EP0918907B2 - U-shaped sheet pile with low cut-through resistance - Google Patents

Abstract

A U-shaped sheet pile comprising a flat flange (10), two flat webs (12) connected to the flange (10) so as to be symmetrical with respect to a plane (8) perpendicular to the flange (10), and an interlocking element located at the end of each of the two webs (12). The sheet pile has a depth/useful width ratio greater than or equal to 0.18. The concave corners (18) defined by the two flange/web connections are significantly flattened by an extra thickness (26) of material so as to obtain a reduction in the resistance of the sheet pile to pile-driving. The extra thickness (26) is sufficient for a fictitious cylindrical surface (38), which has a radius at least equal to 75 mm and which is tangential to the planes extending the inner faces of the flange and the web (32, 34), to be completely located inside the said extra thickness (26) between its two tangential generators. The convex corners (16) are slightly rounded, the radius of curvature being less than or equal to 25 mm, and the connecting surfaces defining the concave corners (18) comprise cursed surfaces (30).

Description

The present invention relates to a "U" -shaped sheet pile with low driving resistance.

For more than 80 years, several million tons of U-shaped sheet piles have been used worldwide for the construction of retaining curtains, for example during excavations, construction of dams, dikes and embankments. water retention ponds.

A "U" shaped sheet pile has a flat back (called the sheet pile) to which are connected two legs (called sheet piles) carrying interlocking locks, so that the sheet pile has a plane of symmetry perpendicular to the back. To form a retaining curtain, these "U" shaped sheet piles are assembled using interlocking locks, with their back alternately located on either side of the plane passing through the central axes of the interlocking locks. . This plane then forms the neutral bending plane of the "U" shaped sheet pile wall.

Conventional methods for driving sheet piles into the ground are threshing and vibrating. It is known that these driving operations require the development of a significant energy, which is proportional to the resistance to recess of the sheet pile. For a given sink method, this sink resistance is mainly a function of the soil characteristics and the cross section of the sheet pile.

The term "height" or "depth" of a U-shaped sheet pile, the distance separating a plane passing through the central axes of the two interlocking locks of the outer face of the core, and " useful width of a U-shaped sheet pile, the distance between the central axes of the two interlocking locks of the sheet pile, sheet piles having a large useful width in principle make it possible to reduce the costs of implementation, as fewer sheet piles need to be driven into the ground to achieve a given curtain length, deep sheet piles can have reduced material thicknesses in the fender and webs, while providing a high strength modulus, which reduces The cost of sheet piles is understood, hence the interest of using large and deep "U" -shaped sheet piles with reduced material thicknesses at the wing and webs.

Today U-shaped sheet piles, available on the market as standard profiles, have useful widths of 400 to 600 mm and a "depth / width" ratio of 0.18 to 0.54. The most common "U" shaped sheet piles have a "depth / useful width" ratio greater than or equal to 0.25, or even greater than 0.30. The thickness of the wing is between 7 and 20 mm and the thickness of the cores between 6 and 12 mm.

However, it should be noted that wide and deep sheet piles with low material thickness at the wing and souls also become quickly unstable in difficult conditions of driving. Hence the interest of limiting the stresses to which these sheet piles are exposed during their driving, that is to say to have sheet piles with a resistance to penetration as small as possible. However, although the decrease in material thickness at the wing and souls certainly has a positive influence on the driving resistance, it is found that an increase in the "depth / width useful" ratio unfortunately has a very strong effect. negative on the resistance to driving of U-shaped sheet piles.
A sheet pile according to the preamble of claim 1 is known from FR 686 816

It will therefore be appreciated that the present invention has found a solution which makes it possible to have a reduction in the resistance to driving of a U-shaped sheet pile while improving the stability of the sheet pile when it is put into service. artwork.

This solution is defined in the first claim.

Firstly, it should be noted that, contrary to what could be expected a priori, the reduction of the resistance to driving is not obtained by a thinning of the cross section of the sheet pile, but by extra thicknesses of material located at the concave corners defined by the two wing / core connections.

