| 摘要 |
<p>The present invention relates to a method for drilling underground rocks using a bit assembly which induces dust into a casing and spouts dust during drilling. The present invention drills a weak ground using a first inner bit and drills rocks using a second inner bit when the first inner bit reaches the rocks. Moreover, in a case that there is water above the weak ground, the present invention drills the rocks after filling up the area where there is water. The present invention is fast in drilling speed and is economical because it does not need to dig the weak ground or stop water in order to drill rocks. Furthermore, when the inner bit for drilling the weak ground and the inner bit for drilling rocks have different sizes, drilling speed is increased.</p> |
