A method for predicting the safety of a sea cave entrance in an extreme sea state

Abstract

The application discloses a method for predicting the safety of a sea-erosion cave entrance under extreme sea conditions, which comprises the following steps: obtaining the geometric size of the sea-erosion cave entrance; obtaining the hydrodynamic parameters of the cave entrance under extreme sea conditions; calculating the impact force of a swell on the cave entrance; calculating the impact force of a stationary wave on the cave entrance; calculating the most unfavorable wave load on the cave entrance; calculating the wave shear stress on the bottom of the cave entrance; obtaining the relationship between the shear strength between the cave entrance material and the cave body and the number of wave cyclic load continuous actions; obtaining the shear strength between the cave entrance material and the cave body at the end of wave action under extreme sea conditions; obtaining the relationship between the tensile strength between the cave entrance material and the cave body and the number of wave cyclic load continuous actions; obtaining the tensile strength between the cave entrance material and the cave body at the end of wave action under extreme sea conditions; determining whether the cave entrance appears sliding damage; determining whether the cave entrance appears lodging; and determining whether the cave entrance is safe. The application has the advantages of convenient use and reliable results.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of marine geological disasters, and particularly relates to a method for predicting the safety of a sea cave entrance under extreme sea conditions. BACKGROUND

[0002] A sea cave is an erosion landform phenomenon developed on a sea cliff. With the continuous action of waves, the depth and height of the sea cave continuously increase. When the cave extends to a certain extent, the cave roof collapses, endangering the safety of human beings and engineering facilities above the cave roof. Therefore, it is an ideal method to close the cave entrance with the same material as the sea cliff to avoid the continuous expansion of wave erosion. However, so far, the safety of the cave entrance mostly relies on engineering experience, and there is no theoretical determination method for the safety of the cave entrance. SUMMARY

[0003] The present application aims to overcome the shortcomings of the prior art and provide a method for predicting the safety of a sea cave entrance under extreme sea conditions, which has the advantages of convenient use and reliable results.

[0004] To achieve the above-mentioned purpose, the technical solution of the present application is a method for predicting the safety of a sea cave entrance under extreme sea conditions, comprising:

[0005] (1) obtaining the geometric dimensions of the sea cave entrance, including the length l, the height h and the thickness d of the entrance;

[0006] (2) obtaining the hydrodynamic parameters of the entrance under extreme sea conditions, including the surge flow velocity v, the standing wave height H, the standing wave period T and the standing wave duration t0;

[0007] (3) calculating the impact force F1 of the surge on the entrance, as follows:

[0008]

[0009] wherein, ρ w is the density of seawater;

[0010] (4) calculating the impact force F2 of the standing wave on the entrance, as follows:

[0011] F2 = ρ w gHlh

[0012] wherein, g is the acceleration of gravity;

[0013] (5) calculating the most unfavorable wave load F on the entrance, as follows:

[0014] F = max(F1, F2)

[0015] wherein, max is a function of taking the maximum value;

[0016] (6) Calculate the wave shear stress τ experienced by the bottom of the portal s As follows:

[0017]

[0018] (7) Obtain the relationship between the shear strength between the portal material and the portal body and the number of wave cyclic load durations, τ = aexp(bN);

[0019] Using large-scale cyclic direct shear tests, the applied shear stress is τ s , the period is T, and the decayed strength τ i is measured at different cycle numbers N i . Using the relationship data between cycle number and decayed strength, the least squares method is used to fit the parameters a and b, and an exponential function relationship between them is established, τ = aexp(bN);

[0020] (8) Obtain the shear strength τ a between the portal material and the portal body at the end of the extreme sea state wave action;

[0021] Substitute the total number of wave cycles N a = t0 / T into τ a = aexp(bN a ), and solve for τ a ; where t0 represents the duration of the standing wave (i.e. the total action time of the wave under extreme sea conditions), and T represents the standing wave period;

[0022] (9) Obtain the relationship between the tensile strength between the portal material and the portal body and the number of wave cyclic load durations, σ t = cexp(dN);

[0023] Using dynamic triaxial tests, the dynamic stress applied is 2τ s , the period is T, and the decayed strength σ ti is measured at different cycle numbers N i . Using the relationship data between cycle number and decayed strength, the least squares method is used to fit the parameters c and d, and an exponential function relationship between them is established, σ t = cexp(dN);

[0024] (10) Obtain the tensile strength σ ta between the portal material and the portal body at the end of the extreme sea state wave action

[0025] Substitute the total number of wave cycles N a = t0 / T into σ ta = cexp(dN a ), and solve for σ ta ;

[0026] (11) determining whether the hole door appears sliding failure

[0027] If τ a ≥ τ s , the hole door will not appear sliding failure, otherwise, the hole door appears sliding failure;

[0028] (12) determining whether the hole door appears collapse

[0029] If Gd + ld 2 σ ta ≥ Fh, the hole door will not appear collapse; otherwise, the hole door appears collapse, wherein G = lhdγ, and γ is a preset value;

[0030] (13) determining whether the hole door is safe

[0031] If the hole door appears sliding or appears collapse, the hole door is not safe; if the hole door will not appear sliding and will not appear collapse, the hole door is safe.

