Partition plate enclosure and suction silt squeezing method on surface of foundation bed during sinking of seabed immersed tube

Abstract

The invention discloses a partition plate enclosure and suction silt squeezing method on the surface of a foundation bed when a seabed immersed tube is immersed, which comprises the following steps of: determining the depth and the width of a furrow of the foundation bed and the thickness distribution characteristics of a back-silting object, and planning the length and the mounting position of a silt blocking partition plate and a layout path of a mud suction head according to the length and the width of the immersed tube; a mud suction head is designed and manufactured according to the shape of the section of a furrow of a foundation bed, and the mud suction head comprises a suction nozzle and a mounting head used for being connected with a mud conveying hose; a silt blocking partition plate is manufactured; after the gravel foundation bed is subjected to leveling construction, a silt blocking partition plate is installed; deploying a mud suction head, placing the mud suction head in the foundation bed furrow close to the bottom of the silt blocking partition plate, ensuring that the bottom of the mud suction head is attached to the foundation bed furrow to obtain support, and enabling the silt blocking partition plate, the immersed tube, the foundation bed and the mud suction head to form a closed space; connecting the sludge conveying hose with the sludge suction pump; and the dredge pump is started while the immersed tube joint is immersed, and the back silts are driven to be sucked out from the bottom of the immersed tube and carried away through the sludge conveying hose.

Description

Technical Field

[0001] The present invention belongs to the technical field of immersed tube tunnel construction, and in particular relates to a method for diaphragm protection and silt suction on the surface of a subgrade when a submarine immersed tube is sunk. Background Art

[0002] Currently, the foundation construction systems for immersed tube tunnels mainly include the pre-laying method and the post-laying method. The pre-laying method requires placing a gravel layer in the excavated foundation trench in the form of alternating ridges and furrows to form the foundation, followed by foundation leveling. After the foundation leveling is completed, the immersed tube segments are placed. Due to the time difference between foundation leveling and segment placement, and the high sand content in some construction waters, the subgrade surface will be covered with silt between the time after foundation leveling and before segment placement. If the immersed tube segments are directly placed without dredging, a series of safety issues will arise, such as the immersed tube not being properly placed, subsequent settlement being excessive after placement, and the immersed tube stress and inclination exceeding safety values. Existing methods for preventing the impact of excessive silt on the foundation surface on the sinking of immersed tube tunnel segments mainly include: covering the foundation surface with geotextiles to prevent silt from falling onto the foundation surface, or using a dragging suction vessel to dredge the foundation surface, or placing a suction head on the foundation surface and using the suction force of the suction head to remove the silt as the dragging suction vessel moves. The above methods have the following problems: the foundation will be disturbed during the construction process, affecting the stress characteristics of the foundation; the construction method is cumbersome, delaying the construction period; the silt will fall back onto the foundation surface after being stirred, resulting in poor dredging effect; the pipe segments cannot be sunk in time after dredging, resulting in the foundation surface being covered with silt again when the pipe segments are sunk. Summary of the Invention

[0003] This patent addresses the shortcomings of existing methods for removing silt from the foundation surface of submarine immersed tube tunnels. It proposes a method for providing bulkhead protection and suctioning silt removal on the foundation surface during the placement of submarine immersed tubes. This method utilizes a sludge suction device to assist in removing silt from the bottom of the immersed tube during the placement of the tube segments. The technical solution is as follows:

[0004] A method for providing bulkhead protection and suction and squeezing silt on the surface of a subgrade during the placement of a submarine immersed tube comprises the following steps:

[0005] (1) Conduct site surveys and measurements, use geological radar or borehole sampling to determine the depth, width, and thickness distribution characteristics of the subgrade ditch, and plan the length and installation position of the silt retaining plate 4 and the layout path of the sludge suction head 1 according to the length and width of the immersed tube;

[0006] (2) Designing and manufacturing a mud suction head 1 according to the cross-sectional shape of the base bed ditch, the mud suction head 1 includes a suction nozzle and a mounting head 2 for connecting a mud transport hose 3; the suction nozzle of the mud suction head 1 is a conical suction nozzle, so that the mud suction head 1 is placed in the base bed ditch and fits with the base bed ditch to obtain support;

[0007] (3) making a silt retaining baffle 4, wherein the silt retaining baffle 4 is a thin-walled rectangle with an upper opening;

[0008] (4) Equipment commissioning and material preparation, check the water tightness of the silt retaining plate 4, the mud suction head 1, and the mud transport hose 3;

