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11 Technical Difficulties of Horizontal Drilling in Trenchless Construction

February 28, 2022

In trenchless construction, some technical difficulties will be encountered during horizontal drilling. Generally speaking, these 11 aspects are included.

1. Stuck drill

Sticking is a common technical difficulty in hole reaming. If stuck, analyze and identify the cause and then deal with it.
1. If the drill is stuck in contact with the underground pipeline, withdraw the drill bit, drag the drill pipe back, move the drill rig, and redo the pilot hole.
2. Bricks and stones stuck in the miscellaneous fill: loosen the torque, turn the drill bit, and slowly expand the hole; large stones and concrete blocks in miscellaneous fill are stuck: try to withdraw the drill bit, move the drill and redo it, Or dig out the stones and continue to ream. Do not be reckless, otherwise the drill pipe will be twisted and the drill tool will be lost in the hole.
3. Large-diameter drill bit reaming, encountering hard clay layer, resulting in frequent sticking, slow down the reaming speed, increase the amount of mud, and sometimes drag a drill pipe back, which takes 40 minutes.
4. When the drill bit meets the root of the tree, it gets stuck, loosens the torque, and expands slowly. After passing through the root, it expands again, and the root is crushed to prevent obstacles during pipe laying.

2. Reduced diameter

When the soft soil layer expands the hole, the phenomenon of diameter shrinkage is easy to occur in the hole. After the drill pipe is removed, the water in the hole flows out from the drill pipe, indicating that the diameter of the hole is seriously reduced. When the diameter is seriously reduced, the laid pipe will be squeezed and deformed, and even the laid pipe will be stuck. In case of serious diameter shrinkage, solid phase mud is used to protect the wall to balance the pressure in the hole and keep the hole formed. Or increase the first-level drill bit for reaming, and then clear the hole and lay the pipe. Use PE and PVC pipes with high hardness and strong lateral pressure resistance. If the diameter is slightly reduced, generally one more hole can be cleaned to lay the pipe.

3. Collapse

Sandy clay layer, sand layer, and loose backfill layer are easy to collapse due to reaming, and the collapsed hole is buried, drilled, stuck, and the pipe is laid, resulting in subsidence of cracks in the pavement. The use of solid phase mud and heavy colloidal solid phase mud to protect the wall can effectively prevent hole collapse. If the hole is collapsed at the pile of stones, the hole can be expanded only after the stones are removed.

4. Expansion of boreholes, clay layers, and Sigda formations swell with water

Drilling and laying pipes in such strata, after the holes are formed, the soil layer in the holes expands, the debris in the holes increases, the pore diameter becomes smaller, and the laid pipes are easy to be flattened. The high-quality non-solid phase protective wall is selected, the mud loses less water, and the contact between the hole wall and the water is reduced. Enlarging the first-level reaming and clearing the holes twice can effectively prevent the formation from expanding and squeezing the pipe laying.

5. Mud leakage

In the loose backfill soil layer, the groundwater level is low, the sandy silt layer, the silt layer, the sand layer, the soft soil layer at the bottom of the river bed, and the sand layer is expanded. The mud does not return from the orifice, but leaks from the hole, increasing the mud concentration and viscosity, and forming a mud skin on the hole wall to prevent leakage, effectively preventing mud leakage. When crossing a river, it is natural for the mud to leak and not stop it.

6. Mud seepage

When reaming the hole and dragging the pipe, it is common for mud to seep out of the ground from the hole. The reason for the mud seepage is that the residual mud in the reaming pipe-laying hole is too much to block the drilling, the mud cannot return from the orifice, and the mud forms high pressure in the hole and seeps from the ground. The second is that the stratum is loose, leaving a channel for the mud, and the mud seeps out of the ground along the channel. In general, it does not matter if the mud seeps from the ground. In some specific environments, special attention should be paid to the fact that the mud cannot seep out of the residential houses, and it cannot seep out of the fish, shrimp, and crab ponds. The measure to prevent mud seepage is to increase the drilling depth. The original design depth of 6 meters can be increased to 9 meters, and the original design depth of 9 meters can be increased to 12 meters. Improve the structure of the drill bit, mix the mud debris in the drilling hole into mud as much as possible, and at the same time increase the viscosity, concentration and flow rate of the mud appropriately, and increase the mud wall protection, suspension and chip removal capacity. A complete channel is formed in the borehole, and the mud returns from the orifice unimpeded.

7. Stop drilling and keep mud

During the process of dragging and laying, the drilling is often stopped due to various reasons, such as welding the pipe in the middle, repairing the protective layer in the middle, and municipal interference. It is necessary to stop drilling and return to dragging the pipe, and the mud cannot be stopped when the drilling is stopped, so that the mud can continue to circulate in the hole, so as to prevent the increase of the drag force of the laid pipe and prevent the pipe from being buried. Especially in sandy formations, the mud cannot be stopped when drilling is stopped. If it is forced to stop the mud, send in thick and sticky mud before stopping the drilling, and then stop sending the mud. After re-drilling, start the pump to pump the mud for ten minutes. After the mud returns well from the orifice, go back to drag the pipe.

8. Hole reaming efficiency

The higher the torque of the drilling rig, the higher the rotation speed, and the higher the reaming efficiency. Under the conditions of the rated torque and rotation speed of the drilling rig, the reaming efficiency is directly related to the soil layer to be reamed, the reaming bit, the quality of reaming mud and the amount of mud. In order to improve the hole reaming efficiency, it is necessary to understand the soil structure and soil composition, select a high-efficiency drill bit suitable for cutting the soil layer, deploy the mud suitable for the soil layer and a reasonable amount of mud, and carry out reaming, and the reaming efficiency is high.

9. Quicksand

When the quicksand layer is expanded, a complete hole cannot be formed after the hole is expanded, and the quicksand has the characteristics of adsorption, which causes resistance to the pipe being laid. Use heavy colloidal solid-phase mud, slow down the back-expansion speed, fully emulsify the mud and quicksand, and suspend the quicksand in the pores to eliminate the quicksand adsorption force. During pipe laying, quicksand flows out of the borehole with the mud.

10. Tube deformation

The viscous stratum expands the hole, and the clay forms lumps and remains in the hole, making it difficult to stir it into mud. When laying the pipe, the mud blocks are piled up and squeezed, and the pipe is squeezed and deformed. Before laying the pipe, clear the hole one more time and then lay the pipe. The deformation of the pipe is small, and the test pass is qualified. The deformation of the pipe is large, and the pipe is pulled out for repair. If it cannot be repaired, it will be scrapped.

11. The tube is stuck

There are a lot of mud blocks left in the hole, the hole collapses, and the diameter reduction is easy to cause the laid pipe to be stuck in the hole. Before it gets stuck, the pressure gauge of the back drag will gradually rise. When the needle rises, pause or slow down the speed of the back drag and increase the amount of mud to avoid the pipe from being stuck. After the pipe is stuck, adjust the bulldozer and excavator to drag the pipe out. Re-clean the hole and lay the pipe.

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    Wuhan Yichao Technology Equipment Co., Ltd. is a professional supplier of horizontal directional drilling rigs. We are XCMG authorized distributor and has nearly 10 years of trenchless pipeline experience.


    Email: m13517277987@163.com

    Tel: 0086-18162684887

    Wechat/WhatsApp: 0086-18162684887/0086-13517277987

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