8/12/2019 Foundation Selection Process
1/38
January 15, 2014
IEEE PES Winter MeetingNew OrleansOverhead Lines Subcommittee
Foundation Selection Process
By: Paul G Cass, P. E.
8/12/2019 Foundation Selection Process
2/38
STRUCTURE FOUNDATION
THE FOUNDATION SELECTION
PROCESS SHOULD BE PART OF THE
STRUCTURE SELECTION PROCESS
8/12/2019 Foundation Selection Process
3/38
FOUNDATION/STRUCTURE SELECTION IS
INFLUNCED BY:
ELECTRICAL CRITERIA AND EFFECTS TOPOGRAPHY/GEOGRAPHY
SITING/ROW LIMITATIONS
ENVIRONMENTAL ISSUES
GEOLOGY
8/12/2019 Foundation Selection Process
4/38
8/12/2019 Foundation Selection Process
5/38
TOPOGRAPHY/GEOGRAPHY
STRUCTURE SPACING /TYPE
ACCESS
CONSTRUCTABILITY
STREAMS/FLOODING
GEOLOGIC HAZARDS
8/12/2019 Foundation Selection Process
6/38
SITING/ROW LIMITATIONS
ROW WIDTHBLOWOUTSTRUCTURE
SPACING
LOCATION AND QUANTITY OF ANGLE
STRUCTURES
AESTHETICS
RESTRICTIONS ON TYPE OF CONSTRUCTION
8/12/2019 Foundation Selection Process
7/38
ENVIRONMENTAL ISSUES
Wetland avoidance/restrictions
Construction noise
Endangered species restrictions Time of construction restrictions
Type of construction limitations
8/12/2019 Foundation Selection Process
8/38
GEOLOGY
WHERE IS TOP OF ROCK?
HARD ROCK ISSUES
WATER ISSUES SOFT/USSTABLE SOIL ISSUES
LANDSLIDES/KARST/MINING/SUBSIDENCE
8/12/2019 Foundation Selection Process
9/38
STRUCTURE CHOICES (TYP)
SELF SUPPORTING LATTICE STEEL TOWER
GUYED-V LATTICE STRUCTURE
STEEL POLE CONCRETE POLE
WOOD POLE
STEEL POLE H-FRAME WOOD H-FRAME
8/12/2019 Foundation Selection Process
10/38
SELF SUPPORTING LATTICE
STEEL TOWER
Best For
High Voltage, large or bundled
conductor
Long Span Construction, hilltop to hill
top
Rigid termination or dead-end
structures
Low material cost
Worst For High structure erection cost
Aesthetics
8/12/2019 Foundation Selection Process
11/38
GUYED-V LATTICE STRUCTURE
Best For
High Voltage, large or bundled
conductor
Long Span Construction, hilltop to hill
top
Low material and erection cost
Worst For
Limited right-of-way width
8/12/2019 Foundation Selection Process
12/38
STEEL, CONCRETE & WOOD POLES
Best For
General purpose structure for most
voltages and varied site conditions
Limited right-of-way widths
Worst For
Sites with shallow hard rock
Sites with deep soft soil
8/12/2019 Foundation Selection Process
13/38
STEEL & WOOD POLE H-FRAMES
Best For
69 to 230kV lines
Medium span construction (400 to
800 feet)
Low cost materials and
construction
Can be guyed for longitudinal
capacity
Worst For
8/12/2019 Foundation Selection Process
14/38
FOUNDATION TYPES
CHOICES
CYLINDRICAL FOUNDATIONS
SHALLOW FOUNDATIONS
GROUP ACTION FOUNDATIONS
ANCHOR TYPE FOUNDATIONS
8/12/2019 Foundation Selection Process
15/38
CYLINDRICAL FOUNDATIONS
DRILLED PIER
DIRECT EMBEDMENT
VIBRATORY POLE OR CAISSON HYBRID POLES
8/12/2019 Foundation Selection Process
16/38
DRILLED PIER
Best For Flexibility in designing
and constructing
foundation
Generally cost
effective for poles
Worst For
Sites with equipment
Access issues
Sites with shallowhard rock
Sites with deep soft or
loose soil
8/12/2019 Foundation Selection Process
17/38
DIRECT EMBEDMENT
Best For Generally more cost effective
than drilled piers
Tangent poles
Worst For
Large angle or dead-end poles
Groundline corrosion
Sites with high water table or
unstable soils
Sites with shallow hard rock Sites with deep soft or loose soil
8/12/2019 Foundation Selection Process
18/38
VIBRATED POLES OR CAISSON
Best For Sites with granular soils
Sites with high water table
Worst For
Stiff clays, shallow rock
Deep foundations
Groundline corrosion
8/12/2019 Foundation Selection Process
19/38
SHALLOW FOUNDATIONS
GRILLAGE OR BASKET
CONCRETE SPREAD FOOTING
CONCRETE MATS CONCRETE RING
8/12/2019 Foundation Selection Process
20/38
GRILLAGE OR BASKET
Best For Sites with normal soil
conditions
Low cost using small
common equipment
Worst For
Groundline corrosion
Sites with deep soft
or loose soil
Sites with shallowhard rock
Structures with heavy
loads
8/12/2019 Foundation Selection Process
21/38
CONCRETE SPREAD FOOTING
Best For Flexible foundation sizing
Heavy loads supported by soil
Potential to incorporate rock
anchors to improve uplift
capacity.
