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

Periodic Reporting for period 7 - TTMJ (NEW DIAPHRAGM WALL JOINT SYSTEM ALLOWING GREATER DEPTHS AND HIGH QUALITY JOINTS)

Reporting period: 2019-09-01 to 2020-02-29

The TTMJ (Tension Track Milled Joint) Project successfully tested a new method for Diaphragm Walls (DW), a technology widely used to allow the construction of underground structures. The DW’s are constructed by completing individual concrete panels one at a time, to form a continuous wall. The joints between two adjacent panels are generally weak points, and relatively small defects in joint continuity are potentially highly dangerous, and the consequences can be disastrous, impairing peoples’ safety and damaging adjacent infrastructures. Each year, this kind of accident 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, and the increase in DW depth raises the question as to how the integrity of the joints can be guaranteed at these greater depths.
The TTMJ project developed and tested a new system that will provide the capability to deliver high quality, tighter and safer DW joints at lower costs. By profiling the primary panel with the TTMJ trimmer guided by GFRP tracks, the concrete-to-concrete contact is improved, hence the quality of the joints in the completed DW is substantially increased, reducing risks of defects.
The TTMJ project proved that the new milled joint system can provide an effective jointing system for deep hydraulic grab excavations, an improved jointing system for hydromill excavation, shear/tension capacity across diaphragm wall joints, and the ability to construct tighter diaphragm wall shafts.
The TTMJ project involved TREVI (Coordinator, IT), CCMJ (beneficiary, UK), and ARUP (beneficiary, NL). The project started on 09/2016, for a total duration of 42 months.
The WP2 included the design and the construction of the trimmer prototype. The detailed design of the TTMJ joint trimmer was completed in the 2nd period, confirming the feasibility to build a machine as expected. Then, the 3D design was completed according to the SOILMEC specifications, and the shop drawings issued to start the purchasing of components (3rd and 4th periods). The construction of the TTMJ prototype was completed by TREVI in Cesena on 02/2019 (end of the 5th period), and the test started immediately (see WP4).
The WP3 covered the design and the manufacturing of TTMJ guide features. As products readily available on the market are not suitable, a purpose-made TTMJ track was designed in early 02/2017, and requests for proposals sent out to three suppliers, for enough guide tracks for laboratory tests and field trials. The order 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, testing various set up of reinforcements. 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 (WP4). Further work was carried out to improve the design of the TTMJ track and the arrangement of the water-stop.

The WP4 dealt with the trial tests, conducted in the SOILMEC test area in Cesena, Italy. We used the 20m deep, 3mx1.5 m rectangular shaft which SOILMEC uses to test their equipment. A Method Statement was prepared to describe the means and methods to carry out the tests. Six sets of 20 m long pre-cast concrete beams (split into two 10m long elements) have been prepared in three different shapes to prove the ability of the trimmer to cut planar (as for linear wall alignments), slanted (as in circular shafts), and irregular concrete bulges surfaces. The test started at the end of 02/2019 and was completed during 03/2019. However, only three sets have been tested, as the results were deemed completely satisfactory. In 04/2019 (see WP6) the results of the tests were presented at the BAUMA, a specialized international fair in Munich, where we presented the system to a large specialized audience, offering the opportunity to run a second test in front of potential customers. The equipment remained at disposal of the potential test until the end of the 6th period (08/2019).
Later in 03/19, we also tested the tension connection, by preparing a formwork and testing the installation of a cage in the secondary panel and concrete backfill. The formed concrete beam was then dissected into three samples in 04/19, and load tested for splitting resistance, confirming the FEM model elaborated by ARUP.
The WP5 deals with the Business Plan, and this project made use of the Exploitation Booster service offered by the EU on 06/2017. The business plan includes a commercialization plan, describing the potential uses of the system and its market in the future years.
For Communication and dissemination (WP6), a captivating TTMJ logo was designed, and the project website (www.ttmj-h2020.eu) launched together with the main social networks. LinkedIn was by far the more effective for dissemination. Several posts have been issued, obtaining a good reaction from the specialized public. The Newsletters that have been sent to a large mailing list are available in the Download section of the website, together with the papers presented.
The results of the tests were presented at the BAUMA exhibition, where we brought one trimmed sample and a diorama with a scaled 3D printed model. To the interested guests, we offered the possibility to witness at the second phase of tests. We collected several subscriptions, but it was later decided to wait for a bigger opportunity.
Two papers have been presented at the DFI conference in New Orleans (24-26 October 2017), and one paper was presented at the DFI-EFFC conference in Rome (06-08 June 2018), and later at the ICOLD conference in Vienna. Then, the results of the tests have been described in a paper presented on 09/2919 in South Africa, at the conference of ISSMGE (INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING) in Cape Town.
The system was supposed to be used in the first project in Manila, but the COVID 19 pandemic has delayed the commencement of the project. We are then chasing other projects in Taipei (3 large shafts) and in Europe.
The TTMJ project successfully designed, built and tested a prototype, used to trim the pre-cast concrete beams. During the tests, we cut at 50-100 cm of joint per minute, regardless of the shape of the beams.
The GFRP guide pipes installed in the pre-cast beams were successful in restraining the joint trimmer machine during the joint profiling. During the split load test, it was also proved that they provide a tension connection across the panel joint, if continuous reinforcing is requested
The TTMJ Project will benefit the Specialized Foundations industry worldwide, and at the same time will bring substantial added value at different levels. For the Construction Sector, there will be cost savings whilst delivering a superior quality product. For Clients, overall project-cost savings, higher-quality product, and a better profile in terms of risk reduction, quality, and durability of walls.
For Economy and Society, this system will allow reducing the impact on the environment by minimizing the risk of impacting the integrity of surrounding buildings in highly urbanized areas.
Guide tracks fixed on the pre-cast beams during tests
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
Split tests runned by Politecnico of Milan on three sawed samples
The TTMJ trimmer machine
Principal roles of TTMJ project consortium members