Retaining Walls

Embedded retaining walls

Embedded retaining walls are used in a wide variety of civil engineering applications including for embankment stabilisation, construction of basement walls, underpasses or tunnel approaches, in ground tanks and other buried structures. The most appropriate system depends upon a number of factors including soil and groundwater conditions, retained height, acceptable deflections and propping options, desired wall geometry and design life. The cost of retaining wall construction varies considerably depending on the process and the conditions in which it is used.

Use of in ground retaining walls can minimise the bulk excavation needed to achieve desired ground profiles. Walls can be used in temporary or permanent conditions.

Piling Contractors offers many types of retaining wall including:

Soldier pile walls (cast in situ concrete bored, CFA or driven steel) – piles are installed at wide spacing’s (can be up to 5 - 8 pile diameters depending on soil conditions). The soil between piles is retained typically by timber lagging or by shotcrete applied to the exposed earth face during excavation. This wall type is not suitable where high water pressures or flows exist in the soil to be retained. This is usually the simplest, fastest and cheapest type of embedded retaining wall often used for temporary works.

Contiguous pile walls (cast in situ bored or CFA) – this wall method is often used in permanent applications. Structural piles are installed at close spacing’s typically with a 100mm gap between piles. The soil is therefore exposed during excavation but will often self support temporarily due to “arching”. This method is suitable in a variety of soils where groundwater lies below the maximum excavation depth.

Secant pile walls (hard / soft, hard / firm or hard / hard, cast in situ bored or CFA). A guide wall is required for this method of construction to ensure that piles are accurately located to achieve an interlock (or secant) cut into the adjacent pile. A secant pile wall uses interlocking male and female cast in situ piles to produce a retaining structure. Construction is carried out sequentially with primary (female) piles installed first then secondary (male) piles cut into the primary piles forming a continuous wall.

A hard / soft wall uses a weak concrete or grout for the female pile, which is usually unreinforced. This wall type provides some degree of water retention but is not watertight. Hard / Firm and Hard / Hard secant walls use the same construction process  however the primary pile is cast from either weak mix concrete (typically 5 – 15 MPa, Hard / Firm wall ) or full strength concrete (hard / hard wall). The primary pile may also be reinforced. The construction sequence becomes particularly critical when needing to cut segments of 40 MPa concrete piles to allow installation of the secondary pile. High torque drill rigs and specially designed cutting tools are required.

Please click to see a timelapse of secant pile wall construction

Secant pile walls can be used without additional construction in front of the excavated face. At exposed heights greater than 9 – 12 m it often becomes uneconomic to achieve continuous pile overlap and hence a diaphragm wall generally is more suitable. 

Piling Contractors has many years experience in retaining wall construction and our in house design teams are skilled at producing economic designs for such structures, backed by an extensive library of monitoring from pervious projects.