Deep foundation work in urban areas are great task to execute , and need to do engineering innovation to accomplish them . Secant pile construction is one of the way to execute .

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Palla Narasimhudu

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Overview of Presentation :-
What is Secant Pile
Where it is applicable
Construction sequence
Problems in construction
Advantages and Disadvantages

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What is Secant Pile:-
Secant pile walls are formed by constructing intersecting reinforced
concrete piles.
The secant piles are reinforced with either steel rebar or with steel beams
and are constructed by either drilling under mud or auguring.
Primary piles are installed first.
Secondary piles will construct between the primary piles with overlap.

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Where it is applicable:-
Generally secant piles are used as earth retaining structure for Deep
foundations.
In these conditions, for deep borings and with the existence of
groundwater level, diaphragm walls and secant pile walls are the only
feasible retaining earth.
Secant pile walls are usually used in hard ground, where it is not possible
to install diaphragm walls, and in rocks, and it is technically possible to
install secant pile walls in a extensive range of grounds.

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Application areas of Secant Piles:-
 Underground Metros and Parking Garages
 Basement Construction
 Cut and cover Tunnels
 Dam Construction
 Waterfront Structures
 Developments that need to maximize space right up to property boundaries
 Projects where excessive vibration will create dangerous soil disturbance
 Urban sites that can’t accommodate large construction areas
 Sites or soil conditions that cannot accommodate heavy specialized equipment
 Hard and Rocky soil conditions
 Wet soil conditions

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Construction sequence:-
 Guide Wall construction :-
• Setting of Co-ordinates by Surveyor.
• Steel template of Guide wall to be placed.
• Nominal reinforcement to be placed and concrete.

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Construction sequence:-
 Boring of Secant Pile:-
• Integrated Piling Rig used for boring.
• MS liner casing driven into bored hole.
• Polymer slurry/Bentonite slurry, those used in foundation
drilled shafts, create a polymer/Bentonite gel membrane
that serves as the barrier between the slurry and soil.
• Reinforcement cage lowering.
• Concrete pouring by tremie pipe.

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Construction sequence:-

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Construction sequence:-

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Problems in Construction:-
 Collapse/Caving of soil
• Excessive water in surrounding Soil.
• Properties of drilling mud deviation.
• Unknown utilities at deep levels.
 Verticality of Bore
• Faulty installation of liner.
• Mechanical problems of Integrated Rig like bends and dents in
rotary Kelly.
• Soil mix with Boulders creates displacement of boring.
 Concrete faults
• Segregation and Bleeding in concrete leads tremie choke.
• Gap in tremie pipe creates air lock.
• Collapse of soil while concrete.

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Advantages and Disadvantages:-
Advantages:-
• Increased construction alignment flexibility.
• Increased wall stiffness compared to sheet piles.
• Can be installed in difficult ground.
Disadvantages:-
• Verticality tolerances may be hard to achieve for deep piles.
• Total waterproofing is very difficult to obtain in joints.
• Increased cost compared to sheet pile walls.

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Construction of structures by Secant Pile Walls:-
Mumbai Metro – Underground StationCut and Cover Portion of Eurasia Tunnel,
Istanbul, Turkey.

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Construction of structures by Secant Pile Walls:-
Underground Metro Station, Shivaji Nagar, BMRCL Bangalore.

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