Soil arching effect is an important precondition of adjacent pertaining or anti-sliding piles working safely and cost-efficiently. In cohesive soils

the spacing between adjacent piles is related to arching effect. By means of the analysis of mechanical concepts

taking geometrical characteristic of arch line and the fracturing face direction angle of Mohr-Coulomb failure to account

the force-balancing condition and strength condition are integrated and simplified to a uniform expression

which is only presented by the normal stress on the cross section plane of arch foot. Based on Mohr-Coulomb failure criterion

the least handy soil strength parameters which only including cohesion c and internal friction angle ?

according to the relationship between the normal stress and arrow-span ratio

the arch line and spacing between piles are obtained. Furthermore

the depth stable condition of soil arch is discussed

pile spacing can be emended more rationally. The application consists with practice projects to a certain extent. A concise estimate method to soil arch effect may be put forward.