GB2277545A - Soil stabilization and consolidation method and compositions - Google Patents

Abstract

A method of consolidating soil to form a water-shedding, load-bearing surface layer thereon which comprises the steps of mechanically intermingling a moist loose soil layer of suitable depth, previously permeated with an aqueous soil-preconditioning liquid having (a) surfactant and/or (b) synthetic or natural resin latex dispersed therein and preferably also a co-solvent, with a dry soil-consolidation powder which comprises discrete particles of a finely-particulate mineral substrate having a particle size not greater than 1,000 microns which have been substantially completely coated with a silane, and preferably thereafter enrobed with hydrogenated alkyl stearamide wax(es), compacting the resultant soil layer to form the desired surface contour, and allowing the thus-treated and compacted soil layer to dry out. The soil-preconditioning liquid preferably is an aqueous dispersion of alkyl quaternary ammonium chloride(s) and natural rubber latex solubilized with isopropanol as co-solvent. The soil-consolidation powder is preferably P.F.A. of 20 - 30 microns particle size coated with dimethyl dichloro methane and thereafter enrobed with up to 6% of hydrogenated alkyl stearamide wax(es). The method and compositions permit easy, quick road-making operations on virtually any soil except peat without major earth-moving operations.

Description

SOIL STABILISATION AND CONSOLIDATION METHOD AND COMPOSITIONS This invention is concerned with a method of consolidating soil, so as to form a water-shedding, load-bearing surface layer thereon, and it also relates to compositions for use in that method.

For the avoidance of doubt, the term "soil" is used herein broadly, not narrowly - so as to embrace (as the context allows) all kinds of earth or ground (with the exception of essentially vegetable matter such as peat) to be found at or immediately below the land-surface, thus both top-soil and sub-soil whether cultivable or barren... but of course it does not extend to massive formations, such as rock, which are not in need of stabilisation and consolidation; nor indeed does the term embrace matter of essentially vegetable origin, e.g. peat, since that is the one thing which we have so far found to be incapable of consolidation by the procedures of this invention.

The transportation of goods and indeed even people is dependent, more than one might at first suppose, upon man's ability to construct roads and other watershedding, load-bearing surfaces across the earth's terrain. Road-making was indeed one of the most fundamental skills possessed by the Romans and for which they are admired and remembered still today.

Though the methods devised by the Romans or perhaps still older peoples have been modernized and updated very greatly, still today the fundamental principles of road-making are much the same as ever they were - one must remove the top-soil, find or create firm, welldrained sub-soil, build upon it an infra-structure which is capable of simultaneously sustaining the point-loading which it is designed to carry and also spreading that load widely over the sub-soil foundation, and then impart a water-shedding surfaceskin over the infra-structure which prevents rain or other water seeping down through the infra-structure into the underlying sub-soil thereby impairing its load-bearing ability, and which instead sheds the water to one or both sides of the roadway where it cannot harm the load-bearing capacity of the whole construction, and indeed is usually carried off and drained away.

Whether roads are made by hand-labour or by roadmaking machinery, it is the conventional wisdom of the ages that proper road-making requires removal of top soil to attain a firm base in well-drained sub-soil if the resultant roadway is to withstand frequent use over a prolonged period of time - and the construction of roadways (or any similar kind of hard-standing for wheeled vehicles) therefore currently necessitates huge earth-moving operations which are time consuming and highly-expensive in terms of labour-input and/or investment in machinery... and which even then can have an additional problem in the disposal of the spoil removed from the site.It is considerations of these kinds which tend to restrict extensive road-making activities to the more developed countries in the world, leaving the under-developed countries bereft of the road systems which perhaps would do more than anything else to promote their development. And yet...

untold centuries of ingrained habit of thought and action seem to have left the world with an unquestioning acceptance that effective road-making can only be done in the old-fashioned way described above.

