This application is the U.S. national phase of PCT Appln. No. PCT/MY2011/000054 filed on May. 23, 2011, which claims priority to MY Patent Application No. PI2010001477 filed on May. 27, 2010, the disclosures of which are incorporated in their entirety by reference herein.
When using the side pile gripping method in association with the hydraulic static pile driver, the pile may fracture or buckled due to peak stress concentrations caused by high non-uniform clamping pressure. In addition during driving, the pile may encounters uneven soil resistances along the pile sides and tip that causes the pile to deviate out of plumb and twist. To connect the next adjoining pile, the clamping methods in the prior arts will force fit the pile vertically on to a twisted and deviated driven pile resulting in a misalignment or a kink at the joint which is vulnerable to slender piles.
By using this innovative pile clamp assembly, it promotes uniform lateral gripping around the pile to give an improved verticality in the driving the pile. More importantly, this clamping mechanism reduces bending in the driven pile by enabling the next adjoining pile to conform as much as possible to the alignment of the existing driven pile and gradually corrects the pile's vertical alignment and twist as it penetrates the ground through interactions of the unique swivelling clamp wedges.
As in CN 200720153070, the clamping force is purely derived from a simple active wedge that moves vertically to push against the passive wedge outwards to clamp against the pile. Unlike the present invention, the clamping force around the pile is not solely derived from the vertical hydraulic clamps but also further resisted by the jamming action of the clamp wedges against the circular clamp housing in response to the externally applied vertical pile driving force. In addition, for unsymmetrical wedge clamping mechanism it would be obvious that unless the active wedge contact is exactly at the centre of the passive wedge, the clamping pressure distribution on to the pile would be trapezoidal and non-uniform. However in the present innovation, if the pile's alignment remains vertical, the top and bottom circular clamp housing will make contact at two equidistant contact point from the centre of the clamps wedge to ensure that uniform pressure will result irrespective of the contact positions of the clamp wedges. Further, the clamping jaws in CN 200720153070 are released by moving the active wedge upwards but the clamping jaws do not retract unlike the current spring loaded clamp wedges.
As in CN2608559Y, although there is a top and bottom wedges, individually the clamp wedge is unsymmetrical and therefore would cause non-uniform clamping pressure as stated earlier. The curvature radius of the contact surface of the clamp wedge is larger than the device box therefore the sides of the clamp wedge is contact with the device box and there will be no rotational play of the wedge in the plan view, which means that the clamps will only grip the pile squarely and vertically. Unlike the present invention, the clamp wedges can swivel within 3 degrees in the horizontal and vertical axis like a “ball and socket” joint inside the circular clamp housing to accommodate the tilt and twist of the pile. Another advantage in the present invention is that the top and bottom circular housing moves in tandem in the opposite directions under a action and reaction force applied by the vertical hydraulic clamp while the clamp wedges are held vertically stationary with respect to the pile, therefore the lower vertical hydraulic clamps can be omitted to save costs, whereas in CN2608559Y all the individual clamps wedges are forced outwards independently for the top and bottom vertical clamps.
CNO3223773.1 uses two adjacent clamp return springs to open the non-swivelling clamp by extending and compressing the spring along the axis of the spring. However apart from allowing the spring to expand and contract along the its axis, the present invention must also allow unrestricted lateral displacement of the spring perpendicularly to the axis of the spring caused by twisting of the adjoining clamp wedges. This is achieved by placing the spring centrally to minimise the twists and allow free movements of the spring within a bell shaped hollow cavity.
The principle in hydraulic static pile driving is to securely grip the pile and push the pile down against a Kentledge. There are numerous method of clamping securely along the sides of the pile. The common method is to apply a plurality of horizontal side clamps wedges inside a box device to grip the pile in which the sides clamping force must be at least two times the vertical driving force to prevent pile slippage.
The alternative pile clamping mechanism is to use a plurality of active wedges to drive it vertically against the slanting side of passive wedges in order to move it horizontally against the sides of the pile. In this way, the horizontal force derived from the vertical wedge principle is multiplied with increasing steepness of the slanting contact wedges which is usually within 15 to 60 degrees to the vertical axis, thus smaller vertical hydraulic clamp is required as compared to the directly applied horizontal clamps method. However, due to the unsymmetrical wedge clamping mechanism it would be obvious that unless the active wedge contact is exactly at the centre of the passive wedge, the clamping pressure distribution on to the pile would be trapezoidal and non-uniform. The present invention overcomes this problem as the clamp wedge is symmetrical and by clamping the top and bottom circular housing, it displaces the clamp wedges at two equidistant contact point from the centre of the clamps wedge resulting in a central horizontal force that gives rise to a more uniform clamp pressure at all times unless the pile is out of plumb.
