APPARATUS FOR SUPPORTING THE WALLS OF TRENCHES

Abstract: A trench shoring box, comprises two opposed shoring plate units or panels (20) provided with vertically directed support members to which struts (A, B, 9, 10) of adjustable length extending substantially normally to the shoring panels (20) are horizontally pivotally attached. The end elements (9, 10) of each strut are additionally resiliently coupled to the shoring panels (20) by leaf springs (12) in order to dampen angular movement between the struts (A, B, 9, 10) and the panels. Additionally, it is preferred that the end elements (9, 10) should have head parts (7, 8) which are in rapid feed screw-threaded engagement with cylindrical strut elements (A, B) so as to be protected from the environment and to permit rapid alteration of the length of the strut by rotation of the cylindrical strut elements (A, B).

Description: This invention relates to apparatus for supporting the walls of trenches, or other excavations, and of the kind generally designated as a trench shoring box and comprised of two opposed shoring panels provided with vertically directed support members to which two opposite ends of struts of adjustable length, normally extending substantially perpendicularly to the shoring panels, are horizontally pivotally attached so that the shoring panels can be relatively displaceable in the vertical direction as excavation progresses. It has been appreciated that during normal handling of a fully assembled trench shoring box there is considerable differential movement between each of the shoring panels and due to the weight of the assembly unless some damping restraint is provided considerable shock forces are applied at the limits of angular movement between the struts and the panels. Various damping assemblies for this purpose have hitherto been employed, such as for instance hydraulically operating dampers or by the provision of two helical springs positioned equally one each side of each strut centre line, but these have not proved entirely satisfactory. For instance with a damping system embodying two helical springs, one spring only at a time can contribute to the damping action. Also in this damping system the stiffness of the damper is fixed by the geometry of the spring which cannot easily be changed to accommodate extremes of use. FR-A-2 195 240, on which the preamble of claim 1 is based, discloses - in Fig. 3 thereof and the related description - apparatus for supporting the walls of trenches, or other excavations, and of the kind generally designated as a trench shoring box and comprised of two opposed shoring panels provided with vertically directed support members to which two opposite ends of struts of adjustable length, normally extending substantially perpendicularly to the shoring panels, are horizontally pivotally attached so that the shoring panels can be relatively displaceable in the vertical direction as excavation progresses, wherein each strut is additionally resiliently coupled to the shoring panel by a leaf spring which is adapted to dampen angular movement between the strut and the panel, a portion of the leaf spring being secured to the end of the strut and extending perpendicularly thereto, a remote end of the leaf spring being connected to the shoring panel, the spring exerting damping action against deviations of the strut from its normal position substantially perpendicular to the shoring panel. However, opposite halves of the leaf spring in Fig. 3 of FR-A-2 195 240 are prestressed to act in opposition to each other, so that any deviation of the panel from its normal angular position relative to the strut is aided by one half of the spring, which half depending upon the direction of the deviation, and opposed by the other half of the spring. Moreover, both halves of the spring are greatly curved, with a puzzling effect. It appears that the strut is constrained to pivot about the the pin at the centre of the boss in FR-A-2 195 240, so that there would be circumferential movement of the curved spring, moving one extreme end of the spring out of the associated slot and transferring the reaction to the adjacent bar. The other extreme end of the spring would be pushed deeper into the associated slot, also causing eventual reaction from the adjacent bar. Apparently there is no end stop to limit angular deviation. Also, the leaf spring in Fig. 3 of FR-A-2 195 240 appears to be of spring steel and yet shown welded to the strut and not to the boss, which is not good practice. The present invention has been devised with the general object of providing a damping system which does not have the above mentioned disadvantages. The apparatus of the present invention is characterised in that each spring is substantially rectilinear, so that substantially the entire spring extends substantially parallel to the shoring panel, and in that substantially the entire spring opposes any deviation of the strut, in either direction, from its normal position in which the strut is substantially perpendicular to the panel. In order however that the invention may be more readily understood reference should be made to the following description of a preferred embodiment which is illustrated in the accompanying drawings. In these drawings:- Fig. 1 is a side elevation, partly in section, of an adjustable length strut for attachment between opposite shoring panels; Fig. 2 is a plan view of a shoring panel end post showing the mode of connection of an adjustable length strut thereto; Fig. 3 is an elevation view on the inside of a shoring panel; and Fig. 4 is an elevation view on arrow IV in Fig. 3. Referring now to the drawings, Fig. 1 shows a heavy duty strong box strut which comprises a central cylinder 1 formed in two cylindrical parts A, B, with abutting flanges 2, 3 secured together by bolts 4 and nuts 5 and each formed from end to end internally with a quick feed screw thread 6. Retained within the cylinder parts A and B, are the correspondingly screw-threaded cylindrical heads 7, 8 of a pair of thrust rods 9, 10. Attached to the outward end of each of these thrust rods 9, 10 is a perpendicular plate 13 which supports a central part of a multi-leaf spring 12 which is clamped thereto by a second plate 11 by means of bolts 14 and nuts 15, so that the leaf spring 12 extends perpendicularly to the strut. Attached to the outward side of each plate 11 is a U-shaped saddle 16 by which the strut is swivelably mounted on an horizontal pin 17 which, as shown in Fig. 2, extends between a pair of end post plates or brackets 18 which project at right angles from a shoring panel 20, and which are part of an end post 19 fixed to the shoring panel 20 as shown in Fig. 4. The ends of each leaf spring are located in slotted tubes 21 which are welded between the end post plates or brackets 18 of the side panel 20, these details being shown more clearly in Fig. 2, and also in Figs. 3 and 4. The centre lines C of the struts are indicated in Fig. 4. Rapid extending or retracting of each strut is effected by turning the cylinder 1 in a clockwise or counter-clockwise direction by use of any suitable tool such as for instance a lever arm inserted into one or other of four radial openings in a collar 22 which is welded to the cylinder part B. In Fig. 1 there is also illustrated by a chain-dashed line a lifting bracket which is attached only to the topmost extension strut. It will be appreciated that adjustment of the length of a strut is based on the turnbuckle or bottlescrew principle but it is a requirement that strut release should be rapid. A satisfactory screw thread pitch for the elements A, B, 7, 8 would be one which alters the strut length by 48 mm for each revolution of the cylinder 1. The construction is of course such that none of the screw-threading is exposed in use to the environment in which the shoring box operates. Also, in the formation of the screw threading, the minimum amount of metal is removed from the cylinder parts A, B consistent with the maximum designed load-carrying capacity of the strut. This will provide greater local strength and will minimise the possibility of dents being formed in the cylinders during normal use of the struts. It is characteristic of the invention, and advantageous that: a) Any deviation of the strut, in either direction, from its normal position perpendicular to the panel 20, results in restraining action by both halves of the leaf spring 12, that is, the upper spring half and the lower spring half, relative to the horizontal pin 17; b) The stiffness of each spring is easily changed by the addition or reduction of the number of leaves; c) The spring may be shaped to give the maximum stiffness for each leaf, or may be shaped to approach the configuration of constant strength, whereby the stiffness is reduced for the same thickness. d) To guard against injury, in the event of the spring leaves breaking, a guard leaf of a ductile steel may be fitted on the clear side of the spring leaf assembly to prevent a piece of the more elastic and brittle steel spring from flying out and causing personal injury.

