A sea cliff safety and stability prediction method considering rainfall effects

Abstract

The invention discloses a method for predicting the safety and stability of a sea cliff considering the influence of rainfall, and relates to the field of marine geological disaster prediction. The safety and stability of the sea cliff are analyzed by combining a sea cliff model based on physical concepts with soil mechanics and hydraulics, and then a sea cliff early warning method is obtained. The effect of rainfall on the sea cliff is usually that a large amount of rainwater infiltration leads to an increase in the water content of the soil, a decrease in the shear strength of the soil, an increase in the bulk density of the sea cliff soil, and a sliding force of the sea cliff that is greater than the anti-sliding force. Therefore, the sea cliff undergoes shear failure due to landslide. The invention uses an improved Green-Ampt model and Coulomb shear strength theory, considers the influence of rainfall on the bulk density and shear strength of the sea cliff soil, establishes a sea cliff safety stability coefficient prediction model, and predicts the sea cliff safety stability coefficient under rainfall conditions.

Description

Technical Field

[0001] The invention relates to the field of marine geological disaster prediction, and in particular to a method for predicting the safety and stability of sea cliffs taking rainfall influence into consideration. Background Art

[0002] The formation of sea cliffs is affected by crustal movement and wave erosion, and sea troughs often develop at their bottom. Rainfall can significantly affect the physical properties of sea cliff soil, increase its bulk density and reduce its shear strength, ultimately leading to sea cliff collapse and instability. Currently, there is no effective technology that can fully consider the relationship between the change in moisture content of sea cliff soil and sliding stability under rainfall conditions. Therefore, it is of great significance to provide a method that can accurately predict the impact of rainfall on sea cliff stability. Summary of the invention

[0003] The purpose of the present invention is to provide a method for predicting the safety stability of sea cliffs taking into account the influence of rainfall, taking into account the influence of rainfall on the bulk density and shear strength of sea cliffs, and proposing a segmented calculation model for the relationship between moisture content and rainfall time, which can accurately predict the safety stability coefficient of sea cliffs.

[0004] The present invention adopts the following technical solution:

[0005] On the one hand, a sea cliff safety stability prediction method considering the influence of rainfall includes:

[0006] S101, obtaining physical and mechanical parameters of sea cliff soil and rainfall data;

[0007] S102, calculating the time when water starts to accumulate on the top of the sea cliff based on physical and mechanical parameters and rainfall data;

[0008] S103, compare the time when water accumulation starts and the rainfall time, if the rainfall time is not greater than the time when water accumulation starts, proceed to S104, otherwise, proceed to S105;

[0009] S104, water does not begin to accumulate on the top of the sea cliff, and the relationship between the moisture content of the soil infiltration zone and the change of rainfall time is calculated according to the rainfall time and the soil moisture content, and then the process goes to S106;

[0010] S105, water begins to accumulate on the top of the sea cliff, and considering the existence of the saturated layer and the transition layer, the relationship between the soil moisture content and the rainfall time at different infiltration zone depths is calculated, and then go to S106;

[0011] S106, if the rainfall time is not greater than the time when water accumulation begins, the shearing force and the sliding force of the sea cliff are calculated based on the relationship between the moisture content of the soil infiltration zone and the rainfall time; otherwise, the shearing force and the sliding force of the sea cliff are calculated based on the relationship between the moisture content of the soil at different infiltration zone depths and the rainfall time;

[0012] S107, calculating the ratio of the shearing force to the sliding force, and when the ratio is greater than a preset value, judging that the sea cliff is safe and stable, otherwise, judging that the sea cliff will collapse.

[0013] Preferably, in S101, the physical and mechanical parameters of the sea cliff soil and rainfall data include:

[0014] Beach slope in front of cliff , soil air intake value , fitting coefficient of soil pore size distribution characteristics , soil saturated permeability coefficient , soil saturated moisture content , natural moisture content of soil , soil residual moisture content , Cohesion of saturated sea cliff soil , Sea cliff height , the depth of the trough , the height of the trough , natural cohesion of sea cliff soil , internal friction angle , natural gravity of sea cliff soil Rainfall intensity in the Haiya area .

