Huai’an No. 3 Line Ship Lock Project
About The Project
The Huai’an Ship Lock is located on the North Jiangsu Canal Channel in the lower reaches of the intersection between the Beijing-Hangzhou Grand Canal and the North Jiangsu Irrigation Grand Canal in Huai’an City, Jiangsu province. The existing first and second line locks are 20m x 230m x 5m, and 23m x 230m x 5m respectively. The construction scale of the new three-line ship lock is 23m x 260m x 5m.
OSP’s Premium Technical Consultation
Due to the restrictions of the first-line ship lock and the river leading to Shazhuang, the construction of the third-line ship lock here couldn’t be carried out through general large excavation. What OSP proposed instead therefore was a vertical excavation underneath the temporary steel sheet pile structure for the upper and lower gates, while the lock chamber structure uses a multi-channel anchor pull-back sheet pile system as shown below:
Compared to U-shaped steel sheet piles, Z-shaped ones (especially the AZ type) have a width and height profile that are much larger, thus reducing the number of sheet piles needed to fill a row, reducing overall costs for each project as well as making the construction process much more convenient. Additionally, Z shaped steel sheet pile (compared to U shaped steel sheet pile) can save at least 10%-20% of the amount of steel used to produce the same length for a sheet pile wall.
The lock plate flange on the Z-shaped steel sheet pile has several unique characteristics, primarily that there is rarely any relative displacement between adjacent sheet piles (due to shear force at the flange area being approximately zero) as well as zero interference towards the bending capacity as the single sheet piles ensure that bending occurs along the centreline of the wall even in situations where there is relative displacement of adjacent sheet piles (in situations where there is uniform force applied along the walls axis). Therefore, the bending modulus of Z-shaped steel sheet pile need not be reduced, and material strength can be fully exerted onto the wall.
Additionally, the Z-shaped steel sheet pile has two parallel flanges to control the alignment accuracy of the pile throughout construction. This can effectively control and limit the amount of deviation, perpendicular to the axial direction of the wall, during construction.
Preservation of Steel Sheet Piles
In order to maximise the service life of the steel sheet pile chamber wall in this project as well as adding value by additionally reducing any future maintenance workload, OSP adopted the following anti-corrosion coating procedure:
Applying a surface pre-treatment, beginning with sand blasting to clean and remove any rust.
Applying a zinc spray coating which thickness of 180-200μm;
A final water-based, zinc rich, coating with a sealing thickness of 40-50μm.
Given the elevation level of the top of the steel sheet pile in the gate chamber is +12.3m, with a floor surface elevation level of +12.3m as well as groundwater levels reaching +6.0m, parts of the sheet metal joints are more prone to water seepage and OSP had to take the necessary precautions that would be different from working in clean and dry conditions.
In order to maintain the good construction quality of the project as well as enhancing the anti-corrosion effect, we took the following precautionary measures during construction to ensure project success:
Beginning construction at the larger areas without any risk of water seepage, while ensuring that water seepage areas are left left.
Reducing the groundwater level as much as possible (generally to a level below +5.0m) so as to reduce water seepage area and volume. This is to ensure the safety and stability of the lock chamber.
Utilising a flamethrower to dry the surface of steel sheet piles during construction, subsequently using steam spray-guns to blow off any impurities and dust. Quality control is done immediately and carried out throughout each step of the construction.
What is the screening method?
The staggered piling process ensures that prior to piling, steel sheet piles are assembled into a screen in advance as a guiding framework. This method allows us to more efficiently control the construction quality, especially in more demanding construction environments such as this where absolute precision is necessary.
Choosing the Optimal Pile Installation Method
In order to control the verticality and cumulative axial deviation of the wall, we had to abandon the traditional limitations of of simple pile-by-pile piling process and innovate on the new screening method (also known as the staggered piling process).
In this case, the locking lugs on both sides snap together without additional piling, ensuring that the frictional resistance on both sides is balanced and thus ensuring maximum precision during installation. The sheet piles are piled in stages followed by penetration into soil in order to ensure optimal verticality. Guide posts area driven into the two sides of steel sheet pile, allowing the transverse position (as well as verticality) of the sheet piles to be adjusted according to these pots.
Using AZ26-Type Sheet Piles
The strengths found in the structural characteristics of the AZ26 sheet pile is that it has a larger and thinner profile that were found to be more suitable for the project. Due to the high requirements of the wall for hauling and navigation ship locks, the structural requirements and quality of the sheet pile is naturally higher than other structures.
The AZ steel sheet pile has been successfully applied in a variety of docking projects at home and abroad. In consideration of the factors above, the AZ steel sheet pile was the obvious solution for projects such as the Huai’an third-line ship lock chamber walls. 1563 tonnes of Luxembourg AZ steel sheet piles were used for this project, amounting to a total of 8600 meter-square of single-sided area.