We however have found, at first by happy accident and thereafter by prolonged and laborious trial and error, that by suitable treatment it is possible to consolidate at least many kinds of top soil (or indeed sub-soil, if brought to the surface) into a watershedding, load-bearing surface layer which makes it easily possible to form roadways and other hardstanding for wheeled vehicles, horses, farm animals and pedestrians with a minimum of soil-disturbance, usually without any necessity for major soil-removal and disposal, and yet thereby to create roadways & . which (on the evidence which we have secured over the period of our investigations) show every prospect of being enduring. The treatment involved is moreover relatively inexpensive, and certainly far less costly and also much, much quicker than conventional roadmaking techniques.

It appears that our new method and of course the compositions which are used in it therefore open the way to the construction of roads and other forms of hardstanding in places for instance in under-developed countries where roads are badly needed but economics have till now debarred their construction, while of course a technique good enough in such places will also find ample use in well-developed countries.

According to one aspect of this invention we provide, in a method of stabilising and consolidating soil to form a water-shedding, load-bearing surface layer thereon, the steps of: - optionally but usually first loosening the surface of the soil and thereby or otherwise securing a loose soil layer having a depth commensurate with the desired thickness of the water-shedding, load-bearing surface layer to be formed; - if desired adjusting the moisture content of the loose soil layer into approximately a known or predetermined optimum range for subsequent compaction by permeating it as necessary with water or with an essentially aqueous preconditioning liquid, advantageously one containing surfactant and/or dispersed natural and/or synthetic elastomeric resin latex in an essentially aqueous continuous phase optionally also containing a water-miscible organic cosolvent;; - mechanically intermingling the moist loose soil layer with a dry soil-consolidation powder which apart from impurities comprises discrete particles of a mineral substrate having a particle size usually not greater than 1 ,000 microns which have been substantially completely coated with a silane, and optionally but very preferably also enrobed with up to 6% by weight of hydrogenated alkyl tallow stearamide wax(es); - thereafter rolling, tamping or otherwise compacting the resultant soil layer to form the desired surface contour; and - allowing the thus-treated and compacted soil layer to dry out.

The initial step of loosening the surface of the soil is optional in the sense that some soils, e.g.

those of a light sandy nature, might be already loose enough for subsequent treatment, but save in such exceptional circumstances it is a practical necessity so as to ensure thorough and even incorporation of subsequently applied materials.

The adjustment of the moisture content of the loose soil layer by adding water thereto so as to bring it into an optimum range for subsequent compaction is a technique already well-understood by those concerned with the construction of temporary earth-tracks, e.g.

the military, and needs no further explanation here.

It is however a much preferred feature of this invention to moisten the loose soil layer not merely with water but with a specially-formulated aqueous preconditioning liquid which, as previously indicated, contains latex and/or surfactant. The latex in the pre-conditioning liquid is believed to adhere to the soil particles, and promote their subsequent networking with the subsequently-incorporated (preferably waxenrobed) silane-coated mineral particles. The surfactant is believed to assist even permeation of the loose soil by other added components.

While synthetic elastomeric resins can be made to work, we have found that (for reasons we do not understand) it is highly preferable that the elastomeric resin latex which is desirably present in the pre-conditioning liquid should consist of or include a natural rubber in the form of its latex.

In our experience it is very desirable that a surfactant should be employed in the pre-conditioning liquid, and while so far as we have yet ascertained any anionic, amphoteric or cationic surfactant (or compatible mixtures thereof) may be used we prefer that the pre-conditioning liquid should be or include a cationic surfactant, advantageously a quaternary ammonium surfactant, and above all an alkyl quaternary ammonium chloride cationic surfactant.

It is in fact a highly preferred feature of this invention adequately to permeate the loose soil layer with an essentially aqueous pre-conditioning liquid which comprises both elastomeric resin latex and a surfactant, and in that event of course the surfactant assists to keep the resin solids dispersed as a stable suspension or emulsion in the essentially aqueous continuous phase. It appears at present that the relative proportions by weight of resin dry solids to surfactant can advantageously lie in the range of from 1 : 10 to 1 : 50.

Although the pre-conditioning liquid must (if only for economic reasons) be essentially aqueous it can nevertheless usefully include a water-miscible solvent, normally a polar solvent such as an alcohol e.g.

isopropyl alcohol, to serve as co-solvent and presumably thereby assist in establishing and maintaining the desired fine dispersion of the surfactant and the latex emulsion, and prevent it from coagulating.

