A method for reducing pile slippage during sinking of a large steel pipe pile

Abstract

The present application belongs to the technical field of steel pipe pile sinking, and particularly relates to a method for reducing pile sliding in the process of sinking large steel pipe piles, and the method is specifically as follows: 3-5 layers of geonets are arranged on the inner wall of the steel pipe pile in the vertical direction at intervals, wherein the interval between the two adjacent geonets is 6-10 m, and the distance between the lowermost geonet and the lower end surface of the steel pipe pile is 6-10 m; by arranging the geonets on the inner wall of the steel pipe pile, the additional resistance provided by the geonets can effectively slow down the penetration speed of the pile body, inhibit the continuous acceleration development of the pile sliding, thereby reducing the risk of major safety accidents such as the violent shaking of the sinker system, the instability of the crane ship, the rupture of the steel wire rope, and even the falling of the hammer body into the sea caused by the uncontrollable rapid sinking of the pile body, and significantly improving the safety of the construction workers and the ship machine equipment.

Description

Technical Field

[0001] This invention belongs to the field of steel pipe pile driving technology, specifically relating to a method for reducing pile slippage during the driving of large steel pipe piles. Background Technology

[0002] With the acceleration of the global energy transition, offshore wind power, as an important component of clean energy, is entering a stage of large-scale development. my country's offshore wind farms are developing towards deeper and larger seas. As water depth increases and single-unit capacity grows, the external load on the wind turbine foundations is also gradually increasing. The steel pipe piles that provide load-bearing capacity for the wind turbine foundations are also gradually becoming larger. Currently, the length of steel pipe piles in domestic offshore wind farms has exceeded 100 meters, the maximum diameter has exceeded 10 meters, and the pile weight has even reached several thousand tons.

[0003] In the construction of large-diameter steel pipe piles for offshore wind farms, pile slippage refers to an abnormal phenomenon in which the steel pipe pile suddenly experiences a sharp increase in penetration velocity, a sudden drop in hammer blows (or even zero), and uncontrollable rapid sinking of the pile under its own weight and the load from the superstructure. The root cause of pile slippage lies in the nonlinear response of pile-soil interaction under complex marine geological conditions, as well as the enormous weight of the steel pipe pile and the softness or abrupt changes in the geological layers. When using impact hammers or hydraulic hammers for pile driving, the enormous impact energy causes severe disturbance to the soil at the pile tip and sides. For seabeds with weak soil layers mainly composed of alternating layers of sand, silt, or soft clay, the excess pore water pressure in the soil accumulates rapidly and cannot dissipate instantly, leading to a sharp reduction in effective stress and a sudden and significant weakening or even liquefaction of the soil's shear strength. Especially when the pile tip penetrates the hard soil layer and enters the underlying soft layer, or when the soil on the pile side undergoes a sudden change in "shear dilatation" and "shear contraction", the side friction and end resistance and the weight of the steel pipe pile instantly lose balance. Under the action of its own weight and hammer inertia, the pile body falls uncontrollably and rapidly, resulting in pile slippage.

[0004] Pile slippage has become a frequent occurrence during the driving of ultra-long diameter steel pipe piles in offshore wind farms both domestically and internationally, posing a serious threat to offshore wind power construction. Firstly, the sudden and uncontrollable nature of pile slippage can easily lead to major safety accidents. An out-of-control pile can cause violent shaking of the hammer system, instability of the crane vessel, wire rope breakage, or even the hammer falling into the sea, directly threatening the safety of personnel and equipment. Secondly, pile slippage can lead to a sudden increase in pile penetration, making it difficult to control the verticality of the pile during driving. This can cause structural damage to the pile, flange deformation, or significant deviations in pile top elevation, thereby affecting the installation accuracy and long-term operational stability of the upper wind turbine tower, and even leading to pile foundation failure, resulting in substantial project delays and economic losses.

