2. 2
Groundwater Effects
Shallow groundwater affects shear strength in two ways:
Reduces apparent cohesion that takes place when soils
are not saturated; may necessitate reducing the
cohesion measured in the laboratory
Pore water pressure increases; reduces both effective
stress and shear strength in the soil (same problem as
is experienced with unsupported slopes)
11. 11
Correction of Standard penetration number
It has been suggested that the SPT be standardized to some
energy ratio Er which should be computed as
Note that larger values of Er decrease the blow count N nearly
linearly, that is, Er45 gives N = 20 and Er90 gives N = 10;
Example of N for Er45 = 20 we obtain for the arbitrarily chosen
Er = 70, (Er70):
N for Er70 = 13