GB2159959A

GB2159959A - A device for testing the strength of the ground

Info

Publication number: GB2159959A
Application number: GB08507837A
Authority: GB
Inventors: Dr Sin Fatt Chan; Kok Keong Chong; Lee Pee Hong
Original assignee: PILECON ENGINEERING BHD
Current assignee: PILECON ENGINEERING BHD
Priority date: 1984-03-26
Filing date: 1985-03-26
Publication date: 1985-12-11
Also published as: GB8407786D0; GB8507837D0

Abstract

A ground-strength testing device includes a tubular member 1 closed at the top by a weight 2. At the bottom is an aperture 3 from which a probe 4 projects. A spring 6 acting on a plate 5 fixed to the top of the probe 4 biasses the probe 4 into its position of maximum protrusion from the member 1. Lowering of the device onto the ground causes the probe 4 to be retracted and raise a non-return follower 9 until the member 1 comes to bear on the ground. The final position of the follower 9 along a calibrated scale 12 indicates the strength of the ground. <IMAGE>

Description

SPECIFICATION Device for testing the strength of the ground This invention relates to a device for testing the strength of the ground.

According to the present invention, there is provided a device for testing the strength of the ground, comprising a body, a probe slidabiy mounted on said body, biassing means urging said probe into a position of maximum protrusion from said body, and indicating means arranged to indicate the degree of displacement of said probe relative to said body against the action of said biassing means upon pressing of said probe against the ground until said body bears against the ground.

Advantageously, the weight of the body is greater than the downward force exerted by the biassing means on the probe when the probe is fully retracted relative to the body.

Preferably, the weight of the body is at least one tonne, better still at least two tonnes, and the downward force exerted by the biassing means on the probe when the probe is fully retracted relative to the body is also preferably at least one tonne, better still at least two tonnes. Preferably the probe, in its position of maximum protrusion, projects at least fifteen centimetres from the body.

Preferably, the body includes an outer sheath in which the other parts of the device can be lowered, the sheath acting as a guide when, for example, the device is being used to test the strength of the ground at the foot of a borehole.

The inner end of the probe may be attached to a plate in a tubular member of the body, the bias acting on the plate. The bias may be provided by a compression spring in the tubular member.

A follower can be mounted in a guide on the outside of the tubular member and can carry an indicator, the follower being moved by a part connected to the probe, this part protruding from a longitudinal slot in the tubular member so as to be able to draw the follower upwards upon depression of the probe into the tubular member against the bias. A calibrated scale can be provided alongside the indicator in order to give the required measured reading.

The device may also include a pulley system attached to the top of the weight to facilitate lifting and lowering of the device.

Preferably, the tubular member incorporates various sealing arrangements to prevent ingress of water, mud etc, thereinto.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a diagrammatic side view of part of a device for testing the strength of the ground, Figure 2 is a diagrammatic cross-sectional side view of the part of the device shown in Figure 1 and viewed at right angles thereto, Figure 3 is a diagrammatic cut-away view of the complete device showing it in a condition before it is lowered into, for example, a borehole, and Figure 4 is a view similar to Figure 3 showing the device when it has been inserted into the borehole.

Referring to the drawings, a tubular member 1 is closed at an upper end by a substantial weight 2 which is preferably about 3 tonnes, the weight 2 being joined to the tubular member 1 by welding.

The other end of the tubular member 1 has a plate 20 extending across it, this being formed with a central aperture 3 from which protrudes a hard chrome steel rod probe 4, which has a pointed tip 4A. The inner end of the probe 4 within the tubular member 1 is attached to a plate 5 on the opposite face of which one end of a compression spring 6 acts in order to urge the probe 4 in a direction out of the tubular member 1. Such outward travel is limited by a shoulder 4B on the probe 4 coming into abutment with the edge of the aperture 3.The other end of the compression spring 6 bears against the lower face of the weight 2.

A longitudinal slot 1A is provided in the tubular member 1 and extends over a substantial part of the length thereof.The plate 5 carries a tubular shell 7 which extends approximately half the length of the tubular member 1 and surrounds the spring 6. An upper end of the shell 7 carries a lug 8 which extends out of the tubular member 1 through the slot 1A. A follower 9 is fitted in a guideway 10 which is on the outside of the tubular member 1, beyond and parallel to the slot 1A. The follower 9 can slide up and down in the guideway 10 and carries an indicator 11 which is designed to stay in whatever position is reached by the follower 9 in its upward travel. A calibrated scale 12 is fitted alongside the run of the indicator 11.

In order to prevent ingress of mud and water etc.

into the tubular member 1, a sealing arrangement is provided between the probe 4 and the aperture 3, the probe 4 passing through a greased bush arrangement 13 fitted in the aperture 3. Moreover, the slot 1A is enclosed by the scale 12, which has a clear perspex front to it. The lower end of the guideway 10, beneath the scale 12, is open and the follower 9 extends into it through a sealing arrangement 12A at the foot of the scale 12.

In order to be able to draw the follower 9 back down after it has been lifted by the lug 8 consequent upon movement of the probe 4, the lower end of the follower 9 is formed as a T-piece 9A so that the follower 10 and its indicator 11 can be drawn down until the indicator 11 reaches the bottom of the scale 12.

All of the parts so far described are encased within a tubular outer sheath 14 which has a length of the order of twice the total length of the parts described above within it. The sheath 14 acts as a guideway for the parts therein so that the device can be used in boreholes etc. of considerably greater diameter than the diameter of the device without risk of the parts toppling over in such a borehole.

