Commercial Push Pier Systems
Foundation Underpinning in Connecticut and New York
The Foundation Supportworks Push Pier System utilizes high-strength round steel tubes and a load transfer bracket (retrofit foundation repair bracket) to stabilize and/or lift sinking or settling foundations. The foundation bracket is secured against the existing footing and pier sections are driven hydraulically through the foundation bracket and into the soil below using the combined structural weight and any contributory soil load as resistance. Pier sections are continuously driven until a suitable load-bearing stratum is encountered. At that point, the structure either begins to lift or the target pressure/load is achieved. The weight of the structure is then transferred from the unstable soil, to the foundation brackets, through the piers, and to firm load-bearing soil or bedrock.
The Foundation Supportworks Push Pier System develops a factor of safety against pier settlement by the pier installation methods used and the sequence with which multiple piers are driven and then re-loaded. Piers are first driven individually using the maximum weight of the structure and any contributory soil load. After all of the piers are driven, the piers are re-loaded simultaneously, and the total reaction load is distributed over the multiple pier locations. Since the average load on each pier during the load transfer operation is less than the load during pier installation/driving, a factor of safety against settlement is achieved. Typical factors of safety against pier settlement range from about 1.5 to 3.0, with higher values generally achieved for structures with greater rigidity. These factors of safety conservatively ignore any additional long-term frictional component to the pier's capacity (see below for more information).
Foundation Supportworks™ Model 288 Pier System Specifications
- Bracket: Weldment manufactured from 0.25", 0.375", and 0.50"-thick steel plate. Yield strength = 36 ksi (min.), tensile strength = 58 ksi (min.).
- External Sleeve: 3.50" OD x 0.216" wall x 30" or 48" long with sleeve collar welded to one end. Yield strength = 50 ksi (min.), tensile strength = 62 ksi (min.).
- Pier Starter Tube: 2.875" OD x 0.165" wall x 50" long, triple-coated in-line galvanized. Yield strength = 50 ksi (min.), tensile strength = 55 ksi (min.). 3.375" OD x 0.188" wall x 1" long friction reducing collar welded to one end.
- Pier Tube: 2.875" OD x 0.165" wall x 36" long, triple-coated in-line galvanized. Yield strength = 50 ksi (min.), tensile strength = 55 ksi (min.). 2.50" OD x 0.180" wall x 6" long internal coupler at one end with 3" extending out of pier tube.
- Pier Cap: 5.0" wide x 9.0" long x 1" thick plate with confining ring welded to one side. Yield strength = 50 ksi (min.), tensile strength = 65 ksi (min.).
- All-Thread Rod: 0.75" diameter x 16" long, zinc plated, Grade B7, tensile strength = 125 ksi [min.].
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Foundation Supportworks™ Model 288 Capacity Summary
|
Soil Strength Parameters(2) |
Allowable System Capacity(1,2,3,4,5) (kips) |
Allowable System Capacity(1,2,3,4,5) (kips) |
||||
|
Soil Type |
Consistency/ |
SPT, N-Value |
Cohesion (psf) |
Friction Angle (degrees) |
48" Ext. Sleeve |
30" Ext. Sleeve |
|
Clay |
Very Soft |
< 2 |
< 250 |
- |
23.5 |
19.2 |
|
Clay |
Soft |
2-3 |
250-500 |
- | 27.0 |
21.5 |
|
Clay |
Medium Stiff |
4-7 |
501-1,000 |
- |
32.0 |
23.9 |
|
Clay |
Stiff |
8-15 |
1,001-2,000 |
- |
34.5 |
26.9 |
|
Clay |
Very Stiff |
16-31 |
2,001-4,000 |
- |
34.5 |
30.8 |
|
Sand |
Very Loose |
< 3 |
- |
26-30 |
33.0 |
24.2 |
|
Sand |
Loose |
4-9 |
- |
28-34 |
33.0 |
24.2 |
|
Sand |
Medium |
10-29 |
- |
30-36 |
34.0 |
26.3 |
|
Sand |
Dense |
30-39 |
- |
34-40 |
34.5 |
27.2 |
(1) ‐ Retrofit brackets shall be used for support of structures that are considered to be fixed from translation. Structures that are not fixed from translation shall be braced in some other manner prior to installing retrofit bracket systems.
