Assessment of Seismic Bearing Capacity of a Strip Footing Resting on Reinforced Earth Bed using Pseudo-Static Analysis

This article presents the finite element modeling (FEM) based settlement analysis of two high-rise buildings founded on the stiff raft foundations 12.0 m below the ground level in Neogene clay using a modified hypoplastic model with the concept of intergranular strains. The numerical prognoses of the settlement for different phases i.e., deconsolidation, short term and long-term consolidation deformations pertaining to excavation, construction, and operation, respectively, were compared with the real-scale geotechnical monitoring (GTM) data acquired through deformeter installed in a borehole below the foundation. The results showed that the prediction of the settlement of high-rise buildings in stiff Neogene clay using the hypoplastic model can be equitable to the actual values given that calibration of model based on precisely performed laboratory tests, i.e., triaxial oedometer, simple shear and small strain element tests, high coefficient of earth pressure (K0 > 1.0) and appropriate design loads are considered for the analysis. The optimization of intergranular strain parameters showed that mR value in conjunction with r parameter affected the predicted deformation in the excavation, construction and operational phases of high-rise buildings, whereas, βr only affected the deformations during excavation and construction phases. Overall, the predictions of deformation of excavation and short-term consolidation phases using the hypoplastic model were close to the GTM as compared to that of the long-term consolidation phase, which was found to be sensitive to the contact load, σol. Moreover, in comparison to Mohr Coulomb's and cam clay models, the hypoplastic model yielded more reliable subsoil deformation for high-rise buildings based on directly calibrated parameters, proving to be a more value-added model for meticulous numerical analysis. The difference between the predictions of total settlement using the hypoplastic model for all optimization schemes was observed to be in a reasonably good range of 16–29% in comparison to the real-scale settlement. 

Appraisal of the hypoplastic model for the numerical prediction of high-rise building settlement in Neogene clay based on real-scale monitoring data

Behavior of Back-to-Back MSE Walls: Interaction Analysis Using Finite Element Modeling

Soil nailing is commonly used to stabilize cut slopes and earth retaining structures, embankments and sometimes to reduce the lateral earth pressure on retaining wall. This is an in-situ reinforcement technique that uses passive rigid bars usually made up of steel that can withstand tensile forces, shearing forces, and bending moments. In the present study, an attempt has been made to analyze the behavior of soil slope reinforced with soil nails by numerical simulation under seismic loading using a finite element numerical modeling tool, OptumG2. Two-dimensional models of the slope are considered (with and without nails) and subjected to static and dynamic loading to investigate the possible modes of failure (base failure, slope failure, and toe failure). The corresponding factor of safety values for unreinforced soil slope is calculated using the strength reduction method (SRM) at different slope angles (\(\beta )\) at 30°, 40°, 50°. Based upon the obtained critical slope surface in the case of the unreinforced slope, soil nails are provisioned in the slope and the same is analyzed under gravity and seismic loading. A detailed investigation of reinforced soil slope has been conducted considering the key factors governing the factor of safety of reinforced slope namely length of the soil nails, the number of soil nails, spacing of soil nails (s), the inclination of soil nails (\(\theta\)) in different slope angles (\(\beta )\) under seismic loading with a peak horizontal ground acceleration = 0.12 g. The present study also investigates the possible failure patterns under static and seismic conditions, along with the analysis of the development of internal reactions in soil nails such as bending moment and shear force.

Numerical Studies on the Behavior of Slope Reinforced with Soil Nails

Whenever a need arises to construct a high retaining wall, the construction of a mechanically stabilized earth (MSE) retaining wall in a multi-tiered configuration is a viable approach than the construction of a single-tiered (rectangular wall). However, the behavior of multi-tiered MSE walls is complex, and unfortunately, the behavior of such walls under seismic loading has not yet been entirely investigated. Therefore, this study performs an exhaustive comparative analysis, on multi-tiered and rectangular MSE walls through a finite element method-based numerical computational tool to look into its performance under seismic loading and their potential failure envelope, i.e., wedge angle. Additionally, this study investigates the influence of the parameters such as the number of tiers, offset distance (D), and horizontal seismic acceleration coefficient (kh) on the walls. The potential failure envelopes of the various wall models are explored, which indicate a combination of overturning and sliding failure accompanied by a distortion of the leveling pad of the walls. However, the sliding behavior reduces as the kh increases and the overturning failure is more prominent. This study proposes a wedge angle correction factor (CΘ) to normalize the deviation of the angle of the potential failure plane under seismic loading, based on the assumption that the standard value of the potential failure plane defined by Federal Highway Administration (FHWA) is valid for all multi-tiered walls since none of the design manuals have suggested clear guidelines that can demonstrate the formation and progression of the wedge angle under seismic loading conditions for multi-tiered walls. The factor of safety (FOS) of the various wall models simulated in the present study satisfies the FHWA guidelines, thus suggesting the construction of tiered walls, at places where huge excavation required for the construction of a rectangular wall is impractical. In the numerical simulations, where the FOS obtained is unsatisfactory as per FHWA guidelines, the current study suggests increasing the length of reinforcement and/or decreasing the vertical spacing between the reinforcing layers to enhance the overall stability of such walls.

