CENTRIFUGAL MODELING OF CONTINUOUS SHALLOW TUNNELS CROSSING ACTIVE REVERSE FAULTS

Tunnels are long lifelines which are at damage risk due to faulting in earthquake-prone areas. Interaction of soil and tunnel at an intersection with an active fault will be a useful guide for tunnel design engineers. In the present study, a series of centrifuge tests were designed and tested on modeled tunnels at a 60-degree reverse faulting. Mechanism and location of damage to the tunnels is assessed. Four damage state are defined and damage progress are monitored with increase in permanent ground displacement (PGD). The ground surface deformations and strains, the surface trace of the fault, the fault scarp and the sinkhole caused by the fault movement are explained. The tunnel is vulnerable to reverse fault rupture and its operation may be stopped by few displacements. Most of the earthquakes are associated with plate tectonic and a sudden movement on the fault plane which releases large amounts of energy is an earthquake (Kusky & Kusky, 2008). The ground breaks are accompanied by horizontal, vertical or combined displacement and may cause considerable damages (Hung et al., 2009). If the hanging wall moves upwards in relation to the footwall, the fault is called reverse (Twiss & Moores). Surface faulting is the propagation of displacement along a fault in soil deposits that reaches the ground surface. (Ghalandarzadeh et al., 2016). Faulting can cause severe damage to tunnels and can stop its operation. Faulting can cause ground settlement, crack in tunnel lining, soil falling and complete collapse (MRl, 2003). (Konagai et al., 2006) outlined key points for designing civil-infrastructures near seismic faults. The damage to eight tunnels caused by faulting in Japan, the United States and Turkey has been highlighted. Despite the tunnels are vulnerable to activity of faults, research in this area is very limited (Burridge et al., 1989; Kiani et al., 2016).For most laboratory researches at the University of Tehran, Firouzkuh #161 sand is used (Bayat & Ghalandarzadeh, 2017; Haeri et al., 2012; Kiani et al., 2016). For each continuous tunnel model, a 6 mm thickness PVA fiber-cement cylinder was used. The compressive strength was obtained by a uniaxial compression test and flexural strength using a two-edge bearing test (Aashto, 2001; Fahimi et al., 2016; Peyvandi et al., 2014; Young & Trott, 2014). According to the tests, compressive strength 27 MPa, tensile strength 20 MPa and elasticity modulus 18 GPa were obtained.

کلیدواژه ها:

Reverse fault rupture ، Continuous tunnel ، Geotechnical centrifuge ، Sinkhole ، Ground surface deformations