A METHOD OF CONSTRUCTING A RETAINING SCREEN, PROFILED METAL SECTIONS FOR CARRYING OUT THE METHOD, AND A RETAINING SCREEN CONSTRUCTED FROM SUCH METAL SECTIONS

Abstract: In a method of constructing a retaining screen which is intended to retain soil and debris dug from the ground when excavating a shaft into which concrete pipes, cables and the like are to be laid, and also to retain such soil and debris subsequent to excavation, there are used so-called ''planks'' in the form of profiled aluminium sections (30) which are carried singly from a storage site and placed in a vertical, upstanding position and then driven singly into the ground, to form shaft supporting walls.

Description: A method of constructing a retaining screen, profiled metal sections for carrying out the method, and a retaining screen constructed from such metal sections. The present invention relates to a retaining screen which is intended to retain soil and debris dug from the ground when excavating a shaft into which pipes, cables or the like are to be laid, and also to retain said soil and debris subsequent to said excavation. The method is of the kind set forth in the preamble of the following main claim. Soil retaining screens of the kind intended comprise two mutually opposing and essentially parallel support walls which are driven into the ground to a depth which is greater than the depth of the shaft to be excavated and which are guided at their upper-end parts in a res¬ pective side-piece, wherewith both side-pieces are joined together by means of adjustable spacer devices, such as screw devices, and the walls are constructed from a plurality of profiled metal sections which overlap at their respective edges. These known profiled metal sections are made of steel. They may have different widths and lengths, depending on the size of the shaft to be excavated. An example of a conventional metal profiled section of this kind is one which has a width of about 40 cm, is corrugated and has a thickness across its front and back surfaces of about 6 cm. The length is about 3 m. The meter-weight of this metal section is about 20 kg and the combined weight is thus about 60 kg. -The total weight of thicker and longer profiled metal sections is much greater. Mechanical auxiliaries are required to transport and to manipulate profiled metal sections of such heavy weights. Normally, it is necessary to use some form of mobile crane to this end. This adds to the cost of the retaining screen and requires ready access to such a crane, since.._the work involved cannot be carried out at a satisfactory work rate solely with the aid of the digger used to excavate the shaft. The crane is used to lift the sections, transport said sections to the shaft site and to fit the sections into the side-piece gui¬ des, and then to bring the sections to an upstanding position. The crane must then be driven to one side, so as to make room for the digger, which is normally used to drive the sections into the ground, by hammering on the upper ends of the sections with a digger-bucket. A separate pile driver must be used in the case of larger sections. This time consuming and relatively expensive working technique has instilled in building constructors, over the last 50 years, a certain reluctance to take those protective measures implied by retaining screens with the aid of supporting walls. For instance, the task of driving protective walls into the ground is neglected in far too many cases, resulting in considerable risk of soil and debris slipping into the shaft while con¬ crete pipes and the like are being laid therein. Such soil slips often occur, resulting in personal injury to those working in the shaft and, on occasions, fatal injuries. Accordingly, the object of the invention is to provide a method which will greatly facilitate the work of transporting profiled metal sections to the aforesaid side-pieces and raising said sections to an upstanding position in respective guides, such as to bring the sections into a starting position in which they can be driven into the ground. This object is realized with a working method which, in accordance with the invention, has the characterizing features set forth in the characterizing clause of the following main claim. The aforedescribed profiled metal sections used hither¬ to and having a total weight of about 60 kg or more are thus replaced, in accordance with the invention, with profiled sections made of an aluminium alloy which renders the sections approximately three times lighter in weight and enables the sections to be handled manu¬ ally by one single workman with no difficulty. In the case of one particularly suitable profile embodiment according to the invention, the profiled section is so configured that when possessing the same width, height and length as a corresponding profiled steel section will have essentially the same ability as the aforesaid steel section in resisting those loads which occur. Thus, the invention removes all the serious drawbacks that have been encountered over many years with the use of profiled steel sections without suggestions as to how these drawbacks could be readily overcome. The only drawback-with the novel lightmetal profiled sections is that they are several times more expensive to manufac¬ ture, although this additional cost is counteracted significantly by the relatively high repurchase price for scrap sections. The increase in cost is also compensated to a great extent by the fact that the work involved can be carried out quickly and without the aid of a crane. Primarily, however, the inventive method will greatly reduce the reluctance of contractors to construct a retaining screen, so that such a screen will probably be erected in practically all instances where the risk of hazardous soil slips prevail. The method according to the invention will be explained with reference to the accompanying drawings, which illustrate a known retaining-screen construction built with the aid of known profiled steel sections, and also part of a retaining screen construction built in accor¬ dance with the invention with the aid of profiled sections made of an aluminium alloy. Figure 1 is a schematic, perspective view of a known retaining screen which comprises two mutually opposing support walls constructed with the aid of profiled steel sections, of which support walls only one is shown. Figure 2 illustrates two known profiled steel sections arranged adjacent one another in the support wall shown in Figure 1. Figure 3 illustrates part of the known support wall comprising profiled steel sections in larger scale; and Figure 4 illustrates part of a support wall incorpora¬ ted in the retaining screen constructed in accordance with the invention with the aid of lightmetal profiled sections of particular configuration according to the invention. The construction illustrated in Figure 1 includes a guide frame 10 comprising two mutually parallel side- pieces 12, 14 which are connected adjustably to one another by means of spacing devices in the form of shore-spacing screws 16, such that the walls are held at a predetermined distance apart. The frame corres¬ ponds to the size of the shaft to be excavated from the ground between the walls, for pipe or cable-laying purposes. The frame is buried some meters in the ground. The known profiled steel sections are fitted to the side- pieces of the frame with the aid of a mobile crane, not shown. The sections are then driven to desired depths in the ground, with the aid of a digger, not shown. As will be seen from Figures 1 and 2, the side edges of the sections overlap one another, to form a supporting wall 20 on each side of the shaft (only one wall is shown) . The known steel profiled sections normally weigh at least about 60 kg and are so heavy that one workman is unable to carry and manipulate the sections on his own. Figure 3 is a sectional view of the known wall shown in Figure 1, in which a number of steel sections overlap one another. The joins 24 between the sections face in towards the shaft, which means that the joins can be damaged by the bucket of the digger used to excavate the earth 26 located between the supporting walls. The steel section ' s 18 form relatively wide channels 27 or troughs which are mutually separated by relatively narrow ridges located at the joins 26. Figure 4 is a sectional view of a supporting wall 28 forming part of the inventive retaining screen and constructed, in accordance with the invention, with the aid of aluminium profiled sections 30 of particular profile configuration in accordance with the invention. The profiled sections engage one another at the mutual- ly overlapping side parts 32. The wall-building profiled sections 30 are manufactured by the extrusion of an aluminium alloy. The weight of the inventive profiled sections is about one third the weight of a corresponding profiled steel section. A study of the lightmetal profiled sectionS / 30 illu¬ strated reveals that the section has a substantially corrugated configuration, with three relatively wide ridges 34 and intermediate channels or troughs 36 having relatively narrow bottoms 38. The planar upper surfaces of the ridges 34 and the planar bottom sur¬ faces 38 of the troughs are connected by sloping side- walls 40. The distance between the planar upper sides of the ridges and the outside of the trough bottoms constitutes at least one fifth of the width of the sections between the side-edges 32, 34 of respective sections. The planar upper surfaces of the ridges and the planar bottoms of the troughs also have approxi- mately the same wall thickness, which is approximately twice the thickness of the side-walls. The inventive aluminium profiled section 30 has essen¬ tially the same properties as a corresponding profiled steel section with respect to resisting the loads which occur on the supporting walls of the retaining screen. In this respect, the profiled section is configured in a manner to achieve desired mechanical strength with the least possible material consumption, so as to maintain material costs at a low level. As will be seen from Figure 4, the broad upper sides of the ridges 34 face in towards the shaft, so that the inner surface of the shaft will only be broken by the relatively narrow intermediate troughs 36, and conse¬ quently soil and debris material 26 will obtain a good anchorage in the relatively broad troughs or channels formed on the insides of the ridges 34.

