Underwater geotextile laying method

Abstract

The invention discloses an underwater geotextile laying method, belongs to the technical field of water conservancy projects and underwater construction, and particularly solves the problem that geotextile is easy to displace or tear after being laid due to dynamic change of water flow and complex riverbed terrain in the prior art. According to the method, the water flow speed, the water depth and the riverbed gradient of a construction area are measured in real time, and the ballast weight and the anchoring distance needed by geotechnical cloth are dynamically calculated; the ballast weight is dynamically adjusted based on the water flow speed, the water depth and the geotechnical cloth current collection area through a formula in combination with the gradient and the water depth correction coefficient. During construction, rivets are driven row by row from the boundary datum line in the water flow direction, and the overlapped edges are fixed through hot melting welding. The method is suitable for stable laying of geotechnical cloth in river, lake and coast protection engineering, and the water flow impact resistance and the long-term service performance can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water conservancy engineering and underwater construction, and more particularly to a method for laying underwater geotextiles. Background Art

[0002] Traditional underwater geotextile installation methods typically employ fixed ballast weights and anchor spacing, failing to fully consider the dynamic coupling effects of water velocity, water depth, and riverbed slope. In practical applications, changes in water velocity can significantly alter the drag force on the geotextile, while variations in riverbed slope can lead to insufficient anchoring force. For example, in muddy riverbeds or steep slopes, fixed-spaced anchors can fail due to insufficient local soil bearing capacity, causing the edges of the geotextile to be lifted or even torn by the current. Furthermore, existing methods are poorly adaptable to areas with sudden changes in water depth. When the water depth increases suddenly, insufficient ballast weight can cause the geotextile to float or settle unevenly. Due to the lack of quantitative control over the ratio of geotextile tensile stress to water velocity, the design of seam overlap width often relies on empirical experience, which can lead to seam leakage and stress concentration. Although some technologies have attempted to incorporate sensor-based measurement parameters, these are often limited to single-variable correction and fail to dynamically adapt to multiple factors. This results in construction accuracy and stability that cannot meet the requirements of complex underwater environments. Summary of the Invention

[0003] One purpose of the present invention is to provide a method for laying underwater geotextiles, which solves the problems that the existing methods fail to dynamically adapt to changes in water flow velocity, water depth and riverbed slope, resulting in unreasonable design of ballast weight and anchor spacing, and the geotextile is prone to displacement or tearing.

[0004] In order to achieve these objectives and other advantages of the present invention, according to one aspect of the present invention, the present invention provides a method for laying an underwater geotextile, comprising the following steps: Step 1: Obtain the water flow velocity, water depth and riverbed slope of the construction area; Step 2: Calculate the ballast weight of the geotextile according to the water flow velocity and water depth, and then determine the anchor spacing according to the riverbed slope and water depth; Step 3: transport the geotextile to the underwater construction area by ship, evenly distribute the ballast on the surface of the geotextile according to the ballast weight, and start from the boundary baseline of the underwater construction area. Drive anchors into the riverbed row by row along the direction of water flow at the anchor spacing to form a rectangular grid structure. Overlap the edges of adjacent geotextiles and fix them by hot-melt welding to complete the underwater geotextile laying work; Wherein, the ballast weight W is calculated according to the formula Calculation; when the formula calculation result W / A>200kg / m 2When, take W = 200 A; k is the safety factor; ρ is the density of water, kg / m³; v is the water flow velocity, m / s; A is the projected surface area perpendicular to the water flow direction of the geotextile, m²; h is the water depth, m; h0 is the reference water depth, with a value of 10 m; is the correction coefficient for the ballast water depth; The anchoring spacing L is determined according to the formula and the anchoring spacing L is not less than the reference spacing L0, where L0 has a value of 0.5 m. When the calculated result L < L0 from the formula, take L = L0; where, is the slope correction coefficient; is the riverbed slope; is the correction coefficient for the anchoring water depth; is the terrain compensation coefficient, and its value range is 0 to 1.

[0005] Preferably, it also includes obtaining the tensile stress of the geotextile and correcting the overlapping width B of the adjacent geotextile edges according to the ratio of the tensile stress σ to the water flow velocity v. Specifically: When the ratio of the tensile stress σ to the water flow velocity v, σ / v ≤ 5 kN·s / m 3 then, 0.5 m ≤ B < 0.6 m; When 5 kN·s / m 3 <σ / v ≤ 8 kN·s / m 3 then, 0.6 m ≤ B < 0.7 m; When σ / v > 8 kN·s / m 3 then, 0.7 m ≤ B < 0.8 m.

[0006] Preferably, the water flow velocity in the construction area is obtained by measuring with a flow velocity sensor, the water depth is obtained by measuring with a water depth sensor, the riverbed slope is obtained by a multi-beam sonar, and the tensile stress of the geotextile is obtained by measuring with a stress sensor.

[0007] Preferably, the method for obtaining the value of the safety factor k is: When the ratio of the water flow velocity v to the water depth h, v / h ≤ 0.3 s -1 then, k = 0.15; When 0.3 s -1 < v / h ≤ 0.6 s -1 then, k = 0.18; When v / h > 0.6 s -1 then, k = 0.25.

[0008] Preferably, the value of the slope correction coefficient β is related to the type of riverbed soil: For a silt riverbed, β = 0.08, and when the riverbed slope θ > 20°, β is additionally increased by 0.05; For sandy riverbeds, β = 0.05, and when the water depth h > 15 m, β decreases by 0.02; For rocky riverbeds, β=0.02.

[0009] Preferably, the ballast water depth correction factor The method for determining the value of the anchoring water depth correction coefficient α is: For muddy riverbeds, =0.05, α=0.08; For sandy riverbeds, =0.03, α=0.05; For rocky riverbeds, =0.01,α=0.02.

[0010] Preferably, the terrain compensation coefficient The value of is: For muddy riverbeds, =0.2; For sandy riverbeds, =0.1; For rocky riverbeds, =0.

[0011] Preferably, anchor reinforcement measures are also included, specifically: After the underwater geotextile is laid in step 3, the riverbed is scanned with a multi-beam sonar at a cycle of 1 hour to generate a digital elevation model with a grid resolution of 0.2m×0.2m, and the settlement of each grid cell is calculated as Δh=H0-H t , where H0 is the initial elevation, H t is the current elevation; The local settlement area is defined as an area with more than three consecutive grid cells with Δh>0.2m; In the local settlement area, additional anchors are placed at the geometric center points of the rectangular grid area formed by every four adjacent original anchors.

[0012] Preferably, the length of the additional anchor is satisfy: When Δh≤0.3m, = +0.2; When Δh>0.3m, = +0.5+0.1Δh; where is the length of the original anchor, m.

[0013] The present invention includes at least the following beneficial effects: The present invention significantly improves the anti-displacement ability of geotextiles under complex water flow and terrain conditions and reduces the risk of tearing by dynamically calculating the ballast weight and anchor spacing. The overlapping width is graded and controlled based on the ratio of tensile stress to water velocity, which not only avoids seam leakage, but also reduces material redundancy and saves construction costs. The safety factor is dynamically adjusted with the ratio of water flow to water depth, taking into account both safety and economy under different working conditions and avoiding over-design. The slope correction coefficient is set based on the differentiation of soil types to enhance the adaptability of the anchor spacing in special terrains such as soft soil and steep slopes.

[0014] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0015] The present invention will be further described in detail below in conjunction with specific embodiments so that those skilled in the art can implement the invention with reference to the description.

[0016] It should be understood that terms such as “having”, “including” and “comprising” used herein do not preclude the existence or addition of one or more other elements or combinations thereof.

