Static soil liquefaction entails the sudden loss of strength of loosely packed saturated sand or silt, resulting in a sudden collapse of the sand body. Contrary to “ordinary” slope failure, in which the instable soil mass slides along a clear rupture surface while staying more or less intact, in a liquefaction flow slide the instable mass of sand (or silt) flows laminar like a viscous fluid.
Generally, for static liquefaction in an under-water slope the following conditions are required (1) the presence of a sufficiently large zone of loosely packed, non-lithified, and water-saturated sand or silt; (2) the stress state of the loosely packed sand elements should be close to the so-called metastability point (i.e. the intermediate maximum in the stress path). For this, both mean stress and shear stress should be sufficiently large, which is only the case in a sufficiently high and steep slope; and (3) the presence of a trigger, for example a (small) load change.
SLIQ2D is a 2D computer program which calculates whether a submerged slope of sand or silt may liquefy or notsilt contains such metastability points or not, based on slope geometry, relative density and material properties of the sand or silt. In case no metastable point are calculated, the occurrence of a liquefaction flow slide may be excluded. The first DOS version of the program was developed by Grondmechanica Delft in 1994, commissioned by Rijkswaterstaat. Background information . In 2009 a Windows-version was released. That version was implemented in D-FlowSlide. The theoretical background of SLIQ2D can be found in for example Handboek Zettingsvloeiingen
Background informations about SLIQ2D can be find . Background information on the Windows version of the model and guidance to determination of the input parameters can be found in the User Manual of SLIQ2D.
Determination of the imaginary surface
In this program, the fictive slope height and the fictive slope inclination are determined using the following steps:
Step 1: Determination of the fictive height
The height of the part of the slope above water (h1) is increased until h2 with a factor equals to the ratio between the soil unit weight above water table and the soil below water table:
h2 = (1 + w) . γs . h1 / (γs – γw)
Step 2: Determination of the fictive slope inclination
By means of the least squares method, the submerged slope (red line in the figure below) compared to the fictive submerged slope is determined and subsequently the fictive slope inclinaison (αR)
