Construction method of steel sheet pile foot protection structure for shallow rock layer steel sheet pile cofferdam

Abstract

The invention discloses a construction method of a steel sheet pile foot protection structure for a shallow rock layer steel sheet pile cofferdam, which belongs to the field of underground engineering foundation construction, and comprises the following steps: S1, determining the range and the burial depth of a hard soil layer, and determining parameters of a steel sheet pile-steel pipe pile structure and basic parameters of soil and water; s2, a steel sheet pile-steel pipe pile model is constructed, cooperative calculation is carried out through the parameters in the step S1, according to modeling of the steel sheet pile-steel pipe pile model, steel sheet piles are regarded as upper elastic foundation beams, steel pipe piles are simplified into lower elastic foundation beams in a vertical state, and the connecting positions of the steel sheet piles and the steel pipe piles are arranged to be hinged points of hinged connection; s3, steel sheet piles are driven in, steel pipe piles are driven in local drilling, the steel pipe piles are obliquely arranged towards the outside of the foundation pit, and grouting consolidation is conducted; and S4, the displacement of the steel pipe pile is monitored through an inclinometer pipe. According to the method, the steel pipe piles are obliquely driven into the grooves of the steel sheet piles, the stability of the steel sheet piles is improved, and skirting instability damage is prevented.

Description

Technical Field

[0001] This invention relates to the field of underground engineering foundation construction technology, and in particular to a construction method for a steel sheet pile toe structure for a steel sheet pile cofferdam in shallow rock formations. Background Technology

[0002] Sheet pile cofferdams are commonly used temporary support structures in deep-water bridge foundation construction. Traditionally, these cofferdams require a certain embedment depth of the sheet piles to ensure stability. However, in geological conditions where the hard soil layer is shallow (such as in a major bridge project where the top surface of the strongly weathered silty mudstone is only 1-4m lower than the bottom surface of the cushion layer), sheet piles are difficult to drive into the soil, resulting in insufficient embedment depth. This can easily lead to excessive displacement at the pile bottom and subsequent "kick-out" instability failure.

[0003] Traditional solutions involve increasing the size of the cofferdam, adding internal slopes, or increasing the number of support layers, and using methods such as rotary pressing. However, these methods can lead to increased project costs, increased construction complexity, and extended construction periods. Summary of the Invention

[0004] The purpose of this invention is to provide a construction method for a sheet pile toe structure for a sheet pile cofferdam in shallow rock formations. By driving steel pipe piles at an incline into the grooves of the sheet piles, the stability of the sheet piles is increased, preventing the toe from becoming unstable and damaged.

[0005] To achieve the above objectives, the present invention provides a construction method for a sheet pile toe protection structure for a sheet pile cofferdam in shallow rock formations, comprising the following steps: Step S1: Determine the extent and depth of the hard soil layer, and determine the structural parameters of the sheet pile-pipe pile and the basic parameters of the soil and water bodies; Step S2: Construct a sheet pile-steel pipe pile model and perform collaborative calculations using the parameters from Step S1. The sheet pile-steel pipe pile model is modeled by treating the sheet pile as an upper elastic foundation beam and simplifying the steel pipe pile as a vertical lower elastic foundation beam. The connection between the sheet pile and the steel pipe pile is set as a hinged connection. The incremental method is used to simulate the construction process and calculate the axial force of the steel support. The elastic support method is used to calculate the interaction force and displacement of the hinged point. Step S3: Drive in sheet piles and drive in steel pipe piles in local boreholes, with the piles inclined outwards from the foundation pit, and then grout them for consolidation. Step S4: Use inclinometer tubes to monitor the displacement of the steel pipe piles.

[0006] Preferably, in step S1, the basic parameters of the soil and water body include the internal friction angle of the soil. Soil cohesion Water pressure intensity Horizontal resistance ratio coefficient of foundation soil Unit weight of each soil layer Thickness of each soil layer Structural parameters include the bending stiffness of the sheet piles. and the bending stiffness determined based on the selection of steel pipe piles. steel support cross-sectional area steel support elastic modulus .

[0007] Preferably, in step S2, the formula for calculating the distributed load of the sheet pile-steel pipe pile model is as follows: ; For the depth of sheet piles Total lateral pressure at the location; Among them, active earth pressure intensity The calculation formula is as follows: = ; For the depth of sheet piles The vertical pressure at the point is calculated from the unit weight and thickness of each soil layer determined in step S1: = ; This refers to the cohesion of the soil particles in the corresponding soil layer; The active earth pressure coefficient is calculated from the internal friction angle of the soil determined in step S1. = ; The hydrostatic pressure is calculated from the water level elevation determined in step S1 and the specific weight of water. ; It is the density of water.

