Selection and Application of Rotary Drilling Bits in Rotary Drilling Machine Construction

Rotary drilling construction is an advanced pile construction method developed rapidly in recent years in China. Rotary drilling rig construction has many characteristics, such as high efficiency, low noise, environmental protection, high quality of drilling and high degree of mechanization. Rotary drilling rig is the executor of this construction method. Whether it is foreign products or domestic equipment, its structure and working principle are quite different, but the strata it constructs vary greatly. The specific technical requirements of construction are different, so only by choosing different bits to meet the above requirements, scientifically choosing and reasonably using the bits, can the construction technology of rotary drilling rig be enriched to a certain extent, and the construction field of rotary drilling rig be broadened.

There are many factors affecting the selection of rotary drilling bits. Generally speaking, there are three main aspects: formation conditions; drilling rig function; specific requirements of hole depth, aperture, thickness of ballast, wall protection measures, etc.

1. Classification of common rotary drilling bits at present

_Common rotary drilling bits are spiral drills, rotary buckets, barrel coring bits, bottom reaming bits, impact bits, punch-grab cone bits and hydraulic grabs, which are briefly introduced below.

_1 and 1 auger bits

(1) Cone: Double-headed twin-screw, suitable for hard bedrock. It is suitable for weathered bedrock, pebble, frozen soil and so on. The above bits are equipped with various cutters, and many types of bits can be derived by changing the tooth type, pitch and helix angle.

(2) Straight screw bit:

_a, Bucket-toothed straight snail: double-headed twin snail, suitable for sand, small diameter gravel layer with poor cementation; double-headed single snail, suitable for sand, soil layer; single-headed single snail, suitable for large diameter pebbles with poor cementation, clay and hard cement.

B, straight snail of pick: twin snail, three snail and four snail, suitable for hard bedrock or gravel.

_1 and 2 rotary drilling buckets

_can be divided into pick bucket and bucket bucket according to the teeth installed; can be divided into double bottom bucket and single bottom bucket according to the number of floor; can be divided into double open bucket and single open bucket according to the number of door opening; can be divided into conical bucket and straight bucket according to the taper of bucket; can be divided into bottom bucket and flat bottom bucket according to the shape of bottom plate. With the combination of the above structural forms and the changes of the ventilation holes and the door opening mechanism, dozens of rotary drilling buckets can be assembled. Generally speaking, double bottom drilling bucket is applicable to a wide range of strata, single bottom is only applicable to strong cohesive soil, double door drilling bucket is applicable to a wide range of strata, single door drilling bucket is only used for large diameter pebbles and hard cement.

_1 and 3-barrel coring bits

At present, there are two kinds of common: pick barrel drill (suitable for medium-hard bedrock and gravel), cone drill (suitable for hard bedrock and big drift stone). In the two types of barrel coring bits, there are coring devices and no coring devices, which mainly depend on the difficulty of coring. Because the cone core bit is mainly used in hard rock drilling, and the drilling ring area is large, if conditions permit, reverse circulation drilling can also be installed in the bit part to improve drilling efficiency.

_1,4 bottom reaming bits

_On the basis of no increase in pile diameter and pile depth, in order to improve the bearing capacity of single pile, design departments often use bottom-enlarged piles. The bottom-enlarged construction of rotary drilling rig can be carried out without any modification, and only the bottom-enlarged bit can be selected. Bottom enlargement bits are mainly mechanical ones. They are easy to use and maintain. They are open-top and open-bottom. The opening mechanism is generally four-bar, which is used in soil, strong wind, medium weathered strata and even hard bedrock. Because rotary drilling is non-circular drilling, slag can be removed with dreg barrel after bottom enlargement.

1,5 percussion bit and punch-grab cone bit

_In drilling large diameter pebbles, boulders and hard bedrock, it is particularly effective to use impact bits and punch-and-grab cone bits to cooperate with rotary drilling. This kind of bit is operated by rotary excavator auxiliary hook suspension. Because of the impact effect, it requires the auxiliary hook to have the function of free rope release.

_1,6 hydraulic grab
A kind of
At present, there are more and more construction projects of diaphragm wall and cutoff wall. If the rotary drilling rig is changed slightly, it can work. The opening and closing of hydraulic grab is driven by hydraulic pressure. There is only one cylinder on the hydraulic grab, so only two oil pipes and one control valve are needed.

2. Selection of drill bits according to geological conditions

_Rotary drilling rig's main function is to form grooves on the surface of the earth. The working object is rock. Because of the shallow depth of the pile hole, the rock undergoes complex changes in structure, grain size, porosity, cementation condition, occurrence and compressive strength through tectonic movement and natural mechanical and chemical action. In addition to the vast territory of our country, the object of rotary drilling rig's work is rock. It's particularly complicated. In summary, there are the following categories.

_is divided into shale, sandstone, limestone and granite according to lithology, magmatic rock, sedimentary rock and metamorphic rock according to genesis, and solid, plastic and loose according to mechanical characteristics. So how to choose the drill bit according to the formation condition? The following categories are introduced.

(1) Clay: single-layer bottom rotary drilling bucket is selected, if the diameter is small, two-petal bucket or bucket with unloading board can be used.
(2) Mud, weak cohesive soil, sand, and pebble with smaller size of poor cementation can be equipped with double bottom drilling bucket.
(3) Hard cement: single-entry rotary drilling bucket or bucket-tooth straight screw is selected.
(4) Frozen soil layer: low ice content can be used bucket teeth straight screw drill bucket and rotary drill bucket, ice content