A method for predicting the length of a hard shell layer of a submarine to be pulled apart

Abstract

The application relates to a method for predicting the cracking length of a seabed hard shell layer. The working principle of the method is that when a weak underlayer causes the overlying hard shell layer to slide in a disturbance process, the wave friction force on the surface of the hard shell layer, the gravity of the hard shell layer and the friction force of the underlayer are the forces causing the hard shell layer to crack, and the internal strength of the hard shell layer is the force resisting cracking, and when the two are equal, the cracking length can be solved. The method has the advantages of simple structure, strong process nature and convenient use.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of ocean engineering, and particularly relates to a method for predicting the length of a seabed hard crust layer. BACKGROUND

[0002] The seabed hard crust layer is a unique stratum structure and is relatively common in some seabed environments. When extreme weather such as typhoon and storm surge occurs, the soft underlying layer under the hard crust layer can be disturbed and its strength can be reduced, and the soft underlying layer can slide down along the slope, at this time, the hard crust layer above the soft underlying layer also slides down along the soft underlying layer to the lower part of the slope, and the hard crust layer is pulled and cracked. The pulled and cracked block continues to slide down along the slope and collides with the structures such as the lower seabed pipeline and pile foundation, and the size of the impact force is closely related to the length of the pulled and cracked block. As for the length of the pulled and cracked block, there is no other theoretical method for calculating the length of the pulled and cracked block except for post-investigation measurement. Therefore, the present application provides a method for predicting the length of the seabed hard crust layer, which has the advantages of simple structure, strong process and convenient use. SUMMARY

[0003] The present application aims to provide a method for predicting the length of a seabed hard crust layer, which has the advantages of simple structure, strong process and convenient use.

[0004] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows: a method for predicting the length of a seabed hard crust layer, comprising the following steps:

[0005] (1) determining the wave parameters at the position of the hard crust layer in extreme weather, including the wave height H, the period T, the wave length L and the water depth d;

[0006] (2) determining the maximum flow velocity u of the wave on the surface of the hard crust layer max ;

[0007] (3) determining the friction force τ0 generated by the wave on the surface of the hard crust layer;

[0008] (4) determining the thickness H0 and the inclination angle β of the hard crust layer;

[0009] (5) determining the saturated unit weight γ of the hard crust layer sat ;

[0010] (6) determining the cohesion c and the internal friction angle φ of the hard crust layer

[0011] (7) determining the undrained shear strength c of the soft underlying layer u ;

[0012] (8) determining the pulling force T1 caused by the wave friction force in the hard crust layer;

[0013] (9) determining the pulling force T2 caused by the self-weight of the hard crust layer;

[0014] (10) determine the tensile force T3 caused by the sliding of the weak underlayer;

[0015] (11) determine the tensile resistance R of the hard shell layer;

[0016] (12) solve L0 by solving the equation T1+T2+T3=R, which is the tensile length of the hard shell layer.

[0017] Compared with the prior art, the present application has the following beneficial effects: the working principle of the present application is that when the soft underlayer is disturbed, the sliding of the overlying hard shell layer is caused, the wave friction force on the surface of the hard shell layer, the gravity of the hard shell layer itself and the friction force of the underlayer are the forces causing the tensile cracking of the hard shell layer, and the internal strength of the hard shell layer itself is the force resisting the tensile cracking, when the two are equal, the tensile cracking length can be solved. DETAILED DESCRIPTION

[0018] Next, the technical scheme of the present application will be specifically described.

[0019] The present application is a method for predicting the tensile length of a hard shell layer on the seabed, comprising the following steps:

[0020] (1) determine the wave parameters at the position of the hard shell layer in extreme weather, including wave height H, period T, wave length L and water depth d.

[0021] According to the wave parameter value experience of the place, the above wave parameters are determined.

[0022] (2) determine the maximum flow velocity u of the wave on the surface of the hard shell layer max .

[0023]

[0024] Wherein, k is the wave number, k=2π / L.

[0025] (3) determine the friction force τ0 generated by the wave on the surface of the hard shell layer.

[0026] τ0=ρ w fu max 2

[0027] Wherein, ρ w is the density of seawater, taking 1025kg / m 3 ; f is the friction coefficient, taking 0.02.

[0028] (4) determine the thickness H0 and the inclination angle β of the hard shell layer.

[0029] The thickness H0 is determined by drilling results, and the inclination angle β of the hard shell layer is tested by placing an inclination angle instrument on the surface of the hard shell layer.

[0030] (5) Determine the saturated unit weight γ of the crust sat .

[0031] Take a typical undisturbed soil sample in the crust with a drilling rig, transport it to the laboratory, and test its density with the ring knife method, then multiply it by the acceleration of gravity to obtain its saturated unit weight γ sat .

[0032] (6) Determine the cohesion c and internal friction angle of the crust

[0033] Use the typical undisturbed soil sample obtained to conduct a direct shear test in the laboratory to measure its cohesion c and internal friction angle

[0034] (7) Determine the undrained shear strength c of the soft underlying layer u .

[0035] Use the vane shear apparatus to test its undrained shear strength c in situ u .

[0036] (8) Determine the tensile cracking force T1 caused by wave friction in the crust.

[0037] T1 = τ0L0l0

[0038] Where L0 is the tensile cracking length, a parameter to be solved; l0 is the unit width, taken as 1.0 m.

[0039] (9) Determine the tensile cracking force T2 caused by the self-weight of the crust.

[0040] T2 = H0L0l0γ sat sinβ

[0041] (10) Determine the tensile cracking force T3 caused by the sliding of the soft underlying layer.

[0042] T3 = αL0l0c u

[0043] Where α is the disturbance intensity reduction coefficient, taken as 0.30.

