GB2098329A

GB2098329A - Determining profiles of walls

Info

Publication number: GB2098329A
Application number: GB8111469A
Authority: GB
Original assignee: Kirkpatrick J A & Partners Hol
Current assignee: Kirkpatrick J A & Partners Hol
Priority date: 1981-04-11
Filing date: 1981-04-11
Publication date: 1982-11-17
Also published as: GB2098329B

Abstract

The profile of a wall 1, for example within a tunnel, is determined by projecting a first laser beam 12 onto the wall and projecting a second laser beam 16 from a source 10 spaced from the source 7 of the first beam on to the wall to coincide with the area of incidence of the first beam, and thereby calculating the profile of the wall front the various parameters of the two beams. In the embodiment shown in the figure the first beam 12 is projected by a rotating head 6 to generate a visible line 13 with gaps 14A, 14B etc. caused by projecting pins on board 4, and the second beam is aligned to coincide with each gap in turn and the orientation of the second beam then recorded. <IMAGE>

Description

SPECIFICATION Determination of structure walls This invention relates to a method of determining the profile of a structure wall, especially but not exclusively the internal face of a tunnel wall.

Tunnels which are for passage of vehicles are often subjected to considerable vibration and other stresses set up by the vehicles. This is particularly acute in railway tunnels with the very great weight of the rolling stock, and as a result periodic checks have to be undertaken to ensure that the integrity and profile of the tunnel wall is maintained. Defects such as bulges and the like must be located before they become serious to the point of making the tunnel unsafe.

According to the present invention there is provided a method of determining the profile of a structure wall, comprising projecting a first beam of light from a first laser source onto the wall to define an area of known parameter, providing a second laser source a measured distance from the first laser source, projecting a second beam of light from the second laser source onto the wall in the area defined by the first beam, and measuring parameters of the second beam.

The first beam may be projected onto the wall at a preset angle from its source and the second beam aimed to coincide with its area of incidence with the wall, and the process repeated for a series of measured angles of incidence of the first beam. Alternatively the first beam may be moving, for example rotatably, and areas on its track marked for projection of the second beam; this can be achieved by interrupting the first beam at preset intervals on its track so that the areas for projection of the second beam appear unilluminated on the wall. In one form a rotating first beam can be disposed with its axis adjacent or at the centre of circle on whose circumferential lie a series of spaced solid members, for example pins, so that on rotation of the source the beam described on the wall a line interrupted at intervals proportional to the spacing between the pins.The source can then be directed to project the second beam at the unilluminated areas in sequence, the parameters being recorded at each setting.

The parameters are to enable the wall profile to be calculated, and can be standard parameters employed in surveying techniques, for example the angles of the second beam to the horizontal and vertical and/or the distance from the second source along the second beam to the wall.

Geometric calculation then gives the relative positions of the areas at which the second beam was projected.

An embodiment of this invention will now be described with reference to the accompanying drawing which is a perspective view showing apparatus for putting into effect the method of the invention.

Referring now to the drawing, a railway tunnel has an internal wall 1 to be monitored. A bogey 2 runs on rails 3 and has mounted on it a board 4 from which project wooden pins 5 about 50 mm apart around an arc of a circle. The pins are about 4 inches proud of the board 4. A laser source 5 is positioned at one end of the bogey 2, this source 5 having a continuously-rotatable light-emitting head 6 mounted on a fixed body 7. The axis of the rotatable head 6 lies at the centre of the circle on whose arc the pins 5 lie.

On the extension of the axis of the head 6 is a second laser source 8 whose light-emitting head 9 is swivelably mounted on a fixed base 10 on the bogey 2. Both laser sources 5, 8 are powered by batteries 11, and the distance between the sources is measured accurately.

In use, the light-emitting head 6 of the laser source 5 is rotated at 2 or 3 revolutions per second and the laser beam 12 emitted from it describes a visible line 13 on the tunnel wall, the line 13 having unilluminated gaps 14 corresponding to the areas in which the beam 12 is blocked by the pins 5.

