Raking micropiles through foundations can be applied in low to medium risk buildings where internal and external damage is significant and progressive. The difference between raking and traditional pile and beam is of course the piles are raking but, secondly, the absence of ground beams allows for direct load transfer from the foundation to the pile.
This system may be more cost effective than traditional pile and beam but it is not without its limitations. Unlike pile and beam construction, raking micropiles can only be proven by design as it is very difficult to test in situ micropiles for axial loadings. In some instances, such as raft foundation failure, micropiles can be installed vertically through the raft.
Raking micropiles should be installed through traditional strip foundations, so they may not be appropriate in old random rubble walls or foundations of little or no projection. It is also important to account for the shear forces during load transfer from the micropile to the foundation; therefore, the surface area of the borehole through foundation must be as large as possible.
Furthermore, as micropiles have a relatively low bending moment, such piles may sometimes have to be installed alternating on either side of the wall to negate such lateral and torsional forces. In some circumstances, they can installed from one side of the building. This may also depend on the ability of the soils to withstand such forces and the loads applied. This system is most appropriate during renovation works where the internal floors are being replaced in any instance.