Arching Effect in Soils

Question

Explain Arching Effect in the soils?

Answer 1

Arching takes place when there is a difference of stiffness between the installed structure and the surrounding soil. If structure is stiffer as compared to the soil then load arches onto the structure. Else, if structure is less stiff than the soil then load arches away from the structure.

For example, if part of the rigid support of soil mass produces, adjoining particles move with respect to remainder of the soil mass. This movement is resisted by shearing stresses that reduces the pressure over the yielding portion of support while increasing the pressure on the adjacent rigid zones. This phenomenon is known as arching effect.

Principle of soil arching can be simply demonstrated by the buried pipes. If rigid pipe is installed in the soils, soil columns on both the sides of rigid pipe are more compressive as compared to the soil columns on top of rigid pipe due to the greater stiffness of rigid pipes when compared with the soils. As such, the soil columns on both sides tend to settle more than the soils on top of the stiff pipe and this differential settlement causes a downward shear force acting all along the sides of soil columns on the top of rigid pipe. As such, the load on the rigid pipes becomes higher than the sole weight of soil columns on its top. Likewise, if flexible pipe is adopted rather, the above phenomenon shall be overturned.