[0008] The preferred method for calculating the governing equations of sheet piles is as follows: The differential equation for the force equilibrium of a steel sheet pile is: ; In the formula: The reduced bending stiffness of the sheet pile is obtained from the parameters in step S1; Let be the horizontal displacement of the sheet pile, and let be the objective to be solved. The proportionality coefficient of soil horizontal resistance is obtained from the parameters in step S1; For water and soil pressure load; Let be the horizontal constraint force of the steel pipe pile on the steel sheet pile at the hinge point, and be the parameter to be solved.

[0009] The preferred incremental calculation method for steel supports is as follows: To simulate the cumulative effects of the construction process, the first The supporting force of the road Calculation using the incremental method: ; In the formula: For support stiffness; equivalent support stiffness , For the determined cross-sectional area of ​​the steel support, For elastic modulus, This refers to the length of the steel support. This represents the initial displacement of the steel support at the moment of installation completion. The displacement obtained by solving the current calculation equation.

[0010] The preferred method for calculating the governing equations of steel pipe piles is as follows: The steel pipe pile is considered as an elastic foundation beam vertically embedded in a hard soil layer, with a concentrated force at the top. Function; Utilizing the physical stiffness determined in step S1 Establish the equation: ; Boundary conditions: shear force at pile top equal The bending moment is 0; This represents the resistance coefficient of the hard soil layer. For the steel pipe pile body at depth The horizontal displacement at that location.

[0011] Preferably, the displacement at the bottom of the sheet pile is calculated using the elastic support method. Horizontal constraint force of steel pipe piles on steel sheet piles at hinge joints Ultimately, the displacement and internal forces of the sheet piles and steel pipe piles are obtained.

[0012] Preferably, in step S3, the inclinometer tube is fixed inside the steel pipe pile, and the steel pipe pile toe is driven into a local borehole; the steel pipe pile is driven into the groove of the steel sheet pile and is inclined outward from the foundation pit at an angle of 10° to 20°.

[0013] Preferably, grouting consolidation is performed: during the construction of steel pipe piles, grouting holes are reserved in the steel pipe piles. After the construction of the steel pipe piles is completed, grouting material is pressed into the grouting pipe using grouting equipment. Grouting is stopped when the grouting pressure reaches the required level.

[0014] Preferably, in step S4, an inclinometer is used to monitor the displacement change of the steel pipe pile to determine whether the pile bottom has become unstable, thereby providing timely warning.

[0015] Therefore, the present invention employs the above-mentioned construction method for a sheet pile toe protection structure of a sheet pile cofferdam in shallow rock formation, which has the following beneficial effects: This invention employs a steel sheet pile cofferdam with steel pipe pile toe protection structure, which effectively solves the stability problem of steel sheet pile cofferdams under shallow rock geological conditions. The construction equipment is simple, safe and reliable, and economical. It is particularly suitable for the construction of steel sheet pile cofferdams with shallow rock strata and complex geological conditions, and has significant value for promotion and application.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a construction condition diagram of driving steel pipe piles in an embodiment of the present invention; Figure 2 This represents the most dangerous construction condition in the construction process described in this embodiment of the invention. Figure 3 This is a calculation diagram illustrating the driving of steel pipe piles in an embodiment of the present invention; Figure 4 This is a detailed construction drawing of the steel pipe piles being driven in an embodiment of the present invention; Figure 5 This is a cross-sectional view of the inclinometer tube being embedded in an embodiment of the present invention; Figure 6 This is a diagram showing the bending moment distribution under different working conditions (working condition 1-working condition 7) during the construction process in an embodiment of the present invention; Figure 7 This is a displacement distribution diagram of different working conditions (working condition 1-working condition 7) during the construction process in an embodiment of the present invention; Figure 8 This is a shear force distribution diagram for different working conditions (working conditions 1-7) during the construction process in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0019] It should be noted that the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such as a process, method, system, product, or server that includes a series of steps or units, not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0020] Similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0022] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Example: This invention provides a construction method for a sheet pile toe protection structure for a sheet pile cofferdam in shallow rock formations, comprising the following steps: Step S1: Determine the extent and depth of the hard soil layer, and determine the structural parameters of the sheet pile-pipe pile and the basic parameters of the soil and water bodies.

