week 9 Flashcards
What type of soil classifications exist?
Rock
Igneous rocks, such as granites, basalts which were formed as a result of solidification of molten material
Sedimentary rocks, such as sandstone, chalk and limestone, which were formed by deposition of granular material or sediment
Metamorphic rocks, such as slate which was formed as a result of heat or pressure acting on igneous or sedimentary rocks and changing the crystalline structure
Gravels & Sands
Typically grouped as coarse graded cohesion-less soils .06mm +
Move independently of each other
If treated can provide an adequate building base
Silts & Clays
Typically grouped as fine graded cohesionless soils < .06mm
Subject to changing moisture contents
Dry shrinkage and heave in wet weather
Peat & Organic Soils Large organic material Subject to large changes in compression resulting in decay from organic matter Generally not suitable for building Where is this most commonly found?
define contanimated ground
Any substance which is or could become toxic, corrosive, explosive flammable or radioactive and likely to be a danger to health and safety.
Before foundation types are decided, a number of factors regarding the structure and the site it is to be considered on will have to be considered. These include
Weight of the proposed structure Purpose of the structure Soil composition of the proposed site History of the proposed site Feasibility of costs
what is a foundation
Foundationsare the lower portion ofa buildingstructure that transfers its gravity loads to the earth.
Foundationsare generally broken into two categories: shallowfoundationsand deep foundations.
A tall/heavybuildingmust have a strong foundationif it is to stand for a long time. Basically Foundations act as the interface between loads of the building and the ground.
2 categories of foundatins
shallowfoundationsand deep foundatio
define raft foundation
Raft foundationis actually a thick concrete slab resting on a large area of soil reinforced with steel, supporting columns or walls and transfer loads from the structure to the soil. Usually, matfoundationis spread over the entire area of the structure it is supporting.
adv of raft foundation
Advantages of Raft Foundation:
Raft foundation is economic due to combination of foundation and floor slab.
It requires little excavation.
It can cope with mixed or poor ground condition.
neg of raft foundations
Disadvantages of Raft Foundation:
Raft foundation requires specific treatment for point loads.
Edge erosion occurs if not treated properly.
define pad foundations
Pad foundationsare a form of spread foundationformed by rectangular, square, or sometimes circular concrete ‘pads’ that support localised single-point loads such as structural columns, groups of columns or framed structures.
advantages of pad foundations
Advantages of Pad Foundations
Shallow foundations, so little excavation is required
Economic
Reinforcement for shear and tension can be added
Can be designed to accommodate a tight site
Easy design and
negatives of pad foundatin
Size of pad can be very large
Require bigger support for deep excavations
Weak against forces
Separated foundations
define strip foundation
Strip foundations(orstripfootings) are a type of shallowfoundationthat are used to provide a continuous, level (or sometimes stepped)stripof support to a linear structure such as a wall or closely-spaced rows of columns built centrally above them. Strip foundations are arguably the cheapest form of foundation available.
advantages of strip foundations
and neg
Conventional build method
Good amount of concrete thermal mass in floor.
Require simple excavation & simple formwork
Adapt to sloping sites
Cheap
Disadvantages
Generally requires good ground conditions
explain shallow foundation forms
Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.
Required to cope with point loads
Shapes of pad foundations can be varied to cope with site conditions
Raft foundations can be developed to become buoyant in some circumstances
Pad foundations
Strip foundations
Raft foundations
type of pad foundations
The location of such pads may include;
A series of discrete, well-separated pads.
Balanced base pads that support more than one point load.
Continuous pads, where there are a number of point loads close together
what is a displacement pile
In simple terms during the displacement pilling method, piles are driven into the ground pushing the ground out of the way, as you see in sheet piling.
Displacement pilling is good for contaminated sites where it can cost a lot to remove soil
Piles are forced into the ground by forcing or driving a solid pile or hollow casting into the ground.
Methods of installation can include drop hammer, vibration or using a jack.
There are three broad types of basement wall structure
Tanked (Barrier Protection) – Type A
Waterproof (Structurally Integral Protection) – Type B
Drained (Drained Protection) - Type C
explain tanked
Structures will often be of masonry construction, plain or reinforced concrete may be used. The latter may be in-situ or precast.
The structure is regarded as having no integral protection against water ingress and so relies on the applied waterproofing system to provide the necessary control.
Barrier is commonly a multi coat render, cement based coating, bituminous paint or epoxy coating.
The waterproofing system will, depending on its type, tolerate certain construction cracks or minor defects.
Fine hair-line cracks up to 0.3mm wide in reinforced construction will generally be acceptable.
explain waterproofed
Structures will generally be reinforced or pre stressed concrete.
Since they are specifically designed to be water-resistant, further waterproofing will be required
In some instances, the additional protection may be used to safeguard the structure from aggressive chemicals.
Any noticeable cracking or defect should be brought to the attention of the designer.
explain type c drained
Structures incorporate a drained cavity in the basement
Manages any water that enters the structure.
The drainage channels must be properly formed and positioned and be free from obstructions and be free flowing.
There is a permanent reliance on the cavity to collect groundwater that enters through the fabric of the structure.
The drainage system directs the water to a drain or sump, where it can be removed from the building by gravity or pumping
issues to consider in basement construction
Nature of the site
Access limitations to and within the site boundary Topography Water table/ drainage Proximity of other structures Previous site use
- Building Form Depth of the basement Intended function of the basement
- Legal Issues Rights of adjacent building owners Health and safety
- Economic Issues Maximisation of useable building area Minimisation of construction cost
explain methods of basement construction
Open excavations (Shallow)
Excavations with temporary support (Deep)
Excavation with permanent retaining walls formed prior to main excavation (Deep)
explain open excavation (shallow basement)
Small scale basements
Excavation depth is likely to be relatively shallow
Most economical form is open excavation
Limited to area that is not limited in space
Slope angle depends on soil conditions
Poor soil is prone to collapse so will display a shallow angle of repose
explain deep basement construction
Open excavation is not ideal
Risk of subsidence
Cost of large scale works
Therefore….
Excavations with temporary support (Deep)
Excavation with permanent retaining walls formed prior to main excavation (Deep
advantages of sheet pile wall
Steel sheet piles provides several advantages
- Provides high resistance to driving stresses.
- Light weight
- Can be reused on several projects.
- Easy to adapt the pile length by either welding or bolting
sheet pile wall disadvantages
- Sections can rarely be used as part of the permanent structure.
- Installation of sheet piles is difficult in soils with boulders or cobbles.
- In such cases, the desired wall depths may not be reached.
- Sheet pile driving may cause neighborhood disturbance
The most common types of deep basement construction are
Contiguous piles &
Secant
Contiguous piles
Relies on the placement of many piles immediately beside each other around the perimeter of the basement
Piles are likely to be bored replacement piles
Prevent soil falling into the basement during construction
Bracing must be provided to avoid lateral pressure
Secant
Overlap, rathe than beside each other
More strength & moisture exclusion
Generate a list of criteria against which you might judge the performance of ground conditions when selecting foundation options?
bearing capacity
depth of good strata
composition of ground level
ground level gradients
