As China's urbanization process accelerates, urban transportation construction has deeply affected people's daily work and life. As an important component of urban rail transit, subway construction plays a significant role in enhancing urban transportation capacity. Subway projects are characterized by large engineering volumes and long construction cycles, thus requiring relatively high project investment.

The current construction scope at Qingniangong Subway Station includes the internal structure construction of the main body, removal of columns in the main retaining structure, replacement of struts, sealing of reserved openings, backfilling and compaction of the roof slab, and ancillary structures. The ancillary structures include five entrances/exits and two groups of ventilation pavilions. The buildings that need to be demolished at Entrance/Exit No. 1 have not yet been demolished, and the owner has not yet handed over the construction work face to us. More than half of the retaining pile construction at Entrance/Exit No. 2 was completed in March and April of this year; the remaining small portion of retaining piles at the entrance/exit and the junction with the main body cannot be constructed temporarily due to the influence of rainwater pipes, sewage pipes, and gas pipelines. For the pipelines that need to be relocated, the owner has commissioned the relevant construction units to carry out the preliminary pipe jacking work for pipeline relocation. The enclosure construction at Entrance/Exit No. 3 and Ventilation Pavilion Group No. 2 has been completed, the spray dust suppression system is being gradually improved, and the transportation of muck above the original ground level is underway. Recently, due to strict dust control by government departments, all earthwork operations are prohibited, seriously affecting on-site construction progress. At Entrances/Exits No. 4 and No. 5 and Ventilation Pavilion Group No. 1 at Qingniangong Square, only enclosure work has been carried out. Because the two stone lions have not yet been relocated, subsequent related work cannot proceed. The relevant units are currently negotiating and discussing the relocation of the two stone lions.

Given the large engineering volume and the concurrent design and construction, design changes are relatively significant during the construction phase. Some time ago, we learned that the drawings for Entrance/Exit No. 2, Entrances/Exits No. 4 and No. 5, and Ventilation Pavilion Group No. 1 at Qingniangong Station will be modified, so the parts already constructed may be subject to change; therefore, related construction work at these locations has been suspended. This can effectively avoid unnecessary design changes, improve project quality and progress, and ensure the smooth implementation of the subway project.

During subway construction, project quality control is extremely critical. The engineering characteristics and production/construction environment of subway projects determine the particularity of their project quality. Management and supervision should be stricter during construction, especially for quality control points at key stages and processes. Subway construction methods are diverse, and structural forms vary depending on geological conditions in different regions, which directly leads to certain differences in control priorities and content. The main issues are concentrated in the following aspects:

The first is the excavation method for ancillary structures. Given the current situation at Qingniangong, there is no need to adopt the mined method; the open-cut method can be used. The quality control focus for open-cut works should be on foundation pit support. Subway foundation pits are generally deep foundation pits, and compared with ordinary foundation pits, they require more attention and stricter requirements for construction plans. Excavation and support must be carried out strictly in accordance with the design plan and design specifications. During construction, key observation should be given to surrounding protective structures, soil at the pit edge, and prestress to ensure construction quality. Before foundation pit excavation, surrounding underground pipelines must be identified, and relocation or reinforcement measures must be taken for effective protection to ensure the safety of underground pipelines during construction. At the same time, drainage ditches must be built outside the foundation pit for water interception to ensure operations are carried out under water-free conditions. Foundation pit excavation must strictly follow the principles of layered, segmented, and symmetrical excavation; the width and depth of each excavation must not exceed the specified values; supports must be installed promptly to reduce the time of unsupported exposure, following the principles of "support as you excavate" and "support first, then excavate"; and subsequent monitoring of supports must be carried out, with excavation stopped or compensatory grouting performed when necessary.

The second is quality control of structural works. There are relatively many quality control points affecting structural works. The support system, the quality of concrete pouring, and the quality of the concrete itself all determine the degree of completion of structural works. Components used in the support system must also be guaranteed in quality, and the support surface must remain flat during fabrication. The concrete grade must match the drawing design. During the pouring of mass concrete components, strict compliance with specification requirements is required, and curing work must be done well after pouring is completed.

The last and most critical is waterproofing construction, which is the top priority of construction quality. Waterproofing in subway projects differs from that in ordinary buildings. The diversity of waterproofing materials and construction methods makes choices during construction relatively varied. At the same time, when selecting waterproofing materials and construction methods, the requirements of the waterproofing grade must be strictly met to achieve a completely watertight result. During construction, sampling tests must be conducted when waterproofing materials enter the site, and joint work between panels and treatment of some junction parts must be handled more cautiously. Any damage to the waterproofing layer caused during construction must be repaired promptly, with patches fully adhered. In addition, when carrying out waterproofing construction at special locations such as construction joints and deformation joints, construction, supervision, and corrections must be carried out in accordance with design specification requirements.

In short, every link and detail throughout the entire subway construction process must be constructed to requirements, supervised and corrected, and construction must be standardized, normalized, and civilized. We should build conscientious projects and model projects to achieve good economic and social benefits for the company's projects.