The Unique Challenges of Silt Layers
Drilling with a Down-the-Hole (DTH) hammer in silt is akin to driving a nail into tofu-one must simultaneously maintain borehole verticality and prevent hole collapse. The high water content and low bearing capacity of silt present two major challenges:
Drill Bit Selection: It is recommended to use an extended-type alloy drill bit featuring a 15° angled lead cutting edge design to minimize silt adhesion.
Cuttings Removal Control: Compressed air pressure must be maintained within the range of 0.8–1.2 MPa, with an airflow velocity of no less than 25 m/s.
Rotational Speed Adjustment: Low-speed drilling (200–300 rpm) is recommended to avoid disturbing the surrounding soil strata.
Three Key Process Optimizations
Validated through numerous field trials, the following methods can significantly enhance construction efficiency:
Pre-Grouting Reinforcement: Inject a sodium silicate solution prior to drilling to create a 0.5-meter-wide reinforced zone.
Stepwise Drilling: Pause for 2 minutes after every 1.5 meters of penetration to allow the airflow to fully evacuate the drill cuttings.
Real-time Monitoring: Install an inclination sensor; immediately implement corrective measures if the deviation exceeds 2°.
Emergency Response Protocols
Do not panic if you encounter the following situations:
Stuck Drill Rod: Immediately cease applying thrust pressure; rotate the drill rod in reverse for 3–5 turns, then slowly lift it.
Borehole Constriction: Inject a bentonite slurry into the hole; allow it to set for 4 hours before resuming drilling.
Inefficient Cuttings Removal: Inspect the air compressor's air filter; if necessary, increase the airflow volume by 10%.