Geopier elements improve the stability of soils by increasing the shear strength of the soils in which they are placed. With a friction angle ranging from 49 to 52 degrees, Rammed Aggregate Pier® (RAP) elements can be placed strategically within an unstable soil mass or can support soils for a new embankment to increase the factor of safety to an acceptable level.
The increase in shear strength of the composite mass (soil and Geopier elements) can be calculated based on the area ratio of the elements in the mass as follows:
The composite cohesion intercept (ccomp) is computed with the expression:
ccomp = cg*Ra + cm (1-Ra)
cg = cohesion intercept of the rammed aggregate pier aggregate
cm = the cohesion intercept of the matrix soils
Ra = the ratio of the total RAP area to the gross footprint area of the reinforced soil zone.
The composite friction angle (fcomp) is computed with the expression:
fcomp = arc tan [Ra tan fg + (1-Ra) tan fm]
fg = the friction angle of the RAP material
fm = the friction angle of the matrix soils.
Greater shear resistance can be provided by using Rammed Aggregate Pier® systems, CTA Piers, or GeoConcrete™ Columns.
The composite shear strength of the RAP zone is then input as a discrete soil layer/rectangle within conventional stability programs. Based on the results, the area can be increased or decreased and the shear strength can be adjusted by adding or deleting piers or increasing shear strength using cement treated materials.