[0009] (5) After the gravel base bed is leveled, the silt retaining baffles 4 are installed in the following manner: symmetrically place the silt retaining baffles 4 on both sides of the base bed ridge to ensure that the top of the silt retaining baffles 4 is higher than the thickness of the silt; place the silt retaining baffles 4 on the foundation surface close to the boundary of the immersed tube, and the placement length of the silt retaining baffles 4 is equivalent to the length of the immersed tube section to form a continuous enclosure barrier; fix and connect adjacent silt retaining baffles 4 to form a continuous closed enclosure structure. The silt retaining baffles 4 are used to prevent the silt from overflowing during the silt squeezing process of the immersed tube, and during the sedimentation process of the silt, the silt can be deposited in the silt retaining baffles 4, playing the role of collecting mud;

[0010] (6) Deploy the suction head 1 and place it in the base bed ditch near the bottom of the silt retaining baffle 4, ensuring that the bottom of the suction head 1 fits in the base bed ditch for support, and that the silt retaining baffle 4, the immersed tube, the base bed, and the suction head 1 form a closed space;

[0011] (7) Connecting the mud transport hose 3 to the mud suction pump 5: The mud transport hose 3 is located outside the construction area. One end of the mud transport hose 3 is connected to the mounting head 2 of the mud suction head 1 under the silt retaining baffle 4, and the other end is connected to the mud suction pump 5 on the water surface. The mud suction pump 5 is located on the ship above the water surface;

[0012] (8) Calculate the power required by the sludge suction pump 5 and start the sludge suction pump 5 while the submerged tube section is being sunk. During the silt squeezing process of the submerged tube, the sludge suction pump 5 provides a stable negative pressure to drive the silt to be sucked out from the bottom of the submerged tube and transported away through the sludge transport hose 3.

[0013] Furthermore, sludge suction pumps of different powers are selected according to the rheological parameters of the silt. The method for determining the sludge suction pump power is as follows:

[0014] Rheological shear experiments were carried out on the silt to obtain the rheological curve of the silt, and the Herschel-Bulkley model was used to fit the rheological curve.

[0015] Calculate the Reynolds number Re by treating the silt as a non-Newtonian fluid MR ;

[0016] According to the Reynolds number MR Determine the flow state of the silt. If the silt is laminar, calculate the friction coefficient. If the backflow is judged to be turbulent, the friction coefficient f is determined experimentally;

[0017] Calculate the pipeline friction loss and obtain the pressure difference ΔP on both sides of the hose:

[0018]

[0019] Where: ΔP is the pressure difference on both sides of the hose, L is the length of the mud transport hose;

[0020] Calculate the total pump head:

[0021]

[0022] Where: H is the total head of the pump, ρ is the density of the silt, h is the elevation of the hydrostatic head, and v is the flow velocity of the silt.

[0023] Calculate the required pump power:

[0024]

[0025] Where P is the pump power, η is the pump efficiency, Q is the flow rate of the mud hose when the pipe section is laid, and Calculation, b is the sum of the widths of a ridge platform and a ridge ditch, l is the width of the sunken pipe, c is the thickness of the backfill, and t is the sinking time of the pipe section.

[0026] Furthermore, the Herschel-Bulkley model is used to fit the rheological curve in the form of:

[0027] τ=τ0+K·γ n

[0028] Where: τ is the silt stress, τ0 is the initial yield stress of the silt, K is the consistency coefficient, γ is the shear rate, and n is the flow index.

[0029] Furthermore, the Reynolds number of the silt MR Using the Metzner-Reed Reynolds number, the calculation method is as follows:

[0030]

[0031] Where: ρ is the density of the silt, v is the flow velocity of the silt, and Calculation, D is the diameter of the mud hose, m is the local gradient factor, according to the formula Sure.

[0032] Furthermore, if Re MR Less than 2100, the silt is laminar flow, the friction coefficient If MR Greater than 4000, the backflow is turbulent.

[0033] Furthermore, the Darcy-Weisbach formula is used to calculate the pipeline friction loss and obtain the pressure difference ΔP on both sides of the hose:

[0034]

[0035] Where: ΔP is the pressure difference on both sides of the hose, L is the length of the mud transport hose

[0036] Furthermore, the height of the mud suction head is 5 cm lower than the height of the base bed ridge; an anti-clogging filter is provided at the opening of the mud suction head, and the diameter of the filter mesh is not greater than the gravel diameter of the gravel base bed.

[0037] Furthermore, the width of the silt retaining baffle is the same as the width of the area outside the immersed pipe on the gravel base bed surface.

