Hydraulic and earth engineering – Earth treatment or control – Chemical
Patent
1996-10-21
1998-10-13
Taylor, Dennis L.
Hydraulic and earth engineering
Earth treatment or control
Chemical
106606, 106697, 106900, 405258, 405266, E02D 312, C09K 1700
Patent
active
058203028
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of stabilising soil aggregate mixtures, structures formed by said method, and compositions for use in the method.
BACKGROUND OF THE INVENTION
The term "soil" as used herein may include within its scope all unconsolidated materials above bedrock or the natural medium for growth of land plants and may also include a mixture of silt, gravel and sand. Soil may also normally contain fines which may be considered to be plastic material comprising mainly of particles having diameters less than 0.074 mm (i.e. silt) and also particles less than 0.002 mm (i.e. clay). Such particles may be colloidal particles and thus may be considered to be a loose, earthy, extremely fine grained natural sediment or soft rock characterised by high plasticity and by a considerable content of clay minerals. Clay minerals are one of a complex and loosely defined group of finely crystalline, metacolloidal or amorphous hydrous silicates essentially of aluminium and sometimes magnesium and iron. The most common clay minerals belong to the kaolin, montmorillonite (smectite) and illite groups. Clay particles may form a plastic, mouldable mass when finely ground and mixed with water which retains its shape on drying and becomes firm, rigid and permanently hard on heating.
There are many different types of soils containing varying percentages of clay. However, soils which may be used in relation to construction of structures based on soil aggregate mixtures will usually contain from 0.5-20% of clay. When soils contain higher percentages of clay e.g. black soil, such soil is usually not appropriate for forming structures.
Aggregate which includes crushed rock or stone may be naturally present in admixture with the soil or may be added to the soil for construction of structures which may include road pavements, wall structures or other building products. In relation to construction of the abovementioned structures cement may be mixed with soil aggregates to strengthen the resulting substrate caused by hydration of the cement at a "macro" level to bind the soil aggregate into a resulting stabilised matrix.
Tests known as "Atterberg Tests" are carried out on all soil aggregates to determine their physical properties to indicate the likely percentage required of the cement additive and ratios required to achieve a target strength for the soil aggregate structure. Further tests that may be carried out include California Bearing Ratio (CBR) which measures the degree of penetration into the soil of a standard weight and Unconfined Compressive Strength (UCS) which measures the degree of compression of the soil after mechanical compaction.
The Atterberg Tests may follow an initial procedure which includes passing the soil through a 75 micron sieve to determine the fines component of the soil wherein the fines are defined as finely divided particles having a diameter of 0.074 mm or less.
A linear shrinkage (LS) test may then be carried out wherein soil at optimum moisture content (OMC) is placed into a standard mould and cured (i.e. dried out). The amount of shrinkage observed thereby determines the linear shrinkage i.e. (LS).
The "optimum moisture content" is defined as that moisture content at which soil achieves maximum dry density (MDD) using standard compaction effort e.g. by usage of a proctor hammer.
The conventional procedure therefore in ascertaining the amount or percentage of cement required to be added to the soil aggregate in relation to road pavements for example was to determine the LS result and subsequently carry out a series of CBR and/or UCS tests and from these results determine by linear interpolation the amount of cement additive required.
Generally in relation to road pavements the amount of cement required was proportional to the LS value of the soil sample. For example, in general terms, a cement percentage of 2-3% would correspond to a LS of 4-5 and the maximum cement additive utilised was 5-8% corresponding to an LS of the soil sample of 10-12. In this regard the pe
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Atkinson Peter
Calos Nicholas James
Oliver David Lethbridge
Roberts Michael Stephen
AD-Base Pty Ltd.
Taylor Dennis L.
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