A method for predicting the depth of hard crust collapse under wave action

Abstract

This invention provides a method for predicting the subsidence depth of a hard-shell layer under wave action, comprising the following steps: determining the thickness z1 of the hard-shell layer and the water depth d; determining the undrained shear strength c of the hard-shell layer soil. u Determine the unit weight γ1 of the hard shell and the unit weight γ2 of the underlying soft soil; determine the cohesion c of the underlying soft soil; determine the wave parameters at the hard shell under extreme sea states, including wave height H and wavelength L; determine the extreme pressure p0 exerted by waves on the hard shell; determine the average wave pressure p1 within the collapse area; determine the side length B of the collapse; determine the self-weight G of the hard shell collapse; determine the sinking depth h of the hard shell collapse under wave action.

Description

Technical Field

[0001] This invention relates to the field of marine engineering, specifically a method for predicting the depth of collapse of hard crust blocks under wave action. Background Art

[0002] A hard crust is a geological structure developed within the seabed surface strata, and its strength is higher than that of the underlying strata. Under extreme sea conditions, such as storm surges and typhoons, the strong wave action causes the underlying strata, with their lower strength, to soften or liquefy, while the hard crust, with its higher strength, is less prone to liquefaction. This reduces the strength and supporting capacity of the underlying soil, making it susceptible to tearing and collapse under its own weight and wave loads. These collapses then further subside under wave loads. Determining the depth of this subsidence is crucial for analyzing its impact on marine engineering and understanding the evolution of seabed strata. To date, no method has been found to definitively determine the depth of this subsidence. Summary of the Invention

[0003] The main technical problem to be solved by this invention is to propose a method for predicting the depth of collapse of hard shell blocks under wave action, which has the advantages of strong process and reliable results.

[0004] To address the aforementioned technical problems, this invention provides a method for predicting the subsidence depth of a hard shell block under wave action, comprising the following steps:

[0005] (1) Determine the thickness z1 of the hard shell and the water depth d;

[0006] (2) Determine the undrained shear strength c of the hard-shell soil. u ;

[0007] (3) Determine the unit weight γ1 of the hard shell layer and the unit weight γ2 of the underlying soft soil;

[0008] (4) Determine the cohesion c of the soft soil mass beneath the hard shell layer;

[0009] (5) Determine the wave parameters at the hard shell under extreme sea states, including wave height H and wavelength L;

[0010] (6) Determine the extreme pressure p0 exerted by the wave on the hard shell:

[0011]

[0012] Where, γ w The specific gravity of seawater is taken as 10.25 kN / m. 3 ;

[0013] (7) Determine the average wave pressure p1 within the collapsed area:

[0014]

[0015] Where B is the side length of the collapsed block, and is the parameter to be determined;

[0016] (8) Determine the side length B of the collapsed block;

[0017] Solve the equation to determine the side length B of the collapsed block, p1B = 4z1c u Take the smaller of the results;

[0018] (9) Determine the self-weight G of the collapsed hard shell block;

[0019] G = B 2 z1γ1

[0020] (10) Determine the sinking depth h of the collapsed hard crust block under wave action:

[0021] Solve the equation to determine the depth of the depression, h.

[0022] (B 2 +4Bh)c+γ2B 2 h = B 2 p1+G

[0023] In a preferred embodiment: In step 1, drilling is performed at the hard shell layer, and the thickness z1 of the hard shell layer is determined using the drilling results; at the hard shell layer, the water depth is measured using a water depth measuring tool to determine the water depth d at the hard shell layer.

[0024] In a preferred embodiment: Step 2 involves using undisturbed soil samples obtained from drilling through the hard shell layer, transporting them back to the laboratory for microvane shear tests to determine the undrained shear strength c of the hard shell layer soil. u .

[0025] In a preferred embodiment: In step 3, the undisturbed soil samples obtained by drilling through the hard shell layer and the underlying soft soil are transported back to the laboratory for density testing. After the density is tested, it is multiplied by the gravitational acceleration to obtain the unit weight γ1 of the hard shell layer and the unit weight γ2 of the underlying soft soil.

