A rotary drilling rig is a construction machine suitable for hole-forming operations in construction foundation projects. It is widely used in foundation construction projects such as municipal construction, highways and bridges, and high-rise buildings. It can be used with different drilling tools and is suitable for dry (short spiral), or wet (rotary bucket) and rock formation (core drill) hole-forming operations, rotary drilling rigs have the characteristics of large installed power, large output torque, large axial pressure, flexibility, high construction efficiency and multi-function. Rotary drilling rigs are adapted to the soil geological conditions in most areas of our country and have a wide range of uses. They can meet the needs of bridge construction, foundations of high-rise buildings, and other projects. At present, rotary drilling rigs have been widely used in various bored pile projects. Therefore, it is of great significance to technically discuss the construction preparation of rotary drilling rigs and common clear water construction techniques.
1. Construction preparation
1. Data Preparation
(1) Before starting construction, site engineering geological data and necessary hydrogeological data, pile foundation project construction drawings, and drawing review minutes should be available.
(2) Survey data on underground pipelines (pipes, cables), underground structures, dangerous buildings, precision instrument workshops, etc. in the site and adjacent areas.
(3) Technical performance data of the main construction machinery and its supporting equipment, inspection and mix ratio testing of the required materials, physical property testing of the required materials, and entrusting a qualified laboratory to conduct testing based on the raw materials used. Good concrete mix test.
(4) Have an effective construction organization design or construction plan for the pile foundation project, and test reference materials related to load and construction technology.
2. Joint review of drawings
Make detailed safety technical briefings, fully promote democracy before construction, mobilize the enthusiasm and creativity of employees, enable all employees participating in the construction to participate in the discussion of the construction plan, increase the emphasis on safety production and quality assurance, and conduct evaluations of various departments.
2. Construction machinery and equipment
The measuring instruments used, such as a theodolite, level, steel tape measure, rotary drilling machine, electric welding machine, and other mechanical equipment must have factory certificates.
3. Requirements for small and medium-sized machines
(1) Mixer
The machine body must be installed solidly and stably, with a rainproof operating shed; all types of clutches, brakes, wire ropes, and protective covers must be safe, reliable, and effective; operators must hold certificates; and must have good individual grounding.
(2)Hand-held power tools
The leakage protector must be installed separately; the protective cover is safe and effective; the shell must be grounded or connected to zero; the rubber cord must not be damaged.
(3) Electric welding machine
There are reliable rainproof measures; there is good grounding or zero protection; there should be complete protective covers at the primary and secondary wire connections; wire noses should be used for secondary wires; wiring is not allowed to be randomly placed or pulled, and the welding handles are insulated Good; welders work with certificates.
(4) Gas cylinder
Various types of gas cylinders have obvious color codes and anti-shock rings, and are not allowed to be exposed in the open air; the distance between acetylene gas and oxygen cylinders should be greater than 5m; acetylene gas cylinders must be equipped with flashback preventers when in use; the leather hose should be tightened with a chuck; Operators must be certified to work.
4. Install drilling tools
Drilling tools have a certain degree of rigidity and will not move or shake during drilling or other operations. The installation of drilling tools should comply with the manufacturer’s standards. During construction, short spiral drill bits, rotary buckets, core drill bits, core rotary drill bits, and other drill bits of various specifications can be used. During construction, different rotary drilling machine drill bits should be selected according to the following regulations according to different soil and geological conditions: short spiral drilling tools, suitable for clay soil, silt soil, fill soil above the water table, and sandy soil with medium density and above. , weathered rock formations. The spiral rotary head adopts mud wall protection and is suitable for clay soil, silt soil, sand soil, fill soil, gravel soil, and weathered rock formations above the water table. A core auger bit is suitable for gravel soil, medium-hard rock, and weathered rock formations. Core drill bit, suitable for weathered rock formations and cracked rocks. The drill bit specifications are selected by the user according to the actual project conditions.
5. Commonly used clean water construction techniques
The rotary drilling process of the drilling machine: The rotary drilling process first uses a barrel drill bit with a valve at the bottom to rotate and break the rock and soil, and then directly loads it into the drill bit, and then the drilling machine lifts the device and The telescopic drill pipe lifts the drill bit out of the hole to unload soil, and this cycle continues to take out soil and unload soil until the drill reaches the designed depth. For rock and soil layers with good cohesiveness, dry or clean water drilling processes can be used, without the need for mud wall protection. For loose and prone-to-collapse strata, or where groundwater is distributed and the hole wall is unstable, the static mud wall protection drilling process must be used, and wall protection mud or stabilizing fluid must be put into the hole to protect the wall. The following only discusses the construction technology of the rotary excavation dry soil drilling method.
(1) Hole-forming process flow of clean water construction process:
During the hole-forming process, there is no need for mud to protect the wall. Instead, the mud created by the drill bit during the slow-speed rotary drilling process plays a certain stabilizing role in the hole wall. During the rotary drilling process, the drill bit travels back and forth between the bottom of the hole and the surface. , the hole wall formed is relatively rough. The bite between the pile and soil of rotary bored piles is strong, which can better reflect the interaction effect between the concrete pile body and loess and silty clay.
