UNDER-REAMED DIAPHRAGM WALLS

Abstract: A method of stabilising soil is disclosed comprising a diaphragm wall whose lower end is anchored in an under-reamed cavity filled with concrete, together with an under-reaming tool for constructing the cavity. The under-reaming tool comprises a hydraulically operated, circular cutting tool (8) mounted on the end of a supporting arm (6). The supporting arm pivots about the end of a long positioning arm (5) by means of a hydraulic arm (9) acting on a plate (7) fixed to the supporting arm in the same plane as its pivotal movement.

Description: UNDER-REAMED DIAPHRAGM WALLS This invention relates to the stabilisation of soil structures and, more particularly but not exclusively, to methods of stabilisation and tools for use in those methods . According to one aspect of the present invention, there is provided a method of stabilising soil, which comprises constructing a diaphragm wall the lower end of which is anchored in an under-reamed cavity filled with concrete. The invention also provides a diaphragm wall the lower end of which is anchored in an under- reamed cavity filled with concrete. Such a diaphragm wall can, in certain conditions, be shallower than a conventional wall without, for example, sacrificing its containment or load-bearing properties. The shape and extent of the under-reamed cavity will be selected according to the prevailing ground conditions and the intended function of the diaphragm wall . For example, a barrel-shaped cavity filled with concrete and extending around at least the lowermost end of the wall can impart improved load-bearing properties and/or provide a passive anchorage integral with the wall . According to another aspect of the present invention, there is provided an under-reaming tool which comprises a positioning arm; a supporting arm pivotally attached to a first point which is at or close to one end of said positioning arm; a cutting tool carried by said supporting arm and pivotally mounted thereon at a second point which is at or close to that end of said supporting arm remote from said positioning arm; a plate fixed in position relative to said supporting arm or integral therewith, the plate lying in or parallel to the plane swept out by said supporting arm as it rotates around said first point; and means for moving said plate so as to cause the supporting arm to pivot about said first point, thereby permitting controlled movement of said circular cutting tool in arcuate path. Generally, the positioning arm will be an elongate member so as to facilitate use of the under-reaming tool at depths of several metres, or several tens of metres, below ground level. The length of the positioning arm and its form of construction will be selected according to the operating conditions in which the tool is required to function. The cutting tool is advantageously circular in form. The means for moving said plate so as to cause the supporting arm to pivot about said first point is preferably a rigid or semi-rigid linkage extending between (a) a point of connection on the plate itself and (b) a position close to the axis of the positioning arm and on that side of said first point opposite to said second pivot point when the supporting arm is positioned so as to extend as a continuation of the positioning arm. Thus if the positioning arm extends downwardly into the ground, one end of the linkage will be connected to the plate and the other end of the linkage will be connected to a point above the distal (bottom) end of the positioning arm. A suitable linkage can be provided by using a hydraulic ram. Preferably, the plate is triangular, and more preferably it is in the form of an equilateral triangle. The pivot point between the supporting arm and the positioning arm - termed herein the "first point" - may pass through the body of said plate. Conveniently said first point can be at or close to the centroid of the triangle when the plate is triangular. The arrangements described permit the tool to be operated so as to generate an under-reamed cavity which is circular in cross-section in the plane of the cutting tool (which will often correspond to a vertical plane). Other forms of articulation between the cutting tool and the positioning arm may be adopted if desired; these may permit variations in the geometry of the cavity which is formed by use of the tool . In one embodiment, the supporting arm is fixed in length; in other embodiments, its length can be varied. This variation in length also permits different cavity geometries to be formed if desired (either during a single under-reaming operation or so as to generate cavities of different dimensions in successive operations, whether at the same or different locations ) . When a tool in accordance with this invention is used, the positioning arm will be located as desired, for example at the base of a trench which may typically be from 3 to 50 metres below ground level . The positioning arm is preferably located by means of a guide - e.g. a tubular structure through which the positioning arm and other components of the tool are passed. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: FIGURE 1 is a plan view of a trench in which a diaphragm wall of this invention is installed; and FIGURE 2 is a side elevation view through the trench of Fig. 1 during construction with an under-reaming tool of this invention in position within the trench. Referring to the drawings, a diaphragm wall 1 six metres in width is anchored, at its base, by a barrel- shaped anchorage 2 whose lateral extent exceeds that of wall 1 by 500mm on either side. The width of the anchorage is five metres - there being a section of wall approximately 500mm in extent adjacent to the stop ends 3 where the anchorage is absent. In Fig. 2, an under-reaming tool 4 is shown at the base of trench 10. A tubular guide 11 is used to position the tool 4 within the trench. Tool 4 comprises an elongate positioning arm 5; a supporting arm 6; a rigid triangular plate 7; a circular cutting tool 8; and a hydraulic ram 9. Supporting arm 6 and plate 7 are fixed together; they are pivotally connected to the lower end of arm 5 at point PI, as shown. Cutting tool 8 is mounted on supporting arm 6 so as to be able to rotate about point P2. Hydraulic ram 9 connects with one of the triangular vertices of plate 7 by means of a rigid link 12. When the tool is in use, hydraulic ram 9 is operated so as to cause arm 6, and hence cutting tool 8, to pivot about point PI. This pivotal movement moves the tool 8 with respect to the axis of arm 5; one position of tool 8 close to its extreme limit of movement is marked as 8b. The cutting tool 8 is hydraulically operated. The pivotal movement just described results in the formation of a cavity whose cross-section is generally circular. If the arm 5 is lifted upwardly after an initial cutting operation, the cavity will become barrel-shaped; if the lifting continues, the cavity will tend towards a slab-like form. Operation of the cutting tool 8 is carried out in a conventional manner, e.g. in the presence of a drilling fluid and with extraction of debris through the guide member 11. Concrete can be supplied to the cavity through a tremie (not shown). If desired, the concrete may be reinforced by conventional reinforcements - e.g. by steel rods or meshes.

