Dynamic Plasticity in Pile-Soil Interaction Problems

The dynamic soil-pile interaction problem is solved by the method of characteristics. The nonlinear, non-homogeneous problem was idealized as a piecewise linear problem. The numerical instability of semi-infinite soil column model has been reported, and a stable model, wherein the soil column below, the pile tip is replaced by a single spring and dashpot, has also been presented. The results obtained from the method of characteristics have been compared with those obtained by explicit finite difference scheme. The convergence and stability were studied numerically

Integrated Analysis of Turbomachinery Frame-Foundation-Soil Interaction

For the smooth functioning of turbomachines, the design of the rotor, the bearings, the supporting structure, and the foundation should be carried out as an integrated system. The frequency domain method in conjunction with FEM is chosen for the analysis. The modified influence matrix boundary condition method is applied to reduce the number of equations to be solved. Results for 4 idealized cases are compared. It is shown that the interaction effects are significant in the lowest frequency domain

Effect of Compaction Stresses on Performance of Back-to-Back Retaining Walls

Back-to-back reinforced soil retaining walls are commonly used for approach embankments of bridges and flyovers. Existing design guidelines (FHWA/BS/IS codes) do not provide a mechanistic approach to design back-to-back reinforced soil retaining walls. Lateral pressures on the facing and at end of reinforced zone are required for stability checks (both internal and external). During stage-wise construction of back-to-back walls, compaction stresses should be incorporated to obtain realistic lateral earth pressures on the walls. The present paper describes the effect of the compaction stresses on the lateral pressures in such reinforced soil retaining walls. The variation of lateral pressures at the end of reinforced zone along the depth of the wall is obtained from numerical modeling of back-to-back reinforced soil walls. A surcharge load of 30 kPa is applied at the end of the construction of the wall. It is observed that the effect of surcharge load is not significant after certain depth of the wall for lower spacing between walls to wall height ratios. A comparison on lateral pressures with and without compaction stresses for different distances between the ends of reinforcements of two walls is presented. Effect of connection of reinforcement is also studied

Reclamations – Case Studies

Increasing demands for urban water fronts and the need for continually operational airports coupled with shortages of land spaces has led to the growth of lands reclaimed from the near and off-shore regions of the world. Case histories of reclamations of recent times in the east, especially in Japan, Hong Kong, Korea, Singapore, etc. are reviewed. The paper also reports the methods of reclamation, the improvement of reclaimed ground and examples of observed settlements in typical cases

Analysis of Single and Back-to-Back Reinforced Retaining Walls with Full-Length Panel Facia

Back-to-back mechanically stabilized earth (MSE) walls have several applications in infrastructure development. Present study firstly discusses on the kinematics of deformation of MSE wall with full-length panel facia. Secondly, single and back-to-back MSE walls with full-length panel facing are modelled using finite difference based software (Fast Lagrangian Analysis of Continua). The reinforcements in the back-to-back walls extend through and through from one wall facing to the other wall facing. Lateral pressures, vertical stresses, and lateral deformations at the facing for various reinforcement stiffness values are evaluated for both single and back-to-back walls under working stresses. Reinforcement stiffness values of 500 kN/m, 5000 kN/m and 50,000 kN/m are considered. For single MSE wall with stiff reinforcement, lateral pressures at the facing are higher than those for active earth pressure. Lateral deformations of facing with reinforcement of low stiffness are higher than those with reinforcement of high stiffness. In back-to-back walls, the lateral deformation of wall facing with reinforcement of high stiffness is slightly inwards near the top of the wall. Reinforcement stiffness is found to have significant effect on the vertical stress in both single and back-to-back walls. Lateral pressures of both single and back-to-back connected walls are compared. Lateral pressures on single MSE wall are found to be lesser than those for back-to-back wall at the top of the wall. However, lateral pressures near the bottom of single wall are higher than those of back-to-back wall

Behavior and Design of Back-to-Back Walls Considering Compaction and Surcharge Loads

