UNDERPINNING AND SHORING

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UNDERPINNING AND SHORING Powered By Docstoc
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PRESENTED BY:



  NASRULLAH MASOOD
                (2009-MS-CEG-02)


 MUHAMMAD AAMIR JAVED
                (2008-MS-GEO-14)



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                 CONTENTS
•   Definition of Underpinning
•   Purpose of Underpinning
•   When Underpinning is Required?
•   Requirement of an Underpinning Design
•   Methods for Underpinning
•   Limitations of Underpinning




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        DEFINITION OF UNDERPINNING

•   In general, underpinning means material or
    masonry used to support a structure or
    foundation.

•   underpinning means the rebuilding or deepening
    of the foundation of an existing building to
    provide additional or improved support

•   underpinning is the installation of temporary or
    permanent support to an existing foundation to
    provide either additional depth or an increase in
    bearing capacity

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        DEFINITION OF UNDERPINNING

•   underpinning is the process of strengthening and
    stabilizing the foundation of an existing building or
    other structure

•   Foundation underpinning is a means of transferring
    loads to deeper soils or bedrock.




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         PURPOSE OF UNDERPINNING

•   To obtain additional foundation capacity

•   To modify the existing foundation system

•   To create new foundations through which the
    existing load may be wholly or partially
    transferred into deeper soil




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          PURPOSE OF UNDERPINNING

•   Underpinning is generally used for remedial
    purposes

•   To arrest the excessive settlement

•   To improve the future performance of the existing
    foundations




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       WHEN UNDERPINING IS REQUIRED?

Underpinning is required when:

•     Construction of a new project with deeper foundation
      adjacent to an existing building.

•     Change in the use of structure

•     The properties of the soil supporting the foundation
      may have changed or was mischaracterized during
      planning.

•     To support a structure which is sinking or tilting due to
      ground subsidence or instability of the super structure

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    WHEN UNDERPINING IS REQUIRED?(contd..)

•     As a safe guard against possible settlement of
      the structure when excavating close to or below
      its foundation level.

•     To enable the foundation to be deepened for
      structural reasons e.g to construct the basement
      beneath the building

•     To increase the width of the foundation to
      permit heavier loads to be carried e.g when
      increasing the story height of the building


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NASTY RESULTS OF POOR FOUNDATIONS
    REQUIREMENT OF AN UNDERPINNING
                DESIGN

The art of underpinning requires an engineer to:-
• Analyze the existing structure
• Determine the loads
• Determine the bearing capacity of the soils
• Design an underpinning system to support the
  structure with minimum of settlement




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    CONSIDERATIONS BEFORE UNDERPINNING


•    Height of the building
•    Column spacing
•    Wall thickness
•    Type and material of construction
•    Different loads acting on the building
•    Condition of the building




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     METHODS USED FOR UNDERPINNING


•   Pit Underpinning
   Push Piers System
•   Helical Pier System
•   Pile Underpinning
•   Other Methods
    • Chemical Grouting
    • Microfine Grouting
   Micropiles



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               PIT UNDERPINNING


•   The most common and oldest method of
    underpinning

•   Accomplished by installing piers under a
    structure’s foundation, filling them with concrete
    and wedging up to transfer the load to the new
    piers

•   Requires careful and skilled work as loss of
    ground will cause building settlement

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                PIT UNDERPINNING


•   Columns/ walls above the affected footing should
    be braced as much as possible

•   A pit of 3’ wide, 4’ long and 5’ deep is excavated in
    front of the footing to be underpinned




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               PIT UNDERPINNING


•   Pit is extended laterally to reach under the
    foundation to be underpinned

•   The foundation is then deepened to the required
    depth

•   Vertical formwork is built in the pit and then is
    concreted up to the foundation

•   Dry packing operation is then carried out
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PIT UNDERPINNING




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PIT UNDERPINNING




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PIT UNDERPINNING




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PIT UNDERPINNING




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PIT UNDERPINNING




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              PIT UNDERPINNING


•   Workable above water table in dry ground

•   Difficult to use below water level




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• Push Pier systems utilize high-strength steel pier sections that are
    hydraulically driven through heavy-duty steel foundation brackets to
    reach deep down to competent load-bearing strata.

•   The piers have the ability to reach far below the problem soils and do
    not rely on friction for capacity.

• Foundation Support works Push Piers effectively stabilize settling
    foundations and provide the best opportunity to lift your home back
    to a level position.

• Push pier systems are an easy, economical solution providing with a
    long-lasting result. Manufactured with industrial-strength, galvanized
    steel, Foundation Support works piers have a high resistance to
    corrosion with a 100+ design life in moderate soil conditions.
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Push Pier Advantages:

 Piers reach greater depth than other options
 Long life span – galvanized steel is resistant to
  corrosion
 Does not require the use of invasive equipment
 In most cases can lift foundation back to level
  position
 Restores Property Value


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Step 1:    Footing is exposed and prepared   Step 2:    Foundation Bracket is secured to
for the bracket.                             the footing.




