The current situation and construction key points of domestic rotary drilling RIGS

The rotary drilling rig is a type of construction machinery suitable for hole-forming operations in building foundation engineering. The rotary drilling rig adopts a hydraulic crawler-type telescopic chassis, a self-lifting and lowering foldable drill mast, telescopic drill pipes, and is equipped with automatic verticality detection and adjustment, digital display of hole depth, etc. Rotary drilling RIGS, in combination with different drilling tools, are suitable for dry (short spiral) or wet (rotary bucket) and rock layer (core drilling) hole-forming operations. Rotary drilling RIGS can also be equipped with long spiral drills, underground continuous wall grabs, vibrating pile hammers, etc., to achieve multi-functional features. They have high construction efficiency and are ideal foundation construction equipment for municipal construction, railways, highway Bridges, underground continuous walls, water conservancy, anti-seepage and slope protection, etc. Rotary drilling RIGS are suitable for fill layers, clay layers, silt layers, silt layers, sand layers, and strata containing some pebbles and crushed stones that short spiral drilling cannot penetrate. Core drill bits can also be embedded in rock strata. I. The Current Situation of Rotary Drilling RIGS in China The main enterprises that have developed rotary drilling RIGS in China are shown in Table 1

Table 1: Major domestic enterprises that have developed rotary drilling RIGS

Serial Number: Enterprise Production Model and Features, Applicable Scope

Torque of XCMG RD18 power head: 180kN·m, pile diameter: 1500mm-2000mm, drilling depth: 60m

Sany SYR200, power head torque: 200kN·m. Pile diameter: 2000mm, drilling depth: 60m

Beijing Jingwei Juli Construction Machinery Co., LTD. ZY-120, ZY-200 power head torque: 120kN·m, 200kN·m Pile diameter: 1500-2000mm Drilling depth: 40-60m

Hebei Shijiazhuang Coal Mining Machinery Company XZ-20, Power head torque: 200kN·m. Pile diameter: 2000mm, drilling depth: 60m

5 Inner Mongolia Construction Machinery Co., LTD. ZY-200, Power head torque: 200kN·m. Pile diameter: 2000mm, drilling depth: 60m

Lianyungang Huanghai Machinery Factory GZX-12, Power head torque: 120kN·m. Pile diameter: 1500mm, drilling depth: 40m

Lanzhou General Construction Machinery Factory ZY-150, ZY-220, Power head torque: 150kN·m, 220kN·m, pile diameter: 1500-2000mm, drilling depth: 40-60m

8 Zhengzhou Jinniu Group Zhengzhou Kancha Machinery Co., LTD. KUI 500, power head torque: 150kN·m. Pile diameter: 1500mm, drilling depth: 40m

North Sinotruk ZY-200, power head torque: 200kN·m, pile diameter: 2000mm, drilling depth: 60m

10 Henan Shanhe Intelligent Machinery Co., LTD. SWDM-20: Power head torque: 200kN·m, pile diameter: 2000mm, drilling depth: 60m

Harbin Sihai Construction Machinery Co., LTD. LGB1500KU2000LGBl500: Power head torque: 200KN·m, pile diameter: 1500-2000mm, drilling depth: 66m

Xuzhou Dongming TRM160, TRM200, power head torque: 140kN·m, 200kN·m, pile diameter: 1500-2000mm, drilling depth: Friction drill pipe: 60m, internal locking drill pipe: 45m

13 Beijing Futian, Changsha Institute, Northeast Foundation Company, etc. 20 Power head torque: 200kN·m Pile diameter: 2000mm Drilling depth: 60m

Ii. Construction Technical Points 1. Construction Process Steps of Rotary Drilling Rig: Step 1: Positioning of the rotary drilling rig Step 2: Gently touch the ground with the drill bit, rotate it, and start drilling. It is best to use the self-weight of the drill bit as the drilling pressure to better ensure the accuracy of the pile foundation. Step 3: When the drill bit is filled with soil and sand, lift it out of the hole. Pay attention to the water level below the hole and replenish water in time to prevent collapse. Step 4: Rotate the rotary drilling rig back in place and pour the soil and sand inside the drill bit onto the earthmoving truck or the ground. Step 5: Close the drill bit valve, rotate the rotary drilling rig back to its original position, and lock the rotating body of the drilling rig. Step 6: Lower the drill bit. Step 7: Bury the casing and pour in the mud. According to the soil conditions at the construction site, lower a certain length of the casing. The diameter of the guard tube should generally be 100mm larger than the diameter of the pile to allow the drill bit to rise and fall freely inside the hole. Prepare the mud according to the on-site soil conditions. If the soil quality on site is all relatively good clayey soil, it is advisable to consider drilling directly without injecting mud or clear water. Step 8: Drilling is completed. Conduct the first hole cleaning and measure the depth. Step 9: Place the steel cage. Step 10: Place the conduit. Step 11: Conduct the second hole cleaning. Step 12: Perform underwater concrete pouring. Step 13: Pull out the casing, clean the pile head, settle the silt and backfill, and complete the pile.

