Soil stabilisation

Soil stabilisation is the process of improving the engineering properties of the soil to increase its bearing capacity and hence its strength. The process involves the use of hydraulic binders such as cement, lime, lime/cement mix and pulverised fuel ash often with lime or blast furnace slag by itself or mixed with cement. This is known as additive stabilisation or chemical stabilisation. In all cases, the hydraulic additives intermingle with the soil material at the project site. Additive stabilisation rarely takes place away from the project site. 

Another type of stabilisation is mechanical stabilisation. Mechanical stabilisation is accomplished by mixing or blending soils of different gradations to obtain a material meeting the requirements. Soil blending may take place at the project site, in a central plant or in a borrowed site. 

The decision to choose between additive stabilisation or mechanical stabilisation depends on the type of soil, the cost of the resulting material including transportation cost, availability and suitability of borrowed material and the availability of the required equipment. 

It must be noted that, for the construction of a capping layer, both techniques are considered equally effective. 

In the case of the additive stabilisation process, the percentage of the hydraulic binder to be added as well as the amount of water should always be determined in the laboratory by executing CBR, M, (resilient modulus) or unconfined compressive strength tests, whichever is appropriate. 

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Potential applications for PHA include feminine hygiene products, packaging, appliances, electrical and electronics, consumer durables, agriculture and soil stabilisation, nonwovens, biomedical device adhesives, and automotive parts. 

Electrical and electronics Consumer durables Agriculture and soil stabilisation Adhesives, paints and coatings Automotive... 

UV-visible spectrophotometry enables giving indications about the pollution maturation level in contaminated soils. Stabilised leachates from old contaminated soils are characterised by a monotonous decreasing spectrum (soil A), while younger ones show a specific spectrum where additional compounds are responsible for visible accidents (soil B). 

The demand for various grades and qualities of ground quicklime has grown rapidly ever since the 1950s. Particle size requirements vary from relatively coarse products used for soil stabilisation (e.g. 99 % less than 2 mm with 50 % less than 75 pm) to very finely divided products for specialist applications (e.g. more than 99 % less than 50 pm). 

In some markets (eg the neutralisation of gaseous and aqueous acids) lime products compete with the still more expensive soda ash and caustic soda. In flue gas desulfurisation and soil stabilisation, lime products compete with limestone and other products. In building and construction the main competitive products are cement, fillers and air-entraining agents. 

Quicklimes used for lime treatment should (provisionally) meet the requirements of Types CL 70, CL 80, or CL 90 as specified in ENV 459-1 [26.18] and summarised in Table 26.2. It requires that the MgO content in building limes used for soil stabilisation should not exceed 5 % in CL 70, and 10 % in CL 80 and CL 90. In the long-term, however, [26.17] will specify the characteristics for limes used in road construction. A high reactivity, as defined in section 13.2, is an advantage when quicklime is used for drying a site. 

MgO content of up to 7% is acceptable, for uses other than soil stabilisation, if the soundness test is passed. 

A variety of binders are used for road bases and sub-bases, capping layers, soil stabilisation and soil improvement, depending on the availability of materials and local traditions. This section refers to factory blended mixtures of binders. In-situ treatment of materials, using lime and other binders is described in section 26.3. 

P.T. Sherwood, Views of the Road Research Laboratory on Soil Stabilisation in the United Kingdom , Cement Lime and Gravel 42, No. 9,1967,277-280. 

P.T. Sherwood, Soil stabilisation with cement and lime , HMSQ, London, ISBN 0-11-551-171-7. 

A considerable amount of effort has been, and still is being directed to minimising wastes from lime production. They may be blended into commercial products (e.g., lime for building, soil stabilisation, hydration and pelletisation). Such blending should be carefully controlled and the resulting products should be segregated from premium products. 

Most mechanics-of-solids textbooks analyse the necking instability that occurs in a tensile test. The analysis will be extended here to deal with products made by the stable propagation of a neck (textile fibres and the Tensar soil stabilising grids shown in Fig. 8.4). The analysis starts with two assumptions ... 

Figure 8.4 A tensile neck in a polyethylene Tensar soil stabilising grid. Curvature of the principal stress directions increases the average yield stress on the section AA.

The HBMs in the United States are called chemically stabilised material (CSM). They can also be referred to as cementitious stabilised materials. The latter is a general terminology that also covers soil stabilisation for subgrade improvement. 

The thickness removed is typically between 0.5 and 1.0 m. Suitable materials for subgrade improvement are those used for capping layer (see Section 10.3.1 for soil stabilisation, see Section 10.3.2). 

The materials for capping layer may be selected granular material or cement- and lime-stabilised material, as those described in Section 10.3.1. Soil stabilisation is also recommended to be considered, when highly cohesive soil material is encountered. For details, see Section 10.3.2. 

The absorption of polyphosphate anions is believed to take place primarily on the positively charged edges of the plate-like clay particles, although there is evidence that some absorption on the plate faces may also occur (Figure 12.13b). At the edges of the clay particles, the polyphosphate anions have easier access to the AF+ cations in the clay (Figure 5.55), which are then believed to be complexed. Under acid conditions this AP may be extracted and insoluble aluminium phosphates formed. This happens with phosphoric acid soil stabilisation (Chapter 5.1) and in the setting of some refractory cements (Section 12.10). 

Figure 56. Compressive strength development of concrete mixes of PG-BPD-BOS-ROSA 2.1.6.3. Soil Stabilisation...

Figures 57 and 58 show the strength development of the two stabilised soils at 7 and 28 days. The stabilised soil with 60% of binder incorporating ROSA (Binder-B) showed the highest strength (Figure 57), revealing the potential of ROSA for use in soil stabilisation. The mix with 50% by weight of Binder-A performed satisfactorily according to TRL recommendations. Comparison with the compressive strength of stabilised soil with no binder reveals the beneficial effect of the novel blended binders in stabilising these two types of soil.

The trial included two major works undertaken to evaluate the feasibility and perfomiance of the Coventiy Binder for use in soil stabilisation and also as a binder itself. The construction layers of the 22 metres of temporary access road were designed to compare conventional cement stabilised soil and bituminous base course layers with Coventiy Binder stabilised soil and semi-diy compacted paste (grout). Figure 98 shows the layout of the designed layers for each section of the trial access road. 

Table 45 presents the proportions of materials used for soil stabilisation and the semi-dry paste. The volume of stabilised soil needed for the site trial was estimated at 72 m (in a loose... 

A 300-mm layer of soil stabilised using Coventry Binder was placed on the prepared area. First, the soil was spread and levelled using a JCB machine (Figures 101 and 102). As the allocated area sloped, all efforts were made to spread the soil with the same thickness along the road (Figure 103). 

Admixtures are used to stabilise soils in the field, particularly fine-grained soils. The most common admixtures are lime, cement and fly ash. The main purpose of soil stabilisation is to ... 

For piled foundations, a consideration could be that settlements are not relevant as long as negative skin friction and relative deformations are taken into account. The need for limiting residual settlements to small values in the range of cm s or even mm s should always be verified thoroughly since such requirements can simply not always be met or would require excessive cost for soil stabilisation or other soil improvement techniques. 

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