extended to above the water surface using a string of hollow bars so an optical measuring point could be mounted where the results from digital sensors were correlated with precise geodesy. The task of assembling the equipment was a challenge for the divers. The work was carried out in limited visibility, and the required precision of the assembly was key for the success of the entire task — any imperfections could result in damage to the structure, equipment or micropiles. Thus, before the load testing program commenced, the diving team was trained. The whole procedure, including assembling and positioning the frame and measurement equipment, was firstly practiced at the ground level. Then each of the components (i.e., beams, displacement transducers, jack, etc.) were lowered and the testing structure was assembled and positioned underwater with use of special templates to assist the divers. The actual test procedures, other than being underwater, did not differ from typical Polish standard testing procedures performed on the surface. Each of the installed micropiles achieved more than the required test load of 2,300 kN (517 kip) with associated displacements stabilizing in 30 to 40 min that did not exceed 25 mm (1 in). Summary The scale of the task and its complexity were exceptional, and the pressure of the tight schedule intensified the level of difficulty. There was no room for any material, technological or executive shortcomings, and the success or failure was determined by the details. The project required an individual approach and the use of unique technical solutions. The Titan micropile, supported by expert know-how, proved its effectiveness and allowed the project to succeed. The success clearly demonstrates the importance of commitment and cooperation of all participants in the process: technology suppliers, subcontractors, the general contractor and the supervisory authorities. Part of the steel frame reaction system is submerged Preparations for test loads- assembly training of the diving team “on dry” Bottom and Foundation Slab Successfully completed test loads paved the way for the last portion of this stage of work — forming the bottom slab. Underwater concreting for the bottom slab with an area of 14,300 sq m (153,924 sq ft) was one of the largest concreting works of this type performed in the world. It was designed and executed by Soletanche Polska. About 25,000 cu m (32,700 cu yd) of embedded concrete “one approach” elements built using Dobber technology was not only record-breaking but also made the bottom slab implementation a very logistically complicated operation. After the concrete achieved the appropriate strength, water was pumped out of the interior of the excavation. After the surface of the bottom slab was cleaned, the micropiles were sealed, insulation was installed and the extensions for the micropiles were tightened to the assembly of the second heads (to join with the foundation slab). Then, the reinforcement work began, and subsequent stages of the construction work proceeded in a conventional manner. 18 • DEEP FOUNDATIONS • JAN/FEB 2020 Acknowledgements This work would not have been possible without the support of Soletanche Polska, Aarsleff, Soley, and Piletest. We thank our colleagues from these companies who provided the technical documentation and expertise that greatly assisted the project and the writing of this article. We are sincerely grateful to all those with whom we had the pleasure to work on this project and we believe that it was the close cooperation of all the partners involved that led to the successful outcome. Natalia Maca is a geotechnical designer and project manager at Titan Polska, part of the Ischebeck Group. Maca undertakes the most difficult geotechnical challenges, creating beautiful underground structures. She is activily involved in conducting training courses, contributing at professional journals and acting in standardization bodies.
