Transmission And Substation Foundations - Technical Design Manual (TD06088E)

Table C-1

PRODUCT SE- RIES

EVALUATED PER AC358

DESCRIPTION

K t

1.25” ROUND CORNERED SQUARE BAR 1.50” ROUND CORNERED SQUARE BAR

SS125

10

SS5

YES

10

SS150 1.50” ROUND CORNERED SQUARE BAR

10

1.75” ROUND CORNERED SQUARE BAR

SS175

YES

10

SS200 2.00” ROUND CORNERED SQUARE BAR

10

2.25” ROUND CORNERED SQUARE BAR 2.875” OD, 0.203 WALL PIPE 2.875” OD, 0.276 WALL PIPE

SS225

10

RS2875.203 RS2875.276

YES YES

9 9

• Type 3 - Combo Pile: A combo pile (Combination Pile) is a compression helical pile that has the advan- tages of both square shaft and pipe shaft. A combo pile has a square shaft lead section that is better at penetrating dense material and generating bearing capacity; and is then transitioned to a pipe shaft for the plain extensions where over- burden soils are softer/less dense and a larger section modulus is desired for lateral stability and/or buckling resistance, or when lateral load resistance is required. An- other advantage provided by combo piles is the torque correlation factor (Kt) is increased compared to the straight pipe shaft pile per the table below. Note as the overall shaft length increases, the Kt fac- tor decreases.

Table C-2 - Combo Pile Length Less than 30’-0

COMBO PILE TYPE SS5/150/RS2875

SAND

CLAY

COMBINED

10

9.5

10

SS175/RS3500 SS200/RS3500

9.5 9.5

9 9

9 9

HELICAL PILES AND ANCHORS

Table C-3 - Combo Pile Length Greater than 30’-0

COMBO PILE TYPE SS5/150/RS2875

SAND

CLAY

COMBINED

9.5

9.5 8.5

9.5 8.5

SS175/RS3500 SS200/RS3500

9

8.5

8

8

• Type 4 - A Helical PULLDOWN Micropile is a helical pile that has the shaft section encased in a small diameter grout column, typically 5” – 7” in diameter. Both square shaft and pipe shaft helical piles can be encased in a grout column, but square shaft is much more common. It has the advantage of the square shaft lead section to penetrate dense material for end-bearing. The added grout column pro- vides greater section properties for shaft stability and lateral resistance in soft soils. Lateral load resis- tance with grouted shafts requires a steel case – typically extending 5’-0 to 10’-0 from the pile head. The grout in contact with the soil will develop side resistance via a bond zone in suitable soil stratum. This can greatly increase the total axial capacity of the pile (end-bearing and side resistance) as well as stiffen the axial load response of the pile. The grout column also provides additional corrosion protec- tion to the steel shaft. Grouted shaft Helical PULLDOWN Micropiles are recommended for square shaft piles in soft soils, when additional capacity via side resistance is needed, or when working loads exceed about 60 kip. To-date, Helical PULLDOWN Micropiles have achieved 450 kip ultimate resistance.

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