The present invention relates to a crimping tool for crimping sheet piles together and, in particular, to a tip of crimping tool. The present invention also relates to the corresponding process for crimping sheet piles.

Before being driven into the ground by hammering, vibration or similar techniques, sheet piles are usually crimped by pair. For U-sheet piles, as the interlocks are on the neutral axis where the shear stress is maximum, such crimping is essential. It allows the transmission of the shear force through the interlocks in a way that the two single U-sheet piles act as one single double pile. This improves the structural resistance of the sheet pile wall and limits its deflection both perpendicular to the wall and in plane of the wall (oblique bending). For Z-sheet piles, as the interlocks are not on the neutral axis, shear forces do not have to be transmitted through the interlocks. Nevertheless, to prevent any rotation during storage, handling or lifting and to limit noise due to shocks between interlocks during driving, Z-sheet piles are usually also crimped by pair. A crimping tool is known from EP0075526. It comprises a stamp head comprising two crimping tips distant from one another and positioned on the bottom of the stamp head. The stamp holder can optionally comprise two crimping tips distant from one another and positioned on the top of the stamp holder so as to crimp both sides of the interlocks.

A method for crimping a pair of sheet piles is also known from EP0898021.

The crimping of the interlocks is done by means of a tip having a semi-spherical shaped free end.

It has nevertheless been observed that the shear resistance of the crimped sheet piles is limited by the power of the presses and by the occurrence of cracks around the crimped points.

The aim of the present invention is therefore to remedy the drawbacks of the equipment of the prior art by providing a crimping tool increasing the shear resistance of the crimped sheet piles while requiring less force for crimping and limiting cracks around the crimped points.

For this purpose, a first subject of the present invention consists of a crimping tip of crimping tool for sheet piles comprising a spherical-shaped free end adjacent to a truncated cone-shaped portion whose aperture is a and whose truncation is of diameter d, wherein a and d, respectively expressed in degrees and millimeters, satisfy the following inequations (1 ) to (4):

a > - 9.24 d + 238.96 (1 )

a > - 1.06 d + 58.28 (2)

a < - 4.17 d + 146.75 (3)

a < - 2.02 d + 94.67 (4)

The crimping tip according to the invention may also have the optional features listed below, considered individually or in combination:

- a and d satisfy the following inequations (5) to (7):

a > - 8.53 d + 226.08 (5)

a > - 0.96 d + 64.02 (6)

a £ - 2.43 d + 101.17 (7)

- the spherical-shaped free end is of diameter D and the ratio d/D is comprised between 0.88 and 0.92.

- aperture a, truncation diameter d and sphere diameter D satisfy the following equation (8):

cos ( a/2 ) = d / D (8)

A second subject of the invention consists of a crimping tool comprising a stamp holder and a stamp head comprising at least one crimping tip according to the invention.

The crimping tool according to the invention may also have the optional features listed below, considered individually or in combination:

- the stamp head comprises two crimping tips,

- the stamp holder comprises at least one crimping tip. A third subject of the invention consists of a process for crimping sheet piles comprising the steps of:

- Providing two sheet piles, each of them comprising at least one interlock, the interlock of one of the two sheet piles being engaged in the interlock of the other sheet pile,

- Positioning the two sheet piles between a stamp holder and a stamp head comprising at least one crimping tip according to the invention,

- Crimping the two sheet piles in at least one point by pressing the stamp head on the engaged interlocks.

A fourth subject of the invention consists of an assembly of at least two sheet piles comprising at least one interlock, the interlock of one of the two sheet piles being engaged in the interlock of the other sheet pile, wherein at least one point of the engaged interlocks has been crimped by the process according the invention.

Other characteristics and advantages of the invention will be described in greater detail in the following description.

The invention will be better understood by reading the following description, which is provided purely for purposes of explanation and is in no way intended to be restrictive, with reference to:

- Figure 1 , which is a view in perspective of a crimping tool according to the invention,

- Figure 2, which is a sectional view of a crimping tip according to the invention,

- Figure 3 which is a sectional view of the crimping tip of Figure 2 along the AA line,

- Figure 4 which illustrates the domain of the crimping tips according to the invention,

- Figure 5 which is an enlargement of part of Figure 4. A cone is formed by a set of line segments, called generatrix lines, connecting a common point, the apex, to all of the points on the perimeter of a base that is in a plane that does not contain the apex.

In the present text, in accordance with the common usage in elementary geometry, it is meant by“cone” a right circular cone, where“circular” means that the base is a circle and“right” means that the axis passes through the centre of the base at right angle to the base plane.

