Level 1 Flashcards
1
Q
What are foundations?
A
Foundations provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity.
2
Q
What often causes unsuitable ground conditions for foundations?
A
Poor soil types - peat or filler ground.
High water table
3
Q
What considerations should be taken into account before designing foundations?
A
The nature of the load requiring support. Ground conditions. The presence of water. Space availability. Accessibility. Sensitivity to noise and vibration.
4
Q
What soil types are you aware of?
A
- Solid rock = high load-bearing, e.g. sedimentary rock
- Clay and silts = prone to shrinkage and expansion through water absorption, leads to swell and heave of ground.
- Peat and organic soils = subject to compression and volume changes. Generally unsuitable.
5
Q
Difference between cohesive soils and non cohesive soils
A
Cohesive soil means clay (fine grained soil), or soil with a high clay content, which has cohesive strength
Cohesive soils consist of large or irregular-sized soil particles with little to no clay content.
6
Q
what are the different types of foundation
A
Strip
Pad
Raft
Trench fill
Pile
Diaphragm wall
Pier
Sheet Pile
7
Q
What is a shallow foundation?
A
Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.
8
Q
What is a deep foundation?
A
Deep foundations are necessary where the bearing capacity of the surface soils is not adequate to support the loads imposed by a structure and so those loads need to be transferred to deeper layers with higher bearing capacity.
9
Q
What is a strip foundation?
A
Strip foundations provide a continuous strip of support to a linear structure such as loadbearing walls.
10
Q
What materials have commonly been used for strip foundations?
A
1) Concrete became common from 1920s onwards (but were used as early as 1875 when recommended by the Public Health Act).
2) Prior to this date, stepped brick footings were used, or just brickwork laid on level ground with no steps
11
Q
When would you use a strip foundation?
A
Most subsoils
Light structural loadings (e.g. low to medium rise domestic dwellings)
12
Q
What is the difference between a standard strip foundation and a deep strip foundation and why may the latter be advantageous?
A
With a deep strip foundation, the trench is filled to a higher level than with a standard strip foundation, meaning:
It is cheaper (although deeper than 1000mm becomes uneconomic)
Fewer man hours required
Working space for bricklaying not required
Requires less skilled trades
Uses ready mixed concrete, so less materials to store on site (clearer and easier to manage)
13
Q
When did deep strip foundations become common?
A
1970s onwards
14
Q
How would strip foundations be constructed on sloping sites?
A
The strips would be stepped to reduce the amount of excavation and materials required
15
Q
How wide are strip foundations?
A
The size and position of strip foundations is typically related to the wall’s overall width. The depth of a traditional strip foundation is generally equal to or greater than the overall wall width, and the foundation width is generally three times the width of the supported wall. This results in the load being transmitted at 45º from the wall base to the soil.
16
Q
What is the Building Regulations Document that sets out minimum widths for strip footings?
A
Approved Document A- Structure
defines minimum widths for strip footings based on the type of ground and load-bearing wall (although advisable to consult SE)
17
Q
What unit of measure is total load of load-bearings wall calculated?
A
kN/linear metre
18
Q
What types of ground & Condition of Ground are referred to in Table 10 Minimum width of strip foundations?
A
1 Rock (Not inferior to sandstone, limestone, firm chalk
2 Gravel/sand- medium dense
3 Clay/Sandy Clay- Stiff
4 Clay/Sandy Clay- Firm
5 Sand/Silty Sand/Clayey Sand- Loose
6 Silt/Clay/Sandy Clay/Clay or Silt- Soft
7- Silt, Clay, Sandy Clay, Clay or silt- Very Soft
19
Q
What Field Test is applicable for each type of ground (1-7)
A
1- Pneumatic/mechanically operated pick for excavation.
2- Pick for excavation/wooden peg 50mm sq in cross section to be driven beyong 150mm.
3-Thumb test (slight indent).
4- Thumb test (easy impression)
5- Can be excavated with spade/ wooden peg easily driven.
6- Finger pushed- 10mm
7- Finger pushed- 25mm.
20
Q
How to prevent Frost Action in strip foundations?
A
At least 450 mm unless they are bearing on rock, and at least 1 m on high shrinkage clays.
21
Q
For Wide Strip Foundations what is usually included?
A
Reinforcement.
22
Q
Limitations of strip foundations?
A
Higher localised loads, ground conditions are poor or settlement is likely or impractical for individual strips.
23
Q
What is a Pad foundation?
