Advantages / Disadvantages of Piling Methods. Continuous Flight Auger (CFA)

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1 Advantages / Disadvantages of Piling Methods In this Piling Advice Note we will explore the advantages and disadvantages of differing types of piling methods. Continuous Flight Auger (CFA) The pile is formed by means of a continuous helical auger which can extract the soil as it progresses. Concreting can be achieved by injection under high pressure through a hollow central stem as the auger is removed. Pile reinforcement is dropped down into the wet concrete by a crane. Advantages Minimal levels of vibration Lower noise levels generated by piling rig More suitable for tension loads at stability elements depending on ability to install cage prior to concrete drying out Collapse of pile bore in sands below water table. Requires driven steel casings to be installed, generating noise and vibration. Longer piles required than driven (not driven to a predetermined set). Longer continuous noise exposure than driven piles. Removal and disposal of potentially contaminated soil arisings is required. Potentially more costly with longer installation programme 8 weeks. Obstacle drilling cannot be implemented (rotary chiselling would be required refer to Rotary Bored Piles) More construction traffic delivery of steel and concrete and removal of arisings. Craneage required to install pile reinforcement. Risk of in situ concrete drying out due to sand leeching may cause issues with cage installation.

2 This is a cast in place cylindrical concrete pile. The pile is a non-displacement pile, bored with a temporary recoverable steel casing for stabilising the adjacent soil. Rotary Bored Advantages Minimal levels of vibration Lower piling rig noise levels generated than by precast Obstacle drilling is possible More suitable for tension loads at stability elements depending on ability to install cage prior to concrete drying out Disadvantages Removal of potentially contaminated soil arisings is required. Chiselling may be required through buried obstructions and would cause significant noise and vibration. Potentially the most expensive/slowest of the methodologies presented (estimated programme 8 weeks). Driven steel casings required in sandy/ granular site soils below water table leading to additional noise and vibration. Drilling liquid may be used and require disposal. More construction traffic delivery of steel and concrete and removal of arisings Longer piles required than driven (not driven to a predetermined set) longer continuous noise exposure. Longer continuous noise exposure. Craneage to install reinforcement cages. Risk of in situ concrete drying out due to sand leaching may cause issues with cage installation

3 A precast concrete pile is a prefabricated, high strength concrete column, delivered to site and impact driven into the soil by means of a hydraulic or diesel hammer. Driven Precast Piles Advantages Quick installation reduced programme (estimated 3 weeks) Cost effective/efficient based on existing site soil conditions Less construction traffic pile delivery only No soil removal reduces potential contamination issues Good level of quality control achievable Flexibility to remove and re-pile at buried obstructions Disadvantages Higher levels of intermittent percussive noise pollution Higher levels of intermittent vibration Cannot drive through buried obstruction Not suitable for high tension loads at stability elements

4 This is a low energy driven fulldisplacement pile with a lost steel tube. The pile is formed using an internal free fall hammer striking a dry concrete plug locked at the bottom of the casing. Concrete is poured into the driven tube. Driven Steel Tubular Piles Suitable for aggressive soil conditions and contaminated soils Suitable for very soft or unstable layers of soil which may leach and dry out in situ concrete Reduced vibration and noise pollution compared to precast as driving performed inside tube No soil removal reduces potential contamination issues Flexibility to remove and re-pile at buried obstructions Disadvantages Potentially slower and more costly than precast driven piles Cannot drive through buried obstructions Not suitable for high tension loads at stability elements Piles are driven to deeper depths therefore potentially longer percussive noise exposure than precast.

5 Controlled Modulus Columns (CMCs) CMCs are used are used to improve the soils characteristics in weak ground and to reduce imposed settlements caused by the proposed structure. CMCs are installed using a specially designed auger that displaces the insitu soils laterally, with virtually no vibration or spoil, and reduced risk of contamination. The auger is screwed in to the soil, to the designed depth, this increases the density of the surrounding soil, and as such increases its strength and bearing capacity. When the auger is extracted a column is developed by pressure grouting, at less than 5 bar, to improve the surrounding soils. The result is a composite ground improvement solution offering enhanced stiffness characteristics, allowing the CMCs and the surrounding soil to share the imposed loadings. After the CMCs are installed, they are covered by a designed load transfer platform, between 0.4 and 0.8m thick, to efficiently transfer load from the structure to the CMC/Soil matrix. CMCs were developed in 1994 and are now used in many countries around the world. Current practice is to install CMCs with a diameter of between 250 and 450mm High torque and high static down thrust displaces the soil laterally using the specially designed auger (Hollow Stem Displacement Auger) 2. During extraction a controlled modulus column is developed by grouting through the hollow stem in the auger. 3. The result is a mm diameter composite soil cement column delivering a ground improvement system. Minimum spoil. High production outputs. Suitable for most soil types. Can deliver reduced settlements for high loads Densification delivers concrete savings. Vibration free installation process Disadvantages Need special installation machine

6 Micro Piles Micropiles are used as foundation support elements to resist static and seismic loads, and to a lesser extent, as in-situ reinforcements to provide stabilization of slopes and excavations. Many of these applications are for transportation structures. Specialist Piling Types of Micropile Pile and Beam Pile and Cantilever Beam Knuckle pile Piled raft Angle pile Cantilever Ring Beam Twin pile Jack Down pile Tripod Piles The use of a tripod rig to install piles is one of the more traditional ways of forming piles.

