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Transient liquefaction of saturated soils near Rammed Aggregate Piers is described in Part I on the basis of radial stress measurements. This is supported by dynamic pore-water pressure measurements, as peak pore pressures approximately equal radial stresses imposed at the pier surface by ramming. Stress measurements outside of the liquefied/plastic zone indicate radial tension cracking in the elastic zone, which is consistent with the observation that pore pressures abruptly drop and momentarily can even become negative as soon as ramming stops. The drainage field created by extended radial cracking and hydraulic fracturing allows Rammed Aggregate Piers to be effective in saturated, fine-grained soils where other dynamic methods are reported to be less effective. Stress measurements indicate that liquefied soil injected into open tension cracks causes stress to be retained in the elastic zone through arching action. A stress path analysis indicates that lateral stress may play an important role in control of foundation settlement, by simulating an increase in the preconsolidation pressure without vertically surcharging the soil or waiting for it to consolidate. [ABSTRACT FROM AUTHOR]

Radial stresses measured with the K0 stepped blade in saturated soils near Rammed Aggregate Piers indicate temporary liquefaction of soil in the vicinity of the rammer. Drainage and compaction proceed during ramming of succeeding layers of the pier, such that the final distribution of radial effective stresses follows plastic cavity expansion theory. A plastic zone and liquefaction can develop only if the radial stress from ramming exceeds the soil compressive strength. If that condition is met, the transient hydrostatic condition allows the zone to expand with additional ramming. A passive condition occurs where radial stresses cannot be fully contained by the overburden pressure, in which case they approximate Rankine passive pressures. The tangential intermediate principal stress then can be modified by ramming of adjacent piers. Stress-induced cracking in the elastic zone contributes to rapid drainage and is discussed in Part II of this two-part series. [ABSTRACT FROM AUTHOR]