GB2276897A

GB2276897A - Apparatus for soil sampling and testing

Info

Publication number: GB2276897A
Application number: GB9406277A
Authority: GB
Inventors: Barrie Hildebrandt; Paul Woodfield
Original assignee: Branlow Ltd
Current assignee: Branlow Ltd
Priority date: 1993-03-30
Filing date: 1994-03-30
Publication date: 1994-10-12
Also published as: GB9406277D0; GB9306631D0

Abstract

An apparatus for soil sampling and testing comprising a tubular casing (8) having a longitudinal bore (22), a sampling tube (2) for taking a soil sample from within the longitudinal bore for testing, and an air displacement hammer (4). The casing (8) has an internal shoulder (26) against which the hammer (4) abuts in order to drive the casing (8) vertically into the ground. The sampling tube (2) is attached to the hammer (4) and is limited in its downward movement within the casing (8) the hammer (4) striking the internal shoulder (26). <IMAGE>

Description

DESCRIPTION AN APPARATUS FOR SOIL SAMPLING AND TESTING The invention relates to an apparatus for soil sampling, and in particular, but not exclusively, to an apparatus for obtaining soil samples to provide site investigation and pile depth prediction for building foundations and subsidence repair work.

In order to assess the depth to which a pile must be driven, it is necessary to know the condition of the ground into which it is to be placed. To this end various machines have been developed which permit the sampling of the soil at various depths below the surface. The samples obtained are analysed and the depth to which the pile must be driven is calculated.

Conventionally for a site investigation, a standard rshell and auger' technique using a tripod rig and standard ancillary equipment has been utilised. Although this equipment is capable of deep investigations, circa 2Om, the bulky and tall nature of the rig renders this technique expensive and inappropriate for many domestic subsidence and light commercial or industrial building projects, since it is unusable or at best difficult to use in areas of close proximity to existing buildings particularly those with limited headroom.

In order to overcome the aforementioned problems, more compact equipment has been developed. In a known machine for soil sampling, a tubular casing is vertically pounded into the ground by repeatedly hitting the top of the casing protruding from the ground with a heavy weight. The casing is normally installed to depths of between 4-5 metres below the surface. A sampling tube is then driven down through the tubular casing on a drill string in order to take a soil sample. The sampling tube is then pulled out of the casing in order to remove the sample. The sampling tube is repeatedly driven down the tube in order to take progressively deeper and deeper samples from within the tubular casing which prevents the earth falling back in on the area from which the samples have been removed.

For foundation and subsidence repair work it is usually desirable to take soil samples down to a level of about ten metres. With the known method and machine for sampling described above, because the casing is being pounded into the ground at or above ground level, the impact is not being transferred to the point, i.e. the descending tip of the casing, where it would be of most use, thereby it is not possible in most ground conditions to install the casing to a depth greater than four to five metres.

It is therefore not normally possible to take soil samples below four to five metres with this method.

Furthermore, the method of subsequently lowering and raising the sampling tube on a drill string is both laborious and time consuming.

The standard tests performed on the samples such as the standard penetration test (SPT) specified by the British Standards Institute, require a minimum 35mm internal diameter sample of soil. This known method only produces a 30mm diameter sample of soil which is insufficient for the test.

Also, in this known method the casing is not reusable but is left in the ground once the site investigation is complete. Problems can occur from, for instance, the build-up and release of methane gas, if the casing is not appropriately treated.

It is an object of the present invention to provide an apparatus for obtaining soil samples which overcomes or alleviates the problems associated with known apparatus.

In accordance with the present invention there is provided a soil sampler comprising a housing with a longitudinal bore and a container for taking a soil sample from within the bore, wherein the container is attachable to a driving means which is arranged to descend into one end of the housing bore and to push the housing, together with the container, vertically into the ground to take a soil sample.

This has the advantage that the driving means can bottom drive the housing of the soil sampler, thereby transferring its energy to the descending base of the housing, whereby the casing is dragged into the ground and achieves a large depth of descent. Since the sampling container is attached to the driving means within the container, it is pushed into the soil as the housing descends, thereby avoiding the need to sink it into the housing once the housing has been sunk. The housing prevents the soil falling in on the area from which the soil has been removed by the sample container.

Preferably, the housing is a tubular casing having an internal shoulder against which the driving means abuts in order to drive the housing vertically into the ground and the sample container which is attachable to the driving means is limited in its downward movement within the housing by the driving means striking the internal shoulder and thereby preventing the sample container protruding into the ground beyond the housing.

The internal shoulder of the housing provides a simple means by which the housing can be driven into the ground and ensures that the sampling container does not extend beyond the housing into the ground.

