Application case analysis of SINOROCK self-drilling anchor--Huangshan Pedestrian Mall foundation support

As an advanced construction technology, self drilling hollow anchor bars are widely used in foundation support projects, effectively solving the construction problems of unstable rock masses such as strongly weathered rocks. In Huangshan Pedestrian Mall foundation support project, the use of R38 self drilling anchor bolts not only overcomes the difficulty of drilling holes in the round gravel layer, but also gives full play to the advantages of it, improves construction efficiency, and reduces comprehensive construction costs.

1. Background and challenges

The total planned land area is about 36372 m2, the building height is 13m. The rock and soil layers from top to bottom in the proposed site are mixed fill, silt, fine sand, round gravel, strong weathered siltstone, strong weathered phyllite, moderately weathered siltstone, moderately weathered phyllite and a lot of construction waste. In actual construction, it is difficult to drill holes in the round gravel layer, so a casing is required. However, drilling with casing is inefficient and costly, and it can cause infrasound damage to the surrounding area. Finally, the construction plan was changed, Sinorock R38 self drilling anchor bolts were used, and drilling and grouting simultaneously can solve the problem of hole formation.

2. Construction plan

Due to the complex geological conditions, the hollow rods need to penetrate the tangent supporting pile and drill into gravel and strong weathered layer. And it is difficult to drill and form holes in the round gravel layer. In order to solve this problem, the constructor uses HYZ133-100A drilling rig, SER38/18 hollow anchor bar, ESF R38/90 drill bit for rotary percussion drilling, and drill hole depth is 18 meters. The grout is pumped through the hollow hole, with a water-cement ratio of 0.5-0.55. The grouting pressure is 0.3-0.5MPa, and the compressive strength of the grouting body is 20MPa. Simultaneously drilling and grouting can directly improve the surrounding soil quality, and improve the anchoring force.

The self drilling anchor rod is used for construction, which is convenient and efficient, and can greatly improve the construction efficiency. When the construction work face is convenient, a team drills up to 500 meters in 12h.

3. Test

After grouting, install breast beam, plate, wedge and hex nut in sequence. The design pull-out value is 15kN/m, the number of test is not less than 3% of the total number, and not less than 5, and the design pulling-out force is 270kN. After testing, the anchoring force of anchor bar meets design requirements.

4. Project Summary

The project was originally designed for construction with casings. Self drilling anchor rods were adopted because it was difficult to make holes in the ground and could not be drilled effectively, thus the construction cost was high. The use of self drilling anchor bolts effectively solve the difficult problem of anchoring in loose rock and soil. The simultaneously drilling and grouting technology makes grouting more full, improve construction efficiency, and guarantee the construction quality.


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