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The double underpass being realized in Hilversum, as part of the HOV in 't Gooi project, is a technical tour de force. "The CSM technique proved to be the safest and most economical solution to realize the double-layer underpass in a heavily built-up environment," says Michael Grondijs, technical consultant at Hoffmann Group, responsible for the realization of the CSM walls on the project.
Given the depth of the underpass and the limited space to adjacent buildings, great demands were placed on the deflection and displacement of the CSM wall. "A traditional CSM wall of 550 millimeters proved insufficient everywhere," knows Melwin Dröse project manager at Hoffmann Group. "We are the only party with sufficient machines with which we can mill 800-millimeter walls, so that the deflection is significantly reduced and thus possible damage to the steel-founded adjacent buildings is prevented. Rather unique to this project, moreover, is the substantial reinforcement. Normally IPE sections of up to 450 mm are used, here HEB 700 beams in lengths of 17 to 18 meters were used. Extremely heavy and extremely difficult to apply within the tolerances and quality requirements of a few centimeters. In addition, we also had to perform the walls at the level of the track in an out-of-service condition. This is unprecedented with the CSM technique, but was extremely successful. Thanks to sophisticated preparation and the efforts of various teams who manned the machines 24/7."
In total, Hoffmann Group completed 690 linear meters of CSM walls. "Most of these are 800 millimeters thick, a small part is traditional," Dröse explains. "The CSM walls were milled up to 20 meters deep, while the earth retaining wall is 6.50 to 14.70 meters. All in all, substantial depths. An additional advantage of the soilmix technique is that you have a better chance of getting to depth compared to pressing a sheet pile wall. After all, the soil is milled loose. Another advantage is that no hollow spaces are created, so there is no settlement and we can work right past steel-founded buildings." Hoffmann Group stood at the cradle of the Cuttersoilmix system and further developed the prototype together with the manufacturer. "We have the longest experience worldwide. Partly due to the perfect cooperation with BAM Infra and all subcontractors, the HOV in 't Gooi project was very successful for us."