[0017] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0018] The present invention provides a method for laying an underwater geotextile, comprising the following steps: Step 1: Obtain the water flow velocity, water depth and riverbed slope of the construction area; Step 2: Calculate the ballast weight of the geotextile according to the water flow velocity and water depth, and then determine the anchor spacing according to the riverbed slope and water depth; Step 3: transport the geotextile to the underwater construction area by ship, evenly distribute the ballast on the surface of the geotextile according to the ballast weight, and start from the boundary baseline of the underwater construction area. Drive anchors into the riverbed row by row along the direction of water flow at the anchor spacing to form a rectangular grid structure. Overlap the edges of adjacent geotextiles and fix them by hot-melt welding to complete the underwater geotextile laying work; Wherein, the ballast weight W is calculated according to the formula Calculation; when the formula calculation result W / A>200kg / m 2 When W=200A, k is the safety factor, ρ is the density of water, kg / m³, v is the water velocity, m / s, A is the projected surface area of the geotextile perpendicular to the water flow direction, m², h is the water depth, m, and h0 is the reference water depth, which is 10 m. is the ballast water depth correction factor; The anchoring spacing L is determined according to the formula and the anchoring spacing L is not less than the reference spacing L0, where L0 is taken as 0.5 m. When the result L calculated by the formula is less than L0, take L = L0; where, is the slope correction coefficient; is the riverbed slope; is the anchoring water depth correction coefficient; is the terrain compensation coefficient, and its value range is 0 to 1.

[0019] In this technical solution, the specific implementation method of the underwater geotextile laying is as follows: In step one, the water flow velocity in the construction area can be measured by an acoustic Doppler current meter. For example, a flow velocity sensor with a range of 0.5 to 3.0 m / s can be selected. The water depth can be obtained by a shipborne echo sounder. For example, a sounding device with a resolution of 0.01 m can be selected. The riverbed slope is generated by scanning topographic data through a multibeam sonar system. For example, a sonar device with an angular coverage range of 120° can be selected. The above devices can be installed at the bottom or side bracket of the survey ship and connected to the deck control unit through cables. During data collection, the ship travels at a constant speed along the grid route in the construction area, and the flow velocity, water depth and slope data are transmitted to the processing terminal in real time. In step two, when calculating the ballast weight, the safety factor k is dynamically selected according to the ratio of the water flow velocity to the water depth, and the calculation can be completed by an industrial computer, and the software has a built-in formula analysis module. In step three, when laying the geotextile, the ship is transported by a flat-bottom barge, and the ballast can be concrete blocks or steel ingots, with a single weight of 50 to 200 kg, and they are evenly arranged on the surface of the geotextile according to the calculation results. The anchor nails can be driven in using a hydraulic impact hammer, and the anchor nail material can be selected as galvanized steel, with a diameter of 20 to 30 mm and a length of 1.5 to 3.0 m. The construction starts from the boundary reference line (such as the riverbank line) and the anchor nails are driven in row by row at intervals of L along the water flow direction. After the adjacent geotextile edges overlap by 0.5 to 0.8 m, they are welded by divers using a hot melt welder, and the welding temperature is controlled at 300°C to 350°C. This method can keep the geotextile stably laid under the impact of water flow, and there is no risk of tearing at the edges.

[0020] Among them, the derivation process of the calculation formula for the ballast weight W is as follows: Basic theory: Balance between water flow drag force and ballast friction force The horizontal drag force on the geotextile in the water flow needs to be balanced by the friction force generated by the ballast weight, that is: F 拖曳力 ≤F 摩擦力 , where the drag force formula is , C D is the resistance coefficient, ρ is the density of water, v is the water flow velocity, and A is the flow-receiving area of the geotextile. The friction force formula is , μ is the friction coefficient between the geotextile and the riverbed, and W is the ballast weight.

[0021] Deriving the expression for ballast weight By equilibrium condition F Drag force ≤ F Friction force, we get: ; Introducing safety factor k, comprehensive C D , μ and engineering margin, that is, W=kρv 2 A, where k is calibrated according to experiments.

[0022] Introducing water depth correction Water depth effect: When the water depth increases, the drag force of the water on the geotextile may increase due to buoyancy or boundary layer effect; through the dimensionless correction term , reflecting the nonlinear effect, and the square root treatment weakens the sensitivity of water depth growth. The final formula is: .

[0023] Upper limit constraint To prevent excessive ballast at extreme flow rates, additional constraints are added: when W / A>200kg / m 2 When , take W=200A.

[0024] The calculation formula of anchor spacing L is derived as follows: Basic theory: balance between anchoring force and sliding force The anchor spacing must ensure that the geotextile does not slip under the drag force of water flow and the sliding force of gravity, and meet the following requirements: F 滑移力 ≤F 锚固力 ; Sliding force: includes the drag force of water flow and the component of gravity along the slope: ; Anchorage force: The total pull-out resistance provided by the anchor per unit width: , where n is the number of anchors per unit width, F 单锚 Pull-out resistance of a single anchor.

[0025] Assuming that the anchors are evenly distributed with a spacing of L, the number of anchors per unit width n=1 / L.

[0026] According to the equilibrium condition F 滑移力 ≤F 锚固力 ,have to: ; Arranged: ; Introducing empirical correction coefficient Reference spacing L0: empirical value determined through experiments under conditions of no slope and still water (L0 = 0.5m); Slope correction term βtanθ: As the slope increases, the slip force increases, and the spacing needs to be reduced; Water depth correction term αh / h0: Increased water depth may weaken the pull-out resistance of anchors, requiring denser anchoring; Terrain compensation correction : Quantify the additional effect of riverbed soil on anchor spacing; Inverse proportional formula: The weakening effect of the comprehensive correction term on the spacing: ; Minimum spacing constraint To avoid the calculation result being too small, the constraint is enforced: L≥L0=0.5m.

[0027] The calculation formula for the ballast weight W balances the ballast requirements of the water drag force, and the correction term reflects the nonlinear enhancement effect of water depth on the drag force. The calculation formula for the anchor spacing L corrects the reference spacing by slope and water depth to ensure that the anchor force covers the slip force, and the denominator quantifies the weakening effect of environmental factors on the anchor density. The parameter k is measured by different water tank tests. v / h Critical ballast weight under , fitting safety factor. γ, α, β, Based on the drag force and anchoring force test data of soil types (silt, sand, rock), the correction coefficient is determined by regression analysis.

[0028] In this technical solution, the combined measurement of acoustic Doppler current meters, echo sounders, and multibeam sonars enables precise acquisition of water velocity, water depth, and riverbed slope data. This provides a reliable basis for the dynamic calculation of ballast weight and anchor spacing, reducing construction deviations caused by errors in environmental parameters. The safety factor k is dynamically adjusted based on the ratio of water velocity to water depth, avoiding both the increased cost of excessive ballast and the risk of geotextile displacement caused by insufficient ballast. The reference water depth is set at 10m, simplifying the adaptation process for different water depth scenarios. The anchor spacing is differentiated by the slope correction factor, which is set based on the soil type. For example, the slope correction factor for a muddy riverbed is 0.15, ensuring that the anchoring force in soft soil or steep slopes meets the pull-out resistance requirements. The ballast is made of 50kg to 200kg concrete blocks or steel ingots, constructed with galvanized steel anchors and a hydraulic impact hammer, ensuring both corrosion resistance and construction efficiency. Anchors are laid out along the direction of water flow from the boundary baseline, supplemented by an overlapping width of 0.5m~0.8m and hot-melt welding technology, which effectively reduces local stress concentration, blocks the erosion of the underlying soil by water flow, and significantly improves the impact resistance and long-term stability of geotextiles in complex underwater environments.