[0005] To address the risk of pile slippage in offshore wind farms, current engineering practices primarily employ two control methods. First, precise geological parameters are obtained through meticulous pre-driving surveys. Software (such as GRLWEAP) is used to simulate the driving process, and combined with geological reports, the depth and length of areas prone to slippage are predicted, allowing for advance adjustments to the construction plan. This method is complex. Second, during pile driving, when entering high-risk areas prone to slippage, "single-pile driving" with the lowest impact energy and flow rate is employed, or a smaller hammer is used to reduce impact intensity and prevent the instantaneous penetration of hard soil layers due to excessive potential energy. Furthermore, Wang Xueduan proposed a device in her paper "Prediction Method and Preventive Measures for Pile Slippage in Offshore Riser Hammering Operations" that dynamically increases hammering resistance when slippage occurs. However, this device has not been widely adopted in engineering projects, and its cost is uncontrollable due to its reliance on theory. Further improvements are urgently needed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method to reduce pile slippage during the driving of large steel pipe piles.

[0007] The present invention adopts the following technical solution:

[0008] A method for reducing pile slippage during the driving of large steel pipe piles, the specific operation of which is as follows:

[0009] Three to five layers of geonet are arranged vertically on the inner wall of the steel pipe pile. The spacing between two adjacent geonets is 6 to 10 meters, and the distance between the bottommost geonet and the bottom end face of the steel pipe pile is 6 to 10 meters.

[0010] The selection methods for different layers of geonet are as follows:

[0011] Determine the resistance that each layer of geonet can provide, multiply the obtained resistance by the safety factor to obtain a judgment value range, select a geonet with suitable puncture strength within the judgment value range, and at the same time, the geonet mesh density should be set from dense to sparse from bottom to top.

[0012] Among them, the resistance provided by each layer of geonet, ,at the same time, In the formula, G is the self-weight of the steel pipe pile; C is the outer perimeter of the steel pipe pile; qsik is the standard value of the side resistance provided by the i-th layer of soil. It is the distance from the pile tip to the mud surface when the steel pipe pile is driven into the i-th soil layer, i.e., the distance from the pile tip to the mud surface, where i is the soil layer number; A is the area of ​​the geonet; and N is the number of soil layers.

[0013] Furthermore, the coefficients in the formula can be adjusted according to the geological conditions and the weight of the steel pipe piles. If the steel pipe piles are heavy, the risk of pile slippage is greater if there are soft soil layers in the geological survey, so a larger value should be taken; conversely, if the steel pipe piles are light, the possibility of soft soil layers in the geological survey is less, so a smaller value should be taken.

[0014] Furthermore, the safety factor is 1.0-2.0.

[0015] Furthermore, the geonet is fixed to the inner wall of the steel pipe pile by steel strips, acrylic structural adhesive, or epoxy resin adhesive.

[0016] Furthermore, when using steel pressure strips to fix the geonet, the outer periphery of the geonet is pressed against the inner wall of the steel pipe pile by the steel pressure strips, and then the steel pressure strips are welded to the inner wall of the steel pipe pile to complete the fixation of the geonet.

[0017] Furthermore, when using acrylic structural adhesive or epoxy resin adhesive to fix the geonet, first use sandpaper to grind the area on the inner wall of the steel pipe pile where the geonet will be placed, so that the connection surface between the inner wall of the steel pipe pile and the geonet is roughened. Then clean the roughened contact with acetone or alcohol. After the connection surface is dry, apply acrylic structural adhesive or epoxy resin adhesive and apply pressure to make the outer periphery of the geonet adhere to the inner wall of the steel pipe pile, so as to complete the fixation of the geonet.

[0018] Furthermore, when acrylic structural adhesive or epoxy resin adhesive is used to fix the geonet, the bonding strength of the acrylic structural adhesive or epoxy resin adhesive is greater than the resistance of the geonet layer.

[0019] Furthermore, the bonding strength of the acrylic structural adhesive or epoxy resin adhesive is 1.0-2.0 times the resistance of the geonet layer.

[0020] Furthermore, the length of the steel pipe pile is 25-40m.

