DESCRIPTION:
The university generates power for operations with a 16 cylinder Ajax-Superior 2408 natural gas fired engine and electric generator. The engine-generator combination is mounted directly to a solid concrete inertia block that measured 23 x 7 x 4 feet tall. The plans called for one inch of Unisorb- I5-500-51 under the block and 1/2 inch of Unisorb on the perimeter. Two steel columns that support piping and a deck for maintenance above the generator had also settled up to 1-1/2 inches. These columns were supported off of concrete spread footings adjacent to the generator inertia block. The combined weight of the engine-generator and inertia block was calculated at 150,000 pounds!

THE PROBLEM:
There was a reported water line break near the Physical Plant prior to the settlement of the inertia block, in addition water was seeping from the engine and piping. The engineers concluded that water infiltrated the underlying soil and softened the bearing strata. The vibrations from the generator agitated the wet clay and sandy soils further reducing the load carrying capacity. In addition, inspection during restoration revealed that there was no vibration absorption material under the block.

SITE CONDITIONS:
Soils testing at the generator revealed that there was water trapped above the clay in a layer of pea gravel fill. Below the soil was brown and light gray clay with sand, soft and wet. Approximately three feet below this clay was brown clayey sand, loose and wet. Due to limited access, the boring was stopped at slightly over 7 feet. Another boring adjacent to the building to a depth of 20 feet showed similar results. Standard Penetration Tests revealed generally blow counts (N) in the range of 7.

THE PLAN:
The Engineer specified Atlas 2-Piece Modified Resistance Piers to be installed on each side of the inertia block. Based upon the estimated weight of the unit at 150,000 pounds, the combined working loads of the six modified piers would provide a design factor of safety of 2:1. The modified pier is a good selection for this application because the pier has an added 4 inch diameter Sleeve over the standard 3-1/2 inch Pier Pipe. The Sleeve stiffens the segmented joints of the pier pipe and was specified to extend through the 7 feet of weak and saturated soil found under the inertia block. The columns were to be restored using Atlas 2-Piece Plate Piers that were welded to the either side of each column. The footing below each column was drilled to pass the Pier Pipe. Following the lift, the engineer specified that the voids were to be filled with structural grout.

The plan view at left shows the general layout of the engine-generator and how the Atlas 2-Piece Resistance Piers were positioned.

THE INSTALLATION: The Atlas 2-Piece Modified Resistance Piers were positioned based upon the center of gravity of both the engine and generator so that the piers would provide uniform lift and support. Each pier was carefully aligned vertically prior to installation to suitable bearing. The square columns offered a slightly different challenge. The engineer specified that two Atlas 2-Piece Plate Piers should be welded to each column with a piece of plate steel installed on the two sides opposite the piers. This would completely encase the column in the area of the Plate Piers and give adequate weld length. The concrete footings below the columns were drilled to pass the Pier Pipe. During the lift, the footings provided lateral support while the double pier design provided a design factor of safety of 2:1.

The photographs show technicians installing Atlas Piers using quiet, vibration free hydraulic equipment. Each Pier was driven to a suitable bearing stratum using portable equipment. The Inertia block or the column, footing and pipe support platform was used as reaction to the driving force. The technicians carefully record the driving forces at 3-1/2 foot intervals.

THE RESTORATION:
Restoration was performed in conjunction with others. First, the Plate Piers on the two columns were lifted carefully and uniformly using 25 ton hydraulic rams connected to a manifold and hand pump. The stresses on the pipes and electrical lines were closely monitored during the lift.

The second phase of the restoration involved stopping the generator. The owner had millwrights remove the supplemental shims and the grout that was installed to keep the engine-generator level and in alignment when the inertia block settled and rotated. The inertia block was then lifted using 25 ton hydraulic rams after the engine-generator was resting directly on the inertia block.

Following the lift, structural grout was installed to fill the void created under the inertia block and under the column footings. Finally, the openings in the service trench were repaired.

  

The hydraulic rams were installed between the temporary Lifting Head and the Atlas 2-Piece Resistance Piers.

Once restored, the load was removed from the rams and transferred to the Atlas Piers. The Lifting Heads and rams were then removed prior to filling the voids.

  

SUCCESS!

The inertia block and engine-generator were restored to level and raised to the original "as-built" elevation. Actual load on the 6 the Atlas 2-Piece Resistance Piers was measured at 216,000 pounds! The variation across the inertia block was measured at less than 1/16 inch! The platform was restored to nearly "dead level". The engine-generator was aligned, and the power was restored!

  

Atlas Piers
INSTALLATION SUMMARY
Pier Installation Log Location Lifting Force, pounds Driving Force, pounds Ultimate Cap., pounds Working F.S. Ultimate F.S. Pier #1 37,080 66,320 90,000 1.8 : 1 2.4 : 1 Pier #2 37,080 66,320 90,000 1.8 : 1 2.4 : 1 Pier #3 31,930 64,662 90,000 2.0 : 1 2.8 : 1 Pier #4 38,110 66,320 90,000 1.7 : 1 2.4 : 1 Pier #5 36,050 66,320 90,000 1.8 : 1 2.5 : 1 Pier #6 36,050 66,320 90,000 1.8 : 1 2.5 : 1             Pier A 17,510 28,186 85,000 1.6 : 1 4.6 : 1 Pier B 17,510 31,502 85,000 1.6 : 1 4.6 : 1 Pier C 7,725 13,264 85,000 1.7 : 1 11.0 : 1 Pier D 7,725 13,264 85,000 1.7 : 1 11.0 : 1	Results Approx. Lift inches Depth to Bearing feet 4-9/16" 88'-3" 4-1/16" 74'-7" 2-7/8" 84'-2" 2-3/16" 84'-0" 2-1/4" 88'-3" 2-7/16" 84'-6"     1-5/16" 36'-7' 1-5/16" 39'-9" 1-1/8" 33'-8" 1-1/8" 33'-8"

 

Chance Civil Construction
1026-B South Powell Road
Independence, MO 64056
Office: (816) 796-6800
Fax: (816) 796-0919
Toll Free: (877) 285-2739
Email: info@atlassys.com