IS EN 12699:2015 Execution of Special Geotechnical Works – Displacement Piles defines a displacement pile as a ‘pile which is installed in the ground without excavation or removal of material from the ground, except for limiting heave and/or limiting vibration as well as removal of obstructions or to assist penetration’. Displacement piles are commonly referred to as ‘driven’ piles, which are installed using impact, vibration, pressing, screwing or a combination of these methods.
IS EN 14199:2005 Execution of Special Geotechnical Works – Micropiles defined micropiles as drilled micropiles with a shaft diameter not greater than 300 mm or driven micropiles with a shaft diameter or maximum shaft cross sectional extension not greater than 150 mm. However, IS EN 14199:2015 Execution of Special Geotechnical Works – Micropiles, which superseded this European Standard, now defines micropiles as ‘drilled piles constructed using a drilling tool with a diameter less than 300 mm’. This European Standard thereby excludes driven piles, transferring them to IS EN 12699:2015 Execution of Special Geotechnical Works – Displacement Piles. We are not sure why this took place, however it is our opinion that as the use of micropiles was not revised in the new standard, the vibration caused by driven piles suggests that they may not be appropriate for underpinning works.
Capacity of a driven pile is determined by driving the pile to a ‘set’. This is a function of the penetration measured against a specific period of time or distance as outlined in the execution specification or driving criteria. A grundomat is self-testing by nature but great care must be taken during design and installation.
This system is most effective in granular or cohesionless soils (sands and gravels) where pore pressure does not need to be considered and boulders are not present. It can also be used on contaminated sites, filled sites and areas where ground water is a concern.
Lining in the form of thin walled sacrificial steel tubes are driven into the ground by a hammer inside the casing. The first tube (‘starter’ or ‘leader’) has a crimped point and a short swaged section at the other end so that the second tube (or ‘follower’) can slide into it. A plug, formed of dry concrete mix, is placed within the bottom of the starter. The connection (or ‘joint’) is formed by welding to prevent disengagement. Subsequent followers are installed until the required set is reached. The piles are then grout filled or grouted and reinforced as per the specification.
Substruck Ltd. offers two types of bottom driven piles: