Session: 06-02-01 Coastal Engineering I

Paper Number: 126116

126116 - Time-Varying Model for Scour Evolution Around Pile Foundations in Clay Soils 

In recent decades, notable advancements have been made in understanding local scour around pile foundations in non-cohesive soils. In contrast, the study of scour in clay soils remains an area of uncertainty. Traditional approaches for predicting scour development in non-cohesive soils have been indiscriminately applied to clay soils. Nevertheless, recent research has revealed that the scour depth around bridge piers in clay soils is relatively shallower compared to non-cohesive soils. Consequently, the use of such methods may lead to unnecessarily deep pile foundations or the unwarranted implementation of scour countermeasures for existing piles, resulting in increased costs. Therefore, it is crucial to develop a comprehensive prediction model for accurately determining scour depth in clay soils in order to facilitate proper pile foundation design.

Due to the inherent complexity of the problem, existing prediction formulas for scour depths around pile foundations in clay soils are typically empirically fitted to experimental data, which is susceptible to scale effects. Some formulas have overlooked significant parameters, rendering them inadequate for providing a meaningful understanding of the scouring process. Furthermore, these prediction formulas only apply to the equilibrium state of scour depth and fail to account for time-dependent variations in scour depth around pile foundations.

       In this paper, we propose a time-varying model to describe the evolution of scour around pile foundations in clay soils under steady flow conditions. A scaling expression for the shear stress resulting from the interaction between eddies impacting the scour-hole surface is proposed, utilizing the two principles of the phenomenological theory of turbulence (PTT). By employing a general sediment transport model and the principle of sediment mass conservation, an ordinary differential equation (ODE) that describes the temporal variations of scour depth is further derived. This equation, when integrated with the shear stress formula under equilibrium conditions, simplifies to an ODE based on fundamental principles of physics, enabling the prediction of the temporal development of scour depth. Notably, this model comprehensively incorporates all dimensional parameters governing the scouring process, thereby eliminating scale-related issues. Additionally, a set of time-varying scour data is collected to assess the applicability of the proposed model. The results conclusively demonstrate a close alignment between the predicted variations and the previously observed scour depth development curves.

Presenting Author: Wen-Gang Qi Institute of Mechanics，Chinese Academy of Sciences

Presenting Author Biography: Wen-Gang Qi is an associate professor in offshore geotechnics at Institute of Mechanics, CAS. His research interests include current/wave-structure-seabed interactions and mechanical properties of marine sediments. He is presiding two National Natural Science Foundation (China) projects. He also has participated in several large projects related to ocean engineering funded by either National Natural Science Foundation of China or major corporations such as CNOOC (China National Offshore Oil Corporation) and CNPC(China National Petroleum Corporation). He is a Technical Program Committee (TPC) Member of the International Society of Ocean and Polar Engineering Conference (ISOPE). He was recommended to join the Youth Innovation Promotion Association CAS in 2020. He has published over 40 papers in international journals or international conferences.

Authors:

Pei-Qing Zhao Institute of Mechanics，Chinese Academy of Sciences
Shun-Yi Wang Institute of Mechanics，Chinese Academy of Sciences
Wen-Gang Qi Institute of Mechanics，Chinese Academy of Sciences
Fu-Ping Gao Institute of Mechanics，Chinese Academy of Sciences