A thickening of material located at a concave wedge defined by two webs of an angled sheet pile has already been described in 1939 in the patent BE-A-433704. In this patent, it is essentially indicated that the extra thickness of material forms a strengthening of the sheet pile corner apex.

FR-A-434497, corresponding to US-A-1012124, discloses special sheet piles having an arched wing, and two curved side members of very low height, which are connected to the arched wing and each carrying an interlocking lock. These fairly massive sheet piles, are supposed to work in tension and replace sheet piles to allow the construction of walls whose total wall thickness in the middle of the wing is not greater than the thickness of two interlocked locks. They can not therefore be assimilated to "U" shaped sheet piles which are the subject of the present invention. These last ones have indeed depths far superior to be able to work in flexion. It will be further noted that in a preferred embodiment described in the French patent, the arcuate wing has an extra thickness of material at the two connections to the side members to have a substantially flat outer surface over its entire width. In the French patent, it is further specified that this material excess, which is located on the outer side of the arcuate wing, substantially increases the moment of inertia and the modulus of resistance of the sheet pile, that it considerably strengthens the section of the sheet pile and that it opposes a deformation of the arched wing under pressure.

Analogous effects are of course also obtained with the thicknesses of material according to the present invention. In particular, the torsion strength of the "U" shaped sheet pile is increased. The extra material in the connecting corners stiffens the souls and the wing, which reduces the danger of buckling. In addition, the plastic moment of the sheet pile and its flexural rotation capacity increase substantially, so that it is known to mobilize reserves of appreciable plastic deformations before the U-shaped sheet pile reaches ruin.

However, the main merit of the present invention is to have discovered that it is possible to reduce the resistance to driving of a "U" shaped sheet pile of given section by a contribution of material at the concave corners. Indeed, according to the present invention, the local extra thicknesses at the concave corners serve above all to flatten the concave corners at the location of the wing / core connection, that is to say to make these concave corners less closed. When driving sheet pile or vibrating sheet pile, this flattening of the concave corners facilitates the flow of soil particles out of the corners. This avoids significant compaction of the soil in the concave corners, which reduces the resistance to driving the sheet pile. It will be noted that the effect obtained is particularly marked in sandy soils.

Cylindrical connecting surfaces, substantially tangent to the faces of the wing and the respective core in said concave corners, seem to give the best results from the point of view of reducing the resistance to the driving of the sheet pile. This conclusion, however, does not exclude the use of any curved surfaces, tangent or non-tangent to the respective wing and core faces, or even polygonal surfaces or a simple flat surface to define the connecting surfaces in said corners. concave, provided of course that the concave wedges thus formed are sufficiently flattened to facilitate the flow of soil particles out of them.

Threshing tests carried out in a standardized sand bed have shown that a really significant reduction in threshing energy is being achieved with a cylindrical connecting surface with a radius of 75 mm which is tangent to the faces of the concrete. wing and respective soul in the concave corners. From this result, it can generally be deduced that, in order to obtain a significant reduction in the threshing time, said excess thickness must be such that the concave corners at the location of the wing / core connections are at least as open as a cylindrical connector. tangent radius 75 mm. In more quantitative terms, said local overthickness must be at least sufficient for a fictitious cylindrical surface, which has a radius of at least 75 mm and which is tangent to the two planes that would have formed the respective wing-soul concave corner. in the absence of said overthickness, is located completely inside said overthickness between the two generators of tangency.

It will be noted that the convex corners at the wing / core connections are only slightly rounded (radius of rounding ≤ 25 mm), so as to give the profile a moment of inertia as high as possible by concentrating a maximum of matter in the outer part of the souls.

It should be noted that the sheet pile according to the invention is advantageously a steel sheet pile obtained by hot rolling.

