The rising of tailings dams using the upstream construction technique can lead to static liquefaction failure if the rate of construction is sufficiently high to cause excess pore pressure to develop in the tailings. Static liquefaction is the accelerating flow deformation process taking place in a loose and saturated granular mass, subject to static undrained loading exceeding the peak undrained strength. The susceptibility of a material to liquefaction is determined from the load-deformation response recorded during undrained strain-controlled laboratory tests. The 'liquefaction response' is observed for loose specimens, when the shear stress exhibits a peak followed by a phase of apparent softening. Static liquefaction takes place when the material specimen is loaded in a stress-controlled manner in excess of the peak strength. The occurrence of apparent softening in undrained loading is associated with the tendency of the material to contract (densify). For some initial loading states, the descending part of the response is followed by an increasing part, leveling-off eventually when the material reaches the final, critical (steady) state.
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