Temporary Earth Retaining System, or TERS, consists of two parts: retaining wall and the strutting system. The commonly used retaining walls are diaphragm wall and sheet pile wall (see separate headings on the left). The others are contiguous bored pile wall (CBP), secant bored pile wall, soldier pile with lagging (sheet pile or timber), caisson, pipe pile wall, etc.

Contiguous Bored Pile Wall (CBP)

Secant Bored Pile Wall

Strut to Diaphragm Wall

Soldier Piles with Sheet Pile Lagging

Service Protection

Work Access

Soldier Piles with Timber Lagging

Inclined Strut

Pipe Pile Wall

Circular Concrete Retaining Structure

Caisson

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Contiguous Bored Pile Wall (CBP)


A contiguous bored pile wall (Ryobi-Kiso catalogue). A small gap is left between each pile, ranging from 25mm to 150mm. JGP or other method is needed to seal the gap for water tightness. Ground anchor can be used to help tie back the piles and enhance the lateral resistance. Maximum depth is about 25m.


Secant Bored Pile Walls

Secant bored pile walls consist of primary piles and secondary piles with overlapping (on plan) by 25mm. Primary piles are constructed followed by secondary piles. The secondary piles use hydrofraise auger that cuts through between the primary piles. Water tightness is better than the CBP wall.

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Strut to Diaphragm Wall
(Circle Line C822 Paya Lebar Station. Contractor: Lum Chang. Nov 2003.)


Strut to diaphragm wall


Strut to diaphragm wall

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Soldier Piles with Sheet Pile Lagging

The steel strutting system consists of layers of struts, king post (for middle support to the struts), waler (for evenly distribution of strut loads), diagonal strut and runner beam (longitudinal ties between struts).

Typical plan of soldier pile with sheet pile lagging is as below. Note the steel member size. For strut, see the table. For king post, 400 x 400 x 172kg/m. For runner beam: 350x350x137kg/m. Material: Steel grade: G50. FSP sheet pile: G43.

Note that soldier piles terminate into OA by at least 1m. Sheet piles penetrate through JGP by about 4m deeper. King posts terminate into OA by 2 or 3m or plug into bored piles.

The typical construction sequence is: strutted excavation till formation level > Casting base slab > Casting wall (usually one casting from completed base slab up to the soffit of roof slab) > Casting roof slab. Installation of strut and excavation are concurrent activities and progressing layer by layer from top to bottom, where the leading activity is the strut installation (taking longer time than excavation). Dismantle of struts is the reverse order of the installation when concrete structure is being built up. To transfer earth load from TERS to the completed structure, sand and concrete plug are backfilled between the gap of the TERS wall and the structure wall.


Plan for Soldier Piles with Sheet Pile Lagging (Common Service Tunnel)

Section for Soldier Piles with Sheet Pile Lagging (Common Service Tunnel)

 

Project Photos
(KPE C423. Contractor: Samsung. Aug 2005.)

 

 


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Service Diversion and Protection
(KPE C423. Contractor: Samsung. Aug 2005.)


Drain diversion


Service support


Water main support

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Work Access
(KPE C423. Contractor: Samsung. Aug 2005.)


Access on strut in construction


Access on strut


Vertical escape access

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Soldier Pile with Timber Lagging


Soldier piles (H pile) with timber lagging

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Inclined Struts (Raker)


Use of inclined strut to support a perimeter wall in basement construction

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Concrete Circular Struts
(The Central. Contractor: Hexagon Construction. Nov 2005.)


Overview of the ring beam (to be demolished after completion of basement)


Close view of the ring beam


Steel platform access

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Caisson
(MRT upgrading project in Bedok. Contractor: Gammon. June 2003.)

Unlike pneumatic caisson, which needs special equipment and technology and is mainly used for under water works, this type of caisson is just a concrete enclosure for soil retaining purpose. When caisson wall is built up layer by layer, excavation inside the enclosure is being carried out so that the whole enclosure structure is gradually sinking down on its own weight.


Outside view at ground level


Caisson internal view. Layers of ring wall can be seen.

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