(2) ‐ Allowable capacities are based on continuous lateral soil confinement in soils with SPT blow counts as listed. Piles with exposed unbraced lengths or piles placed in fluid soils should be evaluated on a case by case basis by the project
(3) ‐ Allowable capacities consider a loss in steel thickness doe to corrosion. Scheduled thickness losses are for a period of 50 years and are in accordance with ICC‐ES AC358.
(4) ‐ Allowable capacities assume a concrete footing with a minimum compressive strength (f'c) = 2,500 psi.
(5) ‐ Allowable capacities with FS350BV retrofit bracket.
-- View Our Push Pier System Product Specifications document --
Foundation Supportworks™ Model 350 Pier System Specifications
- Bracket: Weldment manufactured from 0.38”, 0.50”, and 0.63” thick steel plate, Yield strength = 36 ksi (min.), tensile strength = 58 ksi (min.).
- External Sleeve: Ø4.000” x 0.226” wall x 48” long with sleeve collar welded to one end. Yield strength = 50 ksi (min.), tensile strength = 62 ksi (min.).
- Pier Starter Tube:Ø3.500” x 0.165” wall x 50” long, triple-coated in-line galvanized. Yield strength = 50 ksi (min.), tensile strength = 55 ksi (min.). Ø4.000” x 0.226” wall x 1” long friction reducing collar welded to one end.
- Pier Tube: Ø3.500” x 0.165” wall x 36” long, triple-coated in-line galvanized. Yield strength = 50 ksi (min.), tensile strength = 55 ksi (min.). Ø3.125” x 0.180” wall x 6” long internal coupler at one end with 3” extending out of pier tube.
- Pier Cap: 4.00” wide x 8.50” long x 1.25” thick plate with pier locator plate welded to one side. Yield strength = 50 ksi (min.), tensile strength = 65 ksi (min.).
- All-Thread Rod: Ø7/8” x 18” long, zinc plated. Grade B7, tensile strength = 125 ksi (min.).
-- View Our Push Pier System Product Specifications document --
Foundation Supportworks™ Model 350 Capacity Summary
|
Soil Strength Parameters(2) |
Allowable System Capacity (1,2,3,4,5) (kips) |
||||
|
Soil Type |
Consistency/Relative Density |
SPT, N-value (blows/ft) |
Cohesion (psf) |
Friction Angle (degrees) |
|
|
Clay |
Very Soft |
< 2 |
< 250 |
- |
32.5 |
|
Clay |
Soft |
2-3 |
250-500 |
- | 36.5 |
|
Clay |
Medium Stiff |
4-7 |
501-1,000 |
- |
41.5 |
|
Clay |
Stiff |
8-15 |
1,001-2,000 |
- |
43.5 |
|
Clay |
Very Stiff |
16-31 |
2,001-4,000 |
- |
43.5 |
|
Sand |
Very Loose |
< 3 |
- |
26-30 |
43.5 |
|
Sand |
Loose |
4-9 |
- |
28-34 |
43.5 |
|
Sand |
Medium |
10-29 |
- |
30-36 |
44.0 |
|
Sand |
Dense |
30-39 |
- |
34-40 |
44.0 |
(1) ‐ Retrofit brackets shall be used for support of structures that are considered to be fixed from translation. Structures that are not fixed from translation shall be braced in some other manner prior to installing retrofit bracket systems.
(2) ‐ Allowable capacities are based on continuous lateral soil confinement in soils with SPT blow counts as listed. Piles with exposed unbraced lengths or piles placed in fluid soils should be evaluated on a case by case basis by the project
(3) ‐ Allowable capacities consider a loss in steel thickness doe to corrosion. Scheduled thickness losses are for a period of 50 years and are in accordance with ICC‐ES AC358.
(4) ‐ Allowable capacities assume a concrete footing with a minimum compressive strength (f'c) = 2,500 psi.
