Located in Eshan County, Yuxi City, Yunnan Province, the 17.44km Wanhe Tunnel is the key and difficult critical works for the whole railway. With a maximum burial depth of 586m and a minimum burial depth of only 5m, the tunnel passes through two large faults with the proportion of Class IV and V surrounding rocks as high as 88%. It is classified as a typical soft rock railway tunnel with large deformation. "Especially under high ground stress and unfavorable geological conditions, the steel arches in the primary support are often twisted and even broken in severe cases." Feng Li, manager of the Yuxi-Mohan Railway Project Department of China Railway 12th Bureau Group Co., Ltd., said that only in 2019, the continuous large deformation of the No.3 inclined shaft reached 520m, with the maximum deformation reaching 1.3m, which led to the destruction of the support structure. Only after the second construction was re-organized, could the difficulties be successfully overcome.
The construction of Wanhe Tunnel was accompanied with frequent gushing mud and water, with the maximum daily water gushing reaching 64,000 cubic meters, let alone its under-passing of Kunming-Mohan Expressway, which brought great difficulties to the tunnel's construction.
Since April 2016, the Diannan Railway Construction Directorate of China Railway Kunming Group Co., Ltd. has organized all construction participants to continuously optimize the construction process, strengthen geological forecast and surrounding rock monitoring measurement, and adopt measures such as dynamic adjustment of support parameters, increase of deformation allowance, and addition of a cover arch to control surrounding rock deformation, so as to minimize the risk of surrounding rock deformation and promote tunnel construction in a safe and orderly manner.