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

## TL;DR

This study examines how post-casting belts reduce concrete cracking in tunnel segments during construction.

## Contribution

The paper introduces a temperature-dependent thermal expansion model and quantifies restraint effects of post-casting belts in immersed tube construction.

## Key findings

- Shrinkage strain in full-section casting segments reached 348 με, with hydration heat and drying shrinkage contributing 60% and 40%.
- Restraint-induced tensile stress was 1.4 MPa at a 1.6 m post-casting belt length, with the bottom steel plate contributing 70% of the restraint.
- A temperature-dependent thermal expansion coefficient model was developed to describe concrete strain and hydration heat temperature relationships.

## Abstract

The Chebei integral Immersed Tunnel introduced an innovative full-section interval casting process, where post-casting belts impose restraint effects on the full-section casting segments. To mitigate concrete cracking, this study investigates the influence of the bottom steel plate and steel bars in the post-casting belts on the mechanical behavior of full-section casting segments through comparative analysis of field tests and numerical simulations. Requirements for post-casting belt length are proposed. Key findings include: under post-casting belt restraint, the full-section casting segment’s shrinkage strain reached 348 με, with hydration heat-induced cooling and drying shrinkage contributing 60% and 40%, respectively. A temperature-dependent thermal expansion coefficient model was developed to characterize the nonlinear relationship between concrete strain and hydration heat temperature. Restraint effects diminished with increasing post-casting belt length, and the post-casting belt length should be control. At 1.6 m (Chebei design), restraint-induced tensile stress was 1.4 MPa (restraint coefficient β = 0.12), with the bottom steel plate and steel bars contributing about 70% and 30%, respectively. Relationships between post-casting belt length, stress, and restraint coefficient are established for engineering reference. These research findings have been successfully applied in the Chebei Immersed Tunnel, enabling high-quality prefabrication of full-section interval casting immersed tubes.