Project Background
The project is located in Xingyi Normal University for Nationalities, Dingxiao Town, Xingyi City. It consists of two slopes, the upper part is the public rental housing of the teachers’ dormitory, the middle is the road connecting the upper building, and the lower part is the proposed teaching building. The height of the slope is 11m, and the width of the road on the top is 9m.
The original mortar-masonry counterweight retaining wall was built in 2013, and there is a risk of collapse. After the assessment, the retaining wall needs to be reinforced and repaired. Due to insufficient equipment power and collapsible ground, the original plan of the φ25 reinforcement bar was changed to the R32 self-drilling soil nail system.
Project Overview
| Project duration | September 2020 – October 2020 |
|---|---|
| Service scope | Anchoring materials, anchoring rigs, and on-site technical services |
| Application scenario | Reinforcement and repair of retaining wall of building slope |
| Application structure | Self-drilling anchor bars used as permanent soil nails |
| Project consumption | About 3000m |
| Geological conditions | The slope is composed of plain fill, red clay, strongly weathered dolomite, and moderately weathered dolomite (the soil layer is distributed on the top of the slope with a gentle slope, and the lower part is a rocky slope), and the landform of the proposed site is structured dissolution slow slope landform area. |
Questions and Challenges
According to the geological conditions, the designer designed a retaining wall reinforcement plan of anti-slide piles + anchor support. The plan is to install three rows of steel pipe anti-slide piles at the foot of the slope, install reinforced anchors on the slope to strengthen the support, and then place steel meshes and spray concrete. During construction, it was found that it was difficult to drill a hole in the fill layer behind the retaining wall. The construction party tried every methods, but it’s still unable to install, resulting in project suspension.
Solution
The construction party adopted our suggestion to use R32 self-drilling anchor bars as soil nails, with a single bar length of 1.5m. The drill bit is ESSF R32/76, and the drilling depth is 9m. During construction, the anchor bar drill through the 4m retaining wall first, then through the 5m fill layer and finally drill into the rock. According to the equipment conditions of the pneumatic DTH drilling rig, a special adapter coupling is designed. It was installed at the front end of the impactor, and then connect anchor rod and drill bit.
The self-drilling anchor system consists of a hollow anchor bar, coupler, centralizer, drill bit, plate, and nut. It can combine drilling, grouting, and anchoring functions together, and the anchor bar can be used as a drill rod and reinforcement body.
Construction Process
Materials prepared → Erect scaffolding → Drilling rig in place → Connect hollow anchor bar and drill bit → Percussive rotary drilling → Couple next anchor bar → Repeated drilling and grouting → Drilling completion → Install next row anchor bar → Installation completion
Construction Equipment
Drilling rig: Electric DTH drilling machine JVD-100, equipped with QCZJ90 impactor.
Construction Efficiency: The average net drilling time for a single hole (9m depth) is 25.6 minutes, and one drilling rig’s drilling length per shift (8h) is more than 50m.
