Straight Shaft Pressure-Grouted Ground Anchors

13/gen/2016 13.04.23 hollowbar Contatta l'autore

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Straight Shaft Pressure-Grouted Ground Anchors Straight shaft pressure-grouted ground anchors are most suitable for coarse granular soils and weak fissured rock. This anchor type is also used in fine grained cohesionless soils.

With this type of anchor, grout is injected into the bond zone under pressures greater than 0.35 MPa. The borehole is typically drilled using a hollow stem auger or using rotary techniques with drill casings.

As the auger or casing is withdrawn, the grout is injected into the hole under pressure until the entire anchor bond length is grouted. This grouting procedure increases resistance to pullout relative to tremie grouting methods by:

(1) increasing the normal stress (i.e., confining pressure) on the grout bulb resulting from compaction of the surrounding material locally around the grout bulb;

(2) increasing the effective diameter of the grout bulb.

Post-grouted ground anchors use delayed multiple grout injections to enlarge the grout body of straight shafted gravity grouted ground anchors. Each injection is separated by one or two days. Postgrouting is accomplished through a sealed grout tube installed with the tendon.

The tube is equipped with check valves in the bond zone. The check valves allow additional grout to be injected under high pressure into the initial grout which has set. The high pressure grout fractures the initial grout and wedges it outward into the soil enlarging the grout body. Two fundamental types of postgrouted anchors are used. One system uses a packer to isolate each valve. 

From:https://www.fhwa.dot.gov/engineering/geotech/pubs/if99015.pdf

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