Method for determining gradient of sea area channel dredging side slope

Abstract

The invention discloses a method for determining the gradient of a sea area channel dredging side slope. The method comprises the steps that the maximum wave dynamic load borne by the surface of the dredging side slope and the maximum stress caused by waves in the dredging side slope are determined; determining a soil body strength index of the soil body under the action of the maximum wave dynamic load through an indoor vibration triaxial test; establishing a channel dredging slope soil mechanics stability calculation model, inputting a soil mass vibration strength index value obtained in an indoor vibration triaxial test and a maximum wave dynamic load value borne by the surface of the channel slope, and calculating the stability safety coefficient of the channel dredging slope under the wave dynamic load under a plurality of slope schemes of the proposed channel dredging slope; and selecting the steepest slope degrees of a plurality of slope schemes meeting the stability safety coefficient required by the specification as the slope value of the proposed channel dredging slope. On the basis, scouring calculation of waves and / or tidal currents on the surface of the dredging slope of the proposed channel can be combined, and the gradient is properly slowed down to serve as the gradient of the dredging slope of the proposed channel.

Description

Technical Field

[0001] The present invention belongs to the research and construction fields of the water transportation engineering industry, and particularly relates to a method for determining the slope of a sea channel dredging slope. Background Art

[0002] The determination of the slope of a channel dredging slope is not only related to the stability of the channel dredging slope and the normal operation of the channel, but also related to the size of the dredging work volume and the project investment. Especially for a shallow shoal deep-dredging channel, the excavation thickness is large and the dredging work volume is large. Among them, the slope work volume accounts for about 20-30% of the entire dredging work volume. The determination of the slope of the channel dredging slope is more prominent for the stability of the channel dredging slope, the dredging work volume, and the project investment. In addition, in an open sea area lacking protection such as a breakwater or a natural island, the offshore waves can directly enter and have an impact. Previous studies have qualitatively shown that the waves have a certain softening effect and scouring effect on the surface soil of the sea area, which needs to be paid attention to when the waves are large. At the same time, previous studies have qualitatively shown that the tidal current has a certain scouring effect on fine-grained soil. However, at present, the slope of the channel dredging slope in the current specification is only determined by the look-up table method based on geological data, without considering factors such as excavation thickness, tidal current, waves, and slope stability, which affects the accuracy and economy of determining the slope of the sea channel dredging slope. Especially for the shallow shoal deep-dredging channel in the open sea area, the problem is more prominent.

[0003] In recent years, many ports have carried out research on the observation of the channel dredging slope. One research method is from the perspective of the stability of the slope soil mechanics (i.e., the overall stability of geotechnical mechanics), using the shear strength index of the soil after unloading, calculating the stability safety factor of the channel dredging slope under different slope conditions according to the still water condition, and combining with the on-site local dredging test to observe the stability of the slope after dredging, and then determining the slope of the channel dredging slope; the second research method is from the perspective of the hydrodynamic scouring effect, using qualitative analysis, on-site observation and other methods to study the influence of water flow and waves on the scouring of the channel dredging slope surface. However, the existing research still has the following deficiencies:

[0004] First, when calculating the stability safety factor of the channel dredging slope using the slope soil mechanics stability, the adverse effect of the wave dynamic load on the stability of the channel dredging slope has not been considered, and it cannot meet the needs of determining the slope of the channel dredging slope under the wave action conditions in the open sea area.

[0005] Second, the research on the influence of water flow and waves on the scouring of the channel dredging slope surface is still at a qualitative level and has not reached a quantitative level.

[0006] Third, a systematic design method for determining the slope of the channel dredging slope has not been formed. Summary of the Invention

[0007] The present invention provides a method for determining the slope gradient of a sea - area channel dredging slope, which solves the problems in the prior art that the adverse effects of wave dynamic loads on the soil mechanics stability of the channel dredging slope are not considered, and the effects of water flow and waves on the scouring of the channel dredging slope surface cannot be quantitatively considered, forms a systematic method for determining the slope gradient of the channel dredging slope, meets the needs of determining the slope gradient of the sea - area channel dredging slope, provides a scientific basis for reasonably determining the slope gradient of the sea - area channel dredging slope, and realizes the coordinated unity of dredging slope stability and saving of channel engineering investment.