[0015] Preferably, in S102, the time when water begins to accumulate on the top of the sea cliff is The calculation is based on the improved Green-Ampt rainfall infiltration model as follows:

[0016] .

[0017] Preferably, in S104, water does not begin to accumulate on the top of the sea cliff, and the relationship between the moisture content of the soil infiltration zone and the change in rainfall time is calculated according to the rainfall time and the moisture content of the soil, as follows:

[0018] Calculate the soil moisture content in the sea cliff infiltration area With rainfall time The relationship is as follows:

[0019] ;

[0020] Calculating the depth of the infiltration zone of a sea cliff ,as follows:

[0021] .

[0022] Preferably, in S105, water begins to accumulate at the top of the sea cliff, and considering the existence of the saturated layer and the transition layer, the relationship between the soil moisture content and the rainfall time at different infiltration zone depths is calculated, as follows:

[0023] Calculating different depths of sea cliffs and moisture content The relationship is as follows:

[0024] ;

[0025] in, is the depth of saturated layer; is the depth of the infiltration zone;

[0026] The depth relationship of each layer in the infiltration zone is expressed as follows:

[0027] ;

[0028] in, and is the proportionality coefficient; is the depth of transition layer;

[0029] Calculate the depth of the infiltration zone With rainfall time The relationship is as follows:

[0030] ;

[0031] in, To consider the cumulative infiltration of the transition layer; is the cumulative infiltration without considering the transition layer; is the ratio of pi; It is the generalized matrix suction of the soil at the wetting front.

[0032] Preferably, in S106, the shear resistance of the sea cliff is The calculation method is as follows:

[0033] ;

[0034] in, is the depth of the crack at the top of the sea cliff; is the depth of the infiltration zone; It is the cohesion of soil in the infiltration zone before water accumulates on the top of the sea cliff; It is the average cohesion of the soil in the infiltration area after water accumulates on the top of the sea cliff; This is the time when water begins to accumulate on top of the sea cliff; For rainfall time.

[0035] Preferably, the depth of the crack on the top of the sea cliff is , which is expressed as follows:

[0036] ;

[0037] in, is the tensile stress depth at the top of the sea cliff; is the tensile strength of soil; is the maximum tensile stress at the top of the sea cliff.

[0038] Preferably, the average cohesion of the soil in the infiltration zone is , which is expressed as follows:

[0039] ;

[0040] in, is the cohesion of saturated soil; is the depth of saturated layer; is the depth of transition layer.

[0041] Preferably, in S106, the downward force of the sea cliff is The calculation method is as follows:

[0042] ;

[0043] in, is the dry weight of sea cliff soil; It is water weight; is the depth of the infiltration zone; is the depth of transition layer; is the depth of saturated layer; is the ratio of pi; This is the time when water begins to accumulate on top of the sea cliff; For rainfall time.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The present invention applies the improved Green-Ampt rainfall infiltration model and Coulomb shear strength theory, considers the influence of rainfall on the bulk density and shear strength of sea cliff soil, and proposes a segmented calculation model for the relationship between moisture content and rainfall time, which can accurately predict the safety stability coefficient of the sea cliff. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flow chart of a method for predicting sea cliff safety stability considering the influence of rainfall according to an embodiment of the present invention;

[0047] Figure 2 This is a diagram of a theoretical model for predicting the safety and stability of sea cliffs taking into account the impact of rainfall according to an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0049] See also Figure 1 and Figure 2 As shown, the present invention provides a method for predicting the safety and stability of sea cliffs taking into account the influence of rainfall, comprising the following steps.

[0050] S101, obtaining physical and mechanical parameters of sea cliff soil and rainfall data.