• la Figure 1 montre une section transversale d'une moitié de la palplanche;
• la Figure 2 montre un agrandissement d'un raccord aile/âme de la palplanche de la Figure 1 ;

A preferred embodiment of a sheet pile according to the invention is described on the basis of the accompanying drawings, in which:

• Figure 1 shows a cross section of one half of the sheet pile;
• Figure 2 shows an enlargement of a wing / core connection of the sheet pile of Figure 1;

Figure 1 shows a cross section of half a "U" shaped sheet pile according to the invention. The other half is exactly symmetrical to the half shown, with respect to the plane of symmetry marked by the reference 8. This sheet pile has a substantially planar wing 10 and perpendicular to the symmetry plane 8 of the section. To this wing 10 are connected two substantially planar webs 12, of which only the left web is shown in FIG. 1. Each of these webs 12 carries a lock 14 which makes it possible to form a more or less tight seal by engagement with a corresponding lock. another sheet pile. The central axis of the lock 14, which is perpendicular to the plane of the drawing, is marked by the reference 15. It will be noted that the wing 10 is generally substantially thicker than the webs 12.

In the sheet pile shown, the acute angle α formed between the webs and a plane parallel to the wing is about 74 °. It goes without saying that this angle can naturally be chosen smaller or larger. For the sheet piles concerned by the invention, the acute angle α will normally be between 40 ° and 80 °.

In the following, we will call "convex corners defined by the wing / web connections" (or simply "convex corners"), the corner located on the outer side of the sheet pile and identified in FIG. 1 by the reference arrow 16, as well as its symmetrical wedge not shown; and "concave corners defined by the wing / web connections" (or simply "concave corners"), the corner located on the inside of the sheet pile and identified in Figure 1 by the reference arrow 18, and its symmetrical wedge, not shown .

The convex corners 16 connect the outer plane faces 20 of the webs 12 to the outer plane face 22 of the wing 10 (see also Figure 2). These convex corners 16 have a radius, whose radius "r" is determined by rolling constraints and / or safety considerations (avoid sharp edges). Normally "r" will be larger than 10 mm and smaller than 25 mm. The smaller the "r", the higher the bending resistance modulus of the profile.

To reduce the resistance to driving the sheet pile into the ground, the concave corners 18 are, according to the invention, substantially flattened by a local thickness of the sheet pile at these locations. This modification of the known "U" shaped sheet pile will be studied in more detail using Figure 2. On the latter, the concave wing / core corner of a conventional sheet pile is shown in broken lines (see the lines below). identified by reference numeral 24 in Figure 2). It can be seen that this concave corner 24 has a radius whose radius is determined by rolling constraints and approximately corresponds to the radius "r" of the convex corner 16. The local allowance which has made it possible to flatten the conventional concave corner 24 and make therefore this more open corner, is represented in the same figure by the hatched surface 26. This extra thickness 26 defines a concave fitting surface 30. It should be noted that the symmetrical concave corner naturally has the same appearance.

In the case of the sheet pile shown in FIGS. 1 and 2, the concave fitting surface 30 is a cylindrical connecting surface which is tangent to the inner flat face of the flange 10 and to the inner flat face 34 of the core. 12. The arrows 36 in FIG. 2 show how soil particles can flow freely along the cylindrical fitting surface 30 thus avoiding the formation of a strongly compacted core in the concave wedge 18 which opposes the 'U-shaped sheet piling.

Threshing tests carried out in a standardized sand bed have shown that a significant reduction in threshing energy is achieved with a cylindrical connecting surface with a radius of 75 mm which is tangent to the faces of the wing and respective soul in the concave corners at the location of the wing / core connection. In Figure 2, the trace of this "minimal" cylindrical connection is represented by a circular arc drawn in broken lines and identified by the reference number 38. The arc 38, which is tangent to the traces of the two planes 32 , 34 which would have formed the respective concave wing / soul connection corner in the absence of the excess thickness 26, is supposed to determine the minimum extra thickness in the concave corners necessary to obtain a significant reduction in threshing energy. It can be seen that the thickness of material corresponding to the cylindrical connecting surface 30 is substantially greater, which not only reduces the resistance to penetration, but also increases the plastic moment and the rotational capacity of the flexural profile. . The reference 40 marks the trace of a polygonal connecting surface which lies between the surface 30 and the minimum material surface 38.