[0029] In another technical solution, the tensile stress of the geotextile is obtained, and the overlapping width B of the adjacent geotextile edges is corrected according to the ratio of the tensile stress σ to the water velocity v, specifically: When the ratio of tensile stress σ to water velocity v σ / v ≤ 5 kN·s / m 3 When 0.5m≦B<0.6m; When 5 kN·s / m 3 <σ / v≦8 kN·s / m 3 When 0.6 m ≤ B < 0.7 m; When σ / v>8 kN·s / m 3 When 0.7 m≦B<0.8 m.

[0030] In this technical solution, the overlap width B between adjacent geotextile edges is determined in stages based on the ratio of tensile stress σ to water velocity v. When σ / v ≤ 5 kN•s / m³, B ranges from 0.5m to 0.6m, suitable for stable environments with low stress and low flow velocity. When 5 kN•s / m³ < σ / v ≤ 8 kN•s / m³, B is adjusted to 0.6m to 0.7m, suitable for moderate stress and flow conditions. When σ / v > 8 kN•s / m³, B is further increased to 0.7m to 0.8m, suitable for complex environments with high stress and strong flow. This graded setting ensures that the overlap width matches the actual stress. Geotextile tensile stress can be measured in real time using stress sensors attached to the edges of the geotextile. These sensors can be commercially available resistive strain gauge sensors, which are corrosion-resistant underwater. Water velocity can be measured using Doppler flow sensors mounted on survey vessels or underwater supports. Such equipment can accurately capture water flow data at varying depths. The two are used in conjunction to provide real-time dynamic parameter support for the correction of overlap width. In terms of material selection, the welding rods used for hot melt welding can be selected from polymer welding materials that match the material of the geotextile, such as polypropylene welding rods or polyethylene welding rods, to ensure that the welding strength is consistent with the strength of the geotextile itself. The geotextile itself can continue to use existing materials such as woven fabrics or composite geomembranes. The materials in the overlapping areas must ensure that the surface is clean and free of impurities to allow the welding equipment to effectively weld. Stress sensors can be evenly arranged near the welding area at the edge of the geotextile, with one installed every 1 to 2 meters to ensure that the tensile stress changes at the edge can be captured; flow rate sensors can be installed at water flow monitoring points in the construction area, usually 0.5 meters below the water surface or 1 meter above the riverbed, to obtain representative water flow velocity data. The installation locations of the two must avoid being blocked by ballast or anchors to ensure the accuracy of data collection. During operation, a stress sensor monitors the tensile stress σ of the geotextile under the action of water flow in real time. A flow velocity sensor simultaneously obtains the current water velocity v, and the ratio of the two, σ / v, is calculated. Based on the range of this ratio, the corresponding overlap width B is selected. During welding, underwater hot-melt welding equipment is used, moving at a constant speed along the overlap edge to ensure a uniform and continuous weld. After completion, the weld quality is inspected to avoid cold or leaky welds. The overlap width is adjusted directly based on the real-time monitoring of σ and v. No fixed values are required; instead, it is determined dynamically by calculating the ratio. The stress sensor's measurement range can be selected based on the geotextile's designed tensile strength, typically covering 0 to 50 kN / m. The flow velocity sensor's measurement range can be selected from 0 to 5 m / s, meeting the monitoring requirements of most underwater construction environments. Functional testing involves placing geotextile seam specimens with varying overlap widths in a test tank simulating a water flow environment. By adjusting the water flow velocity and applying a tensile load, the tear resistance and sealing properties of the seams are tested. The experimental method involved preparing specimens with different overlap widths corresponding to different σ / v ratios, applying progressively increasing water flow impact and tensile stress, recording the load data at the time of joint failure, and analyzing the correlation between overlap width and joint strength. The rationality of the correction method was verified through statistical analysis of at least 30 valid sample groups. This technical solution monitors the dynamic relationship between tensile stress and water velocity in real time, and specifically adjusts the overlap width of adjacent geotextiles to match the strength of the joint area with the actual stress environment. This avoids the potential sealing issues and material waste that can arise from fixed overlap widths under complex water flow conditions, improving the overall sealing and water flow resistance of the geotextile installation, and ensuring the stability and reliability of underwater projects under long-term water flow. In another technical solution, the water flow velocity in the construction area is measured by a flow velocity sensor, the water depth is measured by a water depth sensor, the riverbed slope is measured by a multi-beam sonar, and the geotextile tensile stress is measured by a stress sensor. In this technical solution, the flow velocity sensor has a measurement range of 0 to 5 m / s, with an accuracy of ±0.01 m / s, to meet the monitoring needs of different water flow velocity conditions; the water depth sensor has a measurement range of 0 to 50 m, with a resolution of 0.01 m, to adapt to possible changes in water depth in the construction area; the multi-beam sonar has a depth measurement accuracy of ±1% of the water depth, and an angular resolution better than 1°, ensuring the accuracy of riverbed slope measurement; the stress sensor's range is selected based on the design strength of the geotextile, covering 0 to 50 kN / m, with an accuracy of ±0.5% FS, to meet the real-time monitoring requirements of tensile stress. In terms of equipment selection, Doppler flow sensors can be used to measure water flow velocity. This type of device calculates water flow velocity by emitting and receiving sound wave signals and is suitable for different water depth environments. Ultrasonic water depth sensors can be used to measure water depth, which uses the principle of sound wave reflection to obtain water depth data in real time. Riverbed slope detection can use a multi-beam sonar system, which can simultaneously emit multiple beams to cover a wide riverbed and generate high-precision underwater topography data. Geotextile tensile stress monitoring can use a resistive strain gauge stress sensor. By sticking it on the surface of the geotextile, it collects strain signals and converts them into real-time tensile stress values. These devices are all mature underwater measuring instruments on the market and are waterproof and corrosion-resistant. During operation, the flow sensor, water depth sensor and multi-beam sonar are first installed on the survey ship, and the equipment is calibrated and debugged to ensure the synchronization of data from each sensor. The survey vessel travels at a constant speed along the route of the construction area. The multi-beam sonar emits sound waves in real time to scan the riverbed, obtain the water depth and coordinate data of each measuring point, and generate the riverbed slope distribution through data processing software; the flow rate sensor and the water depth sensor synchronously collect the water flow velocity and the water depth value at the corresponding position, and store them in the data acquisition system. During the laying process of the geotextile, the stress sensor is attached to the edge of the geotextile and lowered underwater with the geotextile to monitor the tensile stress under the action of the water flow in real time. The signal is transmitted to the display terminal on the ship through a waterproof cable. After all the measurement data are summarized, they are used for the subsequent calculation of ballast weight, anchor spacing and overlap width. This technical solution uses mature underwater measurement equipment to achieve accurate acquisition of water flow velocity, water depth, riverbed slope and tensile stress of geotextile in the construction area, providing reliable data support for subsequent ballast weight calculation, anchor spacing determination and overlap width correction. The reasonable assembly and parameter setting of each sensor ensure the real-time and accuracy of data acquisition, avoid measurement deviations caused by environmental factors, thereby improving the pertinence and reliability of the underwater geotextile laying plan, and ensuring dynamic monitoring and adaptive adjustment of the geotextile's stress state during the laying process.

[0031] In another technical solution, the method for determining the value of the safety factor k is: When the ratio of water velocity v to water depth h is v / h≤0.3 s -1 When k=0.15; When 0.3 s -1 <v / h≤0.6 s -1 When k=0.18; When v / h>0.6 s -1 When k=0.25.

