Definitions Flashcards
Where are retaining walls required?
Where the slopes are steep and not stable in the long term
Where the building platform on natural ground is considered too small and construction of retaining walls will help to enlarge the building platform to its required plan shape and/or dimensions.
What is rock facing?
It’s used as a retaining structure to protect otherwise stable slopes
It can provide limited resistance to lateral earth pressures
Used primarily for erosion protection.
What is shotcrete?
Fine aggregates and mortar are the main constituents of shotcrete
Generally, shotcrete is applied pneumatically and placed in a layer of 50 to 100 mm
What are soil nails?
They can be used on either natural or excavated slopes.
It involves drilling holes for steel bars to be inserted into a slope face which is then grouted in place
Mesh is attached to the bar ends to hold the slope face in position
What is hydroseeding?
It is permanent slope protection with natural grass
The grass stabilises the slope structure and prevent slope erosion
Effective and less maintenance
When is shallow (less than 1.2m) trench required?
Construction of strip foundations, laying of pipes, sewers and drains
When is lateral support to the two sides of the trench required?
Soil is poor in strength
Soil is subject to the effects of ground water
Soil’s stability affected by other reasons (e.g. adverse weather, excessive vibrations/loading)
When is open timbering support needed?
For trench excavation >1.2 m but <1.8 m
When should sides of trenches be close-boarded?
For trenches >1.8 m
How are shallow trenches sheeted?
With boards laid horizontally
The ground is excavated 225 mm at a time and sides lined with a pair of boards which are temporarily strutted
When full depth is reached, poling boards are placed in pairs, one on each side against the sheeting and strutted
Temporary struts are then removed
What is the process of steel sheet piling?
Light trench sheeting consists of corrugated sheets driven by compressed air or or petrol hammers so the edges overlap
Withdrawal by crane
Heavier types are provided with interlocking edges
Driven by drop hammers, diesel hammers or double-acting steam or compressed air hammer
Withdrawn by large extracting grips used in conjunction with a crane, a double-acting hammer or hydraulic jacks
Piles over 12 m require very large extracting force so sometimes cheaper to leave the pile in position
What is a diaphragm wall?
It is a reinforced in-situ concrete wall that is cast in panels excavated into the ground
They may provide a safe and cost-effective solution to construct permanent retaining structures