[0024] Hard soil layers are those with a Standard Penetration Index (SPEI) greater than 30, in which sheet piles are typically difficult to drive. The embedment depth in hard soil layers is usually between 4-15 meters. Basic parameters of soil and water bodies include the soil's internal friction angle. Soil cohesion Water pressure intensity Horizontal resistance ratio coefficient of foundation soil , soil weight of each layer Thickness of each soil layer Structural parameters include the bending stiffness of the sheet piles. and the bending stiffness determined based on the selection of steel pipe piles. steel support cross-sectional area steel support elastic modulus .

[0025] Step S2: Construct a sheet pile-steel pipe pile model and perform collaborative calculations using the parameters from step S1. For example... Figure 1 , Figure 2 As shown, construction conditions and the most dangerous construction conditions are presented respectively when driving steel pipe piles. Figure 2 The most dangerous construction condition is when the sheet pile embedment depth is very small or non-existent. This step is calculated based on the most dangerous condition.

[0026] This method employs the approach of "simplified computational model and displacement-coordinated solution." Model simplification explanation: Although steel pipe piles are inclined in actual construction to resist kicking forces, in the mechanical calculation model, for simplification and safety considerations, the steel pipe piles are simplified as vertically placed elastic foundation beams. The upper part of the sheet pile-steel pipe pile model consists of sheet piles, and the lower part is a steel pipe pile toe cap. The connection point (bottom of the sheet pile and top of the steel pipe pile) is simplified to a hinge point, meaning that at this point the bending moment is 0, the shear force is continuous, and the horizontal displacement is equal.

[0027] The specific calculation process and formulas are as follows: The formula for calculating distributed loads is as follows: ; For the depth of sheet piles Total lateral pressure at the location; Among them, active earth pressure intensity The calculation formula is as follows: = ; For the depth of sheet piles The vertical pressure at the point can be calculated from the unit weight and thickness of each soil layer determined in step S1: = ; This refers to the cohesion of the soil particles in the corresponding soil layer; The active earth pressure coefficient can be calculated from the internal friction angle of the soil determined in step S1: = ; The hydrostatic pressure can be calculated from the water level elevation determined in step S1 and the specific weight of water: ; It is the density of water.

[0028] The calculation method for the governing equations of sheet piles (superstructure) is as follows: The sheet pile is considered as a beam supported on an elastic foundation, and its force equilibrium differential equation is: ; In the formula: The reduced bending stiffness of the sheet pile is obtained from the parameters in step S1; Let be the horizontal displacement of the sheet pile, and let be the objective to be solved. The proportionality coefficient of soil horizontal resistance is obtained from the parameters in step S1; For water and soil pressure load; is the horizontal constraint force (reaction force) of the steel pipe pile on the steel sheet pile at the hinge point, and is the parameter to be solved.

[0029] The incremental calculation method for steel supports is as follows: To simulate the cumulative effects of the construction process, the first The supporting force of the road Calculation using the incremental method: ; In the formula: For support stiffness. Equivalent support stiffness. , For the determined cross-sectional area of ​​the steel support, For elastic modulus, This refers to the length of the steel support. This represents the initial displacement of the steel support at the moment of installation completion. The displacement obtained by solving the current calculation equation.

[0030] The calculation method for the control equation (vertical simplified model) of steel pipe piles (lower toe protection) is as follows: The steel pipe pile is considered as an elastic foundation beam vertically embedded in a hard soil (or rock) layer, with a concentrated force at the top. Function. Utilizing the physical stiffness determined in step S1. Establish the equation: ; Boundary conditions: shear force at pile top equal The bending moment is 0. This refers to the resistance coefficient of hard soil (or rock) layers. For the steel pipe pile body at depth The horizontal displacement at that location.

[0031] The displacement at the bottom of the sheet pile is calculated using the general elastic support method (existing algorithm). and reaction force .

[0032] Through the above calculations, the displacement and internal force of the sheet piles and steel pipe piles are obtained. If the calculation results meet the safety factor required by the specifications, the inclined driving construction is carried out according to step S3.

