Ground Anchors ~ these are a particular application of post-
tensioning prestressing techniques and can be used to form ground
tie backs to cofferdams, retaining walls and basement walls. They
can also be used as vertical tie downs to basement and similar
slabs to prevent flotation during and after construction. Ground
anchors can be of a solid bar format (rock anchors) or of a wire or
cable format for granular and cohesive soils. A lined or unlined
bore hole must be drilled into the soil to the design depth and at
the required angle to house the ground anchor. In clay soils the
bore hole needs to be underreamed over the anchorage length to
provide adequate bond. The tail end of the anchor is pressure
grouted to form a bond with the surrounding soil, the remaining
length being unbonded so that it can be stressed and anchored at
head thus inducing the prestress. The void around the unbonded or
elastic length is gravity grouted after completion of the stressing
operation.
Prestressed Concrete