[0051] Specifically, the physical and mechanical parameters of the sea cliff soil and rainfall data, including: the slope of the beach in front of the cliff , soil air intake value , fitting coefficient of soil pore size distribution characteristics , soil saturated permeability coefficient , soil saturated moisture content , natural moisture content of soil , soil residual moisture content , Cohesion of saturated sea cliff soil , Sea cliff height , the depth of the trough , the height of the trough , natural cohesion of sea cliff soil , internal friction angle , natural gravity of sea cliff soil , Rainfall intensity in Haiya area .

[0052] In this embodiment, the saturated moisture content of the sea cliff soil is Determined by immersion method; the natural moisture content of the sea cliff soil Residual moisture content of sea cliff soil Determined by drying method; the sea cliff soil air intake value Determined by tensiometer method; the fitting coefficient of the soil pore size distribution characteristics The saturated permeability coefficient of the sea cliff soil is determined by a pore size tester and statistical methods; Determined by Darcy's law; the natural cohesion of the sea cliff soil , internal friction angle and cohesion of saturated sea cliff soil Determined by direct shear test; the natural weight of the sea cliff soil Determined by the ring knife method.

[0053] S102, calculating the time when water starts to accumulate on the top of the sea cliff based on physical and mechanical parameters and rainfall data.

[0054] Specifically, calculate the time when water begins to accumulate at the top of the sea cliff. ,as follows:

[0055] .

[0056] Cumulative infiltration of sea cliff soil during rainfall , which is expressed as follows:

[0057] ;

[0058] in, .

[0059] Relative suction of soil at the wetting front of the sea cliff , which is expressed as follows:

[0060] ;

[0061] in, It represents the relative moisture content of sea cliff soil, which is expressed as follows:

[0062] ;

[0063] Permeability coefficient of sea cliff soil , which is expressed as follows:

[0064] .

[0065] S103, compare the time when water accumulation starts and the rainfall time, if the rainfall time is not greater than the time when water accumulation starts, proceed to S104, otherwise, proceed to S105.

[0066] S104: Water has not yet accumulated on the top of the sea cliff. According to the rainfall time and the soil moisture content, the relationship between the moisture content of the soil infiltration zone and the rainfall time is calculated, and then the process goes to S106.

[0067] Specifically, the rainfall time When the water does not accumulate on the top of the sea cliff, the soil moisture content in the sea cliff infiltration area is With rainfall time The relationship is as follows:

[0068] ;

[0069] Rainfall time When the water does not accumulate on the top of the sea cliff, the infiltration depth of the sea cliff is ,as follows:

[0070] .

[0071] S105, water begins to accumulate on the top of the sea cliff. Considering the existence of the saturated layer and the transition layer, the relationship between the soil moisture content and rainfall time at different infiltration zone depths is calculated, and then go to S106.

[0072] Specifically, the rainfall time Water began to accumulate on the top of the sea cliff, and the rainfall lasted for Cumulative infiltration of the sea cliff ,as follows:

[0073] ;

[0074] in, is the infiltration rate of sea cliff soil at different rainfall times, .

[0075] .

[0076] Water accumulation on the top of the sea cliff, rainfall time When the sea cliff is at different depths and moisture content The relationship is as follows:

[0077] .

[0078] Transition layer depth and the depth of the entire infiltration zone The relationship is as follows:

[0079] .

[0080] Calculate the cumulative infiltration considering the transition layer ,as follows:

[0081] ;

[0082] in, is the infiltration into the saturated layer, is the infiltration amount of transition layer.

[0083] Calculate the cumulative infiltration without considering the transition layer ,as follows:

[0084] .

[0085] Calculate the depth of the infiltration zone With rainfall time The relationship is as follows:

[0086] .

[0087] S106, if the rainfall time is not greater than the time when water accumulation begins, the shearing force and the sliding force of the sea cliff are calculated based on the relationship between the moisture content of the soil infiltration zone and the rainfall time; otherwise, the shearing force and the sliding force of the sea cliff are calculated based on the relationship between the moisture content of the soil at different infiltration zone depths and the rainfall time.

