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NEW DIAPHRAGM WALL JOINT SYSTEM ALLOWING GREATER DEPTHS AND HIGH QUALITY JOINTS

Periodic Reporting for period 6 - TTMJ (NEW DIAPHRAGM WALL JOINT SYSTEM ALLOWING GREATER DEPTHS AND HIGH QUALITY JOINTS)

Reporting period: 2019-03-01 to 2019-08-31

The TTMJ (Tension Track Milled Joint) Project aims to test and validate a new method in Diaphragm Walls (DW) technology. DW are widely used to support structural open shafts or to build retaining walls for construction of underground structures.
The DW’s are constructed by completing individual rectangular reinforced concrete elements (panels) one at a time, to form a continuous wall. The vertical interface between two adjacent panels is called a joint. A diaphragm wall structure could have hundreds of joints, which are generally weak in transferring shear stresses. Relatively small defects in joint continuity are potentially highly dangerous, as the consequences can be disastrous, impairing peoples’ safety and damaging adjacent infrastructures. Each year, this kind of accidents due to settlements and/or collapses is responsible for people injury and worldwide damages totaling hundreds of millions of euros.
When depth goes beyond 40 m, traditional methods to construct DW joints become less safe. The increase in DW depth raises the question as to how the integrity of the joints can be guaranteed at these greater depths. The aim of the TTMJ project is the development, validation and commercialization of a new system that will provide foundation specialists with the capability to deliver high quality, tight and safe diaphragm wall joints at lower costs. The new system offers the possibility to construct better joints, profiling the primary panel with the TTMJ trimmer, guided by tracks previously cast into the adjacent panel, after the closure panel has been excavated and before its concreting, ensuring the quality of the joints in the completed DW.
TTMJ project’s objective is to provide a step-by-step validation and commercialization of the new milled joint system with the following technical advantages:
-an effective jointing system for deeper hydraulic grab excavations (up to 60m deep)
-an improved jointing system for hydromill excavation
-shear/tension capacity across diaphragm wall joints
-the ability to construct ‘tighter’ diaphragm wall shafts.
TTMJ is a collaborative project involving TREVI (Coordinator, IT), CCMJ Systems (beneficiary, UK) and ARUP (beneficiary, NL). The project started on 09/2016, and will have a total duration of 36 months.
An an independent peer review of the project will be conducted by an Advisory Board composed of 3 international experts.
In WP2, detailed design of TTMJ joint trimmer stage was completed in the 2nd period, confirming that it is possible to build a joint trimmer as expected. The mechanical designers completed the shop drawings, implementing the information received from the components suppliers. No significant obstacles to the manufacturing stage are currently expected, and purchasing of components started in the 3rd period and continued in the 4th. Construction of the TTMJ prototype was completed in February 2019.
The WP3 covers design and manufacturing of TTMJ guide tracks. After discovering that products ready available on the market are not suitable, a purpose made TTMJ track was designed and manufactured. The design was completed in early February 2017, and the new guide track drawings attached to request for proposals sent out to three suppliers. An order to supply enough guide tracks for laboratory tests and field trials was placed in early 03/2017 and the goods received in 07/2017. The initial phase of guide track testing was carried out by CCMJ in summer 2017 in Inverness, UK, using an uncomplicated setup. Six test samples were made and tested. Further testing was carried out in autumn 2017 using larger test blocks and different reinforcement, to assess if higher tension capacity is available. The second phase of testing produced results fully in line with expectations and allowed the Consortium to move forward with planning the field trials. Further work was carried out to improve the design of the TTMJ track and the arrangement of the water-stop.
In WP4, field trials will be conducted in the SOILMEC premises in Cesena, Italy. A Method Statement describing the means and method to carry out the tests has been prepared. In the demonstration field test, six full scale sets of concrete beams will be tested to prove the ability of the trimmer to cut in planar (as for linear wall alignments), slanted (as in circular shafts), and with irregular concrete bulges. The tests started end of February 2019 and the first phase completed in March 2019.
Under WP5, for the preparation of a Business Plan, this project made use of the Exploitation Booster service offered by EU in June 2017.
Regarding Communication and dissemination (WP6), a captivating TTMJ logo was designed, and the project website (www.ttmj-h2020.eu) launched together with the social network. Two papers have been presented at the DFI conference in New Orleans (24-26 October 2017), and at DFI-EFFC conference in Rome (06-08 June 2018). A booth has been purchased for both events.
For WP4 the field trials method statement was reviewed and adapted to the setup at the Soilmec facility. Preparation of the test panels was witnessed. First trial runs were attended. Full report to be submitted in the next period after finalizing the first series of test. Initial provisional outcomes look favourable.
The new TTMJ system is designed to:
-Increase depth range of DW (especially excavated by grabs)
-Remove the need for Stop-ends or Joint formers
-Allow for a Shear Key at the joint
-Allow for a Water Stop to be installed at the joint
-Permit Continuous Reinforcement across the joint
-Optimise reinforcement density and hence concrete flow
-Allow joints in corner panels eliminating the need for “L” shaped cages and reducing large single-pour concrete volumes and slurry storage capacity requirements
-Facilitate the construction of square and circular deep shafts (especially useful for city-centre sites) smaller than those that would be obtained with current methods.
The TTMJ project expected results are:
-construction of a prototype of joint trimmer: a machine similar to a road planer, to remove a concrete layer from the primary panel to create continuity in the diaphragm walls. The expected performance is cutting 50-60 linear m of joint per hour in standard conditions
-guide tracks: a pair of tubular pipes installed with the reinforcement cage of the primary panel that must restrain the joint trimmer machine during the joint profiling and provide a tension connection across the panel joint, if continuous reinforcing is requested
-method statement: a document that details the way through which the TTMJ system will be implemented in real working situations
-system accreditation: a formal validation of the new system.
The TTMJ Project will bring innovation to the market for the benefit of the foundations industry worldwide, and at the same time will bring substantial added value at different levels:
-Construction Sector: benefits for companies using the system will include cost savings whilst delivering a superior quality product.
-Clients: commercial advantage implies project-cost savings, higher-quality product and a better profile in terms of risk reduction, quality and durability of walls
-Economy and Society: improvement will be sustainable and have a lesser impact on the environment by minimizing the risk of impacting the integrity of surrounding buildings in highly urbanized areas.
The slanted concrete beam after trimming
The concrete block after sawing. Visible the joint and the GFRP pipes
The trimmer suspended by the base carrier, ready to start the tests
Simplified sketch of the tension joint arrangement
The TTMJ trimmer machine
Principal roles of TTMJ project consortium members
Guide tracks fixed on the primary panel