GB2403964A

GB2403964A - Ground improvement

Info

Publication number: GB2403964A
Application number: GB0316859A
Authority: GB
Inventors: R A Bullivant
Original assignee: Roxbury Ltd
Current assignee: Roxbury Ltd
Priority date: 2003-07-18
Filing date: 2003-07-18
Publication date: 2005-01-19
Anticipated expiration: 2023-07-18
Also published as: EP1498550A2; GB2403964B; GB0316859D0; EP1498550A3

Abstract

Ground 26 is improved by repeated dropping of a tapered weight 10, to form depressions 30A. Additional material 32A is introduced into each depression 30A, before the weight 10 is dropped again. The additional material includes soil mixed with a ground amelioration material, such as cement or other settable binder material. The result is the formation of a body 36 of ameliorated soil, providing local ground improvement. The degree of penetration of the weight is used to indicate the ground state which has been achieved.

Description

Ground ImDrovement The present invention relates to ground improvement,

particularly, but not exclusively, prior to building.

The present invention provides a method of ground improvement in which a weight is repeatedly dropped onto the ground at substantially the same position, the weight being tapered to a downwardly facing nose which, in use, provides the point of first contact with the ground, each drop leaving a depression in the ground, and in which additional material is introduced into the depressions so formed, the additional material being fonmed by mixing at least soil and a ground amelioration material, and in which the process is repeated until the penetration of the weight indicates that a desired ground state has been achieved.

In this specification, the tenm Ground amelioration material" refers to a material which consists of, or includes, a binder capable of increasing cohesion in material such as soil. The binder may be a gettable material such as a cementitious material. Preferably, the binder is cement. Altematively, bitumen may be used as a binder. Ground amelioration material may also incorporate additional granular material such as pulverised fuel ash, and hydrophilic material such as quick lime, to assist in controlling pore pressure of the material and of the surrounding ground. The term Ameliorated soil. is used to refer to soil, preferably derived locally, into which ground amelioration material has been mixed.

Additional material is preferably introduced prior to each drop. The additional material may include lime. Preferably, the ground amelioration material includes a cementitious binder, which may be cement. The ground amelioration material may include bitumen and/or pulverised fuel ash and/or quick lime.

The weight preferably has a mass of at least 2,500 kg and may have a mass of at least 7,500 kg. The weight preferably tapers at an angle of at least 14 and preferably in the range of 14 to 20 , preferably 17 . The weight preferably has a single tip as aforesaid.

Preferably, after the desired ground state has been achieved, a further depression is fommed, at substantially the same position, and is filled with gettable material to form a structural member supported by the improved ground. The gettable material is preferably concrete.

Examples of the present invention will now be described in more detail, by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of an example of a weight for use in the method of the present invention; Figs. 2 and 3 are schematic views of the weight and the ground, before and after the weight is dropped; Figs. 4 and 5 correspond with Figs. 2 and 3, and relate to a subsequent drop of the weight; i Fig. 6 illustrates the weight being used to form a cap shown in Fig. 7; and Fig. 8 shows an alternative weight being used to form a discrete footing shown in Fig. 9.

Fig. 1 illustrates a weight 10 for use in the method of the invention.

The weight 10 has a relatively narrow nose 12 which provides, in use, the point of first contact with the ground. The device tapers down to the nose 12, over a portion 14. A clevis arrangement 16 allows the weight 10 to hang from a cable 18, so that the weight 10 may be raised by a crane (not shown), and then dropped to the ground. Below the clevis 16, a relatively wide disc 20 is arranged generally horizontally, to form a shoulder 22 around substantially the entire periphery of the weight 10. The tapering portion 14 is below the shoulder 20, when the weight 10 is hanging from the clevis 16, so that the nose 12 will be lowermost when the weight 10 is dropped, and will thus form the point of first impact with the ground.

The weight 10 preferably has a mass of at least 2,500 kg but a much greater weight, such as at least 7,500 kg may be used. The tapering portion 14 preferably tapers at an angle of at least 14 . (The angle of taper is used herein to refer to the angle between the central (vertical) axis of the weight 10, I and the outer surface of the tapering portion 14, measured at the nose 24).

