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

(3) Reasonably control the lifting speed of the drill bucket

When starting to drill or passing through the junction of soft and hard layers, to keep the drill pipe vertical, it is advisable to advance slowly. If during the drilling process, the drill pipe is found to be shaking or difficult to drill, it may be due to encountering hard stones, blocks or hard objects, etc. At this time, the drill should be lifted immediately for inspection. Only after the cause is identified and properly handled should the drill be resumed to avoid severe tilting or displacement of the pile hole, or even twisting or damaging the drill pipe and drill tools. During the drilling process, accumulated soil at the hole opening and scattered soil on the ground should be removed at any time. When encountering abnormal situations such as water seepage, hole collapse, and neck constriction in the hole, the drilling tools should be lifted out of the hole and properly handled. When drilling with slurry, the lifting speed of the drill bucket should be reasonably controlled. The reference values of the main indicators are shown in Table 5, and the reference values of the control speed of the drill bucket are shown in Table 6.

Table 5: Main reference values for reasonably controlling the lifting speed of the drill bucket when drilling with slurry

Table 6: Reference Value Table for Drill Bucket Speed

The lifting speed of the empty drill bucket

Pile diameter (mm), lifting speed (m/s)

700 0.973 700 1.210

800 0.973 800 1.21

1000 0.858 1000 1.02

1200 0.748 1200 0.830

1500 0.575 1500 0.830

2000 0.438 2000 0.62

2500 0.231 2500 0.31

Soil quality of the stratum

Topsoil

Clay-based silty clay, silty silty soil, silty silty clay, silty clay, etc

Sandy silty soil mixed with silty sand, silty soil, silty sand and silty clay, etc

Fine sand, fine sand, coarse sand, etc

Rotational speed (r/min

0 to 10

0 to 20

0 to 15

0 to 8

(4) Steel cage

① Fabrication of steel cage

Steel cage fabrication and hoisting: According to the design, calculate the material length of the stirrups and the distribution section length of the main bars. After straightening the required steel bars, cut them in batches with a cutting machine for later use. As the specifications and dimensions of the main bars, stirrups and wound bars to be welded are not the same, please place them separately to prevent misuse. Make stirrups on the steel bar ring manufacturing table and weld them as required. Place the support frames at intervals of 2 to 3 meters on the same horizontal surface, aligning them with the center line. Then, place the main bars of the fixed length straight on the welded support frames. Insert the stirrups into the main bars as per the design requirements (or insert the main bars into the stirrups) and keep them perpendicular to the main bars, then perform spot welding or binding. After the stirrups are welded or bound to the main bars, the winding bars are wound around them at the specified intervals, bound with binding wire and fixed by spot welding at intervals.

② Technical standards for the processing of steel cages

The basic requirements for processing steel cage: The thickness of the main reinforcement protective layer is 70mm. The main bars should be rust-removed and straightened. The reinforcing ring bars should be round (the difference between the long diameter and the short diameter should not exceed 10mm). The lap joints of the main bars should be staggered by no less than 900mm (≥35D), and the number of joints in the same cross-section should not exceed 50% of the number of main bars. The main reinforcement butt welding shall be carried out by butt welding or arc lap welding. When arc lap welding is adopted, the lap length for single-sided welding shall not be less than 10d, and for double-sided welding, it shall not be less than 5d. Steel bars should have factory certificates of conformity and re-examination reports. When processing steel cage, the dimensional deviation should comply with the provisions of the steel cage manufacturing allowable deviation table. The inspection quantity should be checked and each pile should be inspected. The geometric dimensions meet the following requirements. The reference values are shown in Table 7:

Table 7: Allowable Deviations for Steel Cage Fabrication

Serial number item allowable deviation (mm)

The spacing of the main bars is ±10

The spacing of the stirrups is ±20

The diameter of the 3 steel cage is ±10

The overall length of the 4 steel cage is ±100

The curvature of the 5 main tendons is less than 1%

The curvature of the steel cage is less than 1%

Inspection method

Measure with a ruler

③ Reference Value Table 8 for Quality Inspection Standards of Steel Cages and Reference Value Table 9 for Quality Inspection Standards of Concrete Cast-in-place Piles

Table 8: Quality Inspection Standards for Steel Cages (m)

Design requirements

1 Bearing capacity

According to the technical specifications for foundation pile inspection

2 pile diameters

Plus or minus 50

3 Mud specific gravity

1.15-1.20

4. Sedimentation thickness

80 mm or less

5. Concrete slump

160-220.

6. Installation depth of the steel cage

+ 100

7. Concrete filling coefficient

Greater than 1, less than 1.3

The top elevation of the 8 piles

+30, -50