How to choose the rotary drilling tools correctly

Ⅰ. Classification of common rotary drilling tools

Common rotary drilling tools include auger, drilling buckets, core barrel, belling bucket, chopping bit, punching taper drill bit and hydraulic grab bits, which are briefly introduced below.

（2）Straight Auger:

A、Straight Auger with flat teeth :Double-headed double screws are suitable for sandy soil and small-diameter gravel layers with poor cementation; double-headed single screws are suitable for sandy soil and soil layers; single-headed single screws are suitable for large-diameter pebbles with poor cementation, clay soil and hard clay.

B、Straight Auger with bullet teeth : There are double screws, triple screws and quadruple screws, suitable for hard bedrock or pebbles.

2. Drilling bucket

According to the installed teeth, it can be divided into drilling bucket with bullet teeth and drilling bucket with soil teeth; according to the number of bottom plates, it can be divided into double bottom drilling bucket and single bottom drilling bucket; according to the number of door openings, it can be divided into double door bucket and single door bucket; according to the taper of the cylinder, it can be divided into conical drilling bucket and straight drilling bucket. The above structural forms are combined with each other, coupled with the change of whether there is a ventilation hole and the opening mechanism, dozens of kinds of rotary digging drill buckets can be combined. Generally speaking, the double bottom sand hopper is suitable for a wide range of strata, the single bottom is only suitable for a strong viscous soil layer, the double door drill bucket is suitable for a wide range of strata, and the single door drill bucket is only used for large diameter pebbles and hard mud.

3. Core barrel

Currently there are two common types: core barrel with bullet teeth (suitable for medium hard bedrock and gravel) and core barrel with roller bits (suitable for hard bedrock and large drifters). Among the two major types of core barrel, there are those with and without coring devices, which mainly depends on the difficulty of coring. Because core barrel with roller bits is mainly used for hard rock drilling, and the drilled annular area is large. If conditions permit, reverse circulation drilling can be installed on the drill bit to improve drilling efficiency.

4. Belling bucket

In order to improve the bearing capacity of single pile, the design department often realizes by expanding bottom pile on the basis of not increasing pile diameter and pile depth. Rotary drilling rig construction bottom expansion can be constructed without any changes, only the selection of bottom expansion drill can be. Expanding bottom drill is commonly used to mechanical type, the use and maintenance of this drill are relatively simple, there are open and open, the opening mechanism is generally four-link, for soil, strong winds, weathered strata and even hard bedrock. Because rotary drilling is non-cyclic drilling, it can be used to clean the slag after bottom expansion.

5. chopping bit and punching taper drill bit

When drilling large diameter pebbles, boulders and hard bedrock, the use of impact bits, impact cone bits in combination with rotary drilling is particularly effective. The use of this kind of drill is through the rotary excavator auxiliary hook hanging to work. Because of the impact effect, it is required that the auxiliary hook has a free rope function to better effect.

6. hydraulic grab bits

At present, the construction of continuous wall and cutoff wall is becoming more and more common. If the rotary drilling rig is slightly modified, it can operate. The opening and closing of the hydraulic grab bucket is driven by hydraulic pressure, and there is only one cylinder on the hydraulic grab bucket, so only two oil pipes and a control valve can be entered and left.

II. Select drilling tools according to geological conditions

The main function of a rotary drilling rig is to form holes on the surface.The work object is rock. Due to the shallow depth of the pile holes constructed, the rock has undergone complex changes in structure, particle size, porosity, cementation status, occurrence, compressive strength, etc. due to tectonic movements and natural mechanical and chemical effects. In addition, our country is vast, so the objects that rotary drilling rigs work on are particularly complex. To sum up, there are the following categories:

According to the lithology, it is divided into mudstone, sandstone, limestone, granite, etc.; according to the origin, it is divided into magmatic rock, sedimentary rock, and metamorphic rock; according to the mechanical properties, it is divided into solid, plastic and loose. So how to choose a drill bit according to the formation conditions? The content is as follows:

（1）Clay: Use a single-bottom sand bucket. If the diameter is too small, you can use an open-type drilling bucket.

（2）For silt, weakly cohesive soil layers, sandy soil, and pebble layers with poor cementation and small particle size, a double bottom drilling bucket can be used.

（3） Hard clay: Use a drilling bucket with a single cut (single or double bottom is acceptable), or a straight auger with soil teeth.

（4）Frozen soil layer: If the ice content is small, a straight auger bucket with flat teeth and a drilling bucket can be used. A conical auger can be used if the ice content is large. It should be noted that the auger bit is effective for soil layers other than silt. However, it must be used in the absence of groundwater, so as not to produce suction effect and cause stuck.

（5）Cemented pebbles and strongly weathered rocks: It need to be equipped with a conical auger and a double-bottomed drilling bucket (single cut for larger particle sizes, double cut for small particle sizes)

（6）Stroke bedrock: Equipped with core barrel with bullet teeth,- conical auger ,- double bottom drilling bucket, or a straight auger with bullet teeth ,-double bottom drilling bucket.
（7）Slightly weathered bedrock: Equipped with a core barrel with roller bits,-conical auger, double bottom drilling bucket. If the diameter is too large, a graded drilling process will be adopted.

III Select drilling tools based on the functions of the rotary drilling rig

If the rotary drilling rig has the function of continuous construction, it can be equipped with a liquid grab or double-wheel milling for continuous construction. If the auxiliary winch has an automatic rope release function, you can choose an impact drill bit and a punch drill bit to drill large-diameter pebbles or boulders. If equipped with an air chamber and a faucet, gas-liquid drilling can be performed. If equipped with dual power heads or pipe rubbing machines, casing drilling is an effective method to solve quicksand, broken pebbles, and silt layers.

IV Select drilling tools based on several other factors

If the thickness of ballast is more strict or in the bottom expansion drilling, it is necessary to be equipped with a special ballast hopper. The gap between the bit and the casing is small when drilling into the tube sleeve. In order to prevent the bit from hitting the casing and reduce the suction effect, the bit of the rotary drilling rig should be equipped with air holes. The drill is equipped with a guide device, and the opening and closing device is as close as possible to the center of the drill, and it is best to be machine-hand integrated. Some special problem can also be solved by using a combination of drill bits.