On the 22nd, the right-line shield tunnel between South Saimachang Station and Lianjie Street Station of the civil works Section 12 of Kunming Rail Transit Line 4 was holed through. With this, the main works of all 8 shield-driven tunnel sections in Section 12 of Metro Line 4 have been fully completed. The Kunming Rail Transit Line 4 project is the first batch of PPP projects implemented in Kunming. The line is 43.38 km long and has 29 stations in total (28 newly built), making it the longest line in Kunming's rail network at present. Once completed, it will effectively connect Kunming South Railway Station with the main urban area of Kunming, and play an important role in promoting the passenger exchange function between the Kunming South Railway Station transport hub and the main city. Among them, the civil works Section 12 of Kunming Rail Transit Line 4 has a total length of 5.7 km, mainly including the West Saimachang Station to South Saimachang Station section, the South Saimachang Station to Lianjie Street Station section, the Lianjie Street Station to Chenggong East Station section, and the Chenggong East Station to Kunming South Railway Station section, comprising 8 two-way shield tunnel sections, as well as 2 stations, Lianjie Street Station and Chenggong East Station.

A relevant person in charge of the contractor introduced that the right line of the section from South Saimachang Station to Lianjie Street Station is 1,979 meters long. The alignment runs in an “S” shape beneath the Lianjie Street overpass, with a curve radius of 2,000 meters, a “V”-shaped longitudinal slope with a maximum gradient of 21‰, and a minimum tunnel cover depth of 16.6 meters. The geological structure of the section is complex, with excavation passing through more than 160 meters of poor peat soil geology and more than 500 meters of hard rock zones, among which the maximum rock strength of the moderately weathered sandstone intercalated with mudstone geology reaches 79 MPa. Problems such as high rock strength in the excavation range, severe wear of the shield cutterhead, and high risk in underpassing existing buildings are important factors affecting the excavation construction of this section. In the face of complex and changeable construction conditions, the project department organized management personnel from construction, technical, safety and other systems many times to study and discuss plans, and prepared and reviewed a number of special shield construction plans, including the "Special Safety Plan for Shield Chamber Opening Inspection and Cutter Replacement in the Section", the "Special Safety Plan for Launching and Receiving in the Sai-Lian Section", the "Special Safety Plan for the Section Underpassing Special Buildings", and the "Construction Plan for Poor Geology Reinforcement in the Sai-Lian Section". By controlling the shield machine's excavation attitude and grouting pressure, monitoring ground settlement, and opening the chamber for cutter replacement and other measures, the "Qihang" shield machine was ensured to successfully complete the excavation task.

The right line from South Saimachang Station to Lianjie Street Station is the last tunnel among the 8 shield tunnel sections undertaken by the project. The smooth holing-through of this shield section marks the full completion of the main works of Lianjie Street Station, Chenggong East Station, and the shield-driven tunnel sections undertaken by civil works Section 12 of Kunming Rail Transit Line 4.

As of January 22, 23 of the 28 newly built stations on the entire Kunming Rail Transit Line 4 have been capped, and the remaining 5 are under main structure construction; 40 of the 60 single-line shield tunnel sections on the entire line have been holed through; and all 9 post-station construction units and road surface restoration units have entered the site and started work such as equipment area masonry, conventional equipment installation, and track laying.