Loading Rate Effects on the One-Dimensional Compressibility of Four Partially Saturated Soils

摘要

The one-dimensional or uniaxial strain response of most soils subjected to high-intensity transient loads differs from the response measured under static conditions. As the time to peak pressure decreases, most soils exhibit a stiffening of the stress-strain response. That stiffening is usually referred to as a loading rate effect. Some researchers have suggested that, as the time to peak pressure approaches the submillisecond range, an increase up to fivefold in the modulus occurs. Other researchers have shown no loading rate effects for a soil under uniaxial strain conditions. An explosive-loaded uniaxial strain test device was modified and used in this study to obtain submillisecond loading times in the laboratory. The results obtained in this device were supplemented with those from an existing state-of-the-art uniaxial strain device to obtain measurements of loading rate effects for rise times to peak pressure ranging from submilliseconds to minutes. Test results at pressures typically on the order of 10,000 psi (69 MPa) at strain rates up to 100 percent/msec were obtained for four soils--two clean sands, a clayey sand, and a silty clay. These test results showed that a drastic stiffening did not occur in the sumbillisecond range. Instead, a gradual stiffening occurred. The maximum ratio of the measured dynamic-to-static modulus was approximately 2. Based upon these test results, a strain-rate and strain-level dependent modulus stiffening model was developed.