With the head 6 rotating, the second source 8 has its light-emitting head 9 aimed at the tunnel wall 1 so that the visible spot 1 5 where the beam 1 6 impinges on the wall 1 bisects the first gap 1 4A. A recording is then taken, either manually or electronically, of the angle of the beam from the vertical and from the horizontal. The distance of the spot 1 5 from the head 9 can also be recorded by detecting the reflectance of the beam 14 from the wall 1.

When the first recording has been taken, the head 9 of the second source 8 is swivelled on the base 10 so that the spot 1 5 appears in the centre of the second gap 1 4B. A second recording is taken in that situation, followed by subsequent recordings when the spot 1 5 is in the centre of each sequential gap until the final gap 1 4Z.

From the recordings taken, the profile of the tunnel wall 11 at the locus of the line 1 3, and the rate of change of its curvature between points, can be calculated geometrically. As the bogey 2 in this embodiment is not positioned centrally of the tunnel in view of the position of the rails 3, allowance is made for the different chord length of the beam 16 as it is moved around from the first gap 1 4A to the final gap 1 4Z, and this can be included in the calculation.

After this set of recordings has been taken, the bogey 2 is moved along the rails 3 to a new position which may be, say, twenty metres along the track from the initial position, and a new set of recordings are taken at that location, thus giving data for the wall 1 profile and curvature there.

Subsequent recordings are then taken in turn in the same way at spaced intervals along the tunnel, and on completion a series of data is available.

Comparisons can then be made of the profile, rate of curvature change and other parameters at the various positions, and the tunnel wall 1 thus checked for uniformity.

In practice, the profile most resembling the original profile of the wall 1 (if known, and if not, the most uniform profile) is taken as a base and the other measured profiles compared with it to determine the extent of deviation at each location.

If the profile at a location differs significantly from the base, further recordings can be taken at, say, one metre intervals from that location to trace the deformation in more detail. The nature and likely stability of the deformation can thus be checked.

The recordings can be stored for comparison with later recordings from the same tunnel in orderto monitor changes in the profile and in known deformations thereby ensuring that early warning is obtained of potentially serious defects in the tunnel wall.

As an alternative to the rotating head 6, the first laser source can be of similartype to the seond, and can be swivelled into fixed positions around the tunnel wall 1, projecting thereon on a spot of light instead of the broken line 1 3. The beam 16 can then be projected from the second head 9 so as to coincide with the spot from the first beam. Measurements and recordings can then be made of the angles and chord lengths of the beams and the tunnel wall parameters calculated as in the above-described embodiment.

The method of this invention can be used in railway and road tunnels as well as bridges and other structures.

Modifications and improvements may be made without departing from the scope of the invention.

Claims

1. A method of determining the profile of a structure wall, comprising projecting a first beam of light from a first laser source onto the wall to define an area of known parameter, providing a second laser source a measured distance from the first laser source, projecting a second beam of light from the second laser source onto the wall in the area defined by the first beam, and measuring parameters of the second beam.

2. A method according to Claim 1, wherein the first beam is projected onto the wall at a preset angle from its source and the second beam is aimed to coincide with the area of incidence of the first beam with the wall.

3. A method according to Claim 1 or 2, wherein the process is repeated over a series of measured angles of incidence of the first beam with the wall.

4. A method according to Claim 1 or 2, wherein the first beam is in motion through a range of angles of incidence with the wall and areas on its track are marked for projection of the second beam.

5. A method according to Claim 4, wherein the first laser source constantly rotates to project the first beam in a sweep across the wall.

6. A method according to Claim 4 or 5, wherein the projection of the first beam in a sweep against the wall is interrupted at intervals to produce areas from which the beam is absent.

7. A method according to Claim 6, wherein the interruption is achieved by providing a series of solid members spaced along the path of sweep of the first beam.

8. A method of determining the profile of a structure wall, substantially as hereinbefore described with reference to the accompanying drawings.