The Effects of Vertical Stress on the Liquefaction Potential Originated from Buildings in The Urban Areas: A Case Study

Introduction

Liquefaction is a phenomenon when there is loss of strength in saturated and cohesionless soils in consequence of increased pore water pressure and hence reduced effective stresses due to dynamic loading. In other words, strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. This phenomenon is usually accompanied by a large amount of ground surface subsidence. Occurrence of soil liquefaction beneath shallow foundations can also lead to excessive permanent deformations of buildings and other structures (Shahir & Pak, 2010).

Many authors have suggested solutions for seismic loads; Meyerhof (Meyerhof, 1953; 1963) considered a pseudo-static approach in which an inclined load could lead to similar stress conditions, although without concerning the inertial effects on the loaded soil mass. Other authors (Sarma & Iossifelis, 1990; Richards et al., 1993; Budhu & Al-Karni, 1993; Chien et al., 2002; Kumar, 2003; Choudhury & Subba Rao, 2005; Buchheister & Laue, 2007; Shafiee & Jahanandish, 2010) also considered the effect of seismic forces on both the structure and the loaded soil mass. Vessia and Venisti (2011) developed liquefaction damage potential PDL at Barletta site, located in Puglia Region while Assimaki and Li (2012) studied liquefaction effect specifically to site conditions and ground motion synthetics in southern California. The most widely used method for liquefaction potential evaluation initiated by Seed and Idriss (1967). The simplified procedure was developed based on field observations as well as field and laboratory tests with a strong theoretical basis. However, the simplified procedure (Seed et al., 1985; Youd et al., 2001; Çetin et al., 2004; 2012; Boulanger & Idriss, 2012a; 2012b; Idriss & Boulanger, 2006; 2010; 2014) relied almost entirely on case histories of liquefaction/no-liquefaction. The method was developed from field liquefaction performance cases at sites that had been characterized with in situ SPTs. Using a deterministic method, liquefaction of soil is predicted to occur if the factor of safety (F_S), which is the ratio of the cyclic resistance ratio (CRR) over cyclic stress ratio (CSR), is less than or equal to one. No soil liquefaction is predicted if F_S > 1. Despite the significant uncertainties in the different variables involved in this deterministic method, practical liquefaction risk assessment is still rooted in deterministic analysis. Reliability calculations provide means of evaluating the combined effects of uncertainties and logical framework for choosing factors of safety that are appropriate for the degree of uncertainty and the consequences of failure. Thus, as an alternative or a supplement to the deterministic assessment, a reliability assessment of liquefaction potential seems to be useful in providing better engineering decisions (Jha & Suzuki, 2009).

This paper presents an example of applications of vertical stress distribution calculations to investigate the soil liquefaction potentials exhibited by 5-storey buildings in the study area. The vertical stresses were chosen randomly for some buildings with foundation depths of 3,00 m; 4,50 m and 6,00 m at a selected area (Burdur, Turkey). The influence of 5-storey buildings on the liquefaction potential of soils was evaluated in terms of the factors of safety (F_S) against liquefaction along soil profiles for different earthquakes using SPT, based on simplified empirical procedure. Afterwards, vertical stress distribution was calculated in examining the soil liquefaction potential effects of 10 buildings.