[0038] Furthermore, in step (6), a mud suction head is arranged at the open end of each base bed ditch along the length direction of the immersed tube, the axis of which is parallel to the axis of the base bed ditch, and the front end reaches the junction of the silt retaining baffle and the immersed tube.

[0039] Furthermore, in step (8), the silt is transported to a ship on the water surface, and the silt sucked out by the dredging pump is temporarily stored on the ship. After the dredging work is completed, the silt is transported outside the foundation trench for treatment.

[0040] The present invention can utilize the silt squeezing load at the bottom of the immersed tube and the dredging pump to simultaneously squeeze and suck the returned silt. It is a partition protection and suction silt squeezing method for the surface of the base bed when the submarine immersed tube is sunk. The returned silt on the surface of the foundation can be cleaned without disturbing the foundation and the returned silt on the surface of the foundation, thereby avoiding the returned silt falling back onto the foundation after dredging and improving the dredging effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of mud suction head

[0042] Figure 2 Schematic diagram of mud suction head

[0043] Figure 3 Schematic diagram of silt retaining plate

[0044] Figure 4 System cross-sectional diagram

[0045] Figure 5 Schematic diagram of the location of the silt retaining plate, mud suction head and mud transport hose

[0046] In the figure, 1-mud suction head; 2-installation head; 3-mud transport hose; 4-silt retaining baffle; 5-mud suction pump; 6-sunk pipe; 7-gravel base bed; 8-base bed ridge ditch; 9-base trench; 10-return silt. DETAILED DESCRIPTION

[0047] The present invention provides a baffle enclosure and suction silt squeezing system and design method for sinking a pipe segment, which can efficiently remove excessively thick silt on the foundation surface while avoiding disturbance to the foundation and the silt.

[0048] The present invention provides a dredging system and design method for a subgrade surface. A specific example is provided for explanation. The subgrade of the Hong Kong-Zhuhai-Macao Bridge is used as an example for calculation. The width of the immersed tube is 37.95 m, the width of the ditch is 1.05 m, the width of the ridge platform is 1.8 m, and there is a relatively thick 0.2 m thick silt on the surface of the immersed tube. The implementation method is as follows:

[0049] 1) Conduct site surveys and measurements, using geological radar or borehole sampling to determine the depth, width, and thickness distribution of the subgrade ditch. Based on the length and width of the immersed tubes, plan the length and installation location of the silt retaining plate (4) and the layout path of the suction head (1).

[0050] 2) Design and manufacture a suction head 1 according to the cross-sectional shape of the base bed ditch. The suction head 1 includes a suction nozzle and a mounting head 2 for connecting a mud transport hose 3. The suction nozzle of the suction head 1 is a conical suction nozzle, so that after the suction head 1 is placed in the ditch, it fits with the ditch to obtain support. The height of the suction head 1 is 5 cm lower than the height of the base bed ditch. An anti-clogging filter is provided at the opening of the suction head 1. The diameter of the filter mesh is not greater than the diameter of the gravel of the gravel base bed.

[0051] 3) Making a silt retaining plate 4, which is a thin-walled rectangular plate with an upper opening and is made of a steel plate or a polymer composite material plate;

[0052] 4) Equipment debugging and material preparation, check the water tightness of the silt retaining baffle 4, mud suction head 1, and mud transport hose 3.

[0053] 5) Install the silt-blocking baffles 4 after the gravel base bed is leveled. Immediately after the foundation is leveled, place the silt-blocking baffles 4 symmetrically along both sides of the base bed ridge to ensure that the top of the silt-blocking baffles 4 is higher than the thickness of the silt. Place the silt-blocking baffles 4 on the foundation surface close to the boundary of the immersed tube. The width of the silt-blocking baffles 4 is the same as the width of the area outside the immersed tube on the gravel base bed surface. The placement length of the silt-blocking baffles 4 is equivalent to the length of the pipe section, forming a continuous enclosure barrier. Connect adjacent silt-blocking baffles 4 with bolts or snaps to form a continuous closed enclosure structure to prevent the silt from overflowing. At the same time, in the later stage of the silt sedimentation process, the silt can be deposited in the U-shaped silt-blocking baffles 4, playing a role in collecting mud.

[0054] 6) Deploy the suction head 1 and place it in the ditch at the bottom of the silt retaining baffle 4, ensuring that the bottom of the suction head 1 fits in with the base bed ditch for support, and that the silt retaining baffle 4, the immersed tube, the base bed and the suction head 1 form a closed space to efficiently perform the silt squeezing and suction operation.

