Abstract:
Jet grouted seals are an established construction method to built watertight excavation pits in inner city areas .Environmental aspects focus to prevent ground water draw down outside of the construction site.
The construction sequence connects secondary rows of columns to primary columns to form a continous waterproof slab below the excavation level.
The energy transfer induced by the high power beam into hardened primary columns provides possibilities to check the interlock of secondary columns to primary columns.
Installing vibration sensors into hardened columns allows to record, read and evaluate the contact quality of new secondary columns with relation to hardended primary columns.
Field tests have been carried out in Berlin to explore the influence of the type of construction joints, the relevant distance of sensors to the jetting location and the curing time of the hardened columns.
The results allow to develop acceptance criteria based on the sound connection of new to old columns.
These recorded vibration graphs show clear acceptance criteria and false signals that demonstrate defective contact.
Using the contact vibration records referenced on basic acceptance criteria enables the project team to anticipate contruction failures already during construction.
Nikolaus Schneider
Berlin, 29.6.2024