BUILDING FOUNDATION INSTABILITY INDUCED BY TSUNAMI SCOUR

Mara Jauane Nicholas Mara Jauane Nicholas,Tomoya Shibayama,Ravindra Jayaratne Ravindra Jayaratne,Takayuki Suzuki Takayuki Suzuki

doi:10.9753/icce.v36v.currents.29

Abstract

Understanding the role of tsunami-induced scour in building foundation instability can allow for the proper design of buildings located in areas prone to tsunami events. The process of tsunami scour around building foundations reduces the bearing capacity of the soil to support loading, lateral resistance and loss of soil- foundation friction (i.e. piles). Scour can cause loss of material around a foundation, due to increased pore pressure within the soil and removal of the soil during the tsunami, resulting in reduced bearing capacity of the soil (Macabuag et al., 2018). During the 2004 Indian Ocean Tsunami and the 2011 Great East Japan Earthquake and Tsunami, three similar failure modes of building foundations were experienced, namely overturning, sliding and bearing (scour) failure (Macabuag et al., 2018). According to Wright (2015), shallow foundations such as strip, slab or pad are vulnerable to erosion of surrounding soil causing scour during a tsunami. The present paper discusses the application of the scour depth predictive model of Nicholas et al. (2016) and the development of a Relative Risk Index for future design of building foundations accounting for tsunamis.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/u6QSmUe8YqA

Highlights

Understanding the role of tsunami-induced scour in building foundation instability can allow for the proper design of buildings located in areas prone to tsunami events
Soil weakening following a tsunami wave can result in foundation failure for shallow foundation buildings, mainly due to bearing failure which causes undermining and subsequently, tilting, as seen in Fig. 1
Such loss of soil can result in loss of skin friction of the pile or pile group resulting in reduced pile resistance and causing buildings to overturn during the tsunami event

Summary

INTRODUCTION

Understanding the role of tsunami-induced scour in building foundation instability can allow for the proper design of buildings located in areas prone to tsunami events. He et al (2019) noted that scour increases the over-consolidation ratio and reduces the shear strength of the undrained soil This can weaken undrained soils with potential foundation failure while drained soils can undergo from deep scour failure (Wright, 2015). In the 2004 Tohoku tsunami, less severe failure (light undermining and tilting) was found in areas where there was shallow localized scour around the foundations, small scour extents and where foundation depths were equivalent or deeper than the scour depth (Fig. 1). Soil weakening following a tsunami wave can result in foundation failure for shallow foundation buildings, mainly due to bearing failure which causes undermining and subsequently, tilting, as seen in Fig. 1 (taken from Fraser et al, 2013). Adequate scour predictive models suggested by Nicholas et al (2016) such as the Tonkin et al (2003) model and Nicholas et al (2016) model can be used

RISK ASSESSMENT MATRIX FOR SHALLOW FOUNDATION FAILURE

MITIGATION OF BUILDING FOUNDATION FAILURE

CONCLUSIONS