SOILANCHORS ROCKANCHORS SOIL ANCHORS ROCK ANCHORS

FS  PERMANENT GROUND ANCHOR  SYSTEM  "REGROUTABLE"

Foundation Specialists [ FS ] has a long and successful experience in the installation of ground anchors, both temporary and permanent.

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, among others,  installed anchors in Luneta (MANILA) for the anchoring  against  uplift forces, of the National Museum  vast  underground  reinforced concrete water reservoir.

In Baguio City, FS has,  in 1987 (twenty one years ago) ,  installed permanent ground anchors (regroutable) on a sub-vertical slope, for a composite diaphragm wall designed to save, from collapse by heavy scouring and a large landslide,  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 intensity 7.6 earthquake [Ritcher Scale], while several neighbouring structures   including the Hyatt Hotel collapsed.

Also in the Baguio area, Foundation Specialists has installed   permanent anchors to support the abutment structures  of the Camp 5 bridge along Kennon  Road, in 1986, while in 2007 Foundation Specialists  has installed over 300 Permanent SoilAnchors 42 to 44 meters long, to anchor a Pilewall retaining an 18 meter high slope.

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.

DESCRIPTION OF 
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.  The 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.  The 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.

PROCEDURES FOR
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 assembly 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.