[0032] The above description of the present application can know that, compared with the prior art, the present application has the following beneficial effects:

[0033] The present application has the advantages of convenient use and reliable results.

[0034] The present application will be further described in detail below in combination with the drawings and examples, but the present application is not limited to the examples. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 The flow chart of the present application is shown in the figure. DETAILED DESCRIPTION

[0036] The technical solutions in the examples of the present application will be described and discussed in detail below in combination with the drawings of the present application. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0037] Referring to Figure 1 the figure, the present application is a method for predicting the safety of a sea-eroded cave hole door under extreme sea conditions, which comprises:

[0038] S101, obtaining the geometric size of the sea-eroded cave hole door, including the length l, the height h and the thickness d of the hole door.

[0039] According to the hole door design data, the above parameters are obtained.

[0040] S102, obtain the water dynamic parameters of the portal under extreme sea conditions, including the surge flow velocity v, the standing wave height H, the standing wave period T and the standing wave duration t0.

[0041] According to the marine meteorological and hydrological observation data or theoretical calculation, the above water dynamic parameters are obtained.

[0042] S103, calculate the impact force F1 of the surge on the portal.

[0043]

[0044] wherein, ρ w is the seawater density, taken as 1025 kg / m 3 .

[0045] S104, calculate the impact force F2 of the standing wave on the portal.

[0046] F2=ρ w gHlh

[0047] wherein, g is the gravity acceleration.

[0048] S105, calculate the most unfavorable wave load F of the portal.

[0049] F=max(F1,F2)

[0050] wherein, max is a function of taking the maximum value of the latter parameter.

[0051] S106, calculate the wave shear stress τ s of the portal bottom.

[0052]

[0053] S107, obtain the relationship formula τ=aexp(bN) between the shear strength between the portal material and the portal body and the number of wave cyclic load durations.

[0054] By using a large-scale cyclic direct shear test, the applied shear stress is τ s , the period is T, the decayed strength τ i is measured at different cycle numbers N i , by using the relationship data between the cycle number and the decayed strength, by using the least square method, the parameters a, b are fitted to establish the exponential function relationship between them, τ=aexp(bN).

[0055] S108, obtain the shear strength τ a between the portal material and the portal body at the end of the wave action under extreme sea conditions.

[0056] Substitute the total cycle number of the wave N a =t0 / T into the τa = aexp(bN a ), find σ a . Where t0 represents the duration of the wave action (i.e. the total time of wave action under extreme sea conditions), and T represents the wave period.

[0057] S109, obtain the relationship between the tensile strength between the hole material and the hole body and the number of wave cyclic load duration, σ t = cexp(dN).

[0058] Using dynamic triaxial test, the dynamic stress applied is 2τ s , the period is T, the strength σ i after attenuation at different cycle numbers N ti is measured, using the relationship between cycle number and attenuation strength data, using the least square method, fitting the parameters c, d, to establish the exponential function relationship between them, σ t = cexp(dN).

[0059] S110, obtain the tensile strength σ ta between the hole material and the hole body at the end of the wave action under extreme sea conditions.

[0060] Substitute the total cycle number of the wave N a = t0 / T into τ a = aexp(bN a ), find σ ta .

[0061] S111, determine whether the hole door appears sliding failure.

[0062] If τ a ≥ τ s , the hole door will not slide failure, otherwise, the hole door appears sliding failure.

[0063] S112, determine whether the hole door will appear to fall.

[0064] If Gd + ld 2 σ ta ≥ Fh, the hole door will not fall; otherwise, it will appear to fall, where G = lhdγ, γ takes 25.0 kN / m 3 .

[0065] S113, determine whether the hole door is safe.

[0066] If the hole door appears sliding or appears to fall, the hole door is not safe; if the hole door will not appear sliding and will not appear to fall, the hole door is safe.

[0067] In the embodiment, the extreme sea condition is the meaning disclosed in the prior art, specifically refers to storm surge phenomenon caused by typhoon, due to severe atmospheric disturbance, such as strong wind and pressure change, resulting in abnormal rise and fall of seawater, the phenomenon that the tidal level of the affected sea area greatly exceeds the normal tidal level.

[0068] The working principle of the present application is that after the construction of the hole door, under the action of one of the cyclic loads of the surge wave or the standing wave, the shear strength between the hole door bottom and the hole body is continuously reduced, if the wave shear stress exceeds the shear strength of the bottom, the hole door slides, if the wave force is too large, exceeding the anti-avalanche capacity provided by the self-weight and the tensile strength of the bottom, the hole door appears to be avalanching. Therefore, if the hole door does not appear any one of sliding or avalanching, the hole door is in a safe state, otherwise, the hole door is unsafe.

[0069] Due to long-term wave erosion, a typical sea cave is developed on a coastal cliff in the southeast coast of China. In order to ensure the safety of the facilities above the sea cave, the hole door is closed by ramming soil. In order to determine the safety of the hole door under extreme sea conditions, the method of the present application is used for prediction.