[0021] As can be seen from the above description of the present invention, compared with the prior art, the beneficial effects of the present invention are:

[0022] First, this invention involves arranging 3-5 layers of geonet vertically at intervals along the inner wall of the steel pipe pile. When the pile tip penetrates into a weak soil layer or crosses the boundary between soft and hard soil layers and slips, the pile rapidly sinks, causing the soil plug inside the pile to move upwards. The geonet, relying on its own puncture strength, provides resistance to the soil plug inside the pile, which is transmitted to the pile wall through a fixed connection (such as welding with steel pressure strips) between the outer periphery of the geonet and the inner wall of the steel pipe pile. During the rapid sinking of the pile, the additional resistance provided by the geonet effectively slows down the pile's penetration speed, inhibiting the continued acceleration of slippage. This reduces the risk of major safety accidents caused by uncontrolled rapid sinking of the pile, such as severe shaking of the hammer system, instability of the crane vessel, wire rope breakage, or even the hammer falling into the sea, significantly improving the safety of construction personnel and equipment.

[0023] Secondly, compared with the prior art, the present invention only requires fixing the geonet to the inner wall of the steel pipe pile at a predetermined interval before pile driving. The construction process is simple and does not require additional complex construction equipment or changes to the existing pile driving process, making it easy to promote and apply in engineering. Moreover, the geonet material used is widely available, inexpensive, and easy to construct, which has significant engineering practicality and economy.

[0024] Third, this invention establishes a quantitative formula relating the resistance of the geogrid to the self-weight of the steel pipe pile and the lateral resistance of the soil layer beside the pile. This allows for the scientific determination of the resistance range required for each layer of geogrid based on specific geological conditions and pile parameters, thus enabling precise selection. The lower limit in the formula ensures that the geogrid provides sufficient resistance to effectively resist pile slippage. The upper limit avoids excessive resistance that could unduly hinder normal pile driving, ensuring that the geogrid only provides resistance when pile slippage occurs, without affecting the smooth progress of normal pile driving. Furthermore, by multiplying the calculated resistance value by a safety factor of 1.0-2.0 during selection, a safety margin is further guaranteed, making the overall safety of the scheme more controllable.

[0025] Fourth, the coefficients in the resistance calculation formula of this invention can be adjusted according to the geological conditions and the weight of the steel pipe piles. When the steel pipe piles are heavy and there are soft soil layers and a high risk of pile slippage, the coefficients are taken as large values ​​to provide greater resistance reserves. When the steel pipe piles are light and there is a low probability of soft soil layers and a low risk of pile slippage, the coefficients are taken as small values ​​to avoid over-design. This flexible adjustment mechanism enables this invention to be applicable to different geological conditions and different pile types, and has wide applicability.

[0026] Fifth, the method of setting the grid density from dense to sparse from bottom to top is scientific and reasonable. During the pile penetration process, the lower geonet bears greater soil plug pressure and dynamic impact load, so it is necessary to select geonet products with higher grid density and greater puncture strength to provide sufficient resistance. On the other hand, the upper geonet bears relatively smaller loads, so it is possible to select geonets with lower grid density and lower puncture strength. This setting method not only ensures that each layer of geonet can effectively play a resistance role in its position, but also avoids excessive use of materials, thus meeting functional requirements while taking into account economy.

[0027] Sixth, this invention provides three fixing methods: steel pressure strip welding, acrylic structural adhesive bonding, and epoxy resin adhesive bonding, which can be flexibly selected according to actual construction conditions. When steel pressure strip welding is used, the weld is continuous and fully welded, resulting in high connection strength and good reliability. When structural adhesive bonding is used, surface treatment processes such as grinding to form a rough surface and cleaning with acetone or alcohol are used to ensure that the bonding surface is clean and rough, improving the bonding effect. Furthermore, the bonding strength is required to be 1.0-2.0 times greater than the required resistance of the geonet layer, ensuring that the geonet can effectively play a resistance role and not fall off prematurely when pile slip occurs, thus effectively guaranteeing the reliability of the connection.

[0028] Seventh, the additional damping force provided by the geonet slows down the sinking speed of the pile during the pile sliding process, which helps to control the verticality of the pile body and reduce problems such as pile structure damage, flange deformation and serious deviation of pile top elevation caused by sudden increase in penetration. This ensures the installation accuracy and long-term operational stability of the upper wind turbine tower, avoids the scrapping of the pile foundation, and reduces construction delays and economic losses.