The soil-consolidation powder employed should be as fine a powder as is conveniently possible, in order to facilitate its application to the soil and nearuniform incorporation therein. So far as we can determine at present the particle size of the powder should not exceed about 1,000 microns. It is in fact greatly preferred that the overall size of the particles in the powder employed should not to any significant extent exceed 100 microns. We currently find it advantageous to employ a powder with a sizedistribution up to about 100 microns but consisting predominantly of particles with an average particle size distribution in the range of from about 20 to about 30 microns.

The mineral particles must be substantiallycompletely and substantially-homogeneously coated with a silane, to render them hydrophobic. We believe that in principle any conveniently-available alkyl halo silane may be employed for this purpose. During the silane-coating operation there appears to be a reaction between the silane and the mineral particles (at least in the case of the preferred mineral particles identified hereinafter) which results in the evolution of the corresponding halo-acid gas. For reasons of both economy and pollution control we therefore usually prefer to employ alkyl chloro silanes. Currently we find it usually advantageous to use lower (C1 -C6) alkyl chloro silanes.There are a number of such lower alkyl chloro silanes which are commercially available and may be employed, including for instance trimethyl chloro silane and various butyl chloro silane(s), especially tert. butyl trichloro silane. We currently prefer to use dimethyl dichloro silane.

Since the mineral particles are intended and believed to be substantially completely silane-coated, it is assumed that it is the coating of silane which imparts the necessary properties to them and that therefore the nature of these mineral particles is more or less immaterial, and that they serve the function only of a carrier for the silane-coating. Accordingly we know of no technical limitation on the nature of the mineral substrate particles which are subsequently silane-coated. For economic reasons the mineral powder employed should however be readily available and cheap.

A variety of partly- or wholly-siliceous materials therefore come to mind, and above all waste byproducts. We greatly prefer at present for both economic and technical reasons to employ powdered flyash (P.F.A.).

As is well-known, fly-ash is the very fine ash produced by combustion of powdered coal with forced draught, recovered for reasons of pollution control from the flues of e.g. coal-burning electric powergeneration stations, usually with some difficulty by for instance electrostatic precipitators, and is a waste by-product of power-generation containing considerable percentages of CaO, MgO, silica and alumina. These materials may for instance be purchased from either National Power or PowerGen in the United Kingdom. We have found them highly suitable, both technically and economically, for use in this invention. It may be mentioned that while the exact composition of fly-ash may vary from one source to another, we have used fly-ash from different sources without observing any difference in its effectiveness for our purposes.

Reasonable results can be secured without further treatment, but far superior results are obtained and it is therefore a much preferred feature of this invention if the silane-coated particles are also thereafter treated with up to 6% by weight of one or more hydrogenated alkyl tallow stearamide wax(es). The effect of such wax treatment seems to be to enrobe the silane-coated particles with either a continuous or semi-continuous adherent film of the wax, or perhaps a scattering of discrete adherent wax globules.

The wax-enrobement treatment must be carried out after the silane-coating treatment and for reasons of production convenience and economy it is obviously preferable that the wax-enrobement treatment should be carried out as a second-stage operation in the same equipment as that employed in the first stage silanecoating operation.

The currently-preferred waxes are hydrogenated alkyl tallow stearamides. We have succeeded in applying such waxes emulsified (above their melting temperature) in water, but for both technical and economic reasons this is not recommended. In our experience the wax-enrobement of the silane-coated particles is best performed by spraying the molten wax(es) at a temperature a little above their melting point, e.g. at about 600C, in a finely-atomized spray directly onto the silane-coated particules.

The mechanical intermingling of the dry soilconsolidation powder with the moist, loose soil layer may be accomplished in any convenient way, even by hand - but for practical purposes when treating any significant area of terrain and where such machinery is available it is usually best accomplished by the use of conventional rotary cultivators (or 'rotavators") as widely employed these days in agriculture and horticulture. Since the more uniformly the powder is incorporated in the soil the better, it may be desirable to subject the powder-treated soil to several passes of such rotavation.

