Seabed bottom height and diameter prediction method

Abstract

The invention discloses a seabed bottom height and diameter prediction method, which belongs to the technical field of marine geological disasters, is used for predicting the seabed bottom height and diameter, and comprises the steps of determining seawater parameters of a hard shell layer, calculating soil parameters of the hard shell layer, and predicting the seabed bottom height and diameter. The pore pressure of the top of the soft soil layer, the initial height of the seabed bottom wall, the equivalent internal friction angle of the soft soil layer and the height, eroded by waves, of the top of the seabed bottom wall are sequentially calculated, and the actual height and the diameter of the seabed bottom wall are obtained. According to the method, calculation is carried out from the principle of bottom generation, the process is simple, the flow is high, the result is reliable, and verification of three embodiments shows that the method can accurately calculate the height and diameter of the bottom.

Description

Technical Field

[0001] The invention discloses a method for predicting the height and diameter of a seabed diapir, and belongs to the technical field of marine geological disasters. Background Art

[0002] Seabed diapir, also known as "mud volcano," is a geomorphic phenomenon on the seabed. Its formation is related to seabed wave action or gas outflow, and its development can endanger the safety of submarine engineering facilities. The higher the diapir, the greater the danger. To determine the height and diameter of seabed diapir, existing technologies typically rely on post-survey measurements, which is time-consuming, labor-intensive, and costly. Another approach is to use mathematical models for prediction, such as machine learning models to predict diapir parameters. This method only captures the inherent patterns in the data and does not calculate based on the principles of diapir formation. This method is often inaccurate and relies heavily on long-term observations of diapir data for model training. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for predicting the height and diameter of seabed diapir to solve the problems in the prior art of high cost of post-investigation and measurement of diapir and low accuracy of diapir parameter prediction by machine learning model.

[0004] A method for predicting the height and diameter of a seabed diapir comprises determining seawater parameters of a hard crust layer, calculating soil parameters of the hard crust layer, and sequentially calculating the pore pressure at the top of a weak soil layer, the initial height of the seabed diapir, the equivalent internal friction angle of the weak soil layer, and the height of the top of the seabed diapir eroded by waves, thereby obtaining the actual height and diameter of the seabed diapir.

[0005] Pore ​​pressure at the top of the soft soil layer include:

[0006] ;

[0007] Where, is the extreme value of the wave pressure on the surface of the hard shell layer, is the thickness of the hard shell layer, It is the saturated density of the hard crust soil.

[0008] Initial height of seabed diapir include:

[0009] ;

[0010] Where, It is the density of the original soil sample obtained by the drilling rig in the soft soil layer. is the density of seawater, is the acceleration due to gravity.

[0011] Equivalent internal friction angle of soft soil layer include:

[0012] ;

[0013] Where, It's cohesion. is the internal friction angle .

[0014] The height of the top of the seabed diapir eroded by waves include:

[0015] ;

[0016] Where, is the velocity of the wave.

[0017] Actual height of seabed diapirs include:

[0018] .

[0019] Diaper diameter include:

[0020] .

[0021] The velocity of the wave is:

[0022] ;

[0023] Where, It's a cycle.

[0024] The hydrodynamic parameters of the crust include wave height ,wavelength , water depth at the hard crust and period, the extreme value of the wave pressure on the hard shell surface is:

[0025] ;

[0026] Where, is a hyperbolic function.

[0027] The soil parameters of the hard shell layer include the thickness of the hard shell layer, the saturated density of the hard shell layer soil, and the natural density of the soft soil layer; a drill is used to drill in the hard shell layer to obtain the thickness of the hard shell layer, the density of the original soil sample obtained by the drill in the hard shell layer is tested using the ring knife method, and the saturated density of the hard shell layer soil is obtained by multiplying it by the acceleration of gravity, the density of the original soil sample obtained by the drill in the soft soil layer is tested using the ring knife method, the soft soil layer is fully disturbed, and placed in a direct shear apparatus to test the cohesion and internal friction angle.

