Laboratory Study of the Influence of Mineral Salts on Swelling ( KCl , MgCl 2 )

Swelling and shrinkage of expansive soils occur mainly due to a change in the moisture regime and pose serious problems to foundations causing damage to structures founded on them. However, construction on this type of soil requires a good companion for the recognition of identification, characterization of their swelling potential and Treatment processing. In this work we are interested by two aspects: 1) The first is on the tests recommended for the identification of diferants expansive soils in the region of Tlemcen in the north western Algeria. 2) The second is to perform stabilization tests on remolded samples by salts (KCl Potassium Chloride, Magnesium Chloride MgCl2) with deffrants concentrations and see their influence on physic-chemical parameters and swelling. The results obtained show that stabilization by the addition of salts modifies the physico-chemical characteristics of soil and the results are quite satisfactory in significantly reducing the phenomenon of swelling, as regards the effect of salt on the swelling pressure it varies from salt to another and concentration to another.


Introduction
Expansive soils are mostly found in the arid and semi-arid regions of the world.
The presence of montmorillonite clay in these soils imparts them high swell-shrink potentials (Chen, 1988).Low rainfall has hindered the weathering of the active montmorillonite mineral into low active clay types such as illite and kaolinite.Further, the rainfall has not been sufficient to leach the clay particles far enough so that the overburden pressure can control the swell.
The swelling soils are commonly known by the name of black cotton soils (Amer, 2006).For swelling to occur, these soils must be initially unsaturated at some water content.If the unsaturated soil gains water content, it swells.On the other hand, if a decrease in water content occurs the soil shrinks.
In Algeria in many cases very damaging disorders, associated with swelling have been reported.We include two pathological cases the first in the east and the second in South of Algeria: -The Hospital Sidi Aissa in Msila -The oil refinery in Ain-Amenas To resolve this problem in practice, many stabilization methods are available; we are interested in the stabilization by the addition of minerals salts.

Material Studied
The soils objects of this study are reworked clays coming from different regions of Tlemcen: bentonies of maghnia, boughrara (North West of Algeria), in an active area of swelling perspective (Figure 1).Whatever the objectives sought in geotechnical study, the rule is to make initial identification of concerned soils.This procedure is used to guide further geotechnical analysis and especially to make a classification of encountered materials.The parameters required for this classification are both physico-chemical and granulometric.
The results of all tests performed on the soils studied are listed in Table 1.

Classification Qualitative of Expansive Soils
Carry out a proper classification of expansive soils implies that the geotechnical parameters are known representative of the swelling.The problem lies in the definition of these parameters (Djedid et al., 1997).Practice has it that the pressure and the magnitude of swelling that are used to characterize expansive soils.
The literature contains a considerable number of empirical approaches that assess qualitativement the swelling potential of soils.Some authors believe this potential link to a single parameter.Thus, as shown in Table 2, below, Altmeyer, Ranganatham and Satyanarayan (Aissa et al., 2009), and Snethen (Aissa et al., 2009) propose classifications which give respectively the swelling potential depending WR, IR, IP (Table 3).

Correlation between Swelling And Physico-Chemical Parameters
To test the comparison of the classifications listed above, they have been applied to soil samples from sites of Tlemcen, The identifications are given in Table 4.
Of these classifications, there emerges the following remarks: Some classifications like that of Altmeyer tend to overestimate the swelling potential of soils as it provides all the samples as highly expansive.
The various classifications do not converge to the same qualification all the expansive potential for the same sample.
These contradictions find their explanation in the number and nature of the parameters taken into account by each of these classifications.It should be noted that the determining parameters in the expansive character of a soil are known.By cons, the influence of each parameter in this expansive is difficult to quantify.

Classification Quantitative of Expansive Soils
The literature is replete of the formulas estimate quantitatively the swelling depending on the parameters physic Chemical Type.
The table below combines the differs statistical forms that gives the amplitude and the swelling pressure according of physicochemical parameters.We note that a fur and as the number of parameters introduced increases the quality of the correlation improves.Since these models only serve to obtain approximate values, it is better to be content with his simple models one or two parameters and for reliable estimation, nothing can replace direct measurement.