[0044] (11) Determine the tensile cracking resistance R of the crust.

[0045]

[0046] (12) Solve the equation T1 + T2 + T3 = R to obtain L0, which is the tensile cracking length of the crust.

[0047] Implementation Case

[0048] In a certain sea area of ​​my country, a hard crust has developed on the seabed. Under extreme weather conditions, this hard crust fractures and slides down the slope, threatening pipelines below. To determine the fracture length of the hard crust, the method of this invention is used for prediction.

[0049] Based on experience with wave parameters in this area, the wave parameters at the location of the hard crust during extreme weather are determined, including a wave height H of 4.1 m, a period T of 5.2 s, a wavelength L of 52.7 m, and a water depth d of 7.8 m. The maximum wave velocity u at the surface of the hard crust is then determined. max The velocity was 7.62 m / s. The frictional force τ0 generated by the wave on the surface of the hard crust was determined to be 1.19 kPa. Using drilling results, the thickness H0 of the hard crust was determined to be 2.1 m. An inclinometer was placed on the surface of the hard crust, and the dip angle β was measured to be 1.2°. Typical undisturbed soil samples were taken from within the hard crust using a drilling rig and transported back to the laboratory. The density was measured using the ring cutter method, and then multiplied by the gravitational acceleration to obtain the saturated unit weight γ of the hard crust. sat 19.6 kN / m 3 Using typical undisturbed soil samples, direct shear tests were conducted in the laboratory. The cohesion c of the hard shell layer was measured to be 24.7 kPa, and the internal friction angle was [missing value]. The angle was 18.6°. The undrained shear strength c of the weak underlying layer was determined in situ using a vane shear apparatus. u The stress is 12.3 kPa. The tensile fracturing force T1 caused by wave friction within the hard shell is determined to be 1.19L0. The tensile fracturing force T2 caused by the hard shell's own weight is determined to be 0.86L0. The tensile fracturing force T3 caused by the sliding of the weak underlying layer is determined to be 3.69L0. The tensile resistance R of the hard shell is determined to be 17.46 kN. Solving the simultaneous equations T1 + T2 + T3 = R, the tensile fracturing length L0 of the hard shell is found to be 3.04 m.

[0050] The above are preferred embodiments of the present invention. Any changes made to the technical solution of the present invention that do not exceed the scope of the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for predicting the tensile fracture length of a hard crust on the seabed, characterized in that, The method comprises the following steps: (1) determining wave parameters at the position of the hard shell layer in extreme weather, including wave height H, period T, wave length L and water depth d; (2) determining the maximum flow velocity u of the waves on the surface of the hard shell layer max ; (3) determining the friction force τ0 generated by the wave on the surface of the hard shell layer; (4) determining the thickness H0 and the inclination angle β of the hard shell layer; (5) determining the saturation weight γ of the hard shell layer sat ; (6) determining cohesion c and internal friction angle of the hard shell layer (7) determining the undrained shear strength c of the weak underlying layer u ; (8) determining the tensile force T1 caused by the wave friction in the hard shell layer; (9) determining the tensile force T2 caused by the self-weight of the hard shell layer; (10) determining the tensile force T3 caused by the sliding of the soft underlying layer; (11) determining the tensile resistance R of the hard shell layer; (12) solving L0 by simultaneously solving the equation T1+T2+T3=R, wherein L0 is the tensile length of the hard shell layer.

2. A method of predicting the length of a hard shell layer of a subsea pipeline according to claim 1, wherein, In step (2), the maximum flow velocity u of the wave on the surface of the hard shell layer max The calculation formula is: Wherein, k is the wave number, k=2π / L.

3. The method of claim 1, wherein, In step (3), the calculation formula of the friction force τ0 generated by the wave on the surface of the hard shell layer is: t0 = p w fu max 2 wherein p w is the density of seawater, taken as 1025 kg / m 3 ; f is the friction coefficient, taken as 0.

02.

4. The method of claim 1, wherein, In step (4), the thickness H0 and the inclination angle β of the hard shell layer are determined by using drilling results to determine the thickness H0, and placing an inclination angle instrument on the surface of the hard shell layer to test the inclination angle β of the hard shell layer.

5. The method of claim 1, wherein, In step (5), the saturated unit weight γ of the hard shell is determined. sat The method is as follows: a typical undisturbed soil sample is taken from within the hard crust using a drilling rig, transported back to the laboratory, and its density is tested using the ring cutter method. Then, it is multiplied by the gravitational acceleration to obtain its saturated unit weight γ. sat .

6. The method of predicting the length of a hard shell layer pull-apart according to claim 1, wherein, In step (6), the cohesion c and the internal friction angle of the hard shell layer are determined are determined by performing a direct shear test on the typical undisturbed soil sample in a laboratory 7. The method of predicting the length of a hard shell layer of a subsea pipeline according to claim 1, wherein, In step (7), the undrained shear strength c of the weak underlayer is determined u by in-situ testing of its undrained shear strength c u using a vane shear apparatus.

8. The method of predicting the length of a hard shell layer of a subsea pipeline according to claim 1, wherein, In step (8), the calculation formula of the tensile force T1 caused by the wave friction in the hard shell layer is: T1=τ0L0l0 Wherein, L0 is the tensile length, a parameter to be solved; l0 is the unit width, which is 1.0 m; In step (9), the calculation formula of the tensile force T2 caused by the self-weight of the hard shell layer is: T2 = H0L0l0γ sat sinβ In step (10), the calculation formula of the tensile force T3 caused by the sliding of the soft underlying layer is: T3 = a L0 l0c u Wherein, α is the disturbance intensity reduction coefficient, which is 0.30; In step (11), the calculation formula of the tensile resistance R of the hard shell layer is:

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