[0029] Eighth, the geonet layout method of the present invention can be used in conjunction with existing control measures such as refined geological survey prediction and low-energy single-click pile driving. Based on the prediction of the risk area of ​​pile slippage, the geonet provides additional physical resistance protection, forming a multi-control system of "prediction + protection", which further improves the reliability of pile slippage prevention and control. Attached Figure Description

[0030] Figure 1 Schematic diagram of the arrangement of geonet on the inner wall of steel pipe pile;

[0031] Among them, 1-steel pipe pile, 2-geogrid. Detailed Implementation

[0032] The present invention will be further described below through specific embodiments.

[0033] A method for reducing pile slippage during the driving of large steel pipe piles, the specific operation of which is as follows:

[0034] Three to five layers of geonet 2 are arranged vertically on the inner wall of the steel pipe pile 1. The spacing between two adjacent geonets 2 is 6 to 10 m, and the distance between the bottommost geonet 2 and the lower end face of the steel pipe pile 1 is 6 to 10 m.

[0035] The selection methods for different layers of geonet are as follows:

[0036] Determine the resistance that each layer of geonet can provide, multiply the obtained resistance by the safety factor to obtain a judgment value range, select a geonet with suitable puncture strength within the judgment value range, and at the same time, the geonet mesh density should be set from dense to sparse from bottom to top.

[0037] Among them, the resistance provided by each layer of geonet, ,at the same time, In the formula, G is the self-weight of the steel pipe pile; C is the outer perimeter of the steel pipe pile; qsik is the standard value of the side resistance provided by the i-th layer of soil. It is the distance from the pile tip to the mud surface when the steel pipe pile is driven into the i-th soil layer, i.e., the distance from the pile tip to the mud surface, where i is the soil layer number; A is the area of ​​the geonet; and N is the number of soil layers.

[0038] Specifically, the coefficients in the formula can be adjusted according to the geological conditions and the weight of the steel pipe piles. If the steel pipe piles are heavy, the risk of pile slippage is greater if there are soft soil layers in the geological survey, so a larger value should be taken; conversely, if the steel pipe piles are light, the possibility of soft soil layers in the geological survey is less, so a smaller value should be taken.

[0039] In this embodiment, the safety factor is 1.0-2.0. The length of the steel pipe pile is 25-40m.

[0040] In this embodiment, the geonet is fixed to the inner wall of the steel pipe pile by steel strips, acrylic structural adhesive, or epoxy resin adhesive.

[0041] When using steel strips to fix the geonet, the outer periphery of the geonet is pressed against the inner wall of the steel pipe pile by the steel strips, and then the steel strips are welded to the inner wall of the steel pipe pile to complete the fixation of the geonet.

[0042] When using acrylic structural adhesive or epoxy resin to fix the geonet, first use sandpaper to sand the area on the inner wall of the steel pipe pile where the geonet will be placed, creating a rough surface at the connection between the inner wall of the steel pipe pile and the geonet. Then clean the roughened contact surface with acetone or alcohol. After the connection surface is dry, apply the acrylic structural adhesive or epoxy resin, and apply pressure to adhere the outer periphery of the geonet to the inner wall of the steel pipe pile, thus completing the fixation of the geonet. Furthermore, when using acrylic structural adhesive or epoxy resin to fix the geonet, the bonding strength of the acrylic structural adhesive or epoxy resin should be greater than the resistance of the geonet layer. Specifically, the bonding strength of the acrylic structural adhesive or epoxy resin should be 1.0-2.0 times the resistance of the geonet layer.

[0043] Example 1

[0044] A method for reducing pile slippage during the driving of large steel pipe piles, the specific operation of which is as follows:

[0045] Step 1: Determine the basic parameters of the steel pipe pile.

