17-12-2012, 05:42 PM
Reducing the Expansion of Clays through Lime Stabilization and Overloading
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ABSTRACT:
Expansive clay soils are present in many regions of Mexico and throughout the
world. They pose a major problem for the construction industry due to the volumetric changes
associated to humidity variations that cause fissures in pipes, foundations, and structures. Although
there are different solutions to this problem, most of them do not approach the contribution of
structure overloads in reducing soil expansion. In such circumstances the aim of this research is to
study the reduction of volumetric changes in expansive soils generated by the action of natural clays
stabilized with lime as well as the effect of utilizing overloads transferred by the structure, and the
simultaneous application of both solutions to the problem, which consequently will also reduce the
stabilization cost. After completing the project it was concluded that the overload that reduces
significantly the expansion (approximately 1.5%) of this particular soil (clay of high
compressibility) without lime stabilization is of 8 Ton/m2. On the other hand, 6% lime (regardless
of overloads) in relation to dry weight also reduces the expansion. When applying both solutions
simultaneously (overload and lime stabilization) it was found that the overload actually contributes
to reducing the soil expansion with the resulting combinations of 2 Ton/m2 with 4% lime in relation
to dry weight, and 4 Ton/m2 with 2% lime in relation to dry weight.
INTRODUCTION
Expansive soils pose many problems when building on them. This, because when the water content
increases, the soil swells, and when it shrinks the ground collapses in both cases causing fissures in
the constructions.
Lime treatment is one of the many options for improving existing expansive soils. However, it is
usually determined and applied in dosages that do not take into account the factor of construction
overloads of the structure to be placed on them. Lime stabilization is a very common method used
to reduce the expansion potential of so-called expansive soils.
This research seeks, therefore, to reduce the specified percentage of lime added to the soil while
simultaneously applying gradually increasing overloads in order to find – as far as possible – the
optimal combination of both to reduce the expansion.
The city of Querétaro, in the state of Querétaro, Mexico, is predominantly built on clay soil with a
significant presence of montmorillonite, around 40% (Zepeda, 1989). The region’s climate is
semiarid, which causes the soil to be subject to significant moisture changes—dehydration in times
of drought and hydration in the rainy season. As other regions of Mexico, the Bajio, which is
located in the central part of the country, offers similar conditions (Zepeda, 2004).
Part of the problem of the deficient performance of foundations built on expansive soils lies in
ignoring the nature of the soil, its behavior, and the influence of environment and human actions
(Bowels, 1988).
RESULTS AND DISCUSSION
Table 1 shows the meassures of the index properties (Atterberg Limits and specific gravity of solid)
of the natural soil stabilized with lime. The maximum dosage of lime is determined, once the index
properties have stopped decreasing. The identification of the natural soil stabilized with lime
according to the Unified Soil Classification is performed in conjunction with the Plasticity Chart.
CONCLUSIONS
• For this particular expansive soil (clay of high compressibility), the lime content,
regardless of overloads, reducing the soil expansion is 6% in relation to its dry weight.
Also, the overload that reduces the soil expansion significantly (1.5%), without
stabilizing it with lime, is of 8 Ton/m2, although it is likely that 10 Ton/m2 will reduce
the expansion to values less than 1%.
• In the implementation of both solutions (overloads and lime stabilization) it is found that
the overload actually contributes to the stabilization of soil expansion when decreasing
the dosage of lime determined (6%), resulting combinations of 2 to 4 Ton/m2 with 4%
lime in relation to dry weight, and 4 Ton/m2 with 2% lime in relation to its dry weight.
• Consequently, this translates into cost savings as it reduces the amount of lime used due
to the utilization of the overload under discussion. Besides, there are alternatives to using
both solutions.
• Additionally, it was found that by increasing the lime added to the soil; the conditions of
optimum humidity and maximum specific weight of the natural soil are also modified.
Thus, it is noted that to a higher content of lime (in the range of the studied dosages of 2,
4 and 6%), the specific weight decreases while the humidity increases.