SEISMIC ANALYSIS OF LARGE-DIAMETER FLEXIBLE UNDERGROUND PIPES

A pseudostatic analysis method is proposed to identify the main causes of the transverse buckling of flexible circular underground structure s, such as culverts and large-diameter corrugated metal pipes, during earthquakes. The method was initially developed to understand the coll apse of a 2.4-m-diameter corrugated metal pipe in the Lower San Fernan do Dam (LSFD), which was apparently caused by the intense near-field g round motion of the 1994 Northridge earthquake. However, a detailed fi eld investigation revealed that this particular failure could not be a ttributed solely to either large ground accelerations or liquefaction of nearby hydraulic fills. The simplified analysis considers as factor s leading to failure, static overburden pressure, peak ground accelera tion, liquefaction-induced ground displacement, pore pressure buildup, and nonlinear soil response. The analysis reveals that the observed f ailure of the LSFD pipe was caused by the cyclic pore pressure build u p in the embedding soils, and their resulting reduction in stiffness. It also points out that liquefaction was a contributing but not a nece ssary factor for failure. The proposed analysis, although developed fo r a particular case, is applicable for evaluating the response of flex ible underground conduits subjected to earthquakes.