Browsing by Author "Amalu, P.A."

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    A Review on Behavior of Piled Raft Foundations Under Various Loads
    (Springer Science and Business Media Deutschland GmbH, 2022) Amalu, P.A.; Jayalekshmi, B.R.
    Piled raft foundations are a combined system of deep foundation and shallow foundation. In this type of foundation systems, the pile footings are provided beneath a raft or mat footing. Thus, the piled raft foundations can be constructed either by providing raft foundation connected to the pile footings or by providing a cushion layer between raft and pile footings. The first type of piled raft foundation is generally termed as connected piled raft foundations, and the latter piled raft foundations. Piled raft foundations is termed as disconnected can be subjected to different types of loadings, like vertical and inclined loading depending on the type of superstructure, lateral loading induced by earth pressure as well as seismic loads and moments induced by the eccentricity in loadings. Numerous studies have been conducted on the behavior of piled raft foundations under independent and combined effects of these loadings. This article aims to summarize these literature works to review the behavior of piled raft foundations under static and dynamic loadings acting in different directions. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
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    Analysis of Cushion Effects in Unconnected Piled Raft Foundation
    (Springer Science and Business Media Deutschland GmbH, 2022) Amalu, P.A.; Jayalekshmi, B.R.
    The piled raft foundations are an economical solution as well as a settlement reducer in the construction of high-rise buildings. Unconnected piled raft foundation is an innovative technique where a cushion separates the pile and raft. The cushion takes the load transferred from the raft and safely distributes over the piles beneath. This article analyses the seismic behaviour of connected and unconnected piled raft foundation of a multistorey building using ANSYS software based on the finite element method. An 8 m × 8 m × 1 m raft and 0.4 m × 0.4 m square concrete piles with depth of 12 m resting on a very soft clay stratum were modelled. The soil block of 16 m × 16 m plan dimension with a depth of 16 m was provided with transmitting boundaries at all lateral edges with properties corresponding to shear wave velocity of clay (150 m/s) and was analysed for the response under the ground motion corresponding to El Centro 1940 earthquake. The building load acting on the raft was considered as a uniformly distributed load of 0.2 MPa. The vertical and lateral displacements at the top of the raft were analysed with cushions having different elastic modulus and thickness. An increase in the elastic modulus of cushion tends to reduce the settlement considerably whereas, a positive correlation was observed between the depth of cushion layer and corresponding settlement. It is evident from the results of the numerical analysis that the stiffness of cushion layer and thickness are two important aspects which determine the displacements of unconnected piled raft systems. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
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    Geofoam integrated separation layer for enhancing seismic resilience in modified piled raft foundations
    (Springer Science and Business Media B.V., 2024) Amalu, P.A.; Jayalekshmi, B.R.
    Modified Piled Raft (MPR) foundations have the potential to reduce seismic force transmission to the superstructure compared to connected piled raft foundations. However, the responses of the separation layer in improving the seismic resilience of the structure were not extensively parameterized before. To address this gap, the investigation explores the potential for enhancing the seismic resilience of MPR foundations in seismically active regions by integrating sustainable materials in the separation layer between the raft and pile group. A novel separation layer is proposed by integrating geofoams with different types of soils. The performance of this novel separation layer is explored through a comprehensive 3D finite element analysis under both static and dynamic loading conditions. Using the OpenSees software platform, an extensive numerical analysis was undertaken to examine the influence of various key parameters on the system's behaviour. A comprehensive analysis of these parameters was conducted to evaluate the responses of MPR foundations with and without geofoam in the separation layer, specifically in the context of ground motion analysis. Raft thickness, pile configuration, separation layer thickness, and the materials used in the separation layer were all considered. The findings indicate that raft thickness and pile length are crucial influencing factors on the dynamic response of the MPR system. Furthermore, the inclusion of EPS geofoam in the separation layer demonstrated its effectiveness in reducing the acceleration amplitude at the top of the raft by 44.25% and lateral displacement by 47.84%, effectively mitigating the impact of seismic waves reaching the upper surface of the raft. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.
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    Influence of Separation Layer Properties on Seismic Response of Modified Piled Raft Foundations
    (Springer, 2025) Amalu, P.A.; Jayalekshmi, B.R.
    Conventional piled raft foundations, with the raft and piles interconnected, severely restrict lateral movement, especially during seismic events. These constraints result in substantial stresses at the connection, posing a risk of potential breakage. Therefore, in seismic-prone areas, where transient lateral loadings of larger magnitudes are expected, conventional piled raft foundations are not feasible. Providing a separation layer between the raft and pile foundations is a viable solution to improve the performance of conventional piled raft foundations. The performance of such a modified piled raft system depends largely on the properties of the separation layer introduced. However, limited studies have been conducted to evaluate the seismic performance of these separation layers by considering the effect of soil–structure interactions. The present study thus aims to investigate the performance of modified piled raft systems by comparing them with their conventional counterpart. The existing conventional piled raft foundation of the Treptower building has been chosen as the prototype and is numerically analysed for static and dynamic loading conditions. Further, a separation layer has been introduced between the pile and raft, and the performance of the modified piled raft foundation is analysed under similar loadings. The results of these analyses are comprehensively compared to ascertain the performance of modified piled rafts under seismic excitation. It is found that the modified piled raft foundation with PE foam in the separation layer is advantageous in damping the propagation of seismic waves to the superstructure, reducing settlement and lateral displacements, and thereby decreasing the potential risk of failure of superstructures in seismic-prone areas. © The Author(s), under exclusive licence to Indian Geotechnical Society 2024.
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    Seismic Analysis of Piled-Raft Foundations in Mid-Rise Buildings on Soft Soil
    (Springer Science and Business Media Deutschland GmbH, 2024) Amalu, P.A.; Jayalekshmi, B.R.
    The utilization of piled-raft foundations is prevalent in buildings constructed on soft soil to mitigate settlement and increase bearing capacity. Nevertheless, if dynamic loading is not suitably considered during the design phase, these foundations may fail. This investigation utilizes three-dimensional finite element analyses in OpenSees to explore the seismic behaviour of mid-rise buildings with piled-raft foundations founded on soft soil. The principal focus of this study is on the influence of soil-foundation-structure interactions (SFSIs) under earthquake loadings. For this purpose, the El-Centro 1979 earthquake was used as the base acceleration underneath the soil layer to simulate the seismic conditions. The study scrutinizes the influence of pile flexural rigidity and superstructure configuration (G + 2, G + 4, G + 7) on the responses of mid-rise buildings on piled-raft foundations under earthquake loading. The findings revealed that buildings with a higher number of floors exhibit larger inter-storey drift with consideration of SFSI. Additionally, an increase in pile flexural rigidity significantly diminishes lateral displacements and shear force during earthquake loading. This study highlights that the flexural rigidity of pile and superstructure configuration are two pivotal factors that determine the response of piled-raft foundations of mid-rise buildings under earthquake loading. Proper consideration of these factors during the design phase can help mitigate the risk of failure and improve the performance of buildings with piled-raft foundations founded in soft soil. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.