SBC and SPT in conjunction to in situ moisture

[Sanjeev Kumar]

Dear Guys
I've been always at awe with a fact that we obtain soil samples at varying moisture content at different seasons. We test them and get the results and apply these results into the standard equations to obtain SBC or other parameters so to say. Much often, the N count is higher in dry seasons than in rains but I am unable to understand how to handle such a situation because it will certainly lead to erratic results. What is the correct methodology as regards this concern.
Thanks
Er Sanjeev Kumar Jain

 

[GeoEnvGuy]

The reason shear resistance is higher similar soils with varying moisture content is due to matric suction. To determine the actual effective stress condition you would need to determine the soil water characteristic curve. In practice no benefits of matric suction is included in the analysis as you cannot count on the strength which varies when it rains.

The brumhadinho expert report states the deformation modelling was best fit when matric suction was accounted for and it was this loss of matric suction in the rainy season which contributed to the instability.