The internal friction coefficient ( )of sandy soil exactly exerts influence on the stability of sandy soil surrounding rock. From the perspective of influencing factors of the stability of sandy soil surrounding rock and the stability classification of surrounding rock

this paper explores the influencing factors of internal friction coefficient which are related to the stability of sandy soil surrounding rock. It is discovered that the content of fine granules ( 0.075 mm) of sandy soil has distinct influence on the internal friction coefficient of sandy soil. The relationship between the compactedness and internal friction coefficient is not always a direct ratio which is relevant to the content of fine granules of sandy soil and water content of fine granules. It is held that it is more rational to adopt the water content of fine granules rather than water content of sand soil to access the internal friction coefficient of moist sandy soil. This article also makes a conclusion for the influencing rules of the water content of fine granules on the internal friction coefficient of sandy soil.