Excess Pore Pressures Around Underground Structures Following Earthquake Induced Liquefaction

Reduction In Excess Pore Pressure Due To Soil-Structure Interaction

In the analysis of pipelines and tunnels buried in liquefiable soil deposits, reduction of excess pore pressure around the structure was observed by Ling et al. (2003), Stringer and Madabhushi (2007), Chian and Madabhushi (2011), and Chou et al. (2011) in centrifuge and 1-g shaking table tests. The reduction in pore pressure as compared to the far-field was observed to be most significant at the invert and crown of the pipe. Ling et al. (2003) suggested that the reduction in pore pressure around the structure was due to implied flow along the vicinity of the pipe. Stringer and Madabhushi (2007) postulated that suction beneath the pipe exist and causes the soil under the pipe to retain its full shear strength, thereby inhibiting the pipe from floatation. Chou et al. (2011) indicated that the hydraulic gradient towards the middle of the base of the structure draws water and soil at the invert of the structure to fill the space vacated by the uplifting structure. This can be inferred by the soil displacement vectors pointing towards the pipe invert in Figure 1.

Figure 1.

Cumulative displacement vectors of soil and structure in a centrifuge test (Chian and Madabhushi, 2010)

Figure 2.

Force components acting on an underground structure in static condition