With very large properties either side, the basement could not be excavated and constructed in the traditional manner. As a result, the perimeter of the basement was stabilised with the installation of sheet piles.
The piling was carried out by a specialist piling contractor, working closely with Beautiful Basements‘ design and construction teams to install these piles.
| Categories: | |
| Location: | Central Birmingham |
| Surface Area: | 350 square metres |
| Completed: | 2019 |
| Architect: | Ben Parsons Designs |
| Link: | Visit project |
With such a confined space, the primary challenge to the design team was to produce a method statement for the excavation that would keep the team below and the neighbouring properties above safe.
The solution was to create a sheet piled perimeter around the entire footprint of the basement and then construct the basement inside these large steel sheets.
Steel sheet piles were drilled and hammered in to the ground, 10 metres deep. The top of all the sheet piles were connected with a reinforced concrete ground beam. This ground beam at the top and nearly 4m below formation at the ground lock the piles in place.
With the concrete ground beam cast & cured, the excavation could begin. It was done to around 3m first with a large temporary steel propping system installed to stop the sheet piled walls collapsing as the deeper excavations took place.
Fully propped, the full depth of 6m was achieved and a waterproof concrete, reinforced slab was installed at the base to secure the piles.
Once the base was cast the sheet piled perimeter walls were structurally sound all the temporary propping could be removed.
Reinforcing for the waterproof concrete walls was welded to the sheet piles, giving maximum strength to the structure. Sections were then shuttered with temporary timber shutter pans and cast with waterproof concrete.
With the sheet piled perimeter now fully cast in concrete, the internal walls and split levels were built. This included a large basement floor level swimming pool. The rest of the lower ground floor level was built on blockwork and block and beams, steel beams installed to carry the ground floor and finally large pre-cast concrete planks were lowered onto the walls to form a watertight basement.
The waterproofing regime on this project had to include a dual-protection system to satisfy the requirements of the warranty provider. Beautiful Basements was the designer and installer for both systems.
Type B – Waterproof concrete integral protection
All external walls inside the sheet piles, all concrete slabs (lower and upper levels) were cast with concrete including a waterproof additive. The steel reinforcing within this structure was designed to reduce the cracking to less than 0.3mm, also providing integral protection. All construction and day joints have a crystalising waterproofing slurry and an expanding waterbar applied to them to waterproof natural weak points.
Type C – Drained cavity protection
With the primary waterproof concrete system providing most of the protection, the secondary system was installed.
At the base of all external walls a recessed concrete channel was created within the slab. All walls and the floor were lined with a cavity drainage membrane (CDM). These membranes were linked to sump chambers via the recessed perimeter channels. Within the sump is two pumps and a high-level alarm. This system is designed to catch any water that is not stopped by the primary system and discharge it automatically. Flushing and maintenance points were installed to allow future servicing of the system. The front and rear lower sections are linked with a underground pipe.
Both waterproofing systems were designed by Structural Surveyors in Structural Waterproofing (CSSW) in accordance with BS8102:2009
All waterproofing materials were supplied by Triton Systems Ltd