Microtensiometer probes with a tip radius <1 mm were used for direct measurement of the change in pore water pressure caused by tensile loading at different strain rates in soils. These probes responded rapidly to changes in pore water pressure during testing and demonstrated that the applied tensile stress was transmitted almost entirely through the pore water, as would be expected. Above a strain rate of 1% min−1, viscous effects became significant, leading to a significant increase in the fracture stress. The results are described using an extended version of the Kelvin–Voigt model of rheological behavior. At low strain rates, capillary forces dominate the fracture stress. Above the critical strain rate, the viscosity of the soil also contributes to the fracture stress.

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