The valve at the bottom of auger can prevent drilling bits entering hollow pipe during operation. When drilling pipe is taken out and concrete grout is injected, the valve will be opened.

Stones drilling bit: Use for drilling stones, concrete, firebrick etc. Various type and specification.

The present technique is a new thin cutoff wall construction method by modifying the original method as to use flat drill bit instead of cross bit and adopt positive and negative circulating system.