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S. J. Shukla ¹, A. K. Desai ¹, C. H. Solanki ¹

Affiliations
1 Applied Mechanics Department, Sardar Vallabh Bhai National Institute of Technology, Surat, Gujarat., IN

Abstract

A raft foundation transfers load directly on subsoil. The concept of piled raft foundation combines the pile, raft and subsoil as load bearing elements and composite structure. In this foundation the piles usually are not required to ensure the overall stability of the foundation but to reduce the magnitude of settlements, differential settlements and the resulting tilting of the building and guarantee the satisfactory performance of the foundation system. The bearing behaviour of a piled raft foundation is characterized by complex soil-structure interactions (Katzenbach et al. 1998). The modelling of these interactions requires a reliable and powerful analysis tool, such as the Finite Element Method in combination with a realistic constitutive law. Different researches have been realized investigations about the numerical modelling of piled rafts with FE analysis and different constitutive models. The present research combines the 3D modelling with a modern and realistic constitutive model. An increasing number of structures, especially tall buildings are founded on piled rafts (O'Neil et al. 1996; Katzenbach et al. 2000, Poulos 2001). For this reason, it is important to develop a methodology to study the bearing behaviour of piled rafts. In this paper author had tried to study the effect of subsoil on the dynamic behaviour of 25 storeys building with pied raft foundation during low to medium intensity earthquake. The results are generated for different height of the structure in the terms of displacement and acceleration response.

Keywords

Settlement, Soil Structure Interaction, Sub Grade Reaction

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Y. K. Tandel ¹, J. B. Baruah ², S. Budde ², S. Kumar ², C. H. Solanki ², B. G. Patel ³

Affiliations
1 Applied Mechanics Department, Government Engineering College, Dahod 389 151, IN
2 Civil Engineering Department, Sardar Vallabhbhai National Institute of Technology, Surat 395 007, IN
3 Civil Engineering Department, GIDC Degree Engineering College, Navsari 396 406, IN

Abstract

Stone column (SC) or granular column is widely used as a soil improvement method for flexible foundations such as oil storage tanks, embankments and rigid foun­dations. The confining pressure exerted by the surrounding soil allows the SC to develop its bearing capacity. The soft soil surrounding a SC may not provide sufficient lateral confinement. So, the design bearing carrying capacity may not be achieved. In such soils, a pervious concrete column (PCC) may be applied which deals with reinforcement as well as drainage. PCC can be constructed up to the full depth of soft soil or on the upper portion of a stone column up to which bulging is predominant. This study presents a parametric analysis of the performance of SCs, PCCs and composite columns (CCs) using three-dimensional numerical analyses. The parameters consider are: PCC diameter, PCC length in CCs surrounding soft clay cohesion, and full PCC length. Furthermore, the load transfer mechanism of pervious concrete is compared to that of a SC. In comparison to ordinary SCs, the findings of this study show that pervious concrete columns have a substantially better load carrying capacity and experience less lateral displacement. Furthermore, in a CC, the length of pervious concrete up to four times the column diameter may be sufficient to enhance the load carrying capacity of an ordinary SC.

Keywords

Finite element analyses, land carrying capacity, pervious concrete column, soil improvement, stone column.

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Chandra Bogireddy ¹, C. H. Solanki ¹, S. A. Vasanwala ¹

Affiliations
1 Applied Mechanics Department, S. V. NIT, Surat - 395007, Gujarat, IN

Abstract

Objectives: Tropical residual soils are widely available in the southern part of India and the construction in this type of soils more challenge issue to the geotechnical engineers to design the structure in the settlement criteria. Analysis: Tropical residual soils are in general are regarded as multi component, polyphase, and particulate system with compositional and/ or structural discontinuities. Both index and engineering properties of natural soils primarily depend on mineralogy and percentage of fine fraction. Findings: In this paper, eight soil samples are considered for to obtain the influence of the fine fraction on shear parameters and consolidation behavior of tropical residual soils in Tirupati region. Shear strength tests and one-dimensional compression tests have been conducted apart from the classification and identification tests. Application/ Improvement: Based on the experimental test results and analysis, it has been found that the percentage fine fraction has a greater significant influence on engineering properties like cohesion, angle of internal friction and compression index of tropical residual soils.

Keywords

Compression Index, Fine Fraction, Shear Parameters, Scanning Electron Microscopy, Tropical Residual Soil.

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V. J. Sharma ¹, S. A. Vasanvala ¹, C. H. Solanki ¹

Affiliations
1 Department of Applied Mechanics, Sardar Vallabhai National Institute of Technology, Ichchhanath, Surat-395007, Gujarat, IN

Abstract

In order to mobilize shallow soil to participate in the interaction of piled raft foundation sufficiently, the concept of piled raft has been modified to new type of foundation named composite piled raft. In the system of composite piled raft, the short piles made of flexible materials were used to strengthen the shallow soft soil, while the long piles made of relatively rigid materials were used to reduce the settlements and the cushion beneath the raft was used to redistribute and adjust the stress ratio of piles to subsoil. In traditional foundation design, it is customary to consider first the use of shallow foundation such as a raft (possibly after some ground-improvement methodology performed). If it is not adequate, deep foundation such as a fully piled foundation is used instead. In the former, it is assumed that load of superstructure is transmitted to the underlying ground directly by the raft. In the latter, the entire design loads are assumed to be carried by the piles. In recent decades, another alternative intermediate between shallow and deep foundation, what is called piled raft foundation or settlement reducing piles foundation, has been recognized by civil engineers. The concept of piled raft foundation was firstly proposed by Davis and Poulos in 1972, since then it has been described by many authors, including Burland et al. (1977), Cooke (1986), Chow (1987), Randolph (1994), Horikoshi and Randolph (1996), Ta and Small (1996), Kim et al. (2001), Poulos (2001), and many others. Now the piled raft concept has been used extensively in Europe and Asia. In this concept, piles are provided to control settlement rather than carry the entire load. Piled raft foundation has been proved to be an economical way to improve the serviceability of foundation performance by reducing settlement to acceptable levels. The favourable application of piled raft occurs when the raft has adequate loading capacities, but the settlement or differential settlement exceed allowable values. Conversely, the unfavourable situations for piled raft include soil profiles containing soft clays near the surface, soft compressible layers at relatively shallow depths and some others. In the unfavourable cases, Finite element method was applied to study the behaviour of this new type of foundation subjected to seismic forces. This paper focuses on behaviour of various components of foundation system such as long pile, short piles and subsoil under seismic force (Koyna 1967) in layered soil related to Surat city geological condition. A comparative study is done to understand the effect of cushion on axial stresses, shear stresses and shear forces along long pile and short piles.

Keywords

Piles, Raft, Foundation, Analysis.

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