An Investigation of Factors Affecting the Design of Model Piled Raft Foundations in Laboratory

Year 2019, Volume: 3 Issue: 1, 35 - 41, 15.07.2019

Rahim Kağan Akbulut , Özcan Tan

Abstract

Piled raft foundation applications are a combined foundation application which is being used frequently today. There are a limited number of studies on the model piled loading tests in the literature. In addition, in the past pile loading experiments, especially in model piled raft experiments; pile tip, skin friction and loads covered by the raft cannot be reliably measured. In the light of the previous studies, large scale model tests were performed in order to minimize boundary effects. In the study, the model piles were manufactured from concrete, like the actual situation, in the soil region where the pile will be formed, thus preventing different environmental conditions from affecting the pile design. Within the scope of this study, the model piled rafts on a sandy soil were axially loaded in the laboratory and the load-settlement curves and the raft load-sharing percentage curves were obtained depending on the settlement ratio. In this experimental study the experiments, the model piles of different lengths (L = 320 mm and 520 mm) and diameters (D = 50 mm and 60 mm) and different raft sections (150x150 and 200x200 mm) were prepared in sand bed. These model piles and rafts are combined with the load cell and model piled rafts are obtained in the middle under the raft and two piles in the corner. Piled rafts were loaded into the model tank by placing two different relative densities such that the test sand was loose (Dr: 27%) and dense (Dr: 65%). The model test results of the study showed that the raft foundation contributes to the total load that the system can carry. In the piled raft foundation system, it was seen that the load was initially carried by the raft and the load was transferred to the piles in very small settlement levels. It has been determined that the raft has a ratio of 25-40% of the total load. The load-sharing ratio corresponding to the 40mm settlement of the raft and the load-sharing ratio corresponding to 1mm settlement increased by 30- 100%.

Keywords

Model piled raft, Sand soil, Loading test, Raft load sharing percentage

References

• [1] Poulos HG. Piled Rafts in Swelling or Consolidating Soils. Journal of Geotechnical Engineering (1993) 119(2):374–380. doi:10.1061/(ASCE)0733-9410(1993)119:2(374).
• [2] Mendonça AV, Paiva JB de. A boundary Element Method for the Static Analysis of Raft Foundations on Piles. Engineering Analysis with Boundary Elements (2000) 24(3):237–247. doi:10.1016/S0955-7997(00)00002-3.
• [3] Prakoso WA, Kulhawy FH. Contribution to Piled Raft Foundation Design. Journal of Geotechnical and Geoenvironmental Engineering (2001) 127(1):17–24.
• [4] Small JC, Zhang HH. Behavior of Piled Raft Foundations Under Lateral and Vertical Loading. International Journal of Geomechanics (2002) 2(1):29–45. doi:10.1061/(ASCE)1532-3641(2002)2:1(29).
• [5] Tan YC, Chow CM. Design of Piled Raft Foundation on Soft Ground. In: GSMIEM Forum: The Roles of Engineering Geology & Geotechnical Engineering in Construction Works. Kuala Lumpur, Malaysia: University of Malaya, Department of Geology (2004).
• [6] Poulos HG. Piled Raft and Compensated Piled Raft Foundations for Soft Soil Sites. In: Vipulanandan C, Townsend FC, editors. Geo-Frontiers Congress (2005). p. 214–235.
• [7] Liang F, Chen L, Han J. Integral Equation Method for Analysis of Piled Rafts With Dissimilar Piles Under Vertical Loading. Computers and Geotechnics (2009) 36(3):419–426. doi:10.1016/j.compgeo.2008.08.007.
• [8] Mu L, Huang M, Finno RJ. Tunnelling Effects on Lateral Behavior of Pile Rafts in Layered Soil. Tunnelling and Underground Space Technology (2012) 28:192–201.
• [9] Cao XD, Wong IH, Chang M-F. Behavior of Model Rafts Resting on Pile-Reinforced Sand. Journal of Geotechnical and Geoenvironmental Engineering (2004) 130(2):129–138.
• [10] Khoury MC, Alzamora AJ, Ciancia AJ. A Piled-Raft Foundation for the Tallest Building in Brooklyn. In: Han J, Alzamora DE, editors. Geo-Frontiers Congress 2011 (2011). p. 3818–3827.
• [11] Akbulut RK. Kazıklı Radye Temellerin Tasarımını Etkileyen Faktörlerin Araştırılması [Investigation of Factors Affecting Design of Piled Raft Foundations]. PhD Thesis. Selcuk University. Konya (2014).
• [12] ASTM D 3080-98. Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions. West Conshohocken, PA: ASTM International (1998). doi:10.1520/D3080_D3080M.