WorksheetsAdvantages and Disadvantages of Trench-Fill
Total questions: 20
Worksheet time: 10mins
Which advantage best explains why trench-fill foundations are suitable for clay soils?
Concrete cures slower in clay conditions
Trenches can be completed speedily in clay
Clay absorbs water from fresh concrete
Clay allows deeper excavation without shoring
A site has limited access for large vehicles. What is the most likely drawback when using trench-fill foundations?
Clay soil will inevitably swell or shrink
Trench bases require manual finishing
Concrete lorry access may be inadequate
More planking and strutting becomes necessary
Which safety-related benefit is associated with trench-fill foundations?
Soft spots at trench base cannot be bridged
No need for people to work at trench base
Risk of trench collapse increases after placing
Workers remain at trench base during pouring
Which soil conditions are most suitable for strip foundations as shown in the diagram?
Highly expansive topsoil layers
Peat soils with organic matter
Firm clays and compact sands
Loose silts with high water
A site has firm clay subsoil. To limit seasonal volume-change effects, what typical minimum trench depth should be targeted before placing a strip foundation?
Approximately 1500 mm deep
About 500 mm deep
Around 750 mm deep
At least 1000 mm deep
You are planning trench-fill for a load-bearing wall. The excavation wanders off line and is 80 mm shallow in places. Which action best maintains proper load distribution and wall alignment?
Leave it and widen the wall footing
Backfill with soil and continue
Hand-dig to correct depth and straighten
Pour extra concrete on one side only
Heavy rain is forecast overnight for an open trench awaiting concrete. Which action best reduces deterioration and safety risks while maintaining practical constraints?
Cover trench and schedule prompt concrete pour
Leave trench open until soil consolidates
Delay work and remove all excavated spoil
Increase trench width to drain water away
Choosing trench fill thickness above the minimum should primarily consider which practical factors?
Trench width, material costs, labour availability
Window orientation and solar gains
Architectural façade color schemes
Roof pitch and guttering details
What typically triggers the start of blockwork after foundation concrete placement?
Concrete has set over a few days
Cavity wall ties are installed on site
Architect issues the completion certificate
Concrete has reached full 28-day strength
Who usually determines whether foundation blockwork uses cavity construction or wide trench blocks?
Building control officer approving materials
Architect or developer making design decisions
Structural engineer during inspection
Site foreman based on crew preference
Which statement best describes the primary function of a raft foundation on soft soils?
Concentrates loads at column bases for stiffness
Spreads structural loads over a wide continuous area
Anchors the building using piles driven to bedrock
Transfers loads solely through deep end beams
A site has low soil bearing capacity and closely spaced columns. Which foundation choice minimizes interaction and reduces differential settlement?
Individual pad footings under each column
Strip foundations along load lines
Raft foundation with integral ribs or beams
Pile cap supported by long friction piles
In a raft foundation section, which layer directly supports the concrete raft slab across the site?
Screed placed above waterproof membrane
75 mm sand binding above hardcore base
Deepening of edge beam at perimeter
Damp-proof course beneath wall masonry
In a raft foundation, what is the primary structural role of the rigid concrete slab reinforced with steel as shown in the diagram?
Isolates walls from settlement but not floors
Spreads building load across the ground floor area
Concentrates loads under edge beams only
Transfers loads to deep individual footings
A site has soft, variable ground with potential differential settlement. Based on the diagrammed system, which foundation choice best manages this condition?
Timber piles supporting isolated pads
Raft foundation with reinforced rigid slab
Pad footings under each column only
Strip footings with minimal reinforcement
In which site condition is a raft foundation typically preferred because it spreads loads and reduces risk from ground movement?
Mining areas with potential subsidence
Stable rock with high bearing capacity
Permafrost requiring thermosyphon piles
Hilly sites requiring deep caissons
A building’s pad or strip footings would cover more than half of the ground area. Which foundation choice best suits this scenario to manage low bearing capacity and variable compressibility?
Driven piles with small pile caps
Raft foundation covering the whole footprint
Strip footings under load-bearing walls
Isolated pad footings at each column
In the typical raft section shown, what is the usual slab thickness range across spans between beams?
200 mm to 350 mm
150 mm to 300 mm
250 mm to 400 mm
120 mm to 200 mm
When constructing rafts on made-up ground, which statement best describes the role of engineering fill beneath the raft?
Replaces reinforcement to save material cost
Acts as a drainage layer to remove groundwater
Creates level support and reduces deeper foundation needs
Provides decorative edging for exposed concrete
In modern raft design on poor compressibility soils, where is reinforcement mesh commonly required?
At the top and bottom faces of the slab
Only within perimeter beams for bending resistance
Exclusively inside internal beam downstands
Only at column pads to prevent punching
