I am installing a retaining wall in front of an existing bridge abutment that is supported by a spread footing. Because of the geometry of the site, ground anchors are required to help support the wall. These ground anchors will be be bored under the spread footing of the abutment.
The bored diameter of the ground anchors is approximately 6". These holes will be filled with grout after the steel anchors have been installed. The distance from the bottom of the spread footing to the anchor can be as little as a few feet vertically. This has raised a few concerns.
The biggest concern seems to be causing the bridge abutment to settle while the borehole is advanced. A secondary concern is the bored hole collapsing from the high soil pressure before it can be filled with grout.
Are these concerns reasonable and what methods can be used to mitigate the risks?
If these boreholes were typical drilled shafts, I would say that the holes should be cased while being drilled or slurry should be used. Neither of these options seems to be a common practice for ground anchors. This can't be a unique situation though.