[0008] To achieve the above - mentioned purpose, the technical solution adopted by the present invention is as follows:

[0009] A method for determining the slope gradient of a sea - area channel dredging slope, the method comprising:

[0010] S0: According to the geology of the proposed channel and engineering practice experience, initially propose several slope - gradient schemes for the dredging slope of the proposed channel; alternatively, according to the geology of the proposed channel, based on the provisions of the "General Design Code for Seaports" (such as Table 6.4.9 "Channel Slope Gradients for Different Rock and Soil Categories" in JTS165 - 2013), combined with engineering practice experience, initially propose several slope - gradient schemes for the dredging slope of the proposed channel;

[0011] S1: According to the design service life of the dredging slope of the proposed channel, determine the design wave recurrence - period standard and corresponding design wave elements for the dredging slope of the proposed channel, and then determine the maximum wave load under different preset water - level conditions;

[0012] S2: Determine the soil - strength index of the soil under the action of the maximum wave dynamic load through indoor vibration triaxial tests;

[0013] S3: Establish a soil - mechanics stability calculation model for the channel dredging slope, input the soil vibration strength index value obtained from the indoor vibration triaxial test and the maximum wave dynamic load value received by the channel - slope surface into the model, and calculate the stability safety factor of the channel dredging slope under wave dynamic load for several slope - gradient schemes of the proposed channel dredging slope;

[0014] S4: Select the steepest slope of several slope - gradient schemes that meet the specification requirements for the stability safety factor as the slope - gradient value of the proposed channel dredging slope.

[0015] Optionally, step S1 specifically includes:

[0016] S11: Determine the design wave recurrence period standard for the dredging slope of the proposed waterway according to the designed service life of the dredging slope of the proposed waterway (for example, if the designed service life of the dredging slope is 6 months, 1 year, 5 years, 10 years, or 20 years, the design wave recurrence period standards are respectively taken as once in 1 year, once in 1 - 5 years, once in 5 - 10 years, once in 10 - 20 years, and once in 20 - 50 years), as well as the combinations with different preset water level conditions, where the water levels of the different preset water level conditions include the extreme low water level, the designed low water level, the designed high water level, the extreme high water level, and the medium water level;

[0017] S12: Determine the design wave elements corresponding to different preset water level conditions under the design wave recurrence period standard for the proposed waterway by using one of the methods of statistical calculation based on measured waves, or calculation by the method in the "Code for Port and Waterway Hydrology", the Putian wave formula, or the wave mathematical model. The design wave elements include the water depth h, the seawater specific weight γ w , the significant wave height H s of a series of wave heights H 1％ ~ H 100％ , the wave length L, the wave period T, and the wave action time D u ;

[0018] S13: Determine the wave dynamic loads on the surface of the dredging slope of the proposed waterway corresponding to different preset water level conditions under the design wave recurrence period standard, and select the maximum wave dynamic load on the surface of the dredging slope of the waterway among different preset water level conditions.

[0019] Optionally, in step S13, to determine the wave dynamic loads on the surface of the dredging slope of the proposed waterway, it can be obtained through on - site measurement, indoor physical model test, or calculation by computational fluid dynamics software.

[0020] Optionally, in step S13, to determine the wave dynamic loads on the surface of the dredging slope of the proposed waterway, it can be obtained through calculation by relevant calculation formulas, specifically:

[0021] The formula for calculating the wave dynamic loads on the surface of the dredging slope of the waterway is:

[0022] p = p 0 sin2π(x / L - t / T) (1)

[0023]

[0024] In the formula: p is the wave dynamic load on the surface of the dredging slope of the waterway; p 0 is the pressure; x is the horizontal coordinate relative to the wave node; L is the wave length; T is the wave period; t is the time; H is the wave height or preferably take the series wave height H 1％ ~ H 100％, the significant wave height H can also be taken s ; γ w is the specific weight of water; h is the water depth.

[0025] Optionally, step S2 specifically includes:

[0026] S21: Through geological exploration, representative soil samples are obtained on the cross-section of the proposed waterway. Sampling must cover all major soil layers related to soil mechanics stability. Each major soil layer should contain at least two soil samples, upper and lower, and the soil samples must be undisturbed samples;

[0027] S22: According to the design wave elements corresponding to different design water levels under the design wave recurrence period standard, and in accordance with the maximum wave dynamic load at the specific section of the proposed waterway obtained, determine the maximum stress caused by waves at different depths and positions inside the dredging slope at the soil sample location. Together with the wave period and wave action time of the design wave elements, they are used as the loading for the indoor dynamic triaxial test;

[0028] Optionally, in step S22, to determine the maximum stress caused by waves at different depths and positions inside the dredging slope at the soil sample location, it can be obtained through on-site measurement or indoor physical model test.

[0029] Optionally, in step S22, to determine the maximum stress caused by waves at different depths and positions inside the dredging slope at the soil sample location, it can be calculated using the finite element method or relevant theoretical formulas based on the wave dynamic load on the surface of the dredging slope of the proposed waterway obtained in S13.

[0030] S23: Conduct indoor dynamic triaxial tests to obtain the dynamic strength indexes of each soil sample under wave dynamic loads. For silt, silty soil, cohesive soil, and silty clay, the shear strength indexes can be selected as the triaxial unconsolidated undrained shear index after vibration or the unconfined compressive strength index after vibration.

