What Is Rotary Drilling?

Rotary drilling is a construction technology suitable for hole formation in building foundation engineering. Widely used in municipal construction, highway bridges, high-rise buildings and other foundation construction projects, with different drilling tools, suitable for dry (short spiral), or wet (rotary bucket) and rock formation (core drilling) hole-forming operations.

Rotary drill

Rotary drilling is a construction technology suitable for hole formation in building foundation engineering. Widely used in municipal construction, highway bridges, high-rise buildings and other foundation construction projects

1.Classification of common rotary drill bits

Common rotary drill bits include auger bits, rotary buckets, barrel core drills, enlarged bottom drills, impact drills, punching cone drills and hydraulic grabs, which are briefly introduced below by category.

1.1 auger drill

(1) Conical: Double-headed double-spiral, suitable for hard bedrock. Double-headed single snail, suitable for weathering bedrock, pebble, frozen soil and so on. The above drill bits are equipped with various picks, and many types of drill bits can be derived by changing the tooth shape, pitch, and helix rise angle.

(2) Straight Auger Bit:

a, bucket tooth straight screw

Double-headed double snail, suitable for sandy soil, small diameter gravel layer with poor cementation; Double-headed single snail, suitable for sandy soil, soil layer; single-headed single screw, suitable for large-diameter pebble with poor cementation, cohesive soil and hard cement .

b. Straight spiral snails: there are double snails, three snails and four snails, which are suitable for hard bedrock or cobblestone.

1,2 Rotary Drilling Bucket

According to the installed teeth, it can be divided into picket bucket and bucket tooth bucket; according to the number of floor plates, it can be divided into double bottom bucket and single layer bottom bucket; according to the number of doors, it can be divided into double door buckets and single door buckets; Taper can be divided into cone bucket bucket and straight bucket bucket; according to the shape of the low plate can be divided into pot bottom bucket and flat bottom bucket. The above structural forms are combined with each other, and whether there are changes in whether there is an air vent or a door opening mechanism, dozens of rotary drilling buckets can be combined. Generally, the double-layer bottom bucket is suitable for a wide range of strata. The single-layer bottom bucket is only suitable for the soil with a strong viscosity. The double-door drill bucket is suitable for a wide range of strata. The single-door drill bucket is only used for large-diameter pebble and Hard cement.

1, 3 barrel core drill

There are currently two common types: picket barrel drills (suitable for medium hard bedrock and gravel), cone roller drills (suitable for hard bedrock and large pumice stone). Among the two major types of drill core barrel drills, there are core and non-coring devices, which mainly depend on the difficulty of coring. Because the roller core bit is mainly used for hard rock drilling, and the drilled ring area is large, if conditions permit, it can also be installed in the drill part to reverse circulation drilling to improve drilling efficiency.

1, 4 bottom drill

On the basis that the pile diameter does not increase and the pile depth does not increase, in order to improve the bearing capacity of a single pile, the design department often achieves by expanding the bottom pile. Rotary drilling rig construction can be carried out without any modification. Bottom drill is sufficient. Reaming drill bits are mainly mechanical, which are relatively simple to use and maintain. There are top-opening and bottom-opening types. The opening mechanism is generally a four-bar linkage. It is used for soil, strong wind and moderate weathering. The formation is even hard bedrock. Since rotary drilling is a non-circular drilling, the slag can be cleaned with a slag bucket after the bottom expansion is completed.

1, 5 impact drill, punching cone drill

When drilling large-diameter pebble, large pumice stone and hard bedrock, the use of impact drills, punching cone drills and rotary drilling is particularly effective. The use of this type of drill is carried out by hanging the auxiliary hook of the rotary excavator. Shock effect, so it is better to require the secondary hook to have the function of free rope release.

1, 6 hydraulic grab

At present, there are more and more construction projects for continuous walls and impervious walls. If the rotary drilling rig is modified, it can be operated. The opening and closing of the hydraulic grab is driven by hydraulic pressure. There is only one oil cylinder on the hydraulic grab, so only Need to enter and exit two oil pipes, one control valve can be.

2.Select drill bit according to geological conditions

The main function of the rotary drilling rig is to form holes in the ground. The working object is rock. Due to the shallow depth of the pile hole being constructed, the rock undergoes tectonic movement, mechanical and chemical action in nature, structure, particle size, porosity and cementation. There have been complex changes in the state of occurrence, compressive strength, etc. In addition to the vastness of our country, the targets of rotary drilling rigs are particularly complicated. To sum up, there are the following categories.

According to lithology (common), it is mud shale, sandstone, limestone, granite, etc .; according to its genesis, it is divided into magmatic rock, sedimentary rock, metamorphic rock; it is divided into solid, plastic and loose according to its mechanical characteristics. So how to choose a drill bit according to the formation situation? The classification is introduced below.

(1) Clay: A single-layer rotary digging bucket is used. If the diameter is too small, a two-lobed bucket or a bucket with a slab can be used.

(2) Mud, weakly cohesive soil layer, sandy soil, and pebble layer with relatively small particle size can be equipped with a double bottom drilling bucket.

(3) Hard cement: Use single inlet (single or double bottom) rotary drilling bucket or straight toothed bucket.

(4) Frozen soil layer: available bucket-tooth straight screw drills and rotary drilling buckets with low ice content, and conical spiral drill bits with large ice content. It should be noted that spiral drill bits are used in soil layers (except (Except sludge) are effective, but it must be used in the absence of groundwater, so as not to cause suction and cause seizure. (5) Cemented gravel and strongly weathered rocks: need to be equipped with a conical auger bit and a double-deck rotary digging bucket (single port with larger particle size and double port with smaller particle size)

(6) Stroke bedrock: Equipped with a truncated barrel-type core bit-a conical spiral drill-a double-layered rotary drilling bucket, or a truncated straight spiral drill-a double-layered rotary drilling bucket.

(7) Micro-weathered bedrock: equipped with cone-type core drills-conical spiral drills-double-layered rotary drilling buckets, if the diameter is too large, a graded drilling process shall be adopted.

3.Select the drill bit according to the function of rotary drilling rig

If the rotary drilling rig has a continuous function, it can be equipped with a liquid grab or double-wheel milling for continuous construction. If the secondary winch has an automatic rope release function, you can choose to drill a large diameter pebble or drifting stone with an impact bit and a grab bit. Gas-liquid drilling is possible if equipped with air chamber and faucet. If it is equipped with a double-power head or an accessible casing for pipe rubbing, this is an effective method to solve quicksand, broken gravel, and silt layers.

4. Select drill bit according to some other factors

If the thickness of the sinker is more stringent or when expanding bottom drilling, a special bucket is required. When drilling into the pipe sleeve, the gap between the drill bit and the casing is small. In order to prevent the drill bit from hitting the casing and reducing the suction effect, the drill bit should be equipped with a ventilation hole. As close to the center of the drill as possible, preferably with a robot. You can also solve this special problem by using a combination of drill bits.