[0033] Step S3: Drive in sheet piles and, in some areas, drive in steel pipe piles at an angle towards the outside of the pit, then grout for consolidation. The specific steps are as follows: like Figure 3 As shown (the supporting spring in the figure is the steel support in this invention), steel sheet piles are driven in sequence along the guide frame using a 90kW vibratory hammer. The steel sheet piles should be driven to the rock surface or at an elevation of -10.0m. The first horizontal support (steel support one) is installed at 5.8m, and water is pumped out to 3m; the second horizontal support (steel support two) is installed at 3m, and water is pumped out to 1m. The inclinometer tube is fixed inside the steel pipe pile. When installing the third horizontal support (steel support three) at 1.8m, a drilling rig is used to drill a hole, and a steel pipe with a diameter of 128mm, a wall thickness of 5mm, and a length of 9m is driven into the predetermined steel pipe pile driving point using a pile driver. The steel pipe pile should be driven into the groove position of the steel sheet pile and inclined outwards at a certain angle, between 10° and 20°, preferably 15°. During the construction of steel pipe piles, grouting holes are pre-drilled in the steel pipe piles. After the steel pipe pile construction is completed, cement grout is injected into the grouting pipes using grouting equipment. Grouting is stopped when the required grouting pressure is reached, ensuring that the steel pipe pile toe is not damaged and forming a reliable bottom support. Figure 4 , Figure 5 As shown. The excavation was carried out by pumping water to -1m, and the fourth horizontal support (steel support four) was installed at -0.20m; the excavation was carried out by pumping water to -2.50m, and the fifth horizontal support (steel support five) was installed at -2.00m; the excavation was carried out by pumping water to -5.00m, and the sixth horizontal support (steel support six) was installed at -3.60m; finally, the excavation was carried out by pumping water to -5.575m.

[0034] Step S4: Use an inclinometer to monitor the change in horizontal displacement of the steel pipe pile, such as... Figure 5 As shown, during the period from the driving of the steel pipe piles to the completion of construction, the displacement change of the steel pipe piles is monitored once a day to determine whether the pile bottom (kick) is about to become unstable and to provide timely warning.

[0035] To verify the safety of the support structure throughout the construction process, seven key working conditions were selected for internal force and displacement analysis. Figure 6 , Figure 7 and Figure 8Curve numbers 1 to 7 correspond to the following construction conditions: Condition 1: Install the first support at +5.8m and pump water to +3.0m; Condition 2: Install the second support at +3.0m and pump water to excavate to +1.0m; Condition 3: Install the third support at +1.8m and drive steel pipe piles for toe protection; Condition 4: Install the fourth support at -0.2m and pump water to excavate to -2.5m; Condition 5: Install the fifth support at -2.0m and pump water to excavate to -5.0m; Condition 6: Install the sixth support at -3.6m and pump water to excavate to -5.0m; Condition 7: Pump water to excavate to the bottom of the pit (-5.575m). This embodiment is based on actual data from a certain bridge and uses the following silt layer parameters: density =15.5kN / m3, cohesion =6 kPa, internal friction angle =6°; Support 1 adopts: 530×8 steel bars are used for supports two, three, and six. 800×10 steel bars are used for supports four and five. 800×12 steel bars. Water was pumped out and soil was excavated layer by layer according to the work procedure, and the supports were activated.

[0036] The calculation results obtained through the construction design method in this embodiment are as follows: Figure 6 , Figure 7 , Figure 8 As shown in the results analysis, the steel sheet pile-steel pipe pile model obtained by the construction method of this invention has a maximum bending moment of less than 900KN / m and a maximum displacement of less than 30mm under all working conditions in the project. It has high safety and reliability in the construction process and meets the actual engineering requirements.

[0037] Therefore, the present invention adopts the above-mentioned construction method of sheet pile toe protection structure for shallow rock sheet pile cofferdams, which increases the stability of the sheet pile and prevents the toe from becoming unstable and damaged by driving steel pipe piles into the grooves of the sheet piles at an inclination.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A construction method for a sheet pile toe protection structure for a sheet pile cofferdam in shallow rock formations, characterized in that, Includes the following steps: Step S1: Determine the extent and depth of the hard soil layer, and determine the structural parameters of the sheet pile-pipe pile and the basic parameters of the soil and water bodies; Step S2: Construct a sheet pile-steel pipe pile model and perform collaborative calculations using the parameters from Step S1. The sheet pile-steel pipe pile model is modeled by treating the sheet pile as an upper elastic foundation beam and simplifying the steel pipe pile as a vertical lower elastic foundation beam. The connection between the sheet pile and the steel pipe pile is set as a hinged connection. The incremental method is used to simulate the construction process and calculate the axial force of the steel support. The elastic support method is used to calculate the interaction force and displacement of the hinged point. Step S3: Drive in sheet piles and drive in steel pipe piles in local boreholes, with the piles inclined outwards from the foundation pit, and then grout them for consolidation. Step S4: Use inclinometer tubes to monitor the displacement of the steel pipe piles.

