The Baoji–Chengdu railway, Bao–Cheng railway or Bao–Cheng Line was formerly designed as a rail line that connects Tianshui and Chengdu called Tianshui–Chengdu railway () or Tiancheng railway (). The line is a mixed single- and double-track, electrified, 676-kilometer railroad in China between Baoji in Shaanxi province and Chengdu in Sichuan province. It is one of main lines that connects southwestern with northwestern China and a part of the Lanzhou–Kunming Corridor of the Eight Verticals.
The line finished construction on 12 July 1956, after which it began operating on 1 January 1958. The rail line is also the first one in China to be electrified. The Baoji–Guangyuan section of the line is under the control of China Railway Xi'an Group, while the rest is in charge of China Railway Chengdu Group. The railway was added to the List of China's Industrial Heritages for Conservation in January 2018.
Line description
The Bao–Cheng Line runs southwards from Guanzhong Plain to Sichuan Basin and traverses the Qinling, Daba Mountains, and Jianmen after leaving Baoji. The rail line goes through 5 different zones of geological structures (including granite, quartzite, greenschist, conglomerate and slate); around 80% are in the mountainous area. The line stretches along the ancient roads and Qingjiang River after entering the Qin Mountains, as the track elevates with a slope of 30‰ in the Renjiawan–Yangjiawan section; the steepest section can reach 33‰. A spiral by 3 horseshoe-shaped tracks and a figure-8 one, which is stacked in 3 layers and raised up to 817 meters, allows the rail line to navigate topological difficulties.
To avoid the overheating of brakes during the downhill journey, Qingshiya Station was established in the spiral to make the locomotives cool down, as the station is also the highest and steepest station with the smallest radius throughout the line.
A 2363.6-meter-long tunnel brings the line to the Jialing River's drainage basin, after which the line starts its 12‰ downhill slope towards Guangyuan with 14 bridges across the river in Qinling–Lüeyang section. Overall, the line has 304 tunnels and 1,001 bridges, which collectively account for 17% of the total track length. The 4-kilometer Huilongchang Tunnel is the longest tunnel of the line. Additionally, the train is the first to-capital train for residents throughout southwestern China.
Additionally, the line features several sections where slopes are long and steep with multiple curves, especially the Baoji–Qinling section. The power of steam locomotives was so low that it had greatly degraded the line's transporting capabilities after the line's operation began; the Guanyinshan Spiral took trains almost the same time to pass as pedestrians. Therefore, the line was listed high on the agenda for rail electrification.
The line finished electrification in 1976 and has been using electric locomotives since. Bank engines are still employed to secure the abundant power during the mountain climb and brakes for downhill journeys in Baoji–Qinling section with the help of HXD3 locomotives: one for passenger coaches and two for freight coaches. The aggregate weight of trains to climb the mountains is limited to no more than 3000 tons and 2600 tons for the downhill ones.
The line began its construction for another track in 1993; the double-track section came into operation on 26 December 1999. The rail tracks succeeded in making cities along the line into core regions of the Third Front and played a key role in the fundamental supplies for the cities within the plan. Later, the opening of the Xi'an–Chengdu Highspeed Railway on 6 December 2017 made the number of passenger trains on the line beginning at Baoji decrease to roughly 20.
In Baoji, the line meets the Longhai railway, on which trains can travel east to Xi'an and the Central Plains or west to Lanzhou and the northwest, and Baoji–Zhongchuan railway. At Yangpingguan, the line intersects with the Yang'an railway which branches eastward along the Han River Valley. In Chengdu, the line connects with the Chengyu Line to Chongqing, the Chengqian Line to Guizhou, and the Chengkun Line to Kunming. The line meets Xi'an–Chengdu Highspeed Railway and Lanzhou–Chongqing railway in Guangyuan.
History
Construction
The Bao–Cheng line was originally proposed in Sun Yat-sen's 1913 China National Railway Plan as part of the Datong–Chengdu railway. However, it wasn't implemented back then due to the oversized scale.
The Beiyang government later suggested schemes regarding a rail line that connected Tianshui with Chengdu in 1920. The aerial topographical surveys for the line's section in Shaanxi Province were conducted by the project group in 1936, which was followed by 1940 and 1947 surveys. However, the blueprint was still not put into practice.The PRC Ministry of Railways (MOR) managed to conduct further surveys for the Tianshui–Lüeyang section of the 1920 scheme along with a brand-new Baoji–Lüeyang one with the assistance of experts from Soviet Union, after which the new one was selected following comparisons of the geological and transportation network conditions with the former one. Construction of the line was added to the first five-year plan afterwards.
