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2. REPAIR WORK CARRIED OUT
Because of the poor state of the foundation, a decision was made to carry out the recommended work immediately, and the Alphatec team mobilized in record time. Materials and equipment were delivered to site on Monday 18 June, and work started the same afternoon.
There are 4 main components of the repair work effected: injection repair of the foundation; grout removal and support of the machine; alignment of all components; and forming and regrouting of all machine bases.
2.1 Injection Repair:
A preliminary core was drilled from ground level to determine the depth of the underground mat. Including the final floor thickness, there was 900 mm of concrete to be added to the foundation's mass.
Several deep holes were drilled from the foundation top through the main block, and into the pile cap. These holes were drilled with a diamond core drill, with a 60 mm ø bit, and with a rotation-percussion rock drill.
Once the holes had been flushed clean, high-strength reinforcing steel bars (DYWIDAG rods) were inserted into these holes with copper tubing attached. The top of the hole was then sealed for pressure resistance of up to 300 bar. ALPHATEC® 300 injection grout was pumped into the holes until flow out was observed from the vent tube. The vent was crimped shut, and pressure applied to the hole to push the resin into all separations, cold joints, fissures, stress cracks, shrinkage cracks, honeycombs, and any other void or imperfection intersected by the hole. Evidence of coverage was seen at various places around the foundation, and the pressure was maintained on each hole until the site supervisor was satisfied that optimal coverage had been achieved. The injected resin cured in approximately 24 hours, and the protruding tubes were cut off. The repaired foundation will show much greater resistance to movement, and its ability to damp out vibrations will be greatly enhanced by this repair.
Additional injection work was done on the crankcase and frame extension anchor bolts, after the main chipping work was complete. No evidence of loose bolts was found.
Two of the suspect pipe support plinths were repaired by pressure injection, since the baseplates appeared to be relatively well grouted. The plinths, however, were not properly fastened to the underlying concrete mat, and the injection work has solved this problem.
2.2 Grout Removal:
The existing grout and underlying damaged concrete was removed by pneumatic chippers to a depth of approximately 150 mm beneath the motor baseplates. Work on the compressor was delayed due to problems removing piping and wiring.
As this picture shows, the method of installing the baseplates left a lot to be desired, with multiple shims, and gaps between baseplate and grout.
The grout was removed in sections, with at least 50% of the original grout being left in place while the initial supports were put in place. The baseplate was supported by the ALPHAPAD® system, consisting of specially designed hydraulic jacks, with a ball joint incorporated to ensure parallel support on the underside of the machine flange.
These jacks were placed on epoxy grout pads to ensure proper stress distribution into the concrete. Corrosion of the baseplate was found to be negligible.
The remaining grout was then chipped out.
The bearing pedestal grout was then chipped out, and the sleeves around the anchor bolts cut away.
Note the steel packers driven into the sleeves to push the anchor bolts into the correct position. This became something of a pattern, since all anchor bolts on this machine appear to have been "persuaded" into their final positions. Photo 13 Work on the crankcase and frame extensions eventually started on 21 June, and progressed rapidly. Approximately 200 mm of grout and oil-soaked concrete was removed under the crankcase and frame extensions, as can be seen in the picture below.
Grout removal around the pipe supports resulted in the complete demolition of the plinth in some cases, since there was no bond at all to the floor level concrete.