Uniform Surcharge Research Articles

Quantitative analysis of shallow unreinforced and reinforced piled embankments with different heights subject to cyclic loads: Experimental study

Reinforced piled embankment is an important technique which is widely used for construction on soft ground due to its benefits in reducing settlement, construction time and cost effectiveness. Most of the existing research has considered the response of deep embankments subjected to a uniform surcharge static load. Limited studies have examined the effect of cyclic loading or the influence of varying the height of the embankment. In this study, the effect of applying cyclic loading on a particular area of unreinforced and reinforced embankments of different heights was experimentally investigated and analysed. Twelve main experiments were undertaken to investigate the effects of monotonic and cyclic loading conditions, the number of reinforcement layers (n) and increasing the mean value and amplitude of the loading cycles on the behaviour of embankments of different heights. The experimental results showed that the transfer of loads to the piles was increased during the monotonic loading stage but at a lower rate with increasing the embankment height. Under cyclic loading conditions, arching of the soil was adversely affected during the initial stages of cyclic loading regardless of the embankment height. However, by increasing the number of cycles, arching of the soil started to regain some degree of improvement. Including layers of reinforcement increased the magnitude of the loads transferred on piles. However, the improvement was more obvious for a thinner embankment. Finally, the surface settlement increased with raising the embankment height but decreased when the number of reinforcement layers was increased, while the extent of heaving outside the loaded area was reduced with increasing both the embankment height and the number of reinforcement layers.

Advanced analysis of masonry retaining walls using mixed discrete–continuum approach

A study was carried out into extending the use of the mixed discrete–continuum approach for advanced numerical analysis of masonry retaining walls. This included incorporation of soil plasticity, irregular wall morphology and application to a real-life scenario to identify the causes of observed damage patterns. Backfill soil was simulated by way of a deformable continuous medium, while masonry units were represented as polyhedral rigid blocks interacting with each other. Upon validation, the approach was used to simulate the behaviour of an historical masonry retaining wall suffering from severe cracks, large deflections and partial collapse due to material degradation and differential soil settlement. To understand the progressive response of the structure better, a parametric analysis was performed on the tensile strength of masonry when the system was subjected to differential settlement. Further static analyses were performed to assess the capacity of the wall under uniform surcharge pressure. The results demonstrated the sensitivity of the macro behaviour of the wall to the tension capacity of masonry. The study also showed that the proposed modelling approach can provide useful performance information on existing retaining walls that are vulnerable, and that such validated numerical models should be used to determine any interventions and repairs.

Effect of Soil–Wall Friction Angle on Behaviour of Sheet Pile Wall Under Surcharge Loading

In this study, a solution is derived in the framework of the limit equilibrium approach for the design of cantilever sheet pile walls under both static and seismic conditions in cohesionless soil with uniform surcharge load located at the top of the wall. The proposed method satisfies the horizontal force equilibrium and moment equilibrium about toe simultaneously. From the results of the study, it is highlighted that the application of surcharge load increases the magnitude of bending moment along the depth of the sheet pile wall and deflection at the top of the wall. Further, the increase in plastic zone due to mobilisation of earth pressure is also observed. A parametric study is done by varying the soil–wall friction angle and magnitude of uniform surcharge load acting on the backfill of the cantilever sheet pile walls. From the results, it is observed that as the soil–wall friction angle increases, the maximum bending moment, deflection, depth of plastic zone and settlement adjacent to sheet pile wall decrease. Further, the increase in the magnitude of uniform surcharge increases the maximum bending moment, deflection, depth of plastic zone and settlement adjacent to sheet pile wall.

Influence of soil type on static response of cantilever sheet pile walls under surcharge loading: a numerical study

Deep excavation is the need of present time due to increase in construction work in urban congested areas. This requires proper planning of support systems for the stability of retaining wall. Therefore, in the present study, influence of uniform surcharge load on the ground surface at a distance from the wall is analyzed for bending moment, net earth pressure, deflection, and settlement behavior of cantilever sheet pile walls using finite difference-based computer program FLAC2D. The results indicate that the presence of the uniform surcharge at the top of the wall influences the cantilever sheet pile wall significantly and as the distance of uniform surcharge increases, the influence gets reduced and beyond 2 times excavation depth, the influence is insignificant. Mobilization of earth pressure takes place up to a greater depth with excavation depth greater than 60% of the total length of the wall and causes more settlement and deflection. The present numerical model is validated with existing literature.