[0055] 7) Connect the mud transport hose 3 and the dredge suction pump 5 to ensure that the connection between the mud transport hose 3 and the dredge suction pump 5 will not fall off during operation. The mud transport hose 3 should be located outside the construction area. One end of the mud transport hose 3 is connected to the mounting head 2 of the dredge suction head 1 under the silt retaining baffle 4, and the other end is connected to the dredge suction pump 5 on the water surface. During the submerged tube squeezing process, the silt is transported from underwater to the ship on the water surface. The mud transport hose 3 should be made of pressure-resistant and wear-resistant materials to meet the bending requirements of complex terrain. The dredge suction pump 5 is located on the ship above the water surface, providing a stable negative pressure to drive the silt to be sucked out from the bottom of the submerged tube and transported to the ship on the water surface through the mud transport hose 3. The mud transport hose 3 and the mounting head 2 are connected by a diver diving installation method. Ensure that the connection between the mud transport hose 3 and the circular mounting head 2 will not fall off during operation. During the submerged tube squeezing process, the silt suction head 1 sucks the silt into the mud transport hose 3 through negative pressure suction;

[0056] 8) Start sinking the submerged pipe segment. Ensure the accuracy of the submerged pipe segment and prevent the submerged pipe segment from squeezing the silt retaining baffle 4.

[0057] 9) Calculate the power required by the sludge suction pump 5. If the silt is completely squeezed out within t = 2 minutes, the flow rate of each sludge suction head 1 when the pipe section is sunk is Q = 0.18m 3 / s. Rheological shear experiments were conducted on the silt, and the rheological curve was fitted using the Herschel-Bulkley model. The results were τ0 = 30 Pa, n = 0.6, K = 0.1, pipe diameter D = 0.3 m, pipe length L = 40 m; and fluid density ρ = 1200 kg / m 3 , pump efficiency η = 80%. The calculated return sediment velocity v = 2.55m / s, m = 0.024, Reynolds number Re MR =1773, friction coefficient ΔP=9.36kPa, total head H=41.13m, pump power=108.8KW.

[0058] 10) While the submerged tube segment is being sunk, the dredge suction pump 5 is started to transport the silt at the bottom of the submerged tube into the ship's compartment.

[0059] 11) Observe the state of the material sucked out by the dredge pump 5 on board. When there is almost no silt in the material sucked out, stop the dredge suction operation, remove the silt retaining baffle 4, and transport the silt retaining baffle 4 and the silt in the ship's compartment to outside the base trench for treatment.

Claims

1. A method for providing bulkhead protection and suctioning silt removal on the bed surface during the placement of a submarine immersed tube, comprising the following steps: (1) Conduct site survey and measurement, use geological radar or borehole sampling to determine the depth, width and thickness distribution characteristics of the base bed ditch, and plan the length and installation position of the silt retaining plate (4) and the layout path of the sludge suction head (1) according to the length and width of the immersed tube; (2) designing and manufacturing a mud suction head (1) according to the cross-sectional shape of the base bed ditch, wherein the mud suction head (1) comprises a suction nozzle and a mounting head (2) for connecting to a mud transport hose (3); the suction nozzle of the mud suction head (1) is a conical suction nozzle, so that the mud suction head (1) is placed in the base bed ditch and fits with the base bed ditch to obtain support; (3) making a silt-blocking baffle (4), wherein the silt-blocking baffle (4) is a thin-walled rectangle with an upper opening; (4) Equipment commissioning and material preparation, check the water tightness of the silt retaining plate (4), the mud suction head (1), and the mud transport hose (3); (5) After the gravel base bed is leveled, the silt retaining baffles (4) are installed in the following manner: the silt retaining baffles (4) are symmetrically placed on both sides of the base bed ridge to ensure that the top of the silt retaining baffles (4) is higher than the thickness of the silt; the silt retaining baffles (4) are placed on the foundation surface close to the boundary of the submerged pipe, and the placement length of the silt retaining baffles (4) is equivalent to the length of the submerged pipe section to form a continuous enclosure barrier; the adjacent silt retaining baffles (4) are fixedly connected to form a continuous closed enclosure structure. The silt retaining baffles (4) are used to prevent the silt from overflowing during the submerged pipe squeezing process, and during the sedimentation process of the silt, the silt can be deposited in the silt retaining baffles (4), playing the role of collecting mud; (6) deploying the sludge suction head (1), placing the sludge suction head (1) in the base bed ditch near the bottom of the silt retaining baffle (4), ensuring that the bottom of the sludge suction head (1) fits in with the base bed ditch to obtain support, and forming a closed space with the silt retaining baffle (4), the immersed tube, the base bed and the sludge suction head (1); (7) Connecting the mud transport hose (3) and the mud suction pump (5): The mud transport hose (3) is located outside the construction area, one end of the mud transport hose (3) is connected to the mounting head (2) of the mud suction head (1) under the silt retaining baffle (4), and the other end is connected to the mud suction pump (5) on the water surface, and the mud suction pump (5) is located on the ship above the water surface; (8) Calculate the power required by the sludge suction pump (5), start the sludge suction pump (5) while the submerged tube section is being sunk, and provide a stable negative pressure during the silt extrusion process of the submerged tube to drive the silt to be sucked out from the bottom of the submerged tube and transported away through the sludge transport hose (3).