• a) par une résistance à l'enfoncement plus faible, qui se fait surtout remarquer dans des sols sablonneux lors d'une mise en oeuvre par battage ou par vibrations;
• b) par une augmentation notable du moment plastique et de la capacité de rotation en flexion qui va de pair avec la réduction de la résistance à l'enfoncement, ce qui permet une augmentation significative du rendement sur le chantier;
• c) par une amélioration de la résistance à la torsion de la palplanche.
• d) par un bon rendement "module de résistance élastique/poids" pour un écran formé de telles palplanches, du fait de la possibilité d'économies au niveau des épaisseurs de l'âme et de l'aile en dehors des raccords aile/âme;
• e) par une meilleure transmission des efforts dans le cas d'écrans de soutènement munis de liernes et/ou de plaques d'ancrage.

It will be appreciated that the sheet piles described are distinguished from known "U" shaped sheet piles, in particular:

• a) by a lower resistance to sink, which is especially noticeable in sandy soils when used by threshing or vibration;
• b) a noticeable increase in plastic moment and bending rotation capacity which goes hand in hand with the reduction in driving resistance, which allows a significant increase in the efficiency on the construction site;
• c) by improving the torsion resistance of the sheet pile.
• d) by a good yield "modulus of elastic resistance / weight" for a screen formed of such sheet piles, because of the possibility of savings in the thicknesses of the soul and the wing outside the connections wing / soul ;
• e) better transmission of forces in the case of retaining screens with liernes and / or anchor plates.

In conclusion, the present invention presents a profile of threshing and vibration sinking ideal for implementation in difficult conditions.

Claims (7)

1. U-shaped sheet pile comprising a flange (10) which is flat over substantially the whole of its width, two flat webs (12) connected to the flange (10) so as to be symmetrical with respect to a plane (8) perpendicular to the flange (10), an interlocking element located at the end of each of the two webs (12); the said sheet pile having a depth/useful width ratio greater than or equal to 0.18, where the useful width is defined as being the distance between the central axes of the interlocking elements (14), and the depth is defined as being the distance separating a plane passing through the central axes of the two interlocking elements (14) and the outer face (22) of the flange (10); each of the two flange/web connections defining a convex corner (16) on the outer face of the sheet pile and a concave corner (18) on the inner face of the sheet pile;
   characterised in that said concave corners (18) are significantly flattened by an extra thickness (26) of material so as to obtain a reduction in the resistance of the sheet pile to pile-driving;
   in that the said extra thickness (26) is sufficient for a fictitious cylindrical surface (38), which has a radius at least equal to 75 mm and which is tangential to the planes extending the inner faces of the flange and the web (32, 34), to be completely located inside the said extra thickness (26) between its two tangential generators; and
   in that the convex corners (16) are slightly rounded, the radius of curvature being less than or equal to 25 mm.
2. Sheet pile according to Claim 1, characterised in that the connecting surfaces defining the concave corners (18) comprise curved surfaces (30).
3. Sheet pile according to Claim 2, characterised in that the connecting surfaces defining the concave corners (18) comprise curved surfaces (30) which are tangential to the inner flat faces of the flange and the web (32, 34).
4. Sheet pile according to any one of Claims 1 to 3, characterised in that the connecting surfaces defining the concave corners (18) comprise polygonal surfaces (40).
5. Sheet pile according to any one of Claims 1 to 4, characterised in that the connecting surfaces defining the concave corners (18) comprise a flat surface.
6. Sheet pile according to any one of Claims 1 to 5, characterised in that the sheet pile is a hot-rolled steel sheet pile.
7. Sheet pile according to any one of Claims 1 to 6, characterised by a depth/useful width ratio greater than or equal to 0.25.

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