[0026] In a preferred embodiment: In step 4, the undisturbed soil sample taken from the lower soft soil body is transported back to the laboratory for a direct shear test to determine its cohesion c.

[0027] In a preferred embodiment: in step 5, wave parameters of the hard shell under extreme sea conditions are determined based on measured data or theoretical calculations, including wave height H and wavelength L.

[0028] The working principle of this invention is as follows: when waves act on a hard shell layer, the high strength of the hard shell makes it difficult to liquefy, while the lower, weaker soil is more prone to liquefaction. Once liquefied, the lower part of the upper hard shell loses support, leading to a collapse. The dimensions of the collapsed block are calculated using the principle of mechanical equilibrium. Then, the wave pressure and the block's own weight are calculated; these forces cause the block to sink, while the supporting force and buoyancy of the soil at the bottom prevent further sinking. The depth of the collapse is then determined using mechanical equilibrium methods. Therefore, this method has the advantages of being highly streamlined and providing reliable results. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed", "equipped", "sleeved / connected", "connected", etc., should be interpreted broadly. For example, "connection" can be a wall-mounted connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0031] This embodiment provides a method for predicting the subsidence depth of a hard shell block under wave action, including the following steps:

[0032] (1) Determine the thickness z1 of the hard shell and the water depth d.

[0033] Drilling is conducted at the hard shell layer, and the thickness z1 of the hard shell layer is determined using the drilling results. Water depth is measured at the hard shell layer using a water depth measuring tool to determine the water depth d at the hard shell layer.

[0034] (2) Determine the undrained shear strength c of the hard-shell soil. u .

[0035] Undamaged soil samples obtained from drilling through the hard shell layer were transported back to the laboratory for microvane shear tests to determine the undrained shear strength c of the hard shell soil. u .

[0036] (3) Determine the unit weight γ1 of the hard shell layer and the unit weight γ2 of the underlying soft soil.

[0037] Uncirculated soil samples were drilled from the hard shell and the underlying soft soil and transported back to the laboratory for density tests. After the density was measured, it was multiplied by the gravitational acceleration to obtain the unit weight γ1 of the hard shell and the unit weight γ2 of the underlying soft soil.

[0038] (4) Determine the cohesion c of the soft soil body under the hard shell layer.

[0039] Uncirculated soil samples taken from the underlying soft soil were transported back to the laboratory for direct shear tests to determine their cohesion c.

[0040] (5) Determine the wave parameters at the hard shell under extreme sea conditions, including wave height H and wavelength L.

[0041] Based on measured data or theoretical calculations, determine the wave parameters of the hard shell under extreme sea conditions, including wave height H and wavelength L.

[0042] (6) Determine the extreme pressure p0 exerted by the wave on the hard shell.

[0043]

[0044] Where, γ w The specific gravity of seawater is taken as 10.25 kN / m. 3 .

[0045] (7) Determine the average wave pressure p1 within the collapse area.

[0046]

[0047] Where B is the side length of the collapsed block, and is the parameter to be determined.

[0048] (8) Determine the side length B of the collapsed block.

[0049] Solve the equation to determine the side length B of the collapsed block, p1B = 4z1c u Take the smaller of the results.

[0050] (9) Determine the self-weight G of the collapsed hard shell.

[0051] G = B 2 z1γ1

[0052] (10) Determine the depth h of the collapse of the hard shell block under wave action.

[0053] Solve the equation to determine the depth of the depression, h.

[0054] (B 2 +4Bh)c+γ2B 2 h = B 2 p1+G

[0055] Implementation Cases

[0056] In a certain sea area of ​​my country, a hard crust is developed on the seabed surface, and there are many oil pipelines in the area. In order to assess the impact of the collapse of the hard crust on the oil pipelines, it is necessary to determine the sinking depth of the collapse under the action of waves in advance. The method of this invention is used for prediction.