2. Construction precautions

(1) Casing construction

The significance of the casing burial: The casing burial work marks the beginning of the construction of the rotary drilling machine. Whether the planar position and verticality of the casing are accurate, and whether the periphery of the casing and the bottom feet of the casing are tight and impermeable, all have a significant impact on the quality of hole and pile formation by the rotary drilling machine. When laying the casing, the position of the rotary drilling machine's drilling should be marked at the bottom of the pit through the positioning control pile layout. Then hoist the casing into the pit, find the center position of the casing, mark the top or bottom of the casing with a cross line, and then move the casing so that the center of the casing coincides with the center position of the rotary drilling machine's drilling hole. At the same time, use a level or a plumb Bob to check and make the guard stand straight and firm. After that, symmetrically and evenly backfill the clay with the optimal moisture content around the casing, and compact it layer by layer to achieve the best density. When tamping and filling, it is necessary to prevent the casing from tilting.

The principles for the fabrication and installation of casing:

① The protective tube is made of steel casing. For lengths within 4 meters, steel plates with a thickness of 4 to 6mm are used; for lengths over 4 meters, steel plates with a thickness of 6 to 8mm are used. When the casing is buried relatively deep, multiple sections of the casing are connected for use. The connection form is welding. During welding, ensure that the joint is smooth while meeting the requirements of rigidity, strength and leak-proofing.

② The inner diameter of the casing is larger than that of the drill bit. The specific diameter of the casing should be selected according to the design requirements.

③ The burial depth of the casing shall meet the design and relevant specification requirements. In rivers, the casing shall be buried in a relatively hard and dense soil layer at a depth of more than 0.5 meters.

The top of the guardrail is 1.5 to 2.0 meters above the construction water level or the groundwater level, and 0.3 meters above the construction ground.

Before the casing is buried, accurate measurement and layout should be carried out to ensure that the deviation of the top surface position of the casing does not exceed 5cm. During the burial, the slope of the casing should not exceed 1%

(2) Mud

① The significance of mud

The preparation of mud is the key to whether a rotary drilling rig can form a hole, and it is also the key factor affecting the drilling progress and the quality of the pile foundation concrete. When the mud is too thin, it cannot float, which affects drilling. When it is too thick, the mud adheres to the hole wall and the reinforcing bars, affecting the quality of the concrete for the pile foundation. Hole formation is carried out by preparing slurry for the hole pile wall protection. The slurry materials selected are bentonite or clay, polyacrylamide and caustic soda. The slurry preparation is conducted in a slurry pool. Each cubic meter of slurry requires 450-100 kg of bentonite. Adding an appropriate amount of caustic soda can increase the viscosity of the slurry. Experiments have proved that: Such mud clay particles are uniformly suspended, with less sedimentation and stable performance, meeting the requirements for drilling.

② Mud performance indicators

Before pulping, the clay blocks should be crushed as much as possible first. Then, the mud is made into mud by a mud mixer outside the well hole and used. In order to recover mud raw materials and reduce environmental pollution, mud circulation and purification systems should be set up. During the drilling process, based on the different conditions of the formation, a certain hydrostatic head pressure should be maintained. The mud management work should be guided by the principle of balanced drilling. The formation clay should be utilized as much as possible to naturally produce mud. When the mud consistency cannot meet the requirements, clayey soil with strong slurge-making ability and high viscosity should be selected for slurge-making to increase the mud consistency and ensure that the hole does not collapse or shrink during the drilling process.

The reference values of the performance indicators of engineering slurry are shown in Table 3

Table 3: Performance Indicators of Engineering Mud

Indicator: General strata: Loose strata prone to collapse

Relative density: 1.05-1.15, 1.12-1.16

Viscosity (Pa.s) : 18-25, 24-28

The pile hole construction adopts a one-time, comprehensive and uninterrupted operation. During the construction, the soil layer structure is judged based on the slag discharge situation, and the performance indicators of the mud are adjusted in a timely and reasonable manner. When encountering loose strata, the relative density and viscosity of the mud are appropriately increased to maintain the water head height in the hole and minimize the impact of the flushing fluid on the hole wall. At the same time, the rotational speed and drilling pressure are reduced to meet the quality control requirements of the construction.

③ Mud performance parameters

The mud pit can be built according to the actual conditions on site. In addition, two mud pits made of welded steel plates are prepared by ourselves. The reference values of the mud performance parameters are shown in Table 3 as follows

Design requirements

Soil layer performance

Clayey soil

Sandy soil

Pebble

Specific gravity of mud

1.05 1.10

1.15

Viscosity (s

15 to 16

16 to 18

18 to 25

Sand content

< 8%

< 8%

< 8%

PH > 8 > 8

"8

Ratio: water, bentonite, alkali, CMC 100:6:3:0.8 100:6:30 0.8

100:10:1.8:0.8 100:15:1.8:0.8

④ To prevent the collapse of the hole wall, the necessary viscosity reference values of the stabilizing fluid used are as shown in Table 4 below

Table 4: Reference Values of Necessary Viscosity for Stabilizing Liquid

Soil quality

Sandy silt

Sand (N < 10

Sand (0≤N < 20)

Sand (N≥ 20

Gravel mixed with clay

Gravel

Necessary viscosity (S) (500/500CC)

20 to 30

> 45

25 to 45

2, 3 to 25

25 to 35

> 45