Claims: 1. Apparatus for supporting the walls of trenches, or other excavations, and of the kind generally designated as a trench shoring box and comprised of two opposed shoring panels (20) provided with vertically directed support members to which two opposite ends of struts of adjustable length, normally extending substantially perpendicularly to the shoring panels (20), are horizontally pivotally attached so that the shoring panels (20) can be relatively displaceable in the vertical direction as excavation progresses, wherein each strut is additionally resiliently coupled to the shoring panel (20) by a leaf spring (12) which is adapted to dampen angular movement between the strut and the panel (20), a portion of the leaf spring (12) being secured to the end of the strut (1) and extending perpendicularly thereto, a remote end (21) of the leaf spring (12) being connected to the shoring panel (20), the spring (12) exerting damping action against deviations of the strut from its normal position substantially perpendicular to the shoring panel (20), characterised in that each spring (12) is substantially rectilinear, so that substantially the entire spring (12) extends substantially parallel to the shoring panel (20), and in that substantially the entire spring (12) opposes any deviation of the strut, in either direction, from its normal position in which the strut is substantially perpendicular to the panel (20). 2. Apparatus as claimed in Claim 1 wherein at least some of the leaf springs (12) are comprised of a plurality of leaves of varying length and/or thickness. 3. Apparatus as claimed in claim 2 wherein the stiffness of each leaf spring is changeable by changing the number of the leaves. 4. Apparatus as claimed in Claim 1, 2 or 3 in which the ends of the leaf springs (12) are received within, and located by, slotted tubes (21) which are fixed indirectly to the shoring panels (20). 5. Apparatus as claimed in any one of Claims 1 to 4 wherein each strut comprises a central internally screw-threaded cylinder (1) and a pair of thrust rods (9, 10) which project one from each end of the cylinder (1) and each having, within the cylinder (1), an externally screw-threaded head (7, 8) which engages the screw threads of the cylinder (1), whereby rotation of the cylinder (1) in one direction or the other causes extension or retraction of the thrust rods (9, 10) relative thereto in order to vary the overall length of the strut. 6. Apparatus as claimed in any preceding claim wherein a guard leaf of a ductile steel is fitted to at least one of the leaf springs (12).

Inventors: COLLINS, JOHN
Applicants: MABEY HIRE LIMITED
Application year: 1989
Main classification: E02D17
IPC codes: E02D17