[0032] In this technical solution, the value of the safety factor k is based on the coupling effect of water drag force and water depth. According to the theory of fluid mechanics, the drag force F on the geotextile is d =0.5C d ρv 2 A, among which C d is the drag coefficient, which varies with the flow state (laminar flow, transitional flow, turbulent flow). When the ratio of water velocity to water depth v / h ≤ 0.3s -1 When the water flow is mainly laminar and the drag force is stable, k=0.15 is taken as the basic safety factor; when 0.3s -1 <v / h≤0.6s -1 When v / h>0.6s -1 When the water flow is turbulent, the drag force increases sharply and is unevenly distributed, so k=0.25 is taken to ensure sufficient safety margin, and safety and economy are balanced through graded settings. In terms of equipment selection, the water flow velocity v can be measured by a Doppler flow sensor, which uses the acoustic Doppler effect to obtain the water flow velocity in real time and is suitable for different water depth environments; the water depth h can be measured by an ultrasonic water depth sensor, which calculates the water depth by emitting sound waves and receiving reflected signals. Both are mature equipment commonly used in underwater engineering, with waterproof and corrosion-resistant properties, and the data output accuracy meets the requirements of the formula calculation. During the working process, the v and h data of the construction area are first collected synchronously by the flow sensor and water depth sensor installed on the measuring ship, and the v / h ratio is calculated in real time. The safety factor k is determined according to the range of the ratio. Substitute the determined k value into the ballast weight formula The required ballast weight is calculated based on the water density ρ, the geotextile's flow receiving area A, and the reference water depth h0, providing a basis for subsequent ballast distribution. Regarding parameter setting, the flow velocity sensor and water depth sensor must be calibrated before construction to ensure accurate measurement data. Calibration involves conducting a comparison test in a standard water tank with known flow velocity and water depth, adjusting the device's zero point and span, and eliminating systematic errors. During data acquisition, the sensor outputs v and h values in real time at a rate of once per second. The average value over 10 seconds is used as the basis for calculation to prevent transient fluctuations from influencing the k value determination. Functional testing involves placing geotextile models in a simulated water tank under ballast weights corresponding to different k values. The experimental method involves setting different v and h combinations, calculating the corresponding k values and ballast weights, securing the models in the water tank, applying water at the corresponding flow rate, and observing whether the geotextile shifts or flips. Each set of conditions is tested five times, and the flow parameters at the critical instability point are recorded to verify whether the k value setting meets the "safety factor" requirements and ensure that the ballast weight calculated by the formula has a sufficient safety margin. This technical solution determines the safety factor k based on the ratio of water velocity v to water depth h. This allows for appropriate adjustment of the ballast weight for varying underwater environmental conditions, thereby ensuring the stability of the geotextile underwater. The rational selection of equipment and materials, along with precise equipment assembly locations, ensures accurate data collection and reliable construction. Functional testing and data analysis further validate the rationality of the safety factor, ultimately guaranteeing the quality and safety of the underwater geotextile installation project.

[0033] In another technical solution, the value of the slope correction coefficient β is associated with the riverbed soil type: For muddy riverbeds, β = 0.08, and when the riverbed slope θ > 20°, β is increased by an additional 0.05; For sandy riverbeds, β = 0.05, and when the water depth h > 15 m, β decreases by 0.02; For rocky riverbeds, β=0.02.

[0034] In this technical solution, the slope correction coefficient β is calculated based on the difference in shear strength of the riverbed soil and the anchoring force. According to the principles of soil mechanics: Where F is the anchor pullout force (N), D is the anchor diameter (m), L is the anchor penetration depth (m), c is the soil cohesion (kPa), φ is the soil internal friction angle (°), and σ is the soil normal stress around the anchor (kPa). This formula shows that the anchor pullout force is directly related to the soil cohesion c, the internal friction angle φ, and the normal stress σ. For different soil types: Muddy riverbed: soil cohesion c Low internal friction angle f Small, shear strength mainly depends on c When the riverbed slope i When the slope increases, the sliding force of the soil along the slope increases, and the slope correction coefficient needs to be increased. β (e.g. additional 0.05) to reduce the anchor spacing L , increase the density of anchors to improve the total pull-out resistance.

[0035] Sandy riverbed: soil cohesion c Low, but the internal friction angle f Higher, shear strength mainly depends on s tan f . water depth h When the soil effective stress increases, the normal stress s Improvement can be achieved by reducing β (For example, reduce by 0.02) Increase the anchor spacing to avoid over-anchoring while ensuring pull-out resistance.

[0036] Rocky riverbed: soil cohesion c and internal friction angle f The shear strength is significantly higher than that of soft soil foundation, so the minimum β value (0.02) to reduce the amount of anchors used.

[0037] The essence of the slope correction factor β is to balance the anchor pullout force F with the flow force and soil sliding force acting on the geotextile by adjusting the anchor spacing L. For example, when β increases, the anchor spacing L decreases, the number of anchors per unit area increases, and the total pullout force increases, thus adapting to low-shear-strength muddy riverbeds. Conversely, in high-shear-strength rocky riverbeds, a smaller β can reduce anchor density and optimize construction costs.

[0038] This formula and correction logic are consistent with the basic principles of soil mechanics. By coupling soil properties (c, φ) with terrain parameters (θ, h), a differentiated design of the anchoring system is achieved to ensure the stability of the geotextile under different riverbed conditions.

[0039] Riverbed soil type can be determined using an underwater coring drill to collect riverbed samples. Combined with geotechnical testing, the soil particle size distribution and plasticity index are analyzed to determine whether the riverbed is silty, sandy, or rocky. Riverbed slope θ is determined using a multibeam sonar system. This system emits a wide sound wave across the riverbed surface, generating a high-precision digital terrain model for slope calculation. Water depth h is measured in real time using an ultrasonic depth sensor. The device is mounted on the side of the survey vessel, with the probe submerged 0.5 m below the water surface to avoid wave interference. These instruments are conventional instruments used in hydraulic engineering surveys and are corrosion-resistant and reliable for underwater operations. During the operation, an underwater coring drill is first used to obtain riverbed soil samples at three to five evenly spaced sampling points throughout the construction area. Laboratory testing confirms the soil type. Simultaneously, a multibeam sonar system is used to scan the riverbed, generating a digital elevation model with a 0.2 m × 0.2 m grid resolution. The riverbed slope θ is calculated for each area. Combined with the real-time water depth h measured by the depth sensor, the β value is determined according to a set of rules. Substituting the determined β value into the anchor spacing formula and combining it with the water depth correction factor α, the calculation provides a parameter basis for anchor arrangement. Regarding parameter settings, the underwater coring drill must penetrate the surface soil of the riverbed to ensure representative samples are collected, typically with a drilling depth of no less than 0.5m. The multibeam sonar's depth measurement accuracy must be better than ±1% of the water depth, with an angular resolution of ≤1° to ensure the slope calculation error is within ±2°. The water depth sensor's measurement range covers 0-50m, with an accuracy of ±0.05m, meeting the correction requirements for various water depths. Functional testing was conducted on simulated riverbed models with different soil types. By adjusting slope and water depth parameters, the effect of anchor spacing on geotextile stability was tested. The experimental method involved laying geotextiles on the surfaces of three model riverbeds: silty, sandy, and rocky. Anchor spacing was calculated according to the corresponding β value, and anchors were driven in. A simulated water flow load was applied, and the geotextile edges were observed for slippage or lifting. Each set of working conditions was tested 10 times, recording the flow velocity and displacement at critical instability. The anchoring effects under different β values were compared to verify the compatibility of the slope correction coefficient with the riverbed soil type. This technical solution achieves differentiated design of anchor spacing by correlating the slope correction coefficient β with the riverbed soil type, slope, and water depth. For muddy riverbeds, due to the low bearing capacity of the soil, the β value is increased in steep slope environments to reduce anchor spacing and increase anchor density. For sandy riverbeds, the β value is dynamically adjusted according to the water depth to avoid over-anchoring in deepwater areas due to increased soil density. For rocky riverbeds, due to their hard surface, the minimum β value is used to reduce the number of anchors. This targeted correction method adapts the anchoring system to different geological conditions, optimizing construction costs while ensuring the stability of the geotextile, and reducing engineering risks caused by insufficient anchoring or material waste caused by excessive anchoring.

