GB2072247A

GB2072247A - A method and an arrangement for the testing of pile behaviour in situ

Info

Publication number: GB2072247A
Application number: GB8107834A
Authority: GB
Original assignee: Vyskumny Ustav Inzenierskych Stavieb
Current assignee: Vyskumny Ustav Inzenierskych Stavieb
Priority date: 1980-03-24
Filing date: 1981-03-12
Publication date: 1981-09-30
Also published as: ATA134981A; YU59681A; AT391505B; GB2072247B; DE3108492A1; DE3108492C2; HU181292B

Abstract

The pile has a footing (1) and a shaft (2) made as separate pieces. A strut (4) bears on the footing and a plurality of pull rods (6) are connected at their lower end to the shaft and at their upper end to a cross-head member (7). Thrust applying means (8) are situated between the strut and the member and apply simultaneously pulling force to the strut and pushing force to said member, said forced being in equilibrium. <IMAGE>

Description

SPECIFICATION A method and an arrangement for the testing of pile behaviour in situ The invention relates to a method and to an arrangement for the testing of pile behaviour in situ.

Presently used methods for the testing of piles made in situ have the drawback that they require an anchored load bridge, a load bridge with a counterweight or some other surface construction for taking up the reaction of the test load, which results in higher costs, and increased amount of labour and time. Another drawback of presently used methods is that for separate determination of the resistance of the pile footing and of the friction of the mantle the tensometric technique has to be used which leads to an increase in costs and to demanding tests.

It is an object of this invention to eliminate these drawbacks and to provide a method and an arrangement for the testing of piles made in situ which is substantially simpler and which allow separate determination of the resistance of the footing and the friction of the shaft. According to this invention a pile footing separated from the pile shaft is pressed downwards in the direction of the pile axis and the shaft is simultaneously drawn out, while the force acting on the pile footing is in equilibrium with the force acting on the pile shaft. The friction of the pile shaft and the weight of the pile shaft are utilized as reaction for generating the test load on the pile footing. Thus the resistance of the pile footing in dependence on its displacement and the friction of the pile shaft in dependence on its displacement are separately determined.

An arrangement according to this invention comprises a jack situated above the ground and resting on a strut arranged slidably within a casing provided in the center of gravity of the cross section of the pile shaft. The strut bears on the pile footing which is separated from the pile shaft by a separating plate. A supporting plate connected by draw bars with the reinforced pile shaft rests on the jack.

The method and arrangement according to the invention have advantages in that no construction of a load bridge is required, saving thus costs when making anchoring piles, costs for transport, assembling and dismantling of a load bridge with a counterweight. It is also possible to operate without high demands on transport and lifting mechanisms and to reduce substantially the time for preparation of the load test. Other advantages of the method and arrangement according to the invention are a separate determination of the resistance of the pile footing and of the friction of the pile shaft without application of tensometric technique whereby the dimensioning of the lifting means is half of the test load used at presently used test methods, with the possibility of repeated application of the majority of used test appliances.

The invention provides a method for the testing of the behaviour in situ of a pile including a shaft and a footing separate from the shaft, the method comprising causing pushing force to act on the footing in the direction of the pile axis, and simultaneously causing pulling force to act on the shaft, the pushing force being in equilibrium with the pulling force.

Advantageously pushing means, preferably a strut situated to pass freely through a hole in the shaft, is caused to bear on the footing, pulling means is firmly connected to the shaft, the pulling means preferably including pull rods firmly connected at their lower parts to the shaft and at their upper parts to a cross-head member, and means for applying a predetermined thrust are caused to act simultaneously on the pushing means and the pulling means, the means for applying the predetermined thrust including preferably a jack.

The invention also provides an arrangement for carrying out the method the arrangement comprising a strut which during testing passes through a hole in the shaft and bears on the footing, pull rods the lower parts of which are firmly connected to the shaft and the upper parts of which are firmly connected to a cross-head member, means for applying a predetermined thrust to said strut and member, and means for detecting or measuring the displacement of the footing and/or the shaft.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Fig. 1 shows the principles of a method of testing according to the invention, Fig. 2 shows a loading diagram obtained by testing according to the invention, Fig. 3 shows a vertical sectional elevation of a pile with the testing equipment according to invention, and Fig. 4 is a cross-section along line I-I in Fig. 3.

