METHOD AND DEVICE FOR PERFORMING GROUND ANCHORAGE

Abstract: Method and arrangement for anchorage in the soil by means of a ground anchor (1) in the form of a tube (2) in which at least two axial slots (3a, 3b) are arranged along at least one region of a tube wall in a part of the tube which is to be driven into the soil. This tube (2) is driven into the soil by cooperating with a pike (4) which is arranged in the tube (2) and which, after the tube has been driven in, is removed therefrom. The method according to the invention is characterized in that the tube (2) in at least one region with axial slots (3a, 3b) is subjected to a radial load by means of a tool (5) which is sunk into the tube and which is actuated so as to exert a controllable radial load on the interior of the tube in the direction towards the tube wall. By virtue of this load a controllable expansion of the tube is brought about in this region. The tool is removed from the tube when a predetermined degree of expansion has been attained.

Description: Method and device for performing ground anchorage The present invention concerns a method of anchoring in soil by means of a ground anchor in the form of a tube in which at least two axial slots are disposed along at least one region of a tube wall in a part of the tube which is to be driven into the soil, the tube being driven into the soil in co-operation with a pike disposed in the tube. The invention also concerns an arrangement for anchoring in soil, said arrangement coπφrising a ground anchor in the form of a tube on which at least two axial slots are disposed along at least one region of a tube wall in a part of the tube which is to be driven into the soil. The invention furthermore concerns a tool such that a tubular ground anchor can be radially expanded in a controlled manner by the method according to the invention. Processes for anchoring soil andiorages which are sunk to a greater or lesser depth, for example, when laying foundations, are well known. The currently most usual type of anchorage consists of a concrete anchorage cast at the intended anchorage site. This type of anchorage is very demanding in terms of time since a casting mould firstly has to be dug in the soil before the concrete casting process itself can be performed. The concrete thai has to be allowed to set before the anchorage is ready to be used. A further disadvantage of concrete anchorages is that they tend to disintegrate after a number of years' use. In order that the durability of the anchorage can be checked, it has to be laid bare. In order to dispense with casting of anchorages it is also known to drive into the soil a metal object which, owing to its shape, is anchored in the soil when it has been driven in. However this type of anchorage or ground anchor is difficult to drive into the soil to a depth sufficient for the anchorage to support high loads. It is also already known to drive into the soil a metal tube, for example, which is then deformed so that reinforcement in the soil is attained. DE-1 484 565 has already disclosed a ground anchor of the above-mentioned type. It consists substantially of a tube with a solid tip. A round bar is disposed in the tube and connected to the tip. Slots are formed in the tube above the tip. These slots are uniformly distributed along the tube and extend in the axial direction along the latter. This ground anchor is anchored in the soil as a result of the round bar and the tube disposed about the latter being driven into the soil. When the tube has been driven into the soil, an axial, upwardly directed force is applied to the round bar whilst the tube is held in place by an axially downwardly directed force. The round bar is therefore actuated such that it moves upwards out of the tube whilst the tube tip approaches the upper part of the tube. The shape of the tube is acted upon in the slotted region so that expansion of the tube is brought about in this region. The round bar can then be removed from the tube. A disadvantage of this known type of anchorage is that it is unsuitable for deep anchorage and can only be used for ground anchors of very small dimensions. In the case of large tube dimensions and deep anchorage, the method is difficult to carry out, both practically and economically. Furthermore the method is unsatisfactory when a plurality of expanded regions are desired in each tubular anchorage in the ground. The object of the present invention is to overcome the stated problem by providing a soil anchorage consisting of a ground anchor in the form of a tube with axial slots. This object is achieved by the method according to the invention which is characterized in that the tube in at least one region with axial slots is subjected to a radial load by means of a tool which is sunk into the tube and which is actuated so as to exert a controllable radial load on the interior of the tube in the direction towards the tube wall, whereby a controllable expansion of the tube is brought about in this region; and in that the tool is removed from the tube when a predetermined degree of expansion has been attained. In order to permit further expansions of the ground anchor, according to a particular feature of the invention, each tube comprises two or more regions each having two or more slots. According to a further particular feature of the invention, the radial load is applied in each slotted region in order to increase the bearing capacity of the anchorage. In order to be able to evaluate the bearing capacity of the anchorage, according to a further feature of the invention, data -concerning expansion are measured during the anchorage process, these measured data further being used to provide a preliminary geotechnical evaluation of the properties of the soil. The object of the present invention is also to provide a ground anchor to be used according to the above method. This object is achieved by the arrangement according to the invention which arrangement is characterized in that the tube is open over its entire length and is arranged to be driven into the soil by means of a pike which is disposed in the tube and which has a lower pointed end and whose length is adapted such that the lower pointed end of the pike projects out of the lower end of the tube during the driving-in process; in that, when being driven in, the pike and tube are operatively connected to each other at their respective upper ends, such that these upper ends can be made to move at the same time as the pike and tube are being driven in; and in that the pike is arranged to be removed from the tube when it has been driven in, whereupon the tube is arranged such that, at at least two opposite points on each side of the interior of the tube, midway between the slots, it can receive a radial load brought about by a tool sunk into the tube, the load being applied in the direction towards the tube, such that controllable expansion of the tube can be brought about in this region. A further object of the present invention is to provide a tool for bringing about the controllable radial expansion of the tubular ground anchor when the method according to the invention is carried out. This object is achieved by the tool according to the invention which tool is characterized in that it comprises: a tool body adapted such that it can be sunk into the tubular ground anchor; at least two radially directed pistons which are disposed at equal spacings and movably mounted in corresponding radial recesses in the tool body, which recesses in one direction each open out at the periphery of the tool