Breakout Session: Understanding Ground Bearing Capacities Ground stability is one of the most important factors to be considered with crane set up. This session will review the underlying physics and reaction forces, as well as group pressures. Learn best practices in ground stabilization methods and techniques including crane pads and mats; cribbing and shoring; crawler crane pads and more. Speakers: Jeff Steiner, Owner, Bigfoot Construction Equipment Mike Walsh, President, Dearborn Companies

1. Understanding Ground
Bearing Capacities
Crawler & Outrigger Loading / Ground Bearing Pressure
Distribution & Cribbing

3. Agenda
• Housekeeping / Brief Introduction to Dearborn
• Need For Ground Stability
• Review of Ground Pressure & Basic Physics
• Ground Condition Investigation Methods
• Surcharges & Excavated Areas
• Questions & Answers

4. Dearborn Companies Overview…
 Continuous Operation Since 1954
 Second (and third) Generation
Company
 Chicago Based - Operating Nationally
 Primary Service Offerings
 “Construction Engineers”
 As-Is Documentation (Reality
Capture)
 Heavy Lift, Rigging Engineering &
Heavy Transport Consulting
 Non-Destructive Examination
(NDE)
 “Mud on our Boots”
Construction Engineers ● Consultants ● Technologists

5. • Existing Ground Condition
Documentation & Evaluations
• 3D Laser Scanning, Modeling &
Clearance Evaluations
• Haul Route Surveys &
Engineered Evaluations
• Rigging Engineering (BTH) &
Engineered Lift Planning
• Ground Stabilization
Engineering & Shoring Design
Dearborn - Heavy Lift & Transport Overview…

6. Focus of Today’s Session…
Understanding ground
pressure and and how
to stabilize ground
conditions for mobile
cranes…

7. …An hommage to an icon of this industry and his “bible”…

8. Primary Regulatory Driver in the U.S.…
29 CFR 1926
Subpart CC
Cranes & Derricks
In Construction

9. The Practical Need for Ground Stability…

10. MOST IMPORTANT – PERSONAL SAFETY!!!
Everyone goes home intact at the end of the day!

11. Ground “defined”…
Ground1 noun
1. the solid surface of the earth.
synonyms:floor, earth, terra firma
…however, it can take
different forms too…

12. Quick Caveat – Ground Conditions Apply Equally To…
• Assist Cranes
• Telehandlers
• Heavy Haul & Transport Routes
• Laydown Areas, Temporary Vessel Supports, etc.
• Material Hoists & Skips
• Concrete Pumps
• Boom Trucks, Spider Cranes, Carry Decks, etc.

13. Point in fact…

14. 2nd Quick Caveat – Ground Condition Effects Apply Equally
To ALL Mats & Pads…
• Wood / Timber
• Thermoplastic
• Fiber
• Steel

15. What is “Ground Bearing Pressure”?
• All objects on Earth exert some
amount of downward force on the
Earth’s surface due to gravity.
o Include live and dead loads
o Reactive forces – gravity
opposed by tension forces of
ground surface
• Pressure is the amount of force
distributed over a given area

16. Basic physics review…
Newton’s Third Law
• In every interaction
there is a pair of forces
acting on the two
interacting objects
• Magnitude of F1 = F2
• The direction (vector)
of F1 is opposite of F2
• “For every action
there is an equal and
opposite reaction”

17. Basic physics review - Stresses…
Tension stress (or tensile stress)
occurs when two forces pull on
an object in opposite directions
so as to stretch it and make it
longer and thinner.
Compression pushes or presses
an object so as to make it
shorter and thicker.

18. Basic physics review - Stresses…
Torsional loading, which we
usually just call torsion, is when
forces acting on a structure
cause a twist about its
longitudinal axis.
Shear stress is two forces acting
parallel to each other but in
opposite directions so that one
part of the object is moved or
displaced relative to another
part.

19. Basic physics review - Stresses…
A bending moment is the reaction induced in a structural element when
an external force or moment is applied to the element causing the element
to bend

20. Crane Mat Stresses…

21. Load Effects on Mats & Plates (FEA)…
Timber Mat Steel Plate

22. Symmetrical & Static Loads?

23. Asymmetric & Dynamic Loads…

24. Symmetric Loading
(load & cwt balance)
Symmetric Loading (load
forward)
Asymmetric
Loading
Plan view of crawler crane car body; crawlers
splayed for clarity of GBP position
Reaction Transfer Across / Between Crawlers
Center of Gravity (CG)
Represents magnitude of ground bearing
pressure (GBP) beneath track
Front
Rear
Front
Rear
Front
Rear
Crawler Reactions

25. Reaction Transfer Among Outriggers

26. Calculated GBPMAX…

27. More Definitions…
• Ground Bearing Capacity:
o Actual capacity of soil to support
applied loads on a sustained basis,
without settlement or shear failure
in the soil
• Allowable Ground Bearing Pressure:
o Calculated or assumed capacity of
soil to support applied loads on a
sustained basis, without settlement
or shear failure in the soil

28. Methods of determining bearing capacity…
Visual Assessment

29. Methods of determining bearing capacity…
Geophysical
Assessment
Dynamic Cone
Pentrometer
(DCP)

30. Methods of determining bearing capacity…
Geotechnical
Assessment

31. Additional methods of determining
underground conditions…

32. Mat Size Based on Soil Bearing Capacity
• Most commonly used method:
o Mat Area = TOTAL calculated
reaction force (including mat
dead load) divided by
ALLOWABLE GROUND
PRESSURE
o Divide mat area by mat width
to derive mat length (needed
to calc mat bending & shear
stresses
• Assumptions:
o Uniform distribution of forces
throughout mat
o Uniform soil conditions below
mat
o Uniform contact between
bottom of mat and ground
surface

33. Uneven Ground Surface Effects…

34. Solution???
De-rate
the mat
size!

35. “Hard” vs “Soft” Conditions for Crawlers…

36. Indirect or Lateral Loads (Surcharges)…
Poisson Effect
• Material compressed
in one direction, tends
to expand in the other
two directions
perpendicular to the
direction of
compression.
• Negative ratio of
transverse to axial
strain = Poisson’s Ratio

37. Surcharge Effects on Utility
Structures & Foundations…
Poisson Effect

38. Rule of Thumb Stand-Off Calc…
Vertical Ratio (2:1) Method
• Quick computational
method for stand-off
distance from utility
structures &
basements
• 1:1 ratio is safer yet

39. Placement Near Excavated Areas

40. Placement Near Excavated Areas

41. Dealing With Inadequate Ground Conditions
Available Options
• “Lighten the Load”
• Modularize or break down the loads to
be lifted
• Better Distribution of
Ground Pressures
• Increase the “foot-print” of the lift
through increased SF of mats & plates
• Modify the Ground
Conditions

42. …in the end, DON’T DO THIS!

43. Questions???