Method for fixing an anchor for anchoring earth-retaining walls, buildings, bank sheet-pilings, quay walls and the like

Abstract: An anchor is fixed in the ground for anchoring earth-retaining walls, buildings, bank sheet-pilings, quay walls and the like. A steel tube (1) is first placed at an angle in the ground, and an anchor rod (2) or cable is pushed into said tube. The bottom end of the rod or cable has a screw connection with a nut (4) provided with internal screw thread or semi-screw thread. A plastic pipe (7), connected to the nut (4) or a part fixed thereto, is fitted around the rod or cable. A number of cylinders of high-grade concrete (8) are placed around the bottom part of the rod (2) or cable enclosed by the plastic pipe (7), directly above the nut or the part fixed thereto. Cement grout (9) is introduced all around the nut (4) and these cylinders (8) stacked on top of each other, and at the same time the steel tube (1) is withdrawn. After the cement anchoring element formed has set, the rod (2) or cable is subjected to tensile stress and is connected by means of a plate or girder to the anchored element. Due to the fact that after removal of the rod (2) or cable the part of the anchor remaining in the ground consists of a nut (4), a relatively thin cement casing (9) and cylinders of high-grade concrete (8) stacked loose on top of each other, the anchoring element will not constitute any obstacle if a pile is driven through the element, or if an earth drill passes through it, because it can easily be knocked or drilled into small pieces.

Description: The invention relates to a method for fixing an anchor for anchoring earth-retaining walls, buildings, bank sheet-pilings, quay walls and the like, comprising: placing a steel tube at an angle in the ground, inserting an anchor rod or cable into the tube, placing cement grout in the bottom part of the tube and at the same time withdrawing the tube, subjecting the rod or cable to tensile stress after the cement anchoring element formed has set, and connecting the rod or cable to a plate or girder of the element to be anchored. Grouted anchors comprising a steel rod or bundle or wires, the bottom end of which is surrounded by hardened cement paste, are used to absorb tensile forces as disclosed in DE-A-2637676. They derive their ability to absorb tensile forces from the shear stresses between the cylindrical surface of the cement grout element and the earth surrounding it. Grouted anchors can be used both for temporary and for permanent structures. They do not mar the landscape, roads do not need to be broken up, and the presence of buildings is no obstacle. A drawback of grouted anchors fixed by known methods is, however, that they could impede the subsequent placing of driven piles or bored piles in the ground. Even if the steel rod or cable could be removed, the hardened cement paste anchoring element with a length of between 3 and 8 metres constitutes an obstacle for piles subsequently being driven into the ground. This hardened cement paste anchoring element must contain steel compression bars to enable it to absorb high compressive stresses, and it is thus difficult to break. The object of the invention is to solve the abovementioned problem, and to this end the bottom end of the rod or cable has a screw connection with a nut provided with internal screw thread or semi-screw thread, a plastic pipe, connected to the nut or a part fixed thereto, is fitted around the rod or cable, and a number of cylinders of high-grade concrete are placed around the bottom part of the rod or cable enclosed by the plastic pipe, directly above the nut or the part fixed thereto. It is essential that the rod or cable can be removed by unscrewing and that the parts remaining in the ground are small enough to be pressed away by a sheet piling plank or pile to be driven into the ground. The concrete cylinders with a length of between 5 and 75 cm are made of high-grade concrete (high compressive strength), so that when the rod or cable is tensioned they can absorb a high compressive force, but when they come into contact with a pile the cylinders can be pressed away laterally in the ground without any problem. The relatively thin grout element connects to the concrete cylinders, the external surface of which has been made rough for good adhesion with the cement grout. In the event of contact with a sheet piling plank or pile to be driven into the ground, the grout casing can easily be broken up. The plastic pipe protects the steel rod or cable from water. In order to protect the screw connection between nut and rod or cable from corroding up, an anti-corrosive lubricant can be placed inside the nut. The invention will now be explained in greater detail with reference to the figures. Figure 1 illustrates the fixing of a grouted anchor according to the invention. Figure 2 shows a finished anchor construction. Figure 3 shows the bottom part of the anchor before the cement grout is applied. Figure 4 shows the bottom part of the finished anchor after unscrewing and removal of the anchor rod. It can be seen in the figures that for fixing a grouted anchor according to the invention a sturdy steel tube 1 is placed at an angle in the ground, and a steel rod 2 provided with screw thread or semi-screw thread 3 along at least part of its length is then pushed into said tube and screwed with said screw thread into an internally threaded nut 4. A cover 5 is welded onto the outer end of the nut, in order to prevent water from penetrating into the nut. Welded onto the nut is also a sturdy ring 6, to which a plastic pipe 7, which encloses the steel rod 2 and blocks lateral access of water to the rod, is fixed. Separate cylinders 8 made of concrete with high compressive strength (for example, 80 N/mm² cubic compressive strength) are stacked on the ring 6 over a length of 3 to 8 metres. The length of the rings is 5 to 75 cm. In order to prevent the edges of the end faces of the cylinders from breaking apart when there is high compressive force on the cylinders, these edges can be bevelled. The space between the tube 1, on the one hand, and the nut 4 and the cylinders 8, on the other, is finally filled under pressure with cement grout 9, while the steel tube 1 is withdrawn at the same time. After the grout has set, the rod 2 is placed under tensile stress and connected to a plate or girder of the element to be anchored, in which case the shear stress between the cylindrical surface of the grout element and the earth surrounding it provides the anchoring. After the anchor has done its work, the rod 2 can be unscrewed from the nut 4 and removed. The resulting situation can be seen in Figure 4. If the anchoring element comprising the nut 4, grout element 9, concrete cylinders 8 and plastic pipe 7 is touched by a driven pile, the relatively thin grout casing 9 will break easily, and the concrete cylinders 8 and the nut 4 can easily be pressed away as separate relatively small elements. It is essential for the idea of the invention that the prefabricated cylinders 8 made of high-grade concrete can absorb great compressive stresses, and that the rod 2 can thus be brought to high pretension without problems, while as a result of the fact that the relatively small cylinders 8 are stacked loose on top of each other, after removal of the rod 2, the parts of the anchor remaining in the ground cannot give rise to problems when piles are being driven later. An anti-corrosive lubricant will be placed inside the nut, so that rod 2 can be unscrewed from the nut easily later on. In order to ensure that the external surface of the cylinders 6 is rough and adheres very well to the cement grout casing 9, the cylinders 6 can be worked by known techniques on said surfaces. Various modifications are possible within the scope of the invention.

