15-3-1 Foundation soil resistance

The first concern in the seismic verification of a plant is that the foundation soil of the buildings and other components doesn't collapse in an earthquake. With the help of a geologist, the possibility of surface faulting must be ruled out, that is that the sliding along the causative fault of an assumed earthquake cannot directly or indirectly affect the plant. Generally, this means verifying that the plant is not sited on active faults which are capable of sliding. (Attempts have also been made to set up design rules in the presence of surface faulting.)

The second and very important verification, for plants resting on saturated sandy soils, that is with a relatively shallow water table, is to ensure that the foundation soil cannot be affected by the very insidious phenomenon of soil liquefaction (IAEA, 1985, 1999; Seed, Idriss and Arnago, 1983; Seed et al., 1985; Seed and deAlba, 1986; Robertson and Campanella, 1985). ^AR587 When it happens, the shear strength of the soil becomes zero, as in a liquid, and sliding of the foundation soils of buildings and other characteristic phenomena may happen. A typical scenario of many earthquakes (in particular, the 1964 Niigata earthquake in Japan) is that whole buildings effectively lie down because the soil resistance disappears. In the Niigata earthquake, according to eyewitnesses, many inhabitants exited overturned buildings by walking on their facades, which had reached an almost horizontal position. Some buildings were recovered by simply rotating...