Piling / Piling Caps Flashcards
Definition of a pile foundation…
Pile foundations are a series of columns constructed or inserted into the ground to transmit the loads of a structure to a lower level of subsoil
Piles are used due to to (4)
1) Natural low bearing capacity of the sub soil
2) High water table
3) Presence of layers of highly compressible sub-soils such as peat and recently placed fill materials
4) Subsoils which may be subject to moisture movement or plastic failure
4 classifications of piles are
1) End bearing
2) Friction or floating
3) Replacement
4) Displacement
End bearing pile…
Transmits load direct to firm strata below
Friction or floating pile…
Transmit load to surrounding soil via friction between surface of pile and soil
Replacement piles are formed by
Boring hole in ground with material removed from ground and resultant void filled
Displacement piles are formed by…
Driving preformed piles into the ground, displacing the subsoil through which it passed
Factors which affect the choice of piling to be used are (5)
1) Location
2) Nature of ground
3) Cost
4) Structural performance
5) Durability
4 Types of piling we are focussing on are
1) Driven
2) CHD - Continuous Helical Displacement
3) CFA - Continuous Flight Auger
4) Rotary Bored
Driven piles are a form of ________________ piles
Displacement
Driven pile method - brief description
Precast segment piles are driven into the ground via a hydraulic hammer driven pile rig. A steel helmet if placed on the top of the pile section to ensure the concrete doesn’t break during the driving process. Pre-formed holes on top of sections and pin on bottom allow for sections to be joined together on site during the piling process. Can be coated to provide protection to the pile sections and increase friction properties.
Advantages of driven piling (6)
1) Good choice for deep piles
2) Can be used in aggressive or contaminated soils
3) Sections pre-fabricated off site
4) Wide selection of different sizes and lengths
5) High bearing capacity due to being displacement pile
6) Minimal waste material
Disadvantages of driven piles (5)
1) Cost of transport due to weights / dimensions
2) May not be suitable for ground with poor drainage
3) Not suitable for compact sites where vibrations may affect surrounding buildings
4) Noisy to install - consideration to surroundings.
5) Not always possible to determine sizes required - results in splicing or cut off techniques being used which has time / cost affect
Item to sketch / annotate for driven piles (9)
1) Piling rig
2) Bracing on rig
3) Leader of rig
4) Drop hammer
5) Helmet on top of pile section
6) Pile sections
7) Joins in pile sections
8) Reasonably level ground surface
9) Precast concrete or steel show unit at bottom of piles
CHD is also known as… (2)
1) Rotary Soil Displacement
Or
2) Screw Displacement
CHD piles are a form of _____________ piles
Displacement
CHD method - brief description
Multi flight, bullet ended shaft, driven by high torque rotary head bored in the subsoil / strata. Concrete is pumped down shaft and out of the tip of the drilling rig while the shaft is reverse rotated and withdrawn from the bore. Steel reinforcement is added once drilling rig removed and before concrete sets. Steel left protruding from pile.
Advantages of CHD piling (4)
1) Minimal waste / spoil due to displacement
2) Minimal vibration and noise
3) High bearing capacity due to displacement
4) Speed of installation
Item to sketch / annotate for CHD piles (5)
1) Drilling rig
2) 5 Stages - rig in position, drilling, reaching design point, removal and filing of concrete, insertion of steel reinforcement.
3) Arrows showing displacement of soil outwards to surrounding soil
4) Concrete delivery vehicle
5) 3 sections to drilling head, screw section, flat section, screw section
Continuous Flight Auger (CFA) is a form of ___________ piling
Replacement
CFA method - brief description
Hole is bored using CFA - hollow stemed auger. Design depth reached. Concrete pipe connected to head of auger stem before withdrawal. Concrete injected down hollow stem and out tip of auger to fill void as the stem is slowly withdrawn, bringing spoil material with it. Extraction is controlled and monitored to ensure positive pressure in the concrete being pumped, ensuring hole does not collapse. On completion of stem removal and concrete injection steel reinforcement added.
Advantages of CFA piling (5)
1) Virtually vibration free
2) One of quietest forms of piling
3) Suitable for most strata
4) Can be used in water bearing strata
5) Quick and economical install
Item to sketch / annotate for CFA piles (5)
1) Drilling rig begins drilling - spiral drill section extends entire length of hole.
