Study of Curing Time Of Stabilized Soils

T. López-Lara

Posgrado de Ingeniería, Universidad Autónoma de Querétaro
Cerro de las Campanas SN, CP 76010, Santiago de Querétaro, Querétaro, México
e-mail: lolte@uaq.mx

J. B. Hernández Zaragoza, G. R. Serrano Gutierrez

Posgrado de Ingeniería, Universidad Autónoma de Querétaro
Cerro de las Campanas SN, CP 76010, Santiago de Querétaro, Querétaro, México
e-mail: bosco@uaq.mx and rsguti@uaq.mx, respectively.

V. Castaño M.

Instituto de Física Aplicada y Tecnología Avanzada,
Universidad Nacional Autónoma de México, AP 1-1010, Santiago de Querétaro, Querétaro, México
e-mail: meneses@servidor.unam.mx

 

ABSTRACT

Stabilization of expansive clay soils treated with Lime is an effective method, its aim being to diminish, as much as possible, volumetric changes when these types of soils are in contact with water. However, in the curing stage, whose objective is to maintain hydrated the mixture soil-lime for a given time, it is generally recommended to do it for eight or more days, thus, this method is commonly discarded. Because of the above, in this work, the study of curing time of stabilized expansive soils with lime is reported. Different water contents and times of initial curing were considered for determining the optimum curing time. Clearly, this will reduce costs and maybe will be more attractive its application.

Keywords: Curing, expansive clays, soil stabilization, lime, soil treatment, clays, expansive soils, lime stabilization.

 

INTRODUCTION

Because of the problems related to expansive soils, there exists different solutions for foundations, among others, one can mention soil volumetric stabilization using Lime. Experiences of soil stabilization reported in the literature, are generally related to roads and highways (Hernandez, 1992). However, expansive clays have given rise to many damages at homes, some of them ending in partial or total destruction. Most of the construction entrepreneurs know the effectiveness of soil stabilization with Lime. This technique has been applied very little as a solution to foundations on expansive soils. This could be due to the un-knowledge of some aspects on its behaviour and construction procedure, which is mostly empirical. The recommended procedure, generally accepted for construction, for a stabilization of clay soil, once the optimum percentage of Lime has been determined, is to realize it by layers of thickness equal to or less than 15 cm in the sequence followed: Escarification and pulverization, Lime sparse, Preliminary mixture and humidification, Initial curing, Final mixture and powdering, Compactness and Final curing.

Regarding the Initial curing, is generally recommended to do it for eight or more days before its compactness which, in turn, has an effect on costs, time and thus, this method is commonly discarded (López-Lara, 1998).

Because of the above mentioned, in this research, the behaviour of a compacted soil-lime mixture for different times of initial curing, after realizing the mixture, is analyzed. The result will help to decide the best choice of initial curing for compactness.

EXPERIMENTAL STUDY

Used materials

The soil being used corresponds to a highly expansive clay of the CH (high plastic clay) type according to the chart of Plasticity for soils. The Lime used as stabilizer was a commercial hydrated lime. Soil was taken form a place located at the Libramiento Noroeste of Celaya, Guanajuato, México.

Tests performed

To determine the optimum percentage of lime, the tests described below were done.

Plasticity Limits of both, natural and stabilized soils with 2, 4, 6, 8 y10 % of Lime, with respect to the dry weight, were determined and classified according to the Plasticity Chart.

Dry Volumetric Weight and soil moisture were determined via Standard Proctor test.

Odometer expansion tests were performed in both, the unaltered and the stabilized soil with the percentage of lime determined after realizing Plasticity limits to the determined volumetric weight and humidity, in order to define the best lime percentage, taking into account both, plasticity and expansion.

Once the lime percentage was determined for stabilization with the Plasticity Limits (6%), the material was passed for a mesh No. 4. Mixture soil-lime was done with different moistures and the material compacted in the Proctor mold at several times, after addition of material (1, 24, 100, and 150 h). Simultaneously to these times, consistency limits were also obtained.

RESULTS AND DISCUSSION

Percentage of Lime with the Plasticity Limits

Results of Plasticity Limits of both, natural and stabilized soils with 2, 4, 6, 8 y 10 % lime are displayed in Table 1, whereas its location and material behaviour in the Plasticity chart is shown in Fig. 1.

Table 1. Results of Plasticity Limits of natural soil and with for different percentages of lime.


Figure 1. Natural soil classification, and with different lime percentages according to the Plasticity chart (CH is high plastic clay, MH is high plastic silt, OH is high plastic organic soil, OL is low plastic organic soil, ML is low plastic silt and CL is low plastic clay).

The optimal volumetric weight and moisture obtained for the natural soil via Standard Proctor Test were Maximum dry specific weight, ?dmax= 1355 kg/cm3 y Optimum Moisture, ?opt = 32%. To guarantee that 6 % of lime (respect to the dry weight) was sufficient for stabilization, expansion tests were carried out for both, natural soil and mixture lime-soil with this percentage. Samples of unaltered soil showed an initial moisture of an average of 51 %. In these samples, the expansion in the odometer was 4 % in the average. This is shown in Table 2. As can be seen from Fig. 1, according to the Plasticity Limits, with 6 % of Lime, soil cannot reach an MH (High Plastic Silt), only with the 8 %. However, due to its closeness to border line, for defining the optimum percentage of Lime to stabilize the soil, two probes of stabilized soil with 6 % of lime were subjected to expansion ten days after being stabilized and compacted.

