Characteristics and Drilling Challenges of Gravelly Soil#custom drilling#
△ Composition and Engineering Properties of Gravelly Soil
Gravelly soil, also known as cobble soil, has a complex composition, mainly consisting of weathered rock fragments of varying sizes and shapes, as well as primary minerals such as quartz and feldspar. This soil exhibits a single-grain structure, accompanied by blocky and pseudo-porous textures. Its characteristics include high porosity, high permeability, low compressibility, and high shear strength. However, its specific engineering geological properties are affected by the intergranular filler, which is typically clay or sand. For drilling operations, it is generally recommended to use a rotary drilling rig with a mechanical lock rod. It is particularly important to note that drill rods used in gravelly soil layers may break due to impact.
△ Risks and Preventive Measures for Rotary Drilling Rigs
The following is an analysis of potential engineering accidents that may occur when a rotary drilling rig is drilling in gravelly soil:
Potential engineering accidents that may occur when a rotary drilling rig is drilling in gravelly soil include:
① The formation or borehole diameter exceeds the rated torque range of the drill rod;
② Improper selection of drilling speed, leading to excessive torsional or bending stress on the drill rod, resulting in damage;
③ Hard geological conditions and excessively fast drilling speed, causing excessive load on the drill rod;
④ Foreign objects in the borehole suddenly increase resistance, and the operator fails to stop drilling in time.
To prevent these accidents, the following measures can be taken:
① Ensure that the formation and borehole diameter are within the rated torque range of the drill rod;
② Select an appropriate drilling speed to reduce the stress on the drill rod;
③ In hard geological conditions, control the drilling speed to avoid overloading the drill rod;
④ Closely monitor the borehole conditions, and stop drilling immediately if foreign objects or a sudden increase in resistance are detected.
02 Drilling Strategy for Rotary Drilling Rigs
△ Precautions During Drilling
When selecting drill rods, calculations must be performed based on the borehole diameter and geological characteristics to ensure that the selected drill rods meet the actual working conditions. If the torsional strength of the drill rod is found to be insufficient to meet the drilling requirements, a staged drilling method can be adopted to reduce the potential damage to the drill rod during a single drilling operation.
② Severely bent drill rods are strictly prohibited from use. It is essential to ensure that each section of the drill rod is properly connected, and the connection between the drill rod and the drill bit must also be secure. To prevent the drill rod joint from reversing and loosening during drilling, appropriate locking devices should be provided.#custom drilling#
③ During drilling, the feed rate and rotation speed must be strictly controlled to ensure drilling safety and efficiency.
△ Drill Bit Selection and Application
Appropriate drilling tools should be selected based on different formation characteristics. For example, in formations with high gravel content, short drill barrels can be used in conjunction with clay and mud for wall protection drilling; for formations containing boulders, boulders, or harder rocks, long and short auger bits can be selected. If the formation is densely cemented and difficult to drill, a tubular drill bit can be used for staged drilling, followed by hole sweeping to achieve the designed hole diameter; alternatively, a tubular drill bit with increased pressure can be selected for single-pass drilling. During initial drilling, light pressure and slow drilling should be used to prevent hole deviation. Staged drilling is usually accomplished using a rock-socketed drill bit with a stabilizer.
This type of drill bit is not only suitable for staged drilling but also exhibits unique advantages in drilling gravel layers. Specifically, its centrally mounted small tubular drill bit has excellent gravel-carrying capacity, thus achieving a high drilling speed. After drilling a small hole in a gravel layer, the drill bit effectively loosens the surrounding geology, reducing the difficulty of subsequent second-stage drilling using a cuttings scoop. Furthermore, the loosened gravel quickly falls back into the previous hole, which not only improves drilling efficiency but also simplifies the cuttings retrieval process.#custom drilling#
