If, during the piling process, it is observed that the mud level inside the well casing suddenly rises and overflows the casing, then sharply drops and bubbles emerge, this should be suspected as a sign of hole collapse. This can be detected using a sounding hammer. If the sounding hammer, which was originally suspended above the concrete surface and not removed, is now buried and cannot be lifted, or if the sounding hammer does not reach the original depth when detecting the concrete surface, with a significant difference, this can confirm the occurrence of a hole collapse.

The cause of the hole collapse may be due to water leakage around the bottom of the casing, a decrease in the water level inside the hole, or in tidal rivers, when the tide rises, the difference in water levels inside the hole decreases, failing to maintain the original hydrostatic pressure. Additionally, the placement of heavy objects around the casing or vibrations from machinery can also cause a hole collapse.

After a hole collapse occurs, the cause should be identified, and corresponding measures should be taken, such as maintaining or increasing the head of water, moving heavy objects away, eliminating vibrations, etc., to prevent further collapse. Then, use a mud suction pump to remove the mud that has collapsed into the hole. If the collapse does not continue, normal pouring can be resumed. If the collapse is not severe, backfilling above the collapse position may be possible, and measures such as improving the properties of the mud, increasing the head of water, and burying the casing deeper can be taken to continue drilling. In the case of a severe collapse, the entire borehole should be immediately backfilled with sand or gravel mixed with clay, and drilling should be suspended for a period until the cause of the collapse is determined and corresponding measures are taken to re-drill. If the collapse site is not deep, the method of burying the casing deeper can be adopted, compacting the soil around the casing and re-drilling.