[0031] Optionally, for the proposed waterway with a relatively large to large wave frequency, consider the scouring effect of waves on the slope surface of the dredging slope of the proposed waterway; for the proposed waterway with strong tidal current dynamics, consider the scouring effect of tidal current on the slope surface of the dredging slope of the proposed waterway. After step S4, it further includes:

[0032] S5.1: Establish a mathematical model of the wind field, wave field in the project sea area, and a three-dimensional tidal current sediment scouring mathematical model with fine local grid division. Select measured wind, wave, current, and sediment concentration data to verify and calibrate the model;

[0033] S5.2: Use the verified and calibrated wind, wave, and three-dimensional tidal current sediment coupling mathematical model to simulate the dynamic field and sediment concentration field in the project sea area during typical strong wind and large wave and / or spring tide processes;

[0034] S5.3: Using the verified and calibrated three-dimensional coupled mathematical model of wind, waves, tidal current and sediment, quantitatively calculate the scour depth of the slope surface of the proposed channel at different water depths of the beach surface during typical strong winds, big waves and spring tides. Combining with the frequency of occurrence of typical strong winds and big waves in a year, analyze whether the impact of scour caused by waves and tidal currents on the slope surface maintenance of the proposed channel is within an acceptable range;

[0035] S5.4: Based on the calculation of the scour of the dredged slope surface of the proposed channel considering waves and tidal currents, and combining with the feasible slope value of the dredged slope of the proposed channel obtained from the calculation of the soil mechanics stability of the dredged slope of the proposed channel under the action of wave dynamic load, comprehensively determine the slope value of the dredged slope of the proposed channel.

[0036] Optionally, in step S5.4, the specific method for comprehensively determining the slope of the dredged slope of the proposed channel is as follows:

[0037] S5.4.1: For a channel with a relatively short design service life (such as less than 5 years) of the dredged slope of the proposed channel, the steepest slope with a stability safety factor obtained from the calculation of the soil mechanics stability of the dredged slope of the proposed channel under the action of wave dynamic load meeting the requirements of the "Code for Design of Foundations of Water Transportation Engineering" can be used as the slope of the dredged slope of the proposed channel;

[0038] S5.4.2: For a channel with a relatively long design service life (such as greater than or equal to 5 years) of the dredged slope of the proposed channel, on the basis of S5.4.1, combined with the calculation of the scour of the dredged slope surface of the proposed channel by waves and / or tidal currents, the slope can be appropriately slowed down as the slope of the dredged slope of the proposed channel.

[0039] Advantages of the present invention:

[0040] 1. When calculating the stability safety factor of the dredged slope of the channel by soil mechanics stability of the slope, the reduction of the strength index of the soil body of the channel slope under the action of wave load is quantitatively considered, and then the adverse impact on the soil mechanics stability of the dredged slope of the channel is solved. The problem that the prior art does not quantitatively consider the adverse impact of wave dynamic load on the soil mechanics stability of the dredged slope of the channel is solved;

[0041] 2. Using the three-dimensional coupled mathematical model of wind, waves, and tidal current and sediment, the influence of waves and water flow on the scour of the dredged slope surface of the channel is quantitatively calculated, and the problem that the prior art cannot quantitatively consider the influence of waves and water flow on the scour of the dredged slope surface of the channel is solved;

[0042] 3. A systematic method for determining the slope gradient of channel dredging has been formed, which can meet the needs of determining the slope gradient of sea area channel dredging, solve the problem that the current method of determining the dredging slope by looking up tables lacks clear theoretical support and does not consider the adverse effects of wave and tidal dynamic loads on the stability of channel dredging slopes, provide a scientific basis for reasonably determining the slope gradient of open sea area channel dredging, achieve the coordinated unity of ship navigation safety and saving of channel engineering investment, and make the determination of channel dredging slopes more comprehensive and reasonable.

[0043] The technical solutions and methods of the present invention are applicable to the research and construction fields of coastal channel engineering in the water transportation engineering industry, and are particularly applicable to the determination of the slope gradient of deep excavation channel dredging constructed on shoals with fine-grained soil in open sea areas with significant wave effects. Brief Description of the Drawings

[0044] Figure 1 It is the calculation result of the stability of the channel dredging slope without considering the influence of wave dynamic load (slope gradient 1:8).

[0045] Figure 2 It is the layout diagram of the vibration triaxial test sample points of the channel dredging slope.

[0046] Figure 3 It is a schematic diagram of the soil mechanics stability calculation model of the channel dredging slope.

[0047] Figure 4 It is the calculation result of the soil mechanics stability of the channel dredging slope considering the influence of wave dynamic load (slope gradient 1:8).

[0048] Figure 5 It is the calculation result of the soil mechanics stability of the channel dredging slope considering the influence of wave dynamic load (slope gradient 1:7).

