Spontaneous liquefaction in saturated granular deposits: State controlled boundary and surface reconfiguration

Manfred Heinrich Wittig

In the case of water-saturated, granular deposits that are at risk of liquefaction, engineers need reliable information about the spatial extent of soil deformation in the event of liquefaction. It is not so important for them to know the exact location of the first failure. However, existing anal-yses primarily deal with the triggering of liquefaction and offer only limited information on how large the areas affected by liquefaction can become.
This study presents a state-based interpretation of soil deformation after liquefaction, in which the boundary of terrain deformation is determined by the energy distribution at the system level, with the starting point of liquefaction playing a subordinate role. The analysis focuses explicitly only on the state after liquefaction and does not address the triggering conditions that ultimately led to the onset.
The concept is supported by Event 42, a large-scale field event in Lusatia that can be interpreted as a natural experiment. The ground surface of an inner dump of a former lignite mine was de-liberately designed with very shallow initial slopes (approx. 3°) to avoid local triggering due to slope instability. Despite these conditions, liquefaction occurred, spreading over a large part of the site until a clearly defined and reproducible boundary, which is obviously characteristic of the prevailing material condition, was reached. High-resolution surface surveys before and after the event made it possible to quantitatively determine the geometry, while independently availa-ble historical aerial photographs confirm the large-scale extent of the newly configured area in terms of size.
The observed invariance of the boundary and heights with respect to the orientation of working profiles shows that the final shape is independent of the location where liquefaction began. This suggests that the geometric changes to the terrain after liquefaction are a state-controlled process. Based on this interpretation, the spatial extent of the change in slope geometry can be determined on the basis of the initial geometry and soil mechanical parameters without knowing where liq-uefaction began. A proposal for the practical calculation of the boundaries of an area affected by liquefaction is included in the appendices.