How do screw piles compare with conventional concrete foundations?
Answer: Screw piles are quick to install; use no concrete or wet trades; produce no muck away; create no disturbance or contamination; use lightweight plant and are installed to a measured capacity.
What are the advantages of screw piles?
Answer: In addition to the above screw piles work in freezing conditions, can accept load immediately and are one of very few acceptable foundations that can be used as standard in close proximity to protected trees or that work in expansive soils. In short, screw piling often succeeds where other foundation types fail.
Where can you use screw piles?
Answer: The answer is virtually anywhere – it is worth highlighting that screw piles are particularly suited to confined spaces or sites where access forbids the use of excavators or piling rigs. Screw piles will penetrate most soils – if the ground is fractured to solid rock, then they likely won’t be economical, but we have screw piles in our range that work really well in many soft soils such as peat.
Can screw piles be removed easily?
Answer: Yes, screw piles can be easily unscrewed, but may need 20-25% more torque for removal than insertion. It should be noted that tent erection contractors use them all the time for reliability and reusability.
Can screw piles be used for tension loads?
Answer: Yes, screw piles can be used for both tension and compression applications. Provided they are installed a minimum of 3m into the soil, their tension capacity is the same as the publicised compression capacity.
Do screw piles offer lateral resistance?
Answer: Screw piles are better suited to direct compression and tension applications, but it appreciated that this is not always the case. Intuitively a relatively slim pile shaft (60mm-89mm outside diameter) has poor lateral resistance – we suggest up to 5kN. To overcome this, we manufacture conical extensions as standard which increase lateral resistance up to 10kN. Bespoke conicals can be made if lateral resistances greater than this are required.
How are screw piles installed?
Answer: Screw piles are essentially installed just like a woodscrew, but using hydraulic motors rather than an electric drill. There are two options for installation: a portable hand held pile installer such as our 400H & 650H models; or excavator mounted torque heads such as our 500X, 1600X & 2500X models. You can achieve greater installation torque (and therefore greater tension/compression resistance) using our excavator mounted torque heads.
Do screw piles corrode?
Answer: All steels corrode, but the process requires an electrolyte (water) and air therefore the area at ground level is of greatest concern. Our piles are thicker than our competitors and are all galvanised. Please read our screw pile specifications or corrosion literature for more information.
How accurately can you install screw piles?
Answer: Hand installed piles will usually be within 50mm of the correct position. Use of our rock tip pile generally improves this to 25mm. Machine installation can be more accurate and use of one of our specialist adjustable terminations will ensure accuracy to within a few mm.
What is the life expectancy of screw piles?
Answer: We aim for a minimum life of 60 years. In most non-aggressive soils our galvanised piles will last 100 years or more.
What happens if you hit rock or obstructions?
Answer: We produce a “rock tip” pile which can penetrate fractured rock, provided there is room for the point and shaft to displace the material. Sometimes we use a rock auger to “pilot drill” a pole through hard layers although this is costly and often quite difficult. The worst case scenario is where hard material or another obstruction is encountered and the pile simply spins, not progressing any further. It may be possible in certain cases to reposition the pile to avoid the obstruction or install a pair of piles spanning the obstruction
How deep can you install screw piles?
Answer: As piles can be extended in 2m lengths, the theoretical depth of a screw pile is unlimited. For practical and economic reasons it is better to keep the total length less than 14 metres. Screw piles work in a slightly different way to other forms of piling and rely on end bearing on the helix plates only – skin friction is negligible. Concrete piles – because they depend on skin friction and end bearing – need to be quite deep (10-12 metres is typical). Screw piles generally need less length to achieve the same capacity, as the helix plates on a screw pile in practice act like a multiple set of end bearing piles all on a common shaft. Screw piles typically “torque out” (i.e. reach maximum capacity) at 6-8 metres.
What happens if you can’t screw the piles in to finish height?
Answer: If a pile “torques out” before reaching the intended level, it will need to be cut off on site and a spray galvanising coating applied to the cut end. This is not uncommon practice and involves trimming the pile to length, before often drilling an additional set of holes in the shaft to allow a termination to be bolted on.
How do you set the finished height of screw piles?
Answer: Use of a laser level will ensure piles are within a few mm of level. If positional accuracy is critical we offer a termination that is adjustable in terms of height, horizontal position and pitch.
Can piles be installed without using an excavator?
Answer: Yes – we regularly hire out our 400H & 650H handheld portable pile installers. These are ideal for extensions, underpinning and lighter weight buildings. All parts fit through household doorways.
Do screw piles generate any spoil?
Answer: Screw piles produce no spoil – no muck away required!
Can screw piles be installed at any angle?
Answer: Screw piles can be installed at any angle required with either the handheld or excavator mounted equipment.
What soils are unsuitable for screw piling?
Answer: Screw piles are not designed to penetrate solid bedrock, nor are they able to penetrate through obstructions such as boulders or buried concrete. Most other soil types are acceptable.
What distance should screw piles be installed from each other?
Answer: Ideally, piles should be placed 5 of the largest helix diameters apart. A reduction in final load capacity of 20% will allow this to be reduced to 3 diameters. It is possible to angle the piles so that the tops are touching, yet full capacity is achieved.
Can screw piles be terminated above ground level?
Answer: Screw piles cannot protrude above the ground as a stilt without suitable bracing. The slender pile shaft has a tendency to bend when not fully supported by soil along its full length. We have developed an alternative above ground stilt solution which has far higher strength and can often be installed without the need for bracing.
What size excavator will I need to install screw piles?
|Pile Size||Working Loads||Torque Head/PAD Required||Excavator Size Required||Speed of Install|
|60R||Up to 48kN||400H Handheld PAD||–||30m per day|
|Up to 60kN||500X/XG Excavator Mounted||2-7 Tonne||50-60m per day|
|76R||Up to 73kN||650H Handheld PAD||–||30m per day|
|Up to 180kN||1600X Excavator Mounted||5-8 Tonne||50-60m per day|
|89R||Up to 250kN||2500X/XG Excavator Mounted||5-10 Tonne||50-60m per day|
Do I need to inform planning/building control?
Answer: You should always consult an appropriate building control engineer before using screw piles. Most now accept the system and many specify it, especially in difficult situations.
Can I use screw piles next to trees?
Answer: Screw piles are the ideal solution for use next to valued or protected trees and have the least destructive impact on tree roots of all micropiles. Increasingly we have found that screw piles are the preferred foundation solution of leading Arboriculturalists and Local Authority Tree Protection Officers for projects sited in close proximity to trees.
Will screw piles move if soil heave is an issue?
Answer: Expansive (and contracting) soils present no problem for screw piles. Assuming the helices on the pile are installed to a depth where soil heave is not expected, upper soil layers are free to expand and contract without moving the pile or affecting the stability of the superstructure. As the pile shaft is so slender, soil simply moves past it uninhibited i.e. with negligible adverse skin friction.