Transmission And Substation Foundations - Technical Design Manual

SECTION 4: DESIGN METHODOLOGY

Chance Helical Pile/Anchor Ultimate Bearing Capacity

Adhesion factor a for piles with penetration lengths less than 50 m in clay (data from Dennis and Olson, 1983 a & b; Stas and Kulhawy, 1984)

Values of a versus undrained shear strength

1.2

Driven pile Drilled shaft

1.0

1.0

0.8

0.6

0.5

0.4

α Adhesion Factor

Adhesion Factor, α

0.2

0

0

40 80 120 160 200 240 280

0.25 0.5

0.75 1.0

2.0

Undrained cohesion c u , kN/m 2

c Undrained Shear Strength, TSF

Variation in Adhesion Factor with Undrained Shear Strength of Clays [Murthy (2003)] Figure 4-8

Variation in Adhesion Factor from American Petroleum Institute [ASCE (1993b)] Figure 4-9

COMPRESSION Compression

TENSION Tension

COMPRESSION Compression

Q c c

Q T T

Q c c

GROUND SURFACE Ground Surface

GROUND SURFACE Ground Surface

GROUND SURFACE Ground Surface

5 ft (1.5 m) OR 5B (WHICHEVER IS 5 ft (1.5 m) or 5B (Whichever Is Greater) Min Depth GREATER) MIN DEPTH

DEPTH D Depth

Q f Q f

Q f

Q f

SIDE RESISTANCE Side Resistance

5B MIN DEPTH 5b Min Depth

PRESENT ONLY ON LEAD SECTION Present Only On Lead Section

B

Q f Q f

Q BT Q BT

AREA OF PLATE REDUCED TO ACCOUNT FOR SHAFT Area Of Plate Reduced To Account For Shaft

Q BC BC

B

B

Q c = Q BC + Q f Q c = Q + Q f

Q T = Q BT + Q f Q T = Q BT + Q f

Q C = Q BC + Q f Q c BC + Q f

Q BC BC

5-12a BEHAVIOR OF SHALLOW ROUND SHAFT HELICAL PILES 4-10a Behaviour Of Shallow Round Shaft Helical Piles

5-12b BEHAVIOR OF SHALLOW ROUND SHAFT HELICAL ANCHORS 4-10b Behaviour Of Shallow Round Shaft Helical Anchors

5-12c BEHAVIOR OF DEEP ROUND SHAFT HELICAL PILES WITH COUPLINGS 4-10c Behaviour Of Deep Round Shaft Helical Piles With Couplings

Individual Bearing and Side Resistance Models for Helical Piles and Anchors with Round (Pipe) Shafts Figure 4-10

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