Pore Pressure Development And Bearing Characteristics Of Suction Foundation In Silty Soil

As one of the fast-developing foundation types of offshore wind turbines,the suction caisson has attracted considerable attention.Eastern coastal areas in China are rich in offshore wind energy resources.And the seabed is widely distributed in silty soil layers,whose dynamic characteristics are relatively complex.The caisson foundation is subjected to cyclic loading during its service,and dynamic response has received widespread attention.However,there are few studies on the pore pressure response of the soil around the caisson foundation in silty soil.In this thesis,research is carried out by vibrating triaxial test,model test and theoretical analysis.The main research content and results include the following aspects:Firstly,the development model of silt pore pressure under different fine particle contents was studied by vibration triaxial test.Based on the traditional analysis method,the influence of clay content and silt content on pore pressure development law is studied.The results show that the clay content of 9% is the turning point of the change of the cumulative law of silt pore pressure.The smaller the clay content or silt content is,the faster the pore pressure accumulation speed will be.A formula for calculating the development of silt pore pressure considering the effect of fine particle content is established.Based on the energy analysis method,the relationship between pore pressure-cumulative loss energy of silty soil with different fine particle contents and its normalization was studied.The results show that the smaller the silt or clay content is,the looser the distribution of dynamic stress and strain hysteresis loops will be,and the faster the pore pressure accumulation rate will be.A silt pore water pressure-cumulative energy consumption normalization formula is established.Secondly,the dynamic response and bearing capacity of the soil around the suction caisson foundation under horizontal cyclic loading were studied using model tests.Load tests of suction caisson foundation under different horizontal cyclic loading frequencies,amplitudes and vertical loads were carried out.The changes of pore pressure were monitored at the cylinder wall at 0.8D and 1.2D from the cylinder wall.The results show that after cyclic loading,the accumulation of pore pressure at the depth of 0.1L ? 0.3L of the soil around the caisson foundation is obvious,but it has little effect on the part below 0.3L.The farther away from the cylinder wall,the lower the degree of pore pressure accumulation is.The greater the load amplitude and the greater the load frequency,the higher the accumulation of pore pressure in the upper part of the side wall of the cylinder will be.The increase of vertical load will limit the lateral disturbance and reduce the cumulative level of pore pressure.At the same time,the undrained shear strength of the soil at a depth of 0.2L before and after cyclic loading showed different degrees of attenuation.The greater the degree of attenuation,the closer to the cylinder wall,the higher the strength attenuation rate,and the attenuation of the shear strength leads to a reduction in the horizontal bearing capacity of the cylinder base.Finally,the calculation formula of silt pore pressure development considering the effect of fine particle content is used as the source term.Based on the one-dimensional consolidation theory,the theoretical value of the pore pressure development of the soil around the cylinder foundation is calculated,which has a good agreement with model test data.The relationship between the attenuation parameter and the frequency,amplitude and vertical load of the horizontal cyclic load is established and used to modify the calculation formula of the horizontal ultimate bearing capacity of the suction caisson foundation.