Wetting edge has odd and very high suction for transient flow (flow only) in unsaturated soils

Question

I did an analysis of pipe burst-induced transient flow (flow only) in unsaturated soils. I did the analysis as below: 
 (1) Assign pressure head at boundaries and evaluate the pore water pressure with suction using steady state flow method; 
 (2) Assign pipe burst pressure near the top surface (closed flow BC), and evalute the wetting extent using transient flow method. 
 However, during my analysis, very high suction points were observed in the front of the wetting extent (as shown in the suction plot below, where black line means the phreatic level). 
 This is confusing to me, why such high suction can be found near the wetting extent? In particular, it seems that when I use a finer mesh, the suction points become less, but still exist. 
 Hope someone can tell me how to address this issue. Thanks! 
 
 (a) Initial suction distribution after Step 1 (steady state flow) is achieved. 
 
 (b) Distribution of suction during transient flow after pipe burst starts 
 
 (c) Comparison of suction in coarser and finer mesh

Faseel Khan · Answer

The area with suctions is the area in between the original phreatic level and the wetting area. This area hasn&rsquo;t been wetted yet by the pipe burst and has therefore still the original suction as from before the pipe burst. 
 Suction is caused by the capillary flow against gravity, so the suction in a point depends on how deep is the saturated flow below that point. The fact that there is fully saturated soil just above has no influence on the suction. 
 For transient analysis, element size is dependent on time step used. Larger time step requires smaller element size for accurate results and vice versa.