The book series entitled Geotechnical, Geologicaland Earthquake Engineering has been initiated toprovide carefully selected and reviewed information from the most recentfindings and observations in these engineering fields.Researchers as well as practitioners in theseinterdisciplinary fields will find valuable information in these book volumes,contributing to advancing the state-of-the-art and state-of-the-practice.This book series comprises monographs, editedvolumes, handbooks as well as occasionally symposia and workshop proceedingsvolumes on the broad topics of geotechnical, geological and earthquakeengineering. The topics covered are theoretical and applied soil mechanics,foundation engineering, geotechnical earthquake engineering, earthquakeengineering, rock mechanics, engineering geology, engineering seismology,earthquake hazard, etc.
Soil Mechanics And Foundation Engineering.epub
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This book also doubles as a textbook with an explanation of basic theory, knowledge, and skills in soil mechanics as well as the most updated codes and standards in China. Also included are guidelines at the beginning of each chapter and English-Chinese-Japanese translations of frequently-used words and expressions in the Appendix. It aims to be a reference book for students and technical staff in civil engineering, hydraulic engineering, mining engineering, and transportation engineering.
Geotechnical engineering has often been challenged by demands from technically and economically bold construction projects, such as that of tall buildings. The architectural requirements of these buildings have increased and concentrated the loads from structural systems without proportionally increasing plant area. New forms of using load capacity and settlement control have been assessed to optimize conventional designs. Thus, piled foundations started to allow for the contribution of block-soil contact, being conceptually named piled raft. In this sense, this study analyzed the contribution of contact in piled foundations composed of one, two, three and four instrumented bore piles 25 cm in diameter (ϕ) and 5 m in length (L). Experimental results showed a 21% average contribution of block-soil in relation to the total piled foundation capacity. This result demonstrates the need to re-evaluate traditional calculation requirements, aiming at rationalizing the geotechnical design and improving the overall safety/stability of the system.
The growth of large urban centers and the verticalization of cities has challenged geotechnical engineering, demanding technically and economically bold projects that meet technical and economic criteria. The architectural requirements of tall buildings are an example for the use of the piled raft technique, which seeks to solve the problem of load increase and concentration arising from structural systems. Thus, piled foundations started to allow for the contribution of block-soil contact, conceptually named piled raft. According to Mandolini et al. (2013Mandolini, A., Di Laora, R., and Mascarucci, Y. 2013. Rational Design of Piled Raft. Procedia Engineering, 57(0): 45-52. Elsevier B.V.doi:10.1016/j.proeng.2013.04.008. ), the piled raft concept considers piles cooperating with rafts instead of being considered an alternative to this shallow foundation element.
Physically, a pile group (or pile block), which is a traditional foundation form, can be considered a piled raft when the connecting block between the piles contacts the soil, thus fulfilling the shallow foundation element role (Sales, 2000Sales, M.M. 2000. Behavior analysis of piled rafts. Civil and Environmental Engineering Department, University of Brasilia, DF, Brazil.).
Several studies have been developed regarding of piled raft foundation. Nevertheless, they are mainly theoretical, numerical or reduced-scale modeled, for example, the studies from Chung et al. (2013Chung, N.D, Kim, D, Jo, S. 2013. Settlement of piled rafts with different pile arrangement schemes via centrifuge tests. Journal of Geotechnical and Geoenvironmental Engineering; 139(10): 1690-8.), De Sanctis e Mandolini (2003Mandolini, A. 2003. Design of piled raft foundations: practice and development. In BAP IV, International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles. Vol.1. pp. 59-80., 2006), Janda et al. (2009Janda, T., Cunha, R. P., Kuklik, P. E Anjos, G.M. 2009. Three-dimensional finite element analysis and back-analysis of CDA standard pile groups and piled rafts founded on tropical soil. Soil and Rocks, Vol. 32, n. 1, p. 3-18.), Leung et al. (2010Leung, Y.F., Klar, A., Soga, K. 2010.Theoretical study on the pile length optimization of pile groups and piled rafts. Journal of Geotechnical and Geoenvironmental Engineering; 136(2): 319-30.), Makarchian and Poulos (1994Makarchian, M., Poulos, H.G. 1994. Underpinning by piles: A numerical study. In: Proceedings of the 13th International Conference on Soil Mechanics and Foundation Engineering, Vol.4. New Delhi. p. 1467-70.), Mandolini et al. (2013), Novak et al. (2005Novak, J.L., Reese, L.C., Wang, S.T. 2005. Analysis of pile-raft foundations with the 3D finite element method. In: Structures Congress 2005: Metropolis and Beyond. ASCE. (171)93. (171)93... ), Omeman (2012Omeman, Z.M. 2012. Load sharing of piled-raft foundations in sand subjected to vertical loads. PhD Thesis. Montreal, Canada: Concordia University. 131p.), Poulos (2001), Poulos et al. (2011), Russo et al. (2013Russo, G., Poulos, H. G., Small, J. C. 2013. Re-assessment of foundation settlements for the Burj Khalifa, Dubai. Acta Geotéchnica, v. 8, p. 3-15.) Viggiani et al. (2012Viggiani, C., Mandolini, A., Russo, G. 2012. Piles and Pile Foundations. Editora: Spon Press - New York - USA. 278p.).