[0040] In another technical solution, the ballast water depth correction factor The method for determining the value of the anchoring water depth correction coefficient α is: For muddy riverbeds, =0.05, α=0.08; For sandy riverbeds, =0.03, α=0.05; For rocky riverbeds, =0.01,α=0.02.

[0041] In this technical solution, the values of the ballast water depth correction factor γ and the anchor water depth correction factor α are closely related to the riverbed soil type. For muddy riverbeds, γ is set to 0.05 and α is set to 0.08. This is because muddy soil has low cohesion and weak shear strength, requiring a larger correction factor to increase the ballast weight and reduce the anchor spacing to improve the stability of the geotextile. For sandy riverbeds, γ is set to 0.03 and α is set to 0.05. Although sandy soil has low cohesion but a large internal friction angle, a medium correction factor can balance anchoring force and construction cost. For rocky riverbeds, γ is set to 0.01 and α is set to 0.02. Due to its dense structure and high shear strength, a smaller correction factor can meet project requirements. This tiered value is based on the mechanical properties of different soil types in soil mechanics to ensure that the correction factor matches the riverbed's bearing capacity. Riverbed soil type can be determined using an underwater coring drill. This equipment can collect surface soil samples for laboratory analysis of particle size distribution and plasticity index, thereby accurately determining the soil type. Riverbed depth can be measured using ultrasonic depth sensors, which use the principle of sound wave reflection to obtain real-time depth data. The measurement range covers 0-50 meters and meets engineering requirements for accuracy. These devices are common instruments used in water conservancy engineering surveys and have excellent underwater operation performance, providing reliable data for determining correction factors. Regarding material selection, concrete blocks can be used for ballast, as they have stable density and high strength, making them suitable for underwater ballast. Stainless steel anchors can be used for their corrosion resistance and long-term underwater use. Polyester woven fabrics can be used for geotextiles, which combine high tensile strength with aging resistance, making them suitable for complex underwater environments. These materials are mature, widely used in water conservancy projects, and are reliable and readily available. The underwater coring drill can be installed on the deck of the workboat, using a retractable drill rod to penetrate the riverbed surface for sampling. The ultrasonic water depth sensor can be mounted on a bracket on the outboard side of the vessel, with the probe vertically immersed 0.5 meters below the water surface to prevent interference from surface fluctuations. This arrangement ensures stable operation and accurately collects riverbed soil and water depth data, providing accurate on-site parameters for determining the correction factor. During operation, the underwater coring drill first collects riverbed soil samples at 3-5 sampling points evenly spaced across the work area. These samples are then sent to a laboratory for testing to determine the soil type. Simultaneously, the ultrasonic water depth sensor measures the water depth h of the work area, and the corresponding γ and α values are determined based on the soil type. For muddy riverbeds, γ = 0.05 is substituted into the ballast weight formula to increase the ballast density; α = 0.08 is substituted into the anchor spacing formula to reduce the anchor spacing for closer anchoring. For sandy and rocky riverbeds, the ballast weight and anchor spacing are adjusted according to the corresponding correction factors. After completing the parameter calculation, ballast is evenly laid on the surface of the geotextile, and anchors are driven in according to the calculated anchor spacing to ensure that the geotextile fits tightly against the riverbed.In terms of parameter setting, the drilling depth of the underwater coring drill must be controlled within 0.5-1.0m to ensure representative soil samples are collected. Ultrasonic water depth sensors must be calibrated to the tide level before construction to eliminate tidal measurement errors, with calibration intervals no more than two hours. The weight of each ballast block is determined based on the calculated ballast weight, typically 50-100kg, to ensure uniform distribution during construction. The diameter of the anchor bolts is selected based on the required anchoring force, generally 16-22mm, to ensure sufficient pullout resistance after being driven into the riverbed. Functional testing is conducted on simulated riverbed models with different soil types. Geotextiles are laid in each model and applied with ballast weights and anchor spacing calculated using corresponding correction factors. The experimental method involves simulating water flow loads in a laboratory environment, gradually increasing the water velocity, and observing whether the geotextile exhibits displacement, lifting, or anchor pullout. The water flow parameters at the critical instability point are recorded, and the experimental data obtained under different correction factors are compared to analyze the compatibility of the ballast and anchoring effects with the soil type. Each set of working conditions was tested 10 times, and the average value was taken as the basis for evaluation to verify the rationality and reliability of the correction coefficient value. This technical solution achieves differentiated design of ballast weight and anchor spacing by associating the ballast water depth correction coefficient γ and the anchor water depth correction coefficient α with the riverbed soil type. Ballast and anchoring are strengthened in view of the weak characteristics of silt riverbeds, material consumption is reduced in view of the stable characteristics of rocky riverbeds, and an intermediate correction coefficient is used for sandy riverbeds to balance safety and economy. This correction method based on soil mechanical properties enables the geotextile laying plan to better adapt to different riverbed conditions, optimize resource allocation while ensuring project stability, reduce construction costs and improve long-term operation reliability.

[0042] In another technical solution, the terrain compensation coefficient The value of is: For muddy riverbeds, =0.2; For sandy riverbeds, =0.1; For rocky riverbeds, =0.

[0043] In this technical solution, the terrain compensation coefficient τ is used to quantify the additional impact of riverbed soil quality on anchor spacing. Its value is positively correlated with riverbed stability: For muddy riverbeds (τ = 0.2), the soil is weak and unstable, requiring a higher compensation coefficient to reduce anchor spacing; for sandy riverbeds (τ = 0.1), the soil is medium-density and stable, requiring moderate compensation; and for rocky riverbeds (τ = 0), the soil is hard and stable, requiring no compensation. The terrain compensation coefficient τ, combined with the existing correction coefficients (β and α), forms a multi-level correction system that covers all riverbed types, from weak to hard, improving the formula's adaptability to extreme geological conditions.

[0044] Another technical solution also includes anchor reinforcement measures, specifically: After the underwater geotextile is laid in step 3, the riverbed is scanned with a multi-beam sonar at a cycle of 1 hour to generate a digital elevation model with a grid resolution of 0.2m×0.2m, and the settlement of each grid cell is calculated as Δh=H0-H t , where H0 is the initial elevation, H t is the current elevation; The local settlement area is defined as an area with more than three consecutive grid cells with Δh>0.2m; In the local settlement area, additional anchors are placed at the geometric center points of the rectangular grid area formed by every four adjacent original anchors.