[0028] Compared with the prior art, the present invention has the following beneficial effects: the present invention performs calculations based on the principle of diapir generation, and the process is simple, the flow is strong, and the results are reliable. Verification through three groups of examples shows that the present invention can accurately calculate the height and diameter of the diapir. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0030] A method for predicting the height and diameter of a seabed diapir comprises determining seawater parameters of a hard crust layer, calculating soil parameters of the hard crust layer, and sequentially calculating the pore pressure at the top of a weak soil layer, the initial height of the seabed diapir, the equivalent internal friction angle of the weak soil layer, and the height of the top of the seabed diapir eroded by waves, thereby obtaining the actual height and diameter of the seabed diapir.

[0031] Pore ​​pressure at the top of the soft soil layer include:

[0032] ;

[0033] Where, is the extreme value of the wave pressure on the surface of the hard shell layer, is the thickness of the hard shell layer, It is the saturated density of the hard crust soil.

[0034] Initial height of seabed diapir include:

[0035] ;

[0036] Where, It is the density of the original soil sample obtained by the drilling rig in the soft soil layer. is the density of seawater, is the acceleration due to gravity.

[0037] Equivalent internal friction angle of soft soil layer include:

[0038] ;

[0039] Where, It's cohesion. is the internal friction angle .

[0040] The height of the top of the seabed diapir eroded by waves include:

[0041] ;

[0042] Where, is the velocity of the wave.

[0043] Actual height of seabed diapirs include:

[0044] .

[0045] Diaper diameter include:

[0046] .

[0047] The velocity of the wave is:

[0048] ;

[0049] Where, It's a cycle.

[0050] The hydrodynamic parameters of the crust include wave height ,wavelength , water depth at the hard crust and period, the extreme value of the wave pressure on the hard shell surface is:

[0051] ;

[0052] Where, is a hyperbolic function.

[0053] The soil parameters of the hard shell layer include the thickness of the hard shell layer, the saturated density of the hard shell layer soil, and the natural density of the soft soil layer; a drill is used to drill in the hard shell layer to obtain the thickness of the hard shell layer, the density of the original soil sample obtained by the drill in the hard shell layer is tested using the ring knife method, and the saturated density of the hard shell layer soil is obtained by multiplying it by the acceleration of gravity, the density of the original soil sample obtained by the drill in the soft soil layer is tested using the ring knife method, the soft soil layer is fully disturbed, and placed in a direct shear apparatus to test the cohesion and internal friction angle.

[0054] In the present invention, the hydrodynamic parameters of the hard crust are calculated empirically or theoretically based on data from local marine hydrological and meteorological observation stations. The pore pressure at the top of the weak soil layer is caused by wave action and the deadweight of the hard crust. The working principle of the present invention is that after the weak soil mass below the hard crust is fully disturbed by wave cyclic loads, the internal pore pressure rises, causing upward overflow along the weak position of the hard crust. The dynamic condition of the lower overflow source is equal to the excess pore pressure after the upper load is fully disturbed. According to the mechanical equilibrium condition, the top of the diapir is eroded by waves due to its small diameter and weak shear resistance, while the bottom can be preserved. This determines the height of the diapir, and then the diapir diameter is determined based on the diapir's stability angle.

[0055] In a research project on the release of buried pollutants caused by seabed liquefaction induced by wave-induced pore pressure accumulation, the release of pollutants from sediments caused by liquefaction of the sediment bottom under wave action was studied. The experiment found that under the action of wave dynamic loads, the excess pore water pressure inside the sediment showed a nonlinear cumulative effect. When the effective stress dropped to the liquefaction critical value, the seepage-crack coupling effect was triggered, and vertical cracks were formed inside the sediment. With the increase of wave intensity and the increase of action time, the vertical migration channel in the liquefaction zone promoted the fluidization of the sediment-pore water two-phase system, which in turn induced vertical cracks and the formation of small "mud volcanoes", namely seabed diapirs. Because the development of seabed diapirs can endanger the safety of submarine engineering facilities, the calculation of seabed diapir parameters was considered. The present invention conducted three groups of experiments. The marine engineering in the experimental area is widely distributed, and there are also developed diapirs, which pose a certain threat to the safety of marine engineering. In order to determine the height and diameter of the diapir development in this sea area, the method of the present invention was used to predict them.

[0056] In Experiment 1, based on the data from the local marine hydrological and meteorological observation station, the tides were regular and irregular semi-diurnal tides, with an average tidal range of 2.1m to 3.3m and a high tide range of about 4.7m. The waves were mainly wind waves, with an average wave height of about 0.6m and a maximum wave height of 3.5m to 5.0m. According to the marine geological survey, a typical seabed diapir was found in one sea area. After measurement, the actual height of the seabed diapir was 0.8m. Determine the diapir diameter The prediction method of the present invention is used to predict the bottom split height and diameter at this location.

