AU719665B2 - Method and apparatus for testing piles - Google Patents

Description

Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

(ORIGINAL)

*Name ofApplicant: Vibro-Pile (Aust) Pty Ltd Actual Inventor(s): Charles Pol Vuillier *Address for Service: DAVES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000.

Invention Title: Method and apparatus for testing piles Details of Associated Provisional Application(s): No(s): PO5819/97 filed 24 March 1997 The following statement is a full description of this invention, including the best method of performing it known to me/us: -1- Q:\OPER\KAT\P05819-9.83 24/3/98 P:\OPER\KAT\PILES2.PRO -24/3/98 1A- METHOD AND APPARATUS FOR TESTING PILE STRUCTURES This invention relates to a method and apparatus for testing pile structures, particularly but not exclusively for static load testing of foundation piles.

When piles are positioned in the ground for providing foundations for structures, it is necessary to test the piles under static load conditions in order to assess the performance of the piles before structure is erected utilising these. It is possible to undertake compression testing by placing kentledge (usually steel or concrete blocks) on a platform suspended above an upper end of the pile and then to utilise a load cell to record the load applied to the pile.

Alternatively, a dead weight such as a beam ,nay be placed centrally over the pile and each end of the beam anchored into the ground using piles or ground anchors whereafter a jack is again used to measure the pile performance. In either case, the deflection, ie the resultant **downward movement, of the pile is measured, to provide a load settlement curve for indicating pile performance.

These methods are costly and somewhat inconvenient. The present invention seeks to provide an alternative testing method utilising a tension test.

According to one aspect of the present invention there is provided a method for static load testing of a foundation pile structure comprising: forming a bore hole; forming a base of the pile structure at a lower end of the bore; positioning an upstanding shaft and an upstanding reinforcement cage on the base so that the shaft is positioned within the cage; pouring wet concrete into the bore above the base so that, when set, the concrete and P:\OPER\KAT\PILES.PRO 24/3/98 -2reinforcing cage are interengaged to form a pile and arranged for movement relative to the shaft, the cage and set concrete together with the base forming the pile structure; positioning an extensible jack and a load cell between the shaft and an upper part of the cage; extending the jack to apply a load between the base and shaft; and 10 measuring deflection of at least one of the shaft and pile, resulting from the applied S"load.

In another aspect, there is provided an apparatus for load testing a pile structure including a base of a pile structure positioned in a bore in a ground surface, an upstanding shaft and an upstanding reinforcement cage interengaged with concrete to form a pile arranged for movement relative to the shaft, wherein the pile and the base together form the pile structure So and wherein an extensible jack and a load cell are connected between the shaft and an upper part of the cage such that the jack, when extended, applies a load between the base and the S...i shaft to allow for measurement of deflection of at least one of the shaft and the pile.

The base may be formed in-situ by pouring concrete, or pre-formed in a block which is lowered into the bore. Preferably, a pad, such as a metal plate, is positioned centrally of the base for abutment with a lower end of the shaft. Preferably, a suitable tubular element is provided for surrounding the shaft, and the concrete forming the pile is cast therearound, to substantially avoid contact between the pile and the shaft, for the purpose of minimising frictional forces between the shaft and surrounding cast concrete and facilitating the relative movement therebetween.

The invention is further described, by way of non-limiting example only, with reference to the accompanying drawings in which: P:\OPER\KAT\PILE.PRO -24/3/98 -3- Figures 1A to 1E inclusive illustrate apparatus and steps used in practising the method of the invention.

In practising the method illustrated in Figures 1A to 1E, a bore 12 is first formed in ground 14 by, for example, drilling inwardly from a ground surface 16. The bore 12 is drilled to the desired depth of the required pile to be formed. Then, as shown in Figure 1A, a lower part of the bore is filled with wet concrete which, when set, forms a base 18 at the lower end of the bore.

10 Next, as shown in Figure 1B, a metal plate 20 is positioned centrally on the base 18. A plastics tube 22 is then positioned on the base 20, so as to extend upwardly and to slightly above the desired position of the top end of the pile to be formed. Then, a metal shaft 24 is positioned within the tube 22 so as to abut the base plate 20 at its lower end and, at its upper end, to extend somewhat above the ground surface 16. The shaft 24 may have, at its upper end, a load platform 26.

As shown in Figure 1C, a cylindrical mesh cage 30 of reinforcing steel or the like, forming a tubular structure is then positioned on the base 18, outside the perimeter of the plate 20, and so as to extend upwardly from the base to a height some distance above that of the platform 26.

As shown in Figure 1D, the space between the periphery of the bore 12, and the outer surface of the tube 22, is then filled with wet concrete which, when set, forms a pile 40, and this, together with the base 18, forms a pile structure 45. The concrete is positioned in the bore 12 as necessary to form the pile to a desired height, in this case it is shown as terminating, at the upper end, just below the ground" surfa-e 16, adjacent the upper end of the tube 22.