[0045] In this technical solution, the key parameters of the anchor reinforcement measures are strictly set according to the actual needs of the project. The grid resolution of the digital elevation model generated by multi-beam sonar scanning is 0.2m×0.2m, ensuring that subtle topographic changes in the riverbed can be captured; the settlement Δh is defined as the difference between the initial elevation H0 and the current elevation H tWhen Δh>0.2m for more than three consecutive grid cells, it is determined to be a local settlement area. This threshold combines the normal settlement range of the riverbed soil with the engineering safety requirements to avoid misjudgment or omission. The position of the additional anchor is set as the geometric center point of the rectangular grid area formed by every four adjacent original anchors to ensure that the new anchors are evenly distributed in the settlement area and form a coordinated force structure with the original anchors. In terms of equipment selection, the riverbed scanning can use a mature multi-beam sonar system on the market. This equipment can emit wide-band sound waves to cover the riverbed surface and generate a high-precision digital terrain model to calculate the elevation data of each grid cell. A hydraulic underwater pile driver can be used for additional anchors, equipped with a high-precision positioning system. It can accurately locate the original anchor position underwater and calculate the geometric center point to ensure that the additional anchor is driven in according to the design requirements. These equipment are commonly used tools for underwater construction of water conservancy projects. They are waterproof and pressure-resistant and can adapt to complex underwater working environments. In terms of material selection, replacement anchors can be made of stainless steel or high-strength alloys, matching the original anchors' mechanical properties and corrosion resistance, ensuring compatibility between the old and new anchors. Stainless steel offers excellent seawater corrosion resistance, making it suitable for long-term underwater use. High-strength alloys reduce anchor weight while maintaining pullout resistance, facilitating installation. Stress sensors on the edges of the geotextile can be resistive strain gauge sensors. Adhesive sensors can monitor tensile stress in real time, providing data support for the need for replacement anchors. The multibeam sonar system can be installed within the work vessel's hull shroud, ensuring that the sonic wave transmission direction is parallel to the vessel's bottom. This system covers a 60-90° detection range on either side of the bottom, minimizing interference from the vessel's structural integrity. A hydraulic underwater pile driver can be mounted on the work vessel's deck, with a retractable robotic arm used to adjust the pile driving position. A positioning probe at the end of the arm accurately identifies the rectangular grid formed by the original anchors, ensuring the replacement anchors are located at the geometric center. During the work process, the underwater geotextile is laid and the original anchors are laid first. Then the multi-beam sonar system is started to scan the riverbed with a cycle of 1 hour, generate a digital elevation model and calculate the settlement Δh of each grid unit. The system automatically identifies areas with more than 3 consecutive grid units with Δh>0.2m as local settlement areas. For each settlement area, the position of the original anchor is determined by the positioning system, and the geometric center point of the rectangular grid formed by every four adjacent original anchors is calculated. The operator controls the hydraulic underwater pile driver to move to the center point, adjusts the pile driving angle and drives in additional anchors to ensure that the new anchors do not interfere with the original anchor structure. In terms of parameter setting, the scanning frequency and grid resolution of the multi-beam sonar need to be calibrated before construction to ensure consistency with the design requirements; when calculating the settlement, the elevation changes caused by the tide need to be deducted and corrected by real-time access to tide level monitoring data.The positioning accuracy of the supplementary anchors must be controlled within ±5cm to ensure accurate positioning at the geometric center. The pressure parameters of the pile driver are adjusted according to the riverbed soil type to avoid damage to the riverbed structure due to excessive impact force or insufficient anchor penetration due to insufficient force. Functional testing was conducted on a simulated riverbed model with geotextiles laid. By artificially creating a localized settlement area (e.g., with a preset Δh = 0.3m within a 3×3 grid cell), the accuracy of multibeam sonar in identifying and locating the settlement area was tested. Supplementary anchors were placed according to the design within the settlement area. Simulated water flow loads and soil settlement were applied. The strain distribution and displacement of the geotextile in the supplementary anchor area were observed, and the pull-out force data of the anchors were recorded. Each set of conditions was tested 15 times, and the average settlement, displacement, and pull-out force were calculated to verify whether the supplementary anchors effectively suppressed the tensile deformation of the geotextile caused by settlement and to analyze the effect of the supplementary anchor location on the overall stability of the anchoring system. This technical solution uses periodic riverbed scanning and settlement monitoring to promptly identify and accurately locate localized settlement areas. By adding anchors at the geometric center points of the original rectangular grid, the new anchors are evenly distributed across the settlement area, forming a denser force network with the original anchors and effectively sharing the tensile stress of the geotextile caused by settlement. This reinforcement measure avoids the drawbacks of blindly adding anchors based on experience. It utilizes geometric positioning to ensure that the additional anchors work in synergy with the original anchors, improving the overall stability of the anchoring system and reducing the risk of geotextile edge lifting and tearing caused by uneven riverbed settlement, thereby ensuring the structural reliability and safety of underwater projects in long-term operation.

[0046] In another technical solution, the length of the additional anchor is satisfy: When Δh≤0.3m, = +0.2; When Δh>0.3m, = +0.5+0.1Δh; where is the length of the original anchor, m.

[0047] In this technical solution, the length of the additional anchor is determined by the settlement amount. When Δh≤0.3m, = +0.2, this setting is suitable for areas with slight settlement. It adds 0.2 meters to the original anchor length to ensure that the anchor still has enough depth to resist the soil displacement caused by slight settlement. When Δh>0.3m, = +0.5+0.1Δh. As settlement increases, in addition to the fixed 0.5-meter increase, an additional 0.1-meter length is added for every additional meter of settlement. This allows the anchors to penetrate deeper into the stable soil layer, meeting the higher anchoring force requirements during severe settlement. This linear growth relationship is based on the positive correlation between anchor pullout resistance and burial depth in soil mechanics, ensuring that supplemental anchors provide reliable support under varying settlement conditions. Settlement monitoring can be achieved using a multi-beam sonar system. This system transmits a wide-band sound wave to scan the riverbed, generating a high-precision digital elevation model to calculate the elevation change of each grid cell. Its grid resolution is 0.2 m × 0.2 m, and its depth measurement accuracy is better than ±1% of the water depth, enabling accurate capture of riverbed settlement details. Supplemental anchoring can be achieved using a hydraulic underwater pile driver equipped with a depth sensor and a positioning system. The former monitors the anchor penetration depth in real time, while the latter ensures that the anchors are precisely driven into the soil according to the designed length. These devices are proven equipment for underwater operations in water conservancy projects. They are waterproof and high-pressure resistant, adapting to the complex underwater construction requirements. In terms of material selection, the replacement anchors can be made of the same stainless steel or high-strength alloy as the original anchors. Stainless steel anchors offer excellent corrosion resistance and are suitable for long-term underwater immersion. High-strength alloy anchors offer reduced weight while maintaining pullout resistance, making them easier to operate with the pile driver. The same material as the original and replacement anchors prevents anchor failure due to electrochemical corrosion and ensures that the mechanical properties of the new and old anchors are compatible when subjected to synergistic forces. The multi-beam sonar system is installed in the center of the workboat's bottom. Its acoustic wave transmission direction is perpendicular to the bottom, covering a 60-degree angle on either side of the vessel to prevent interference with the riverbed scan from the hull structure. The hydraulic underwater pile driver is mounted on a rotatable bracket on the deck. The bracket's height is adjustable, ensuring the pile driver's drill bit is aligned with the replacement location and the pile driving direction is perpendicular to the riverbed, ensuring accurate anchor penetration. During the work process, after the geotextile is laid, the multi-beam sonar system scans the riverbed in a cycle of 1 hour, generates a digital elevation model and calculates the Δh of each grid unit. When more than 3 consecutive grid units with Δh>0.2m are identified, it is determined to be a local settlement area. For the additional anchors in this area, the length is first determined according to Δh. Then, the hydraulic underwater pile driver drives the anchors of customized length into the settlement area according to the guidance of the positioning system to ensure that the new anchors are staggered with the original anchor positions to avoid mutual interference. In terms of parameter setting, the scanning parameters of the multi-beam sonar need to be calibrated before construction, including grid resolution, sounding frequency and elevation data filtering algorithm, to ensure that the Δh calculation error does not exceed ±0.05m. The depth sensor of the hydraulic pile driver needs to be linked with the anchor length calculation module. When the driving depth reaches The original anchor length is recorded in the construction record and can be directly retrieved when additional driving is required to ensure the accuracy of length calculation. In the functional test, the experimental object is a simulated riverbed device with geotextile laying, and the settlement Δh is manually controlled to 0.2m, 0.4m, 0.8m and other working conditions. The experimental method is: calculate according to the formula in different settlement areas The anchors were laid out and horizontal loads were applied to the geotextile using a tensile testing machine. The maximum tensile force when the anchors were pulled out was recorded. The pull-out force data of different anchor lengths under the same settlement were compared to verify the Whether the anchoring performance is effectively improved with the increase of Δh. Each group of working conditions was tested 20 times, and the correlation between the average pull-out force and the settlement was statistically analyzed to analyze the rationality of the formula for the length of the supplementary anchor. This technical solution realizes the dynamic adjustment of the anchoring depth by quantitatively correlating the length of the supplementary anchor with the settlement. In case of mild settlement, the length is increased moderately to avoid material waste; in case of severe settlement, the length is increased proportionally to ensure that the anchor is embedded in the stable soil layer to provide sufficient pull-out force. This grading value method combines the relationship between the pull-out force of the anchor and the depth of burial in soil mechanics, so that the supplementary anchor can accurately adapt to the riverbed environment with different settlement degrees, complement the original anchoring system, effectively improve the stability of the geotextile under uneven settlement conditions, reduce the risk of pull-out due to insufficient anchor depth, and ensure the long-term operation reliability of the underwater project.