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Step 3: Steel pier sections are hydraulically   Step 4: The weight of the home is
                                                transferred through the piers to load bearing
driven through the bracket to competent soil
or bedrock                                      strata. Home is lifted back to level if possible.




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•   Helical piers are used to support foundation of
    existing structures.

•   Piers are drilled under the affected foundations to
    a specified depth with the help of a hydraulic
    motor attached to a backhoe.

•   Difficult to use below water level




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Damaged Foundation   Repaired Foundation



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•   Excavate down to the footing at each designated pier
    location

•   Notch out foundation footing to accommodate
    support bracket

•   Screw piers into excavated site to a desired depth
    using a hydraulic motor attached to a backhoe

•   Connect bracket to base of foundation and the top the
    pier

•   Backfill all excavated pier locations
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•   Fast installation
•   Economical
•   Can be installed in confined space
•   Minimum disturbance to site
•   Immediate loading
•   All weather installation
•   Applicable for saturated soil conditions




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•   This technique is used to overcome the extremely
    difficult working circumstances encountered when
    pit underpinning action become unsuitable

•   Piles are often used where water condition make it
    difficult to dig below the footing




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BORED OR DRILLED, CAST IN-SITU CONCRETE
                PILES

A series of holes are drilled along the length of
the existing foundation.

Some hand working is done to create a bearing
surface under the old foundation.

Say every second or third one is partly filled
with concrete.

After the concrete in these holes is set a small
but powerful hydraulic jack is used to lift the
existing foundations.

The machine that augers the holes, quite often
has the jack as an accessory and it is drive by a
hose connected to the machine hydraulic
system.


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The gap is packed with steel packers and the jack withdrawn and used
again.

When the correct height is reached and the foundation securely packed they
are filled with mass concrete, or with a re-bar cage and concrete




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•   Perforated pipes are drilled into the ground at
    spacing and a solution of Sodium Silicate is
    pressure-injected into the ground and then
    Calcium or magnesium chloride is injected as the
    pipe is withdrawn.

•   The two chemicals react to form a gel that binds
    the soil particles into a mass similar to sandstone

•   If some other method has lifted the structure,
    then pressure injection of grout into the voids
    formed by the lifting process will greatly improve
    the repair strength.
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•   A perforated pipe is drilled into ground and fluid
    grout mixture is injected by pressure
•   The mixture consist of
    - water + Cement
    - water + cement + fly ash or lime




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   WHAT ARE MICROPILES

 Piles with a diameter less than
    300 mm are called micropiles.

 The first micropiles, Pali radice
    (root piles), were invented for
    underpinning in 1952 in Italy,
    micropiles are also called root
    piles, pin piles, and minipiles.
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ADVANTAGES
  They can be used where there is insufficient head
  space for a conventional piling rig
 They are applicable to all foundation conditions if
  drilling is possible
 They can be arbitrarily installed at any angle of
  inclination
 Vibration and noise during construction can be
  limited to the minimum extent.



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             Existing Tower




Micropiles


                Shield Tunnel


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   Straightening of a tilted tower by
    use of micro piles




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   PROBLEMS
 The mechanism of micropiles developing the bearing capacity is
  not yet fully understood.
 The design method is based on the conventional design method
  for pile groups.
 The contribution of the footing has not been considered.
 Consequently, the effect of interaction between the footing and
  micropiles on bearing capacity has not been considered.




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When underpinning is installed to a stratum that is
competent and capable of supporting the structure, it will
stop downward movement of the area of the foundation
that is supported. Underpinning is generally not designed
to keep the foundation from moving upward if the original
support clays swell due to an increase in moisture.
Subsequent upward movement will often occur, which will
result in a distorted foundation and cracking in the finishes




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Underpinning is only as good as the contact or connection
point between pier/pile and the structure. If the grade
beam, thickened slab, or steel beam support is faulty, pier
support will not be fully transferred to the foundation and
downward movement may occur




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Trees, bushes and other vegetation will draw moisture from
under the foundation during times of drought. If the
perimeter of a slab-on-grade foundation is underpinned
and trees withdraw moisture from under the slab, the
interior bearing soil will dry and shrink in volume. As a
result, the interior slab may settle and cracking will likely
occur in the interior of the home. It is also possible that
tree roots under a slab will grow large enough to push the
slab upward.


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In the works of civil
engineering, foundation
engineering is often taken as a
step child and when the step
child goes to take revenge, the
results are very nasty…
                  KARL TERZAGHI
   Expectation of Underpinning by W. Tom Witherspoon, P.E. with help from
    Robert F. Pierry, Jr., P.E. and Steve Gregory


 http://www.builderbill-diy-help.com/brick-underpinning.html


 http://www.foundationsupportworks.com/foundation-repair/push-
    pier-systems.php


 Previous presentations




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THANK YOU




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