عنوان مقاله [English]
When the metal is in contact with the soil, there is the possibility of sticking soil to the metal surface. For determining the tension stress for soil separating from metal surface the cone pullout device designed. In this apparatus, a cone penetrates into the soil, stopping it for a specific time and, then, separating from the soil. In the present research, according to previous studies and ideas about this subject, cone pullout test device is designed and manufactured. By performing 90 tests on a montmorillonite clay soil with different values for stope time and separation speed, the effect of these variables was studied. The results showed optimum stope time (t =5 min), and separation speed cone (15 mm /min) was determined. To evaluate the reproducibility of the results, by performing other 60 tests on two other kaolinite clay soils, coefficient of variation ($14.49 \geq Cv \geq 1.4$) and accuracy index ($1.22 \geq P \geq 1.01$) were determined. these values showed which results were reputable and acceptable. Because of the effect of moisture content on the engineering properties of fine-grained soil, the effect of moisture changes on tensile stress for separation of metal from soil was studied. The results of the study showed that with an increase in water
content, the tension stress decreased. Accordingly, linear relationships were
proposed between soil moisture content and tensile stress for montmorillonite
and kaolinite clay soils. Slope of the curve moisture content versus tension
stress for montmorillonite clay soil and kaolinite clay soil are 1.25 and 0.82
respectively. Therefore, it can be concluded that the slope of the curve corresponds to the soil type; increasing plastic index increases tension stress.