The Changling Tunnel - Jiangsu ARIT new materials Co., LTD

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Name

The Changling Tunnel

BACKGROUND

The Changling Tunnel is an important component of the Yichang-Xingshan section of the Yichang-Xiangyang High-Speed Railway, located within Xingshan County, Yichang City, Hubei Province. The tunnel is designed with a swallowtail structure, with the import section being 563 meters long as a single-bore double-track and the export section being 1,880 meters long as a double-bore single-track. During construction, the tunnel faced numerous challenges, including karst development, karst caves and cavities, water gushing from dissolution channels, and collapse risks in local faulted and fractured zones, which made the construction highly difficult and posed significant safety risks.

On December 29, 2022, after 20 months of construction, the left line of the Changling Tunnel was successfully completed and became the first tunnel of the Yichang-Xiangyang High-Speed Railway project to achieve full-line penetration. The successful completion of the tunnel laid a solid foundation for the early completion and operation of the Yichang-Xiangyang High-Speed Railway.

PROJECT CHALLENGE

The accelerator corrodes workers' skin, has a high rebound rate during spraying, and fails to meet the strength requirements in later stages.

The accelerator used on site is an alkaline liquid accelerator produced by another manufacturer. During on-site construction, it has a strong irritating odor, and workers' skin is often corroded and burned. The rebound rate during spraying is as high as 30%. Tests revealed that the pH value of this alkaline accelerator is 14, which severely corrodes human skin. Laboratory tests show that the 28-day mortar compressive strength ratio is only 65%, which does not meet the national standard requirement of 70% for accelerators.

Solution from ARIT

The cement used on site is Huaren P.O42.5. Compatibility tests were conducted using ART-SL37 with the on-site cement, and the test results are shown in Table 1. The mix proportion of C25 shotcrete is shown in Table 2.

Table 1 Compatibility of ART-SL37 with Huaren Cement

Dosage/%	w/c	Cement	Initial setting/min:s	Final setting/min:s
8	0.35	Huarun	0.077777778	0.215277778

Table 2 Mix Proportion of Shotcrete C25

Cement (kg/m3)	Sand (kg/m3)	Gravel（5-10mm） (kg/m3)	Water (kg/m3)	Reducer (kg/m3)	Accelerator (kg/m3)
456	888	788	178	4.56	36.48

Table 3 Comparison of On-Site Usage of Two Accelerators

Accelerator	pH	Rebound /%	28d Strength/%	Construction environment
Original product	14	About 30	65	Strongly alkaline, with irritating gas
ART-SL37	3	About 12	98	Weakly acidic, odorless

When used on site, the situation has been significantly improved. Table 3 compares the trial spraying effects of the two accelerators.

Through trial spraying, the problems of strong corrosiveness of the on-site accelerator, low later strength and high rebound rate have been solved. Moreover, due to its non-corrosive nature, it is friendly to workers and the construction environment, and the product's usage effect has received unanimous praise from the project department. The following Picture 1 shows the construction site.