By truncated cone, it is meant a cone with a region including its apex cut off by a plane parallel to the base. The intersection of the plane and the cone is referred to as the truncation.

By aperture of the cone, it is meant the maximum angle between two generatrix lines; if the generatrix makes an angle Q to the axis, the aperture is 2Q.

By spherical-shaped free end, it is meant a free end whose shape is a truncated sphere, the truncation being located between the sphere center and the point of the sphere corresponding to the extremity of the free end.

In the present text, sheet piles are steel sections comprising, along at least two longitudinal extremities, longitudinal interlocks engageable into one another. The sheet piles can be notably H-sheet piles, Z-sheet piles or U-sheet piles. The interlocks can be notably claws, clamped-shape locks, Larssen-type locks, Frodingham-type locks, ball-shaped toe engaging with a female socket, locks as disclosed in standard prEN10248-2:2006.

With reference to Figure 1 , the crimping tool 10 according to the invention first comprises a stamp head 12 and a stamp holder 14. The stamp head is movable along a vertical axis so that sheet piles can be crimped between the stamp head and the stamp holder. Optionally, the stamp holder is also movable along the vertical axis.

The stamp head 12 can indifferently comprise one, two, three or more crimping tips 16, preferably evenly separated from one another. The choice is done depending on the requirements in term of shear resistance of the crimped sheet piles and on the power of the press.

According to one variant of the invention, the stamp holder 14 also comprises a crimping tip 16. This lower crimping tip is aligned with the crimping tip of the stamp head (referred to as the upper crimping tip) when the crimping tool is closed. This allows crimping a point of the engaged interlocks of two sheet piles on both sides, which increase the shear resistance and stiffness of the crimped point. Preferably, the stamp holder comprises as many crimping tips as the stamp head.

Preferably, the crimping tool 10 comprises series of stamp heads and stamp holders so that several series of crimping points are performed simultaneously on the sheet piles.

With reference to Figures 2 and 3, the tip 16 of the crimping tool comprises a spherical-shaped free end 18 of diameter D adjacent to a truncated cone-shaped portion 20 whose aperture is a and whose truncation is of diameter d. The truncated cone-shaped portion 20 flares in the opposite direction of the spherical-shaped free end 18. In particular, the truncation of the spherical-shaped free end corresponds to the truncation of the truncated cone-shaped portion, i.e. the truncation of the spherical-shaped free end is also of diameter d.

Angle a and diameter d, respectively expressed in degrees and millimeters, satisfy the following inequations (1 ) to (4):

a > - 9.24 d + 238.96 (1 )

a > - 1 .06 d + 58.28 (2)

a < - 4.17 d + 146.75 (3)

a < - 2.02 d + 94.67 (4)

As it will be illustrated later on with the examples, these 4 equations delimit a domain for which the tips having the corresponding angle a and diameter d require less force for crimping, increase the shear resistance and limit cracks around the crimped points while allowing a broader range of indentation depths.

Preferably, angle a and diameter d, respectively expressed in degrees and millimeters, satisfy the following inequations (5) to (6):

a > - 15.90 d + 376.88 (5)

a > - 1 .18 d + 69.68 (6)

a £ - 2.43 d + 101 .17 (7)

As it will be illustrated later on with the examples, these 3 equations delimit a smaller domain, included in the main domain, for which an even broader range of indentation depths can be obtained without cracks around the crimped points. The truncation of the truncated cone-shaped portion is preferably dimensioned so that the ratio d/D is comprised between 0.88 and 0.92.

Preferably, the truncation has a diameter d comprised between 20 and 24 mm.

Preferably, there is no discontinuity between the spherical-shaped free end and the truncated cone-shaped portion. In other words, the angle between the sphere truncation and the tangent of the spherical-shaped free end at its intersection with the truncation is equal to a/2. In other words, aperture a, truncation diameter d and sphere diameter D satisfy the following equation (8):

cos ( a/2 ) = d / D (8)

Consequently, sharp edges are not embossed in the sheet piles, which further prevents the crimped point from being fragilized.

According to the embodiment illustrated on Figures 2 and 3, the base of the truncated cone-shaped portion 20 might be adjacent to a cylindrical portion 22, itself prolongated by a sleeve 24 so that the crimping tip can be easily mounted on the crimping tool.

According to one embodiment not illustrated, the base of the truncated cone- shaped portion 20 might be adjacent to another truncated cone-shaped portion whose aperture a’ differs from aperture a. Aperture a' is preferably higher than a to stabilize the tip when it is mounted on the crimping tool. This additional truncated cone-shaped portion doesn’t have any impact on the quality of the crimped points as long as the height of the truncated cone-shaped portion 20 is bigger than the maximum indentation depth the crimping tip can reach.