(5) ‐ Allowable capacities with FS350BV retrofit bracket.
-- View Our Push Pier System Product Specifications document --
Foundation Supportworks™ Model 400 Pier System Specifications
- Bracket: Weldment manufactured from steel plates with integrated pipe sleeve. Steel plate: 0.38” and 0.50” thick steel plate, yield strength = 36 ksi (min.), tensile strength = 58 ksi (min.). Pipe sleeve: Ø4.50” x 0.237” wall x 14.50” long. ASTM A53 Grade B Type E & S, yield strength = 35 ksi (min.), tensile strength = 60 ksi (min.).
- Pier Starter Tube:Ø4.00” x 0.226” wall x 36” long. ASTM A500 Grade B or C, yield strength = 50 ksi (min.), tensile strength = 62 ksi (min.). Ø4.50” x 0.237” wall x 1” long friction reducing collar welded to one end.
- Pier Tube:Ø4.00” x 0.226” wall x 36” long. ASTM A500 Grade B or C, yield strength = 50 ksi (min.), tensile strength = 62 ksi (min.). Ø3.50” x 0.216” wall x 8” long internal coupler at one end with 4” extending out of pier tube.
- Pier Cap: 4.00” wide x 8.50” long x 1.25” thick plate with pier locator plate welded to one side. ASTM A572 Grade 50, yield strength = 50 ksi (min.), tensile strength = 65 ksi (min.). All-Thread Rod: Ø0.875” x 18” long, zinc plated. ASTM A193 Grade B7, tensile strength = 125 ksi (min.).
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Foundation Supportworks™ Model 400 Capacity Summary
Allowable System Capacity: 39,000 lbs. (with FS400BV Bracket)
Notes:
1.Retrofit brackets shall be used for support of structures that are considered to be fixed from translation. Structures that are not fixed from translation shall be braced in some other manner prior to installing retrofit bracket systems.
2.Concrete bearing assumes a minimum compressive strength (f’c) of 2,500 psi. Local concrete bending and other local design checks should be evaluated on a case by case basis by the project engineer.
3.Mechanical capacity is based on continuous lateral soil confinement in soils with SPT blow counts ≥ 4. Piles with exposed unbraced lengths or piles placed in weaker or fluid soils should be evaluated on a case by case basis by the project engineer.
-- View Our Push Pier System Product Specifications document --
Design Considerations
Push piers are installed directly adjacent to the existing structure utilizing side-load brackets. This introduces eccentricity into the system. The Model 288 Push Pier System incorporates an external sleeve at the top of the pier to aid in resisting the bending forces generated by this loading condition. This helps preserve the axial compressive capacity of the pier shaft. The external sleeve extends through and below the foundation bracket to essentially create a bracket that is 48 inches tall.
The moment or bending force is localized within a relatively short distance below the bracket. Although the bending force is dissipated quickly by the pier bearing against the confining soil, it is significant and cannot be ignored. The depth or length of sleeve and pier over which the bending force dissipates is a function of the soil stiffness near the surface. The depth is greater in soft clay and loose sand, and less in stiff clay and dense sand. In soft or loose soils, a small portion of the bending force may be transferred to the pier below the sleeve, thereby reducing the pier's allowable axial compressive capacity. A modified, lower capacity system is also available with a shorter, 30-inch long sleeve for low headroom applications.
Friction Reducing Collar
The first pier section advanced into the ground includes a larger-diameter "friction reducing collar" welded to the lead end. This collar, being larger in diameter than the pier tube, effectively creates annular space around the pier as it is advanced through most clayey soils. In soft clay or clean sand and gravel, an annular space may only temporarily be created. However, the larger diameter collar causes soil disturbance or remolding to occur, which also significantly reduces frictional resistance on the outside surface of the pier during driving. The result is a driven pier that generates most of its capacity in end bearing. Over time, the soils surrounding the pier relax back into the annular space and against the pier shaft. This provides an additional frictional component to the pier's capacity. Even though this frictional capacity may be significant, it is conservatively ignored in the determination of the pier's factor of safety against pier settlement.
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