Study on Restraint Effect of Post-Casting Belt in Full-Section Interval Casting Immersed Tube

Area of Science:

• Civil Engineering
• Materials Science

Background:

• The Chebei Immersed Tunnel utilizes a full-section interval casting process with post-casting belts.
• These belts introduce restraint effects on concrete segments, potentially leading to cracking.

Purpose of the Study:

• Investigate the influence of bottom steel plates and steel bars in post-casting belts on segment mechanical behavior.
• Mitigate concrete cracking in full-section casting segments.
• Propose requirements for post-casting belt length.

Main Methods:

• Comparative analysis of field tests and numerical simulations.
• Development of a temperature-dependent thermal expansion coefficient model for concrete.
• Evaluation of restraint effects based on varying post-casting belt lengths.

Main Results:

• Under restraint, segment shrinkage strain reached 348 με, with hydration heat and drying shrinkage as major contributors.
• Restraint effects decrease as post-casting belt length increases.
• At 1.6 m belt length, restraint-induced tensile stress was 1.4 MPa, with steel plates and bars contributing 70% and 30% respectively.

Conclusions:

• Post-casting belt length is a critical factor influencing restraint effects and tensile stress.
• Established relationships between belt length, stress, and restraint coefficient provide engineering guidance.
• Findings support high-quality prefabrication of immersed tunnel segments.