Thanks to the specific shape of the tip, crimped points with higher shear transmission are formed while minimizing the crimping force. Moreover, cracks around the crimped points are limited. It is also worth mentioning that this tip shape allows reducing the number of required crimped points, each crimped point roughly resisting 1 .5 times more than a crimped point obtained with the crimping tool of the prior art. It is thus possible to use a double crimping tool instead of a triple one.

Accordingly, the process for crimping sheet piles comprises the steps according to which:

- Two interlocked sheet piles are provided, - They are positioned between a stamp holder and a stamp head comprising at least one crimping tip according to the invention,

- They are crimped in at least one point by pressing the stamp head on the engaged interlocks.

Preferably, the displacement of the crimping tip during contact with the engaged interlocks, i.e. the indentation depth, is comprised between 15 and 21 mm.

It is inventors’ understanding that the sheet piles crimped by the process according to the invention show crimped points whose shapes differ from the shapes of the crimped point according to the prior art and/or whose stresses in the vicinity of the crimped point differ from the stresses in the vicinity of the crimped points according to the prior art. Thanks to these differences, the crimped points according to the invention show a better shear resistance and cracks around the crimped points are limited. Numerical simulations were performed with aperture a varying from 10 to 80 degrees, diameter d varying from 10 to 40 mm and indentation depth varying between 15 and 21 mm. Results were investigated in order to find the tip geometry for which the crimping force does not exceed 90% of the machine capacity, so that the machine is not used at its maximum capacity and the cracks around the crimped points are limited, while the shear resistance of the crimping point is above 120kN/point. Each couple (a, d) was attributed one point for each indentation depth where the shear resistance exceeded 120kN/point while the crimping force did not exceed 90% of the machine capacity. The sum of the points attributed to each couple (a, d), i.e. the score, represents the robustness of the corresponding crimping tip, i.e. its ability to make strong crimped points whatever the indentation depth. The scores, ranking from 0 to 5, are plotted on Figure 4. Only tip geometries with a score equal to or greater than 4 were selected as robust enough to increase the shear resistance of the crimped sheet piles while requiring less force for crimping and limiting cracks around the crimped points, whatever the indentation depth. The domain for which the tip geometries scored 4 or higher is delimited by points A, B, C and D which coordinates are:

- A: 20.0mm, 54.2°

- B: 22.1 mm, 34.8° - C: 28.5mm, 28.0°

- D: 24.3mm, 45.5°

The corresponding equations are:

- Segment AB: a = - 9.24 d + 238.96

- Segment BC: a = - 1.06 d + 58.28

- Segment CD: a = - 4.17 d + 146.75

- Segment DA: a = - 2.02 d + 94.67.

Preferably, tip geometries with a score equal to 5 are selected. The corresponding domain is illustrated on Figure 5 which is an enlargement of part of Figure 4. It is delimited by points E, F and G which coordinates are:

- E: 20.46mm, 51.52°

- F: 21 4mm, 43.5°

- G: 25.31 mm, 39.75°

The corresponding equations are:

- Segment EF: a = - 8.53 d + 226.08

- Segment FG: a = - 0.96 d + 64.02

- Segment GE: a = - 2.43 d + 101.17

Tests have been performed with a crimping tip according to the invention whose aperture a was 50° and truncation diameter d was 22mm. It was compared to a crimping tip whose aperture a was 45° and truncation diameter d was 18.5mm (thus positioned outside of the domain of the invention illustrated on Figure 4).

The tests have been performed on two different sheet pile profiles: PU18 (with a 9mm interlock thickness) and PU32 (with a 1 1 mm interlock thickness), both in steel grade S355GP.

According to EN1993-5, prEN 10248 (Annex E). the shear resistance at 5mm of displacement should be superior to 75kN/point, which implies a minimum required stiffness of 15kN/mm/point.

The statistical analysis of the results showed that the crimping tip according to the invention allowed an increase of the indentation depth from 15mm to 18mm without appearance of cracks while increasing the shear resistance at 5mm of displacement and decreasing the crimping force. In particular, for profile PU32, the shear resistance at 5mm of displacement, which was already above the standard requirement, increased by 32% and the stiffness, which was also already above the standard requirement, increased by 56%. As for profile PU18, the shear resistance at 5mm of displacement which was already above the standard requirement, increased by 57% and the stiffness, which was also already above the standard requirement, increased by 72%.