Case Study
Foundation Technology in Action
Gerdau- Rebar Foundry Machinery Support Pad Stabilization
“A firm footing is the key to a solid foundation.” “We fix both!”
Hot steel running through the plant
Services Nationwide
Foundation Construction Technology, Inc. 25217 Anza Drive, Santa Clarita, CA 91355 Toll Free. 855.650.2211 Local. 661.294.1313 HTTP://FoundationTechnology.com/machine-foundation/
Gerdau North America is one of the leading producers of Rebar in the United States. Rebar is used in bridges, buildings, skyscrapers, homes, warehouses, foundations and roads to increase the strength of the concrete and ultimately help hold up the structures. With construction booming, their product is in high demand. Recently Foundation Technology was contacted to provide repair solutions for an integral piece of machinery at their Rancho Cucamonga foundry, which was settling
Hot rebar transportation systen
due to poor soil conditions, vibration, and the extreme high weight of the machine itself. (NKK Rebar shear- Estimated weight with concrete and steel pedestal- 70 tons). When the machine was placed in operation forty years ago, not much was done to compact the loamy sand mixed with gravel, the machinery pedestal was sitting upon. The shear is the only machine of its kind in operation at this facility, and if this machine goes off line for any reason, production stops until it is fixed. A previous repair in 2004 required complete disassembly and removal, via 100 ton crane and a large contingent of workers, to modify the foundation base to stop settlement. The 14 ft. x 8 ft. concrete base was also wrapped in one inch steel plate adding additional weight to the now, 70 ton, NKK rebar shear and pedestal. Amazingly, nothing was done at that time to modify or stabilize the loose soil, which resulted in the same problem of settlement reoccurring almost immediately upon completion of the earlier repair procedures.
70 Ton Rebar Shear
Machinery Support Leveling Pump Pad/Support Repair Concrete Restoration Heavy Machine Isolation Epoxy Injection Below Grade Waterproofing Chemical Grouting Pressure Grouting Void Filling Polyurethane Foam Slab Raising Geotechnical Foams Helical/Push Piers c 2017 All Rights Reserved-Foundation Construction Technology
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Machinery Support Pad Stabilization, (cont.)
Inspection Cutting through the steel plate
Coring the pier access holes
Initial investigation of the site was performed with a detailed machinery plan set in hand. During the shear operation inspection, mild vibration was experienced from the rebar conveyor as far out as twenty feet from the shear. The shear cuts hot stamped rebar into correct lengths immediately after each piece exits from the stamp mill, twenty pieces at a time. There was an additional vibration felt at each cut, exacerbated by the loose sand and gravel soil beneath the shears pedestal. At that time a laser was placed to determine a 0.75 inch settlement on the tail end of the pedestal. This caused undue stress and misalignment on the conveyor attachments. Multiply adjustments and costly modifications have been performed over the past thirteen years to no avail. The shear was still settling. A U.S.G.S. soils map was produced to determine initial soil types before any test holes were dug. Upon excavation it was determined that, although the soil was tightly compacted directly at the surface, within three feet the soil quickly fell apart due to the extremely high sand and gravel makeup. Basic vibration tests were performed to determine machine operation integrity. Everything was within acceptable tolerance here, but it's best to cover all bases on a project of this magnitude. Problem # 1: Settlement It was determined that Earth Contact Products, (ECP), Model 350 Wall mount “Resistance push piers” would be the most economical way to lift the machine pedestal, without completely disassembling the shear, (as in the prior repair operation).
Each pier is Proof Load tested
Each model 350 WM pier has an ultimate lift/load capacity of 86,000 lbs. Using a safety load factor of 2.5 times the total pedestal weight of 140,000 lbs., it was determined that a total of five piers would be installed to lift and support the settled end of the machine pedestal, giving a total of over 200,000 lbs. of additional lift/load support. Two piers were installed on each side three feet apart and two feet from the settled end of the pedestal, and one pier was installed on the falling end of the pedestal. Since the pedestal was wrapped in one inch steel, in addition to installing 1 in. dia. x 12 in. bolts to attach the brackets to the sides of the pedestal, the wall mount brackets would be welded to offer additional protection against any vibration during the shear operation. 4 in. holes will drilled through the 18 in. concrete floor to facilitate the installation of the 3.5 in. x 0.166 in. galvanized high strength pier pipe, wich would be pushed to competent stratum.
Pushing Pipe For additional strength, each pier was filled with 14,000 psi grout. Piers were pushed to an average depth of 65 ft. and a hydraulic load of 8,600 psi.. This equated to a working load of approximately 48,000 per pier, and a total load capacity of 240,000, surpassing the 2.5 safety load factor. ECP's manifold lift system was attached to all piers and a lift was initiated to bring the pedestal level. Once loaded, each pier was locked off and secured by welding all bracket hardware. 14,000 psi grout was pumped underneath the existing pedestal to fill and compact any void created by the lift.
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Machinery Support Pad Stabilization, (cont.)
Final welding of the bracket
Locked and Loaded
Problem # 2: liquefaction of the sandy soil due to vibration. Excavation during the pier installation portion of the project proved the poor soil conditions the machine pedestal was built upon. The high sand content soil fell apart with every shovel proving the potential for liquefaction and settlement due to vibration of the shear and conveyor. Something needed to be done to modify the soil for more support without necessitating a complete removal and replacement of the soil bedding. A ridged compaction grout was ruled out due to the low level vibration associated with the rebar deliver conveyor and the shear operation cycling, and the potential for fracture of the grout injection columns. Foundation Technology determined that a plural component fast reacting Polyurea soil stabilizer, (Elastomer that is derived from the reaction product of an isocyanate component and a synthetic resin blend), could be used to “glue” the sand, while providing an elastomeric, non-ridged compaction to the loose bedding. It was estimated that this soil had a void capacity of 12-15% due to the sand/rubble mixture. HMI 401G polyurethane foam was chosen due to its excellent void fill characteristics, and rapid expansion, providing the desired compaction results. One inch holes were drilled at three feet interval patterns around the pedestal base to a distance of approximately twenty feet from the shear. The holes were drilled to a depth of six to eight feet. HMI 401G Polyurethane foam was injected under pressure into each hole using steel rods and injection ports. Approximately 8-10 lbs. were injected into each hole, lifting the injection rod up two feet at a time to ensure compaction was extended throughout the hole. The compaction capacity of 10 lbs. per hole was at least 3cu. ft. of dimensional expansion, providing a substantial increase in soil stability.
Final Results
Sealing the access holes
The complete project took six days, start to finish, and was completed during a bi-annual plant maintenance shut down, thereby minimizing production issues. Maintenance and engineering from Gerdau were quite amazed and pleased with the speed and proficiency in which the job was completed. The machine pedestal is level, and initial reaction is positive to the reduction in vibration around the shear operation from the HMI polyurethane foam injection. Costs associated with this project versus the previous lift and level repair, are less than 30%, offering even more total project satisfaction.
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To learn more about Foundation Technology and the services we offer Visit us on line at: HTTP://FoundationTechnology.com/machine-supports/ or call: 855.650.2211
ECP www.earthcontactproducts.com
HMI
HMI 401G Polyurethane Foam Injection
Foundation Tech, Inc. d.b.a. Foundation Construction Technology 25217 Anza Drive Santa Clarita, CA 91355
HMI Polyurethanes “Gold”Certified Installers
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