Evolution of Physicochemical Characteristics
The swelling of soils is sometimes correlated with some physico-chemical parameters in order to study the influence of stabilization on these parameters, measurements of Atterberg limits and VBS were made with salts (MgCl 2 , KCl) at different percentages (0.05, 0.1, 0.2 mol/l).
Figure 2 shows the path followed by the studied soils after treatment with differs concentration of salts 0.05, 0.1, 0.2 mol/l.
We notice that the clays which high plasticity seen after treatment with salts, consistence progress to low plasticity.This change in the consistence related to the concentration of salts, translates into a decrease of plasticity index which partly due to ionic reactions of salts (KCl, MgCl 2 ) with clay minerals which causes a flocculation of the soil.
We also note a continued decrease in blue value and the index of shrinkage according to the increased concentration of salts.
Figure 2. Physics-chemical variation of the parameters according to concentration of salts

Influence of Salts on the Amplitude of Swelling and Pressure
To study the effect of salts on the swelling of studied clays, we imbibed the samples with the necessary additions (KC, MgCl 2 ) to different concentrations for testing odometer swelling.
The chosen method in this study is in accordance with standard ASTM d-4546-90-méthode A this choice is explained by the fact that the method adopted to correct the effect of realignment by applying a charge-discharge cycles, the final pressure of the cycle is the equivalent weight of the land before extraction of the sample.
Swelling of the latter, obtained by imbibitions, will follow until stabilization.The swelling pressure is equal to the pressure that would have handed the sample to its original height.The amplitude of swelling corresponds to the maximum deformation between the beginning and the end of the swelling phase (Figure 3). Figure 4 shows the evolution of swelling according to salts concentrations to the tested soil, we find that the pressure and the amplitude of swelling decreased significantly.
We note that Potassium chloride minimize swelling soils studied more then Magnesium chloride.

Evolution in Swell Potential with Concentration of Salts
The study of the swelling potential examined the natural clays and clays treated with salts that been the subject of our research.
The kinetics of obtained swelling were approached by the the hyperbolic law proposed by Dakshanamurty (1978) and Vayssade (1978): Where B is the half swelling, t is it's time; is swelling and is the final swelling.
In writing Equation 1 in the coordinate system (t, t/Δh/h) we get a straight line enabling the determination of the final potential of swelling and half-swelling.The results for the studied soils are given in Figure 5, An examination of the plots in these figure (Figure 5) shows that the variation in swelling potential corresponding to the variation of concentration of salts follows similar trends as those observed in soils tests.For untreated soils a decrease in swell behavior is observed as the concentration salts increase.

Conclusion
Based on results obtained on studied clays and in light of the interpretations of these results, a number of conclusions were made.
From simple tests performed in practically all campaigns preliminary reconnaissances, it is possible to qualitatively and quantitatively identify expansive soils and to obtain correlations from approximate estimates of swelling.
The adition of salts (KCl, MgCl 2 ) modifies the physico-chemical characteristics of treated clays and reduces its adsorption capacity.The treatment reduces the plasticity index, the blue value.
The influence of salt solutions and their concentrations, their valencies and sizes on the magnitude of swelling have a very pronounced effect.But the effect of valence is probably the determining factor in the ability to exchange or replace cations can easily replace higher cations of lower value.Magnesium chloride and potassium chloride minimize swelling soils studied the effect of reducing the swelling even in low concentrations.

Figure 1 .
Figure 1.The geographical situation of studied sites geographical situation of studied sites

Figure 3 .
Figure 3. Method of swelling according to the standard ASTM D-4546-90-method A

Figure 4 .
Figure 4. Swelling pressure and amplitude versus salts concentrations

Figure 5 .
Figure 5. Evolution of swelling potential with defferants concentration of salts

Table 1 .
Physicochemical characteristics of studied soils

Table 2 .
Empirical approaches between physicochemical characteristics and swelling

Table 3 .
Empirical approaches between physicochemical characteristics and swelling

Table 5 .
Classification quantitative of soils