Impacts of Delayed Inundation during One-Dimensional Consolidation Testing

Delayed inundation during one-dimensional consolidation tests is a common practice in California, especially for soft clays. This approach, which is compliant with ASTM standard D2435, is often used due to equipment limitations, the need to inhibit swelling, or to simulate unsaturated conditions. However, our case history indicates that the timing of inundation affects the measured consolidation characteristics, a factor not well documented. A preliminary study was conducted on soil samples from a major infrastructure project in the southern San Francisco Bay Area. The samples varied in saturation (above or below the groundwater level) and plasticity (high or low plasticity clays). Results showed that inundation timing—at seating load versus delayed—led to differences in preconsolidation pressure and overconsolidation ratio. The potential implications of these preliminary results, particularly for unsaturated soil mechanics, are discussed.