2) Design depth reached - pump, concrete mixer and silo connected.
3) Auger removal, hole beginning to fill with concrete, spoil at top of hole either side.
4) Complete removal of auger and hole filled with concrete
5) Steel reinforced cage added.
Rotary Bored piles are a form of ___________ piling
Replacement
Rotary Bored Pile method - brief description
Drilling rig with telescopic Kelly bar and auger head bores hole in ground. Steel guide casings inserted as hole formed -Tremmie pipe - sometimes full depth of hole, sometimes on first few metres. Drill down to design depth. Remove drilling auger - bringing spoil back to ground level. Concrete poured in hole. Steel guide casings removed. Steel reinforcement added if required. Optional - toe of pile can be under-reamed up to 3x shaft diameter (conical shape) to increase end bearing capacity.
Advantages of Rotary Bored piling ()
1) Bigger diameter piles that CFA can be formed.
2) Virtually no vibration
3) Higher load capacity than driven piles
Item to sketch / annotate for Rotary Bored piles (9)
1) Heavy duty crane / rig
2) Suspension rope
3) Kelly bar swivel connection (box at top)
4) Rotary telescopic Kelly bar
5) Kelly bar drive unit
6) Rotary auger
7) Bore hole lined with casings
8) Steel reinforcement
9) Underreamed section at toe of pile
What are pile caps
Pile caps finish off a cluster of piles near formation level with a reinforced concrete pad which often incorporates the holding bolts for a steel frame or concrete kicker for a concrete frame
There are 3 main shapes of pile caps which normally incorporate a set amount of piles. These are (3)
1) Square shape with 4 piles
2) Triangle shape with 3 piles
3) Rectangular shape with 2 piles
The reinforcement bars in the piles are….
Linked into the reinforcement bars in the pile cap to create continuity
Pile caps are linked together with…
Reinforced concrete ground beams
The stages to forming pile caps are (8)
1) Excavation around the pile to create a pit for the pile cap. Soil is removed to landfill.
2) Top section of concrete removed from pile using cropper to expose steel rebar.
3) Blinding concrete is poured to the base of the pit to provide smooth platform for reinforcement cage.
4) Steel fixers prepare reinforcement cages.
5) Steel reinforcement cages placed with spacers at base separating cage from blinding concrete.
6) Permanent formwork installed along outside of pit with spacers separating from steel cage.
7) Backfill to formwork with spoil to provide support.
8) Concrete poured/placed, compacted and cured in pit. Holding down bolts / bolt boxes can be cast at this stage for continuity.
3 types of testing piles are
1) Dynamic Load Test
2) Static Load Test
4) Sonic Integrity Test
Dynamic load testing is carried out by… (6 Parts)
1) Two strain transducers and accelerometers are firmly attached to the head of the pile.
2) The pile is restruck using a pile hammer.
3) Force and acceleration of the pile is measured.
4) This information is relayed to the pile driving analyser.
5) Data digitally sorted.
6) Stress wave analysis conducted on data giving shaft friction distribution, bearing capacity and load settlement behaviour information.
Advantage of dynamic load test…
1 pile can be done in a matter of minutes meaning a large number of piles can be tested on one visit to site.
2 most common methods of static load testing are
1) Kentlidge block system
2) Anchor pile method
Static load testing is carried out by… (4 parts)
1) Hydraulic jack mounted on test pile
2) Load placed on top
3) Measurements taken and recorded - data stored electronically
4) Information presented in graph detailing displacement characteristics of pile.
Sonic integrity testing is carried out by… (5 parts)
1) Using small hand held hammer a series of low strain acoustic showcase waves are passed down the pile.
2) The wave rebounds where changes in impedance occur.
3) This rebound or echo is then recorded by a small accelerometer held against the pile head.
4) Responses stored digitally.
5) Information plotted in graph.
Sonic integrity test is used to determine the (3)
1) reliability
2) morphology
3) quality of construction
Of a pile
An advantage of sonic integrity testing is…
Test can be carried out quickly meaning a large number of piles can be tested in one visit to site.
Disadvantage of static load testing is…
It is more time consuming to set up and carry out in comparison to other methods.
As concrete is delivered to site it should be tested by doing a ______ ______ to make sure it is the correct grade
Slump test