A
Pad foundations are rectangular or circular reinforced concrete pads used to support localised loads such as columns.
24
Q
When would you use a Pad foundation?
A
Used to support localised loads, such as columns
Most subsoils except loose sands, loose gravels and filled areas
25
What would be some potential limitations with Pad foundations?
They can be large in plan shape and may not be effective against differential settlement, uplift forces or wind forces.
26
What is a Raft foundation
Reinforced concrete slabs that cover a wide area, often the entire footprint of a building, Raft foundations may incorporate beams or thickened areas to provide additional support for specific loads.
27
When would you use a Raft foundation?
1) Poor ground conditions are poor, settlement is likely
2) Where impractical to create individual strip or pad foundations.
3) Where subsidence is likely (e.g. above former mining areas or landfill)
4) On deep areas of fill where piling would be uneconomic
5) Used to spread the load of the superstructure over a large base to reduce the load per unit area being imposed on the ground
28
What is a Trench fill foundation?
Trench fill foundations are a variation of strip foundations, in which the trench excavation is almost completely filled with concrete (avoids bricklaying below ground).
29
When would you use a Trench foundation?
Trench fill is often used when soil is loose or in areas with a high water table, although in loose ground it can be difficult to predict the quantity of concrete required, and the quantity can be quite high if trenches meet or cross at right angles.
30
When constructing trench foundations, what would you need to do if there is the presence of trees or heavy?
Trench fill foundations can be taken deeper in areas with heavy clay or in the presence of trees, to a level where the subsoil moisture content is unaffected. In these situations, mesh reinforcement is often required. In addition, one or both trench faces may need to be lined with a compressible batt. This can also mitigate against the tendency in some situations for the trench strips to pick up longitudinal or lateral ground strains which may occur in the strata immediately around the foundation.
31
What is a common issue with trench foundations?
Another issue to consider is that the height of the concrete can create access problems for drainage and other services, as well as issues with landscaping and planting.
32
What is a Rubber-Trench fill foundation?
A further variation of trench fill foundations, and are a traditional construction method which uses loose stone or rubble to minimise the use of concrete and improve drainage.
33
Where there are higher localised loads, such as columns- what foundation would you recommend?
Pad.
34
Where ground conditions are poor, settlement is likely, what foundation would you recommend?
Raft.
35
When did pile foundations start being used?
Rarely found before 1970, except as remedial underpinning
36
When would you use a Pile Foundation?
1) Where a firm layer of ground is at a considerable depth (i.e. where strip foundations would be uneconomical)
2) On shrinkable clays with new or felled trees
3) Large structures
4) Recently placed filling materials that have not sufficiently consolidated
High water table
37
What different types of piling are you familiar with?
1) End bearing piles - most friction is developed at the toe of the pile, bearing on a hard layer
2) Friction/floating pile - most of the friction is developed by shear stresses along the sides of the pile, where harder layers are too deep to reach
38
How can pile foundations be installed?
1) Replacement/bored piles - poured insitu (if boring and pouring takes place simultaneously they are called Continuous Flight Augured (CFA) piles)
2) Displacement/driven piles - prefabricated off site and then driven into the ground
39
Describe the components of a piled substructure and their functions.
```
Pile shaft - provides friction and stability in the ground
Pile cap (aka ground beam) - spans from pile to pile, carrying the floor structure and walls (either formed in situ or pre-cast)
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40
What are the different types of Pile Walls?
By placing piles directly adjacent to one another, a permanent or temporary retaining wall can be created. These can be closely-spaced contiguous pile walls, or interlocking secant walls, which depending on the composition of the secondary intermediate piles can be hard/soft, hard/firm or hard/hard secant walls.
41
What ancillary activities are carried out in connection with piling?
Site constraints (e.g. headroom limitations of driven piles)
Monitoring adjacent sites (e.g. vibration of driven piles)
Health and safety
Underground services scan
42
What is a Diaphragm wall?
Diaphragm walls are made by excavating a deep trench that is prevented from collapsing by being filled with engineering slurry such as bentonite and then the trench is filled with reinforced concrete panels, the joints between which can be water-tight.
43
When would you use a Diaphragm wall?
This is commonly used for top-down construction, where a basement is constructed at the same time as above ground works are carried out. Diaphragms walls are often used on congested sites, close to existing structures, where there is restricted headroom, or where the excavation is of a depth that would otherwise require the removal of much greater volumes of soil to provide stable battered slopes.
