Analysis Of Disturbance Mechanism In Coring Process Of Deep Seabed Sediment Drilling

The ocean is a treasury with great development potential.Sampling of deep seabed sediments is the precondition for carrying out research on marine geology,exploration of seabed mineral resources and marine engineering investigation.It is of great significance to obtain core samples with high quality and low disturbance.In this paper,the disturbance model of sediment sampling process is established based on the cores disturbance during the seafloor drill press-in sampling process,and the simulation sampling experiment is carried out.The experimental results and theoretical analysis results are compared and verified.It provides theoretical basis for the design of drilling tool structure and selection of drilling parameters for deep-sea sediment sampling,and is of great significance for the development of low-disturbance exploration sampling technology for deep-sea subsea drilling rigs.The specific contents and innovations of this paper are as follows:Firstly,based on the structure of drilling tools and coring principle of seafloor drill,the disturbance water pressure model of sediment coring process is established to innovatively study the disturbance water pressure which affects the quality of coring,and the influences of drilling tool pressure speed,size of sampling pipe and diameter of overflow orifice on disturbance water pressure are analyzed.Secondly,based on the engineering geological characteristics of deep seabed sediments,the core penetration process of sediments is analyzed.Considering the influence of seawater penetration in sediments during coring drill,a radial disturbance model of sediment coring is established based on the spherical hole expansion theory.The ratio of the radius of sediment with plastic deformation around the spherical hole to the radius of core is used as an index to evaluate the radial disturbance of sediment.An example is used to analyze the distribution of stress and strain fields in sediments during spherical expansion and the influencing factors of radius of radial disturbance area(plastic area)and their laws.Thirdly,based on the previous research results,an axial disturbance model of sediment sampling is established for the first time based on the ultimate bearing capacity model,and the core rate of sediment is taken as the axial disturbance index to analyze the variation rule of the core rate with sampling depth in sediment sampling process,taking into account the structural parameters of sampler,physical properties of seafloor sediments and coring process parameters.Finally,the GDS stress path triaxial tester is used to carry out triaxial tests on the sediment samples used for the test,and the mechanical parameters such as elastic modulus and internal friction angle of the sediment are determined by using the Moore-Coulomb yield criterion.In order to verify the sediment coring disturbance model established previously,an experimental platform for sediment disturbance was established and the sediment coring process was simulated.The radial stress and pore water pressure of sediment during coring process are monitored by sensors arranged inside the sediment and the change of coring rate in each stage of coring process is measured to verify the correctness of the disturbance model.