[0057] First, determine the hydrodynamic parameters of the hard crust, including the wave height under extreme sea conditions. The wavelength is 4.1m The water depth at the hard crust layer is 54.7m. is 12.8m, and the cycle Determine the extreme value of wave pressure on the surface of the crust under extreme sea conditions is 9.2kPa. Determine the velocity of the wave The speed is 8.4m / s. The thickness of the hard shell layer is revealed by drilling in the hard shell layer. The original soil sample obtained by drilling in the hard crust layer was transported back to the laboratory and its density was tested by the ring knife method. Then, the saturated density of the hard crust layer soil was obtained by multiplying it by the acceleration of gravity. 19.1kN / m 3 Determine the top of the soft soil layer due to wave action and the deadweight of the hard crust. The original soil sample obtained by drilling in the soft soil layer was transported back to the laboratory and tested by the ring knife method. 1708kg / m 3 The soft soil layer is fully disturbed and then placed in a direct shear tester to test the cohesion. is 3.6kPa and the internal friction angle is 7.2°. Determine the initial height of the seabed diapir 3.4m. Determine the soft soil layer after it is fully disturbed. is 23.8°. Determine the height of the top of the seabed diapir eroded by waves 2.6m. Determine the actual height of the seabed diapir 0.8m. Determine the diapir diameter The predicted result is consistent with the measured result of "the actual height of the seabed diapir at this location". 0.8m. Determine the diapir diameter The value is close to 15.1 m", which shows that the prediction method of the present invention is reliable.

[0058] In Experiment 2, the tides in the sea area were regular and irregular semi-diurnal tides, with an average tidal range of 2.2m to 3.0m and a high tide range of about 4.1m. The waves were mainly wind waves, with an average wave height of about 0.7m and a maximum wave height of 4.0m to 5.5m. According to marine geological surveys, a typical seabed diapir was found in the sea area. After measurement, the actual height of the seabed diapir was 0.9m. Determine the diapir diameter The prediction method of the present invention is used to predict the bottom split height and diameter at this location.

[0059] Based on the data from the local marine hydrological and meteorological observation station, the hydrodynamic parameters at the hard crust layer were determined, including the wave height under extreme sea conditions. 3.5m wavelength The water depth at the hard crust layer is 57.9m. is 13.5m, and the period Determine the extreme value of wave pressure on the surface of the hard shell under extreme sea conditions is 7.9 kPa. Determine the velocity of the wave The speed is 8.6m / s. The thickness of the hard shell layer is revealed by drilling in the hard shell layer. The original soil sample obtained by drilling in the hard crust layer was transported back to the laboratory and its density was tested by the ring knife method. Then, the saturated density of the hard crust layer soil was obtained by multiplying it by the acceleration of gravity. 19.2kN / m 3 Determine the top of the soft soil layer due to wave action and the deadweight of the hard crust. The original soil sample obtained by drilling in the soft soil layer was transported back to the laboratory and tested by the ring knife method. 1710kg / m 3 The soft soil layer is fully disturbed and then placed in a direct shear tester to test the cohesion. is 3.7kPa and the internal friction angle is 8.0°. Determine the initial height of the seabed diapir 3.6m. Determine the soft soil layer after it is fully disturbed. is 24.1°. Determine the height of the top of the seabed diapir eroded by waves 2.7m. Determine the actual height of the seabed diapir 0.9m. Determine the diapir diameter The predicted result is consistent with the measured result of "the actual height of the seabed diapir at this location". 0.9m. Determine the diapir diameter The value is close to 16.0 m", which shows that the prediction method of the present invention is reliable.

[0060] In Experiment 3, the tide was mainly regular semi-diurnal tide, with a large tidal range of up to 4.93m. The waves were mainly swells, with the highest average wave height in winter and the lowest in summer. During the preliminary survey for the construction of the cross-sea bridge in this area, a typical seabed diapir was discovered. According to the survey results, the actual height of the seabed diapir is 0.5m. Determine the diapir diameter The prediction method of the present invention is used to predict the bottom split height and diameter at this location.