[0049] Figure 6 It is the transverse distribution diagram of the scour thickness of the channel dredging slope under the action of waves and tides. Detailed Embodiments

[0050] The present invention provides a method for determining the slope gradient of a sea area channel dredging, and the method includes:

[0051] S0: Initially propose several slope gradient schemes for the proposed channel dredging slope;

[0052] S1: According to the design service life of the dredging slope of the proposed channel, determine the design wave recurrence period standard and the corresponding design wave elements of the proposed channel dredging slope, and then determine the maximum wave load on the surface of the channel dredging slope under different preset water level conditions. Specifically as follows:

[0053] S11: Determine the design wave recurrence period standard for the dredging slope of the proposed waterway and its combinations with different preset water level conditions according to the design service life of the dredging slope of the proposed waterway. The water levels of the different preset water level conditions include the extreme low water level, the design low water level, the design high water level, the extreme high water level, and the medium water level.

[0054] In step S11, the design service life of the dredging slope can be 6 months, 1 year, 5 years, 10 years, or 20 years, and the design wave recurrence period standards are respectively taken as once in 1 year, once in 1 - 5 years, once in 5 - 10 years, once in 10 - 20 years, and once in 20 - 50 years.

[0055] S12: Determine the design wave elements corresponding to different preset water level conditions of the proposed waterway under the design wave recurrence period standard by using one of the methods of statistical calculation based on measured waves, or calculation by the method in the "Code for Port and Waterway Hydrology", the Putian wave formula, or a wave mathematical model. The design wave elements include water depth h, seawater specific weight γ w , significant wave height H s , series wave height H of a train of waves 1％ ~wave height H 100％ , wave length L, wave period T, and wave action time D u .

[0056] S13: Determine the wave dynamic loads on the surface of the dredging slope of the proposed waterway corresponding to different preset water level conditions under the design wave recurrence period standard, and obtain the maximum wave dynamic loads on the surface of the dredging slope of the waterway in different preset water level conditions.

[0057] In step S13, to determine the wave dynamic loads on the surface of the dredging slope of the proposed waterway, it can be obtained through on-site measurement, indoor physical model test, calculation by computational fluid dynamics software, or calculation by relevant calculation formulas. The formula is:

[0058] p = p 0 sin2π(x / L - t / T) (1)

[0059]

[0060] In the formula: p is the wave dynamic load on the surface of the dredging slope of the waterway; p 0 is the pressure; x is the horizontal coordinate relative to the wave node; L is the wave length; T is the wave period; t is the time; H is the wave height or preferably the series wave height H of a train of waves 1％ ~H 100％ , and it can also be taken as the significant wave height H s ; γ w is the specific weight of water; h is the water depth.

[0061] Calculate the wave dynamic loads on the surface of the channel dredging slope under different preset water level conditions, and obtain the preset water level with the maximum wave dynamic load on the surface of the channel dredging slope among different preset water levels and its corresponding design wave element combination, which is the most unfavorable preset water level and design wave element combination.

[0062] S2: Determine the soil strength indexes of the soil under the action of the maximum wave dynamic load through indoor vibration triaxial tests. Specifically as follows:

[0063] S21: Through geological exploration, obtain representative soil samples on the cross-section of the proposed channel. Sampling must cover all main soil layers related to soil mechanics stability. Each main soil layer should contain at least two soil samples, upper and lower. The soil samples must be undisturbed samples;

[0064] S22: According to the design wave elements corresponding to different preset water level conditions under the design wave recurrence period standard, determine the maximum stresses caused by waves at different depths and positions inside the dredging slope at the specific section of the proposed channel according to the maximum wave dynamic load on the surface of the channel dredging slope obtained. Together with the wave period and wave action time of the design wave elements, it is used as the loading for the indoor vibration triaxial test;

[0065] Optionally, in step S32, to determine the maximum stresses caused by waves at different depths and positions inside the dredging slope at the soil sample location, it can be obtained through on-site measurement or indoor physical model test;

[0066] Optionally, in step S32, to determine the maximum stresses caused by waves at different depths and positions inside the dredging slope at the soil sample location, it can be calculated using the finite element method or relevant theoretical formulas according to the wave dynamic load on the surface of the channel dredging slope obtained in S23;

[0067] S23: Conduct indoor vibration triaxial tests to obtain the dynamic strength indexes of each soil sample under wave dynamic loads. For silt, silty soil, clay, and silty clay, the shear strength indexes can be selected as the triaxial unconsolidated undrained shear indexes after vibration or the unconfined compressive strength indexes after vibration.

