Induced liquefaction experiment in relatively dense, clay-rich sand deposits

In this paper we report results from a controlled blast-induced liquefaction experiment at the field scale. The physical and mechanical properties of the materials at the subsurface are characterized by a suite of in situ and laboratory tests, including the Standard Penetration Test (SPT); downhole and cross-hole seismic velocity tests; density, porosity, and gradation tests; and direct shear tests. Since the blast experiment was performed above groundwater table, the subsurface was saturated by a sequence of controlled infiltration tests. A 50-kg TNT charge was detonated at a depth of 10 m, and seismic ground motions were recorded in a vertical geophone array positioned at a horizontal distance of 30 m from the blast borehole. Obtained liquefaction features include a water fountain that erupted from the blast borehole, prolonged bubbling of the water surface inside the infiltration trench (a process equivalent to "sand boils" typically observed at sites which have experienced liquefaction), lateral spreading, and surface settlement. We argue that in contrast to conventional predictions, liquefaction may be induced in relatively dense silty and clayey sands (shear wave velocity >300 m s ^-1 relative density = 63-89%) relatively rich in clays (fines content >30%) and that the driving mechanism should not necessarily be restricted to cyclic shear stress loading.