Early planning As early as 1944 and 1945, the Ministry of Communications of the
Republic of China sent a survey team to survey the railway from
Guangyuan,
Sichuan Province to
Xiangyang,
Hubei Province, but it was not built in the end. The planned route at that time ran from Guangyuan, along the
Jialing River to
Chaotian, turned northeast, crossed the watershed between the
Jialing River and the
Han River, passed through
Mian County and
Hanzhong, went down along the Han River, passed through
Chenggu County and
Shiquan County to
Ankang, and then along the river through
Xunyang County and
Baihe County into Hubei Province. There were two plans for the Shiquan to Ankang section. The southern route went from Shiquan via
Ziyang to Ankang, and the northern route went from Shiquan via
Hanyin County to Ankang. Of the two plans for Chaotian to Mianxian, one went via Yangpingguan and turned east to Mian County, and the other turned northeast from Chaotian to Mian County. In January 1965, according to members of the Planning Committee of the Northwest Bureau of the
Chinese Communist Party, the First Railway Institute re-surveyed and designed the section from Yangpingguan to Hanzhong. By December 1970, all design documents for this line were completed. During the construction of this line, the total amount of earthwork was , of which were earthwork. The stonework was ; Mianxi station, where the construction volume was relatively concentrated, accounted for , Shiquan station excavated 1.6 million cubic meters, and Xujiaba Station accounted for due to the project of changing the river course. The construction team did not realise that nearly half of the line was on
expansive soil, which led to multiple geological disasters after the opening of the line. It was not until the 1980s that it gradually stabilised after repeated treatment. There are 146 tunnels along the entire line, totaling , accounting for 17.3% of the total length. In the sections from Guandong to Daijiaba in Yangping and from Chazhen to Shiquanxian, the proportion of tunnels reached 60.3% and 75.2% respectively. Due to poor geology, several tunnels showed varying degrees of deformation before and after completion. A total of 311 bridges were built along the entire line, with a total length of , accounting for 7.8% of the total length of the line, including 3 very large bridges, , 72 large bridges, , 115 medium bridges, , and 121 small bridges, . In May 1970, the engineering command mobilised a number of experienced drivers and technicians to transport the
class JF steam locomotive No. 3827 and 5 passenger car carriages from Lueyang Locomotive Depot (under the Xi'an Bureau) to Mianxian station, providing conditions for future temporary transportation and engineering transportation. By 1972, the track had been laid to
Xixiang County in February,
Shiquan County in June, and
Ankang City on 8 October, with a total of of main line and of station track. The total investment for the entire line was ¥970m, of which ¥915m was for line engineering, with an average construction cost of ¥2.611m per kilometre. This line uses direct power supply and has five substations located in Da'an, Baohe, Shahekan, Chazhen and Hanyin. In addition, the Yuehe substation of Xiangyu Railway is used. The transformer is a single-phase transformer. Since the electrification construction and line improvement work were carried out simultaneously, there was often interference between them.
Problems Due to the tight construction schedule and poor geology along the line, geological problems occurred several times along the entire line after completion. Nearly half of the section along the line was expansive soil, but the construction team did not have a clear understanding of this at the time. As a result, after the line was opened to traffic, 120 embankments were loose, more than 500 cuttings were displaced, more than 20 landslides occurred, and a large amount of mud came out of the foundation. In terms of tunnels, the Daheigou, Daixiaohe, Jiangjiahe No. 2, Bangou, Malingguan, Caogou No. 2 and other tunnels passed through many unfavourable geological conditions and experienced varying degrees of deformation before and after completion; the Shimengou tunnel collapsed due to the decay of the supporting wooden pillars; the Xinyuba and other five tunnels had rough site surveys and hasty construction due to temporary changes in the construction design. In addition, the tunnels passed through of unconsolidated material, and they were severely deformed many times since the beginning of construction. ==Capacity expansion and transformation==