3Foundation Shape & Size Dependant on type of structure, weight, soil bearing capacity & sensitivity of structurePressure under foundation= structure weight + imposed loadsarea of foundation * F.O.SNote effect of wind or horizontal loading
10Replacement - Rotary Bored Piling 300mm to 2400mm diameterUp to 50M depthAuger ‘screws’ into ground, breaking up soilAuger withdrawn with soilBack spun to releaseMay require temporary casing
11Continuous Flight Auger (CFA) Auger not removed during drilling – supports bore sidesWhen design depth reached concrete delivered through centre of auger to base of bore and auger removed at same rate as concrete infillReinforcement cage added to wet concreteQuietExcavated soil to be disposed of
16Vibro Replacement1. Vibrator penetrates weak soils under action of vibrations and 'compressed air' jetting medium and forms a hole to design2. After being held at depth for a short time, the vibrator is withdrawn and a charge of stone is placed into the hole.3.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.
18Dynamic 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.
20Health & Safety Issues Heavy plant manoeuvring on site – use banksman Other plant eg concrete deliveries need to work close byOverhead working on many applicationsNoise of driven pilesDeep excavations to be protectedPiles designed on basis of site investigation
21Environmental IssuesNoise from driven piles – ear protectors, neighboursVibration from driven pilesRemoval of excavated material from replacement pilingProtection of groundwater, particularly drilling mud (bentonite)Diesel storage