Drag head for a trailing suction hopper dredger and method for dredging using this drag head

Abstract

The invention relates to a drag head of a trailing suction hopper dredger. The drag head comprises a visor which is dragged over the bottom and herein loosens soil, and a suction pipe which is connected to the visor and which discharges the loosened soil. The visor comprises at least two individually movable pressure elements transversely of the dragging direction which comprise a number of substantially disc-shaped penetrating bodies. The penetrating bodies transmit forces to the bottom via their peripheral edge under the influence of the weight of the pressure element in which they are received, whereby the bottom is broken. The drag head has an improved efficiency.

1 - 16 . (canceled) 
     
     
         17 . A drag head of a trailing suction hopper dredger, comprising a visor which is dragged over the bottom and therein loosens soil, and a suction pipe which is connected to the visor and which discharges the loosened soil, wherein the visor includes at least two individually movable pressure elements transversely of the dragging direction, wherein a pressure element is provided with a number of penetrating bodies which transmit forces to the bottom under the influence of the weight of the pressure element. 
     
     
         18 . The drag head as claimed in  claim 17 , wherein the pressure elements are received in the visor by means of guide means, this such that the pressure elements are translatable in a direction substantially perpendicularly of the bottom. 
     
     
         19 . The drag head as claimed in  claim 17 , wherein the penetrating bodies comprise disc-shaped penetrating bodies which transmit forces to the bottom via their peripheral edge under the influence of the weight of the pressure element. 
     
     
         20 . The drag head as claimed in  claim 19 , wherein the disc-shaped penetrating bodies extend in one line and substantially transversely of the dredging direction. 
     
     
         21 . The drag head as claimed in  claim 20 , wherein the pressure elements are provided with a series of teeth extending substantially transversely of the dragging direction and engaging on the bottom upstream of the disc-shaped penetrating bodies during use. 
     
     
         22 . The drag head as claimed in  claim 21 , wherein the pressure elements are provided with support means which during use engage on the bottom upstream of the disc-shaped penetrating bodies. 
     
     
         23 . The drag head as claimed in  claim 21 , wherein the pressure elements are provided with support means which during use engage on the bottom upstream of the disc-shaped penetrating bodies and the teeth. 
     
     
         24 . The drag head as claimed in  claim 21 , wherein the support means comprise slide blocks. 
     
     
         25 . The drag head as claimed in  claim 21 , wherein the disc-shaped penetrating elements have a penetration depth, and that the teeth engage on the bottom higher than the disc-shaped penetrating bodies. 
     
     
         26 . The drag head as claimed in  claim 21 , wherein the teeth have a penetration depth, and that the support means engage on the bottom higher than the teeth. 
     
     
         27 . The drag head as claimed in  claim 17 , wherein the number of disc-shaped penetrating bodies per pressure element lies between 2 and 10, and more preferably between 3 and 5. 
     
     
         28 . The drag head as claimed in  claim 17 , wherein the number of pressure elements lies between 2 and 8, and more preferably between 3 and 5. 
     
     
         29 . The drag head as claimed in  claim 17 , wherein the drag head is provided with closing means which substantially close the opening between the visor and the bottom. 
     
     
         30 . The drag head as claimed in  claim 17 , wherein the drag head comprises at least one series of jet pipes for injecting water under high pressure. 
     
     
         31 . A method for dredging an at least partially hard bottom under water with a trailing suction hopper dredger, equipped with a drag head having a visor which is dragged over the bottom and therein loosens soil, and a suction pipe which is connected to the visor and which discharges the loosened soil, wherein the visor includes at least two individually movable pressure elements transversely of the dragging direction, wherein a pressure element is provided with a number of penetrating bodies which transmit forces to the bottom under the influence of the weight of the pressure element, the method comprising the steps of:
 lowering the drag head onto the bottom and dragging it thereover, wherein a suction force is exerted through the suction pipe on the space at least partially closed off via closing means and enclosed by the visor and the bottom, so that the disc-shaped penetrating bodies penetrate via their peripheral edge into the bottom and cause cracks therein under the influence of the weight of the pressure elements and the underpressure, and wherein the broken-off soil chips are suctioned up through the suction pipe.   
     
     
         32 . The method as claimed in  claim 31 , wherein, during the dredging, the pressure elements translate independently of each other in a direction substantially perpendicularly of the bottom. 
     
     
         33 . The method as claimed in  claim 32 , wherein the support means of a pressure element engage first on the bottom, wherein the pressure element is forced to follow the contour of the bottom, wherein the teeth then engage on the bottom so that the bottom is at least partially leveled, after which the penetrating bodies engage on the bottom.