Drill Selection for Ground Adaptability in Horizontal Directional Drilling Construction

Horizontal directional drilling (HDD) construction, as an advanced trenchless technology, is widely applied in many fields due to its unique advantages. It precisely controls the drilling direction through a guidance system and follows a pre-designed trajectory to drill underground, achieving the objective of crossing obstacles and laying underground pipelines.

Importance of Drill Selection

During the HDD construction process, the choice of drilling tools is critical, especially when facing different geological conditions. Geological characteristics vary widely, from soft sand to hard rock, and each type presents unique challenges to the drilling tools. Appropriate selection of drilling tools can enhance drilling efficiency, ensure borehole accuracy, extend the service life of tools, and reduce construction risks and costs. If the drilling tools are not chosen properly, it may lead to slow drilling speed, significant borehole deviation, and even severe issues such as tool damage or jamming, affecting the construction progress and quality. Therefore, a reasonable selection of drilling tools is one of the key factors for the success of HDD construction.

Drill Selection Technology

In HDD construction, choosing the right drilling tools to adapt to different geological conditions is crucial. The characteristics of different types of geological formations vary greatly, and only tools that match these characteristics can ensure efficient and high-quality construction.

Soft Soil Layers

Soft soil layers typically include silt and silt sand. These layers cause less wear on the drill bit but are prone to collapse. Therefore, the choice of drilling tools tends to focus on those with greater flexibility, high cutting efficiency, significant differential pressure, and lighter weight to ensure quick drilling and borehole stability. For relatively soft layers, bucket reamers are generally recommended. Also known as compressive reamers, the front end of bucket reamers is equipped with cutting blades to cut through the soil, while the rear end is bucket-shaped. They are lightweight within the borehole due to mud buoyancy. The appropriately designed bucket chamber based on reamer diameter aids in compressing the borehole wall during reaming, thereby protecting and stabilizing the borehole, preventing collapse, and correcting the borehole walls.

Rock Layers

Rock layers are structurally more stable with stable borehole walls but present challenges due to low drilling efficiency, difficulty in deflection, and slow reaming. In conventional trenchless drilling, the rotation speed of drilling tools is slow, primarily relying on pushing force to complete the borehole's construction. However, for rock layers, the rotation speed is a crucial factor affecting efficiency. Hence, in rock drilling, applying the principle of "high rotation speed, low pressure" is essential for achieving higher efficiency, and choosing tools with relatively small differential pressure is advisable.

For HDD crossings through rock layers, the most widely used tool is the rock reamer hole opener. Its performance advantages include the rolling of the roller cone, which disperses drilling pressure, reduces localized wear of the drill bit, and enhances drilling efficiency. It can adapt to various hardness levels of rock formations in current HDD projects. The rock reamer hole opener consists of the reamer body and the tricone unit, which can be individually replaced when worn. The efficiency of rock reamer hole openers is greatly influenced by factors such as the diameter of the roller cone, the number of cones, cone angle, and the type of cutting teeth. Therefore, it is important to choose a suitable rock reamer based on rock hardness and reamer diameter before reaming.

Rock reamer hole openers are well-suited for HDD construction due to their high strength, wear resistance, long service life, and good safety performance. They can be further subdivided into milled tooth and insert tooth types. Typically, milled-tooth reamers are used for soft rock and hard soil layers, while insert-tooth reamers are used for hard rock construction.

• Milled Tooth Rock Reamer Hole Openers: Milled tooth rock reamer hole openers feature teeth that are milled on the roller cone base, which have relatively poorer wear resistance.

• Insert Tooth Rock Reamer Hole Openers: Insert tooth rock reamer hole openers use teeth made of hard alloy embedded into the roller cone's casing. These teeth possess high hardness, excellent wear resistance, and a longer service life.

In HDD construction, when selecting drilling tools, it is crucial to fully understand the geological characteristics and consider actual construction requirements while comprehensively analyzing the performance indicators of the tools. A successful selection of drilling tools can ensure efficient and smooth construction, while any shortcomings provide directions for future improvements, contributing to the continuous optimization and refinement of drilling tool selection technology.