Numerical study of the behaviour of geosynthetic-reinforced soil retaining walls under a uniform surcharge

The geosynthetic technique of reinforcing retaining walls is one of the techniques that are currently being developed in the field of geotechnics. This article focuses on a numerical study, using two-dimensional finite difference Fast Lagrangian Analysis of Continua FLAC2D software, to investigate the influence of a uniform surcharge application on the behaviour of a geosynthetic-reinforced soil retaining wall, especially on the maximum tensile force and wall displacement at the end of construction. A parametric study was undertaken taking into account the surcharge load, the width and its distance from the continuous facing panel. The results show that the tensile forces in the reinforcement and the horizontal displacements of the facing panel increase with increasing the uniform surcharge. Furthermore, a small effect was noted on the maximum tensile force in the geosynthetic layers with varying the surcharge distance from the back of the facing panel.

Lateral earth pressure and bending moment on sheet pile walls due to uniform surcharge

Cantilever sheet pile walls are subjected to surcharge loading located on the backfill soil and at different distances from the top of the wall. The response of cantilever sheet pile walls to surcharge loadings at varying distances under seismic conditions is scarce in literature. In the present study, the influence of uniform surcharge load on cantilever sheet pile wall at varying distances from the top of the wall under seismic conditions are analyzed using finite difference based computer program. The results of the numerical analysis are presented in non-dimensional form like variation of bending moment and horizontal earth pressure along the depth of the sheet pile walls. The numerical analysis has been conducted at different magnitudes of horizontal seismic acceleration coefficient and vertical seismic acceleration coefficients by varying the magnitude and position of uniform surcharge from the top of the wall for different embedded depths and types of soil. The parametric study is conducted with different embedded depth of sheet pile walls, magnitude of surcharge on the top of the wall and at a distance from the top of the wall for different angles of internal friction. It is observed that the maximum bending moment increases and more mobilization of earth pressure takes place with increase in horizontal seismic acceleration coefficients, magnitude of uniform surcharge, embedded depth and decrease in the distance of surcharge from the top of the wall in loose sand.

Numerical study of the behaviour of geosynthetic-reinforced soil retaining walls under a uniform surcharge

Numerical study of the behaviour of geosynthetic-reinforced soil retaining walls under a uniform surcharge

SLOPE STABILITY ANALYSIS CONSIDERING WEIGHT OF TREES AND ROOT REINFORCEMENT

We study the effect of roots of alder trees on soil reinforcement and slope stabilization. Two types of soil, i.e. Marl and Clayey soils and alders of three ages are considered. The slope stability is studied according to the tree indices based on tree age and soil type. The effect of root reinforcement on slope stability is considered by an additional cohesion. The stability analyses are carried out by the FEM. We perform parameter studies considering tree age, soil type and surcharge. The results indicate that soil type is effective on cohesion. The results also showed that with increasing age of trees from 7 to 15 years, the amount of additional root cohesion increased and with the increase of the age of trees to 20 years this amount slightly decreased. Also, with regard to a constant slope geometry, the type of soil and the uniform surcharge pressure, 7-year-old trees have shown better performance in slope stabilization. It has been observed that as the age of alder trees grows, although the amount of additional root cohesion increases, however, due to increased surcharge pressure, the overall slope stability factor decreases.

Evaluation of the combined effect of facing inclination and uniform surcharge on GRS walls

In the current paper, using experimental studies and numerical analyses, the combined effect of facing inclination and uniform surcharge on the behaviour of geosynthetic-reinforced soil (GRS) walls under working stress conditions is evaluated. Data from four well-instrumented GRS walls at the end of construction and under surcharge applications were used considering different facing types, inclinations, and toe conditions. The numerical analyses were carried out considering different wall heights, facing inclinations, and surcharges. Moreover, data from the physical and numerical model studies were utilised to verify the predictability of the AASHTO simplified (2017) and Ehrlich and Mirmoradi (2016) design methods and some limitations of each method are discussed. The results clearly indicate that for better representation of the actual conditions, the uniform surcharge and facing inclination should not be independently taken into account in the design procedures.

