Patent Publication Number: US-8540461-B2

Title: Circular pile head for underpinning a slab

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is the U.S. national phase of PCT Appln. No. PCT/MY2009/000164 filed Oct. 1, 2009 which claims priority to Malaysian application P120091130 filed Mar. 20, 2009, the disclosures of which are incorporated in their entirety by reference herein. 
     TECHNICAL FIELD OF THE INVENTION 
     This innovation refers to a circular pile head assembly that can facilitate driving of the underpinning pile in a raft foundation using a pile driving machine and locking-off the transferred load to the underpinning pile. To achieve this purpose, it would be necessary to have features in the pile head that can accommodate the entry of the underpinning pile through the pile head and yet the pile head can be easily inserted into a small pre-bored hole in the slab. 
     BACKGROUND OF THE INVENTION 
     In the prior art U.S. Pat. No. 7,300,230 B2 requires the excavation of a hole to access the pile cap or ground beams and using transfer beams to attach the pile head. However this would be undesirable in the case of a raft foundation, as this excavation will weakened the slab. Moreover, in most cases the slab will be strong enough to support the underpinning pile if it can be placed underneath the slab. Hence, a pin hole pre-bored in the slab will ensure that the shear in the concrete slab is not compromised, especially if the underpinning pile is placed near to the main support columns. 
     In the prior art U.S. Pat. No. 2006/0216117 A1, teaches the insertion of a bracket through an opening and far enough into the excavated area underneath the slab. The soil below the enlarged opening is excavated to allow room for the subject bracket to be inserted below the slab. The bracket is then welded with rebar and concrete is introduced into the excavated region and hardened around the bracket and rebar to produce a three dimensional plug so that it can support the slab. Clearly, until the concrete hardens in this prior art, the full structural capacity of the slab around the opening will be compromised during lifting. Whereas the present invention overcomes this difficulty and allows the slab to be immediately lifted up or used to drive the underpinning pile without using concrete, rebars or likes to form a plug. In this same prior art, the lifting mechanism is through tightening the screws in the pair of threaded rods, which is independently attached to the tubing which is not connected directly to the brackets. Thus any failure in the weakest link can occur between tubing and the treaded rods or between the tubing and the bracket. The present invention has large welding contact areas and a plurality of welded wedges to support the pile head directly on to the slab, thus avoiding a double weak link as in faced in the prior art. 
     . SUMMARY OF THE INVENTION 
     This innovation refers to a circular pile head assembly that can facilitate driving of the underpinning pile in a raft foundation using a pile driving machine, and locking-off the transferred load to the underpinning pile. The components used in the circular pile head assembly consists of a twin beam lifting attachment, the circular pile head, pile head plate and a section of an underpinning pile. 
     A pre-bored hole will be made in the slab to a size complementary to the outer circular pile head diameter so that it can be inserted through the opening of the pre-bored hole. The circular pile head has a concentric bearing plate with two edges trimmed off so that it be inserted unobstructed into the pre-bored through a hole in the slab, and then displaced in opposite directions as a pair of the circular pile head, ready to receive the underpinning pile. 
     The circular pile head assembly will be connected to the pile driving machine at both ends of the twin beam. The lock pins will be inserted through the upper hook and a lower through hole correspondingly of the twin beams that is aligned to the through opening of the pile driving machine. 
     The downward driving process of the underpinning pile through the circular pile head assembly, is achieved by the counter-reaction in the shearing of the top and bottom lock pins held down against uplift by the upper body section of the circular pile head through the protruding hook and resisted against the soffit of the slab by the concentric bearing plates at the lower ends of the circular pile head. In this way, the circular pile head assembly can allow the dead weight of the foundation, and the pile driving machine to provide sufficient kentiledge to drive the next underpinning pile downwards. 
     The locking mechanism is achieved by placing the circular pile head plate over the top of the underpinning pile and securing the circular pile head plate preferably through welding to the body section of the circular pile head and further strengthened by a plurality of wedges. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further understanding of the aspects of the present invention and their advantages will be discerned after studying the detailed description in conjunction with the accompanying drawings in which: 
         FIG. 1  shows the blown apart components of the circular pile head assembly with twin beam lifting attachments. 
         FIG. 2  shows the details of the components of the circular pile head that will be inserted through a pre-bored hole in the slab. 
