Tubazioni interrate in zona sismica

Principles and application rules for the seismic design of the structural aspects of facilities composed of buried pipeline systems are discussed. Reference document is Part 4 of Eurocode 8, section 6: Specific principles and application rules for buried pipelines. Earthquake effects are represented in two different scenarios: a) seismic waves propagating on firm ground and producing different ground shaking intensity at distinct points on the surface and spatial soil deformation patterns within the soil medium; b) permanent deformations induced by earthquakes such as seismic fault displacements, landslides, ground displacements induced by liquefaction. The first scenario is proved to be non significant, in general, if the seismic wave propagation is accounted for in agreement to EC8, Part 4. According to EC8, Part 5, the basic model for pseudo-static analysis shall consist of the tube as a retaining structure of a soil wedge over the structure, supposed to be in a state of active limit equilibrium, of any surcharge loading acting on the soil wedge, and, possibly, of a soil mass at the foot of the wall, supposed to be in a state of passive equilibrium. To produce an active soil state, a sufficient amount of wall movement is necessary to occur during the design earthquake which can be made possible for a flexible structure. Different situations are envisaged depending on the shape of the tube, i.e. if it is a box type, of a rectangular cross section, or it is one of circular cross section.