Mitigation of lateral ground displacements of liquefied soils with underground barriers

摘要

Analyses of damage data from earthquakes in the last 35 years show that very high financial losses have resulted from cases where liquefaction of soils was associated with ground lateral displacements towards a free boundary such as a shoreline, a river channel, or an open trench. Lateral displacements in excess of 10 m have been documented in the literature [Bartlett and Youd, J. Geotech. Engng, ASCE 121 (1995) 316]. In fact, in many cases, displacements amounting to only a fraction of this number are capable of causing considerable disruption to man-made works. Several factors contribute to the extent of lateral spreading: surface and subsurface geometry, soil characteristics, and intensity of ground motion. Ground displacements can be minimized or even arrested in practice with an underground structure properly designed to counter the driving forces, gravity and inertia combined. Mitchell et al. suggested practical guidance for the design of such structures, or barriers, in 1998 [Geotech. Spec. Publ. 75 (1998) 580]. However, to date there is no standard procedure to carry out the analysis of such barriers. The paper describes several recent designs of underground barriers that have been constructed in highly seismic environments. Three types of underground barriers are described: clay fill, a grid of structural piles, and a grid of cement-treated soil. The design of the cement-treated cell barrier is discussed in detail as it accounts for the most unfavorable combination of all forces acting on the structure: lateral stresses induced by liquefied soil, hydrodynamic effects, inertia forces, and loss of ground.