[0068] S3: Establish a soil mechanics stability calculation model for the dredged channel slope. Input the soil vibration intensity index values obtained from the indoor vibration triaxial test and the maximum wave dynamic load value acting on the surface of the channel slope into the model, and calculate the stability safety factor of the dredged channel slope under wave dynamic load for several slope schemes of the proposed dredged channel slope. In this embodiment, according to the geology of the proposed channel and engineering practice experience, initially propose several slope schemes for the proposed dredged channel slope; it is also possible to initially propose several slope schemes for the dredged channel slope according to the geology of the proposed channel, based on the provisions of the "General Design Code for Seaports" (such as Table 6.4.9 "Channel Slope Gradients for Different Rock and Soil Types" in JTS165-2013), combined with engineering practice experience. Calculate the stability safety factor of the dredged channel slope under wave dynamic load for several slope schemes of the proposed dredged channel slope through the above model.

[0069] S4: Select the steepest slope among several slope schemes with a stability safety factor meeting the specification requirements as the slope value for the proposed dredged channel slope.

[0070] S5: For proposed channels with a relatively high frequency of large to very large waves, consider the scouring effect of waves on the slope surface of the proposed dredged channel; for proposed channels with strong tidal currents, consider the scouring effect of tidal currents on the slope surface of the proposed dredged channel. Combining the slope value of the dredged channel slope obtained in step S4, comprehensively determine the slope value of the proposed dredged channel slope. The specific steps are as follows:

[0071] S5.1: Establish a mathematical model of the wind field and wave field in the project sea area, as well as a three-dimensional tidal current sediment scouring mathematical model with fine local grid division. Select measured wind, wave, current, and sediment concentration data to verify and calibrate the model.

[0072] S5.2: Use the verified and calibrated wind, wave, and three-dimensional tidal current sediment coupling mathematical model to simulate the dynamic field and sediment concentration field in the project sea area during typical strong wind and wave and / or spring tide processes.

[0073] S5.3: Use the verified and calibrated wind, wave, and three-dimensional tidal current sediment coupling mathematical model to quantitatively calculate the scouring thickness of the slope surface of the proposed channel at different water depths of the beach surface during typical strong wind and wave and spring tide processes. Combining the frequency of occurrence of typical strong wind and wave in a year, analyze whether the impact of scouring caused by waves and tidal currents on the maintenance of the slope surface of the proposed channel is within an acceptable range.

[0074] S5.4: Based on the scouring calculation considering waves and tidal currents on the slope surface of the proposed dredged channel, combined with the feasible slope value of the dredged channel slope under the action of wave dynamic load for the proposed dredged channel, comprehensively determine the slope value of the proposed dredged channel slope.

[0075] In step S5.4, the specific method for comprehensively determining the slope of the proposed channel dredging slope is as follows: For a channel with a relatively short design service life of the proposed channel dredging slope (such as less than 5 years), the steepest slope that satisfies the requirements of the "Code for Design of Foundations of Water Transportation Engineering" in the soil mechanics stability calculation of the proposed channel dredging slope under the action of wave dynamic load can be used as the slope of the proposed channel dredging slope; For a channel with a relatively long design service life of the proposed channel dredging slope (greater than or equal to 5 years), on the basis of S5.4.1, combined with the scour calculation of the proposed channel dredging slope surface by waves and / or tides, the slope can be appropriately slowed down as the slope of the proposed channel dredging slope.

[0076] Each of the above-mentioned on-site observations, on-site measurements, indoor physical model tests, Putian wave formula, wave mathematical model, computational fluid dynamics software, finite element method, indoor vibration triaxial test, post-vibration triaxial unconsolidated undrained shear test, post-vibration unconfined compressive test, and three-dimensional wind-wave-tidal current-sediment coupled mathematical model and other technologies themselves are mature technologies and will not be elaborated.

[0077] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the implementation manners of the present invention are not limited thereto.

[0078] Engineering conditions: A certain channel is located in the open sea, outside the entrance of the breakwater. The natural seabed elevation of section A of the channel is -8m (i.e., 8m below the local theoretical lowest tide level), and the length is 1km; The existing lower-grade channel in section A of the channel is a 1.5 million-ton channel, with a navigable width of 230m and a bottom elevation of -16.5m (i.e., 16.5m below the local theoretical lowest tide level); The proposed channel in section A of the channel is a 3 million-ton channel, with a navigable width of 350m, and the bottom elevation of the channel is -22m (i.e., 22m below the local theoretical lowest tide level). The design service life of the dredging slope is tentatively set at 5 years; The geology of section A of the channel is silt with low shear strength, and the bottom elevation of the silt layer is -22.0m. Below is a hard clay layer with very high shear strength; The design high water level is 5.36m.

[0079] Step 1, since the geology of the channel is silt, according to Table 6.4.9 "Channel Slope Gradients for Different Geotechnical Categories" in the "Code for General Design of Seaports" (JTS165-2013), the dredging slope gradients of the proposed 3 million-ton channel are proposed as 1:8 and 1:7.

