeling of objects as a finite limited area, the question of choosing the lower limit of the calculation model in the study of subsidence is acute.
 The stiffness of soils in their natural state increases with the depth of their occurrence. In simple soil models, such as the Mohr-Coulomb model, soil stiffness is a constant value. This circumstance leads to the fact that during numerical calculations, the deformations of subsidence increase linearly when the dimensions of the calculation model increase vertically.
 Advanced models, such as Hardening Soil, can take into account the soil strengthening when the stress level increases, however they require a wide range of soil characteristics, which are determined by experimental methods, using special equipment, and the determination of a number of parameters is not regulated by regulatory documents.
 It is shown that the use of the reinforced soil model proposed by the authors, which, on the one hand, complies with state building regulations, and on the other hand, does not require the involvement of additional physical and mechanical characteristics of soils, allows obtaining more accurate values of the parameters of the stress-strain state of the foundation.

Determination of the Effect of Sidewall Friction in Reinforced Soil Retaining Wall Experiments

Abstract A simple approach to estimate sidewall friction in reinforced soil model experiments conducted in parallel-sided test boxes with unlubricated walls is proposed. Analytical solutions are developed for reinforced soil slopes and retaining walls subjected to self-weight or external loading. It turns out that the frictional effect depends on the shape of the failure zone and the value of friction coefficient between soil and a sidewall material. The theoretical predictions were verified in laboratory experiments in a test box with lubricated and unlubricated sidewalls. It was shown that the method can be used to estimate sidewall friction not only under failure conditions, but also under all stages of surcharging prior to failure.

Dynamic Responses of Reinforced Soil Model Wall on Soft Clay Foundation

This paper investigated the relative seismic response of reinforced soil retaining wall overlying a soft clayey soil layer—applicable to road or railway embankment. A series of 1D shaking table tests, 0.1 to 0.5 g, were conducted on the 1 m high physical model. The scaled physical model was subjected to harmonic sinusoidal input motions at frequencies of 1 Hz, 3 Hz, 5 Hz, 10 Hz, 12 Hz, and 15 Hz. A laminar box was used to enclose the soil during the experiment. The variation of parameters such as base motion excitations; frequencies; and surcharge pressures were studied. The results of this study revealed that these parameters have a significant influence on the model wall and vary along the elevation; impacting pore water pressure as well. It also had an impact on the variation along the depth of the clayey soil layer. Maximum face deformation was observed at the top layer of the wall.

Influence of wire mesh characteristics on reinforced soil model wall failure mechanisms-physical and numerical modelling

This paper presents the details of experimental and numerical analysis performed on three 0.8 m-high reinforced earth model walls with strip footing surcharge near the wall facing. The study investigates how wire mesh strength and geometry affect the failure mechanism. All three walls were nominally identical, except for reinforcement strength and geometry. The displacement field of the entire cross section was captured by high-resolution digital camera through transparent sidewall. The resulting images were analyzed using digital image correlation software. The results indicate that both reinforcement strength and aperture size influence the type of failure mechanism. Numerical modelling was also applied to assess the influence of sidewall friction (3D model) and reinforcement stiffness and strength (2D model) on the failure mechanism of the walls. The parameters for the numerical models were derived from independent tests and results, which were compared with the experimental observations. A good level of agreement with measurements was confirmed, even for the 2D model that excluded sidewall friction.

Experimental study on performance of geosynthetics reinforced soil model walls on rigid foundations subjected to static footing loading: Response to discussion by J. T. H. Wu, M. T. Adams, and J. E. Nicks

Experimental study on performance of geosynthetics reinforced soil model walls on rigid foundations subjected to static footing loading: Response to discussion by J. T. H. Wu, M. T. Adams, and J. E. Nicks

Flume Tests on Fine Soil Reinforced with Geosynthetics: Walls of the Salt Pans (Aveiro Lagoon, Portugal)

This paper presents exploratory work on the use of geosynthetics for reinforcing fine soils, particularly for applications in the Aveiro lagoon, Portugal. The behaviour of local fine soil reinforced with geosynthetics under hydraulic actions was studied using flume tests. The case study was a typical cross section of the walls of the salt pans of the Aveiro lagoon. A preliminary design of a structure was done, for different reinforcements (geogrid, geocomposite, association of geogrid and geotextile). Local soil was collected and characterised using laboratory tests. The flume tests included performing permeability, erosion and overtopping tests, for actions typical of the lagoon environment. The models reinforced with geogrid GGR exhibited the highest global permeability, due to the difficulty of soil lumps to penetrate the geogrid openings. Although this type of reinforcement provides low resistance to erosion, promoting vegetation growth or including other elements can reduce surface erosion. The other reinforcements (sheets) enabled containing the soil. Non-uniformity of the soil compaction caused local differences of permeability. Thus, ensuring uniform compaction on site is necessary; however it can be challenging, particularly for fine soils. The results indicate that seepage is likely to induce some clogging of the reinforcements. The reinforced soil models tested exhibited higher permeability and lower resistance to erosion and overtopping than the traditional solution (soil matrix with vegetation). The results indicate that a possible alternative solution for the walls could use fibre reinforcement. Further work is necessary to ensure adequate (low) permeability of new solutions for these walls.