Claims: CLAIMS 1. A method of constructing a retaining-screen struc- ture which is intended to retain the soil and debris dug from the ground while excavating a shaft into which pipes, cables or the like are to be laid, and also to retain said soil and debris subsequent to such excava¬ tion, and in which method wall-forming corrugated, profiled metal sections are moved singly from a ground storage site or some other location to the location at which the profiled sections are intended to form two mutually opposing supporting walls in the shaft, and in which the profiled sections are raised to a vertical, upstanding position adjacent a profiled section which has previously been driven into the ground, and in which the upright profiled section is then driven to a desired depth in the ground such that subsequent to driving a predetermined number of profiled sections into the ground there is obtained one of said two supporting walls forming part of the retaining screen construction, characterized by using corrugated pro¬ filed sections (30) made of an aluminium alloy, and by carrying,said profiled sections by one single workman to the site at which said sections are to be driven into the ground, and raising the profiled sections manually to an upright position constituting the start¬ ing position for subsequent driving of the sections into the ground. 2. A profiled section made of an aluminium alloy for carrying out the method according to Claim 1, said profiled section having a corrugated configuration which includes .at least three ridges having planar upper surfaces, and intermediate troughs having planar bottom surfaces which merge at their side edges with inclined side-walls adjoining the side-edges of the upper sides of the ridges, characterized in that the distance between the upper sides of the ridges (34) and the outside of the bottoms (36) of the troughs is at least one fifth of the width (42,44) of the profiled sections; in that the bottoms (38) of the troughs have a width which is smaller than the width of the upper sides of the ridges (34); and in that the planar upper sides of the ridges and the bottoms of the troughs have substantially the same wall thickness, which is essen¬ tially greater than the wall thickness of the side- walls (40), preferably about twice the thickness. 3. A retaining screen construction comprising profiled metal sections according to Claim 2, characterized in that the broad upper sides of the ridges (34^ face in towards the shaft, such that the inner surfaces of the support walls are formed by said upper sides with interruptions for the narrower intermediate troughs (36).

Inventors: LUNDGREN JAN, LUNDGREN, JAN
Applicants: LUNDGREN JAN, LUNDGREN, JAN
Application year: 1989
Main classification: E02D5
IPC codes: E02D5, E02D17