body and in another direction are each delimited by a base formed by the tool body; flow connections connecting the recesses at their respective bases to flow attachmαits on the exterior of the tool body; and means for attaching the flow attachments of the flow connections to a hydraulic source. According to a particular feature of the invention, in order to distribute the force of the tool uniformly, mere are three recesses and three pistons. Ac jrding to a further particular feature of the invention, in order to distribute the force of the tool uniformly over a large part of the periphery of the ground anchor there are four recesses and four pistons. According to a final particular feature of the invention, the recesses are located at mutual substantially similar spacings axially along the length of the tool to allow a maximum piston stroke when the ground anchor expands. In the following the invention will be described with reference to the drawings, in which: Figure 1 shows a basic embodiment of a tubular ground anchor; Figure 2 shows the tubular ground anchor in Figure 1 when it is being driven into the soil; Figure 3 shows the tubular ground anchor when the method according to the invention has been carried out; Figure 4 shows in side view an example of a tool for carrying out the controllable radial expansion of the tubular ground anchor by means of the method according to the invention; and Figure 5 shows the tool in Figure 4, in perspective. The method according to the invention is intended to be used for tubular constructions of resilient material, for example a ground anchor 1 in the form of a steel tube 2. This steel tube is open over its entire length and is provided in two different regions of the tube 2 with two axial slots 3a, 3b dispos-ed on each side of the steel tube. The slotted regions are to be driven into the soil. During the process of driving into the soil a pike 4 is disposed in the tube 2. This pike has a lower pointed end 4a which facilitates driving into the soil in that, as it is driven in, it projects from the lower end of the tube. The pike reduces the load on the tube 2 during the driving-in process at the same time as the ground or other material in the soil is prevented from filling the tube. Owing to the pike 4, the tube 2 can be driven into the ground when it consists of rock or frozen soil. Whilst being driven in, the pike 4 and tube 2 are operatively connected to each other at their respective upper ends, such that these upper ends can be made to move at the same time as the pike and tube are being driven in. When the tube 2 has been driven in to the desired depth, the pike is removed from the tube and can then be used again when a further tube is driven in. The driving-in process is performed mechanically, for example by means of a hydraulic hammer. When the tube has been driven into the soil a tool 5 is disposed in the tube, which tool, in a first collapsed position, can easily be displaced in the tube 2. This tool can, for example, consist of the hydraulic tool shown in Figures 4 and 5 but other tools are evidently also possible. The tool 5 according to Figures 4 and 5 is especially adapted for carrying out the controllable radial expansion of the tubular ground anchor 1. The tool 5 consists of a tool body 5a which is adapted such that it can be sunk into the tubular ground anchor 1. The tool body 5a suitably consists of a solid steel unit. The tool body 5a comprises four radially directed pistons 6 which are located at uniform spacings about the periphery of the tool and which are movably mounted in corresponding radial recesses 7 in the tool body 5a. The recesses 7 are located at mutual substantially similar spacings axially along the length of the tool and each open out in one direction at the periphery of the tool body and are delimited in the other direction by a base formed by the tool body 5a, since the recesses do not pass through the entire tool body 5a. The recesses 7 are in the form of bores bored or milled in the tool body 5a for hydraulic pistons 6. The solid tool body 5a comprises flow connections which connect the recesses 7 at their respective bases to flow attachments 8 on the exterior of the tool body. The flow connections are to be attached to a hydraulic source via their flow attachments 8. The hydraulic source is advantageously a double-action high-pressure pump with an operating pressure of up to 1000 bars. Located at the hydraulic source are arrangements for measuring pressure, flow and other significant parameters. The possibility of measuring data ■con-cerning the expansion, i.e. pressure, flow, etc., whilst carrying out the anchorage process, enables the loads in terms of pressure, tension and torque, which the tubular ground anchor can withstand, to be established. The measured data can also be used to provide a preliminary geotechnical evaluation of the properties of the soil. By virtue of the tool the region of the tube comprising axial slots 3a, 3b can be loaded in the radial direction. The load is applied on the interior of the tube in the direction towards the tube wall in a second, collapsed position of the tool. In this position the oil in the tool 5 has been pressurized so that the pistons 6 move outwards. Since all the recesses 7 are connected for flow to one another, when one of the pistons reaches maximum pressure, the oil flows on to the next recess until all the pistons 6 are in the outer position. The slots 3a, 3b in the tube enable the latter to be expanded in this region if the load is applied at at least two opposite points, disposed on each side of the tube, midway between the slots. Expansion or deformation is thereby brought about in the region about the axial slots 3a, 3b. The radial expansion of the tube in the slotted region can be controlled by guiding the tool 5 sunk in the tube. It is thereby possible to adapt the anchorage better to the soil conditions. If expansion is to be brought about in a given region, the tool is actuated so as to recover a shape suitable fear its displacement in the tube. This is brought .about in that the double-action hydraulic source is made to return the hydraulic oil such that the pistons 6 move into the tool body 5a The tool 5 is then moved out of the tube 2 or to a region arranged for further expansion. The same tool can thus be used for carrying out further expansion of the tube 2 in a different region provided with axial slots 3a, 3b. The number of possible expansions in the tube is ultimately limited to the number of regions on the tube which are provided with axial slots. It will be appreciated that it may also be chosen not to expand the tube in a given region of the tube even though this region is provided with axial slots. The invαitiσn provides a method of anchoring in the soil a ground anchor in the form of a tube 2, this method being easy to perform. The finished anchorage comprises a tube 2 which has been deformed in one or a plurality of regions such that the radial periphery of the tube 2 has increased in this region or these regions. However the tube has been deformed in such a way that cavities in this tube are retained over the entire length thereof. It is thereby subsequently easy to examine the tube, for example with respect to corrosion damage or the like. It will be appreciated that the method according to the invention is not restricted to the use of the tool as shown in Figures 4 and 5; this tool is only one example of an arrangement by means of which radial expansion of a tubular ground anchor can be brought about in a given region of this tube.