Claims: Method for fixing an anchor for anchoring earth-retaining walls, buildings, bank sheet-pilings, quay walls and the like, comprising: placing a steel tube (1) at an angle in the ground, inserting an anchor rod or cable (2) into the tube, placing cement grout (9) in the bottom part of the tube (1) and at the same time withdrawing the tube (1), subjecting the rod or cable (2) to tensile stress after the cement anchoring element formed has set, and connecting the rod or cable to a plate or girder of the element to be anchored, characterised: in that the bottom end of the rod or cable (2) has a screw connection with a nut (4) provided with internal screw thread or semi-screw thread (3), in that a plastic pipe (7), connected to the nut (4) or a part fixed thereto, is fitted around the rod or cable (2), and in that a number of cylinders of high-grade concrete (8) are placed around the bottom part of the rod or cable (2) enclosed by the plastic pipe (7), directly above the nut (4) or the part fixed thereto. Method according to Claim 1, characterised in that the length of the cylinders (8) is 5 to 75 cm. Method according to Claim 1 or 2, characterised in that an anti-corrosive lubricant is placed inside the nut (4).

Inventors: VAN DE GRIENDT MICHIEL ADRIAAN, VAN DE GRIENDT, MICHIEL ADRIAAN
Applicants: HOLLANDSCHE BETONGROEP NV, HOLLANDSCHE BETON GROEP N.V.
Application year: 1992
Main classification: E02D5
IPC codes: E02D5