[0046] Taking a large-diameter steel pipe pile in an offshore wind farm as an example, the steel pipe pile is 35m long, 8.0m in outer diameter, and 60mm thick. The self-weight of the steel pipe pile, G, is approximately 4200kN. The outer perimeter of the steel pipe pile is C=π×D=3.14×8.0=25.12m. According to the geological survey report, the following layers are distributed from the mud surface downwards at the pile location: the first layer is a silty clay layer, about 8m thick, with a standard value of lateral resistance qs1k=15kPa; the second layer is a silty sand layer, about 12m thick, with a standard value of lateral resistance qs2k=45kPa; the third layer is a silty clay layer, about 10m thick, with a standard value of lateral resistance qs3k=55kPa; and the fourth layer is a medium sand layer, with a standard value of lateral resistance qs4k=70kPa. Among these, the second silty sand layer is a weak soil layer that may liquefy, posing a risk of pile slippage.

[0047] Step 2: Determine the number and spacing of geonet layers.

[0048] Four layers of geonet are arranged vertically at intervals on the inner wall of the steel pipe pile, with an 8m spacing between adjacent layers. The distance between the bottommost geonet and the bottom end face of the steel pipe pile is also 8m. Specifically, starting from the bottom end face of the steel pipe pile and moving upwards, a layer of geonet is arranged at distances of 8m, 16m, 24m, and 32m from the bottom end face.

[0049] Step 3: Calculation of resistance of each layer of geonet

[0050] Based on geological survey parameters, calculate the resistance range that each layer of geonet needs to provide;

[0051] S1, Resistance calculation of the second layer of geonet (16m from the pile bottom):

[0052] When the pile tip penetrates to a depth of 16m from the mud surface, it has passed through the first layer of silty clay and entered the second layer of silty sand. At this point, the accumulated lateral resistance of the pile side is... =C*(qs1k*L1+ qs2k*L2), where L1=8m (thickness of the first soil layer), L2=16-8=8m (penetration depth of the pile tip in the second soil layer), then: =25.12*(15*8+45*8)=12057.6KN;

[0053] Because of the risk of pile slippage, all coefficients are taken as large values; therefore, the resistance range provided by this geonet layer is:

[0054] Lower limit: When the coefficient is 0.5, 0.5 * 4200 - 12057.6 = -9957.6 kN;

[0055] Since the calculated value is negative, it indicates that the pile side resistance is much greater than the pile weight multiplied by a coefficient. The risk of pile slippage at this depth is low, but for safety reasons, a geonet is still needed to provide additional safety. At this point, a lower limit of 0 kN for the geonet resistance is sufficient, meaning that this layer of geonet only needs to provide basic blocking effect.

[0056] Upper limit: When the coefficient is 1.0, 1.0 * 4200 - 12057.6 = -7857.6 kN;

[0057] Similarly, a negative upper limit value indicates that there is sufficient reserve of pile side resistance at that depth, and the geonet resistance can be taken as a smaller value.

[0058] S2, Resistance calculation of the first layer of geonet (8m from the pile bottom):

[0059] When the pile tip penetrates to a depth of 8m from the mud surface, the pile tip is located in the first layer of silty clay. =25.12*15*8=3014.4KN;

[0060] The lower limit, when the coefficient is 0.5: 0.5 * 4200 - 3014.4 = -914.4 kN;

[0061] The upper limit, with a coefficient of 1.0: 1.0 * 4200 - 3014.4 = 1185.6 kN;

[0062] Calculations show that the lower limit is negative, but the upper limit is positive (1185.6 kN), indicating that the pile side resistance (3014.4 kN) at this depth exceeds 50% of the pile weight (2100 kN), and the theoretical risk of pile slippage is low. However, considering the potential dynamic weakening effect during actual pile driving, and the positive upper limit, it indicates that the geonet can provide some auxiliary resistance. It is recommended that the geonet provide a moderate resistance of 200-500 kN as a safety reserve, while ensuring that the resistance does not exceed 1000 kN, so as not to affect normal pile driving.