Preliminary stage: analyzes the feasibility of a piled raft. The design performance is evaluated without the piles. Estimates of vertical and lateral load, and maximum and differential settlements are made using conventional techniques. The philosophy of the project is chosen considering the load that the horizontal element (raft) can receive. If the horizontal element contributes to a small load capacity percentage of the foundation element, then the philosophy adopted will tend towards a conventional approach. If the top presents adequate resistance - or close to load capacity -, but does not meet total or differential settlement criteria, then the piles should be considered as settlement reducers or be adopted as totally mobilized. Load capacity is evaluated based on failure type, which may occur in individual piles or over the entire soil block. In failure analysis for individual piles, load capacity is the sum of pile resistance and contact caused by the raft, and can be described by the following general formula:
Second stage: evaluates general characteristics of the piles and where these are required. This study is more detailed. The pile requirement is based on foundation loading, in the following situations: at the moment and shear maximum efforts that exceed the allowable structural value of the horizontal element; contact pressure exerted by the horizontal element on the soil exceeds its allowable value; the total settlement is greater than the allowable value.
The geological-geotechnical profile, and the mean parameters for each soil layer were previously obtained through laboratory tests conducted by Gon (2011Gon, F.S. 2011. Caracterização geotécnica através de ensaios de laboratório de um solo de diabásio da região de Campinas/SP. Dissertação de Mestrado. Faculdade de Engenharia Civil, Arquitetura e Urbanismo, Universidade Estadual de Campinas, Brazil.). The mean parameters for the layers were obtained through SPT and CPT tests. The results for the characterization stage of the subsurface in relation to the analyzed piled raft foundations enabled the elaboration of the geological-geotechnical profile of the local subsurface and the identification of the position of the block and piles that are grounded on the sandy silt layer at 2.35 m above the clayey sand layer (Figure 5).
The interaction factor obtained for the piled foundations presents αrp values that are different from those observed by Clancy & Randolph (1992Clancy P. and Randolph M.F. (1992), Analysis and Design of Piled Raft Foundations, Research Report No. G1062, Department of Civil Engineering, The University of Western Australia.), since the area and geometry of piled foundations used in this research are variable (Figure 28). The interaction between piles and the raft decreases as the number of piles increases, since the area of contact with the soil increases.
The plan area inertia of the raft tends to exert influence on the stiffness of the shallow foundation element and on the way, it distributes the loads for the pile group and for the soil. Despite this influence, the contribution from raft-soil contact was 14.4%, 27.5%, 22.4% and 21.3% for piled foundations with one, two, three and four piles, respectively (Figure 29).
The piled raft foundation system, i.e., when the piled foundation considers strength from block-soil contact in its dimensioning, it presents superior load capacity to the conventional system using pile groups;
For piled raft foundations composed of piles spaced with five times their nominal diameter, the contribution of contact was around 21%, showing that even for porous soils, block-soil contact aids in improving load capacity;
The loading capacity of piled rafts increased concomitantly with the increase in the ratio between the net area of soil-block contact and the total foundation plan area (Anet/Atotal). However, this cannot be established generally, since it also depends on the number of piles that compose the group and on the resistance characteristics