Installation Problems - Geotechnical
As with all foundation construction, undiscovered and unknown subsurface conditions will become evident during construction. Alternative procedures should be considered before work commences to minimize downtime.
The excavated-type anchor allows the examination of the bearing soil, at the time of construction, and the selection of the most economical anchor type for installation. The four most common geotechnical problems encountered, and their resolutions, are as follows:
1) Boulders in excavation, too large to excavate. Move the anchor location or overexcavate and remove boulder. The latter solution requires greater amounts of compacted backfill.
2) Bedrock shallower than expected. If removal by a large core-barrel drill is not practical, change the anchor type to grouted-type anchor.
3) High water table. If excavation is possible, backÞll with an ungraded granular backfill and vibrate well during compaction with the largest practical vibrating compactor. Dewatering is sometimes practical by placing a sump hole well outside the projected area of the plate anchor. The sump is to be backÞlled and compacted after the first several lifts of fill are placed on the plate anchor.
4) Very loose or lightweight soil. This condition requires importing select backfll or a mixture of imported and native soil.
Installation Problem - Construction
Construction of excavated soil anchors is similar to construction of spread footing The major construction problem with this type of anchor is the backfll placement.
If the anchor installer is unable to achieve the backfll density required, a select backfll of granular material may have to be imported to replace or mix with the native backfll.
The orientation of the anchor with respect to the guy cable may have to be changed. Geotechnical problems may require the anchor to be installed in a different orientation than that speciÞed by the manufacturer or engineer.
Deadman anchors typically have keys to prevent them from creeping out of the ground under load. The installer must Þrst notify the designer of his intent to change orientation and then modify or add keys as required by the designer. The designer may require that changes to the drawings/specifcations be confrmed by a performance test of the installed anchor.
Construction tolerances for this anchor type are the most flexible. The following three properties should be specified:
2) Anchor rod alignment