14 is the so called Morse angle, generally considered the minimum angle to prevent the dropped weight sticking in the ground within the hole created by its fall. In a preferred arrangement, the taper angle will be between 14 and 20 , preferably about 17 .

Fig. 2 shows the weight 10 hanging above the ground 26. The ground 26 requires improvement. That is, the load bearing capacity of the untreated ground 26 is insufficient for the load it is required to bear, such as the foundations of a building. The method of the invention begins by dropping the weight 10 from the position shown in Fig. 2, to embed in the ground, as shown in Fig. 3. It is expected that, as shown in Fig. 3, the height of the drop will be sufficient to embed the weight 10 completely in the ground, but the shoulder 22 will assist in preventing the weight 10 being lost in the ground.

The tapered shape of the weight 10 results in ground around the weight 10 being compressed outwardly and downwardly, as indicated by the ! arrows 28. This compaction begins to improve the ground bearing capacity of the ground, at the position being treated.

The weight 10 is then removed by lifting it back to the initial raised position, ready for further dropping, as indicated in Fig. 4. This leaves a depression 30 (Figs. 3 and 4). Prior to a further drop, the depression 30 is wholly or partially filled by additional material 32 supplied from a supply indicated schematically at 34. Preferably, sufficient additional material 32 is introduced to fully fill the depression 30.

The additional material is formed, at the time or previously, by mixing at least soil and a ground amelioration material. It is particularly preferred that the additional material 32 is formed by mixing soil with a binder in the form of a cementitious material (preferably cement), and/or quick lime. Once in the ground, the binder is highly hydrophilic, which draws ground water from the surrounding ground 26, thereby reducing pore pressure within the ground 26.

The soil is preferably acquired locally, at the site, to reduce transport costs arising from the transport of soil to the site, and also to reduce the transport costs associated with the removal of waste from the site. Altemative materials for use in the ameliorated soil may include pulverised fuel ash and bitumen.

After the additional material 32 has been introduced into the depression 30, the weight 10 is dropped again and then removed, to the position illustrated in Fig. 5. This forms a further depression 30A and results in additional outward and downward compaction of the surrounding ground 26, as indicated by the arrows 28A. In addition, the additional material 32, introduced prior to the drop, will have been forced out into the surrounding ground 26, forming a body 36 of ameliorated soil around the depression 30A.

The process is then repeated again, by filling the depression 30A with additional material 32A from the supply 34, dropping the weight 10 to form a depression (not shown) and then filling the resulting depression again. It is profaned that additional material is introduced after each drop, but in some circumstances it may be appropriate to drop the weight 10 more than once, before further additional material is introduced.

The number of times the process is repeated will depend on the original state of the ground, and the desired state to be achieved. The ground state which has been achieved (i.e. the load bearing capacity of the ground, as improved by use of the method) can be checked as follows. The weight 10 is dropped from a predetermined height, thereby imparting a predetermined amount of energy to the ground beneath, as a result of the impact.

Appropriate calibration by choice of the weight and the height of the drop will define a minimum load bearing capacity for the ground to resist the dropped weight 10 from fully penetrating the ground. Thus, if the load bearing capacity has not reached the value determined by the calibration, the weight 10 will embed (in the manner illustrated in Fig. 3). If the minimum load bearing capacity has been met, or exceeded, sufficient ground resistance wil! exist to prevent the weight embedding itself and consequently, after the drop, the shoulder 22 will remain above the ground, as illustrated in Fig. 6. This provides a simple visual test of the load bearing capacity of the ground.

It is to be understood that the inclusion of binder material in the additional material 32 will result in the final load bearing capacity of the ground being even greater than this value, as the cement hardens over a period of time.

The final test drop, resulting in the situation of Fig. 6, also results in a further, smaller depression 40 being fonmed in the top of the body 42 of additional material which has previously been introduced and compacted by previous drops. After the weight 10 is removed from the depression 40, for the final time, the depression 40 is preferably filled with gettable material, preferably concrete 44. The result is shown in Fig. 7. The concrete 44 forms a load-bearing structural member (which may form part of a foundation being constructed), and is adequately supported by its location within the improved ground provided by the body 42. Furthemmore, the minimum load bearing potential of the ground below the concrete 44 is known, by virtue of the testing described above.

