This case study presents the foundation reinforcement project for the expansion of Tunxi Modern Experimental School in Huangshan, Anhui Province. The project involved complex urban site conditions, including loose fill, silty clay, round gravel, and weathered sandstone. Proximity to a school and residential area imposed noise restrictions and limited space for heavy equipment.

Technical Challenge

The primary challenge was collapsing boreholes in the round gravel layer, which posed safety and construction efficiency concerns. Conventional methods such as casing or bentonite stabilization were impractical due to site constraints.

Engineering Solution

Self-drilling hollow anchor bars (SER32/19 and SER38/22) were selected as soil nails and micropiles. This method allows simultaneous drilling and grouting, preventing hole collapse while maintaining productivity.

Implementation Details

· Average drilling speed: 1.2 m/min

· Grouting pressure: 2.4 MPa

· Water/cement ratio: 0.8

· Construction crew: 4 operators achieving ~300 m per shift

Key Advantages

· Eliminates the need for casing or bentonite

· Low noise, small equipment footprint suitable for urban environments

· Effective in round gravel and weathered rock formations

· Reduced construction time due to integrated drilling and grouting

Project Outcome

The anchors provided temporary shoring with a 12-month design life. The method ensured site safety, minimized disruption, and achieved client satisfaction.

Key Takeaways

1. Self-drilling anchor bolts are highly effective for mixed soils and urban constraints.

2. Close monitoring of drilling and grouting parameters optimizes efficiency.

3. Documenting on-site performance informs future projects in similar geotechnical conditions.

This project demonstrates the practical advantages of self-drilling hollow anchor bars in challenging urban foundation conditions.

Categories

Pile Foundations

Keywords

Micropile, Self-Drilling Hollow Anchor Bars