A new analytical approach to estimate the seismic tensile force of geosynthetic reinforcement respect to the uniform surcharge of slopes

This paper investigates the pseudo-static analysis of reinforced slopes with geosynthetics under the influence of the uniform surcharge to evaluate the maximum tensile force of reinforcements. The analytical approach has basically been used to develop the new practical procedure to estimate both tensile force and its distribution in the height of the slope. The base of developed relationships has been adapted from the conventional horizontal slice method. The limit equilibrium framework and the assumptions of log-spiral failure surface have directly been used for proposed analytical approach. A new analytical approach considering a single layer of non-cohesion soil and the influence of uniform surcharge has been extracted from the 5n equation and 5n unknown parameters. Results of the proposed method illustrated that the location of the surcharge, amount of internal friction and the seismic coefficient have the remarkable effect on the tensile force of reinforcement and might be 2 times increasing on it. Furthermore, outcomes show that the amount of tensile force has directly until 2 times related to the amount of slope angle and its height range. Likewise, it is observed that the highest value of the tensile force in case of slope degree more than 60-degree is observed on the lower layers. While in case of less degree the highest amount of tensile force has been reported on the middle layers and extremely depended to the seismic coefficient. Hence, it has been shown that the tensile force has increased more than 6 times compared with the static condition. The obtained results of the developed procedure were compared with the outcomes of the previous research. A good agreement has been illustrated between the amount results of developed relationships and outcomes of previous research. Maximum 20 and 25 percent difference have been reported in cases of static and seismic condition respectively.

Effect of Rainfall Infiltration on Deformation of Geobarrier Wall

GeoBarrier system (GBS) is a system that combines geobag wall with capillary barrier concept as stabilization method against rainfall-induced failure, and vegetation as green cover. This paper presents deformation behaviour of a GBS wall constructed as pilot study when subjected to rainfall infiltration. The GBS wall was 4 m high with 70° slope angle. The wall was subjected to uniform surcharge of 10 kN/m2 and rainfall of 22 mm/h for 8 h. Recycled materials were used as components of the capillary barrier. Coupled deformation-seepage finite element analyses were carried out to evaluate the stress and pore-water pressure variations within and behind the GBS wall during and after rainfall. Limit equilibrium analyses were performed at various stages during and after rainfall to assess the near vertical wall stability. The results of the coupled deformation seepage analysis showed that the reinforced zone in the GBS remained unsaturated during rainfall, indicating that the GBS wall performed well in minimizing the rainwater infiltration. However, the GBS wall face deformation pattern altered during and after rainfall, indicating that the rainfall infiltration increased the lateral stress on the top part of the wall. The variation of lateral stress with depth agrees with field measurements from earth pressure cells.

Performance of Model Gabion Type Retaining Walls Built Using Cylindrical Cells: A Laboratory Study

Behavior of gabion walls built using scrap tyres/scrap metal drums in the field, was simulated in the laboratory by constructing gabion type retaining walls using PVC cells. Experimental work was carried out in the laboratory in a steel tank. Gabion type walls were constructed using PVC cells made by cutting 6″ PVC pipe into cells of 5.0 cm in height. The total PVC cells wall is 1.0 m in length, 0.33 m in width and 1.0 m height ‘H’. Dial gauges to measure horizontal deformations were located at the top, one-third, 0.59 and 0.79 m from bottom of the wall. Lateral deformations of PVC cell walls were measured during and at the end of the construction, and with uniform surcharge loading for wall inclinations of 2.5°, 5.0° and 7.5° from the vertical. Horizontal deformations with surcharge loads were more at normalized heights between 0.6H and 0.7H. Face deformations of flexible walls constructed using PVC cells were within the limits as per the guidelines specified by AASHTO, FHWA and EN.

Behaviour of piles in consolidating soil

ABSTRACTThe development of negative skin friction on circular piles in a consolidating layered soil is investigated by an elasto-plastic load transfer theory which accounts for slippage of the soil. The elastic load transfer theory is premised on the compatibility condition that the vertical displacement of the ‘pile’ is equal to the summation of the vertical displacement of the layered soil due to the consolidation of the upper soil layer and the vertical displacement in the ‘soil layers’ along the pile’s centroidal axis caused by a system of pile-soil interactive forces. Slippage of the soil is accounted for by imposing the shear strength of the clay layer as the limit of the pile-soil interface shear stress. The saturated upper clay is consolidating under a uniform surcharge in accordance with Terzaghi’s one-dimensional consolidation theory. The validity of the proposed solution is confirmed by comparison with field measurements. Extensive parametric studies with regard to the effect of pile-soil slip on pile behaviour are presented.