7 Sheet Piling Sheet piling is a form of driven piling using interlocking sheets of steel to obtain a continuous barrier in the ground. The main application of steel sheet piles is in retaining walls and cofferdams erected to enable permanent works to proceed. Soldier Piling Soldier piles are most suitable in conditions where well constructed walls will not result in subsidence such as over consolidated clays, soils above the water table if they have some cohesion, and free draining soils which can be effectively dewatered, like sands.

8 (GN04) PILING ADVICE NOTE Zero Clearance Piling The Zero Clearance Method employs an especially designed press-in machine (the Zero Piler) and Zero Sheet piles (NS-SP-J) to press-in piles with zero dead space between the piles and the adjacent structure. Conventional approaches often fail to provide a solution in civil engineering works on narrow water courses, etc., or building projects requiring efficient utilization of the available land. The Zero Clearance Method enables maximum use of the space in a way that was not possible before. Also, the machinery is compact, so it doesn't dominate the surrounding area and has a lower risk of overturning than conventional piling equipment. And by using the GRB (Giken Reaction Base) System, which requires no temporary works, the construction time is shortened and costs are reduced. This pathbreaking method is hugely beneficial in the development of underground spaces and antiseismic reinforcement work Advantages No Vibration or noise Press-in Machine light and compact Pile bearing capacity can be checked as work progresses High working precision Guidance Note : PILING Doc Version No : 1 Date : July 2017

9 Ground Borne Vibration PPV (anticipated Peak Particle Velocity) - Threshold for cosmetic damage to buildings (data source : CIRIA TN142) Threshold for prevention of structural issues = 8mm/s Traffic (typical non-specific) = 6mm/s Footfalls across a wooden floor = 3mm/s Stamping on a computer room floor = 2mm/s Foot steps a few metres from a home = 0.5mm/s Rotary Bored Soilmec Piling Rig Noise Emissions (Black figures are in db (Decibels))

10 Typical Junttan Precast Driven Piling Rig Noise Emissions (black figures are in db)

11 Piling Noise & Vibration Mitigation The following are piling noise and vibration mitigation measures that may be implemented to minimise the noise and vibration impact. 1. Piling Rig Noise Emissions If a precast piling solution is undertaken then the latest hydraulic rig will be used. Acoustic measures will also be implemented within the rig. An acoustic shroud will now be provided on the rig with low noise impact dollies utilised. The rig will also be fitted with the latest Shark hammer, which offers exceptional noise suppression. 2. Piling Rig Orientation the piling rig noise emissions are greatest from the hammer facing end of the rig. The piling platform should therefore be extended to allow the rig to be orientated to face away from the residential properties during piling operations, reducing noise by up to 5dB. 3. Site Hoarding a solid perimeter site hoarding should be installed to provide low level shielding to absorb and deflect noise from the piling operations. The hoarding will be most effective when the piles are driven to their founding depth where the noise emissions are generally greatest. 4. Site Noise and Vibration Monitoring site noise and vibration monitoring should be implemented on site and from the nearest noise sensitive properties (i.e residential dwellings). Trigger values will be set and telemetry can be provided to allow real time feedback to the site team if threshold values are exceeded, allowing the contractor to take immediate action. 5. Communications with Residents There should be a requirement to undertake leaflet drops to communicate planned construction activities with the local residents and students. A specific leaflet drop to inform residents of the planned piling activities should be undertaken ahead of the works. Site contact details should also be provided in the event of any issues arising. 6. Liaison Any businesses likely to be affected by the activities should be in direct liaison so that any issues with regards to noise and vibration can be dealt with swiftly. 7. Pile Cutting the piles may be cropped using specialist pile cropping machinery. Jack hammers or similar should not be used in order to reduce noise emissions. The determination of the need to use piles and the identification of the range of feasible pile types for a project form part of the design process. In choosing the most appropriate pile type, the factors to be considered include ground conditions and environs, site constraints, plant availability, safety, cost and programme, taking into account the design life of the piles. Normally, more than one type will be technically feasible for a given project. The selection process is in essence a balancing exercise between various, and sometimes conflicting requirements. The choice of the most suitable type of pile is usually reached by first eliminating any technically unsuitable pile types followed by careful consideration of the advantages and disadvantages of the feasible options identified. Due regard has to be paid to technical, economical, operational, environmental and safety aspects.