Secant Piled Walls Dsign 160210011455

7/25/2019 Secant Piled Walls Dsign 160210011455

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Dr Hammida


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Earth Retaining Structures Contiguous Piled Walls

Contiguous Piled WallsA retaining wall construction method in which walls are constructed

with small gaps between adjacent piles. The size of the space is

determined by the nature of the soils.


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An increasingly popular method of creating basement spacesfor new builds or inside existing buildings. Normal Augered orContinuous Flight Auger piles are installed at an engineers pre

determined spacing's and depth. A capping beam is then

placed on top of the piles to link them together. Following this

the excavation of the internal space can begin.


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SECANT PILED WALLS

Secant Piled wall construction procedures:1.Disposition of the wall location with the proper piles center-to-

center distances (the spacing, center to center, of Secant piles is a

matter for judgments by the piling contractor).

2.Guide walls are advisable for the formation of Secant Pilesconstruction to secure the wall alignment and reduce the

construction costs and timing.

3.The overlapping pile diaphragm wall is carried out by boring andconcreting the primary (female) plastic piles, with the proper

center-to-center distances.


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4.Secondary (male) piles are then bored at mid-distance between thefemale piles, the boring equipment cutting a secant section from

them.

Male piles are bored through Female piles before the concrete has achievedmuch of its strength; should this operation be delayed, wear on the cutting

edge to the casing is likely to be much increased.

1.When the whole area is completed; the pile diaphragm wall thick is

about the pile diameter for maximum and 80% of the pile as

minimum (subject to the overlapping distance).

2.Excavation starts and inner guide wall is demolished.3. Spaced anchors or struts may be used to support Secant Piling

using steel waling members or in-situ concrete bearing pads.When this case occurs, the excavation stops at these levelsto execute the proper

strutting (by means of anchors or horizontal struts etc.)

Advantages of Secant Piled wall construction:

Secant Piled wall owes much of its later popularity to itsmany advantages that will be pointed out.1.Low costs and speed of construction for temporary and permanent

soil support where drilling conditions are conductive.

2.Clearness and comparative quietness of the installation process;low level of vibration during piles installation.

3.Wide range of soil conditions in which CFA piles can be used ; softclay, granular soils, cohesive soils, intermediate (c-) soils and soft

rocks; e.g. soft marls and chalk and although mudstone as aresuitable.

4.Inclined walls in secant pilling may also be installed at a smallinclination to the vertical line.

5.The internal side of Secant Piled wall may be lined to have auniformity of finishing.


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6.The Secant Piled method also provides a waterproof wall, whichcan be built to a considerable depth, in the range 30 to 40m, and

can cope with various types of obstruction.

7.Junction with the floor and raft slabs can be made with Secant Piled

walls using bend-out bars or bar connectors and polystyrene blockwork secured to the reinforcement cage.

What are Secant Pile Walls?

Secant piles are constructed so that there is an intersection of

one pile with another. The usual practice is to construct

alternative piles along the line of the wall leaving a clear

space of a little under the diameter of the required

intermediate piles.

The exact spacing is determined by the construction

tolerances which can be achieved.

These initially placed piles do not have to be constructed to the same

depth as the intermediate piles which follow, depending on the way in

which the wall has been designed and reinforced.


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Concrete is added and before it has fully set the intermediate holes are

drilled along a parallel, but slightly offset, line so that the holes cut

into the first piles.

The intermediate piles are placed through a heavy

casing whose cutting edge is toothed and enables the

casing to cut into the concrete of the initial piles on

either side.

Subsequent concreting results in a continuous wall. The

concrete chosen will often have a slow rate of setting in order

to ease the problem of cutting one pile into another.Schematic Plan View of a Secant Pile Wall


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A.Primary Pile (Female Pile)B. The female pile will be constructed as the primary piles for the

secant pile wall. The primary pile will be filled with the specifiedstrength of mass concrete without any steel reinforcement.

B. Secondary Pile (Male Pile) The secondary pile will be constructed in between the primary

piles and overlap with the primary piles with the specified

strength of concrete after the reinforcement cages are loweredinto the bored hole. The secondary pile formed by cutting into theprimary piles to form the interlocking joint by using the specifiedcoring tools. The boring process for the secondary pile

shall only commence upon initial set of the primary piles.

A secant wall is made up of several steps:1.The initial step is to construct a guide wall to set up the

positioning of the secant pile wall.2.Drill and Installation of the 1 meter temporary casing.3.Drilling of the Primary Columns, 1,3,5,7, etc etc.4.Concreting of Primary Columns.5.Drilling of the Overlapping Secondary (Reinforced) Column, 2.4.6.

etc, etc.6.Install the Steel Cage or I-Beam.7.Concreting of Secondary Column.8.Repeating the above steps.


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Secant Wall PilesAlternate female piles are formed using a slow-gain (soft) concrete mix. Theinstallation sequence is normally to install 1 pile every other 3 piles.

After a sufficient curing period (2-4 days) and once each alternate pile is formed, thereinforced 'male' piles are installed using a standard (hard) concrete mix. The maleand female piles overlap by approximately 75-100mm.

The secant between male and female piles ensures that water ingress is minimisedand fines wash-out is prevented. The interlocking secant wall is not watertight;however water flow is greatly reduced. Similar pile sizes and retained heights tocontiguous piling can be offered.


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The secant piles wall consists of two types of piles:


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Piling - Contiguous, Interlocking and Secant

Bored cast in-situ piles are often used as an efficient and cost effective means ofconstructing temporary or permanent retaining walls. Typically used in theconstruction of new build basements, substructures in close proximity to existingstructures requiring restraint and where working space is limited. The techniques

avoids excessive excavation and assists in the control of ground movement.

Typically there are three types of bored pile in current use.

Contiguous


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Typically this technique is suitable to retain stiff and cohesive subsoilsand where ground water levels are below the eventual depth ofexcavation.

Pile diameters range between 450mm and 900mm and are generallyinstalled at pile centres of between 500 and 1000mm respectivelythereby leaving gaps between the piles between 15 and 100mm.

Interlocking Piles


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Firm pile concrete

Firm primary pile concrete is a lower strength concrete that fills the gap between the

hard secondary piles. The concrete mix is designed to be soft enough to allow thesecondary pile to be cut into the adjacent piles.

Hard pile concrete

Hard secondary pile concrete is a reinforced concrete mix that is installed inbetween the soft or firm primary piles when forming a secant wall


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Secantwallmadewithgroutthroughdrillsystem


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Tangent Pile Wall


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Tangent pile walls are a variation of secant pile walls and soldierpile walls. However, tangent pile walls are constructed with nooverlap and ideally one pile touches the other. Compared to secant

pile walls, tangent pile walls offer the following advantages:

1. Increased construction alignment flexibility.2. Easier and quicker construction.

The main disadvantages of tangent pile walls are:1. They are can not be used in high groundwater tableswithout dewatering.2. Each pile is independent from adjacent piles


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Documents

Secant Piled Walls Dsign 160210011455