[0088] Specifically, the shear resistance of the sea cliff ,as follows:

[0089] ;

[0090] Among them, the moisture content of sea cliff soil after rainfall Cohesion The relationship is as follows:

[0091] ;

[0092] It should be noted that the above coefficients are coefficients related to specific soil bodies, and this embodiment is only an example.

[0093] Depth of tensile stress at the top of the sea cliff ,as follows:

[0094] ;

[0095] Soil tensile strength ,as follows: .

[0096] Maximum tensile stress at the top of the sea cliff ,as follows:

[0097] .

[0098] Depth of cracks on the top of the sea cliff ,as follows:

[0099] .

[0100] When water begins to accumulate on the top of the sea cliff, the average cohesion of the soil in the infiltration area is as follows:

[0101] .

[0102] in, is the cohesion of saturated soil.

[0103] Specifically, the downward force of the sea cliff ,as follows:

[0104] ;

[0105] in, is the dry weight of sea cliff soil; is the water density, take 9.8 .

[0106] Sea cliff soil dry weight ,as follows:

[0107] .

[0108] S107, calculating the ratio of the shearing force to the sliding force, and when the ratio is greater than a preset value, judging that the sea cliff is safe and stable, otherwise, judging that the sea cliff will collapse.

[0109] Specifically, calculate the safety stability coefficient of the sea cliff ,as follows:

[0110] .

[0111] In this embodiment, the preset value can be set to 1.

[0112] The following will take the prediction of sea cliff safety and stability in a certain area of ​​the southeast coast as an example to illustrate.

[0113] In a certain area of ​​southeastern coastal my country, the rainfall during the flood season is heavy, which leads to frequent landslides of sea cliffs in the area, posing a great safety hazard. In order to evaluate the safety and stability of the sea cliffs in the area under rainfall conditions, the method of the present invention is applied for calculation and analysis.

[0114] The physical and mechanical parameters and rainfall data of the sea cliff soil in this area are shown in Table 1.

[0115] Table 1. Parameters for predicting the safety stability coefficient of sea cliffs;

[0116]

[0117] According to the method of the present invention, the relationship between different rainfall times and safety factors is calculated, as shown in Table 2.

[0118] Table 2 Relationship between different rainfall times and safety factors;

[0119]

[0120] The calculation of this example shows that the sea cliff safety stability coefficient prediction method can predict the safety stability coefficient of the sea cliff under different rainfall durations.

[0121] Therefore, the present invention adopts the above-mentioned method for predicting the safety stability coefficient of sea cliffs considering the influence of rainfall. This method uses the improved Green-Ampt model and Coulomb shear strength theory, considers the influence of rainfall on the bulk density and shear strength of sea cliff soil, and predicts the safety stability coefficient of sea cliffs under rainfall conditions.

