عنوان مقاله [English]
By growing of urban life and increasing demand for construction, as well as requirement of appropriate space for parking and facilities, excavation has become an integral part of most construction projects. One of the new and effective methods for stabilizing excavation is nailing method. One of the important parameters of the design in this method is bond strength, which is significantly influenced by the grouting process. The grouting process depends on various parameters such as grouting pressure, grouting algorithm and mortar components, but due to the lack of studies on the effect of mortar components on bond strength, the effect of an expansive additive in the grout on the bond strength investigated by a pullout box in the laboratory. The pullout box has different parts such as overburden pressure unit, grouting unit, loading unit and monitoring unit. First the soil strength parameters obtained by direct shear test. Also grout’s compressive strength obtained by grout compressive strength test with UTM. In the pullout test, first the soil with optimum moisture, compacted layer by layer while a steel casing embedded in the middle of the box. After applying overburden pressure with an airbag for 24 hours and setting equilibrium in the soil, the steel casing removed and the steel bar placed in the hole, then grouting process started. Finally, after 5 days, the loading process started, by pulling out the grouted nail using speed of 1 mm/min. Also the grout compression strength tests have done to investigate how expansive additive influences on mortar. The results showed that the use of expansive additive to a certain and optimum extent, despite of reduction in mortar compression strength, causes increase in bond strength in the laboratory sample. Also by increasing the grouting pressure, the pullout resistance increases to high extent, which is recommended in projects.