When laying small-diameter pipelines (communication, power, etc.) with horizontal directional drilling rigs, it is usually possible to drag the pipelines back while expanding the holes after the directional construction is completed; when there are larger-diameter pipelines (oil and gas, water supply and drainage, etc.), then it is necessary to expand the guide hole to a certain extent by expanding the hole in order to drag the pipeline back.
The purpose of reaming is to realize the smooth back dragging of the pipeline, so the reaming diameter needs to be determined according to the specifications of construction pipeline. Refer to the following table for the relationship between pipeline size and reaming diameter:
|Outer diameter of the pipeline (mm)||Reaming diameter (mm)|
|＜200||Outer diameter of pipeline + 100|
|200 to 600||1.5 times the outer diameter of the pipeline|
|＞600||Outer diameter of pipeline + 300|
It should be noted that if the hole size is large, it is usually necessary to carry out grading reaming. The diameter difference of the two-level reaming should be 100 to 150mm, and it can also be increased appropriately when reaming in the soft soil layer.
Choosing a suitable reamer according to the characteristics of the stratum during construction is the main way to improve the construction efficiency. In order to adapt to different stratum, the structure of the reamer is also different. At present, there are mainly extrusion-expanding, runner, cutting, and rock reamers.
1. Extrusion-expanding reamer realizes hole expansion by extruding the ground, so it is often used in soft soil.
2. Runner type reamer has a certain cutting and drillings removal effect while extruding the ground. It has a wide range of application and can be used in most soil layers.
3. Cutting type reamer mainly realizes reaming by cutting the ground, with good drillings removal effect, especially suitable for dense sandy soil.
4. Rock reamer can be divided into cone reamer and hob reamer. The cone can be subdivided into two types: insert teeth and steel teeth (milling teeth). Usually steel teeth are used for soft rock and hard soil layers, insert teeth are mainly used for hard rock projects, and hob reamers are mainly used for hard rock or long-distance rock reaming construction.
1. During the reaming process, it is necessary to strengthen the communication between the operator and the personnel for the loading and unloading of drill pipeline at the excavation site to prevent the staff from suffering personal injury accidents due to the sudden rotation of the drill pipeline when the drill pipeline is connected. In order to ensure the safety of construction, it is recommended to use a transfer case to connect the reamer and the drill rod.
2. During the reaming construction, it is necessary to pump enough mud into the hole, and the drillings in the hole are taken out of the hole through the circulation of the mud to keep the inside of the hole clean. This is also an important premise deciding whether the final back dragging of pipeline can proceed smoothly.
3. In the process of grading reaming, if abnormalities such as torque and pulling force are found to be too large, the necessary hole washing operations can be carried out after the current level of reaming construction is completed so as to ensure the safety of subsequent reaming construction. Particular attention should be paid during construction in rock stratum.