FS has installed ground anchors in various countries for a large spectrum of structures and purposes : in the Philippines FS has successfully installed ground anchors all over the country, for a variety of projects, Power Plants, Dams, Steel Mills, Building Basements, Slope Support, Anchor Blocks for Penstocks, Bridges and Viaducts, Road Tunnels , Water Diversion Tunnels , Diaphragm Walls.
Foundation Specialists has installed anchors even in Luneta (MANILA) for the anchoring against uplift forces, of the National Museum vast underground reinforced concrete water reservoir.
In particular in Baguio City, FS has, as far as 1987 (twenty years ago), installed permanent ground anchors (regroutable) on a sub-vertical slope, for a composite diaphragm wall designed to save, from collapse due to heavy scouring, the Citicorp rest-house complex built on top of the Mine-view slopes. [Interesting to note that the Citicorp complex subsequently survived without damage the 1990 earthquake, while several neighbouring structures collapsed or were severely damaged].
The Permanent Ground Anchors installed by FS are in accordance with ASTM, European and British Standards. In addition to it, to cope with the difficulties created in tropical regions by having to deal with residual soil formations, Foundation Specialists has introduced an additional feature that makes the permanent anchors installed by FS , pressure-groutable and regroutable.
FS PERMANENT GROUND ANCHOR REGROUTABLE
FS PERMANENT GROUND ANCHORS " REGROUTABLE" are assembled using high strength steel strands complying with ASTM standards A416-87a Grade 270. T he bonded length of the strands is accurately cleaned from grease and lubricants to assure a perfect bond with the cement grout. on the other hand, the free stressing length of the strand is kept with the original grease. T he Permanent Casings are made of HDPE (heavy duty poly-ethylene, the “manchette” pipes used for grouting are made of PVC. Likewise the spacers used for the strands and the centralizers employed for the main assembly are made of PVC .
The individual protection of the free stressing steel strands (passive anchor length) is made with grease filled individual HDPE tubes.
The corrugated permanent casing is closed at the anchor bottom end by a watertight cap , while the top end of the corrugated HDPE casing is inserted into a watertight , sealed and grease-filled assembly, which contains the head steel anchor plate, the anchorages, and the anchor head cap.
All material employed comes with mill certificate.
ANCHOR INSTALLATION and GROUTING
Once the hole for the anchor has been readied, the anchor assembly is installed into it, for the entire length of the permanent casing, then grouting begins, from the bottom up, using a non corrosive shrink-compensating cement grout. Both the inner and the outer space of the anchor assembly are backfill-grouted. For the cement grout, care has to be taken to keep the water-cement ratio at a minimum, to avoid to generate bleeding while curing. The cement grout injected inside the permanent casing provides the necessary bond between the active strands length and the corrugated HDPE casing, while the cement grout injected outside the corrugated HDPE casing, to fill the drilled anchor hole, provides the bond between the anchor assembly and the surrounding ground.
The ground anchor , as described here above, is a standard Permanent Ground Anchor . Both the bond between the steel strands and the casing and the bond between the casing and the surrounding ground are provided by the backfill grout as described. The reliability of the system hinges on the efficiency of the shrink compensating grout
additives, which are expected to avoid the formation of a gap at the two interfaces upon completion of grout curing (that usually involves shrinkage ).
It is not uncommon to observe anchors that, when being tensioned, are sliding slowly forward, thus losing tension: when this happens, the anchor has to be pulled out and the job done again.
The fact that some anchors become lose, it is caused sometime by defective grouting procedures, but most often is due to the characteristics of the surrounding ground formations.
To obviate these problems, FS ha introduced implements and procedures such that, with no change to the final characteristics and properties that make the Anchor a " PERMANENT ANCHOR ”, enable the Contractor to further re-grout the Anchors , under increasing pressure. High pressure injections carried away through manchettes greatly improve the efficiency and reliability of the bond between the anchor assemly and the surrounding soil strata by compressing the ground around the anchor by means of pressure injected cement grout (thus the definition of REGROUTABLE) .
The same principle is applied for the inner part of the permanent casing.
The free stressing length of the soil anchor is organized in such a way that while the space between the protective HDPE individual tubing is eventually grouted to prevent accumulation of water or moisture, the strands , inside their individual greased tubing, remain permanently free to stretch (during earthquake), as designed.
At the end of each grouting stage the manchette pipes are washed and cleaned and remain available for further grouting stages, if ever the need for it would arise.
The grout injections are carried out through manchettes (one way valves usually inserted at 50 centimeter intervals on the grout pipes) and flexible double packers properly designed for the purpose.