Assessing Liquefaction Flow Slides: Beyond Empiricism

The liquefaction flow slide is an important failure mechanism for under water slopes composed of sand.

The failure of the sand body is the result of liquefaction of loosely packed sand, which suddenly looses a large part of its strength and starts behaving as a fluid. Liquefaction flow slides occur unexpectedly and develop at a very high rate, resulting in considerable damage. As a consequence, we have little detailed information on this phenomenon; the actual nature of the failure can only be established afterwards. The lack of detailed information constrains the engineer who needs to assess the slope stability. The available methods are strongly simplified, as a basis for more advanced techniques is lacking.

This thesis is aimed at the improvement of the assessment of liquefaction flow slides. The first part contains a theoretical treatment of the underlying physics, which form the basis of an advanced calculation model. In addition, a large scale experiment has been developed, the Liquefaction Tank. We managed to reproduce laboratory liquefaction flow slides by gradually tilting the sand bed. The result is surprising; at a very gentle slope the sand bed suddenly and seemingly spontaneously liquefies. The occurrence of these experimental liquefaction flow slides depends on the density of the sand and the rate of tilting. The measurements provide valuable new insights that can be used for the further development of new models.