Preferably, the housing comprises interconnectable sections which are sequentially added to the housing at ground level, thereby increasing the length of the housing below ground level as the housing is driven vertically into the ground by the driving means.

This provides a simple way of assembling the housing at ground level and of transporting the housing in manageable-size sections. The depth to which the housing is sunk depends on the number of sections added to the housing and since the housing is being bottom driven, depths of ten to twelve metres can be achieved.

Preferably, the driving means and sample container are winched out of the housing above ground level in order to remove a soil sample and the driving means and an empty sample container are winched into the housing to obtain a further sample. Preferably, the winch is an air winch or hand-winch. This provides a rapid means of retrieving a full sample container. The contents of the sample container once removed from the driving means can be analysed, whilst an empty sample container is attached to the driving means and sent down the housing to obtain the next sample of soil from within the housing.

Preferably, the end of the housing which is pushed into the ground is of a slightly narrower bore than the sample container within the remaining bore of the housing. This measure reduces the skin friction of the soil entering the sample tube. Preferably, the sample container has an internal diameter of approximately 5Omm. This size of the housing shoe facilitates the performance of tests such as the SPT and Shear Vane on the soil stratum.

Preferably, the driving means is an air displacement hammer and has a shoulder complementary to the internal shoulder of the housing against which it abuts to provide the downward driving force.

In a preferred embodiment, the hammer has a nonreturn valve. This means that the exhaust air can leave the hammer but water, which may be present within the casing is not drawn into the interior of the hammer.

Preferably, the housing is removed from the ground using an extractor jack. This has the advantage that the housing is re-usable and the danger involved by leaving the casing in the ground is avoided. Furthermore, because the housing is in sections, any damaged sections can be replaced without the need for replacing the entire housing.

Preferably, the container for taking the soil sample comprises at least two sections. This has the advantage that the container can be opened to remove the sample for testing.

By way of example only, specific embodiments of the present invention will now be described, with reference to the accompanying drawings, in which: Fig.l is a schematic illustration of a first embodiment of the soil sampling apparatus constructed in accordance with the present invention; and Fig.2 is an enlarged view of the shoe end of the apparatus of Fig.l.

Fig.3 illustrates the connection of the sample tube to the driving means of the soil sampling apparatus of Fig.1; and Fig.4 illustrates the non-return valve of the driving means of Fig.3.

Referring to Fig.l, the soil sampling apparatus comprises a sampling tube 2 for taking- a soil sample, a driving means 4 which is connected to and drives the sampling tube vertically into the ground, and an outer casing 8 which is driven vertically into the ground with the sampling tube 2 by the driving means and in which the sampling tube 2 and driving means 4 are displaceable.

The casing 8 is a substantially cylindrical tube of approximately 90mm to llOmm external diameter steel casing, which is variable in length up to approximately twelve metres long. The tube of the casing 8 is formed in a plurality of sections 10,12,14 which are interconnected by respective screw fittings.

The lowermost section of the casing, which in use, is the section which first enters the ground, comprises a hardened cutting shoe 10 made for example, from specially hardened steel. The tip 20 of the shoe 10 is pointed and is inclined radially inwards, see Fig.2. The next section of the casing attached to the shoe 10 is a nozzle unit 12 and the section beyond the nozzle unit 12 is one or more interconnected cylindrical tubes 14. Each of the tubes 14 is approximately one metre long and are added as required to the casing 8 to obtain the required length of casing and thereby the required depth to which the casing extends. The outer periphery of the casing 8 is polished to a smooth finish and the overall shape of its outer periphery is streamlined with a gentle taper towards the tip of the shoe to aid installation and extraction of the casing into the ground.

In the upper section of the nozzle unit 12, there is another gentle taper towards the overlying cylindrical tubes 14. This is to reduce the skin friction/adhesion between the soil and cylindrical tubes 14 which will aid installation and extraction.

The internal bore 22 of the casing 8 receives the sampling tube 2 and the driving means 4. The internal bore 22 has an annular recess 24 extending from an upper portion of the shoe 10, through the lower end of the nozzle unit 12 adjacent the shoe 10. The annular recess 24 is such that it encompasses the outer surface of the sampling tube 2 with approximately lmm clearance between the sampling tube 2 and the wall of the annular recess 24, when the sampling tube 2 is at its lowermost position within the casing 8. The inner bore of the nozzle unit 12 beyond the annular recess 24 widens to form an internal shoulder 26 which acts as a stop for the driving means 4 and therefore the sampling tube 2 when the sampling tube 2 is in its lowermost position within the casing 8.The diameter of the remaining internal bore 28 of the casing is substantially cylindrical and has an internal diameter which is sufficient to accommodate the longitudinal movement of the sampling tube 2 and driving means 4 therethrough. The internal diameter of the remaining portion of the shoe 10 is approximately 2mm less than the internal diameter of the sampling tube 2.