The compaction of the powder-treated soil by rolling, tamping or otherwise is important to the quality of the ultimate water-shedding, load-bearing surface thus constructed, but it is essentially conventional in nature and need not be further here described. If any particular contour must be imparted to the ultimate surface, eg. a road-camber, that should be done at this stage.

It is only after the compacted and optionally contoured surface layer has dried out that the desired water-shedding load-bearing surface is fully achieved.

The time required to reach the dry state depends on various factors, including the moisture-content of the compacted surface layer, prevailing atmospheric conditions and especially the ambient temperature and/or humidity of the local climate, as well as perhaps whether any special steps are taken to accelerate drying.

According to another aspect of this invention we also provide a pre-conditioning liquid for use in the method herein disclosed which liquid comprises natural or synthetic elastomeric resin held by a surfactant in a stable emulsion in a predominantly aqueous substrate optionally also containing a polar co-solvent.

As previously indicated in more detail, the elastomeric resin preferably is or includes natural rubber, and the proportion of elastomeric resin solids to surfactant advantageously lies in the range of from 1:10 to 1:50. Again, the surfactant employed desirably is or includes a cationic surfactant, conveniently a quaternary ammonium surfactant, and above all an alkyl quaternary ammonium chloride. It is preferable if the pre-conditioning liquid includes a water-miscible solvent, conveniently a polar solvent such as an alcohol, to serve as co-solvent; and the alcohol may conveniently be isopropyl alcohol.

In another aspect of this invention we also provide a dry soil-consolidation powder for use in the method herein disclosed, which powder comprises discrete particles with an overall particle size usually not greater than 1 ,000 microns, preferably in the range of up to 100 microns, of silane-coated mineral particles, desirably thereafter wax-enrobed with up to 6% by weight of one or more hydrogenated alkyl tallow stearamide wax(es).

As previously explained, it is a much preferred feature of this invention that the subsequently silanecoated and wax-enrobed mineral particles should consist of or include fly-ash.

The particles must be substantially-homogeneously coated with a silane, preferably with an alkyl chloro silane and above all with dimethyl dichloro silane.

The silane-coated mineral particles are advantageously then enrobed in up to 6% by weight of one or more hyudrogenated alkyl tallow stearamide wax(es).

The average size of the particles of wax-enrobed silane-coated mineral in the soil-consolidation powder will desirably be in the range of from 20 to 30 microns.

In order that the invention may be well understood it will now be described in more detail, though only by way of illustration, with reference to the following examples: Example A: Preparation of a Soil Pre-Conditioning Liquid Concentrate First, 5 parts by weight of natural rubber latex (as a 60% dry solids natural rubber emulsion in water) were added and thoroughly mixed into 50 parts by weight of water until a consistent, fully-dispersed more dilute emulsion (containing 5.66% dry rubber solids) was thus obtained.

Separately, 20 parts by weight of an alkyl quaternary ammonium chloride cationic surfactant (namely Arquad 2 HT-75, believed to be di- (hydrogenated-tallow) dialkyl ammonium chloride] were added and thoroughly mixed into 100 parts by weight of water at a temperature of 600C until fully dispersed therein, and to keep the di-(hydrogenatedtallow) dialkyl ammonium chloride in suspension at ambient temperatures and to prevent it from precipitating or coagulating 16 parts by weight of isopropyl alcohol were added to the surfactant.

The previously-prepared latex solution was then added and stirred into the stabilized surfactant solution, followed by a further quantity of water sufficient to bring the resulting liquid concentrate up to 200 parts by weight.

The final composition of the resulting liquid concentrate was as follows: Parts Component by weight (Percentage) Natural rubber (dry solids) .... 5 (2.5%) (Alkyl quaternary ammonium chloride cationic surfactant) .. 20 (10%) Isopropyl alcohol .............. 16 (8%) Water .......................... 159 (79.5%) 200 (100 %) This liquid concentrate was then stored in drums until required for use.