In a subsequent step, shown in Figure 1E, an upper transversely extending bridge member 32, in the form of a thick plate, is connected to the cage 30, above and spaced from the upper end of the shaft 24, more particularly above the platform 26. A jack 34 is then positioned P:\OPER\KAT\PLES.PRO 24/3/98 -4on the platform 26 and a load cell 36 positioned between the upper end of the jack and the bridge member 32. The jack 34 is then operated so as to be extended, whereby to apply forces on the one hand against the bridge element 32 and on the other hand against the platform 26, whereby a load is applied to the lower end of the pile structure 45, particularly to the plate 20 and base 18, while an upwards force is applied to the pile 40, via the load cell 26 and bridge element 32, to the upper end of the cage The described arrangement permits measurement of both the end bearing value of the pile and the shaft resistance, by appropriate measurement of the central steel shaft deflection and the pile deflection.

In that regard, under the described forces exerted by the jack 34, there is a tendency for the pile 40 and cage 30 to move upwardly, and for the shaft 24, plate 20 and pad 18 to move downwardly. The upward movement of the pile is resisted by frictional forces as between the exterior side surface of the pile 40 and the surrounding ground material. The downward movement of the shaft 24, plate 20 and pad 18 is resisted by reaction forces against the underside of the base 18, as the base 18 presses against the underlying ground material.

Thus, by measuring the resultant upward deflection of the pile 40, a measure of the effectiveness of the pile structure 45 acting as a friction pile can be made, while, by measuring the downward deflection of the shaft 24, a measure of the effectiveness of the pile structure as an end bearing pile can be obtained. In each case the magnitude of the deflection is inversely proportional to the effectiveness, that is to say inversely proportional to the expected resistance to downward movement of the pile when subsequently subjected to downward loads in use.

The described arrangement also has the advantage of offering cost savings and may be quickly executed. It also enables measurement of end bearing and wall friction.

The measurement of deflection may be achieved in any suitable known way, for example by comparing markings on the pile 40 and shaft 26 with any suitable fixed vertical reference P:\OPER\KAT\PILES2.PRO 24/3/98 point.

The load cell provides a measurement of the applied load from the jack and facilitates comparative measurements. For example, division of the two deflections in question by the load provides comparative measures, useful in comparing performances of different piles.

The deflections may be measured for one or more pre-selected applied loads, to facilitate such comparison.

S

The tube 22 may be formed of any relatively low friction material, such as plastics or the like. Its inner diameter may be slightly greater than the diameter of the shaft 24.

By the term "deflection" in this specification is meant the extent of vertical movement of the relevant member, ie the pile or shaft.

The described arrangement has been advanced merely by way of explanation any many modifications may be made thereto without departing from the spirit and scope of the invention which includes every novel feature and combination of novel features herein disclosed.

S.

S.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Claims (8)

1. A method for static load testing of a foundation pile structure comprising: forming a bore hole; forming a base of the pile structure at a lower end of the bore; positioning an upstanding shaft and an upstanding reinforcement cage on the base so that the shaft is positioned within the cage; pouring wet concrete into the bore above the base so that, when set, the concrete and reinforcing cage are interengaged to form a pile and arranged for movement relative to the shaft, the cage and set concrete together with the base 9*o* forming the pile structure; positioning an extensible jack and a load cell between the shaft and an upper part of the cage; extending the jack to apply a load between the base and shaft; and measuring deflection of at least one of the shaft and pile, resulting from the V, applied load. 9o9*

2. A method as claimed in claim 1, wherein extending the jack also effects tensioning of o9.9 the pile.

3. Apparatus for load testing a pile structure including a base of a pile structure positioned in a bore in a ground surface, an uptstanding shaft and an upstanding reinforcement cage interengaged with concrete to form a pile arranged for movement relative to the shaft, wherein the pile and the base together form the pile structure and wherein an extensible jack and a load cell are connected between the shaft and an upper part of the cage such that the jack, when extended, applies a load between the base and the shaft to allow for measurement of deflection of at least one of the shaft and the pile.

4. Apparatus as claimed in claim 3, wherein a pad is positioned centrally of the base for abutment with a lower end of the shaft.

P:\OPER\KAT\PILES2.PRO 24/3/98 -7- Apparatus as claimed in claim 3 or 4, wherein a tubular element is provided for surrounding the shaft, and the concrete forming the pile is cast therearound, to substantially avoid contact between the pile and the shaft, for the purpose of minimising frictional forces between the shaft and surrounding cast concrete and facilitating the relative movement therebetween.

6. Apparatus as claimed in any one of claims 3 to 5, wherein the base is formed in situ of cast concrete. o• 10

7. A method for load testing a pile structure, substantially as hereinbefore described with reference to the accompanying drawings.

8. Apparatus for load testing a pile structure substantially as hereinbefore described with reference to the accompanying drawings. S DATED this 24th day of March, 1998 VIBRO-PILE (AUST) PTY LTD By its Patent Attorneys Davies Collison Cave