[0063] S3, Resistance calculation of the third layer of geonet (24m from the pile bottom):

[0064] When the pile tip penetrates to a depth of 24m from the mud surface, it has passed through the second silty sand layer and entered the third silty clay layer. At this point, the cumulative side resistance of the pile is... =C*(qs1k*L1+ qs2k*L2+qs3k*L3), where L1=8m (thickness of the first soil layer), L2=12m (thickness of the second soil layer), L3=24-8-12=4m (penetration depth of the pile tip in the third soil layer), then: =25.12*(15*8+45*12+55*4)=22105.6KN;

[0065] The lower limit, when the coefficient is 0.5: 0.5*4200-22105.6=-20005.6KN;

[0066] The upper limit, with a coefficient of 1.0: 1.0*4200-22105.6=-17905.6KN;

[0067] A negative calculated value indicates that there is sufficient reserve of pile side resistance at this depth, the risk of pile slippage is extremely low, and the geonet only needs to provide basic blocking effect.

[0068] S4, resistance calculation of the fourth layer of geonet (32m from the pile bottom):

[0069] When the pile tip penetrates to a depth of 32m from the mud surface, the pile tip is located in the fourth layer of medium sand:

[0070] =C*(qs1k*L1+ qs2k*L2+qs3k*L3+qs4k*L4), where L1=8m (thickness of the first soil layer), L2=12m (thickness of the second soil layer), L3=10m (thickness of the third soil layer), L4=32-8-12-10=2m (penetration depth of the pile tip in the fourth soil layer), then: =25.12*(15*8+45*12+55*10+70*2)=33912KN;

[0071] The lower limit, when the coefficient is 0.5: 0.5 * 4200 - 33912 = -31812 kN;

[0072] The upper limit, with a coefficient of 1.0: 1.0 * 4200 - 33912 = -29712 kN;

[0073] The calculated value is negative, indicating that the pile side resistance at this depth has far exceeded the pile weight, the risk of pile slippage is extremely low, the geonet in this layer is basically unstressed, and can be used as a safety reserve.

[0074] Step 4, Select Geonet

[0075] Based on the resistance range of each geonet layer calculated in step three, select a geonet with suitable puncture strength. Multiply the resistance provided by each geonet layer by a safety factor of 1.5 to obtain the judgment value range, and select a geonet with suitable puncture strength within this range.

[0076] The geonet mesh density is set from dense to sparse from bottom to top. Specifically:

[0077] First layer (bottommost layer, 8m from the pile bottom): Required resistance 200-500kN, multiplied by a safety factor of 1.5, is 300-750kN; High-strength geonet with a mesh density of 50 mesh and a puncture strength of not less than 750kN / m² is selected.

[0078] The second layer (16m from the pile bottom): the required resistance is 0-200kN, which is 0-300kN after multiplying by a safety factor of 1.5; a geonet with a mesh density of 35 mesh and a puncture strength of not less than 300kN / m² is selected.

[0079] The third layer (24m from the pile bottom): Required resistance 0-100kN, multiplied by a safety factor of 1.5, is 0-150kN. A geonet with a mesh density of 20 mesh and a puncture strength of not less than 150kN / m² is selected.

[0080] The fourth layer (topmost, 32m from the pile bottom): requires a resistance of 0-50kN, which multiplied by a safety factor of 1.5 is 0-75kN. A geonet with a mesh density of 10 mesh and a puncture strength of not less than 75kN / m² is selected.

[0081] Step 5: Fix the geonet

[0082] In this embodiment, a steel pressure strip fixing method is adopted. The specific operation is as follows: the cut geonet is laid on the predetermined position of the inner wall of the steel pipe pile, the outer periphery of the geonet is pressed against the inner wall of the steel pipe pile by the steel pressure strip, and then the steel pressure strip is welded to the inner wall of the steel pipe pile in the circumferential direction. The weld is continuous and fully welded, and the weld height is not less than 6mm to ensure the connection strength between the steel pressure strip and the inner wall of the steel pipe pile, thereby completing the fixing of the geonet.