The analytical predictions on displacement and stress around shallow tunnels subjected to surcharge loadings

Tunnels in urban areas inevitably lie near the ground surface, and will be affected significantly by the loads on the surface. In this study, a new analytical solution is presented for the first time, by means of which the ground responses around circular shallow tunnels subjected to surcharge loadings can be quickly predicted. The ground is approximately assumed as an elastic or viscoelastic medium, and arbitrary distribution of surcharge loads, as well as any viscoelastic models, are accounted for.Case (A) is modelled with surcharge loads applied before the tunnel excavation. The incremental elastic displacements and stresses which occur after the tunnel excavation are provided by Verruijt’s method, combined with a Fourier expansion of the tractions. Case (B) represents the model in which the surcharge loads are applied after the tunnel excavation, and the elastic ground responses due to the presence of surcharge load are proposed by the superposition of modified Flamant’s solutions and the solution of Case (A). The solutions for the viscoelastic problem of the two cases are also proposed by an extended corresponding principle, taking into account the time-dependence of the rock/soil with any types of the linear viscoelastic model.All of these analytical solutions are verified by good agreements of the comparison between the analytical solutions and FEM results. Furthermore, they are consistent with measured data qualitatively. Finally, a parametric study is carried out to investigate the influence of the uniform surcharge load on the stresses and displacements of the ground in the two cases. The proposed new solutions potentially provide an alternative approach in the preliminary designs of future shallow tunnels.

Numerical Evaluation of Passive Earth-Pressure Coefficients under the Effect of Surcharge Loading

AbstractA numerical protocol was developed for the evaluation of the passive earth-pressure coefficients (Kpq) for the case of an inclined rigid wall retaining an inclined cohesionless backfill loaded with a uniform surcharge. The shape of the proposed failure surface is assumed to be a complete log-spiral. The methodology developed herein uses Kotter’s equation, which enables the computation of soil reactive pressure distribution and the resultant soil reaction on the failure surface. Furthermore, all three limit-equilibrium conditions are effectively utilized to identify the unique failure surface for the given parameters, viz, soil frictional angle (ϕ), wall frictional angle (δ), wall inclination angle (λ), and sloping backfill angle (i). Design tables are also presented for several combinations of ϕ, δ, λ, and i. For validation, the Kpq values obtained are compared with those reported by several other researchers and are found to be in good agreement with most of the available theoretical solutions.

Undrained face stability of tunnels in Bangkok subsoils

This paper presents the analysis of undrained face stability of tunnels in Bangkok subsoils. In this study, two-dimensional (2D) and three-dimensional (3D) finite element analyses were employed to analyse the 2D plane strain conditions of transverse (2DT) and longitudinal (2DL) sections as well as the full 3D geometry, respectively. The simplified geometry of 2DT corresponds to the circular face of tunnels subjected to a uniform face pressure, while that of 2DL correspond to the plane strain heading applied by a uniform face pressure at the front plane. For the 2D plane strain transverse and longitudinal sections, the tunnel lining was not considered in the analyses. For 3D cases, tunnel linings were included in the analysis and modelled as the rigid plate element with the fully rough surface along their lengths, while the tunnel face was subjected a face pressure. For all cases, the uniform surcharge was applied all over the ground surface. Strength reduction methods in conjunction with 2D and 3D finite element analyses were employed to determine the stability and the factor of safety of this problem. The stability analyses included ranges of tunnel face pressure measured during the tunnelling process. Effects of three-dimensional stability of tunnel face were also presented and discussed in this paper. Results of analyses were verified and compared with existing methods.

