Foundation Settlement Determination: A Simplified Approach By Adewoyin, O. O., Joshua, E. O., Akinyemi, M. L. Omeje, M., and Joel, E. S. from Covenant University, Ogun State Nigeria
Content of Presentation Introduction Methodology Results and discussion Conclusion
Introduction The problem of foundation settlement due to dynamic load has attracted the attention of researchers since the sixties (Prakash et al ., 2014). Determination of the level of settlement of foundation in soil layer is one of the major challenges confronting the building industry. This is because, it may be one of the factors contributing to some of the building collapse rampant in our country of late (Amadi et al ., 2012; Oyedele et al ., 2012).
Introduction Cont’d Efforts have been made by earlier researchers to determine the rate of settlement of foundations. These methods are mainly theoretical and as such may be difficult and not applicable in all cases. Choobbasti et al ., (2010) confirmed the possibility of numerically evaluating the bearing capacity and settlement of ring footing. Kuo et al ., (2015) examined the settlement of footing founded on two-layered soil profile.
Introduction Cont’d Also, Shahnazari et al ., (2013) showed that it is possible to predict the settlement of shallow foundations on cohesionless soils. Foundation settlement assessment requires that detailed information on the following are available; soil profile, pore water regime, influence of fills,
Introduction Cont’d…… loads from other foundations, excavation and changes in groundwater table (Akintonrinwa and Adesoji, 2009; Das, 2007). This process may be cumbersome, costly and time consuming.
Introduction Cont’d In this research effort, both geophysical (seismic refraction) and geotechnical (cone penetration test) methods were combined. This was carried out in order to proffer a faster and easier method of determining the rate of settlement possible in different soil layers. This study would help civil engineers and those in building industry to make informed decisions on the type and the kind of materials required for foundations and the depth at which foundations must be sited.
Research Methodology Seismic Refraction Method In this study, a total of four seismic profiles were surveyed and the data acquired. A 24-Channel ABEM Terraloc MK 6 seismogram was used for the data acquisition (ABEM Instrument, 1996).
Fig 1 The principles of seismic refraction method (from eo-miners, 2016).
Research Methodology Cont’d…… The profile varied in length between 50 m and 100 m as a result of accessibility (Egwuonwu and Osazuwa, 2011; Bery and Saad, 2012). 2 m geophone spacing was adopted for better coverage of the refractor surface, multiple shots were taken at each shot point along the profile (Reynolds, 1998). The energy source used is a 15 kg sledge hammer and the resulting shots were stacked so as to produce clearer images of the subsurface.
Research Methodology Cont’d…… The essence of the seismic refraction method is to obtain information on the number of layers present in the subsurface, the thickness of each layer and the primary and shear wave velocity. This information can easily be used with various equations in literature to determine the geotechnical parameters of each layer such as the bulk modulus, Young’s modulus, shear modulus.
Research Methodology Cont’d… Cone Penetration Test The cone penetration tests were carried out using 2.5 ton Shell and Auger Penetrometer machine. In this technique a cone tip iron rod of 1 m length each was driven into the subsurface and the resistance of the subsurface to the driving force was measured. This was used to obtain information on the shear strength and the allowable bearing capacity of the subsurface (Hunt, 2005; Das, 2007).
Research Methodology Cont’d… The seismic refraction data was processed using seisImager software (SeisImager, 2009) to obtain 2D seismic refraction image. The cone penetration test result was plotted on a graph using Microsoft excel.
Fig 2 Base map of the study site showing the seismic profiles and the CPT points
2-D Seismic Results and discussion
2- D Seismic Results and discussion Cont’d….. The seismic results delineated two layers with the p- wave velocity ranging between 373 and 554 (m/s). The depth of penetration of the seismic wave ranged between 7.0 and 8.7 m into the subsurface. Dry density-16.746-17.108 kN/m 3
2-D Seismic Results and discussion Cont’d… Shear modulus- 0.081-0.147 (GPa) Young’s modulus - 0.202-0.455 (GPa)
Cone Test Results and discussion Cont’d
CPT Test Results and discussion Cont,d …. The bearing capacity was determined from which the average bearing capacity was also determined within the depth of investigation The average bearing capacity- 2247-4882 (kN/m 2 ) This result was related with the Young’s modulus to determine the settlement possible for each profile.
Results and discussion Cont’d i q f (1) n 1 q a f n q a f (2) d V t s E
Conclusion Seismic refraction and cone penetrometer methods of investigation have been used to characterize the site in the study in order to develop a simplified and faster method of determining the rate of settlement of geomaterial for the purpose of construction. The result showed that the rate of settlement in soil varies in response to the condition of the geologic formation. The rate of settlement for the four profiles varied between 0.019 m and 0.035 m.
Acknowledgements The authors wish to appreciate the management of covenant university for providing financial support for this research work.
References Amadi, A. N., Eze, C. J., Igwe, C. O., Okunlola, I. A. and Okoye, N. O. (2012): Architects and Geologists view on the causes of building failures in Nigeria. Modern Applied Science , 6 (6): 31-37. Akintorinwa, O. J. and Adesoji, I. J. (2009): Application of geophysical and geotechnical investigations in engineering site evaluation. International Journal of Physical Sciences , 4 (8): 443 – 454. Chobbasti, A. J., Hesami, S., Najafi, A., Pirzadeh, S. Farrokhzadi, F. and Zahmatkesh, A. (2010): Numerical evaluation of bearing capacity and settlement of ring footing; case study of Kazeroon cooling towers. International Journal of Research and Reviews in Applied Sciences , 263-271. Das, B. M. (2007): Principles of foundation engineering. 6 th Edition. Thomson, p. 90-91.
References cont’d……… Egwuonwu, G. N. and Osazuwa, I. B. (2011): Geophysical and geotechnical investigation of the origin of structural instabilities shown on some low rise buildings in Zaria, north-western Nigeria. Pacific Journal of Science and Technology , 12 (2): 534-547. EO-Miners (2016): [sourced on 8/03/2016] @ www.eo- miners.eu/earth_observation/eo_ref_eom_geophysical.htm. Hunt, R. E. (2005): Geotechnical engineering investigation handbook. 2 nd edition, Taylor and Francis, 1-3. Kuo, Y. L., Jaksa, M. B., Kaggwa, W. S., Fenton, G. A., Griffiths, D. V., Goldsworthy, J. S. (2015): Probabilistic analysis of multilayered soil effects on shallow foundation settlement . Proceedings of 9 th Australia New Zealand Conference on Geomechanics, Auckland, 541-547. Oyedele, K. F., Oladele, S. and Okoh, C. (2012): Geo-assessment of subsurface conditions in Magodo Brook estate, Lagos, Nigeria. International Journal of Advanced Scientific and Technical Research , 4 (2): 731-741.
References Cont’d……… Prakash, S., Puri, V. K. and Kumar, S. (2014): Seismic settlement of shallow foundations. Proceedings of the 10 th National Conference in Earthquake Engineering, Earthquake Engineering Research Institute, Anchorage, AK. Reynolds, J. M. (1998): An introduction to applied and environmental geophysics. Wiley, p. 417 – 450. SeisImager, 2009. SeisImager/2D TM Manual Version 3.3 Shahnazari, H., Shahin, M. A. and Tutunchian, M. A. (2013): Evolutionary-based approaches for settlement prediction of shallow foundations on cohesionless soils. International Journal of Civil Engineering. 12 (1): 55-64.
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