Rubble trench foundation
This is a variation of the trench fill foundation, and is a traditional construction method which uses loose stone or rubble to minimise the concrete requirement and improve drainage. It follows the same approach as a French drain, with a trench that is filled with crushed stone letting any water drain down and away from the foundation.
This approach has been used in various guises for thousands of years but it was popularised in the 20th century by the architect Frank Lloyd Wright, and has been promoted as being more environmentally-friendly than other foundation types.
The bottom of the trench should slope with an even descent of at least 3 cm for every 1 m of trench, which diverts the water towards one point, from which it can be diverted away through an outlet or to a dry well.
The trench should be lined with a geotextile material to prevent the surrounding soil from clogging up the trench and outlet. It is then filled with angular and washed stones of average size 2.5-5 cm, with them being compacted at every 30 cm layer using either a pneumatic or hand-powered tamper.
The washing of the crushed stone is important since it removes sand, silt and other small particles that could build up in the trench over time.
When it reaches around 20-30 cm below grade, the larger blocks of stone can begin to be built up as a continuous wall.
This type of trench is unsuitable for particularly expansive or poor load-bearing soils. An alternative, less eco-friendly solution, is to combine the rubble fill with a concrete grade beam.
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Not buildings. Happy holiday from DB.
Improving government projects with data and AI
Enabling better outcomes, efficient modern delivery and influential leadership on government projects.
BSRIA Living Laboratory Innovation Challenge
Final days for submission, closing March 29.
Windows, their frames, forms, factors and functions.
The hidden subtleties of U-Value calculations
Different contexts and what to include as variables.
A brief run down with related articles.
Electrical sector calls for safer public EV charge points
Serious concerns about electrical safety in the public domain.
Building Blocks manifesto presented to parliament
Architects Declare call in for support of five critical policies.
The four elements of project management with APM
Analysis, expectations, collaborative communication and partnerships.
City of London launches Heritage Building Retrofit Toolkit
Empowering owners to initiate necessary adaptations.
Guidance on RAAC in listed buildings
Published by Purcell, endorsed by IHBC, SPAB and C20.
Learning from the past.
Reluctance to hire people with criminal convictions revealed
Employing People with Criminal Convictions Report.
Tackling unconscious bias; Women's History Month
Personal reflections, as the last week of March approaches.