International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 12 Issue: 05 | May 2025
p-ISSN: 2395-0072
www.irjet.net
EFFECT OF PILE LENGTH ON THE BEHAVIOR OF PILE RAFT FOUNDATION Mahmoud AboBbakr Elsediak1, Ahmed Hussain zaki2 and Tarek NaguibRadwan3 Faculty of Engineering, Alazher universty, Cairo, EGYPT -------------------------------------------------------------------------***-----------------------------------------------------------------------ABSTRACT: This study investigates the influence of pile length on settlement and straining actions of a piled raft foundation and load-sharing mechanism between piles and the raft. Finite element analysis using PLAXIS 3D and SAP 2000 was conducted to study key parameters such as settlement, bending moment, shear force, and load distribution. It can be observed from the results that with an increase in pile length from 8m to 12m, the settlement reduces by 42%,, while further extension to 14m and 16m results in diminishing returns with reductions of 12.7% and 9.97%, respectively. Regarding bending moment, an increase in pile length from 8m to 12m decreases it by 4.7%, while extending from 12m to 16m results in an additional 5% reduction. Similarly, the raft shear force decreases by 5.26% when pile length increases from 8m to 12m, with marginal reductions beyond that. The load-sharing analysis reveals that at 8m pile length, the raft carries 38% of the total load, which reduces to 22% at 12m and 14m, and 19% at 16m, demonstrating the increasing reliance on piles for load-bearing. The study highlights the optimal pile length for maximizing settlement reduction and efficient load distribution, offering practical guidance for foundation design improvements. Keywords: (Pile length, Settlement,Bending moment, Shear force, Load distribution)
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INTRODUCTION
load behavior plays a key role in the estimation of settlement behavior and long-term foundation stability., the American Society of Civil Engineers (ASCE) has also developed simplified design methods for piled raft foundations, which are highly effective tools at preliminary design levels.These methods enable simple estimation of load sharing between piles and raft, enabling engineers to design the foundation system with respect to performance as well as cost. Thus successful use of piled raft foundations involves a holistic understanding of the relationship between structural members and geotechnical conditions.
.Piled raft foundations are an advanced geotechnical solution in which the load-carrying capacity of piles and rafts interacts synergistically to effectively transfer structural loads to subsurface strata. This hybrid system is particularly useful in optimizing foundation performance, especially in cases where sole raft foundations may be inadequate due to excessive settlement or inadequate bearing capacity. Design and behavior of piled raft foundations are based on several important parameters:Pile Length and Diameter: The diameter and length of piles are essential in determining the capacity of the load and settlement of the foundation. Piles are longer, since they extend deeper into competent strata, causing higher stability and lower settlements. Similarly, pile diameter increase enhances the contact area between the pile and the soil, enabling better load transfer and further minimizing settlement issues.Raft Thickness: Raft thickness plays a significant role in determining the overall stiffness of the foundation system. A thicker raft can distribute loads more evenly and reduce differential settlements within the structure. But the raft thickness must be balanced to avoid excessive material consumption and self-weight, which could adversely affect the foundation performance. Soil Characteristics: The soil properties and type below the foundation play a significant role in determining the design and performance of piled raft systems. Variations in soil stiffness, density, and stratification necessitate comprehensive geotechnical investigations toin form design decisions. Understanding
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By exercising diligent consideration of matters like pile diameter, raft thickness, and soil type, and by strict adherence to current American standards and codes, engineers are able to successfully design foundations that are both strong and efficient in a way that ensures the strength and safety of the structures to be supported. The objective of the research is to study the effect of increase in pile length and its penetration into dense ground on piled raft foundation behavior. The objective of the research is to determine the effect of the increase in pile penetration in high-strength soil on the piles and raft load distribution, and to study its effect on the foundation behavior regarding settlement, bending moment, and shear force. By finite element analysis, the research seeks to determine the pile length that is optimum in that it achieves enhanced stability and minimized settlement as well as less pressure on the raft and improved load distribution between the raft and
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