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Foundations Purpose – To transfer weight of structure (including live loads) to the ground within allowable settlement criteria.

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Presentation on theme: "Foundations Purpose – To transfer weight of structure (including live loads) to the ground within allowable settlement criteria."— Presentation transcript:

1 Foundations Purpose – To transfer weight of structure (including live loads) to the ground within allowable settlement criteria

2 Foundation Failure Leaning Tower of Pisa

3 Foundation Shape & Size Dependant on type of structure, weight, soil bearing capacity & sensitivity of structure Pressure under foundation = structure weight + imposed loads area of foundation * F.O.S Note effect of wind or horizontal loading

4 Mass Concrete Pile Cap

5 Reinforced Concrete Pile Cap

6 Replacement Displacement Driven cast insitu Permanent casing Temporary casing Pre-Formed Concrete Timber Steel Unsupported Supported Permanent Temporary support Casing Drilling mud Or water Types of Bearing Pile

7 Driven Cast Insitu No soil removed Can cause vibration and noise

8 Driven Cast Insitu Pile Rig

9 Driven Piles

10 Replacement - Rotary Bored Piling 300mm to 2400mm diameter Up to 50M depth Auger ‘screws’ into ground, breaking up soil Auger withdrawn with soil Back spun to release May require temporary casing

11 Continuous Flight Auger (CFA) Auger not removed during drilling – supports bore sides When design depth reached concrete delivered through centre of auger to base of bore and auger removed at same rate as concrete infill Reinforcement cage added to wet concrete Quiet Excavated soil to be disposed of

12 Continuous Flight Auger (CFA)

13 CFA Piling

14 Auger Pile Walling 1. Contiguous Piling – small gap between piles 2. Secant Piling – piles interlocked Reinforced Non Reinforced

15 Contiguous Pile Wall (with capping beam)

16 Vibro Replacement 1. Vibrator penetrates weak soils under action of vibrations and 'compressed air' jetting medium and forms a hole to design 2. After being held at depth for a short time, the vibrator is withdrawn and a charge of stone is placed into the hole. 3. The vibrator is reintroduced into the hole, the stone is compacted, forced out and tightly interlocked with the surrounding ground. 4. by adding successive charges of stone and compacting each one, a column of very compact stone is built up to ground level.

17 Vibro Replacement

18 Dynamic Deep Compaction With DDC, the ground is subjected to repeated surface tamping using a heavy steel and concrete weight. Typically the tamper weighs between 5 and 20 tonnes, dropping in free fall from heights of up to 25 metres. The tamper is dropped a set number of times on a grid pattern over the site to form a pass. Two to five passes on a site, dependent on soil type and condition, can be required. The imprints formed at each drop position are infilled with granular material after each pass.

19 Dynamic Deep Compaction

20 Health & Safety Issues Heavy plant manoeuvring on site – use banksman Other plant eg concrete deliveries need to work close by Overhead working on many applications Noise of driven piles Deep excavations to be protected Piles designed on basis of site investigation

21 Environmental Issues Noise from driven piles – ear protectors, neighbours Vibration from driven piles Removal of excavated material from replacement piling Protection of groundwater, particularly drilling mud (bentonite) Diesel storage


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