[0061] Based on the data from the local marine hydrological and meteorological observation station, the hydrodynamic parameters at the hard crust layer were determined, including the wave height under extreme sea conditions. The wavelength is 5.6m. The water depth at the hard crust layer is 59.4m. is 21.7m, and the period Determine the extreme value of wave pressure on the surface of the crust under extreme sea conditions is 5.7 kPa. Determine the velocity of the wave The speed is 7.8m / s. The thickness of the hard shell layer is revealed by drilling in the hard shell layer. The original soil sample obtained by drilling in the hard crust layer was transported back to the laboratory and its density was tested by the ring knife method. Then, the saturated density of the hard crust layer soil was obtained by multiplying it by the acceleration of gravity. 19.2kN / m 3 Determine the top of the soft soil layer due to wave action and the deadweight of the hard crust. The original soil sample obtained by drilling in the soft soil layer was transported back to the laboratory and tested by the ring knife method. 1710kg / m 3 The soft soil layer is fully disturbed and then placed in a direct shear tester to test the cohesion. is 3.2kPa and the internal friction angle is 8.2°. Determine the initial height of the seabed diapir 2.7m. Determine the soft soil layer after it is fully disturbed. is 26.4°. Determine the height of the top of the seabed diapir eroded by waves 2.2m. Determine the actual height of the seabed diapir 0.5m. Determine the diapir diameter The predicted result is consistent with the measured result "the actual height of the seabed diapir at this location 0.5m. Determine the diapir diameter It is close to 10.5m", which shows that the prediction method of the present invention is reliable.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for predicting the height and diameter of a seabed diapir, comprising determining seawater parameters of a hard crust layer and calculating soil parameters of the hard crust layer, characterized in that: It also includes calculating the pore pressure at the top of the soft soil layer, the initial height of the seabed diapir, the equivalent internal friction angle of the soft soil layer, and the height of the top of the seabed diapir eroded by waves to obtain the actual height and diameter of the seabed diapir.

2. A method for predicting the height and diameter of a seabed diapir according to claim 1, characterized in that: Pore ​​pressure at the top of the soft soil layer include: ； In the formula, is the extreme value of the wave pressure on the surface of the hard shell layer, is the thickness of the hard shell layer, It is the saturated density of the hard crust soil.

3. A method for predicting the height and diameter of a seabed diapir according to claim 2, characterized in that: Initial height of the seabed diapir include: ； In the formula, It is the density of the original soil sample obtained by the drilling rig in the soft soil layer. is the density of seawater, is the acceleration due to gravity.

4. A method for predicting the height and diameter of a seabed diapir according to claim 3, characterized in that: Equivalent internal friction angle of soft soil layer include: ； In the formula, It is cohesion. is the internal friction angle .

5. A method for predicting the height and diameter of a seabed diapir according to claim 4, characterized in that: The height of the top of the seabed diapir eroded by waves include: ； In the formula, is the velocity of the wave.

6. A method for predicting the height and diameter of a seabed diapir according to claim 5, characterized in that: Actual height of the seabed diapir include: 。 7. A method for predicting the height and diameter of a seabed diapir according to claim 6, characterized in that: Diaper diameter include: 。 8. A method for predicting the height and diameter of a seabed diapir according to claim 7, characterized in that: The velocity of the wave is: ； In the formula, It's a cycle.

9. A method for predicting the height and diameter of a seabed diapir according to claim 8, characterized in that: The hydrodynamic parameters of the hard crust include wave height ,wavelength , water depth at the hard crust and period, the extreme value of wave pressure on the surface of the hard shell layer is: ； In the formula, is a hyperbolic function.

10. A method for predicting seabed diapir height and diameter according to claim 1, characterized in that: The soil parameters of the hard shell layer include the thickness of the hard shell layer, the saturated density of the hard shell layer soil, and the natural density of the soft soil layer; the hard shell layer is drilled by a drilling rig to obtain the thickness of the hard shell layer, the density of the original soil sample obtained by the drilling rig in the hard shell layer is tested by the ring knife method, and the saturated density of the hard shell layer soil is obtained by multiplying the gravity acceleration, the density of the original soil sample obtained by the drilling rig in the soft soil layer is tested by the ring knife method, the soft soil layer is fully disturbed, and placed in a direct shear instrument to test the cohesion and internal friction angle.

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