RETAINING WALL TYPE

Concrete block retaining wall for S J Prestige Ltd

Project case study

The project was to design a concrete block retaining wall for the construction of a new car park for S J Prestige Ltd.

Wall construction sequence

The existing ground will be excavated to the proposed finished level with a stable temporary slope. The concrete blocks can then be installed as designed and the backfill installed behind them.

Proposed retaining wall system

The concrete gravity block wall consists of interlocking concrete “Lego” style blocks. The retaining wall is a gravity type wall which resists the sliding and overturning forces from the retained material through the mass and interlocking of the concrete blocks.

 

Concrete block retaining wall design parameters

The design parameters and levels used for the soils have been taken from information provided by the client.

The underlying soil is assumed to be a medium-dense sandy silt as described in the SI information provided by the client. If this is found to be inaccurate during construction the design will need to be adjusted or the blocks taken down to a deeper level.

All other parameters have been taken as reasonably conservative values based on a typical medium dense sandy silt soil.

No groundwater issues have been reported, therefore it has not been allowed for in the design. For this reason, it would be prudent to install a filter drain in the backfill behind the wall to prevent water pressures from building up.

Surcharges of 10.0kN/m2 have been allowed for on the higher level ground. This assumes that the area is to be used as car parking or a standard roadway as advised by the client.

Note that cranes, heavy plant and equipment must not be placed immediately behind the wall either during or after construction of the wall.

Inclined Retaining Wall Design

Budget pricing

We have put together some budget rates for the construction of the concrete block retaining wall in this case study. The total length of the wall 72 m x the height 2.4 m = 173 m2.

Self build budget

Supply and deliver of the 800 mm x 800mm interlocking blocks – £125 m2 x 173 m2 = £21,625

Excavate and concrete the foundation – £50 per m x 72 m = £3,600

Place the blocks with a site loader – £25 m2 x 173 m2 = £4,425

Supply and lay land drain – £8 m x 72 m = £576

Total £30,226 / 172 m2 = £176 m2

Specialist contractor build

A specialist contractor will need to add risk, overhead and profit margins to the rates above.

Add 25%  = £37,782 / 172 m2 = £220 m2

Exclusions

The prices above do not include any excavation to form the retaining wall and no stone filling behind the retaining wall. The rate only includes the supply and construction of the retaining wall.

Note

Every project is different regarding soil type, scale, site access and location. Every project needs to be priced from the structural engineer’s calculations, specifications, and drawings. Budgets are July 2022 prices.

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