[0122] Although the specific embodiments of the present invention are described above, those skilled in the art should understand that the specific embodiments described in this application are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for predicting sea cliff safety stability considering the influence of rainfall, characterized in that: include: S101, obtaining physical and mechanical parameters of sea cliff soil and rainfall data; S102, calculating the time when water starts to accumulate on the top of the sea cliff based on physical and mechanical parameters and rainfall data; S103, compare the time when water accumulation starts and the rainfall time, if the rainfall time is not greater than the time when water accumulation starts, proceed to S104, otherwise, proceed to S105; S104, water does not begin to accumulate on the top of the sea cliff, and the relationship between the moisture content of the soil infiltration zone and the change of rainfall time is calculated according to the rainfall time and the soil moisture content, and then the process goes to S106; S105, water begins to accumulate on the top of the sea cliff, and considering the existence of the saturated layer and the transition layer, the relationship between the soil moisture content and the rainfall time at different infiltration zone depths is calculated, and then go to S106; S106, if the rainfall time is not greater than the time when water accumulation begins, the shear force and the sliding force of the sea cliff are calculated based on the relationship between the moisture content of the soil infiltration zone and the rainfall time; Otherwise, the shear force and sliding force of the sea cliff are calculated based on the relationship between soil moisture content and rainfall time at different infiltration zone depths; S107, calculating the ratio of the shearing force to the sliding force, and when the ratio is greater than a preset value, judging that the sea cliff is safe and stable, otherwise, judging that the sea cliff will collapse; In S101, the physical and mechanical parameters of sea cliff soil and rainfall data include: The slope of the beach in front of the cliff β, the air intake value of the soil ψ b , fitting coefficient λ of soil pore size distribution characteristics, soil saturated permeability coefficient K S , soil saturated moisture contentθ s 、Natural soil moisture contentθ i , soil residual moisture contentθ r , cohesion c1 of saturated soil of sea cliff, height H of sea cliff, depth d of sea trough, height d of sea trough, natural cohesion c of sea cliff soil, internal friction angle The natural gravity γ of sea cliff soil and the rainfall intensity R in the sea cliff area; In S102, the time when water begins to accumulate on the top of the sea cliff is t p The calculation is based on the improved Green-Ampt rainfall infiltration model as follows: In S104, water has not yet accumulated on the top of the sea cliff. Based on the rainfall time and soil moisture content, the relationship between the moisture content of the soil infiltration zone and the rainfall time is calculated as follows: The relationship between the soil moisture content θ and rainfall time t in the sea cliff infiltration area is calculated as follows: Calculate the depth z of the infiltration zone of the sea cliff h ,as follows:

2. The method for predicting sea cliff safety stability considering rainfall influence according to claim 1 is characterized in that: In S105, water begins to accumulate at the top of the sea cliff. Considering the existence of the saturated layer and the transition layer, the relationship between soil moisture content and rainfall time at different infiltration zone depths is calculated as follows: The relationship between the different depths z of the sea cliff and the water content θ is calculated as follows: Among them, z s is the depth of the saturated layer; z h is the depth of the infiltration zone; The depth relationship of each layer in the infiltration zone is expressed as follows: Among them, a and b are proportional coefficients; z t is the depth of transition layer; Calculate the depth of the infiltration zone z h The relationship with rainfall time t is as follows: Where I1 is the cumulative infiltration considering the transition layer; I2 is the cumulative infiltration without considering the transition layer; π is the circumference ratio; S f It is the generalized matrix suction of the soil at the wetting front.

3. The method for predicting sea cliff safety stability considering rainfall influence according to claim 1, characterized in that: In S106, the shear resistance T of the sea cliff is calculated as follows: Where y is the depth of the crack at the top of the sea cliff; z h is the depth of the infiltration zone; c θ is the cohesion of the soil in the infiltration zone before water accumulates on the top of the sea cliff; c′ is the average cohesion of the soil in the infiltration zone after water accumulates on the top of the sea cliff; t p is the time when water begins to accumulate on the top of the sea cliff; t is the rainfall time.

4. The method for predicting sea cliff safety stability considering rainfall influence according to claim 3 is characterized in that: The depth y of the crack at the top of the sea cliff is expressed as follows: Where z0 is the tensile stress depth at the top of the sea cliff; s t is the tensile strength of soil; t,max is the maximum tensile stress at the top of the sea cliff.

5. The method for predicting sea cliff safety stability considering rainfall influence according to claim 3 is characterized in that: The average cohesion c′ of the soil in the infiltration zone is expressed as follows: Where c1 is the cohesion of saturated soil; z s is the depth of the saturated layer; z t is the depth of transition layer.

6. The method for predicting sea cliff safety stability considering rainfall influence according to claim 1, characterized in that: In S106, the calculation method of the sliding force F of the sea cliff is as follows: Among them, r d is the dry weight of sea cliff soil; r w is the water density; h is the depth of the infiltration zone; z t is the depth of transition layer; z s is the depth of the saturation layer; π is the circumference; t p is the time when water begins to accumulate on the top of the sea cliff; t is the rainfall time.

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