This document discusses micropiling and heaving of piles. It begins with an overview of micropiles, including their historical background and typical applications for structural support, earth retaining structures, and foundations. Micropiles are defined as heavily reinforced, small diameter piles installed with cement grout. The document outlines the construction aspects and equipment used for micropiling, including drilling and grouting equipment. It describes the advantages of micropiles in providing high capacity support in various ground conditions and loads. Limitations include limited lateral capacity and cost effectiveness compared to conventional piling systems. The document also discusses heaving of piles from soil displacement during installation and from frost heaving in cold climates, which can displace wood pilings upward.
3. Historical Background
Dr. Fernando Lizzi (Italia) in 1950s – pali radice
1950s – soil reinforcement mechanism for historical
structures (lightly loaded elements)
1960s – gained acceptance and usage in Great
Britain and Germany
1970s – introduced to U.S. and global markets
1980s – gained acceptance in U.S.
2000s – increasing (widespread) global use high
capacity steel and grout elements series of
proprietary efforts
4. Micropiles Defined
Heavily reinforced, small diameter, drilled elements
installed with neat cement grout.
Let’s dissect this :
Heavily Reinforced – typically reinforced with drill casing
and/or high strength bars
Small diameter – limited to ≤ 12 inches (typ. 4 to 7 inches)
Drilled – excludes driven piles and other foundation types
Neat Cement Grout – grout does not contain aggregate
(aggregate can be used in certain formations)
5. Classification
Categorized based on design use & installation
means
Used in almost any ground type
Transfer load to a more competent layer
Stabilize/reinforce a potential sliding mass
Design Use
Case I: axially or laterally loaded elements
Case II: group of elements used for soil reinforcement
and stabilization (reticulated micropiles)
Installation process
Types A thru E
Theoretically, any combination of “Design Use” and
“Installation Process” is possible
8. Construction Aspects
Solid Bar Micropiles
Drill the borehole (with/without casing)
Install the reinforcing elements into drilled borehole
Casing (if not same as drill casing)
Reinforcement steel (with proper corrosion protection)
Centralizers
Fill the borehole with cement grout
Typically neat cement grout; no sand added
Hollow Bar Micropiles
Drill and grout simultaneously (typ. a more fluid grout
used)
After depth is reached, flush hole with structural grout
(replacing grout used for drilling)
9.
10.
11. Advantages
High-performance
High capacity – design loads up to 500+ tons
Good for various loading
Tension, compression, lateral, combined
Applicable for wide range of ground conditions
Adaptable for varying height requirements
Used in open headroom and restricted access
Low noise and vibration – due to drilling operation
Can penetrate obstacles
12. Limitation
Lateral capacity limitation for vertical micropiles
High slenderness ratio (length/diameter)
May not be appropriate for seismic retrofit (vertical
micropiles)
Limited experience in their use of slope stabilization
Not cost effective vs. conventional piling systems in
open headroom conditions
High lineal cost relative to conventional piling
systems
Requires good QC / QA
Especially with grouting
Requires specialized equipment
13. Construction Equipment
Drilling :
Rotary only
Drifter,
rotation/percussion
Double Head Systems
Sonic Head
Drill pipe (casing),
augers
Drill and casing bits
Under-reaming and ring
bits
Percussion tooling
Grout Mixers & Operation
:
Grout Mixers
Colloidal Mixers
Paddle Mixers
Grout Pumps
Single / Double
Piston
Screw pump
14. Load Testing
Compression Load Test
Tension Load Test
Lateral Load Test
Deformation Instrumentation
15. Heaving of Piles
Whenever piles are driven, soil is displaced. The
movements induced in the soil itself may have several un
desirable consequences, including the lifting or lateral
displacements of those piles that have already been
driven. The effects of pile and soil displacement on
foundation performance depend to the great extent upon
the type of the piles and the way in which they transfer
the load to the surrounding ground.
16. Frost Heaving of Piling
In regions of cold climate many pile formations are in
ground which is partly subject to seasonal freezing and,
therefore, may be subject to the damaging effect of frost
heaving. Frost heaving has displaced wood piling upward
as much as 14 inches in a single winter season on an
Alaska Railroad bridge near Fairbanks, Alaska. Because
of skin friction and because unfrozen ground squeezes
into the void left as the pile rises-except, perhaps, if the
base of the pile is in permafrost – the pile does not return
to its original position in summer.