Example B: Preparation of a Soil-Consolidation Powder First, 10 parts by weight of dimethyl dichloro silane (SiMe2Cl2) were intimately mixed with 90 parts by weight of very slightly moist "dry" powdered fly-ash (P.F.A.) having a mean particle size of about 30 microns, by spraying it onto the fly-ash while agitating the latter in a trough, ribbon-blade blender for a period of 1 hour at ambient temperature, thus until near-enough every fly-ash particle is substantially uniformly and completely coated with the silane and rendered hydrophobic thereby. A slight moisture content, of less than 1% is ussually necessary in order to initiate the situation reaction between the silane and the P.F.A., but one should use as little moisture as possible as otherwise there will be a wastage of the silane.

The rate of addition of the silane to the powdered fly-ash was such that the exothermic reaction which appears to take place between the silane and the flyash did not significantly raise the temperature of the reaction mixture above ambient temperature, and the ribbon blade blender was vented to allow escape of the HCl-gas evolved in the reaction. The vented HCl-gas was passed through a water-trap (or it can be scrubbed in any other suitable manner) to recover hydrochloric acid therefrom and thereby prevent pollution of the atmosphere and neighbouring environment. Completion of the silane-coating of the fly-ash particles was monitored by determining when HCl-gas evolution ceased.

Since the chlorine content of the SiMe2Cl2 is substantially completely eliminated as HCl-gas, only about 45% of the original silane remains coated on the P.F.A. particles, so that there are about 95.5 parts of silane-coated fly-ash thus obtained.

Subsequently 3 parts by weight of hydrogenated alkyl tallow stearamide wax(es) were melted and raised to 600C, and the molten wax was then sprayed by pump in a fine mist onto the silane-coated fly-ash while continuing agilation in the trough ribbon-blade blender to ensure intimate mixing until enrobement has taken place.

The initial result of this procedure is a weakly coherent granulate of wax-enrobed, silane-coated flyash particles, but agilation of the resultant granulate is continued until it is restored to a fine powder.

The resultant dry, fine powder consists of waxenrobed silane-coated fly-ash particles having a mean overall particle size of 30 microns.

Finally 1 part by weight of the wax-enrobed silane-coated fly-ash is taken to be blended with a further 4 parts of dry powdered fly-ash. This operation is carried out in a trough mixer. This forms the desired soil consolidation powder having a final composition as follows: Parts by Approximate Component weight (Percentage) Dry fly-ash powder .......... 472.00 (98.23%) Dimethyl dichloro silane .... 5.50 (1.14 %) Hydrocarbon wax ............. 3.00 (0.63 %) 480.50 (100 %) The resultant blend of fly-ash with wax-enrobed, silane-coated fly-ash constitutes the finished soil consolidation powder, which is bagged and stored ready for use.

Example C: Preparation of an alternative Soil-Consolidation Powder The procedure of Example B was repeated, using however at the outset a different silane namely trimethyl chloro silane (SiMe3Cl) in a reduced proportion of only 5.6 parts by weight thereof in conjunction with a correspondingly increased proportion of 94.4 parts by weight of the fly-ash.

Example D: Stabilization of Soil A stretch one metre wide and eight metres long of Essex clay top-soil was rotavated to a depth of about 150 mm until a fairly fine tilth was thus obtained.

1 litre of the pre-conditioning liquid concentrate prepared as described in Example A above were diluted with tap water to a final dilution of 1 litre of concentrate per 20 litres of the diluted composition.

The dilution was then sprayed copiously onto the tilth formed by the rotavation, until it had thoroughly soaked into and permeated the rotavated soil.

Then the soil-consolidation powder prepared as described in Example B above was dusted as evenly as possible across the surface of the rotavated and permeated soil, at a rate of approximately 3 kg per square metre. The soil thus treated was then again rotavated so as thoroughly to intermingle the powder on its surface with the underlying soil.

Finally the now fully-treated soil was compacted and consolidated by rolling and/or tamping, as most convenient.

After the stretch of soil had been thus treated and consolidated, it was found to be capable (on a summer's day in a temperature climate) of bearing the weight of a man without permanent indentation after only 5 minutes from completion of the treatment, and to be able to bear the weight of an unladen 3-ton truck, without permanent indentation, no more than 24 hours after the end of the treatment.