[0057] Drilling was conducted at the hard crust layer, and the thickness z1 of the hard crust layer was determined to be 0.66 m using the drilling results. The water depth d at the hard crust layer was measured using a water depth measuring tool and determined to be 11.2 m. Undisturbed soil samples obtained from the drilling of the hard crust layer were transported back to the laboratory for microvane shear tests to determine the undrained shear strength c of the hard crust layer soil. u The density was 26.1 kPa. Uncirculated soil samples were drilled from the hard crust and the underlying soft soil mass and transported back to the laboratory for density tests. After determining the density, each sample was multiplied by the gravitational acceleration to obtain the unit weight γ1 of the hard crust, which was 19.3 kN / m³. 3 The unit weight γ2 of the underlying soft soil is 16.1 kN / m. 3 Uncirculated soil samples taken from the underlying soft soil were transported back to the laboratory for direct shear tests, yielding a cohesion c of 13.6 kPa. Based on theoretical calculations, the wave parameters for the hard shell layer under extreme sea states were determined, with a wave height H of 4.3 m and a wavelength L of 51.7 m. The extreme pressure p0 exerted by the waves on the hard shell layer was determined to be 10.6 kPa. The average wave pressure p1 within the collapsed area was determined to be 10.6 - 0.2B. Furthermore, the side length B of the collapsed block was calculated to be 7.6 m. The self-weight G of the collapsed hard shell layer was determined to be 733.1 kN. Finally, by solving the equations, the sinking depth h of the collapsed hard shell layer under wave action was determined to be 0.35 m.

[0058] The above description is merely a preferred embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention by those skilled in the art within the scope of the technology disclosed in the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A method for predicting the subsidence depth of a hard crust block under wave action, characterized in that... The steps include: (1) Determine the thickness z1 of the hard shell and the water depth d; (2) Determine the undrained shear strength c of the hard-shell soil. u ; (3) Determine the unit weight γ1 of the hard shell layer and the unit weight γ2 of the underlying soft soil; (4) Determine the cohesion c of the soft soil mass beneath the hard shell layer; (5) Determine the wave parameters at the hard shell under extreme sea states, including wave height H and wavelength L; (6) Determine the extreme pressure p0 exerted by the wave on the hard shell: Where, γ w The specific gravity of seawater is taken as 10.25 kN / m. 3 ; (7) Determine the average wave pressure p1 within the collapsed area: Where B is the side length of the collapsed block, and is the parameter to be determined; (8) Determine the side length B of the collapsed block; Solve the equation to determine the side length B of the collapsed block, p1B = 4z1c u Take the smaller of the results; (9) Determine the self-weight G of the collapsed hard shell block; G=B 2 z1γ1 (10) Determine the sinking depth h of the collapsed hard crust block under wave action: Solve the equation to determine the depth of the depression, h. (B 2 +4Bh)c+γ2B 2 h=B 2 p1+G。 2. The method for predicting the subsidence depth of a hard shell block under wave action according to claim 1, characterized in that: In step 1, drilling is carried out at the hard shell layer, and the thickness z1 of the hard shell layer is determined using the drilling results; at the hard shell layer, the water depth is measured using a water depth measuring tool to determine the water depth d at the hard shell layer.

3. The method for predicting the subsidence depth of a hard shell block under wave action according to claim 1, characterized in that: Step 2: Undamaged soil samples obtained from drilling through the hard shell layer are transported back to the laboratory for microvane shear tests to determine the undrained shear strength c of the hard shell soil. u .

4. The method for predicting the subsidence depth of a hard shell block under wave action according to claim 1, characterized in that: In step 3, undisturbed soil samples obtained by drilling through the hard shell and the underlying soft soil were transported back to the laboratory for density tests. After the density was measured, it was multiplied by the gravitational acceleration to obtain the unit weight γ1 of the hard shell and the unit weight γ2 of the underlying soft soil.

5. The method for predicting the subsidence depth of a hard shell block under wave action according to claim 1, characterized in that: In step 4, the undisturbed soil sample taken from the lower soft soil mass is transported back to the laboratory for a direct shear test to determine its cohesion c.

6. The method for predicting the subsidence depth of a hard shell block under wave action according to claim 1, characterized in that: In step 5, based on measured data or theoretical calculations, the wave parameters of the hard shell under extreme sea conditions are determined, including wave height H and wavelength L.

Images