English abstract
Expansive soils are well-known as main cause of many crack problems in civil engineering structures. The phenomenon of shrinkage and swelling due to drying and wetting cycles gave these soils the importance to be studied. This research reports the findings of an experimental study to reduce swelling behavior. For this purpose, an expansive soil was selected from Adam due to many damages on existing buildings and asphalt pavements ranging in age from 3-6 years old. Soil samples were obtained from a site in Adam. The soil was subjected to an extensive laboratory testing such as Atterberg's limits, wet sieve analysis, hydrometer, compaction, California bearing ratio (CBR), unconfined compressive strength, swelling, specific gravity, suction, X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscope (SEM) tests. The soil was stabilized with different stabilizers such as cement, Cement-By-Pass-Dust (CBPD) and lime.
It was found that Adam soil is a highly plastic clay. Liquid limit, plastic limit and plasticity index were 83%, 35% and 48% respectively. It was also found that 69 % of the sample particles are fines (silt and clay) with an amount of clay of about 45%. The percentages of gravel and sand were 16% and 15% respectively. Adam soil is composed of expanding minerals such as montmorillonite, calcite, palygorskite, gypsum and others. These minerals exhibit swelling behavior upon wetting and shrinkage upon drying and that what explain the high swelling potential that exhibited by this type of soil which reached 10.40 % and swelling pressure of about 84 kN/m2 for the untreated soil sample. Moreover, XRF technique showed a high percentage of SiO2, Al2O3 , CaO and Fe2O3 which exceeded 74% of the mineral content. The maximum dry density and optimum water content of the compacted soil were found to be 1.55g/cm2 and 24% respectively. California bearing ratio test was also performed for dry and soaked samples. The soaked samples showed very low value of CBR of about 1.34% whereas value of CBR for dry samples reached 14.72%. The soil was subjected to total and matric suction test using filter paper method. Results showed that both types of suctions decrease with the increase in initial moisture content.
The influence of the stabilizers was studied by mixing the soil with a particular percentage of each stabilizer separately. The soil was treated by mixing CBPD in amounts of 6%, 9%, 15%, 20% and 30% by dry weight of soil. Cement and lime were added in 6% and 9% of the dry weight of soil. Treated soil was subjected to various testing program. The plasticity index was found to be in the range of 41-25% showing that as the percentage of CBPD increases, the liquid limit decreases and the plastic limit increase. It was found also that there is a decrease in the dry density of the soil as the percentage of CBPD increases. Mixes with 9% cement, 9%, 15%, 20% and 30% CBPD showed low swelling values about 3%. CBR test had the highest value with soil stabilized with 15% CBPD. It reached 24%. Moreover, soil treated with 6%, 15% and 30% CBPD showed less total and matric suction values comparing with untreated soil. The effect of stabilization on rutting of pavement was investigated. The lowest value of rutting was obtained 1.2 mm when soil stabilized with 9% cement compared with 2.9 mm for untreated soil.
