Bed separation backfill to reduce surface cracking due to mining under thick and hard conglomerate: a case study

Area of Science:

• Geotechnical Engineering
• Mining Engineering
• Civil Engineering

Background:

• Coal mining can cause discontinuous surface deformation, including cracking and subsidence.
• These deformations pose significant risks to surface structures and infrastructure.
• Specific challenges arise from mining under thick, hard conglomerate strata.

Purpose of the Study:

• Investigate the mechanism of discontinuous surface deformation and cracking caused by coal mining.
• Propose and evaluate bed separation backfill as a method to control surface cracking.
• Protect the Luli bridge from damage due to mining-induced ground movement.

Main Methods:

• Conducted simulation tests using similar materials to study deformation mechanisms.
• Implemented bed separation backfill by injecting water, fly ash, and gangue powder.
• Reinforced bridge structures and foundations.

Main Results:

• Bed separation occurred between conglomerate and weaker strata due to lithological differences.
• Exceeding the breaking span of the separation led to conglomerate fracturing and surface cracks.
• Backfilling reduced conglomerate fracturing, mitigated subsidence, and prevented surface rebound.
• Clay expansion in red strata further supported the conglomerate.
• The Luli bridge experienced a maximum subsidence of 251 mm without obvious surface cracks.

Conclusions:

• Bed separation backfill is an effective method for controlling mining-induced surface deformation.
• The technique successfully protected the Luli bridge from significant damage.
• Understanding lithological interactions is crucial for predicting and mitigating mining impacts.