A Brief Analysis of the Design and Application of Rotary Drilling Buckets

In recent years, rotary drilling RIGS have been favored by construction units for their high efficiency, environmental friendliness, high hole-forming quality, high degree of mechanization and wide adaptability to various strata. Different specifications of rotary drilling RIGS can be seen everywhere on construction sites of Bridges, railways, expressways and other projects. However, due to the vast territory and diverse strata, the geological conditions for construction are complex and unpredictable. During the specific construction process, the technical requirements for different stratum structures also vary. Therefore, how to scientifically select and reasonably use drill bits with different structures in the face of different geological conditions is the key to ensuring the smooth progress of foundation construction.

The drill bits used in rotary drilling RIGS mainly include rotary drilling (rotary) buckets, helical drill bits and rock drill bits. Among them, the rotary drilling bucket is the most widely used, mainly for construction in strata without sand and gravel or with very small particles of sand and gravel and relatively soft. Spiral drill bits are mainly used for weathered bedrock and gravel layers with small particle sizes. Rock drill bits are used for the construction of large bouldering layers and hard rock layers. This article elaborates on the widely used rotary bucket structure.

The rotary drilling bucket is composed of several parts, including the connecting seat 1, the opening and closing mechanism 3, the bucket body 4, the bucket bottom 5, and the reaming mechanism 2. As shown in Figure 1.

Among them, the connecting seat is linked to the drill pipe through a connecting pin. The opening and closing mechanism presses down the bearing rod through the downward movement of the power head's bearing body. The bearing rod drives the hook plate to achieve the opening and closing of the bucket bottom. At the same time, the limit rod restricts the downward movement distance of the bearing body to ensure that the bucket bottom is fully opened without causing damage to related components. Based on construction experience, the bucket structure is generally designed as a regular platform structure. Depending on different geological conditions, there are also occasions where straight cylinder structures are used (which are relatively rare). For different soil conditions (the amount of sand content), the bottom of the bucket can be made into a single bottom plate drill bucket or a double bottom plate sand-picking drill bucket. They are respectively shown in Figures 2 and 3.

In Figure 2, there are two symmetrically arranged hinge doors at the bottom of the bucket that can only open towards the inside of the bucket. When the drill bucket is drilled, the soil and sand cut from the bottom of the hole are pressed into the bucket through the hinge doors. When lifting the drill, under the effect of the gravity of the mud and sand inside the bucket, the two doors close downward to prevent the sand and soil from leaking back into the hole. This structure is easy to manufacture, saves materials and is convenient to use. However, if the soil layer is loose and the effect of gravity is not very reliable, the hinge door will not close tightly, resulting in the leakage of sand and soil back into the hole, thereby reducing the drilling efficiency. At the same time, it will have an adverse effect on the cleaning work at the bottom of the hole before the construction is completed. To overcome the above-mentioned drawbacks, people have designed a double-bottom plate sand-picking drill bucket as shown in Figure 3. Its characteristic is that the bucket bottom is composed of a fixed bucket bottom and a movable bucket bottom. At the end of each rotary drilling operation, the movable bucket bottom can rotate relatively by an Angle to fully open and close the sand and mud inlet of the bucket bottom. The design of the rotation Angle and the size of the door opening should ensure that no soil leakage occurs when the movable bucket bottom is closed. When the drill pipe rotates and drives the drill bucket to rotate clockwise for drilling, the bottom inlet is in an open state. The opening and closing positions of the movable bucket bottom are determined by the limit blocks on the fixed bucket bottom. When the drill pipe is to be lifted, it will inevitably drive the drill bucket to rotate counterclockwise by a certain Angle. Due to the resistance of the soil, the movable bucket bottom remains stationary. The bucket body, along with the fixed bucket bottom, rotates relative to the movable bucket bottom to close the sand and mud inlet. Ensure that all the mud and sand inside the bucket are completely sealed within the drill bucket.

According to the structural differences in Figures 2 and 3, during the construction process of rotary drilling RIGS, drill bits of different bucket bottom forms can be selected based on the differences in geological conditions. Single-bottom plate soil layer drill bucket is suitable for construction under clay layer and dry hole conditions. The double-bottom rotary drilling bucket is mainly suitable for operations in quicksand layers. It is also beneficial for the cleaning of the bottom of the hole in sand soil, gravel layers with poor cemination and small particle size. Under wet hole drilling conditions, the use of double-bottom rotary drilling buckets can also facilitate the hole cleaning construction. Construction practice has proved that in complex strata, the drilling efficiency and bottom hole cleanliness of double-layer bottom drill buckets are significantly better than those of single-layer bottom drill buckets.

In addition, the distribution, number and welding Angle of the bucket teeth are also key factors for improving the operational efficiency of the rotary drilling bucket, directly affecting the wear rate of the bucket teeth and the drilling efficiency. The number and distribution of the bucket teeth should ensure that the load is basically consistent within the drilling and cutting surface to avoid tooth breakage. Particular attention should be paid to the shape and welding position of the edge teeth, as these teeth are on the outermost layer of the cutting process. Regardless of the load and wear, the working environment is harsh. The welding Angle needs to be adjusted in a timely manner according to different geological conditions. Only by promptly grasping the specific conditions of the stratum being constructed and constantly exploring and researching can more experience be accumulated and the potential of the rotary drilling rig be fully exploited.