Numerical Simulation Analysis of Prefabricated Steel Pipe and Larsen Sheet Pile Cofferdam Structure

Literature Overview

This study presents a numerical simulation analysis of a prefabricated cofferdam structure composed of steel pipes and Larsen sheet piles. Cofferdams are temporary structures used in hydraulic engineering to create dry working conditions for foundation construction in rivers, harbors, and marine environments. The prefabricated approach combines the structural efficiency of steel pipes with the water-retaining capacity of Larsen sheet piles, offering a modular and rapidly deployable solution for various water depth conditions.

Core Technical Points

The numerical simulation employs finite element analysis to model the complex interaction between the steel pipe elements, Larsen sheet piles, and the surrounding soil and water. The analysis captures both the structural response of the cofferdam under hydrostatic and hydrodynamic loading and the soil-structure interaction that governs the overall stability and deformation behavior. Key parameters examined include the bending moments in the sheet piles, axial forces in the steel pipe struts, soil pressure distributions, and the overall deformation profile.

The Larsen sheet pile system provides the primary water-retaining function through its interlocking profile, which creates a continuous wall that resists lateral soil and water pressure. The steel pipes serve as internal struts and waling beams that transfer the lateral loads to the sheet piles and provide additional structural support. The prefabricated nature of this system allows for rapid assembly and disassembly, making it economical for temporary applications.

Manufacturing and Quality Control

The Larsen sheet piles used in this application are typically hot-rolled or cold-formed from structural steel plates with yield strengths of 355 to 420 MPa. The interlocking profile is critical for the watertight performance of the cofferdam, and any manufacturing defect in the interlock region could lead to water ingress. Quality control during manufacturing must include dimensional verification of the interlock profile, surface inspection for defects, and mechanical property testing to ensure compliance with the specified material grade.

The steel pipe struts are commonly ERW (electric resistance welded) or HFW (high-frequency welded) pipes, which offer good dimensional accuracy and surface finish. The weld seams must be inspected using ultrasonic testing (UT) to detect any internal defects that could compromise the structural integrity under high axial loads. For critical applications in deep water conditions, additional radiographic testing (RT) of the welds is recommended.

Engineering Practice Implications

This prefabricated cofferdam system is particularly well-suited for applications where rapid deployment is required, such as emergency repairs, short-duration foundation work, or temporary structures in variable water depth environments. The modular design allows for adaptation to different site conditions by adjusting the number of strut levels and the spacing between sheet pile rows.

From a construction perspective, the assembly sequence is critical to ensure proper structural performance. The sheet piles are typically driven into the soil first, followed by the installation of waling beams and steel pipe struts. The strut installation must be sequenced to prevent excessive deformation of the sheet piles during the excavation process. The numerical simulation results provide valuable guidance for determining the optimal strut installation sequence and the required number of strut levels for different excavation depths and soil conditions.

Key Questions and Reflections

The numerical simulation provides a powerful tool for predicting the structural behavior of the cofferdam, but it must be validated against field measurements or physical model tests. The accuracy of the simulation depends heavily on the quality of the input parameters, particularly the soil constitutive model and the boundary conditions. Simplified assumptions regarding soil-structure interaction may lead to underestimation of deformations or overestimation of structural capacity, which could have serious consequences in practice.

The long-term performance of the cofferdam under cyclic loading from waves and currents also deserves attention. The interlock connections between sheet piles may experience fatigue damage under repeated loading, and the steel pipe struts may be susceptible to corrosion in marine environments. The incorporation of corrosion allowance and fatigue assessment into the design process is essential for ensuring the required service life of the cofferdam.

This study demonstrates the value of numerical simulation in the design and optimization of prefabricated cofferdam systems. For engineers involved in hydraulic and marine construction, these simulation results provide a foundation for developing more efficient and cost-effective cofferdam designs that can be rapidly deployed in challenging environmental conditions.