Construction began in Chengdu on 1 July 1952, when Mao Zedong instructed, during the opening ceremony of Chengdu–Chongqing railway, to "keep going on to turn the Tianshui–Chengdu railway into real". The construction throughout Sichuan then began in 1953; track-laying work started from south to north at the Chengdu end in April. The construction featured the technological assistance of over 30 Soviet experts, along with two Hungarian experts, as well as material supplies from residents along the line. The maximum number of workers involved reached 140 thousand during the construction. The line got renamed to the Baoji–Chengdu Railway on 1 December 1952, and construction in Shaanxi Province started from Baoji in January 1954. On 10 August 1955, under the guidance of Soviet experts, China Railway successfully carried out the grand blastings for Guanyinshan Station, which became the first successful large-scale blasting throughout the history of China's railway construction. The line was connected on 12 July 1956 in Huangshahe Village of Huixian County, Longnan, 13 months ahead of schedule, and opened on 1 January 1958. Steam locomotives were employed thereafter.
Electrification
Preparations for the electrification project of Baoji–Chengdu railway began in 1953. The MOR initially set the catenary to 3 kV DC and submitted the plan to the Soviet counterparts for evaluations in June 1955, but in April 1957, it was determined that single-phase electric power of 25 kV with utility frequency should be employed after learning that other countries had been using this upgraded style. The project was re-schemed soon after.
The new design was reevaluated by Moscow in May 1958 and put into practice after the agreement in June. Engineers decided to reduce the demanded amount of transformers from six to four for substations due to lack of key ingredients for silicon steel and high prices for imports resulting from technological denials from the Western countries. Of the transformers, three were implemented in the substations, and one was placed on a flat wagon that travels among the three substations. The decision gave birth to China's first mobile transformer in 1965.
MOR kept insisting that electric locomotives should adopt both domestic and foreign production lines, as the domestic 6Y1 prototype of the Shaoshan series began its experimental run in the 1960s, and 25 imported arrived at ports of mainland China. Later, they became the major type of locomotives after the electrification in Baoji–Fengzhou section finished in 1961. The other four sections finished their electrifications respectively afterward before 1 July 1975 when the ceremony of celebration took place. The electrification upgraded the line's maximum speed to 80 km/h; Further improvements on the shape and flexibility of cables were made around 1978.
The HXD locomotive series was officially employed on the rail line after the 2008 Sichuan earthquake, leading to faster freight transportation with the help of new high-powered locomotives. Substations were gradually replaced by SCADA for smart and automatic controls to ensure continuous and abundant electricity.
Remediation
MOR established an expert group to investigate the frequent landslides on the line in 1955. Three tunnels of a total length of 1,439 meters and 10 culverts of 657 meters had been built in Sichuan late 1957 to improve situation.
Xi'an Group, Chengdu Group, and Lanzhou Group of MOR, in line with the principle of "opening first and then consolidating, taking care of the future", took measures to restore and reinforce the damaged bridges and roadbeds along the line after the 1981 flood. Over 15,000 workers were enlisted for the effort.
Transformation
MOR decided to divert the high-slope section with limited capacity between Luomiaozhen and Majiaoba in December 1959. The diversion began on 15 February 1960 and was suspended in April 1962. The project restarted in November 1964 and finished in September 1969. Several large-scale capacity improvements were then made later on to meet the demands of economic growth and social development.
Another upgrade was made in September 1990 between Guangyuan and Majiaoba on the automatic block signaling of axle counters, making the punctuality increase by 3.9 percent for freight trains and 0.3 percent for passenger trains. The line then completed its heavy rail upgrade in 1993, the year when the second track's construction started. The second track lies on the rail line's Yangpingguan–Chengdu section, and capacity was greatly improved after its finish on 26 December 1999. The second track in the Yangpingguan–Qingbaijiang section is also the first additional in-mountains track among China's electrified railway lines. From 2008 to 2009, the line completed a seamless transformation; in 2014, the line once again upgraded the profiles and ties on the small radius curve of the main line.
In 2021, the Sichuan government issued a plan regarding the provincial multi-layer rail transit system and mentioned that a total length of 24.1 kilometers, as well as 10 stations on the Baoji–Chengdu Railway, would be transformed to fit for a metro-styled operation, with trains traveling with smaller coaches but shorter intervals. The plan also mentioned that the maximum speed of the line's Chengdu–Qingbaijiang section would be increased to 160 km/h as a result of transformation. A few years later, China Railway issued a call for a new wave of capacity improvements on 30 May 2024.
Temporary operations
The Huixian–Chengdu section of the line was once separated into 4 parts for temporary operations, of which the Chengdu–Mianyang section began in October 1953, the Mianyang–Zhongba section began in February 1954, the Zhongba–Guangyuan section began in February 1955, and the rest began in October 1956.
The temporary operation phase mainly focused on deliveries for construction-related materials, and some passengers were also allowed to ride: A total of 2.75 million tons of road materials, along with 2.42 million tons of local materials and 3.02 million passengers, were delivered before the 1958 official openings. The temporary operations also made the line critical for goods and passengers to leave and enter Sichuan Basin in June 1956 when service of roadways had been dropped due to the 19-day storm season. The 1957 urgent food transmission from Sichuan, which was called by the State Council, also involved the Bao–Cheng Line by delivering 800 thousand tons of grains.