The cross-sectional shape of a concrete square piles is not a true square but trapezoidal, as such the clamp wedges must be able twist so that the clamp contact surface is flat against the surface of the pile to avoid crushing the pile. The present invention allows this to happen because the radius curvature of the contact sliding surface of the clamp wedge is slightly smaller than the corresponding radius curvature of the contact sliding surface of the circular clamp housing, thus allowing it to rotate about individual pivot point by about ±3°. The individual pivot point is defined by the meeting at the apex of the top and bottom contact sliding surfaces of the clamp wedge which is located directly behind the centre of the clamp wedge.
An important aspect of the present invention of this clamping mechanism is to avoid bending the piles by conforming the next adjoining pile to the alignment of the existing driven pile that has deviated out of plumb and twisted. This pile clamping mechanism the present invention has the ability to uniformly maintain full flat contact with the sides of the deviated and twisted pile by twisting the clamp wedges like a ball joint through the individual pivot point.
Another advantage in the present invention is that the clamping force around the pile is not entirely derived from the vertical hydraulic clamps but also assisted by the contribution from the inclined jamming reaction of the clamp wedges against the circular clamp housing in response to by as the externally applied vertical pile driving force. Therefore, the additional inclined jamming reaction can reduce the magnitude of the required clamp force. This pile clamp assembly is most suitable for use in the push pull pile driving as equal and opposite clamp force is maintained in both the upwards and downwards directions.
The swivelling clamp wedges mechanism unlike the prior arts also improves the verticality during the driving of the pile by gradually correcting the pile's vertical alignment and twist as it penetrates the ground. This is achieved because when the clamp wedge is rotated to align with the deviated driven pile, further resistance is encountered by the inclined jamming reaction of the clamp wedges against one side of the circular clamp housing in response to the externally applied vertical pile driving force. This uneven vertical force creates a restoring moment in the opposite rotation to the deviation of the pile alignment. Thus, as the pile penetrates the ground, the deviation and the restoring moment will gradually reduce in tandem so that the pile will self adjust to a more vertical axis.
The prior arts commonly uses either one or two separate top and bottom vertical hydraulic clamps that act directly on each separate clamp wedges inside the box device, but the present invention uses only one set of vertical hydraulic clamps for the top of the circular clamp housing that is connected to the bottom circular clamp housing by using the vertical hydraulic clamp rod to simultaneously move the clamp wedges to contact with the pile. This reverse wedge activation mechanisms is opposite to the prior arts which creates a more uniform clamping pressure as the separate vertical hydraulic clamps now acts together to push the solid and stiff circular clamp housing on to the clamp wedges rather than acting individually.
For illustration purposes, the pile clamp assembly may consists of a plurality clamp wedges, vertical hydraulic clamps, is guide shafts and push rods but they arranged in such a way to preserve the centroids to be coincident with the centroid of the pile.
a-3b shows the driving sequence of the pile clamp assembly when thus up or down along the guide shafts by the push rods
a-9c shows the slant of the milling cylinder between the lamp housing and the back of the clamp wedge about 0-3 degrees.
a-10b shows the pile clamp assembly that can swivel to accommodate a deviated pile in the z-axis and self-adjust its verticality.
Referring to the drawings, like numerals indicate like components to facilitate explanation. In order to differentiate two separate entities belonging to like components, a suffix “a” or “b” is used to denote the first and second entity.
Components of the Pile Clamp Assembly (1):
a shows the pile clamp assembly (1) driven down along the guide shafts (7) by the extending push rods (6) and
a show the plan view of the clamp wedges (4) squarely clamping the square pile (8), whereas
a shows the milling cylinder surface (22f, 32f) have same inclination to the z-axis as the milling cylinder surface (22g, 32g).
a shows the top adjoining pile (8a) is placed truly vertical in the z-axis, but the bottom driven pile (8a) is slanted in the anti-clockwise direction and hence a kink (81) is resulted that will bend and fracture the pile (8a,8b) when the axial load is applied to drive the top pile (8b). However, in
Number | Date | Country | Kind |
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PI2010001477 | May 2010 | MY | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/MY2011/000054 | 5/23/2011 | WO | 00 | 11/8/2012 |
Publishing Document | Publishing Date | Country | Kind |
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WO2011/149332 | 12/1/2011 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
7681649 | Cerovsek | Mar 2010 | B2 |
7926577 | Thomas et al. | Apr 2011 | B2 |
7997333 | Angelle et al. | Aug 2011 | B2 |
8002027 | Angelle et al. | Aug 2011 | B2 |
20050006147 | Ayling | Jan 2005 | A1 |
Number | Date | Country |
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2608559 | Mar 2004 | CN |
2697154 | May 2005 | CN |
2723519 | Sep 2005 | CN |
201214790 | Apr 2009 | CN |
3211213 | Sep 1983 | DE |
1884600 | Feb 2008 | EP |
Entry |
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International Search Report for PCT/MY2011/000054, Completed by the Australian Patent Office on Aug. 1, 2011, 2 Pages. |
Number | Date | Country | |
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20130062898 A1 | Mar 2013 | US |