[0083] This embodiment arranges multiple layers of geonet vertically along the inner wall of the steel pipe pile. Based on the comparison between the cumulative resistance of the pile side and the pile weight at each depth, the resistance requirements and grid density of each layer of geonet are determined differently. The upper limit value of the first layer (8m from the pile bottom) is positive (1185.6kN), indicating that this layer has a theoretical bearing capacity and requires a geonet with moderate resistance. The calculated values ​​of the second layer and above are all negative, indicating that the pile side resistance reserve is sufficient and the geonet only needs to provide basic blocking function. Furthermore, the grid density is set from dense to sparse from bottom to top, which ensures the bearing capacity of the lower geonet while taking into account the economy of the upper geonet, effectively reducing the occurrence of pile slippage accidents during the driving of large steel pipe piles.

[0084] Example 2

[0085] The difference between this embodiment and Embodiment 1 is that the method of fixing the geonet is different, while the rest of the steps are the same as in Embodiment 1.

[0086] In this embodiment, acrylic structural adhesive is used to fix the geonet, and the specific operation is as follows:

[0087] First, use sandpaper to sand the area where the geonet will be installed on the inner wall of the steel pipe pile. The sanded area should be larger than the outer perimeter of the geonet, so that the connection surface between the inner wall of the steel pipe pile and the geonet is roughened to increase the bonding area and bonding force. Then, use acetone to clean the sanded contact surface to remove oil, dust, rust and other impurities. After the connection surface is completely dry, apply acrylic structural adhesive evenly to the inner wall of the steel pipe pile and the outer perimeter of the geonet. Attach the outer perimeter of the geonet to the predetermined position and apply appropriate pressure to ensure that the outer perimeter of the geonet adheres tightly to the inner wall of the steel pipe pile. Maintain the pressure until the acrylic structural adhesive is completely cured to complete the fixation of the geonet.

[0088] In this embodiment, the bonding strength of the acrylic structural adhesive is 1.5 times the resistance of the geonet layer, to ensure that the geonet can effectively play a resistance role and will not fall off prematurely when the pile slips.

[0089] Example 3

[0090] The difference between this embodiment and Embodiment 1 is that the method of fixing the geonet is different, while the rest of the steps are the same as in Embodiment 1.

[0091] In this embodiment, epoxy resin adhesive is used to fix the geonet, and the specific operation is as follows:

[0092] First, use sandpaper to sand the area where the geonet will be installed on the inner wall of the steel pipe pile to create a rough surface for the connection. Then, clean the roughened contact surface with alcohol. After the connection surface dries, apply epoxy resin evenly to the contact surface and apply pressure to make the outer periphery of the geonet adhere to the inner wall of the steel pipe pile. Maintain the pressure until the epoxy resin is completely cured to complete the fixation of the geonet.

[0093] In this embodiment, the bonding strength of the epoxy resin adhesive is 2.0 times the resistance of the geonet layer.

[0094] This invention involves arranging 3-5 layers of geonet vertically at intervals along the inner wall of a steel pipe pile. When the pile tip penetrates a weak soil layer or crosses the boundary between soft and hard soil layers and slips, the rapid sinking of the pile causes the soil plug inside to move upwards. The geonet, relying on its own puncture strength, provides resistance to the soil plug inside the pile, which is transmitted to the pile wall through a fixed connection (such as welded steel strips) between the outer periphery of the geonet and the inner wall of the steel pipe pile. During the rapid sinking of the pile, the additional resistance provided by the geonet effectively slows down the pile's penetration speed and inhibits the continued acceleration of slippage. This reduces the risk of major safety accidents caused by uncontrolled rapid sinking of the pile, such as severe shaking of the hammer system, instability of the crane vessel, wire rope breakage, or even the hammer falling into the sea, significantly improving the safety of construction personnel and equipment.

[0095] Compared with existing technologies, this invention only requires fixing the geonet to the inner wall of the steel pipe pile at predetermined intervals before pile driving. The construction process is simple, requiring no additional complex construction equipment or changes to the existing pile driving process, making it easy to promote and apply in engineering projects. Moreover, the geonet material used is widely available, inexpensive, and easy to construct, demonstrating significant engineering practicality and economy. Furthermore, the additional damping force provided by the geonet slows down the sinking speed of the pile during pile slippage, which helps control the verticality of the pile body and reduces problems such as pile structure damage, flange deformation, and severe deviations in pile top elevation caused by a sudden increase in penetration depth. This ensures the installation accuracy and long-term operational stability of the upper wind turbine tower, avoids pile foundation scrapping, and reduces construction delays and economic losses. At the same time, the geonet layout method can be used in conjunction with existing control measures such as refined geological survey prediction and low-energy hammer pile driving. Based on the prediction of pile slippage risk areas, the geonet provides additional physical resistance protection, forming a multi-control system of "prediction + protection," further improving the reliability of pile slippage prevention.

