Construction techniques and precautions for bridge seismic tie rods

The bridge's seismic bracing incorporates various seismic measures, including anti-fall chains, longitudinal tie rods, dampers, rubber gaskets, seismic blocks, and bearings. Dampers are installed between the pier (abutment) cap and the main beam at the bridge expansion joints, and dampers are also installed on the piers and abutments at the expansion joints. Anti-fall chains are replaced by longitudinal blocks and longitudinal tie rods.

Tie-rod retaining walls are a new type of retaining structure formed using reinforced soil and anchor bolt technology. They consist of masonry, tie rods, and anchoring devices. The tie rods are horizontally anchored to both sides of the retaining wall and subjected to a certain prestress. Their working mechanism is twofold: first, the tension of the tie rods balances the pressure of the backfill or the forces exerted on the retaining wall during construction by accidental loads such as earthquakes or vehicle impacts, maintaining the balance of the retaining wall; simultaneously, when one side of the retaining wall tends to overturn or slide, the other side provides passive protection by halting construction through the tie rods; second, the prestress of the tie rods applies lateral pressure to the backfill, subjecting it to triaxial stress, significantly increasing its strength and contributing to overall stability and uniform settlement. Compared to gravity retaining walls, tie-rod retaining walls offer advantages such as lightweight structure, small masonry volume, good economic benefits, and excellent overall seismic performance, making them suitable for road shoulders and embankment sections with limited land area and high seismic fortification intensity.

When constructing a tie-rod retaining wall, masonry work and roadbed filling and compaction should be carried out simultaneously. When the wall is laid 50cm above the corrugated metal pipe, compaction should be performed first, followed by trenching, pipe installation, and backfilling. After the corrugated pipe is installed, the following procedures should be performed in sequence: anchor bolt installation, grouting, adding steel pads, tightening nuts, and sealing the anchor.

Construction Precautions

(1) Before construction, ground drainage should be carried out. The foundation pit should not be excavated in its entirety. A method of skip-excavation and timely segmented masonry construction must be adopted. At the same time, drainage measures and related contingency plans should be strengthened. Temporary support during the construction period should also be strengthened as needed.

(2) Backfilling of the retaining wall back and toe should be strictly carried out according to the design scope. For backfilling of the wall back, crushed stone or gravel should be selected according to different sections. When there is a large gap between the wall back and the ground line, rubble stones should be filled according to the requirements of masonry roadbed. For backfilling of the wall toe, rubble stones or pebbles should be used, with a particle size below which should not be washed away by floods.

(3) The construction of the three-layer anchor rods should proceed sequentially from the bottom layer. Before constructing the next layer of masonry and backfilling, the installation and sealing of the next layer of anchor rods must be completed. The grouting process should proceed from the bottom layer towards the middle, ensuring that both ends are compacted. This utilizes the anchor rods and retaining wall to form a unified whole, enhancing the overall stability of the tie rod retaining wall.