Back-to-back geosynthetic-reinforced retaining walls are commonly used as approach embankments for bridges and flyovers. Compaction and surcharge loads should be incorporated in the model to understand the realistic behavior of mechanically stabilized earth (MSE) retaining walls through numerical modeling. In this study, a finite-difference method-based numerical model, Fast Lagrangian Analysis of Continua (FLAC 2D, Version 7.0), is used to study the effects of surcharge and compaction stresses on lateral pressures and lateral displacements of back-to-back MSE walls. The ratio of the distance between walls to the height of the wall (W/H) in back-to-back walls is varied from 1.4 through 2.0, and the stiffness of reinforcement from 500 to 50,000 kN/m to cover the entire range of stiffness values of extensible to inextensible reinforcements. The coefficient of lateral pressure, Kr, at the end of the reinforcement zone for W/H = 1.4 is found to be 50% less than that for W/H = 2.0. Plots showing the variation of lateral earth pressure coefficients and lateral deformations versus normalized depth of wall are presented. Maximum tensile forces in the reinforcements along the depth of wall are also analyzed. The lateral pressures at the facing appear to be unaffected with W/H ratio. Finally, a design example showing the external stability analysis of reinforced back-to-back walls is illustrated incorporating the lateral pressures obtained from the study

Behavior of Connected and Unconnected Back-to-Back Walls for Bridge Approaches

Back-to-back mechanically stabilized earth (MSE) walls are commonly used in the construction of transportation infrastructure facilities. Federal Highway Administration (FHWA) guidelines discuss briefly the design of reinforced back-to-back walls. In this study, a numerical model was developed to study the behavior of connected and unconnected back-to-back walls under working stresses. The effect of reinforcement stiffness on tensile force profiles, the maximum tensile force developed in the reinforcement, and lateral pressures and lateral deformations for both unconnected and connected walls are discussed in detail. A well-defined critical slip surface was observed for the case of the unconnected back-to-back wall with relatively extensible reinforcement. Lateral pressures at the facing in both the cases were found to be almost equal, and the tensile forces developed in the reinforcement for the connected case were found to be uniform along the length of the reinforcement (except at higher depths)

Influence of Geogrid Properties on Rutting and Stress Distribution in Reinforced Flexible Pavements under Repetitive Wheel Loading

Geogrid reinforcement effectively controls the rutting of pavements under traffic loads, especially when constructed over soft subgrades. In this study, extensive large-scale model pavement experiments (LSMPEs) were performed to quantify the rut depths of flexible pavements. In all, 20 LSMPEs were performed on pavement sections overlying subgrades of different strengths with California bearing ratio (CBR) values varying from 1% to 5%. Three geogrid types were considered to study the effects of material type [polypropylene (PP) and polyester (PET)] and tensile strengths (30-60 kN/m) on the rutting behavior of flexible pavements. LSMPEs were first performed under monotonic loading to obtain the optimum depth of reinforcement within the base layer of flexible pavement. Thereafter, a series of repetitive load (haversine loading) was applied on paved sections of reinforced flexible pavements using a high-end, linear, double-acting actuator system. Rut deformations were measured at both the surface and the subgrade levels of the model pavements. The rut deformations were found to distinctly vary in accordance with the condition of the subgrade, the thickness of the pavement layers, and the type of geogrid used. The rut depth reduction (RDR) at the pavement surface was found to range from 22% to 69% for PP- and PET-geogrid reinforced base layers. Geogrid reinforcement significantly reduced the rut depths at the subgrade level (as high as 90%) compared to unreinforced sections. In addition, the model pavements were instrumented with the earth pressure cells to measure the vertical pressures transferred to the subgrade due to surface loading. The ability of geogrid reinforcement to distribute loads to wider areas was quantified in terms of the vertical stress distribution angle, αmax, at the end of the load cycles (N=100,000 cycles). The αmax maximum values for geogrid (GG1/GG2/GG3)-reinforced pavements built over weak subgrade (CBR=1%) varied from 28.4° to 32.2°, while it was 25.7° for unreinforced pavements. Likewise, αmax values for geogrid-reinforced pavements overlying a relatively fair subgrade (CBR=5%) varied from 34.5° to 43.6° against 30.4° for an unreinforced case. © 2021 American Society of Civil Engineers