Experimental Study on Stiffness Degradation and Liquefaction Characteristics of Marine Sand in the East Nan-Ao Area in Guangdong Province, China

Abstract

Offshore wind power, as an efficient renewable energy source, is being vigorously developed nowadays. However, the liquefaction of marine sand due to earthquakes brings potential safety hazards to the wind turbine structures. In this study, a series of resonant column and undrained cyclic triaxial tests were carried out to investigate the stiffness degradation and liquefaction characteristics of marine sand in the offshore wind farm at the East Nan-ao area in Guangdong Province (China). Results show that the confining pressure increases the shear modulus of sand and restrains the nonlinearity of modulus. The liquefaction resistance of soils significantly increases with the increase of relative density. The effect of particle size on the liquefaction resistance is related to the cyclic shear stress ratio. The additional pressure induced by the presence of the wind turbine structure enlarges the energy required for shallow soil liquefaction. Besides, a model for predicting shear modulus and another modified model based on Seed’s pore pressure development model have been established, which can efficiently fit the dynamic shear modulus and the generation of excess pore water pressures in the tests, respectively.

Instability and Failure of Subsea Structures

“…To investigate the stiffness degradation and liquefaction characteristics of marine sand in the offshore wind-farm construction site at the East Nanao area in Guangdong Province of China, resonant column and undrained cyclic triaxial tests were conducted [15]. Based on the experimental data, a model for predicting shear modulus was established, as well as a model extended from Seed's pore pressure development model.…”

Experimental Study on Stiffness Degradation of Organic Matter-Disseminated Sand under Cyclic Loading

“…(a) The degradation index, δd, can be used to quantify the attenuation of cyclic stif [8]. In the stress-controlled dynamic triaxial test, the ratio of the dynamic elastic mod in the Nth cycle and the first cycle (i.e., the ratio of EN:E1) is the degradation index δ.…”

“…It can be seen that the degradation index curve decre sharply with the increase in vibration cycles under various cyclic loads, which ind that the soil would be destroyed with fewer vibration cycles. Since the δd-N relation The degradation index, δ d , can be used to quantify the attenuation of cyclic stiffness [8]. In the stress-controlled dynamic triaxial test, the ratio of the dynamic elastic modulus in the Nth cycle and the first cycle (i.e., the ratio of E N :E 1 ) is the degradation index δ.…”

“…With the increase in dynamic cyclic load amplitude, the dynamic strain, porosity and pore pressure of soil increase, the internal structure of soil is reshaped as well, which induces the stiffness degradation of soil [2][3][4]. Under the cyclic load, the cumulative deformation of soil varies with vibration cycles [5,6], and due to the nonlinearity of soil, the stiffness acts in a complicated manner [7,8].…”