Study On Quality Evaluation Method Of Seabed Gas Sediment Samples Based On Disturbance Degree

How to evaluate the disturbance of the sample during the sampling process has always been a problem plaguing the geotechnical engineering community.The disturbance caused by the sampling process is likely to change the nature of the sample,making the parameters obtained in the laboratory unrepresentative.In the design and construction,the judgment of the nature of the in-situ soil is incorrect,resulting in safety accidents and casualties.Therefore,in the actual engineering design,the impact of sample disturbance on the project must be considered.Submarine gas-bearing sediment is a kind of soil with special properties.It is distributed all over the world.Its special nature is sensitive to the environment.Once it encounters changes in the sampling process,it quickly destroys its mechanical properties.The special nature of gas-bearing sediments will generate disturbances that are greater than those of other soil types,because as the water depth decreases,the stress around the gas-bearing sediment samples will decrease,and the dissolved gas in pore water will de-solve.The skeletal structure of the granules causes damage,which is much larger than the disturbance caused by the unloading stress release of normal saturated soils or unsaturated soils.If such samples are evaluated by the disturbance evaluation experience of general saturated soils or unsaturated soils,It will certainly cause safety problems in marine engineering.However,in the past,both the terrestrial and the sea disturbance assessment methods focused on general saturated soils or unsaturated soils,but there are few reports on the quality evaluation of seabed gas-bearing sediment samples.In recent years,with the acceleration of the exploration and development of oceans in China,the evaluation criteria for the degree of disturbance of gas-bearing sediments during the sampling process can further improve the level of understanding of marine engineering,provide a basis for survey and design,and provide security for engineering safety.This article takes the “The Belt and Road Initiative”strategy as the background of the era,uses the silty sandy soil of the Hangzhou Bay as the research object,and uses the high-pressure solution independently developed by the Institute of Rock and Soil Mechanics,Chinese Academy of Sciences.Gas saturation instrument,GDS stress path triaxial system and GDS bending element system,and high-precision low-range differential pressure sensor are used to study the properties of the remolded sand sample before and after the perturbation in order to find a method for evaluating the disturbance of the gas-bearing sediment.The content mainly includes:1.In order to bring the experiment closer to the actual situation,the design test simulates the perturbation of the sample during the extraction of gas-bearing sediments from the bottom of the sea to the shore.The sand sample filled with saturated gas-containing water is not Drainage unloading experiments,and measured the shear wave velocity before and after the disturbance.2.Compare the shear wave velocity of the disturbed sample with the undisturbed sample;compare the shear wave velocity before and after the sample disturbance.It is concluded that the shear wave velocity after the sample disturbance is smaller than that before the disturbance,and both the disturbed sample and the shear wave velocity are smaller than the non-perturbed sample.3.Triaxial shear tests were performed on all samples and the resulting shear strength curves were compared with the shear strength curves of non-perturbed samples to assist in the comparison of shear wave velocity results.It is concluded that the shear strength of the sample after perturbation is smaller than that before the perturbation,and both the perturbation sample and the shear strength are smaller than that of the unperturbed sample.The strength test results are consistent with the experimental results of the shear wave velocity and show that the strength of the sample decreases after the unloading disturbance.4.Through CT scan experiments,the difference between the micro-particle images before and after the sample disturbance was compared.It was found that the sand-like particle skeleton had no obvious cracks before perturbation,and the disturbed sand-like particle skeleton was obviously cracked,indicating that the original structure of the sand sample was disturbed.Destruction,corroborating the results of strong wave experiments and shear experiments in a qualitative way.Finally,through the comparison of predecessors' evaluation methods in various terrestrial and sea areas,the limitations of each evaluation method were analyzed,combined with the nature of gas-bearing sediments,the experimental data,and the results of previous evaluations.Method and considering its applicability,finally found a method that can be used to evaluate gas-bearing sediments on the seabed,and successfully evaluated the disturbance of gas-bearing samples.