Large diameter driven piles were used to get cost savings in Oulujoki bridge project. Large diameter pile driving can be done with relatively small hammer on end bearing piles and the proof of capacity is done with a separate drop hammer. 

Project description

Finnish Transport Infrastructure Agency (Väylä) ordered replacement of highway 4 bridges in Finland crossing river Oulujoki and Kreate won the bidding with design-build project delivery. The project comprises of replacing two 143 meters long bridges and the piling is ready for the first part but the second part piling is estimated start in September 2020 after the traffic is switched to the new bridge. The project is estimated to be finished in the fall of 2021.

Piling of new bridge foundation from working platform over Oulujoki. Old bridge on the left.

Reasons for selecting driven piles instead of drilled piles

Drilled piles are widely used when large load bearing capacity from large diameter piles is needed as in many bridges. However it is also possible to secure high load bearing capacity in driven piles when dynamic load testing (PDA) for piles is conducted. In many cases it would be more cost efficient to use driven piles than drilled piles when the overall costs of the project are considered. Kreate had two reasons for selecting driven piles to Oulujoki bridges which were cost savings and easier design of structures above the pile because of the hinge at the bed rock conneertion. The selected piles were SSAB’s RR1200/20 with S440J2H steel grade.

Custom project specific rock shoes

SSAB’s standard rock shoes for large diameter piles are optimized for common capacity utilization to avoid over dimensioning in majority of projects where whole capacity is not utilized for example if large pile size selected to make connection to above structures easier. Given the high utilization of the pile capacity in the Oulujoki bridges project it was necessary to use custom made rock shoes for the project.

SSAB offers both design service and manufacturing for project specific customized rock shoes which are optimized according to the needs in the project. The rock shoes are welded to the piles at the SSAB factory and the piles are delivered as installation ready. In this project the rock shoes were designed to carry over 23.5 MN load which is about 20% more in comparison to the standard rock shoes which are designed to take 19.3 MN loads.

Using custom rock shoes is beneficial when loads are exceeding the capacity of standard rock shoes but there are also other situations where using custom rock shoes might be beneficial. If driven piles are wished to be anchored it is possible to use our hole dowel rock shoes but in some cases the hole is not large enough and expanding the hole needs custom rock shoe design. Another example would be a project with low utilization of pile capacity which would lead to significant saving of raw material in the rock shoe. However using light weight custom rock shoes for cost savings require a decent sized batch to offset one time manufacturing set up costs. The size of the decent batch depends on the pile dimension and loads but SSAB’s sales and technical support will help you in estimating the potential benefits of using custom rock shoes.

Rock shoe FE-Model on left and finished rock shoe welded to pile

Installing and proof of strength of driven piles

In typical Finnish, Swedish and Norwegian soil conditions piles are often designed as end bearing piles which are supported by bedrock. In these circumstances pile driving can be done with relatively light weight equipment which has been utilized especially in Finland successfully. The dynamic load testing is then conducted with different drop hammer to verify decent support from the bed rock. The verifying method is analogue to the small diameter piles which are typically installed with hydraulic rammer and dynamic load tests are done with drop hammer.

In this project the piling is done from working platform comprising of steel beams and steel piles supported from the bottom of 8 meters deep Oulujoki river. The RR1200 piles of the first replaced bridge were installed with 5 ton hydraulic hammer SHK 5 (max. energy 61 kNm) attached to PMx22 rig of Pirkan Rakentajapalvelu. Rig Operator Harri Inget with over 20 years of experience in piling from Pirkan Rakentajapalvelu said that installing RR1200 piles with such equipment is quite convenient and he has done it successfully many times in his career.

Project Manager Ville Tiiro from Kreate has been very satisfied with the driven piles selected for the project and the piles have worked the way they were planned. The installation of the piles has been efficient and it has taken less time than anticipated which has helped in keeping the project on schedule. According to Tiiro it has definitely been a right choice to use driven piles in the project.

The PDA dynamic load tests were conducted by Teemu Riihimäki from Junttan. The impact for testing was done with 10 ton hydraulic release drop hammer manufactured by Junttan. The maximum resulting capacity of 26 MN was achieved and according to Riihimäki it is the greatest PDA test capacity ever recorded in Finland.

PDA dynamic load testing by Junttan

 A drone video from the construction site can be found from the link: Drone video.