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A large part of the Blankenburg connection is being constructed at a depth. Contractor combination BAAK gratefully used the expertise of Verboon Maasland to excavate the complex excavation pits with the help of GPS up to 29 meters (!) below N.A.P. Unique for Dutch standards.
"We are a well-known party in the market with a lot of experience in excavating wet building pits," says general manager Ruud van Wijk. From that expertise, Verboon Maasland is often called in for the more complex jobs. "For example, we have been involved in the Rijnlandroute, the excavation of the parking garage on the Lammermarkt in Leiden and we are currently active on project Rotterdam A16. The latter is somewhat comparable to the Blankenburg connection in terms of the size of the construction pits, but pales in comparison to the depth required here."
With all the knowledge and experience of excavating building pits "in the wet," Verboon Maasland initially worked out a number of scenarios. "We presented these scenarios to BAAK so that they could make a well-considered choice that best fit all the other work," explains Van Wijk. "In particular, the ramps to and from the Maas Delta Tunnel were unique. That brought with it the necessary complexity. We had to excavate the construction pits in phases, so that the civil branch could install the large outrigger frames in the interim. Then it was a matter of carrying out the second 'deepening stroke' very expertly and GPS-controlled in order to maneuver between the huge outrigger frames and avoid damage. Almost at depth, we came across the many hundreds of anchor piles that we had to dig around. The last layers between these anchors were therefore largely extracted with DOP pumps to level out the bottom of the tub and prepare it for the application of a gravel layer and then the pouring of the underwater concrete."
According to Van Wijk, the great strength of Verboon Maasland lies in the specialized equipment, all GPS-controlled, combined with the skilled personnel. "We also have a very creative and resourceful technical department. In fact, in cooperation with BAAK, we have developed special pieces of equipment for the letterbox pit - the pit where the ramp will soon connect to the immersion tunnel. Such as an extended attachment for the wire crane gripper to be able to do our work between the many supports and outriggers. A special "dumping and suction tube" has also been developed to apply gravel to the bottom of the tub. Applying gravel at a depth of 8 to 10 meters within tolerances is already quite a job, let alone at a depth of almost 30 meters. With the 'dumping and suction tube' we were able to apply gravel in the correct layer thickness and finish level in a very dosed manner. The use of these specific pieces of equipment resulted in a careful and controlled production."
Verboon Maasland has now completed the largest bulk of work on the Blankenburg connection. "Until the summer vacations we are still taking care of the last excavations of the connecting construction pits and adjacent earthworks. All in all, we have then been active on the project for over 2.5 years, which has been extremely constructive. Thanks also to the very fine and solution-oriented cooperation with the people of BAAK," Van Wijk concludes.