Table 2. Expansion percentage of natural soil and mixed with Lime.

From the above results, it can be seen that with the 6 % of lime, according to the plasticity limits, soil does not reach an MH (High Plastic Silt). Nevertheless, from the odometer results, it can be seen that with 6 % of lime is sufficient to stabilize the soil, because probes showed a percentage of minimum expansion.

Compactness of the mixture soil-lime for different times of adding material.

Compactness results obtained at 1, 24, 100 y 150 h of times of adding lime (6%) are displayed in Table 3 and the corresponding compactness curves are shown in Fig. 2.

Table 3. Compactness results for different times after mixture, Tm. ? is moisture and ?d is dry specific weight.


Figure 2. Compactness curves for different times of adding lime, Tm.

Consistency limits results at corresponding times are displayed in Table 4 and the variation of the same are plotted in Fig. 3.

Table 4. Consistency limits for different times of adding lime.


Figure 3. Location on the Plasticity Chart of a natural soil and stabilized at different times of adding lime, Tm. (CH is high plastic clay, MH is high plastic silt, OH is high plastic organic soil, OL is low plastic organic soil and ML is low plastic silt)

CONCLUSIONS

To define the percentage of lime for stabilization of some expansive clays, the soil classification does not necessarily changes at the Plasticity Chart, because only at 10% for this specific soil, there is a classification change, from CH (High Plastic Clay) to MH (High Plastic Silt). The mixture soil-lime decreased its expansion with lower percentages of 10% lime, even though its classification remains unchanged.

In other hand, for stabilizing the soil with Lime, the volumetric weight of these tend to lower. In this work, it was shown that such decrease is dependent not only of the Lime percentage addition, but also the time elapsed after the mixture.

From Fig. 2, it can be observed that the compactness behaviour of a stabilized soil does not comply necessarily form the Proctor pattern. Thus, determination of the maximum dry specific weight and optimum humidity will have to be complemented with another tests such as resistance, consolidation and expansion for different moistures.

Regarding the Initial Time of Curing, it can be seen that the specific weights decrease as the time increases. However, the 24 and 100h curves have a similar behaviour. It can also be seen simultaneously that compactness becomes harder as time goes by because of the grumes formation. Thus, the time of curing could be recommended from one day. In this time, it is very likely that the soil-lime mixture has the better resistances.

Some complementary studies to this work is observing the resistance behaviour and expansion of compacted probes with different Times of Initial Curing, hypothesizing that the chemical reaction soil-lime continues developing through time (López-Lara et al, 2002).

REFERENCES

  1. Castaño M.V., T. López-Lara (2001) “Time Dependency of CaO-Treated Expansive Soils”. Electronic Journal of Geotechnical Engineering, Vol. 6, http://geotech.civen.okstate.edu/ejge/ , USA.
  2. Fernández Loaiza, Carlos (1982) Mejoramiento y estabilización de suelos, Ed. Limusa, México.
  3. F.H. Chen (1975) Foundations on Expansive Soils, Elsevier Scientific Publishing Company, Amsterdam, The Netherlands.
  4. Hernández Espino J. J. (1992) Estabilización con cal de arcilla en un pavimento flexible de Querétaro, Curso Internacional de Mecánica de Suelos Arcillosos, U.A.Q., Querétaro, México.
  5. John D. Nelson and Debora J. Miller, John Wiley & sons (1992) Expansive Soils., Inc., E.U.A.
  6. Juárez B.E. y Rico R.A. (1984) Mecánica de Suelos, Tomo I, Ed. Limusa, México.
  7. Lenonm J. Cajuste (1977) Química de los suelos con un enfoque agrícola, Colegio de Postgraduados, Chapingo, México.
  8. López-Lara T., Zepeda Garrido J.A. (1996) Resistencia al esfuerzo cortante en arcillas expansivas de Jurica, Querétaro, tesis de maestría, U.A.Q., Querétaro, México.
  9. López-Lara T. (1998) “Reflexión y análisis sobre el tratamiento de suelos con diferentes materiales”. Curso: Técnicas Modernas de caracterización en la ciencia tecnología de suelos arcillosos, Querétaro, Qro; México.
  10. López-Lara T., Zepeda Garrido J.A. y Castaño M.V. (1999) Comparative study of the effectiveness of different additives on the expansion behavior of clays, Electronic Journal of Geotechnical Engineering, Vol. 4, http://www.ejge.com/index_ejge.htm, USA.
  11. Secretaría de Comunicaciones y Transportes, Subsecretaría de Infraestructura (1987) Normas para muestreo y Pruebas de Materiales, Equipos y Sistemas, Libro 6, México.
  12. Teushcer H. y Adler R. (1975) El suelo y su fertilidad, Ed. C.E.C.S.A., 2da. Impresión, México.
  13. Zepeda Garrido, J. A. (1985) Guerrero Lara J., Olguín Redes R., Estabilización de arcillas expansivas con cal en Querétaro, Reporte de Investigación No. 85-MS-01, U.A.Q., México.

 

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