Experimental Investigation of piled raft foundation on Cohesionless Soil

International Journal of Research and Scientific Innovation (IJRSI) | Volume IX, Issue II, February 2022 | ISSN 2321–2705

Experimental Investigation of piled raft foundation on Cohesionless Soil

Aruna T ¹, K.V.S.B Raju ², Swathi Gowda^3
1Research scholar, Department of Civil Engineering, UVCE -Bengaluru
²Associate Professor, Department of Civil Engineering, UVCE-Bengaluru
³ME student, Department of Civil Engineering, UVCE-Bengaluru

ABSTRACT
The combination of piles and raft foundation is known as piled raft foundation. Piled raft foundations have proven to be more cost-effective and capable of meeting safe bearing capacity and serviceability norms in the case of high-rise buildings on cohesionless soil. The behavior of a stacked raft foundation is influenced by the piles, raft, and soil. The stacked raft system’s bearing capacity is improved and settlement is minimized when the ground beneath the raft foundation bears the burden of supporting the applied loads. The piled raft foundation minimizes total settlement and improves bearing capacity more than the raft foundation.

When isolated footings cover more than 70% of the building area under a superstructure, raft foundations are used, and the present study focuses on the vertical load bearing capability of piled raft foundation systems on cohesionless soil for concentric loading. The use of strategically positioned piles increases the load capacity of the raft while reducing differential settlement. The present study sheds some light on the use of piles as raft foundation settlement reducers, as well as the behavior of a piled raft in sand. A series of small-scale model experiments were carried out. The present investigation studies by varying pile length and alignment on the ultimate load of piled raft foundation. The results indicate that for a 10mm raft thickness, installing 4 piles, 6 piles, and 9 piles by varying L/D ratios of 5,10,15,20 carries significant load. In this present work for a 50mm length of pile, and the value of load improvement ratio increases by 36 percent, 60 percent, and 68 percent, respectively, when compared to plain raft.

Keywords: Piled raft foundation, cohesion less soil, Load improvement ratio

INTRODUCTION: The term “piled raft foundation” describes a foundation that uses both piles and rafts. Piled raft foundations have proven to be more cost-effective and capable of meeting safe bearing capacity and serviceability standards in the case of high-rise buildings on clay. The behavior of a piled raft foundation is determined by the piles, the raft, and the soil. Due to the intricate interaction between the piles and their cap with the soil, the applied loads are assumed to be carried solely by piles, with no contribution given to the soil beneath the raft when building a pile group. This interaction improves the bearing capacity of the piled raft system and lowers settlement when the earth beneath the raft foundation shares in carrying the applied loads. The piled raft foundation minimizes total settlement and enhances bearing capacity more than the pile groups and raft foundation from the previous study, according to the findings.
When raft (mat) foundations are supported by a piling group, they have been demonstrated to be capable of supporting extremely large loads. When estimating the contribution of both raft and piles to carrying the surcharge loads, the stiffness and strength of the soil linked elements in the system, i.e. piles, raft, and surrounding soil, are taken into account. When the focus of the research is on the vertical load bearing capability of a piled raft foundation system on soil for both concentric and eccentric loading. Raft foundations are employed when isolated footings occupy more than 70% of the building area under a superstructure. The use of strategically positioned piles increases the load capacity of the raft while reducing differential settlement. This research sheds some information on the use of piles as raft foundation settlement reducers, as well as the behavior of a piled raft in sand. Small-scale model experiments are carried out. Experimentally, the effects of pile length and alignment on the ultimate load achieved are investigated. [1] Eslami et al., (2011): Three case studies of connected and non-connected pile-raft systems are explored using finite element analysis to see how different parameters, such as pile spacing, embedment length, piling configuration, and raft thickness, affect the design. [2] El-Garhy, B et al., (2011): studied the raft behavior on Settlement Reducing Piles, and found that raising the subsoil stratum stiffness can greatly reduce settlements and raft internal bending moments in non-connected piled-raft systems.[3] Gahlot et al., (2018), analyzed the effect of different length in pile raft foundation. The layout and combinations shown to be crucial in achieving the desired settlement reduction and load sharing with the smallest number of piles in the design on load carrying capability. [4] Poulos et al., (2011), analyzed the effect of soil subgrade reaction and stiffness on the settlement and bending moment. [5] Jaymin D Patil (2014) The impact of pile numbers and raft thickness on load improvement and settling reduction ratios is provided and explored. The tests reveal that as the number of piles beneath the raft rises, the load improvement ratio and settlement reduction ratio also, while the proportion of weight borne by the raft declines. In addition, increasing raft thickness has a modest influence on load improvement ratio and settlement reduction ratio, while raft thickness has a small effect on the load carried by the raft.

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