Rock reamer hole opener must be used in rock formations. At present, rock reamer hole opener can be divided into hob type and tooth wheel type according to different structure forms. The hob type is only suitable for hard rock in soft rock, while the tooth wheel type is safe and suitable for all kinds of rock layers despite of high cost.
Horizontal directional drilling through pipe laying method is the mainstream method of trenchless pipe laying technology at present, which generally goes through three stages. The first is the construction of guide hole, the second is one or more pre-expanding holes, and the third is the backdrag of finished pipe.
It can be said that after the completion of the guide hole, reaming is a very key and the largest workload of a process, and under reamers hole opener is a necessary tool for reaming, and the key of reaming is to select efficient and safe under reamers hole openers according to the actual conditions.
The strata traversed are complex and variable, not only having layers of clay and sand, but also having layers of fluid sand and even encountering layers of rock. For non-rock formations, ordinary under reamers hole openers (e.g., plate reamers, bucket reamers, channel reamers) are suitable.
In the past, the rock layer was forbidden to cross the horizontal directional construction, because the ordinary under reamers hole openers could not do anything about the rock layer. With the increasing progress of science and technology, the rock reamer hole opener has been developed successfully.
Selecting rock reamer hole opener according to the type that passes through the strata. The type that passes through the strata is an important factor to correctly select the size and type of rock reamer hole opener. It is allowed to use rock reamer hole opener with larger diameter and fewer reaming times when reaming in soft rock strata.
The size difference between the two adjacent under reamers hole openers can also be larger, with a level difference of 100 ~ 150mm. When reaming in hard rock strata, the diameter of reaming should not change too much, the level difference should be 50 ~ 100mm, and multiple reaming should be adopted to achieve the best reaming efficiency and smooth discharge of drilling cuttings.
Horizontal directional drilling is a high-risk industry. If there is a little careless, there will be danger at any time. In order to meet the need of releasing jam when changing rock reamer hole opener or sticking drill in the middle of a single reaming, the design of rock reamer hole opener should also consider the function of backing out of drilling hole.
The main purpose of reaming is to remove cuttings from the hole, not just cut cuttings, so when selecting a under reamers hole opener, we aim to produce cuttings small enough to allow the mud to suspend them and discharge them to the surface.