The sample tube 2 is a substantially cylindrical steel tube approximately 500mm long with an internal diameter of approximately 50mm. One end 30 of the sampling tube 2 is open so that soil can be collected therein as it cuts into the ground whilst the driving means 4 is attached to the other end of the sampling tube 2. For this purpose, as best illustrated in Fig.

3 a knob 3 is screw-fitted into the end of the sample tube 2 and the sampling tube 2 is suspended from the end of the driving means 4 by placement of the knob 3 into a complementary recess 5 at the driving end 7 of the driving means 4. An opening 9 is provided in the outer periphery 11 of the driving means 4 for allowing the placement and removal of the sampling tube 2 on the driving means 4. The driving means 4 is of a wider diameter than the sample tube 2. The wider diameter portion of the driving means 4 immediately adjacent the sampling tube 2 forms a shoulder 32 which abuts against the internal shoulder 26 of the casing nozzle unit 12 and thereby acts as the aforementioned stop. The shoulders 26, 32 are inclined at approximately 100 - 120 to the longitudinal axis of the casing 8.

The driving means 4 comprises the hammer head of, for example, an air displacement hammer which is approximately 1.4m long, the head of the hammer is specifically adapted to compliment the nozzle unit shoulder 26 and made from a hardened metal compatible with the hammer and nozzle unit. The end of the hammer remote from the driving head is fitted with a non-return valve 38 for providing a watertight exhaust of compressed air.

The hammer 4 is operated from ground level and is suspended over and into the casing 8 by a rig (not illustrated) on a steel cable 54 attached to a winch powered by compressed air. This unit enables rapid lowering and retrieval of hammer 4 and sample tube 2 from casing 8. The hammer 4 is powered by a compressor providing inflow of air through air hose 41 and stainless steel pipe section 40 into hammer activating piston to produce the hammering action.

As illustrated in Fig. 4 the valve 38 comprises a housing 42 having an internal cavity 43, a series of air ports 44 provided~around the periphery of the valve, each encompassed by the single pneumatic seal 46 which allows the exhaust, illustrated by the single headed arrows in Fig. 4, of the air displacement hammer 4 to leave from the side of the hammer, but acts to prevent the ingress of water. A bung 48 at the upper end 52 of the valve 38, with a pair of hydraulic seals 50 to provide a water and airtight seal between the hammer 4 and short section of stainless pipe 40 which moves up and down as well as rotate in order to change hammer action from forward into reverse and vice-vera. The stainless steel pipe is in turn connected to the rubber air hose 41.

The soil sampler operates as follows. The shoe 10 of the casing 8 is placed tip first on the ground, the ground can be broken if necessary. The nozzle unit 12 is connected, i.e. screw fitted to the shoe 10. The air displacement hammer 4 and sampling tube 2 attached thereto are lowered into the nozzle unit 12.

The sampling tube 2 is thereby lowered into the annular recess 24 and the hammer 4 comes into abutment against the internal shoulder 26 of the nozzle unit 12. The hammer 4 is then put into operation and the percussive effect of the hammer's shoulder 32 hitting against the internal shoulder 26 of the nozzle unit 12 drives the casing comprising the shoe 10 and nozzle unit 12 into the ground.

As the casing 8 descends into the ground the extent of downward movement of the sampling tube 2 increases as the downward extent of travel of the hammer 4 increases. The use of a slightly oversized sampling tube 2 compared to the shoe 10 enables a soil sample to be taken into the sampling tube 2 with a subsequent reduction in skin friction between the soil sample and the sample tube enabling deeper penetration to be achieved.

Once the sampling tube 2 has descended 500mm into the ground and has thereby taken a 500mm vertical sample of soil, the hammer 4 and sampling tube 2 are winched out of the casing 8, the sampling tube 2 is simply detached from the hammer 4 and immediately replaced with an empty sampling tube 2 fitted to the hammer 4. The winch then rapidly lowers the hammer 4 and the new sampling tube 2 down the casing 8, in a controlled manner, where the sampling tube 2 once again descends into the annular recess 24 and the hammer 4 is once again put into action with the shoulder 32 of the hammer 4 striking the casing 8 on its internal shoulder 26 and gradually pushing the casing deeper into the ground. The next and subsequent soil samples are removed as described above with empty soil samplers 2 connected to the hammer 4 before it is returned down the casing 8.As the casing 8 descends into the ground further sections 14 of the casing can be fitted at the surface by adding a cylindrical tube 14 before returning the hammer 4 down the casing 8. Hence the depth to which the casing 8 is driven is increased and is dependent on the number of cylindrical tubes 14 added. Thereby deeper and deeper said samples can be taken and the depth of each individual soil sample is calculated from the number of sections 14 added to the casing 8 as it is driven into the ground.