[0070] According to the design data of the hole door, the geometric size of the hole door of the sea cave is obtained, including the length l of the hole door is 0.79m, the height h is 1.85m, and the thickness d is 0.50m. According to the marine meteorological and hydrological observation data, the hydrodynamic parameters of the hole door under extreme sea conditions are obtained, wherein the flow velocity v of the surge wave is 1.74m / s, the standing wave height H is 0.72m, the standing wave period T is 4.1s, and the standing wave duration t0 is 2.6h. The impact force F1 of the surge wave on the hole door is calculated as 2.27kN. The impact force F2 of the standing wave on the hole door is calculated as 10.57kN. The most unfavorable wave load F of the hole door is calculated as 10.57kN. The wave shear stress τ s of the hole door bottom is calculated as 26.76kPa. By using large-scale cyclic direct shear test, the applied shear stress is 26.76kPa, the period T is 4.1s, and the strength τ i after attenuation at different cycle numbers N i is measured. By using the relationship data between cycle number and attenuated strength, by using the least square method, the exponential function relationship between them is established, and the relationship between the shear strength between the hole door material and the hole body and the cycle number of the wave cyclic load is obtained as τ=9.31exp(-0.00004N). The total cycle number of the wave is calculated as N a =1902. The shear strength τ a between the hole door material and the hole body at the end of the wave action under extreme sea conditions is obtained as 8.63kPa. By using dynamic triaxial test, the applied dynamic stress is 53.52kPa, the period T is 4.1s, and the strength σ i after attenuation at different cycle numbers N ti, using the relationship data between the cycle number and the attenuation intensity, using the least square method, an exponential function relationship between them is established, and the relationship between the tensile strength between the hole door material and the hole body and the wave cycle load duration number is obtained σ t = 7.07exp(-0.00007N). The tensile strength σ ta between the hole door material and the hole body at the end of the wave action in the extreme sea state is 6.19kPa. Since τ a < τ s , the hole door slides and is damaged. Since Gd+ld 2 σ ta is 10.35kN·m, Fh is 19.55kN·m, Gd+ld 2 σ ta <Fh, the hole door collapses, so the hole door is in an unsafe state.

[0071] The above is only one preferred embodiment in the examples of the present application. However, the present application is not limited to the above-mentioned embodiment, and any equivalent changes and modifications made according to the present application, as long as the resulting functional effects do not exceed the scope of the present application, are within the scope of protection of the present application.

Claims

1. A method for predicting the safety of a sea cave entrance in extreme sea conditions, characterized in that, Comprise: (1) Obtain the geometric size of the sea cave entrance, including the length l, height h and thickness d of the entrance; (2) Obtain the hydrodynamic parameters of the entrance under extreme sea conditions, including the surge flow velocity v, stationary wave height H, stationary wave period T and stationary wave duration t0; (3) Calculate the impact force F1 of the surge on the entrance as follows: where p w is the density of seawater; (4) Calculate the impact force F2 of the stationary wave on the entrance as follows: F2 = p w gHlh Wherein, g is the acceleration of gravity; (5) Calculate the most unfavorable wave load F on the entrance as follows: F=max(F1,F2) Wherein, max is the function of taking the maximum value; (6) Calculate the wave shear stress τ at the bottom of the entrance s As follows: (7) Obtain the relationship between the shear strength between the entrance material and the cave body and the number of wave cyclic load duration N, τ=aexp(bN); Using large-scale cyclic direct shear test, the shear stress τ s is applied, the cycle is T, the strength τ i after attenuation is measured at different cycle times N i , using the relationship data between cycle times and attenuation strength, using the least square method, fitting the parameters a and b, establishing the exponential function relationship between them, τ=aexp(bN); (8) Obtain the shear strength τ between the material of the hole mouth and the hole body at the end of the action of the extreme sea state wave a ; N = total number of wave cycles a = t0 / T, substituted into τ a = aexp(bN a ) to find τ a ; where t0 represents the duration of the standing wave and T represents the period of the standing wave. (9) Obtain the relationship between the tensile strength between the portal material and the portal body and the number of wave cycle load continuous action times σ t = cexp(dN); Using dynamic triaxial test, dynamic stress of 2τ s , cycle of T, measured different cycle times N i , the strength of the decay σ ti , using the cycle number and the relationship between the decay strength data, using the least squares method, fitting the parameters c and d, the establishment of the exponential function between the two, σ t =c exp(dN) (10) Obtain the tensile strength σ between the hole material and the hole body at the end of the action of the extreme sea state wave ta The total number of wave cycles is N a = t0 / T, which is substituted into σ ta = c exp(dN a ), and σ ta is found; (11) Determine whether the entrance appears sliding failure If τ a ≥ τ s , then the tunnel portal will not slide, otherwise, the tunnel portal will slide. (12) Determine whether the entrance will appear lodging If Gd + lid 2 σ ta ≥ Fh, the hole gate will not be lodging; otherwise, lodging will occur, where G = lhdγ, and γ is a predetermined value. (13) Determine whether the entrance is safe If the entrance appears sliding or appears lodging, the entrance is not safe; if the entrance will not appear sliding and will not appear lodging, the entrance is safe.

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