44
What are the advantages of Diaphragm wall?
1) suitable for most subsoils
2) installation generates only a small amount of vibration and noise,
3) floor slab connections and recessed formwork can be incorporated into the walls.
45
How are diaphragm walls installed?
Range in thickness from 500 - 1,500 mm and can be excavated to depths of over 50 m.
Rope-suspended mechanical or hydraulically-operated grabs.
46
What are the disadvantages of a diaphragm wall?
The high cost of diaphragm walls can make them uneconomic unless they can be incorporated into part of a building structure. As such, they are suited for deep basements, underground car parks and rail stations, tunnel approaches, underpasses, deep shafts for tunnel ventilation, pumping stations, and so on.
47
What is a Pier Foundation?
Series of thick concrete piers (usually large concrete rings), formed insitu, supports a reinforced concrete ground beam
48
When would you use a Pier Foundation?
Alternative to piling where ground is full of obstructions (e.g. old basements)
If the ground is too steep for piling rigs
49
What is a Sheet Pile?
Sheet piles are sections of sheet materials with interlocking edges that are driven into the ground to provide earth retention and excavation support. Sheet piles are most commonly made of steel, but can also be formed of timber or reinforced concrete.
50
When would you use a Sheet Pile?
Sheet piles are commonly used for retaining walls, land reclamation, underground structures such as car parks and basements, in marine locations for riverbank protection, seawalls, cofferdams, and so on.
51
The selection of a sheet pile depends on?
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The type of work, for example. whether it is permanent or temporary.
Site conditions.
The required depth of piles.
The bending moments involved.
The nature of the structure.
The type of protection required.
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52
What considerations do you have in relation to foundation type?
* Soil type and nature of the ground conditions (subsoil condition:mining)
* Loads to be imposed by building/structure
* Water table
* Cost
* Durability (ability of pile to survive ground conditions, e.g. contaminated, acidic etc
* Location (adjacent structures, e.g. displacement piles)
53
What is meant by the term 'water table' and how may it affect construction?
The level below which ground is saturated with water
Rises and falls with variations of rainfall, temperature, atmospheric pressure and tide (in coastal regions)
Usually below the depth required for strip foundations, however when it is not, additional precautions may be needed, such as:
Change in foundation design to accommodate water levels
Use of sulphate resisting cement to prevent sulphate attack
Use of pumps during construction to rid trenches of water whilst concrete is being laid
54
What is a percolation test and when is it used?
Test to determine the absorption rate of soil by digging a trial pit, filling it with water to a certain level and observing how quickly the water dissipates.
55
Name three types of tests for soil?
California Bearing Ratio & vane shear testing & Percolation test.
56
What is CBR?
Used to determine how strong the ground is and to calculate the bearing capacity of the soil
57
What is vane shear testing?
Used to determine the shear strength of a saturated cohesive soil by inserting a vane into the ground, rotating it until the soil fails and measuring the torque
58
How are earthworks supported and why?
Temporary shoring (or 'sheeting')
59
Describe the different ways of dealing with ground water in excavations?
Pit/sump - excavated below trench level to act as a collection point from which the water can be pumped away
Cofferdams - temporary enclosures (usually interlocking steel sheets) that form watertight perimeter around the area of work
Caissons - similar to cofferdams but usually form an integral part of the finished structure
60
How can you test piles?
It is advisable to test load at least one pile per scheme by forming a trial pile that is in close proximity but does not form part of the actual foundations. The pile should be overloaded by at least 50% of its working load and held for 24 hours. This provides a check on the ultimate bearing capacity of the pile as well as the workmanship involved in forming the pile.
61
What is the British Standard for foundations?
BS 8004:2015 Code of practice for foundations
62
What is a Green Roof?
A roof of a building that is partially or completely covered with vegetation and a growing medium, planted over a waterproof membrane
May also include additional layers such as a root barrier and drainage and irrigation systems
63
What are the different systems available?
Intensive, Extensive & simple intensive.
64
What country is pioneering Green Roofs?
Germany- 10% of all green roofs have been greened.
65
What are the main components of a green roof?
Green roofing systems require a minimum of four components:
1) The root barrier – prevents the roots of vigorous plants penetrating through to the waterproofing and damaging the membrane. The root barrier can either be a biocide or a copper/ heavy grade polythene-based material.
2) The drainage layer – controls the water retention properties of the roof in combination with the substrate. Drainage layers can be composed of either granular materials (e.g. sand and gravel, lava and pumice, crushed brick etc.) or modular/ sheet systems.
