Combined sheet pile walls have the characteristics of high bending strength, reasonable structural stress, and good adaptability to load and geology. They have broad application prospects in water transportation projects. However, there is currently a lack of structural characteristics and specific applications of different forms of combined sheet pile walls. This article starts from the structural characteristics of commonly used composite steel sheet piles, focuses on a comparative analysis of HZ/AZ composite steel sheet piles, steel pipe sheet piles and box composite piles, and combines specific engineering cases to explain the factors that should be considered in the practical application of composite steel sheet piles.
1. Combined sheet pile walls and their development trends
Combined sheet pile walls are composed of sheet piles or steel pipe piles with different cross-section forms. Long and heavy main piles are alternately arranged with short and light auxiliary piles. Combined sheet pile walls have been used earlier in Europe, such as Bremerhaven in Germany (CT3A, CT4 berths), Hamburg Port 7# container berth, Rotterdam Port in the Netherlands, Zeebrugge Wielingen & Albert II Dock in Belgium, etc. In addition, combined sheet pile walls have been successfully used in the second phase expansion project of the container berth of Port Qasim in Pakistan.
Combined sheet pile walls have the characteristics of high bending strength, reasonable structural stress, and good applicability to load and geology. This article starts from the structural characteristics of commonly used combined sheet pile walls, focusing on HZ/AZ Combined sheet pile walls, steel pipe sheet piles and box comparative analysis of the bending resistance, vertical bearing capacity, steel consumption, ease of construction and quality control of type composite piles was carried out. The factors that should be considered in the practical application of composite steel sheet piles were explained based on specific engineering examples to provide guidance for similar projects.
2. Application of combined sheet pile walls
The selection of composite steel sheet piles should comprehensively consider factors such as structural stress characteristics, economy, construction conditions, and construction. The following case uses two typical cases to analyze the application of combined sheet pile walls.
(1) Case 1: Quay wall type shore-to-shore structure
The project is located in Zhongshan City, Guangdong Province, China. It adopts the layout of dug-in harbor and jetty berthing. The shore-connecting structure is an upright quay wall structure. The selection of the shore-connecting structure is one of the key issues of this project.
Waves: The project is located at the Pearl River Estuary and is protected by a breakwater on the outside. The extreme high water level H1% encountered once in 50 years is 1.68m, the wave period is 4.25s, and the wavelength is 13.7m.
Engineering geology: The soil layers from top to bottom are silt, silt, silty clay, fine sand, coarse sand, fully weathered granite, and strongly weathered granite. The significant geological feature of this project is that there is a 20-30m thick silt and other soft soil layers on the surface. The silt has poor shear resistance and has a great impact on the selection of the bank structure.
Design load of the shore structure: crowd load 5kPa; process load 10kPa.
There is a 20~30m thick soft soil layer on the surface of this project. Considering the thick silt layer and the need for backfill construction in the rear land area, the shore structure is planned to adopt an upright sheet pile structure. Combined sheet pile walls can obtain greater flexural strength through reasonable combination, and are suitable for thick soft soil layers.
Considering that under the same flexural strength, box-type composite piles use more steel and have more locks, this project mainly compares HZ/AZ composite steel sheet piles and steel pipe sheet piles. For the proposed HZ1080MA/AZ18-700 combined steel sheet pile and φ1016 steel pipe pile + AZ18-700 steel pipe sheet pile, the main aspects include bending strength, vertical bearing capacity, steel consumption, number of locks, horizontal displacement, construction and quality control.
Under the premise of the same amount of steel, HZ1080MA/AZ18-700 combined sheet pile walls have higher bending strength, smaller horizontal displacement, more convenient construction, and easier quality control, but the vertical bearing capacity is relatively small and the linear meter wall lock The number of mouths is relatively large. The vertical load of this project is small, and the main control index of the structure is horizontal displacement. Therefore, it is appropriate to use HZ1080MA/AZ18-700 combined sheet pile walls.
Case 2: Container and general cargo terminal
Container terminals and general cargo terminals are generally equipped with orbital lifting equipment, such as gantry cranes, quay cranes, etc. The vertical load under the track is large, and the vertical bearing capacity of the lower pile foundation is required to be high. The front sheet pile wall of this type of wharf needs to be able to withstand large horizontal and vertical loads. At this time, the high vertical bearing capacity of steel pipe sheet piles can be better utilized and is a more suitable structural form. For example, the second phase expansion project of the container berth of Port Qasim in Pakistan uses φ2016+AZ26 steel pipe sheet piles.
4. Conclusion
Composite steel sheet piles are currently relatively rarely used in domestic water transportation projects. There is a lack of comprehensive analysis and comparison of the structural characteristics of different forms of composite steel sheet piles and the relevant factors that need to be considered in specific applications. This article analyzes and compares composite steel sheet piles based on specific engineering cases. The conclusions are as follows:
(1) When selecting the type of combined steel sheet pile, it should be comprehensively determined based on the specific use requirements of the structure and hydrological and geological conditions.
(2) Under the premise of the same amount of steel, HZ/AZ Combined sheet pile walls have high bending strength and small horizontal displacement, but their vertical bearing capacity is relatively small, so they are suitable for quay wall structures with mainly horizontal loads.
(3) Steel pipe sheet piles can withstand large horizontal loads and vertical loads at the same time, but require large-scale steel pipe pile piling equipment. They are suitable for situations where both horizontal loads and vertical loads are large, such as quay wall structures under tracks.
