Development Of Mechanical Parameters Of Submarine Soil And Shallow Gas Testing Rod

Marine geological hazards are inevitable hindering factors in the process of marine resources development or marine engineering construction.The main factors for the formation of marine geological hazards are the movement of the submarine soil and the escaping eruption of shallow gas.Therefore,the mechanical parameters of submarine soils need to be examined to guide the design of marine engineering,and the shallow gas masses buried in the seafloor need to be examined to assess the risk.In this research context,this project develops a test rod that enables the simultaneous detection of subsea soil mechanical parameters,methane concentration and air pressure in shallow gas.This project is based on Cone Penetration Testing technology to achieve the detection of subsea soil mechanical parameters.In the part of shallow gas detection,porous ceramics with pore size less than 50 um and waterproof and breathable membrane made of PTFE material are selected to form the mud-water-gas separation structure to realize the extraction of environmental shallow gas.The measurement of methane concentration and pressure in shallow gas is achieved by non-dispersive infrared gas sensor and pressure sensor.The mechanical parameter detection data is transmitted to the shallow gas detection part by acoustic wireless transmission.The hardware selection,mechanical structure design,circuit design and programming of each of these parts are described in detail in this paper.Finally,experiments and tests are conducted on the developed test probes,including Piezocone Penetration Test rod calibration experiments,acoustic wave wireless transmission tests,and waterproof depressurization experiments and field shallow gas detection experiments of the device on a simulated high water pressure experimental platform.Several conclusions were obtained based on the experimental results as follows.(1)The waterproof performance of single-layer waterproof breathable membrane has a certain limit,when the water pressure exceeds a certain level,the membrane will appear water seepage phenomenon.When the water pressure rises,the rate of water seepage will rise to a certain extent,but the overall rate of water seepage is slow.The device can still maintain a good waterproof performance during the short time testing process.(2)In further experiments on pressure dissipation of waterproof and breathable membranes,it was found that water pressure is dissipated to a certain extent after being obstructed by multiple layers of membranes,and under the three-layer membrane structure in the experiments,the water pressure was weakened by 23 k Pa for each layer breached.(3)The multi-layer membrane body can reduce the overall percolation rate.During the experiment,it took about 2 days for water to fill the first chamber and about4 days to fill the second chamber,and this phenomenon can provide ideas for subsequent research to achieve longer detection time under high water pressure environment.(4)The shallow gas pressure detected in the chamber where the sensor is placed is not the same as the shallow gas pressure in the actual environment,but it can be calibrated by the pressure conversion factor.However,the pressure conversion coefficients are different for different environments.(5)The developed probe rod mechanical parameters detection,shallow gas methane concentration and pressure detection error is small,the acoustic wave wireless transmission process is stable and reliable,and the probe rod still has good waterproof performance under high water pressure environment,with the advantages of waterproof,stable and accurate,to meet the needs of related research work.