[0080] Step 2, conduct on-site observations on the dredging slopes of the existing lower-grade channels at the proposed channel location. The observation results show that the overall slope of the dredging slopes of the existing lower-grade channels is stable at 1:6.

[0081] Step 3: Conduct a stability check on the dredging slope of the proposed waterway from the perspective of slope soil mechanics stability; due to large waves, the softening effect of waves on the soil mechanics strength of the dredging slope of the proposed waterway should also be considered, and the adverse impact of wave dynamic loads on the stability of the dredging slope of the waterway should be considered. The specific steps are as follows:

[0082] Step 3-1: According to the geological exploration report, obtain the physical and mechanical indexes of the soil body of the dredging slope of the proposed waterway before excavation, including soil unit weight and shear strength indexes. For silt, silty soil, cohesive soil, and silty soil, the shear strength index can be selected as the unconfined compressive strength index or the triaxial unconsolidated undrained shear index and direct shear quick shear index after unloading. The physical indexes required in this embodiment are shown in Table 1. Using the slope stability calculation formula in the "Code for Design of Foundations of Water Transportation Engineering" (such as JTS147-2017), the slope stability safety factor of the dredging slope with a slope ratio of 1:8 without considering the influence of wave dynamic loads is calculated to be 2.878 (the calculation results are shown in Figure 1 ).

[0083] Table 1 Physical and Mechanical Indexes of Soil Layers

[0084]

[0085] Step 3-2: According to the design service life of the dredging slope of the proposed waterway, determine the design wave recurrence period standard of the dredging slope of the waterway to be once in 5 years, and combine it with the extreme low water level, design low water level, design high water level, extreme high water level, and medium water level;

[0086] Step 3-3: According to the measured wave statistics and wave mathematical model calculation, determine the design wave elements (in the unexcavated state) of the proposed waterway under different design water levels with the design wave recurrence period standard as follows in Table 2;

[0087] Table 2 Design Wave Element Table under Each Characteristic Water Level

[0088]

[0089]

[0090] Step 3-4: According to the design wave elements corresponding to different design water levels under the once-in-5-year recurrence period (i.e., Table 2), determine the wave dynamic load values on the beach surface according to the linear wave theory based on Formulas (1) to (2), which are: 8.4 kPa under the extreme low water level condition, 9.1 kPa under the design low water level condition, 9.2 kPa under the design high water level condition, and 9.0 kPa under the extreme high water level condition. Therefore, the design high water level and its corresponding design wave elements are the most unfavorable combination of design water level and design wave elements.

[0091] Calculated according to the method in the "Hydrology Specification for Ports and Waterways", determine the design wave elements and wave action time corresponding to the design high water level for a 50-year return period in this navigation section. The wave elements in each area (for the area division, see Figure 2 ) are shown in Table 3 below.

[0092] Table 3 Wave Parameters for Each Area of the Slope

[0093]

[0094] Step 3-5: According to the wave parameters for each area of the dredged slope in Table 3, use Formulas (1) to (2) to calculate the wave dynamic load on the surface of the proposed navigation channel dredged slope under the action of the design wave elements corresponding to the design high water level for a 50-year return period. The calculation results are shown in Table 4.

[0095] Table 4 Wave Dynamic Load on the Surface of the Navigation Channel Dredged Slope

[0096]

[0097] According to the wave dynamic load on the surface of the proposed navigation channel dredged slope (Table 4), use the finite element method to calculate the internal soil stress caused by the waves.

[0098] Table 5 Amplitude of Internal Soil Stress in the Proposed Navigation Channel Dredged Slope Caused by Waves

[0099]

[0100] Step 3-6: First, through geological exploration, obtain representative soil samples on the cross-section of the proposed navigation channel. Sampling must cover all the main soil layers related to soil mechanics stability. Each main soil layer should contain at least two soil samples, upper and lower, and the soil samples must be undisturbed samples. Typical sampling points are as shown in Figure 2 ;

[0101] Secondly, use the stress caused by the waves calculated in Table 5, together with the wave period and wave action time of the design wave elements, as the loading for the indoor vibration triaxial test;

[0102] Finally, conduct an indoor vibration triaxial test (vibration triaxial consolidated-undrained test) to obtain the dynamic strength indexes of each soil sample under the wave dynamic load, that is, the dynamic cohesion c d and the dynamic internal friction angle See Table 6 for details.

[0103] Table 6 Dynamic Strength Indexes of Soils in Each Area of the Slope

[0104]

[0105] Step 3-7: Calculate the soil mechanics stability safety factor of the proposed navigation channel dredged slope. The specific steps are as follows:

[0106] First, establish a stability calculation model for the dredged channel slope, and assign the dynamic parameter indexes of the soil in Table 6 to the corresponding model areas.

[0107] Secondly, add the maximum wave dynamic load acting on the surface of the channel slope, as Figure 4 shown.