A pulley system 15 is fitted to the top of the weight 2, the pulley ropes extending out of the top of the sheath 14 so that the whole device can be lifted and lowered by means of a crane. The sheath 14 has near its upper end an inner annular shoulder 16 to limit upward travel of the weight 2 when the device is being lifted by the crane and so the whole device, including the sheath 14, can be lifted.

In use of the device, taking the example where the strength of the ground at the foot of a borehole is to be tested, the device is lifted from its resting place by the crane and the parts assume the condition shown in Figure 3. The whole assembly is then lowered into a borehole 17 until the bottom of the outer sheath 14 reaches and rests firmly on the bottom of the borehole 17. Further lowering of the device (by paying out more pulley rope) allows the weight 2 and the parts suspended therefrom to be lowered gently from the shoulder 16 down through the sheath 14 until the tip 4A of the probe 4 reaches the foot of the borehole 17. Further lowering will cause inter alia the weight 2 to press the probe 4 into the ground beneath the borehole, the penetration depth depending on the strength of the ground at that point.Once the probe 4 can move no further into the ground, further lowering of the pulley rope will allow the weight 2 to compress the spring 6 and move the tubular member 1 down around the probe 4 until the bottom end of the tubular member 1 itself reaches the ground surrounding the probe 4 at the foot of the borehole 17. It will be seen that this action causes the shell 7 carried by the plate 5 on the inner end of the probe 4 to move relatively to the tubular member 1 and thus the lug 8 will effectively slide up the slot 1A dragging the follower 9 with it.

Once this condition has been achieved, with the full dead weight of the parts of the device within the sheath 14 acting against the compression spring 6 pressing on the probe 4, the device is then lifted by the crane out of the borehole 17. All of the parts move back to their original positions, except the follower 9 and its indicator 11, which remain in the resultant position caused by penetration of the probe 4 into the ground.

A window (not shown) is provided in the sheath 14 to facilitate reading of the indication given on the scale 12.

It will be appreciated that the indicator 11 gives the measurement of the penetration depth of the probe 4 and the scale 12 is also calibrated to show the maximum force required to cause the probe 4 to penetrate the ground from the time of contact of the tip 4A with the ground until the probe 4 can move no further into the ground, this latter calibration being achieved by previously calculating the force required to compress the compression spring 6 and knowing how heavy the weight 2 is. Alternatively, the scale 12 can be calibrated as a simple distance scale and a graph can produced of that particular spring's characteristics of load against degree of compression so that the force can be read off from the graph after the position of the indicator 11 has been noted.

The device is intended to be designed to have a range to test the strength of all types of ground from weak ground to very hard ground (rock). In the latter case, of course, there will be scarcely any and perhaps no penetration at all. The device is particularly suitable for greatly varied ground even where it varies in both horizontal and vertical planes.

When piling work is being carried out, the device can be used during the course of drilling a borehole for a pile so that a borehole can be sunk, the ground at the foot of it be tested by the device, the drilling can proceed further down and then the ground tested again and so on.ln fact, the device can be used for testing the strength of the ground in generally inaccessible places, and where, for example, the ground is waterlogged or submersed in water. The device can also be used where deep excavation work is being carried out for example in diaphragm wall construction (which is used to support a property directly adjacent an excavation site).

It will be appreciated that the same machine that produces the borehole can be used to lift and lower the present device into the borehole.

Hand-held penetrometers are known which have to be pushed into the ground; this is usually done by hand. The device shown in the accompanying drawings penetrates into the ground under its own weight. It can be used to measure both the penetration of the probe and the force acting on the probe, this force being deduced from the measured compression of the spring. Neither the force nor the penetration is predetermined. In known penetrometers one of these two parameters is predetermined, whilst the other is measured during the test.

Claims

1. A device for testing the strength of the ground, comprising a body, a probe slidably mounted on said body, biassing means urging said probe into a position of maximum protrusion from said body, and indicating means arranged to indicate the degree of displacement of said probe relative to said body against the action of said biassing means upon pressing of said probe against the ground until said body bears against the ground.

2. A device as claimed in claim 1, wherein the weight of said body is greater than the downward force exerted by said biassing means on the probe when the probe is fully retracted relative to said body.

3. A device as claimed in claim 1 or 2, wherein the weight of said body is at least one tonne.

4. A device as claimed in claim 3, wherein the weight of said body is at least two tonnes.

5. A device as claimed in any preceding claim, wherein said probe, in said position of maximum protrusion, projects at least fifteen centimetres from said body.

6. A device as claimed in any preceding claim, wherein said biassing means exerts on said probe a force which increases with increasing retraction of said probe relative to said body.

7. A device as claimed in claim 6, wherein said biassing means comprises a helical compression spring.

8. A device as claimed in any preceding claim, wherein said body comprises a tubular member provided at a lower end thereof with an aperture in which said probe is retractable.

9. A device as claimed in claim 8, wherein said body includes a mass at the upper end of said tubular member.

10. A device as claimed in any preceding claim, wherein said indicating means comprises a follower arranged to be raised by said probe into a position indicating the maximum said degree of displacement, and retaining means for retaining said probe in that position.

11. A device as claimed in claim 10, wherein said body has a calibrated scale over which said follower moves.

12. A device for testing the strength of the ground, substantially as hereinbefore described with reference to the accompanying drawings.