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.
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
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.
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.
We have a supply chain of reliable suppliers and contractors for all types of retaining walls that cover most of the country. We offer a service to design your project and obtain the best prices, saving you a lot of money and bother.
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