The time taken depended on the moisture content of the soil and the rate of evaporation. The quicker the moisture dried out of the treated soil the quicker the permanent stabilisation was achieved. Once the stabilised soil had dried out, subsequent rain further improved the stabilised surface.

Claims (41)

1. In a method of consolidating soil to form a watershedding, load-bearing surface layer thereon, the steps of: - mechanically intermingling a moist loose soil layer having a depth commensurate with the desired thickness of the water-shedding, load-bearing surface layer to be formed thereon with a dry soilconsolidation powder which apart from impurities comprises discrete particles of a finely-particulate mineral substrate having a particle size not greater than 1 ,000 microns which have been substantially completely coated with a silane; - thereafter rolling, tamping or otherwise compacting the resultant soil layer to form the desired surface contour; and - allowing the thus-treated and compacted soil layer to dry out.

2. A method as claimed in claim 1, in which mechanical intermingling of the moist soil layer with the dry soil-consolidation powder is effected by one or more passes of a rotary cultivator over the powdercovered moist loose soil layer.

3. A method as claimed in claim 1 or claim 2, in which the particle size of the particulate mineral substrate in the soil-consolidation powder does not significantly exceed 100 microns.

4. A method as claimed in any of the preceding claims, in which the mean particle size of the particulate mineral substrate lies in the range of from 20 to 30 microns.

5. A method as claimed in any of the preceding claims, in which the particulate mineral substrate is or includes fly-ash.

6. A method as claimed in any of the preceding claims, in which the discrete particles of the mineral substrate are substantially completely and homogeneously coated with one or more alkyl halo silane(s).

7. A method as claimed in claim 6, in which the silane coating is formed of alkyl chloro silane(s).

8. A method as claimed in claim 6 or claim 7, in which the silane coating is formed of lower (C1 - C6) alkyl halo silane(s).

9. A method as claimed in any of claims 6 to 8, in which the silane employed to form the silane-coating is or includes dimethyl dichloro silane.

10. A method as claimed in any of the preceding claims, which includes the preliminary step of loosening the surface of the soil to secure a loose soil layer having a depth commensurate with the desired thickness of the water-shedding, load-bearing surface layer to be formed.

11. A method as claimed in any of the preceding claims, which includes the preliminary step of adjusting the moisture content of the loose soil layer into an optimum range for subsequent compaction.

12. A method as claimed in any of the preceding claims, which includes the preliminary step of permeating the loose soil layer with an essentially aqueous pre-conditioning liquid containing (a) surfactant and/or (b) natural and/or synthetic elastomeric resin latex, dispersed in an essentially aqueous continuous phase.

13. A method as claimed in claim 12, in which the preconditioning liquid contains both surfactant and elastomeric resin latex in a weight ratio of resin dry solids to surfactant lying in the range of from 1 : 10 to 1 : 50.

14. A method as claimed in claim 12 or claim 13, in which the surfactant employed in the pre-conditioning liquid is or includes a cationic surfactant.

15. A method as claimed in claim 14, in which the cationic surfactant is a quaternary ammonium surfactant.

16. A method as claimed in claim 15, in which the surfactant is or includes an alkyl quaternary ammonium chloride cationic surfactant.

17. A method as claimed in any of claims 12 to 16, in which the essentially aqueous pre-conditioning liquid includes a water-miscible co-solvent.

18. A method as claimed in claim 17, in which the water-miscible co-solvent is or includes a polar organic solvent.

19. A method as claimed in claim 18, in which the cosolvent is or includes an alcohol.

20. A method as claimed in claim 19, in which the cosolvent is or includes isopropyl alcohol.

21. A method as claimed in any of claims 12 to 20, in which the elastomeric resin latex employed is or includes natural rubber latex.

22. A method as claimed in any of the preceding claims, in which the silane-coated mineral substrate particles are also treated to enrobe them with up to 6% by weight of one of more hydrogenated alkyl tallow stearamide wax(es), in the form of a continuous or discontinuous film or globule-scattering of said wax(es) thereon.