Parametric studies using finite element modeling for the evaluation of the performance of tiered MSE walls under seismic loading

Piled raft foundations (PRFs) are essential for improving the load-bearing capacity of the foundation and for controlling the total and differential settlements. For an efficient design of the foundation for high-rise buildings, components of PRF such as length, diameter, and raft thickness are important factors. This study aims to examine the interaction behavior of pile–soil foundations for various parameters, namely the diameter and the length of the pile and also the raft thickness, which plays an important role in improving the behavior of piled raft foundation. The important aspects that must be taken into account to achieve a reliable design and strategies for the optimized design of PRF that is subjected to load–settlement with regard to the distribution of shear force and bending moment are also analyzed. In order to understand the behavior of piled raft foundation subjected to uniform loading, numerical simulations are carried out in this study by using a numerical tool based on the finite element method (FEM), ELPLA. This study reveals that proper pile arrangement can result in a significant reduction in the total and differential settlements, as well as induced shear force and bending moments on the raft.

Studies on the Piled Raft Foundation for a High-Rise Building Using Finite Element Modeling

Present study discusses the behavior of an anchored sheet pile wall supporting a wide excavation based on the analysis using a computational tool based on the finite element method. The soil is modeled using the Mohr-Coulomb material and the sheet pile wall is modeled using the plate elements. A parametric study using numerical modelling is performed to investigate the behavior of an anchored sheet pile wall. The anchoring system is modeled by a combination of connectors (which do not interact with the soil) and geo-grids (which do interact with the soil and are used to account for grouting). The stability of the structure assessed using Strength Reduction Method and factor of safety for various combinations are calculated in the upper and lower bounds analysis. Results obtained from the parametric study indicate that the embedded depth of sheet pile wall, positioning of anchor, and length of anchors, inclination of the anchor govern the overall stability of structures studies in the present study. Moreover, the present study captures the failure modes of the anchored sheet pile wall system with the inclusion of multiple complex interfaces and supports conditions.

Behavior of Anchored Sheet Pile Wall

In this paper, the numerical simulation is performed on two piled raft configurations having uniform loading on a piled raft foundation. To investigate the interaction between various parameters of pile soil foundation with varying components of its length of pile, diameter and raft thickness. These components are critical for increasing the foundation’s bearing capacity. It’s important aspect to achieve a reliable design to optimize piled raft foundations subjected to uniformed load- settlement behaviors of the curves. These load – settlements are basically depending on the changing of their components piled raft foundation. These component of piled raft foundations to choose an optimal selection of embedded length of pile (L/dP), normalized diameter of pile (L/dP) and normalized raft thickness (tR/dP). The effect of load-settlement on distributions of shear force and bending moments is also investigated. In this study, a finite elements methods based on numerical tools ELPLA software is used for numerical simulation. The study’s findings validate the numerical analysis for the calculation of proper pile configuration arrangement, as a result of settlements. It will be generated as formation of contours patterns as shear stress and bending moments on the rafts, may be minimized with the total pile length. The conclusion drawn from the study validates the numerical analysis for the computation of proper pile arrangement can results in total and differential settlements, as well as generated shear stress and bending moments on the rafts, are all being reduced, with identical total pile length. Moreover, it captures the contours patterns of different behaviors of piled raft settlements, maximum shear force and maximum moments.

https://doi.org/10.1088/1757-899x/1236/1/012006

Pratish Kannaujiya

Papers

Studies on the Piled Raft Foundation for a High-Rise Building Using Finite Element Modeling

Behavior of Anchored Sheet Pile Wall

Behavior of Different Configuration of Piled Raft Foundation for a High-Rise Building by using FEM