Effect of Pore Water Pressure Ratio on Stability of Wind Turbine Shallow Foundations on Saturated Sandy Soil Due to Soil Liquefaction: A Case Study in Coastal Area of Soc Trang Province, Vietnam

Wind turbines are structures whose operation is always affected by dynamic loads. Currently, shallow foundations are common for onshore wind turbines. In the case of saturated sandy soils, dynamic stresses caused by wind turbines can cause the sand to liquefy or reduce its shear strength due to increased excess pore water pressure (ΔU). The pore water pressure ratio (Ru = ΔU/σ’) is now often used to evaluate the effect of ΔU on foundation stability. This paper presents a method for determining Ru and establishing equations to determine the shear strength of saturated sand from Ru. From there, it is possible to estimate the bearing capacity of the foundation on saturated sand (q’ult), taking into account the effect of the pore water pressure ratio. Using the concept of influence factor of liquefaction (Finf), this paper proposes a procedure to evaluate the effect of pore water pressure ratio on the stability factor of shallow foundations on saturated sandy soil. Applying the above method to the coastal area of Soc Trang province, Vietnam shows that the values of q’ult and Ru are inverse exponential relationships while Finf and Ru are exponential relationships. In particular, q’ult and Finf have a very close correlation with Ru and can be expressed as the following expression: Finf=0.9907e3.56Ru; q’ult = 44450e-3.56Ru.