3) The substrate (or growing medium) – provides the mechanical strength, pore structure, nutrients, chemical composition and drainage properties for the desired plant species. A wide range of natural and manufactured substrates are available.
4) The vegetation layer – can be established using vegetation mats (e.g. sedum mats), through plug-planting pot grown plants into the substrate, by distributing by hand seeds or cuttings or simply by natural colonisation.
66
What other components cand be specified to a green roof system?
1) Filter membranes,
2) Moisture mats & protection boards,
3) Water retention systems & irrigation systems,
4) Additional thermal insulation.
67
Is there any legislationavailable for green roofs?
Increasing demand for more sustainable and energy efficient buildings. National policy is in place to promote the protection of wildlife, the enhancement of biodiversity, the management of flood risk and to improve the thermal efficiency of buildings. Typical drivers include:
1) Wildlife and Countryside Act, 1981 (as amended)
2) The Water Framework Directive (2000/60/EC)
3) PPS9 Biological and Geological conservation
4) Biodiversity Action Plans (BAPs) at local and national levels- These provide a guide to the priorities for wildlife conservation, the action that needs to be taken and the resources that will be required.
5) PPS25 Development and Flooding- Advises that restriction and reduction of surface water runoff can be encouraged by the provision of sustainable drainage systems (SUDS)
6) Part L, Building Regulation
68
How does the Wildlife and Countryside Act 1981 relate to green roofs?
Any works that may impact on nesting birds or roosting bats needs very careful consideration
69
How does the The Water Framework Directive (2000/60/EC) relate to green roofs?
More sustainable approach to water management.
70
How does PPS9 Biological and Geological conservation the relate to green roofs?
Protection of statutory and non statutory designated wildlife sites.
71
How does the PPS25 Development and Flooding relate to green roofs?
Advises that restriction and reduction of surface water runoff can be encouraged by the provision of sustainable drainage systems (SUDS)
72
How does the Part L, Building Regulation relate to green roofs?
Aims to substantially increase the energy efficiency of new and existing buildings. Green roofs and walls can make a contribution towards increased insulation, especially where retrofitted on to older, lightweight, and poorly insulated buildings.
73
What is an extensive green roof?
Extensive (Thin soil/little-no irragation systems/nutrient poor requirement).
Extensive landscaped roofs are defined as low maintenance, drought-tolerant, self-seeding vegetated roof covers that incorporate colourful sedums, grasses, mosses, and meadow flowers that require little or no irrigation, fertilisation, or maintenance…
Extensive systems can be placed on low-slope and pitched roofs with up to a 40% slope.
74
What is an intensive green roof?
Intensive (Deep soil/irragation requirements/fertile conditions): If there is adequate load-bearing capacity, it is possible to create actual roof gardens on many buildings. This type of eco-roof system may include lawns, meadows, bushes, trees, ponds, and terraced surfaces. Intensive systems are far more complex and heavy than extensive eco-roof systems and hence require far more maintenance.'
75
What is a simple intensive green roof?
(Various substrate depths/combo) Comprise grasses, herbaceous plants and shrubs. Simple intensive green roofs can be constructed using varying depths of substrate, thus combining elements of extensive and intensive roofs (
76
What is the most common type of green roof? And Why?
Extensive green roofs - generally light weight and low cost.
77
What are the enviromental benefits of green roofs?
1) Decreased surface water runoff - retain up to 80% of summer rainfall (35% in winter), reducing demand on drainage systems and less flooding risk.
2) Noise - considerably reduce external sound within a building
3) Energy conservation - minimises internal temperature fluctuations (although less effective in the winter as the substrate is often damp)
4) Roof longevity - protects roof from temperature extremes
5) Air quality - absorbs carbon dioxide and produces oxygen, filtering out dust and smog particles
6) Encourages biodiversity
7) Urban Heat Island Effect
8) Less maintenance costs- reduced temperature fluctuations on green roofs and the protection of the water proof membrane.
8) Increased property value/marketability.
78
What about the maintenance costs if the water proof membrane is punctured?
1) Modern lightweight modular green roof systems include products that are made up of 0.5 m module trays which slot together for a seamless finish and provide plant drainage.
2) The modules are installed over a geotextile filter fabric, which sits on top of the waterproofing. They interlock and need no fixing, so there is very little danger of puncturing the waterproof membrane.
79
What is the UHI effect?
