A bored pile retaining wall has been set up at the building-site in Sickla, Stockholm. The wall enables construction work right next to a busy road without perturbing the traffic, eliminating the risk of a landslide or of any damage to the road.
Due to the close proximity to the roadway, the amounts of slurry and oil mist splashed in the direction of the passing cars had to be minimized, in order for the drilling to be allowed. Furthermore, it was important to eliminate the risks of eroding and pressurizing the formation, which could damage to the road.
Thanks to the inherent safety and cleanness of Wassara’s technology, a small fabric cover was enough to protect the cars from getting dirty and the road from getting damaged. As the high water pressure required to power Wassara’s DTH hammers is reduced to ambient pressure as the fluid leaves the hammer, there was never a risk to pressurize the formation.
In other words, Wassara’s water-powered DTH hammers allowed for efficient drilling while at the same time ensuring a perfectly safe and clean working environment.
Drilling conditions and geology
The retaining wall was set up using RD-piles. The casings were drilled down through the overburden and then one meter further into competent rock. Finally, the piles were connected to one another with an RM/RF locking profile to form an RD-pile wall.
The overburden consists of approximately five meters of construction aggregate, a layer of mud and a layer of moraine.
The rock under the overburden is fractured for the first meters, but afterwards it is found to be competent. The groundwater table is located at a depth of five meter.
Project size and time frame
The project started in December 2015 and is scheduled to last until September 2016. During the months of January through to March 2016, 152 RD-piles (RD 320), 323.9 mm in diameter and 12,5 mm in thickness, were drilled down to a depth between 12m and 20m with an average depth of 15m. The total number of drilled meters amounted to 2 200 m.
The drilling part of the project ran between January and March 2016. The whole project runs between December 2015 and September 2016.
Public water from a fire hydrant was used to power the Wassara hammer. As most of the water dispersed through the overburden, no water treatment system was needed in this project. The small amount of resurfacing water was simply led away from the rig and released on a nearby patch of ground. When drilling in rock, the average water consumption was 400 l/min.
The complete Wassara drill string
Lining up the next pile