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:
1) Location
2) Anchor rod alignment
3) Backfll
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