###### Abstract  
The removal of soil during scouring is crucial to the lateral resistance of piles in bridges of railways or highways. In this process, dilatancy of the interface soil induces variation in normal stress, which in turn influences the interface soil lateral resistance. Due to the lack of analysis in previous studies in terms of cohesionless soil state (i.e., relative density and stress level) in remaining soil after scouring, it is difficult to simulate the properties and behavior of interface soil. The objective of this study is to explain the change of the sand state at the compression interface after scouring, quantify the stress-strain characteristics of the pile during this period and eventually present the prediction p-y curves of the lateral service capacity. The state-dependent constitutive model for saturated sand is employed, combined with the 3D finite element simulation, and the state development of the remaining soil is exhibited. The enhancement of dilation and stress relief of the remaining shallow horizon eventually gives rise to the reduction of the lateral resistance. In addition, the remaining overburden soil surrounding the pile restricts the interface soil, enlarging the normal stress and strengthening the deep horizon. Then, the friction angle considered the influence of state-dependent changes is used to quantify the hyperbolic p-y curves. b +
Footnote †: journal: Applied sciences  
effect on pile-soil interaction structure, the removal of soils subjected to scour could be considered as a slow process of unloading [11]. The lack of remaining soil characteristic analysis makes the existing p-y curves not reasonable and precise enough in the research. During the scour, the stress history of remaining soils changes in the meantime [12; 13], resulting in the state variation of the soil. During the stress state and the normal stress of the remaining soil changed, the dilation of the shear interface brought about a slight rise of the friction angle [7]. As a result, neglecting the variation of stress state would result in a conservative design when considering the lateral capacity of the pile foundation. Piles in cohesionless soil are more vulnerable to scour than cohesive soil by wave or current [6]. To cohesionless soil, the concept of critical state can be applied to assess the tendency of dilatancy. [PERSON] et al. [14] and [PERSON] et al. [15] illuminated that the state parameter, the disparity between the current void ratio and the critical state void ratio corresponding to the current confining pressure, is an effective approach of the measurement of how far the material state is from the critical state. With the parameter as the state variable, a particular form of state-dependent dilatancy is shown to be equivalent to an interpretation whereby the phase transformation stress ratio is variable with the state parameter, an idea introduced by [PERSON] & [PERSON] [16]. As a significant factor of sand under shearing, the dilatancy of the shallow sand horizon in local scour is worth analyzing. To explore the lateral resistance of the remaining sand horizon under scouring, a centrifuge test is applied to make a comparison between the lateral soil resistance in the general scour and local scour [17], indicating that p-y curves for the local scour cases, sand horizon at a given depth below the scour pit base is much stiffer than that at the same depth below the original soil surface, while this characteristic is not founded in the general scour sand horizon. The results reflect a phenomenon that if the deformation of the pile head increased, the lateral resistance of the remaining sand horizon would also increase slightly in local scour conditions. According to the results in the CPT test and 3D finite element model tested by ABAQUS, this increasing stiffness of the p-y curves would be attributed to the constraint due to the sloping overburden soil in local scour cases [18], and then the property of shallow remaining sands changed.