Zeil - Frankfurt am Main
The Zeil, Frankfurt am Main was the site of the first Osterberg cell test in Germany. In April 2004, the largest static load pile test on German soil was performed using Osterberg cells, in the heart of Frankfurt.The bi-directional load test was aimed at confirming the foundation design, before demolition of some of the surrounding older structures. The test was performed on a 1.68m diameter test pile 47m long, installed 12m into the Frankfurt limestone.
Project: FrankfurtHochVier
Location: Frankfurt, Germany
Developer: MAB joint venture with BPF
Architect: KSP Engel und Zimmerman Architekten; Fuksas Associati S.r.l.
Geotechnical Engineer: Ingenieursozietät Professor Dr.-Ing. Katzenbach GmbH Dr Matthias Vogler
Foundation Contractor: Bilfinger Berger AG, Bauer Spezialtiefbau GmbH, and Hochtief Construction AG
Fugro Loadtest Germany: Scanrock
GmbH: Carlos Fischer
Period: April 2004
This large site is located within the heart of the Frankfurt city centre, on the main shopping street, "Zeil". The "FrankfurtHochVier" project is a Class-A mixed-use project. Only a small part of the existing structure will remain, namely, the historical building known as the porticos of the "Thurn und Taxis Palais".
Six O-cells were installed on two separate levels to allowthe behavior of three elements of the pile in the rock socket to be evaluated independently. The cage assembly with O-cells was manufactured off-site in sections and assembled over the bore during installation. Utilizing a feature unique to bi-directional tests, only the section of pile in the rock socket was concreted and the remainder of the bore (35m) backfilled with granular material for stabilization. Subsequently the pile was base grouted and a 5m test section shaft grouted (It is typical practice to shaft and base grout piles in the Frankfurt limestone).
The load test was carried out in two stages as is necessary with a multilevel O-cell arrangement:
• the first stage the upper 5m of rock socket was loaded to 24MN
• the second stage a lower 5m section was loaded against the bottom 2.5m of pile. The effective mobilised capacity was 78MN.
Until now, designers have had to rely on full scale loading test data from 146mm diameter anchors. In practice, there would have been insufficient space to perform a top down loading test and had it been possible, interpretation of the results from the rock socket would have been difficult. The test succeeded in mobilising the ultimate capacity in each of the sections of the rock socket.
