Interpretation Of Strength Parameters Of Seabed Soil Based On The Free-fall Ball Penetrometer With A Booster

The development and utilization of deep-sea oil and gas resources and offshore wind power are inseparable from submarine structures,which directly or indirectly interact with marine clay,and the strength of marine clay is very important to the design of structures.The modified FFBP(Free Fall Ball Penetrometer)with a Booster(FFBPB)combines the booster with the spherical penetrometer,which has the advantages of full-flow penetrometer,large measuring depth range and can improve the prediction accuracy of soil shear strength by combining force and acceleration,thus having obvious superiority in the field measurement of marine clay.The study of the bearing behaviors of FFBPB during continuous penetration in soil and its relationship with the strength parameters of marine clay is of great significance for the application of FFBPB.In the first part of the thesis,the penetration process of FFBPB in homogeneous clay was simulated by commercial software ANSYS CFX which is based on computational fluid dynamics.The effects of interface friction between penetrometer and soil,initial penetration velocity,initial undrained shear strength of soil,strain-rate and strain-softening on the total resistance of Ball and the penetration depth of FFBPB were studied.The results show that the total resistance of Ball is positively associated with all factors studied in this thesis.The effects of interfacial friction coefficient,initial penetration velocity,initial undrained shear strength of soil,rate effect parameter and softening parameter?_rem on penetration depth of FFBPB are all over 20%,while the effect of softening parameter?₉₅ is less than 10%.The location where rate effect and softening effect have the greatest influence on soil strength is near the interface between Ball and soil.In the second part of the thesis,the influence of interface friction coefficient,rate effect and softening effect on bearing capacity factor were analyzed which is based on the results of numerical simulation.The formulas of bearing capacity factor,drag force coefficient,rate coefficient and softening coefficient were put forward.And the back-analysis method of soil strength parameters is established.Soil strength parameters can obtain by combining the force and acceleration measured by sensors during FFBPB penetration and the proposed formula.Finally,the input parameters of numerical simulation and soil strength parameters used in laboratory tests were reversed by the method proposed in this paper.The results show that the proposed method can be used to interpret the strength parameters of soil and the method provide a basis for the application of FFBPB in the measurement of marine clay.