Worst For
Generally higher costs than
other foundation types
Sites with shallow hard rock
8/12/2019 Foundation Selection Process
22/38
CONCRETE MATSBest For
Soft, loose and varied soil conditions
Uplift resistance provided by foundation weight
Reduced bearing pressure on soil
Shallow water
Preventing differential settlement problems
Worst For
Relatively high cost
Normal soil conditions
8/12/2019 Foundation Selection Process
23/38
GROUP ACTION FOUNDATIONS
PILE GROUP
MICROPOLE GROUP
HELICAL PULLDOWN MICROPILE GROUP ROCK ANCHOR GROUP
8/12/2019 Foundation Selection Process
24/38
PILE GROUPSBest For Sites with expected
construction difficulties
associated with water
and side wall caving
Granular soil with
increasing density withdepth
Battered piles to
improve lateral capacity
Worst For
Limited uplift capacityin stiff clays
Relatively high cost
8/12/2019 Foundation Selection Process
25/38
MICROPILE GROUPSBest For Sites with thick layer of
soft or loose soil over
rock or dense soil.
May be cost effective
over drilled piers if rock
excavation is difficult Battered piles to
improve lateral capacity
Worst For Where drilled piers are
cost effective Relatively high cost
8/12/2019 Foundation Selection Process
26/38
HELICAL PULLDOWN MICROPILE GROUP
Best For Granular soils below the water table. Use cased helical micropile where
difficulty in maintaining an open hole
is anticipated.
Battered piles to improve lateral
capacity. Potential for significant cost savings
over drilled piers at difficult sites.
Worst For Where drilled piers are cost effective
PILE GROUPHELICAL PULLDOWN MICROPILE
Ref: AB Chance
8/12/2019 Foundation Selection Process
27/38
ROCK ANCHOR GROUPSBest For
Shallow hard rock May be cost
effective over
drilled piers if rock
excavation isdifficult
Worst For
Deep rock
Where drilled piers
are cost effective
8/12/2019 Foundation Selection Process
28/38
ANCHOR TYPE FOUNDATIONS
HELICAL ANCHORS
DEAD-MAN ANCHORS
EXPANDING ANCHORS ROCK ANCHORS
MALONE FOUNDATION
HELICAL ANCHOR FOUNDATION
ROCK EMBEDDMENT OF TOWER STUB ANGLE
8/12/2019 Foundation Selection Process
29/38
HELICAL ANCHORS
Best For Normal Soil
Flexible depth and helix
configurations.
Worst For
Boulders & cobbles
Deep soft soils
Shallow rock
8/12/2019 Foundation Selection Process
30/38
DEAD-MAN ANCHORSBest For
Anchor capacity in poor soil Improved anchor capacity in
normal soils
Flexible design
Worst For Relative high cost compared
with helix anchors
8/12/2019 Foundation Selection Process
31/38
EXPANDING ANCHORS
Best For
Normal Soil
Flexible depth and expanding
anchors.
Sites with cobbles Poor access sites - jackhammer
installation
Worst For
Shallow rock
8/12/2019 Foundation Selection Process
32/38
ROCK ANCHORS
Best For
Shallow rock
Worst For
Unstable overlying soils
Deep rock
8/12/2019 Foundation Selection Process
33/38
MALONE FOUNDATION
Design and construction similar toFranki foundation
Best For
Sites with loose to medium dense
granularimproves soil
Potential for significant costsavings
Worst For
Non-standard construction
Difficult QC
Sites with stiff clays or shallow
rock
8/12/2019 Foundation Selection Process
34/38
HELICAL ANCHOR FOUNDATION
Best For Towers with stub angles
Granular soils below the water
table
Sites with expected construction
difficulties associated with waterand side wall caving
Potential for significant cost
savings over drilled piers
Worst For Shallow rock
Sites with cobbles
Ref: AB Chance
8/12/2019 Foundation Selection Process
35/38
ROCK EMBEDMENT OF STUB ANGLE
Best For Shallow rock
Towers with stub angles
Low cost
Worst For
Deep rock
Limited flexibility in
foundation depth
8/12/2019 Foundation Selection Process
36/38
Case Study 1ELECTRICAL CRITERIA AND EFFECTS 345kV Single Circuit Line EMF controls structure height , conductor configuration and
phasing
TOPOGRAPHY/GEOGRAPHY Mountainous
SITING/ROW LIMITATIONS 250 ROW shared with existing 345kV tower line
ENVIRONMENTAL Wetland avoidance, Endangered Species
GEOLOGY Shallow Igneous Rocks or Soft Alluvial Deposits over rock
8/12/2019 Foundation Selection Process
37/38
Case Study 2ELECTRICAL CRITERIA AND EFFECTS 230kV single circuit replacing 138kV double circuit on towers
TOPOGRAPHY/GEOGRAPHY Flat
SITING/ROW LIMITATIONS Access limited to only the existing access road (10 except atstructures)
ENVIRONMENTAL Extreme limits on disturbance and time of construction
GEOLOGY High Value Wetlands, 4 organics overlying 30 of loose to
medium dense sand over 100 dense sand
8/12/2019 Foundation Selection Process
38/38
SUMMARY
STRUCTURE AND FOUNDATION SELECTIONS
SHOULD BE MADE TOGETHER.
FOUNDATIONS COST A LOT - 40% TO 100% OF
STRUCTURE COST CONSIDER OTHER INFLUENCES IN
STRUCTURE/FOUNDATION SELECTION PROCESS
Soft unstable soils and hard rock usually causethe greatest problems if the wrong foundation is
chosen