Improvement of strength properties of clayey soils for construction purposes

Soil improvement methods is one of the cheapest methods for soil improvements. This method has used for preventing the settlement, and increase the shear strength and bearing capacity of the soil. So, in this thesis, tried to use the tire crumbs with clay type of soil and sand in different percentages. The amount of, 60%, 70%, 80% and 100% of kaolin clay mixed with 40%, 20%,30% and 0% of river sand. Then the optimum percent of lime powder (5%) added to the soil. After compacting the soil at standard proctor density with optimum moisture content (wopt), the sample had put in to desiccator for 28 days. After 28 days by unconfined compressive tests, the bearing capacity of the soil has determined. In the second part of this thesis, mixture of 60%, 70%, 80% and 100% of kaolin clay mixed with 0%, 20%,30% and 40% of river sand after finding the (wopt) for each sample, the amount of 0%,1%, 2%, %4 of tire crumbs by total weight added to the soils. All samples compacted at the proctor density. After preparing the samples, unconfined compressive strength test (UCS) of all samples were determined. According to test results, it has founded that the optimum ratio of tire crumbs is 2%. After that, the strength decreases dramatically. Adding tire crumbs increases the unconfined compressive strength up to 56%. In second part of the studies it has founded, that adding 5% of lime powder to the kaolin clay-sand mixture can increases the unconfined compressive strength parameter up to 146%. However, the strength ratio is directly depends in sand percentage. While decreasing the sand percentage the strength ratio also decreases.