As a hallmark of modern transportation, high-speed railway places extremely high demands on bridge construction quality. Bridge construction involves numerous complex technical processes; from foundation construction to girder erection, every stage bears on the safety and stability of the overall structure. Foundation construction must adapt to different geological conditions to ensure bearing capacity; pier and abutment construction must guarantee precise structural dimensions and good appearance quality; girder construction requires careful control of precasting and cast-in-place processes as well as erection accuracy. Meanwhile, measurement, deformation and quality control technologies during construction are also of vital importance. An in-depth discussion of these key technologies and practices is of great significance for advancing the development of high-speed railway bridge construction.

1.Pile Foundation Construction Technology and Practice

The practice of bored pile construction requires selecting an appropriate hole-forming method based on geological survey data. Trial holes should be completed before construction to determine reasonable construction parameters. During operation, hole position deviation, hole diameter and hole depth must be strictly controlled, and hole-wall protection and hole cleaning must be properly carried out to ensure hole-wall stability and bottom cleanliness, laying a solid foundation for subsequent processes. Reinforcement cage fabrication must strictly control rebar specifications, spacing and connection quality in accordance with design parameters. Rebar processing must meet mechanical performance requirements, and welded or mechanical splice joints must pass sampling inspection. During installation, precise positioning is required to ensure adequate concrete cover, avoiding deformation and displacement of the reinforcement cage and safeguarding the pile's load-bearing performance. Concrete pouring must use concrete of an appropriate strength grade; pouring speed and tremie pipe embedment depth must be controlled to ensure concrete density. Timely curing must be carried out after pouring, with curing methods and curing periods adjusted according to ambient temperature to prevent concrete cracking and ensure the structural strength and durability of the pile.

2. Open Caisson Foundation Construction Technology and Practice

Caisson fabrication requires prior completion of construction site layout and ground treatment to ensure that bearing capacity meets the loads imposed during fabrication. The cutting-edge cushion layer must be laid evenly and to specification; formwork installation must ensure verticality and sealing; concrete must be poured symmetrically, uniformly and in layers, with strict control of construction joint quality. For sectional fabrication, subsequent sections may proceed only after the previous section's concrete has reached the specified strength. Caisson sinking control requires determining the sinking method according to geological and hydrological conditions. During construction, soil should be excavated in layers, uniformly and symmetrically, with real-time monitoring of sinking elevation and axis displacement; the excavation sequence should be adjusted promptly to achieve dynamic correction, friction-reducing measures should be reasonably adopted, and the sinking rate must be strictly controlled to avoid sudden sinking, over-sinking or tilting, thereby ensuring caisson sinking accuracy. Caisson base sealing must be carried out after the caisson has sunk to the design elevation and stabilized. Before sealing, silt and debris at the caisson bottom must be cleared to ensure the bottom is level and dry; sealing concrete should be poured in layers using suitable materials, with pouring thickness and density controlled, and curing carried out afterward to ensure the waterproofing performance and bearing capacity of the sealed base.

3. Spread Foundation Construction Technology and Practice

Excavation and support of foundation pits require prior verification of site geological and hydrological conditions, preparation of a dedicated construction scheme and submission for approval as required. The support method should be determined according to excavation depth and soil stability. During excavation, slope stability must be monitored in real time, and hazards such as seepage and collapse must be addressed promptly. After excavating to the design elevation, the foundation base should be trimmed as soon as possible to avoid reduced bearing capacity caused by water immersion or prolonged exposure. Foundation formwork installation must follow operating standards, ensuring formwork dimensions and elevations conform to the design, joints are tight with no gaps, and the support system is firm and reliable. After installation, re-inspection and acceptance must be carried out to prevent formwork deformation and displacement from affecting dimensional accuracy, thereby ensuring the appearance and structural quality of the foundation. Foundation concrete construction requires strict control of raw material quality and mix proportions; during pouring, concrete must be vibrated in layers to ensure density; after pouring, timely covering and moisture retention must be applied, with curing measures adjusted according to environmental conditions and curing periods extended to ensure concrete strength meets design requirements and to enhance the integrity and durability of the foundation structure.

Pile foundations, open caisson foundations and spread foundations are the three basic forms of the load-bearing system for high-speed railway bridges, applicable to different geological conditions and load requirements respectively. From hole drilling and reinforcement cage fabrication to concrete pouring and curing, from caisson fabrication and sinking correction to base sealing and waterproofing, from foundation pit support and formwork installation to concrete vibration and curing, the technical essentials of every process directly affect the bearing capacity, structural integrity and long-term durability of the foundation. Foundation construction is highly concealed and costly to rework; only by accurately selecting the foundation type based on geological survey data, strictly implementing trial holes and dedicated scheme approval, and monitoring key parameters such as hole position, sinking elevation and slope stability throughout the process, can quality risks be controlled at the source and solid support be provided for subsequent pier, abutment and girder construction.

Above the foundation lies the key hub for vertical load bearing and transverse force transfer—the pier and abutment. The next article will introduce key technologies and practices in pier and abutment construction of high-speed railway bridges.