Claims: CIAIMS 1. Method of anchoring in soil by means of a ground anchor (1) in the form of a tube (2), in which at least two axial slots (3a, 3b) are disposed along at least one region of a tube wall in a part of the tube (2) which is to be driven into the soil, the tube being driven into the soil by co-operating with a pike (4) which is disposed in the tube and which, after the tube has been driven in, is removed therefrom, characterized in that the tube in at least one region with axial slots (3a, 3b) is subjected to a radial load by means of a tool (5) which is sunk into the tube and which is actuated so as to exert a controllable radial load on the interior of the tube in the direction towards the tube wall, whereby a controllable expansion of the tube is brought about in this region; and in that the tool is removed from the tube when a predetermined degree of expansion has been attained. 2. Method according to Claim 1, characterized in that each tube (2) comprises two or more regions each having two or more slots (3a, 3b). 3. Method according to Claim 1, characterized in that the radial load is applied in each slotted region. 4. Method .according to Claim 2, characterized in that the radial load is applied in each slotted region. 5. Method according to any of the preceding claims, characterized in that data concerning expansion are measured during the anchorage process; and in that these measured data are used to provide a preliminary geotechnical evaluation of the properties of the soil. 6. Ground anchor (1) in the form of a tube (2), in which at least two axial slots (3a, 3b) are disposed along at least one region of a tube wall in a part of the tube (2) which is to be driven into the soil, characterized in that the tube (2) is open over its entire length and is arranged to be driven into the soil by means of a pike (4) which is disposed in the tube (2) and which has a lower pointed end (4a) and whose length is adapted such that the lower pointed end (4a) of the pike projects out of the lower end of the tube during the driving-in process; in that, when being driven in, the pike (4) and tube (2) are operatively connected to each other at their respective upper ends, such that these upper ends can be made to move at the same time as the pike and tube are being driven in; and in that the pike (4) is arranged to be removed from the tube (2) when it has been driven in, whαeupon the tube (2) is arranged such that, at at least two opposite points on each side of the interior of the tube (2), midway between the slots (3a, 3b), it can receive a radial load exerted by a tool (5) sunk into the tube, the load being applied in the direction towards the tube, such that controllable expansion of the tube (2) can be brought about in this region. 7. Tool (5) for performing a controllable radial expansion of a tubular ground anchor (1), characterized in that it comprises: a tool body (5a) adapted such that it can be sunk into the tubular ground anchor (1); at least two radially directed pistons (6) which are disposed at equal spacings and movably mounted in coπ sponding radial recesses (7) in the tool body (5a), which recesses (7) in one direction each open out at the periphery of the tool body (5a) and in another direction are each delimited by a base formed by the tool body (5a); flow connections connecting the recesses (7) at their respective bases to flow attachments (8) on the exterior of the tool body (5a); and means for attaching the flow attachments (8) of the flow connections to a hydraulic source. 8. Tool (5) according to Claim 7, characterized in that there are three recesses (7) .and three pistons (6). 9. Tool (5) according to Claim 7, characterized in that there are four recesses (7) and four pistons (6). 10. Tool (5) according to any one of Claims 7 to 9, characterized in that the recesses (7) are disposed at mutual substantially similar spacings axially along the length of the tool (5).

Inventors: JOHANSSON STEVE, NORMAN TORBJOERN, JOHANSSON, STEVE, NORMAN, TORBJOERN
Applicants: JOHANSSON STEVE, NORMAN TORBJOERN, JOHANSSON, STEVE, NORMAN, TORBJOERN
Application year: 1996
Main classification: E02D5
IPC codes: E02D5