It is envisaged that on most sites, a plurality of positions will be treated in the manner described above, to form an array of positions at which the load bearing capacity of the ground has been locally improved, and which may also include an array of concrete caps 44.

The above description has referred to the use of the same weight 10 to provide a testing function, as illustrated in Fig. 6. Fig. 8 illustrates an alternative weight 10A, which may be used for the testing function. The weight 10A again has a nose 12A at the bottom of a tapering portion 14A, and a clevis 16A to allow the weight 10A to be hung from a cable 18A. The tapering portion 14A depends from a thick plate 46. The weight of the plate 46, relative to the weight of the tapering portion 14A is much greater than the weight of the disc 20 relative to the weight of the tapering portion 14 of the weight 10 (Fig. 1). Moreover, the dimensions of the plate 46 are chosen in conjunction with the requirements of the building foundations to be supported by the improved ground being produced. For example, the thickness (in the I vertical direction) of the plate 46 may be about 10 cm, with a horizontal extent of about 50 cm. The total height of the weight 10A, from the lowermost tip of the nose 12A, to the upper surface of the plate 46, may be about 45 cm. The weight 10A can be used for a calibrated drop, as described above, to test the load bearing capacity of the ground.

Subsequently, a final drop is made, the drop height being sufficiently high to fully embed the weight 10A, including the plate 46, in the ground 26.

The drop of the weight 10A is preferably sufficient to embed the plate 46A beyond its thickness, yielding a trench which is deeper than the thickness of the plate. This results in a depression 48 (Fig. 9) which is the same shape as the weight 10A. An upper region 48A has vertical sides fonmed by the plate 46. A lower region 48B has tapered sides and is fonmed within the body 36A of ameliorated soil.

A concrete footing 50 can then be cast in the depression 48, to provide a pad 52 supported on the ameliorated soil 36A, and located therein by a downward nose 54, integral with the pad 52. The pad 52 fonms a base on which a ground beam 53 can be supported in order to facilitate the construction of brickwork or block work 56. This results in a foundation structure of known performance, by virtue of the testing provided for the ameliorated soil 36A.

In some circumstances, it may not be necessary to use a test drop to test the load bearing capacity of the ameliorated soil. Design assumptions may have previously been made about the number of drops and their height, required to achieve the desired ground state.

Many variations and modifications can be made to the apparatus and methods described above, without departing from the scope of the present invention.

Whilst endeavounng in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it i should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon. i

Claims

1. A method of ground improvement in which a weight is repeatedly dropped onto the ground at substantially the same position, the weight being tapered to a downwardly facing nose which, in use, provides the point of first contact with the ground, each drop leaving a depression in the ground, and in which additional material is introduced into the depressions so formed, the additional material being formed by mixing at least soil and a ground amelioration material, and in which the process is repeated until the penetration of the weight indicates that a desired ground state has been achieved.

2. A method according to claim 1, wherein additional material is introduced prior to each drop.

3. A method according to claim 1 or 2, wherein the additional material includes lime.

4. A method according to claim 1, 2 or 3, wherein the ground amelioration material includes a cementitious binder.

5. A method according to claim 4, wherein the cementitious binder is cement.

6. A method according to any preceding claim, wherein the ground amelioration material includes bitumen.

7. A method according to any preceding claim, wherein the ground amelioration material includes pulverised fuel ash.

8. A method according to any preceding claim, wherein the ground amelioration material includes quick lime.

9. A method according to any preceding claim, wherein the weight has a mass of at least 2,500 kg.

10. A method according to claim 9, wherein the weight has a mass of at least 7,500 kg.

11. A method according to any preceding claim, wherein the weight tapers at an angle of at least 14 .

12. A method according to claim 11, wherein the taper is in the range of 14 to 20 .

13. A method according to claim 12, wherein the taper is substantially 17 .

14. A method according to any preceding claim, wherein the weight has a single tip as aforesaid.

15. A method according to any preceding claim, wherein after the desired ground state has been achieved, a further depression is formed, at substantially the same position, and is filled with gettable material to form a structural member supported by the improved ground.

16. A method according to claim 15, wherein the gettable material is concrete.

17. A method of ground improvement substantially as described above, with reference to the accompanying drawings.

18. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.