Analysis of Raft Foundation with EPS Geofoam for Earthquake Resistant

Applied Mechanics and Materials Vol 695 (2015) pp 613-616 © (2015) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.695.613 Submitted: 2014-09-02 Revised: 2014-09-13 Accepted: 2014-09-13 Online: 2014-11-07 Analysis of Raft Foundation with EPS Geofoam for Earthquake Resistant Mohd Faiz Mohammad Zaki 1, a, Mohammad Fadzli Ramli 2, b, Afizah Ayob 1, c and Mohd Taftazani Ahmad 1,d School of Environmental Engineering, Kompleks Pusat Pengajian Jejawi 3, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia Institute of Engineering Mathematics, Universiti Malaysia Perlis, Kampus Pauh Putra, 02600 Arau, Perlis, Malaysia a faizzaki@unimap.edu.my, bmfadzli@unimap.edu.my, c afizah@unimap.edu.my, d mohdtaftazani89@gmail.com Keywords: EPS, raft foundation, finite element method Abstract It is becoming a great challenge for civil engineers to design a foundation which able to minimize the effect of an earthquake A major earthquake produces a strong ground motion in the subsoil and surface structures supported on the soil mass will be induced to move and absorb the dynamic forces Seismic retrofit of existing foundations is an alternative However, the modification of this existing foundation toward earthquake resistances raises issues which are far from being totally resolved Innovative material such as Expended Polystyrene (EPS) Geofoam is widely accepted in structural engineering due to its characteristic to absorb the dynamic force effectively This EPS material demonstrated the practicality and has been applied for geotechnical engineering for various reasons Based on this, a research which is related to the application of EPS in mitigating the earthquake forces, particularly for raft foundations was conducted properly in this research The various types and thickness of EPS located beneath the raft foundation and over the soft soil are studied A finite element program is utilized to develop the computer simulation models Based on the results, EPS placed beneath the raft foundation is able to produces the minimum settlements when subjected to earthquake loading rather than raft foundation modeled without EPS and increasing the density of EPS will simultaneously decrease the settlement of a foundation Introduction Design of foundations still remains a challenging task for the earthquake geotechnical engineer One of the main reasons is originated from the complexity of the geotechnical problem which requires fundamental knowledge in soil mechanics, foundation engineering, soil-structure interaction and earthquake engineering A parallel between static design and seismic design reveals some similarity but also very marked differences Static design of foundations put much emphasis on the bearing capacity problem with the introduction of an appropriate safety factor, close to 3, the short term settlements were deemed to be acceptable for the structure It is only with the increase in the understanding of soil behavior and the development of reliable constitutive models that sound predictions of settlements could be achieved [1] Building foundations working satisfactorily under static loading may be affected when the shear stress in the subsoil induced by the earthquake added to the already existing static shear stresses reach the shear strength of the soil In case of cohesionless fine sediments, the shear strength properties may be stringly affected during the transient seismic forces mainly when the irrotational waves act at the time of the shear waves The irrotational wave inducing high pore water pressures in the soil will reduce the shear strength of the soil Therefore, in cohesion less soils their action cannot be overlooked [2] All rights reserved No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net (ID: 130.216.129.208, University of Auckland, Auckland, New Zealand-24/06/15,22:50:08) 614 Advanced Research in Materials and Engineering Applications Material and Methodology For this research, the type of soil focussed on the clay soil and its properties as given in Table below Table 1: Clay properties EPS is not a common soil fill replacement materials but invented indirectly to solve geotechnical engineering challenges The used of EPS typically translate into benefits to construction schedules and lower the overall cost of construction because it is easy to handle during the construction EPS geofoams are used for thermal insulation, lightweight fill, and small-amplitude wave damping [3] EPS geofoam is available in numerous material types that chosen by many designer for a specific application Based on ASTM International [4], EPS densities vary for practical civil engineering applications The material properties of EPS Geofoam used in this study are given in Table Simulation of raft foundation and EPS geofoam has shown in Figure Table 2: EPS properties EPS Figure 1: Raft foundation and EPS simulation Results and Discussions This result based on earthquake analysis and immediately after 30 second of the earthquake occurrence, the reading was recorded for the vertical displacement at Point C and D (without EPS) as shown in Figure This figure represents the graph Displacement versus Time Based on the graph, there is a significant change of displacement at point C starting at the first moment The value is 1.8 mm and after second, the displacements value became constant For point D, changes in displacement can considered as constant since it is resulted in insignificant changes It can be concluded from the analysis that the foundation was tilt and unstable Applied Mechanics and Materials Vol 695 615 Figure 2: Deformed shape for Case Study I Graph for vertical displacement versus time is taken at Point C since it has contributed the significant effect towards the stability of the foundation and it was studied for EPS19 with different thickness According to the pattern graph below (Figure 3), EPS located beneath the raft foundation provide a good result in maintaining the stability of the foundation EPS19 with thickness of m able to reduce the vertical displacement while comparing to the other thicknesses Figure 3: Vertical Displacement versus Time (EPS19) Result of settlement for EPS22 as shown in Figure The result is similar to EPS19 and the value obtained for the settlement is much lower than EPS19 Figure 4: Vertical Displacement versus Time (EPS22) 616 Advanced Research in Materials and Engineering Applications Result for EPS29 as shown in Figure below The pattern of result is similar to EPS19 and EPS22 where the same thickness of m presents the minimum settlement value compared to EPS19 and EPS22 The vertical displacement by using this type of EPS is approaching mm The actual maximum value is 0.05 mm Figure 5: Vertical Displacement versus Time (EPS29) Conclusion Conclusively, Expended Polystyrene (EPS) Geofoam that placed beneath the raft foundation and exposed to earthquake loading able produces the minimum settlements rather than raft foundation modeled without EPS Based on the results, increasing the density of EPS will decrease the settlement of a foundation Acknowledgment This research work is supported by the Fundamental Research Grant Scheme (FRGS), Malaysia Grant Number: 9003-00359 References [1] A Pecker, Advance Earthquake Engineering Analysis, Springer Wien New York, France, 2007, pp 43-59 [2] Z Leonardo, Foundation Engineering Handbook, Mexico, Springer Science, Lehigh University, 1991, pp 673-678 [3] Aytekin, Numerical modelling of EPS geofoam used with swelling soil, Geotextiles and Geomembranes 15 (1997), 133–146 [4] ASTM International, D6817; Standard Specification for Rigid Cellular Polystyrene Geofoam, West Conshohocken, United States, 2013 Advanced Research in Materials and Engineering Applications 10.4028/www.scientific.net/AMM.695 Analysis of Raft Foundation with EPS Geofoam for Earthquake Resistant 10.4028/www.scientific.net/AMM.695.613 DOI References [3] Aytekin, Numerical modelling of EPS geofoam used with swelling soil, Geotextiles and Geomembranes 15 (1997), 133-146 http://dx.doi.org/10.1016/S0266-1144(97)00010-1 ... 10.4028/www.scientific.net/AMM.695 Analysis of Raft Foundation with EPS Geofoam for Earthquake Resistant 10.4028/www.scientific.net/AMM.695.613 DOI References [3] Aytekin, Numerical modelling of EPS geofoam used with swelling... properties of EPS Geofoam used in this study are given in Table Simulation of raft foundation and EPS geofoam has shown in Figure Table 2: EPS properties EPS Figure 1: Raft foundation and EPS simulation... the raft foundation and exposed to earthquake loading able produces the minimum settlements rather than raft foundation modeled without EPS Based on the results, increasing the density of EPS