Experimental Study on Interface Characteristics of Sand-Steel Pipe Using Torsional Shear Method

The interface between soil and structures has always been an important research topic in civil and geotechnical engineering.The interfacial shear tests of sand and steel structures were performed by modified motorized laboratory vane tester, factors influencing mechanical properties of sand -steel interface was studied, the effects of shear rate, relative density, stress state and roughness on mechanical properties of sand-steel interface were revealed.The results show that: (1) The shear stress-relative displacement relationship curves of the sand-steel interface have obvious peaks under different shear rates, relative densities, stress states and roughness, and the peak strength and residual strength of the sand-steel interface increase with the increase of relative density, vertical stress and roughness, and decrease with the increase of shear rate.(2)The peak strength and residual strength of the smooth sand-steel interface show a good linear decreasing relationship with the shear rate, which increases with the increase of relative density, and shows a good linear decreasing relationship with the vertical stress and normal stress.The relationship curve between the peak strength and roughness of the sand-steel interface can be fitted well by the exponential model, and there is a critical roughness that effectively affects the strength performance.(3) The shear dilatation and contraction of the smooth sand-steel interface at different shear rates is a dilatation phenomenon.For the smooth sand-steel interface at the three relative densities, the loose sand sample showed shear contraction, the medium dense sand sample first had a dilatation, and then turned into a shear contraction, and the dense sand sample showed a dilatation.Under the action of vertical stress from small to large, the shear dilatation and contraction of smooth sand-steel interface shows the transition from shear contraction to dilatation, and with the increase of vertical stress, the dilatation amount increases first and then decreases, and there is a trend of shear contraction.Under the action of low normal stress, with the increase of the surface roughness of the round steel bar, the shear dilatation and contraction of the sand-steel interface changes from no change in volume to dilatation, and then the dilatation increases first and then decreases, and gradually tends to have no change in volume.The results provide significant guidance to solving mechanical problems between soil and structures in practical engineering.