         FIG. 3  shows the pile driving machine that will be attached to the twin beam lifting attachments and the circular pile head assembly. 
         FIG. 4  shows the completed assembled circular pile head attached to the pile driving machine ready to drive the underpinning pile. 
         FIG. 5  shows the top view of the assembled circular pile head that was inserted snugly through the pre-bored hole in the slab. 
         FIG. 6  shows a cross-section view of the assembled circular pile head during pre-loading of the underpinning pile. 
         FIG. 7  shows the isometric view of the circular pile head with wedges ready to be welded on to the circular pile head plate after completion of preloading the underpinning pile (the pile diving machine&#39;s extended jack not shown for clarity). 
         FIG. 8  shows that the circular pile head is cut-off below the ground level of the slab and cement grout which will be poured into the spaces between the underpinning pile and the pre-bored hole. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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 Circular Pile Head Assembly ( 1 ): 
       FIG. 1  shows the exploded view of the components used in the circular pile head assembly ( 1 ) consisting of the twin beam lifting attachment ( 4 ), the circular pile head ( 2 ) and a section of an underpinning pile ( 71 ). 
       FIG. 2  shows the circular pile head ( 2 ) where at the middle bottom end of the twin  1  beams ( 42 ) there is provided a protruding hook ( 41 ) ( FIG. 1 ) that will be inserted through a tabular cut-out section ( 24 ) in the upper body section of the circular pile head ( 25 ). A concentric bearing plate ( 22 ) is welded near to the base of the body section of the circular pile head ( 25 ), and additionally supported by a plurality of triangular wedges ( 23 ). 
       FIG. 3  shows the exploded view of the connection between the circular pile head assembly ( 1 ) that will be connected to the pile driving machine ( 5 ) at both ends of the twin beam ( 42 ). The lock pins ( 43 ,  46 ) will be inserted through an upper hook ( 44 ) and a lower through hole ( 45 ) of the twin beams ( 42 ) correspondingly that is aligned to the through opening ( 52 , 53 ) of the pile driving machine ( 5 ). 
     As shown in  FIG. 3  and  FIG. 4  during driving of the underpinning pile ( 71 ) through the circular pile head assembly ( 1 ) is achieved by the counter-reaction in the shearing of the top and bottom lock pins ( 43 ) held down against uplift by upper body section of the circular pile head ( 25 ) through the protruding hook ( 41 ) and resisted against the soffit of the slab ( 8 ) by the concentric bearing plates ( 22 ) at the lower ends of the body section of the circular pile head ( 25 ). In this way, the circular pile head assembly ( 1 ) can allow the dead weight of the foundation and the pile driving machine ( 5 ) to provide sufficient kentiledge to drive the next underpinning pile ( 72 ) downwards. 
       FIG. 5  shows the top view of the assembled circular pile head ( 2 ) that was inserted snugly  1  through the pre-bored hole in the slab. The concentric bearing plate ( 22 ) ( FIG. 2 ) has two parallel edges ( 26 ) trimmed off so that it be inserted unobstructed into the pre-bored through hole ( 81 ) in the slab ( 8 ) and then displaced in opposite directions as a pair of the circular pile head ( 2 ) displayed in  FIG. 5  and  FIG. 6 . 
       FIG. 6  shows the circular pile head assembly ( 1 ) when connected to the pile driving machine ( 5 ) at the middle lower sections of the twin beam ( 42 ) through the protruding hook ( 41 ) that was already inserted through a tabular cut-out section ( 24 ) in the upper body section of the circular pile head ( 25 ). To lock up the preload after completion of driving the underpinning pile ( 71 ), the pile driving machine ( 5 ) jack is extended ( 75 ) against the circular pile head plate ( 3 ) located on top of the underpinning pile ( 73 ) such that the concentric bearing plate ( 22 ) will bear up against the soffit of the pre-bored through hole ( 81 ) to lift up the slab ( 8 ). A plurality of wedges ( 23 ) will be welded on to the circular pile head plate ( 3 ) and the inner side of the body section of the circular pile head ( 25 ) to lock up the preloaded foundation load as shown the isometric view of  FIG. 7  and  FIG. 8 . 
       FIG. 8  shows the circular pile head ( 2 ) is cut-off ( 27 ) below the ground level of the slab ( 8 ) and later cement grout will be poured into the voids ( 82 ) between the trimmed parallel edges ( 34 ) and the pre-bored hole ( 81 ).