The individual soil samples together with the rate of probe penetration are then analysed to provide a detailed analysis of the terrain. This will enable the relevant foundation solution to be chosen, and if the solution involves driven mini piles then the data should provide a means of accurately predicting the pile depths.

Once the soil sampling is complete the hammer 4 and sampling tube 2 are removed from the casing 8 and an extractor jack (not illustrated) at ground level is used to hydraulically extract the casing 8 from the ground. As each section of the casing 8 appears above ground level it can be readily disconnected by unscrewing it from the remaining casing 8.

The casing 8, the drive means 4 and the sampling tubes 2 are all re-usable and can be used for further site investigations. With the casing 8 being sectioned, any damaged sections can be easily replaced without replacing the whole casing 8.

The present invention is not restricted to the details of the foregoing embodiment. For example, the invention has been described with reference to a specific air displacement hammer, but different sized air displacement hammers for example 75mm or 95mm, or other driving means could be employed provided that it can bottom drive the casing 8. The casing 8, and sampling tubes 2 have been described as tubular but other shapes could be envisaged such as a casing with a square cross section. Furthermore the length and diameter of the sampling tube and casing could be modified. For example, the internal diameter of the sample tube has been described as 50mm, but could be 65mm or of any diameter suitable for-producing a soil sample for testing. Likewise, the length of the sampling tube can be varied.The sample tube has been described as a cylindrical steel tube but could be a split sample tube which-is openable along its longitudinal axis in order to remove the soil sample for testing. The two sections of the tube could be kept together by screwed connections at either end.

The mating surfaces of the hammer and casing, which transmit the downward movement to the casing has been illustrated as mutually cooperating annular slant surfaces. - However a square shaped mating surface could be provided.

The winch could be a hand-winch having a suitable gearing system, an air winch or any other means suitable for extraction and installation of the driving unit into the steel casing.

The rams of the extractor jack could have a stroke of approximately 300mm and the extractor jack could have an upward thrust capacity of approximately 20 tonne or a thrust and stroke suitable for extracting the casing. The jack could have tapered collets which, upon activation of the upward thrust, grip about the circumference of the outer periphery of the casing. Alternatively, the upper surface of the jacking unit could thrust against the lower edge of the tube collar.

Claims

1. An apparatus for soil sampling comprising a housing with a longitudinal bore and a container for taking a soil sample from within the bore, wherein the container is attachable to a driving means which is arranged to descend into one end of the housing bore -and to push the housing, together with the container, vertically into the ground to take a soil sample.

2. An apparatus as claimed in claim 1, wherein the housing is a tubular casing having an internal shoulder against which the driving means abuts in order to drive the housing vertically into the ground and the sample container which is attachable to the driving means is limited in its downward movement within the housing by the driving means striking the internal shoulder and thereby preventing the sample container protruding into the ground beyond the housing.

3. An apparatus as claimed in claim 2, wherein the driving means is an air displacement hammer and has a shoulder complementary to the internal shoulder of the housing against which it abuts to provide the downward driving force.

4. An apparatus as claimed in any preceding claim, wherein the housing comprises interconnectable sections which are sequentially added to the housing at ground level, thereby increasing the length of the housing below ground level as the housing is driven vertically into the ground by the driving means.

5. An apparatus as claimed in any preceding claim, wherein the driving means and sample container are winched out of the housing above ground level in order to remove a soil sample and the driving means and an empty sample container are winched into the housing to obtain a further sample.

6. An apparatus as claimed in claim 5, wherein the winch is an air-winch or a hand-winch.

7. An apparatus as claimed in any preceding claim, wherein the end of the housing which is pushed into the ground is of a slightly narrower bore than the sample container within the remaining bore of the housing.

8. An apparatus as claimed in any preceding claim, wherein the sample container has an internal diameter of 50mm.

9. An apparatus as claimed in any preceding claim, wherein the driving means has a non-return valve.

10. An apparatus as claimed in any preceding claim, wherein the housing is removable from the ground by an extractor jack.

11. An apparatus as claimed in any preceding claim, wherein the container for taking the soil sample comprises at least two sections.

13. An apparatus constructed and adapted to operate substantially as hereinbefore described, with reference to, and as illustrated in, the accompanying drawings.