The method according to the invention is used to test the behaviour in situ of a pile having a shaft 2 and a footing 1 separate from the shaft 2. As shown in Fig. 3, a separating plate 3 may be used to separate the shaft 2 from the footing 1.

With reference to Fig. 1, the testing according to the invention is so performed that the pile footing 1, situated at the bottom of a bore, is urged downwards in the direction of the pile axis while the pile shaft 2 is simultaneously drawn upwards. The force 1 8 acting on the separate pile footing 1 is in equilibrium with the force 1 7 acting on the pile shaft 2. The force 18 is reacted by resistance 10 of the ground acting on the footing 1. The weight of the pile shaft 2 and the friction 9 between the surface of the pile shaft 2 and the soil in contact therewith act against force 1 7.

When testing according to the invention the load diagram 1 5 is obtained as a diagram showing the sum of the resistance curve 1 4 of the footing 1 and of a curve 13 of the surface friction 9. The resistance curve 14 of the footing 1 is drawn as a line connecting points obtained at individual loading stages, while the force 18, as indicated in Fig. 1, is plotted in the direction of the coordinate axis 11 and the corresponding shifting of the pile footing 1 is plotted in the direction of the coordinate axis 12. The curve 1 3 of the surface friction 9 is drawn similarly. The test force 17, indicated in Fig. 1, from which the weight 16 of the pile shaft 2 is subtracted, is plotted in the direction of the coordinate axis 11.

The testing arrangement according to the invention comprises a strut 4 which is slidably arranged in a casing 5 in the centre of the reinforced pile shaft 2, and three draw bars 6 firmly connected to a cross-head member, which in the illustrated embodiment has form of a plate 7. A jack 8 is situated between the strut 4 and the plate 7.

In operation the pile footing 1 is pressed by the jack 8 via the strut 4 in the direction of the pile axis vertically, or at an angle to the vertical, downwards, while the pile shaft 2, which is separated from the footing 1 by a separating plate 3, is pulled by the draw bars 6 upwards away from the pile footing 1.

In the described embodiment one jack 8 and three draw rods 6 have been used. It is, of course, possible to use a different number of jacks 8 and draw bars 6 in dependence on the diameter of the pile footing, pile shaft 2, cross-section of the pile, the diameter of the jack 8, and magnitude of the test load.

It will be understood by persons skilled in the art that measuring apparatus, known per se, will be used for the method according to the invention.

This apparatus may include a pressure or thrust measuring apparatus and means for measuring the displacement of the footing 1 or strut 4 and/or for the displacement of the pile shaft 2, or at least one of the draw bars 6 or of the plate 7. If the requirements on accuracy of determination of the load are high, the jack 8 may be provided a dynamometer known per se.

Claims

1. A method for the testing of the behaviour in situ of a pile including a shaft and a footing separate from the shaft, the method comprising causing pushing force to act on the footing in the direction of the pile axis, and simultaneously causing pulling force to act on the shaft, the pushing force being in equilibrium with the pulling force.

2. A method according to claim 1 wherein pushing means is caused to bear on the footing, pulling means is firmly connected to the shaft, and means for applying a predetermined thrust are caused to act simultaneously on the pushing means and the pulling means.

3. A method according to claim 2 wherein the pushing means is a strut situated to pass freely through a hole in the shaft and bearing on the footing, and the pulling means includes pull rods firmly connected at their lower parts to the shaft and at their upper parts to a cross-head member, the means for applying the predetermined thrust including a jack.

4. A method according to claim 3 wherein the hole extends substantially axially through the shaft and contains a casing, and the strut is arranged slidably in the casing.

5. A method according to any one of the preceding claims wherein the course of testing the resistance at the footing and/or surface of the shaft, and the corresponding shifting of the footing and/or of the shaft are separately determined.

6. A method for the testing of the behaviour in situ of a pile substantially as herein described with reference to the drawings.

7. An arrangement for carrying out the method according to any one of the preceding claims comprising a strut which during testing passes through a hole in the shaft and bears on the footing, pull rods the lower parts of which are firmly connected to the shaft and the upper parts of which are firmly connected to a cross-head member, means for applying a predetermined thrust to said strut and member, and means for detecting or measuring the displacement of the footing and/or the shaft.

8. An arrangement for carrying out the method according to any one of claims 1 to 6 constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in, the accompanying drawings.