Claims: CLAIMS : 1. A method of stabilising soil, which comprises constructing a diaphragm wall the lower end of which is anchored in an under-reamed cavity filled with concrete. 2. A diaphragm wall the lower end of which is anchored in an under-reamed cavity filled with concrete. 3. An under-reaming tool which comprises a positioning arm; a supporting arm pivotally attached to a first point which is at or close to one end of said positioning arm; a cutting tool carried by said supporting arm and pivotally mounted thereon at a second point which is at or close to that end of said supporting arm remote from said positioning arm; a plate fixed in position relative to said supporting arm or integral therewith, the plate lying in or parallel to the plane swept out by said supporting arm as it rotates around said first point; and means for moving said plate so as to cause the supporting arm to pivot about said first point, thereby permitting controlled movement of said circular cutting tool in arcuate path. 4. A tool as claimed in claim 3, wherein said positioning arm is an elongate member. 5. A tool as claimed in claim 3 or 4, wherein said cutting tool is circular in form. 6. A tool as claimed in claim 3, 4 or 5, wherein said means for moving said plate so as to cause the supporting arm to pivot about said first point is a rigid or semi-rigid linkage extending between (a) a point of connection on the plate itself and (b) a position close to the axis of the positioning arm and on that side of said first point opposite to said second pivot point when the supporting arm is positioned so as to extend as a continuation of the positioning arm. 7. A tool as claimed in claim 6, wherein said linkage is provided by a hydraulic ram. 8. A tool as claimed in any one of claims 3-7, wherein said plate is triangular. 9. A tool as claimed in claim 8, wherein said plate is in the form of an equilateral triangle. 10. A tool as claimed in any one of claims 3 to 9, wherein said first point passes through the body of said plate. 11. A tool as claimed in claims 8 and 10, wherein said first point is at or close to the centroid of the triangle when the plate is triangular. 12. A tool as claimed in any one of claims 3 to 11, wherein said supporting arm is fixed in length. 13. A tool as claimed in any one of claims 3 to 11, wherein said supporting arm is variable in length. 14. An under-reaming tool sunstantially as hereinbefore described with reference to, and as illustrated by, Fig. 2 of the accompanying drawings. 15. A method of constructing a diaphragm wall substantially as hereinbefore described. 15. A diaphragm wall constructed by a method or with a tool as claimed in any of claims 1 and 3 to 14.

Inventors: PAYNE RON, SHOTTON PETER GILBERT, PAYNE, RON, SHOTTON, PETER, GILBERT
Applicants: KVAERNER CEMENTATION FOUND LTD, PAYNE RON, SHOTTON PETER GILBERT, KVAERNER CEMENTATION FOUNDATIONS LIMITED, PAYNE, RON, SHOTTON, PETER, GILBERT
Application year: 2000
Main classification: E02D5
IPC codes: E02D5, E02D17