(4) Box-type composite piles can withstand vertical and horizontal loads and have a large radius of gyration. They are especially suitable for situations with long lengths and less lateral supports. However, they have a larger number of locks and have the same bending strength.
1. Combined sheet pile walls and their development trends
Combined sheet pile walls are composed of sheet piles or steel pipe piles with different cross-section forms. Long and heavy main piles are alternately arranged with short and light auxiliary piles. Combined sheet pile walls have been used earlier in Europe, such as Bremerhaven in Germany (CT3A, CT4 berths), Hamburg Port 7# container berth, Rotterdam Port in the Netherlands, Zeebrugge Wielingen & Albert II Dock in Belgium, etc. In addition, combined sheet pile walls have been successfully used in the second phase expansion project of the container berth of Port Qasim in Pakistan.
Combined sheet pile walls have the characteristics of high bending strength, reasonable structural stress, and good applicability to load and geology. This article starts from the structural characteristics of commonly used combined sheet pile walls, focusing on HZ/AZ Combined sheet pile walls, steel pipe sheet piles and box comparative analysis of the bending resistance, vertical bearing capacity, steel consumption, ease of construction and quality control of type composite piles was carried out. The factors that should be considered in the practical application of composite steel sheet piles were explained based on specific engineering examples to provide guidance for similar projects.
2. Application of combined sheet pile walls
The selection of composite steel sheet piles should comprehensively consider factors such as structural stress characteristics, economy, construction conditions, and construction. The following case uses two typical cases to analyze the application of combined sheet pile walls.
(1) Case 1: Quay wall type shore-to-shore structure
The project is located in Zhongshan City, Guangdong Province, China. It adopts the layout of dug-in harbor and jetty berthing. The shore-connecting structure is an upright quay wall structure. The selection of the shore-connecting structure is one of the key issues of this project.
Waves: The project is located at the Pearl River Estuary and is protected by a breakwater on the outside. The extreme high water level H1% encountered once in 50 years is 1.68m, the wave period is 4.25s, and the wavelength is 13.7m.
Engineering geology: The soil layers from top to bottom are silt, silt, silty clay, fine sand, coarse sand, fully weathered granite, and strongly weathered granite. The significant geological feature of this project is that there is a 20-30m thick silt and other soft soil layers on the surface. The silt has poor shear resistance and has a great impact on the selection of the bank structure.
Design load of the shore structure: crowd load 5kPa; process load 10kPa.
There is a 20~30m thick soft soil layer on the surface of this project. Considering the thick silt layer and the need for backfill construction in the rear land area, the shore structure is planned to adopt an upright sheet pile structure. Combined sheet pile walls can obtain greater flexural strength through reasonable combination, and are suitable for thick soft soil layers.
Considering that under the same flexural strength, box-type composite piles use more steel and have more locks, this project mainly compares HZ/AZ composite steel sheet piles and steel pipe sheet piles. For the proposed HZ1080MA/AZ18-700 combined steel sheet pile and φ1016 steel pipe pile + AZ18-700 steel pipe sheet pile, the main aspects include bending strength, vertical bearing capacity, steel consumption, number of locks, horizontal displacement, construction and quality control.
Under the premise of the same amount of steel, HZ1080MA/AZ18-700 combined sheet pile walls have higher bending strength, smaller horizontal displacement, more convenient construction, and easier quality control, but the vertical bearing capacity is relatively small and the linear meter wall lock The number of mouths is relatively large. The vertical load of this project is small, and the main control index of the structure is horizontal displacement. Therefore, it is appropriate to use HZ1080MA/AZ18-700 combined sheet pile walls.
Case 2: Container and general cargo terminal
Container terminals and general cargo terminals are generally equipped with orbital lifting equipment, such as gantry cranes, quay cranes, etc. The vertical load under the track is large, and the vertical bearing capacity of the lower pile foundation is required to be high. The front sheet pile wall of this type of wharf needs to be able to withstand large horizontal and vertical loads. At this time, the high vertical bearing capacity of steel pipe sheet piles can be better utilized and is a more suitable structural form. For example, the second phase expansion project of the container berth of Port Qasim in Pakistan uses φ2016+AZ26 steel pipe sheet piles.
4. Conclusion
Composite steel sheet piles are currently relatively rarely used in domestic water transportation projects. There is a lack of comprehensive analysis and comparison of the structural characteristics of different forms of composite steel sheet piles and the relevant factors that need to be considered in specific applications. This article analyzes and compares composite steel sheet piles based on specific engineering cases. The conclusions are as follows:
(1) When selecting the type of combined steel sheet pile, it should be comprehensively determined based on the specific use requirements of the structure and hydrological and geological conditions.
(2) Under the premise of the same amount of steel, HZ/AZ Combined sheet pile walls have high bending strength and small horizontal displacement, but their vertical bearing capacity is relatively small, so they are suitable for quay wall structures with mainly horizontal loads.
(3) Steel pipe sheet piles can withstand large horizontal loads and vertical loads at the same time, but require large-scale steel pipe pile piling equipment. They are suitable for situations where both horizontal loads and vertical loads are large, such as quay wall structures under tracks.
(4) Box-type composite piles can withstand vertical and horizontal loads and have a large radius of gyration. They are especially suitable for situations with long lengths and less lateral supports. However, they have a larger number of locks and have the same bending strength.
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