[0108] Finally, use the slope stability calculation formula in the "Code for Design of Foundation in Water Transportation Engineering" (such as JTS147-2017) to calculate the stability safety factor of the dredged channel slope under the wave dynamic load. The calculation results show that when the slope of the dredged channel slope is 1:8, as shown in Figure 4 the figure, the minimum stability safety factor of the dredged channel slope is 1.536. The calculation result is about 45% lower than the stability safety factor under static water conditions, but greater than 1.3 required by the "Code for Design of Foundation in Water Transportation Engineering" (JTS147-2017); when the slope of the dredged channel slope is 1:7, the soil mechanics stability factor of the dredged channel slope is 1.398, still greater than 1.3 required by the "Code for Design of Foundation in Water Transportation Engineering" (JTS147-2017).

[0109] Step 4: Establish a three-dimensional coupled mathematical model of wind, wave, and three-dimensional tidal current sediment to simulate the dynamic fields (flow field, wave field) related to the stability of the dredged slope during the process of superimposing typical strong winds and big waves on spring tides, reproduce its sediment movement process, and quantitatively calculate the scouring amplitude of the proposed dredged channel slope, specifically including the following sub-steps:

[0110] Step 4-1: Establish a mathematical model of the wind field and wave field in the project sea area, and a three-dimensional tidal current sediment scouring mathematical model with fine grid division of the local (channel and dredged slope water area) to form a three-dimensional coupled mathematical model of wind, wave, and three-dimensional tidal current sediment. Select the "Wipha" typhoon as the typical process of superimposing strong winds and big waves on spring tides, and use the measured hydrological data such as wind, wave, current, and sediment concentration of the "Wipha" typhoon, the 150,000-ton channel scale at that time, and the sea area water depth topography to verify the model.

[0111] Step 4-2: Use the verified three-dimensional coupled mathematical model of wind, wave, and three-dimensional tidal current sediment to simulate the dynamic fields (wind field, wave field, flow field) and sediment concentration field in the project sea area during the typical process of superimposing strong winds and big waves on spring tides.

[0112] Step 4-3: Use the verified three-dimensional coupled mathematical model of wind, wave, and three-dimensional tidal current sediment to quantitatively calculate the scouring of the proposed dredged channel slope surface caused by a typical process of superimposing strong winds and big waves on spring tides. The calculation results show that the maximum scouring thickness does not exceed 0.07m. Since the number of occurrences of the typical strong wind and big wave process in a year does not exceed 2 times, it shows that the scouring caused by waves and tides on the proposed channel slope surface is within an acceptable range.

[0113] Step 5: The designed service life of the dredged slope of the proposed waterway is relatively long (5 years), and the scouring amplitude of the dredged slope of the waterway under the action of waves and tides is very limited. The steepest slope of 1:7 with a soil mechanics stability safety factor meeting the requirement of 1.3 in the "Code for Design of Foundations for Water Transportation Engineering" of the water transportation industry specification under the action of wave dynamic load is selected as the slope value of the dredged slope of the proposed waterway.

[0114] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the present invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for determining the slope of a dredged channel in a sea area, characterized in that: The method comprises: S0: Several slope plans for the dredged slope of the proposed channel are initially proposed; S1: According to the design service life of the dredged slope of the proposed channel, determine the design wave return period standard and corresponding design wave elements of the dredged slope of the proposed channel, and then determine the maximum wave dynamic load on the surface of the dredged slope of the channel under different preset water level conditions; S2: Determine the soil strength index under the maximum wave dynamic load through indoor vibration triaxial test; S3: Establish a soil mechanics stability calculation model for the channel dredging slope, input the soil vibration intensity index value obtained in the indoor vibration triaxial test and the maximum wave dynamic load value on the channel slope surface into the model, and calculate the stability safety factor of the channel dredging slope under the wave dynamic load under several slope schemes of the proposed channel dredging slope; S4: Select the steepest slope of several slope schemes that meet the stability safety factor required by the specification as the slope value of the proposed channel dredging slope.

2. The method for determining the slope of the sea channel dredging according to claim 1 is characterized in that: Step S1 specifically includes: S11: according to the design service life of the dredged slope of the proposed waterway, determine the design wave return period standard of the dredged slope of the proposed waterway, and the combination with different preset water level conditions, wherein the water levels of the different preset water level conditions include extreme low water level, design low water level, design high water level, extreme high water level and medium water level; S12: Determine the design wave elements corresponding to different preset water level conditions of the proposed waterway under the design wave recurrence period standard according to the measured wave statistical method, or by using one of the methods of the Port and Waterway Hydrological Code, Putian wave formula, and wave mathematical model. The design wave elements include water depth h, seawater gravity γ w , effective wave height H θ , the series of wave heights H of a series of waves 1％ ~Wave height H 100％ , wavelength L, wave period T, and wave action time D u ; S13: According to the design wave elements corresponding to different preset water level conditions under the design wave return period standard, the wave dynamic load on the surface of the corresponding proposed channel dredging slope is determined, and the maximum wave dynamic load on the surface of the channel dredging slope in different preset water level conditions is obtained.

