Transmission And Substation Foundations - Technical Design Manual

SECTION 4: DESIGN METHODOLOGY

Chance Helical Pile/Anchor Ultimate Bearing Capacity

COMPRESSION COMPRESSION

COMPRESSION COMPRESSION

Q C

Q C

c

c

GROUND SURFACE GROUND SURFACE

GROUND SURFACE GROUND SURFACE

5 B 1 MIN DEPTH 5 B 1 MIN

5 B 1 MIN DEPTH 5 B 1 DEPTH

B

B 1

1

1

1

B 2

B 2

2

2

SIDE RESISTANCE CAPACITY ≈ 0 SIDE RESISTANCE CAPACITY ≈ 0

HELIX SPACING ≥ 3B HELIX SPACING ≥ 3B

HELIX SPACING < 3B HELIX SPACING < 3B

B 3

B 3

3

3

INDIVIDUAL PLATE BEARING 5-3a INDIVIDUAL PLATE BEARING 4-1a

PERIMETER SHEAR 5-3b PERIMETER SHEAR 4-1b

TENSION TENSION

TENSION TENSION

Q T Q T

Q T Q T

5 � (1.5 m) OR 5B 1 (WHICHEVER IS GREATER) MIN DEPTH 5 ft (1.5 m) OR 5B 1 (WHICHEVER IS GREATER) MIN DEPTH

5 � (1.5 m) OR 5B 1 (WHICHEVER IS GREATER) MIN DEPTH 5 ft (1.5 m) OR 5B 1 (WHICHEVER IS GREATER) MIN DEPTH

GROUND SURFACE GROUND SURFACE

GROUND SURFACE GROUND SURFACE

B 1

B 1

1

1

B 2

B 2

2

2

SIDE RESISTANCE CAPACITY ≈ 0 SIDE RESISTANCE CAPACITY ≈ 0

HELIX SPACING ≥ 3B HELIX SPACING ≥ 3B

HELIX SPACING < 3B HELIX SPACING < 3B

B 3

B 3

3

3

PERIMETER SHEAR 5-3d PERIMETER SHEAR 4-1d

INDIVIDUAL PLATE BEARING 5-3c INDIVIDUAL PLATE BEARING 4-1c

Comparison Between Individual Plate Bearing and Perimeter Shear for Compression and Tension Loading Figure 4-1

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