[0096] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for reducing pile slippage during the driving of large steel pipe piles, characterized in that: The specific steps are as follows: Three to five layers of geonet are arranged vertically on the inner wall of the steel pipe pile. The spacing between two adjacent geonets is 6 to 10 meters, and the distance between the bottommost geonet and the bottom end face of the steel pipe pile is 6 to 10 meters. The selection methods for different layers of geonet are as follows: Determine the resistance that each layer of geonet can provide, multiply the obtained resistance by the safety factor to obtain a judgment value range, select a geonet with suitable puncture strength within the judgment value range, and at the same time, the geonet mesh density should be set from dense to sparse from bottom to top. Among them, the resistance provided by each layer of geonet, ,at the same time, In the formula, G is the self-weight of the steel pipe pile; C is the outer perimeter of the steel pipe pile; qsik is the standard value of the side resistance provided by the i-th layer of soil. It is the distance from the pile tip to the mud surface when the steel pipe pile is driven into the i-th soil layer, i.e., the distance from the pile tip to the mud surface, where i is the soil layer number; A is the area of ​​the geonet; and N is the number of soil layers.

2. The method for reducing pile slippage during the driving of large steel pipe piles according to claim 1, characterized in that: The safety factor can be adjusted according to the geological conditions and the weight of the steel pipe piles. If the steel pipe piles are heavy, the risk of pile slippage is greater if there are soft soil layers in the geological survey, so a larger value is taken; conversely, if the steel pipe piles are light, the possibility of soft soil layers in the geological survey is less, so a smaller value is taken.

3. The method for reducing pile slippage during the driving of large steel pipe piles according to claim 1, characterized in that: The safety factor is 1.0-2.

0.

4. The method for reducing pile slippage during the driving of large steel pipe piles according to claim 1, characterized in that: The geonet is fixed to the inner wall of the steel pipe pile by steel strips, acrylic structural adhesive, or epoxy resin adhesive.

5. The method for reducing pile slippage during the driving of large steel pipe piles according to claim 4, characterized in that: When using steel pressure strips to fix the geonet, the outer periphery of the geonet is pressed against the inner wall of the steel pipe pile by the steel pressure strips, and then the steel pressure strips are welded to the inner wall of the steel pipe pile to complete the fixation of the geonet.

6. The method for reducing pile slippage during the driving of large steel pipe piles according to claim 4, characterized in that: When using acrylic structural adhesive or epoxy resin adhesive to fix the geonet, first use sandpaper to grind the area on the inner wall of the steel pipe pile where the geonet will be placed, so that the connection surface between the inner wall of the steel pipe pile and the geonet is roughened. Then clean the roughened connection surface with acetone or alcohol. After the connection surface is dry, apply acrylic structural adhesive or epoxy resin adhesive and apply pressure to make the outer periphery of the geonet adhere to the inner wall of the steel pipe pile, thus completing the fixation of the geonet.

7. The method for reducing pile slippage during the driving of large steel pipe piles according to claim 6, characterized in that: When using acrylic structural adhesive or epoxy resin adhesive to fix the geonet, the bonding strength of the acrylic structural adhesive or epoxy resin adhesive is greater than the resistance of the geonet layer.

8. The method for reducing pile slippage during the driving of large steel pipe piles according to claim 7, characterized in that: The bonding strength of the acrylic structural adhesive or epoxy resin adhesive is 1.0-2.0 times the resistance of the geonet layer.

9. The method for reducing pile slippage during the driving of large steel pipe piles according to claim 1, characterized in that: The length of the steel pipe pile is 25-40m.

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