Basements Flashcards
What are the 3 types of basements?
Retaining wall and raft basements
Box and cellular raft basement
Piled basement
What is a retaining wall and raft basement?
consists of a slab raft foundation (basement
floor) that distributes the building loads, the basement walls are the retaining walls
What is a a box and cellular raft basement?
retaining wall and raft but internal structural walls are used to transmit and spread loads over the raft – divides the basement into cells.
What is a piled basement?
The main superstructure loads are carried to the basement floor by columns and
transmitted to the ground via pile caps and bearing piles (i.e. your basement has a
whole load of columns going through it)
What are the main types of excavation?
Open
Perimeter trench excavation
Complete excavation
What is open excavation?
Uses battered excavation sides cut back to a safe angle, eliminates the need for temporary support work, can easily construct basement walls and fall BUT extra excavation costs and need a lot of free site space
What is perimeter trench excavation?
Trench dug wide enough to form basement walls, this
is supported as required – basement walls are constructed and then the inside of the
basement is excavated.
What is complete excavation?
Used in firm subsoils. The Centre of the basement is
excavated first, then the basement slab cast while the sides of the excavation are
supported by struts
What are the three types of waterproofing to basements under BS8102:2009 ‘The British Standard code of practice for the protection of below ground structures against water from the ground’?
Type A: Barrier Protection (Tanking)
Type B: Structurally Integral Protection
Types C: Drained Protection
What is a tanked basement?
Tanking systems are not recommended unless drainage is provided above the wall/floor membrane lap position and the site is relatively free-draining.
What is an integral system?
Mainly used in the construction of new basements, these systems use concrete retaining walls that resist the ingress of water in differing amounts, depending on thickness, the amount of reinforcement and the density of the concrete. Compaction of the concrete and the installation of water stops at the construction joints are critical. Additional tanking may also be required.
What is a drained system?
Profiled polythene membranes are applied to the vertical surfaces to form a drained and vented cavity layer. For example, Delta Membrane Systems produce damp-proof systems for retro-fitting basements. The moisture is collected in the sump and pumped away. These systems are thought to be much more reliable than other waterproofing systems for retro-fitting. Access hatches for the inspection and maintenance of internal gullies should be provided where possible. Sumps may need back-up pumps. Fixing the membranes to the walls must be carried out with great care.
