Abstarct: The need for various construction projects has usually caused problems such as settlement or shortage of load bearing capacity for civil engineers. Among the measures taken to stabilize the soil is the use of a variety of improvement methods. One of these applications is the use of micropiles or small piles as a structural element in soils. In this research and in a laboratory program, after design and construct of a large-scale physical modeling apparatus, multiple static strain- control loading tests with a displacement rate of 10mm /min were performed to examine various factors such as injection radius, wall cohesion and pounding effect on bearing capacity of micropiles in soils with different relative densities. In this study, SPSS software was used to analyze the results and determine the quantitative effect of parameters. In this study, micropiles with injection radius of 65, 120 and 170 mm with length of 1 meter were used. The soil used is standard Firoozkooh sand, which is used in relative densities of 45% and 90%. Finally, it is determined that the effect of density is considerable on load capacity, which is not mentioned in the code and SPSS software shows that the density effect is 1.47 times of the injection radius in increasing the load bearing capacity. Also, according to laboratory results, in the densities of 45% and 90%, the wall cohesion difference, increased bearing capacity 39% and 43%, respectively.