Modulus and damping from shaking table tests of reinforced soil walls

The paper presents rational procedures to estimate normalised shear modulus and damping ratio from measured responses of reinforced soil model walls tested in a 1-g shaking table. Displacement measured at the top of the model walls and input base acceleration time histories are used to produce equivalent hysteretic responses of the model walls. Equivalent hysteretic loops at different strain amplitudes are developed and used to calculate normalised modulus degradation curves and damping ratio for the tested model walls. Model wall responses are also analysed using the single degree of freedom (SDOF) model to determine damping ratio and phase difference, and to verify the validity of SDOF model for application with reinforced soil walls.Results indicate that the normalised shear modulus significantly decreased at the early stage of the base shaking (i.e. γs < 0.03%). For example, about 68% and 80% reductions in shear modulus occurred at γs = 0.005% and 0.01% respectively. In addition, a 90% reduction in the normalised shear modulus realised at relatively strong input base acceleration (i.e. for γs > 0.03%). Minimum damping ratio of 5% to 10% for both model walls was obtained, increased to 15% to 20% at strain amplitude γs = 0.3%, and reached higher values thereafter. Finally, dynamic properties determined from the proposed method are compared with experimental and empirical relationships proposed in literature as well as resonant column test results.

Seismic displacement analysis of a reinforced soil model wall considering progressive development of reinforcement force

Progressive development of the reinforcement force in a geosynthetic-reinforced model soil retaining wall subjected to irregular ground accelerations was investigated in a pseudo-static-based analytical model. The progressive development of the reinforcement force was expressed as a function of maximum input ground accelerations in the proposed analytical model, which also incorporated a multi-wedge failure mechanism and Newmark's sliding-block theory. This analytical model eliminated a disadvantage inherent in the conventional pseudo-static approach, namely a possible overestimation of the seismic stability of the wall due to the assumption of full mobilization of the reinforcement force regardless of the intensity of ground excitation. It was also found that the value of the critical seismic coefficient [Formula: see text] calculated using a peak internal friction angle (ϕp) and a fully mobilized reinforcement pull-out force can be used to simulate the ultimate state of the model wall when subjected to irregular ground excitations. A softened friction angle of ϕ = 0.9ϕp simulated the wall behavior well when the horizontal displacement of the wall (Dh) was greater than 5% of the wall height (Ht). This finding is consistent with that for a conventional gravity-type soil retaining wall previously reported. A non-uniform distribution of tensile force along the reinforcement, with a peak value at the intersection of the reinforcement and slip surface and a reduced value at the facing-backfill interface was obtained, using a reduction factor of Rr–f = 0.5, based on the calibration of seismic displacements of the tested wall. A reduction factor that accounted for the mobilization of the friction angle along the soil-reinforcement interface, Rr–s, was also calibrated, based on the displacement analysis. It was found that values of Rr–s between 0.7 and 0.8 could be used to represent the pull-out behavior of reinforcement subjected to seismic loading. The proposed method is based on a single set of experimental results and therefore the applicability of the proposed method needs to be verified using more physical tests and/or numerical analyses of various wall geometries and reinforcement configurations.

Effect of backfill thrust on vertical pressure distribution in reinforced soil model walls : Ashaari, Y; Arenicz, R M Geotech Test JV13, N3, Sept 1990, P188–200

Effect of backfill thrust on vertical pressure distribution in reinforced soil model walls : Ashaari, Y; Arenicz, R M Geotech Test JV13, N3, Sept 1990, P188–200

Transition from maximum tension line to actual failure surface in reinforced soil model walls : Arenicz, R M Geotech Test JV13, N2, June 1990, P83–87

Transition from maximum tension line to actual failure surface in reinforced soil model walls : Arenicz, R M Geotech Test JV13, N2, June 1990, P83–87

Effect of Backfill Thrust on Vertical Pressure Distribution in Reinforced Soil Model Walls

Abstract The magnitude and distribution of vertical stress are required for the design of reinforced soil wall. A laboratory investigation utilizing a physical model of reinforced soil wall was performed to determine the effect of backfill thrust on the vertical pressure distribution within the reinforced zone. Results obtained were compared with those predicted by the theoretical vertical pressure distribution (uniform, trapezoid, and Meyerhof's). The model wall behavior, particularly the distribution of vertical stress within the reinforced zone of the structure, was investigated in four series of tests with different boundary conditions and construction procedures. The results obtained were, as expected, different from either of the three theoretical pressure distributions. It was found that thrust of backfill material placed at the back of reinforced zone reduces the vertical pressure near the end of reinforcement strips while increasing it in the remaining part of the reinforced zone. The reduction of pressure near the strip ends conforms to the trapezoid theory. However, the maximum increase in pressure does not occur at the facing as predicted by the theory.

Transition from Maximum Tension Line to Actual Failure Surface in Reinforced Soil Model Walls

Abstract This paper presents the results of laboratory tests conducted on reinforced soil model walls. The effect of model height on distribution of tensile stress in an instrumented reinforcement strip was investigated. It was found that, with increasing height of wall, a continuous redistribution of tensile stress had occurred with the point of maximum tension moving towards the actual failure surface of the model. On that basis, a correlation between the position of maximum tension in reinforcement and the overall safety factor of model walls was investigated. General and specific equations of maximum tension line in terms of wall height and safety factor were suggested.