[0048] Example 1: Laying underwater geotextiles on a muddy riverbed 1. Overview of the construction area The underwater construction area of a river regulation project is a muddy riverbed with a water velocity of v = 1.0 m / s, an average water depth of h = 12 m, a riverbed slope of θ = 15°, a reference water depth of h0 = 10 m, and a geotextile receiving area of A = 100 m. 2 The original anchor length, l0, was 1.8m, and the reference spacing, L0, was 0.5m. Samples were collected using an underwater coring drill, and laboratory testing confirmed that the soil plasticity index was greater than 17, indicating a muddy riverbed.

[0049] 2. Parameter calculation and equipment selection Safety factor and ballast weight: v / h=1.0 / 12=0.083s -1 ≤0.3s -1 , safety factor k=0.15; Ballast water depth correction factor γ = 0.05 (muddy riverbed), substitute into the formula: W≈15900kg, because W / A=159kg / m 2 <200kg / m 2 , so the calculated value is used directly.

[0050] Anchorage spacing: Slope correction coefficient β = 0.08 (muddy riverbed, θ = 15° < 20°), anchoring water depth correction coefficient α = 0.08 (muddy riverbed), terrain compensation coefficient τ = 0.2. Substituting into the formula: L ≈ 0.63m. Since L > L0 = 0.5m, use the calculated value.

[0051] Equipment and materials: Water velocity is measured using a Doppler flow sensor (such as the SonTek FlowTracker II), water depth is acquired using an ultrasonic depth sensor (such as the RBR Concerto), and riverbed slope is generated using a multibeam sonar system (such as the Reson Seabat8125) to generate topographic data. Ballast is provided by 50 kg concrete blocks, anchors are 20 mm diameter stainless steel anchors, and the geotextile is a woven polyester fabric with resistive strain gauge sensors (range 0–50 kN / m) attached to the edges.

[0052] 3. Laying and reinforcement process Ballast and anchoring: The geotextiles were transported to the construction site by flat-bottom barges, and concrete blocks were evenly laid with a ballast weight of 15,900 kg. Starting from the riverbank baseline, anchors were driven into the water flow direction at intervals of 0.63 m to form a rectangular grid structure. The edges of adjacent geotextiles overlapped by 0.6 m (based on the ratio of tensile stress to flow velocity σ / v = 4 kN·s / m 3 Use a hot melt welding machine to weld the seams at 320°C.

[0053] Settlement monitoring and re-injection: After the paving is completed, the multi-beam sonar scans the riverbed every hour. Δh=0.4m>0.2m, it is determined to be a local settlement area. Calculate the length of the additional anchor bolts l 补 =2.34m, and are laid out at the geometric center point of the rectangle formed by four adjacent original anchors. They are driven in using a hydraulic underwater pile driver to avoid overlapping with the original anchors.

[0054] 4. Effect Verification A simulated flow load test showed that when the water velocity increased to 2.5 m / s, the geotextile edge displacement was 10 mm, with no noticeable slippage. The average anchor pullout force was 5.5 kN, meeting the design requirements. After additional anchors were placed in the settlement area, the displacement of the geotextile under a 0.4 m settlement condition was reduced by 55% compared to the pre-placement displacement. This validated the high correction factor for muddy riverbeds and ensured the stable installation of the geotextile on soft foundations.

[0055] Example 2: Laying underwater geotextiles on a sandy riverbed 1. Overview of the construction area The underwater construction area of a coastal mudflat improvement project is a sandy riverbed with a water velocity v = 2.0 m / s, an average water depth h = 18 m (over 15 m), a riverbed slope θ = 10°, a reference water depth h0 = 10 m, and a geotextile receiving area A = 150 m. 2 The original anchor length l0 = 1.5m, and the reference spacing L0 = 0.5m. Particle grading analysis confirmed that the sand content in the soil exceeded 85%, indicating a sandy riverbed.

[0056] 2. Parameter calculation and equipment selection Safety factor and ballast weight: v / h=2.0 / 18≈0.111s -1 ≤0.3s -1 , safety factor k = 0.15; ballast water depth correction factor γ = 0.03 (sandy riverbed), substitute into the formula: W ≈ 18540 kg, W / A = 123.6 kg / m 2 <200kg / m 2 , using the calculated value.

[0057] Anchorage spacing: Because the water depth h = 18 m > 15 m, the sandy riverbed slope correction coefficient β = 0.05 − 0.02 = 0.03, the anchorage depth correction coefficient α = 0.05 (sandy riverbed), and the terrain compensation coefficient τ = 0.1. Substituting into the formula: L ≈ 0.53 m. Since L > L0 = 0.5 m, the calculated value is used.

[0058] Equipment and materials: Water velocity was measured using an acoustic Doppler current meter (e.g., Nortek Vectrino), water depth was measured using a ship-borne echo sounder (e.g., Koden EM-3000), and riverbed topography was scanned using multibeam sonar. Ballast was 80 kg steel ingots, anchors were 25 mm diameter galvanized steel anchors, and geotextiles were composite geomembranes with an edge overlap width of σ / v = 6 kN·s / m. 3 Take 0.65 m.

[0059] 3. Laying and reinforcement process Ballast and anchoring: The steel ingots are evenly arranged according to the ballast weight of 18540kg, the anchors are arranged at a spacing of 0.53m, and the edges of adjacent geotextiles overlap by 0.65m (based on σ / v=6 kN·s / m 3 The hot melt welding temperature is controlled at 330℃ to ensure the joint strength.

[0060] Settlement monitoring and re-injection: If the monitoring detects a local settlement area of Δh = 0.3m, the anchor length should be increased. = 1.5 + 0.2 = 1.7 m. It is filled in at the geometric center point of the original anchor grid. The pressure parameter of the pile driver is adjusted according to the loose characteristics of the sandy riverbed to ensure that the penetration depth of the anchor reaches the standard.

[0061] IV. Effect Verification Laboratory simulation shows that when the water depth is 18 m and the water flow velocity is 3.0 m / s, no sliding of the ballast or pulling out of the anchor nails occurs for the geotextile. The average value of the uplift resistance is 5.0 kN, meeting the design requirements. Compared with the reference spacing, the amount of anchor nails is reduced by 12%, the construction efficiency is improved, and the displacement of the area where the anchor nails are filled in is controlled within 8 mm under a settlement of 0.3 m.