2. The construction method for the sheet pile toe protection structure of a sheet pile cofferdam for shallow rock formations according to claim 1, characterized in that, In step S1, the basic parameters of the soil and water bodies include the internal friction angle of the soil. Soil cohesion Water pressure intensity Horizontal resistance ratio coefficient of foundation soil Unit weight of each soil layer Thickness of each soil layer ; Structural parameters include the bending stiffness of the sheet piles. And the bending stiffness determined based on the selection of steel pipe piles. steel support cross-sectional area steel support elastic modulus .

3. The construction method for the sheet pile toe protection structure of a sheet pile cofferdam for shallow rock formations according to claim 2, characterized in that, In step S2, the formula for calculating the distributed load of the sheet pile-steel pipe pile model is as follows: ； For the depth of sheet piles Total lateral pressure at the location; Among them, active earth pressure intensity The calculation formula is as follows: = ； For the depth of sheet piles The vertical pressure at the point is calculated from the unit weight and thickness of each soil layer determined in step S1: = ； This refers to the cohesion of the soil particles in the corresponding soil layer; The active earth pressure coefficient is calculated from the internal friction angle of the soil determined in step S1. = ； The hydrostatic pressure is calculated from the water level elevation determined in step S1 and the specific weight of water. ； It is the density of water.

4. The construction method for the sheet pile toe protection structure of a sheet pile cofferdam for shallow rock formations according to claim 3, characterized in that, The calculation method for the governing equations of sheet piles is as follows: The differential equation for the force equilibrium of a steel sheet pile is: ； In the formula: The reduced bending stiffness of the sheet pile is obtained from the parameters in step S1; Let be the horizontal displacement of the sheet pile, and let be the objective to be solved. The proportionality coefficient of soil horizontal resistance is obtained from the parameters in step S1; For water and soil pressure load; Let be the horizontal constraint force of the steel pipe pile on the steel sheet pile at the hinge point, and be the parameter to be solved.

5. The construction method for the sheet pile toe protection structure of a sheet pile cofferdam for shallow rock formations according to claim 4, characterized in that, The incremental calculation method for steel supports is as follows: To simulate the cumulative effects of the construction process, the first The supporting force of the road Calculation using the incremental method: ； In the formula: For support stiffness; equivalent support stiffness , For the determined cross-sectional area of ​​the steel support, For elastic modulus, This refers to the length of the steel support. This represents the initial displacement of the steel support at the moment of installation completion. The displacement obtained by solving the current calculation equation.

6. The construction method for the sheet pile toe protection structure of a sheet pile cofferdam for shallow rock formations according to claim 5, characterized in that, The calculation method for the governing equations of steel pipe piles is as follows: The steel pipe pile is considered as an elastic foundation beam vertically embedded in a hard soil layer, with a concentrated force at the top. Function; Utilizing the physical stiffness determined in step S1 Establish the equation: ； Boundary conditions: shear force at pile top equal The bending moment is 0; This represents the resistance coefficient of the hard soil layer. For the steel pipe pile body at depth The horizontal displacement at that location.

7. The construction method for the sheet pile toe protection structure of a sheet pile cofferdam for shallow rock formations according to claim 6, characterized in that, The displacement at the bottom of the sheet pile was calculated using the elastic support method. Horizontal constraint force of steel pipe piles on steel sheet piles at hinge joints Ultimately, the displacement and internal forces of the sheet piles and steel pipe piles are obtained.

8. The construction method for the sheet pile toe protection structure of a sheet pile cofferdam for shallow rock formations according to claim 7, characterized in that, In step S3, the inclinometer tube is fixed inside the steel pipe pile, and the steel pipe pile toe is driven into the local drilled hole; the steel pipe pile is driven into the groove position of the steel sheet pile and is inclined outward from the foundation pit at an angle of 10° to 20°.

9. The construction method for the sheet pile toe protection structure of a sheet pile cofferdam for shallow rock formations according to claim 8, characterized in that, Grouting consolidation: During the construction of steel pipe piles, grouting holes are reserved in the steel pipe piles. After the construction of the steel pipe piles is completed, grouting equipment is used to press the grouting material into the grouting pipe. Grouting is stopped when the grouting pressure reaches the required level.

10. The construction method for the sheet pile toe protection structure of a sheet pile cofferdam for shallow rock formations according to claim 9, characterized in that, In step S4, an inclinometer is used to monitor the displacement change of the steel pipe pile to determine whether instability has occurred at the pile bottom and to provide timely warning.

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