The release and reshock behavior of aluminum from an initial shock stress of 2 GPa (20 kbar) has been examined. It is found that a two-wave structure characterizes both release and recompression, although a definite elastic-plastic structure is not obtained in either case. The velocity of the initial disturbance for both recompression and release agrees with the extrapolated ultrasonic longitudinal velocity, which implies initial elastic response from the precompressed state. The present results are discussed in terms of a rate-independent model which incorporates a distribution of yield states in the precompressed material. Reasonable agreement with experimental reshock and release wave profiles is obtained with this model. A brief discussion of rate effects estimated from an acceleration wave analysis is also presented.

A technique is described for estimating the dynamic yield stress in a shocked material. This method employs reloading and unloading data from a shocked state along with a general assumption of yield and hardening behavior to estimate the yield stress in the precompressed state. No other data are necessary for this evaluation, and, therefore, the method has general applicability at high shock pressures and in materials undergoing phase transitions. In some special cases, it is also possible to estimate the complete state of stress in a shocked state. Using this method, the dynamic yield strength of aluminum at 2.06 GPa has been estimated to be 0.26 GPa. This value agrees reasonably well with previous estimates.

Explosive or percussive breakage of rock relies on impulsive rock fracture and both the fracture stress and fracture energy under such conditions are observed to be significantly greater than measured quasi‐statically. The implication of rate dependence has been verified in recent tensile fracture studies and in the present report this data has been compiled, significant trends noted, and comparisons made with earlier impulsive fracture criteria.

Existing theories and models describing stress changes and consolidation-time effects around a pile were used to derive in-situ permeabilities and undrained shear strengths from piezometer probe measurements in smectite- and illite-rich soils. Permeabilities derived from piezometer measurements are in reasonable agreement with laboratory measurements, and calculated undrained shear strengths agree well with strength measurements using standard field and laboratory techniques. Undrained shear strengths Su were estimated using insertion pressures Ui, determined from both the 10.2- and 0.8-cm-diameter probes, and the relationship, Ui = 6 × Su. A strength measurement determined with the small diameter probe inserted in the disturbed zone of a previously emplaced 2.5-cm-diameter cylinder showed a significant strength reduction equal to half the value determined for the soil (strength) in the zone unaffected by the implanted cylinder. Differences in decay rates were significant, indicating severe soil disturbance in close proximity to the cylinder. Multisensor piezometer probes (2), 10.2 cm in diameter, were deployed in shallow-water fine-grained smectite-rich soils of the Mississippi delta. Pore-water pressures were measured at subbottom depths of 6.5, 12.6, and 15.6 m. Insertion pressures, time-dependent pore pressure decay, and ambient excess pore pressures were determined. Single sensor piezometers (2), 0.8 cm in diameter, were developed for deep-ocean investigations. Before high pressure testing (55 MPa), probes were inserted in reconstituted illitic marine soil to depths of 16.9 and 26.4 cm below the soil-water interface. Insertion pressures and their decay characteristics were monitored. Significant differences were observed in the pore-pressure decay rates produced by the small and large diameter probes. Decay times for the induced pressures to reach t100 values were on the order of tens of hours for the large diameter probes, whereas the t100 values of the small diameter probes were on the order of minutes. These differences in decay times were a function of the differences in probe diameters (radii) and soil permeabilities.

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