2. The method for diaphragm protection and suction and silt removal on the bed surface during the placement of the submarine immersed tube according to claim 1 is characterized in that: According to the rheological parameters of the silt, sludge pumps of different powers are selected. The method for determining the sludge pump power is as follows: Rheological shear experiments were carried out on the silt to obtain the rheological curve of the silt, and the Herschel-Bulkley model was used to fit the rheological curve. Calculate the Reynolds number Re by treating the silt as a non-Newtonian fluid MR ; According to the Reynolds number MR Determine the flow state of the silt. If the silt is laminar, calculate the friction coefficient. If the backflow is judged to be turbulent, the friction coefficient f is determined experimentally; Calculate the pipeline friction loss and obtain the pressure difference ΔP on both sides of the hose: Where: ΔP is the pressure difference on both sides of the hose, L is the length of the mud transport hose; Calculate the total pump head: Where: H is the total head of the pump, ρ is the density of the silt, h is the elevation of the hydrostatic head, and v is the flow velocity of the silt. Calculate the required pump power: Where P is the pump power, η is the pump efficiency, Q is the flow rate of the mud hose when the pipe section is laid, and Calculation, b is the sum of the widths of a ridge platform and a ridge ditch, l is the width of the sunken pipe, c is the thickness of the backfill, and t is the sinking time of the pipe section.

3. The method for diaphragm protection and suction and silt removal on the bed surface during the placement of the submarine immersed tube according to claim 2 is characterized in that: The Herschel-Bulkley model is used to fit the rheological curve in the form of: τ=τ0+K·γ n Where: τ is the silt stress, τ0 is the initial yield stress of the silt, K is the consistency coefficient, γ is the shear rate, and n is the flow index.

4. The method for diaphragm protection and suction and silt removal on the bed surface during the placement of the submarine immersed tube according to claim 3 is characterized in that: Reynolds number of silt MR Using the Metzner-Reed Reynolds number, the calculation method is as follows: Where: ρ is the density of the silt, v is the flow velocity of the silt, and Calculation, D is the diameter of the mud hose, m is the local gradient factor, according to the formula Sure.

5. The method for diaphragm protection and suction and silt removal on the bed surface during the placement of the submarine immersed tube according to claim 2 is characterized in that: If MR Less than 2100, the silt is laminar flow, the friction coefficient If MR Greater than 4000, the backflow is turbulent.

6. The method for diaphragm protection and suction and silt removal on the bed surface during the placement of a submarine immersed tube according to claim 2 is characterized in that: The Darcy-Weisbach formula is used to calculate the pipeline friction loss and obtain the pressure difference ΔP on both sides of the hose: Where: ΔP is the pressure difference on both sides of the hose, and L is the length of the mud transport hose.

7. The method for diaphragm protection and suction and silt removal on the bed surface during the placement of a submarine immersed tube according to claim 1 is characterized in that: The height of the mud suction head is 5 cm lower than the height of the base bed ridge; an anti-clogging filter is provided at the opening of the mud suction head, and the diameter of the filter mesh is not larger than the gravel diameter of the gravel base bed.

8. The method for diaphragm protection and suction and silt removal on the bed surface during the placement of a submarine immersed tube according to claim 1 is characterized in that: The width of the silt retaining wall is the same as the width of the area outside the immersed pipe on the gravel base surface.

9. The method for diaphragm protection and suction and silt removal on the bed surface during the placement of a submarine immersed tube according to claim 1, characterized in that: In step (6), a mud suction head is arranged at the open end of each base bed ditch along the length direction of the immersed tube, the axis of which is parallel to the axis of the base bed ditch, and the front end reaches the junction of the silt retaining baffle and the immersed tube.

10. The method for diaphragm protection and suction and silt removal on the bed surface during the placement of a submarine immersed tube according to claim 1, characterized in that: In step (8), the silt is transported to a ship on the water surface, and the silt sucked out by the dredging pump is temporarily stored on the ship. After the dredging work is completed, the silt is transported outside the foundation trench for processing.

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