[0062] Example 3: Laying underwater geotextile on a rocky riverbed I. General Situation of the Construction Area The underwater construction area of a canyon river regulation project is a rocky riverbed. The lithology of the riverbed is intact moderately weathered sandstone (determined by core sampling). The water flow velocity v = 1.5 m / s, the average water depth h = 8 m, the riverbed slope θ = 8°, the reference water depth h0 = 10 m, the flow area of the geotextile A = 60 m 2 , the original anchor nail length l0 = 1.2 m, and the reference spacing L0 = 0.5 m.

[0063] II. Parameter Calculation and Equipment Selection Safety factor and ballast weight v / h = 1.5 / 8 ≈ 0.1875 s -1 ≤ 0.3 s -1 , the safety factor k = 0.15; the ballast water depth correction factor γ = 0.01 (rocky riverbed), substituting into the formula: W ≈ 12180 kg. Since W / A = 203 kg / m 2 > 200 kg / m 2 , take W = 200 × 60 = 12000 kg.

[0064] Anchoring spacing: The slope correction factor of the rocky riverbed β = 0.02, the anchoring water depth correction factor α = 0.02, and the terrain compensation factor τ = 0.

[0065] Substituting into the formula: L ≈ 0.48 m; since L < L0 = 0.5 m, take L = 0.5 m according to the minimum spacing constraint.

[0066] The water flow velocity is measured by a Teledyne RD Instruments Doppler flowmeter, the water depth is measured by a Valeport Midas ultrasonic water depth sensor, and the riverbed slope is obtained by a Kongsberg EM304 multibeam sonar.

[0067] Concrete blocks were evenly arranged according to a ballast weight of 12,000 kg. The anchors were high-strength alloy anchors with a diameter of 16 mm. The edges of the geotextile were overlapped by 0.5 m (σ / v = 3 kN·s / m 3 ).

[0068] 3. Laying and reinforcement process Ballast and anchoring: Concrete blocks weighing 12,000 kg are evenly arranged, with 2 blocks per square meter, to ensure stable ballast.

[0069] Anchors were driven at 0.5 m intervals, using a high-frequency impact mode for rocky riverbeds, ensuring the anchors penetrated 1.2 m into the soil. Adjacent geotextile edges were heat-melt welded, and the joints were tested underwater to ensure no weld defects.

[0070] Settlement monitoring and re-injection: If local settlement Δh=0.25m occurs, the anchor length should be increased. =1.2+0.2=1.4m, add anchor nails at the center point of the grid, avoiding the original anchor position.

[0071] 4. Effect Verification Field tests showed that under a 25° steep slope and a water flow of 1.5 m / s, the geotextile did not slip, and the average pull-out strength of the anchors reached 8.0 kN, far exceeding the design requirements.

[0072] Because the correction coefficient of the rocky riverbed is small, the amount of anchors used is reduced by 40% compared to the silt riverbed, the construction cost is reduced, and long-term monitoring has not found any structural problems caused by settlement.

[0073] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. The method for laying underwater geotextile is characterized in that: The following steps are involved: Step 1: Obtain the water flow velocity, water depth and riverbed slope of the construction area; Step 2: Calculate the ballast weight of the geotextile according to the water flow velocity and water depth, and then determine the anchor spacing according to the riverbed slope and water depth; Step 3: transport the geotextile to the underwater construction area by ship, evenly distribute the ballast on the surface of the geotextile according to the ballast weight, and start from the boundary baseline of the underwater construction area. Drive anchors into the riverbed row by row along the direction of water flow at the anchor spacing to form a rectangular grid structure. Overlap the edges of adjacent geotextiles and fix them by hot-melt welding to complete the underwater geotextile laying work; Wherein, the ballast weight W is calculated according to the formula Calculation; when the formula calculation result W / A>200kg / m 2 When W=200A, k is the safety factor, ρ is the density of water, kg / m³, v is the water velocity, m / s, A is the projected surface area of the geotextile perpendicular to the water flow direction, m², h is the water depth, m, and h0 is the reference water depth, which is 10 m. is the ballast water depth correction factor; The anchoring spacing L is determined according to the formula and the anchoring spacing L is not less than the reference spacing L0, where L0 is taken as 0.5 m. When the calculated result L of the formula is less than L0, take L = L0; where is the slope correction coefficient; is the riverbed slope; is the anchoring water depth correction coefficient; is the terrain compensation coefficient, and its value range is 0 to 1.

2. The method for laying underwater geotextile according to claim 1, wherein: The method also includes obtaining the tensile stress of the geotextile and correcting the overlapping width B of adjacent geotextile edges according to the ratio of the tensile stress σ to the water velocity v, specifically: When the ratio of tensile stress σ to water velocity v σ / v ≤ 5 kN·s / m 3 When 0.5m≦B<0.6m; When 5 kN·s / m 3 <σ / v ≦ 8 kN·s / m 3 then 0.6 m ≦ B < 0.7 m; When σ / v > 8 kN·s / m 3 then, 0.7 m ≤ B < 0.8 m.

3. The method for laying underwater geotextile according to claim 2, wherein: The water flow velocity in the construction area is measured by a flow velocity sensor, the water depth is measured by a water depth sensor, the riverbed slope is measured by a multi-beam sonar, and the geotextile tensile stress is measured by a stress sensor.

4. The method for laying underwater geotextile according to claim 1, wherein: The method for determining the value of the safety factor k is: When the ratio of water velocity v to water depth h is v / h≤0.3 s -1 When k=0.15; When 0.3 s -1 <v / h≤0.6 s -1 When k=0.18; When v / h > 0.6 s -1 When k=0.

25.

5. The method for laying underwater geotextile according to claim 1, wherein: The value of the slope correction coefficient β is related to the riverbed soil type: For muddy riverbeds, β = 0.08, and when the riverbed slope θ > 20°, β is increased by an additional 0.05; For sandy riverbeds, β = 0.05, and when the water depth h > 15 m, β decreases by 0.02; For rocky riverbeds, β=0.

02.

6. The method for laying underwater geotextile according to claim 1, wherein: Ballast water depth correction factor The method for determining the value of the anchoring water depth correction coefficient α is: For muddy riverbeds, =0.05, α=0.08; For sandy riverbeds, =0.03, α=0.05; For rocky riverbeds, =0.01,α=0.

02.

7. The method for laying underwater geotextile according to claim 1, wherein: The method for determining the value of the terrain compensation coefficient τ is: For muddy riverbed, τ = 0.2; For sandy riverbeds, τ = 0.1; For a rocky riverbed, τ = 0.

8. The method for laying underwater geotextile according to claim 1, wherein: It also includes anchor reinforcement measures, specifically: After the underwater geotextile is laid in step 3, the riverbed is scanned with a multi-beam sonar at a cycle of 1 hour to generate a digital elevation model with a grid resolution of 0.2m×0.2m, and the settlement of each grid cell is calculated as Δh=H0-H t , where H0 is the initial elevation, H t is the current elevation; The local settlement area is defined as an area with more than three consecutive grid cells with Δh>0.2m; In the local settlement area, additional anchors are placed at the geometric center points of the rectangular grid area formed by every four adjacent original anchors.

9. The method for laying underwater geotextile according to claim 8, wherein: The length of the additional anchor nail l 补 satisfy: When Δh≤0.3m, l 补 =l0+0.2; When Δh>0.3m, l 补 =l0+0.5+0.1Δh; where l0 is the length of the original anchor, m.

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