Urban Heat Island Effect- the replacement of natural surfaces with hard impervious surfaces that are generally dark and absorb large amounts of solar radiation.
80
What are the disadvantages of using a green roof in comparison to a traditonal flat roof?
1) Increased capital costs. Extensive Roofs 150-200% more expensive & Intensive Roofs are 200% more expensive.
2) Increased structural loads- 50 and 200kg/m2 of loading to the roof of a structure.
3) Specialist contractors required- green roofs are currently not common in the UK, and thus widespread contractor knowledge is limited.
4) Maintenance requirements- Intensive green roofs require increased regular pruning, feeding, weeding and watering. Extensive sedum roofs are relatively low however- visual inspection every 6 months.
5) The lack of quantifiable data on the benefits of green roofs.
6) The lack of technical information about how to build them.
7) Lack of incentives.
81
What type of roof can a green roof be?
Flat or Pitched.
82
What is a blue roof?
Designed for the retention of rainwater above the waterproofing element of the roof (as opposed to drained).
Blue roofs are typically flat, without any fall, with control devices regulate drainage outlets that enable water to be retained or drained.
83
What is a brown roof?
Roofs which have a layer of soil or other material which provides a habitat or growing medium for plants or wildlife.’
84
What are the benefits of steel vs concrete frame buildings?
Concrete can be cheaper - ingrediant are cheaps
In situ has design flexibility
Concrete has good fire resisitnat properties
```
Steel -
reduced construction time.
Steel is lighter than reinforced concrete
High strength
Create large spans
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85
Can you talk me though the construction of a typical Victorian detached residential property
Roof - timber framed roof, commonly closed couple roofs with slate roof covering (King post truss and queen post truss)
Walls - soild brickwork walls with no cavity (cavity post 1920)
Timber floors suported by the brickwork (not post 1920s, use hangers)
Ground floor - suspended timber ground floors with sleeper walls and ventilations grills
Metal/ timber framed single glazed sash windows
Foundations - shallow corbelled brickwork footings
No DPC prior to 1875 - slate used after
86
Take me through a modern residential house?
Foundations - Strip foundations and raft foundations (150mm concrete footing)
Walls - Cavity wall with blockwork inner wall and cavity insulation held with wall ties
Ground floors - Concrete ground floors, Use damp proof membranes and can include insulation. have suspended concrete floors beam and block)
Upper floor - metal web joists - hung from the wall
Roof - TRADA roof truss from 50s onwards -less material wider spans.
87
Why use a raft foundation instead of a strip foundation?
Reduce the amount of load onto the soil as the whole building takes the weight
88
What is an f-gas
Fluorinated gas - contribute to a global greenhouse effect
89
What are the different types of flat roof
Cold deck
Warm deck
Inverted
Green
90
Name types of flat roof covering and how they are installed.
Single ply roof covering - rolled in sheet and adhered to the deck or insulation. Sheets overlap and welded.
Reinforced bitumen felt - pour & roll (hot bitumen poured and felt applied) and torch-on (flame is applied to underside for it to adhere).
Mastic Asphalt - hot rolled
Zinc
Copper
Steel
Aluminum
NB. Asbestos sheet roofing
91
What does BRE Stand for
Building Research Establishment
92
Name other BRE Digest
BRE251 - assessment of damage
| BRE405 - Carbonation of Concrete and its effect on durability.
93
Tell me the difference between cast in situ concrete and pre-cast?
• In situ concrete is used on-site and is poured into formwork and allowed to cure and set.
o Improved design flexibility
o Less of an issue transporting to site
o Quality control must be monitored on-site, skilled labour etc.
o Longer construction process due to curing periods etc
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• Pre-cast concrete is manufactured off-site and then transported to site in existing mould/framework
o Reduces on-site construction period
o Controlled construction environment
o Consistent/uniform factory finish
o Reduced design flexibility
o Can be issues at joints in structure
o Difficult to transport to site
o Lifting equipment required on-site
```
94
Can you tell me about MMC and name some forms?
* Modern Methods of Construction aim to improve efficiency and quality by undertaking works off-site and in a controlled environment, and therefore minimising the construction period on-site.
* MMC aim to improve efficiency, quality, environmental performance and sustainability
• Examples are:
o Volumetric construction
o Pod construction
o SIPS
95
What are the advantages and disadvantages of MMC
* Advantages = energy efficient, minimal waste, controlled quality, reduced on-site construction
* Disadvantages = increased costs, lack of flexible design, difficult resale value.