Theoretical analysis of earth pressure against rigid retaining walls under translation mode

The soil mass behind a retaining wall gradually yields and separates from the stationary soil mass with the complex shape of the slip surface depending on the mode of wall movement and roughness of the wall surface. In this study, the problem of a rigid retaining wall with a uniform surcharge acting along the horizontal backfill under active translation mode is investigated in a two-dimensional system of equilibrium. Exact stress solutions based on Janssen׳s approach are generalized in rectangular coordinates and are validated with boundary conditions on the retaining wall and at the Coulomb slip line behind the wall. Because the yield condition is not used in Janssen׳s approach, the proposed solution is a merely static stress solution, not statically admissible solution. New equations are developed to estimate the magnitude and distribution of vertical, horizontal and shear stresses in the failure zone behind a retaining wall. The proposed analysis indicates the arching effect behind the retaining wall because the maximum stresses do not appeared at the toe; but at some distance away from the toe of the retaining wall. The results of the proposed formulations are compared with both full-scale and laboratory-scale experimental data as well as the existing formulations. The proposed analysis provides comparable approximations for horizontal active stress distribution, the magnitude and the application height of the horizontal active force at the wall.

A dual beam model for geosynthetic-reinforced granular fill on an elastic foundation

In this study, a new dual beam model was proposed for a geosynthetic-reinforced granular fill with an upper pavement. This dual beam model was subjected to a uniform surcharge loading and resting on an elastic foundation which was simulated by a Pasternak model. The upper pavement was modeled by an Euler–Bernoulli beam while the geosynthetic reinforced granular fill was simulated by a reinforced Timoshenko beam. The explicit derivation process for the behavior of this dual beam-foundation system was presented and an exact solution was obtained. A two-dimensional finite element analysis and a Pasternak model for simulating the granular fill were carried out to validate the reliability of the proposed dual beam model. A parametric analysis was put forward to investigate the behavior of this dual beam-foundation system. It was found that the length of the pavement structure and vertical uniform loading, the stiffness and shear modulus of the foundation soil had significant influences on the behavior of the dual beam-foundation system.

Finite element analysis of a concrete-rigid wall retaining a reinforced backfill

In this paper a rigid wall retaining a reinforced backfill with self-weight as well as with a uniform surcharge load has been analyzed by finite element method. The reinforcement is assumed in the form of strips that are not attached to the wall. Analyses are performed using a software code which is developed in FORTRAN-77 and validated for reported case histories in the literature. This study also can be extended to the other types of reinforced earth systems like segmental walls, mechanically stabilized reinforced earth walls etc. The system is modeled as a plane strain two-dimensional problem. The investigations are conducted to examine the influence of reinforcement, stiffness and Poison’s ratio of backfill and foundation strata on the performance of a rigid wall. The studies show that, there is substantial reduction in the front face displacements of a rigid wall. The extent of reduction in the front face deformations depend upon the stiffness of foundation and backfill strata. The present work also, demonstrates the methodology to derive the design charts for deflections at top and base and height of rotation of a rigid wall by varying the stiffness of backfill and foundation strata for particular geometrical dimensions of wall. These charts are useful to the designer to choose the option of a rigid wall with a reinforced backfill, considering the available foundation and to satisfy the codal provisions regarding the serviceability criteria of a rigid wall. Additionally, the paper highlights potential areas of ongoing and further work that may offer a better understanding of the serviceability limit state of reinforced soil walls.

Seismic active earth pressure of cohesive-frictional soil on retaining wall based on a slice analysis method

The M–O (Mononobe–Okabe) theory is used as a standard method to determine the seismic earth pressure. However, the M–O theory does not consider the influence of soil cohesion, and it cannot determine the nonlinear distribution of the seismic earth pressure. This paper presents a general solution for the nonlinear distribution of the seismic active earth pressure of cohesive-frictional soil using the slice analysis method. A new method is proposed to determine the critical failure angle of the backfill wedge under complex conditions, and an iterative calculation method is presented to determine the tension crack depth of the seismic active earth pressure. The considered parameters in the proposed method include the horizontal and vertical seismic coefficients, wall inclination angle, backfill inclination angle, soil friction angle, wall friction angle, soil cohesion, wall adhesion and uniform surcharge. The classical methods of the M–O and Rankine theories can be regarded as special cases of the proposed method. Furthermore, the proposed method is compared with the test results and previously existing solutions to validate the correctness of the results. Additionally, the parameters׳ effect on the critical failure angle, the resultant force, the application-point position, the tension crack depth and the nonlinear distribution of seismic active earth pressure are studied in graphical form.