Application Of Trenchless Drilling Technology in Power Engineering Construction

It covers a small area, does not occupy ground space, is not affected by road buildings, and does not need to erect towers and wires on the road. It is easy to supply power to the city and makes the city neat and beautiful. Therefore, there are more and more cable projects now. The construction of conventional cable engineering is to lay power pipelines by slotting, which needs to occupy the road surface and hinder traffic during construction; It is easy to damage the original pipeline during excavation and backfilling; Dust leakage caused by muck transportation; Backfilling pits and restoring the road surface is easy to cause uneven settlement, subsidence or protrusion of the road surface, which brings inconvenience to vehicles and pedestrians. Moreover, due to the inconsistent application time of electricity, it is often dug up today, filled in tomorrow, and "ripped open" the day after tomorrow, resulting in the "zipper phenomenon" of the road that citizens hate. Therefore, the conventional construction technology is increasingly unable to meet the needs of urban development.

In this case, the advantages of trenchless technology are reflected. Trenchless technology refers to the new construction technology of laying, replacing or repairing various underground pipelines without trenching (grooving) on the surface by using various technical means of rock and soil drilling, and changing the traditional trenching, pipe laying and repair construction method to drilling, pipe laying and repair. Compared with the traditional trenching construction method, the trenchless technology has the advantages of no impact on traffic, no damage to the environment, short construction period and significant social benefits. It is especially suitable for pipeline laying, renewal or repair in some areas where excavation operations cannot be carried out, such as downtown areas, highways, railways, buildings, rivers, crops and vegetation protection areas. According to the construction technology, it can be divided into: guided drilling pipe laying technology, underground shuttle pipe laying technology, pipe jacking and tunneling pipe laying technology, pipe jacking and pipe laying technology. Among them, the advantages of guided drilling and pipe laying technology are: using the guidance instrument to guide, the combination of guided detection and pipeline detection can effectively adjust the drill bit, avoid the pipeline, and be suitable for construction under complex formation conditions; The pipe laying diameter, length and material range are wide, suitable for pipe diameters below 1000mm, and PE pipe laying and steel pipe laying are mainly used; With small interference to the surface, fast construction speed and high construction accuracy, it is a non excavation construction method with fast development. Because the underground pipe network in Xiamen urban area is relatively complex, the guided drilling pipe laying method is mostly used in the trenchless construction of our bureau. The construction technology of guided drilling pipe laying method is introduced in detail below.

First of all, survey the location and terrain of the laid pipeline, design the drilling curve, and excavate the working pit and receiving pit.

Secondly, carry out the construction of guide drill. First, drill a guide hole that is much smaller than the diameter of the pre laid pipe according to the pre-designed pipe laying line with the guide rig placed on the surface, then pull back the expander to expand the hole diameter to 1.2-1.5 times the diameter of the pre laid pipe, and then pull the pipeline in to realize the trenchless laying of new pipes. The construction of pipe laying with guide drill consists of three stages, namely, drilling guide hole, pulling back reaming and pulling back pipe.

1 drill guide hole

Use a guide drill bit to drill accurately according to the specified pipeline direction from the predetermined soil penetration point at a certain angle. The guide bit is an inclined asymmetric bit with a jet port at the front end. A positioning signal transmitter is placed inside. The jet action of high-pressure mud sprayed from the front end of the bit and the cutting action of the bit jointly form the hole wall underground. The mud also plays the role of lubrication and cooling, and makes the hole wall quickly fixed and formed. On the ground, the receiver can detect the longitude and latitude coordinates, depth, inclination rate, slope direction and other parameters of the drill bit in the underground. Usually, each drill pipe is drilled and positioned once. The length of drill pipe changes randomly. The larger the model is, the longer the drill pipe is. According to the measured parameters, the rig operator judges the deviation between the drilling position and the design track, and makes adjustments at any time to ensure that the drilling moves along the design track. When the rotation and feeding are carried out at the same time, the drilling hole extends in a straight line. When only feeding is not rotating, the drilling hole deflects towards the inclined plane of the drill bit under the action of the inclined plane reaction force. The drill pipe is continuously patched until the bit reaches the receiving well or drills out of the ground from the target position.

2 drag reaming

After the completion of the pilot hole, replace the pilot bit with a conical back expanding head with a diameter larger than the existing pipe hole in the receiving well or at the target position. The surface of this kind of bit has high hardness tungsten carbide metal arranged in a spiral shape, which makes it expand the hole under the action of pulling back the drill pipe. The small holes distributed on the circumference of the bit can spray high-pressure mud, which is similar to the process of drilling pilot holes. During backhaul reaming, the mud pump will provide enough drilling mud to the hole wall, and a wall protection mud layer will be quickly formed on the loose hole wall surface. During backpumping, the drill pipe should be continuously connected at the back of the backreaming head. After the back expansion head arrives at the drilling rig, connect a new back expansion head to the receiving well for back expansion again. The expansion can be repeated many times, so that the diameter of the pipe hole can be expanded step by step until the pipe hole meets the design requirements.

3 pull back pipe

After reaming, the hole shall be cleaned with a hole cleaner. Pay attention to the specific gravity of mud during hole cleaning to ensure the quality of mud. When the hole cleaning meets the requirements of pipe laying, the preparation work before pulling back shall be carried out, and the quality of the pipe and whether it is damaged during handling, and whether the welding (connection) of the pipe meets the requirements. The pipe can be laid after inspection. When pulling the pipe back, the product pipe is suspended in the expanded hole, and the mud is lubricated between the pipe wall and the hole, which not only reduces the drag back resistance, but also protects the wear of the anti-corrosion coating of the pipe during pulling back. At this time, the operator should pay attention to controlling the tension and speed of the drill to ensure that the laid pipes are not damaged.