3. The method for determining the slope of the sea channel dredging according to claim 2 is characterized in that: In step S13, the wave dynamic load on the surface of the proposed channel dredging slope is obtained through field measurement or indoor physical model test, and calculation by computational fluid dynamics software.

4. The method for determining the slope of the sea channel dredging according to claim 2 is characterized in that: In step S13, the wave dynamic load on the surface of the proposed channel dredging slope is calculated by a relevant calculation formula, specifically: The formula for calculating the wave dynamic load on the surface of the dredged channel slope is: p=p0sin2π(x / Lt / T) (1) Where: p is the wave dynamic load on the surface of the channel dredging slope; p0 is the pressure; x is the horizontal coordinate relative to the wave node; L is the wavelength; T is the wave period; t is the time; H is the wave height or a series of wave heights H. 1％ ~H 100％ , or the effective wave height H s ; γ w is the density of water; h is the water depth.

5. The method for determining the slope of the sea channel dredging according to claim 1 is characterized in that: Step S2 specifically includes: S21: Through geological survey, obtain representative soil samples on the proposed channel section. The sampling must cover all major soil layers related to soil mechanical stability. Each major soil layer contains at least two upper and lower soil samples. The soil samples must be original samples. S22: According to the design wave elements corresponding to different design water levels under the design wave return period standard, and according to the maximum wave dynamic load on the surface of the dredged slope of the proposed channel at the specific section of the proposed channel, the maximum stress caused by waves at different depths and positions inside the dredged slope at the soil sample is determined, together with the wave period and wave action time of the design wave elements, as the loading for the indoor vibration triaxial test; S23: Conduct indoor vibration triaxial test to obtain the dynamic strength index of each soil sample under wave dynamic load. For silt, silty soil, clay soil and silty soil, the shear strength index can be the triaxial unconsolidated undrained shear index after vibration or the unconfined compressive strength index after vibration.

6. The method for determining the slope of the sea channel dredging according to claim 5 is characterized in that: In step S22, the maximum stress caused by waves at different depths and positions inside the dredged slope at the soil sample is determined by field measurement or indoor physical model test.

7. The method for determining the slope of the sea channel dredging according to claim 5 is characterized in that: In step S22, the maximum stress caused by waves at different depths and positions inside the dredged slope at the soil sample is determined, and the finite element method and relevant theoretical formulas are used to calculate the wave dynamic load on the surface of the dredged slope of the proposed channel obtained in S13.

8. The method for determining the slope of the sea channel dredging according to claim 1 is characterized in that: After step S4, the method further includes: S5.1: Establish mathematical models of wind and wave fields in the project sea area, as well as a three-dimensional tidal sediment scour mathematical model with fine local grid division, and use measured wind, wave, current and sediment content data to verify and calibrate the model; S5.2: Use the verified and calibrated three-dimensional wind, wave, tidal current and sediment coupling mathematical model to simulate typical strong winds, strong waves and / or high tides, and the dynamic field and sediment content field of the engineering sea area; S5.3: Use the verified and calibrated three-dimensional wind, wave, tidal and sediment coupling mathematical model to quantitatively calculate the scouring thickness of the waterway slope surface at different beach water depths during typical strong winds, waves and high tides. Combined with the frequency of typical strong winds and waves in a year, analyze whether the impact of scouring caused by waves and tidal currents on the slope surface maintenance of the proposed waterway is within an acceptable range; S5.4: The slope value of the proposed dredged channel slope is determined comprehensively based on the calculation of scouring of the proposed dredged channel slope surface by waves and tidal currents and the feasible slope value of the proposed dredged channel slope based on the soil mechanics stability calculation of the proposed dredged channel slope under the action of wave dynamic loads.

9. The method for determining the slope of the sea channel dredging according to claim 8, characterized in that: In step S5.4, the specific method for comprehensively determining the slope of the proposed channel dredging slope is as follows: S5.4.1: For waterways with a design service life of less than 5 years, the steepest slope of the proposed dredged channel slope that meets the requirements of the Code for Design of Foundations for Water Transport Engineering, obtained by calculating the stability safety factor of the proposed dredged channel slope under wave dynamic load, shall be used as the slope of the proposed dredged channel slope; S5.4.2: For waterways with a design service life of 5 years or more, the slope of the proposed dredged slope can be appropriately slowed down based on S5.4.1, combined with the calculation of the scouring of the slope surface of the proposed dredged slope by waves and / or tidal currents.

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