23. A method as claimed in claim 22, in which the wax(es) employed have a melting point not exceeding 600C, and the enrobement treatment is effected by spraying the wax(es) in molten condition in a finelyatomized mist directly onto the silane-coated particles under agilation.

24. In a method of consolidating soil to form a watershedding, load-bearing surface layer thereon, the steps of: - loosening the surface of the soil to secure a loose soil layer having a depth commensurate with the desired thickness of the water-shedding, load-bearing surface layer to be formed thereon; - adjusting the moisture content of the loose soil layer into an optimum range for subsequent compaction, by permeating it with an essentially aqueous pre-conditioning liquid containing both surfactant and dispersed natural rubber latex in an essentially aqueous continuous phase also containing a polar organic co-solvent;; - mechanically intermingling said moistened, loose soil layer with a dry soil-consolidation powder which comprises discrete particles of fly-ash having a particle-size of up to 100 microns substantially completely coated with a lower (C1 6) alkyl chloro silane, and thereafter enrobed with a continuous or discontinuous film or globule-scattering of up to 6% by weight of one or more hydrogenated alkyl tallow stearamide wax(es); - thereafter compacting the thus-moistened soil and intermingled soil-consolidation powder to form the desired surface contour; and - allowing the thus-treated and compacted soil layer to dry out.

25. A method of consolidating soil to form a watershedding, load-bearing surface layer thereon, substantially as herein described.

26. A soil-consolidation powder, for use in the method claimed in any of the preceding claims, which apart from impurities comprises discrete particles of a finely-particulate mineral substrate having a particle size not greater then 1 ,000 microns which have been substantially completely coated with a silane.

27. A soil-consolidation powder as claimed in claim 26, in which the particle size of the mineral substrate does not significantly exceed 100 microns.

28. A soil-consolidation powder as claimed in claim 26 or claim 27, in which the particulate mineral substrate is or includes fly-ash.

29. A soil-consolidation powder as claimed in any of claims 26 to 28, in which the discrete particles of the mineral substrate are substantially completely and homogeneously coated with one or more alkyl halo silane(s).

30. A soil-consolidation powder as claimed in any of claims 26 to 29, in which the silane(s) coating is formed of alkyl chloro silane(s).

31. A soil-consolidation powder as claimed in any of claims 26 to 30, in which the silane(s) coating is formed of lower (C1 - C6) alkyl halo silane(s).

32. A soil-consolidation powder as claimed in any of claims 26 to 31, in which the silane(s) coating is or includes dimethyl dichloro silane.

33. A soil-consolidation powder, for use in the method claimed in any of claims 1 to 25, substantially as herein described.

34. A soil pre-conditioning liquid, for use in the method claimed in any of claims 1 to 25, which comprises both surfactant and elastomeric resin latex in a weight-ratio of resin dry solids to surfactant lying in the range of from 1 : 10 to 1 : 50 dispersed in an essentially aqueous continuous phase also containing a water-miscible co-solvent.

35. A pre-conditioning liquid as claimed in claim 34, in which the surfactant is or includes a cat ionic surfactant.

36. A pre-conditioning liquid as claimed in claim 34 or claim 35, in which the cationic surfactant is or includes a quaternary ammonium chloride surfactant.

37. A pre-conditioning liquid as claimed in any of claims 34 to 36, in which the water-miscible co-solvent is a polar organic solvent.

38. A pre-conditioning liquid as claimed in claim 37, in which the polar organic solvent is or includes an alcohol.

39. A pre-conditioning liquid as claimed in claim 38, in which the alcohol is or includes isopropyl alcohol.

40. A pre-conditioning liquid, for use in the method claimed in any of claims 1 to 25, substantially as herein described.

41. A soil-consolidation kit, for use in the method claimed in any of claims 1 to 25, said kit comprising a dry soil-consolidation powder (optionally in concentrate form, for dilution with additional particulate mineral substrate before use) as claimed in any of claims 26 to 33 in conjunction with an aqueous soil pre-conditioning liquid (optionally in concentrate form, for dilution with additional water before use) as claimed in any of claims 34 to 40.