(2) Principles of venue layout
Reasonably arrange the construction site according to the design requirements, first level the site, remove debris, replace soft soil, and compact it. After leveling the site, organize qualified surveying and setting-out personnel to lay out all pile positions, nail cross protection piles, conduct a survey review, and record the setting-out data for filing; when planning the driving route, keep the access roads and drill holes in the same position. A certain distance; so as not to affect the stability of the hole wall; when the construction site is dry land and the groundwater level is below the original ground during construction, the site should be leveled and compacted and debris removed; when the site is located in shallow water, use an island to install a drilling machine on the top surface, the top surface of the island is about 1.0m higher than the construction water level; the chassis of the drilling machine should not be placed directly on the unsolid fill soil to avoid uneven subsidence; the placement of the drilling machine should take into account the excavated hole during drilling construction Convenience of clearing and shipping.
(3) Staking out pile positions
When setting out the pile position, the position of the pile foundation should be set out according to the “principle from the whole to the part”. When setting out the elevation of the borehole, the elevation of the stake out should be reviewed in time. Use a total station to accurately stake out the positions of each pile point, so that the error is within the specification requirements.
(4) Drilling machine in place
When the drilling machine is in place, check in advance whether the performance of the drilling machine is good. Make sure the drilling machine is working properly.
(5) Buried steel casing
(6) The casing should be buried under the premise of accurate setting out. The method and requirements for burying the casing should comply with the provisions of JTJ041-89 (hereinafter referred to as the “Specification”). If drilling is carried out on land, the pit digging method is generally used, which is relatively simple and easy to implement.
(7) The embedding of the steel casing is the beginning of the construction of the rotary drilling machine. The plane position and verticality of the steel casing should be accurate, and the periphery of the steel casing and the casing feet should be tight and impermeable.
(8) When burying the steel casing, the positioning of control piles should be used to set out, and the position of the drill hole drilled by the drilling machine should be marked on the bottom of the pit. Then hoist the steel casing into the pit, find the center of the steel casing, use a crosshair on the top or bottom of the steel casing, and then move the steel casing so that the center of the steel casing coincides with the drilling center of the drilling machine. At the same time, use a level or vertical ball to check to make sure the steel casing is straight. Thereafter, the clay with optimal moisture content is backfilled symmetrically and evenly around the steel casing, and compacted in layers to achieve optimal density. To ensure its verticality and prevent mud loss, displacement, and falling, if the soil layer at the bottom of the casing is not cohesive soil, the soil should be dug deeper or the soil should be replaced. The bottom of the pit should be backfilled and compacted with 300-500mm thick clay before placing the casing. There is leakage and collapse at the bottom of the casing. When compacting and filling, the steel casing must be prevented from deflecting. The upper mouth of the casing should be tied with wood and hung symmetrically to prevent downward channeling.
(9) Principles for the production and embedding of steel casings
Steel casings with a length of less than 4m are made of steel plates with a thickness of 4-6mm. Steel casings with a length greater than 4m are made of steel plates with a thickness of 6-8mm. When the steel casings are buried deeply, multi-section steel casings are used for connection. , the connection form is welded. When welding, ensure that the joint is round and smooth, and at the same time meets the requirements of stiffness, strength, and leakage prevention; the inner diameter of the steel casing should be larger than the diameter of the drill bit, and the specific size should be selected according to the design requirements; the burial depth of the steel casing should meet the design and Relevant specification requirements. If the pile hole is in a river, the steel casing should be buried to a depth of more than 0.5m in the harder and dense soil layer; the top of the steel casing should be 1.5-2.0m higher than the construction water level or groundwater level, and 1.5-2.0m above the construction water level or groundwater level. The construction ground is 0.3m; before embedding the steel casing, accurately measure the setting out to ensure that the position deviation of the top surface of the steel casing is not greater than 5cm, and ensure that the slope of the steel casing is not greater than 1% during embedding; before burying the steel casing, use a relatively After the large-diameter drill bit is pre-drilled to the elevation position of the bottom of the casing, the drill bucket is raised and the steel casing is pressed into the predetermined position with the drill bucket. Backfill around the outside of the casing with coarse-grained soil and make the backfill dense.
(10)Drilling construction
The drilling machine generally uses clean water construction technology to form holes, without the need for mud wall protection; if there is groundwater distribution and the hole wall is unstable, wall protection mud or stabilizing fluid can be put into the hole to protect the wall. The following are the basic operations of rotary drilling rig drilling construction:
During clear water construction, turn the key switch to the power position. The display of the rotary drilling rig will display the marking screen of the rotary drilling rig. Press any key to enter the working screen. First, the drilling mast of the rotary drilling rig is raised and adjusted, that is, the rotary drilling rig is first moved to the location of the drilling operation, and the display of the rotary drilling rig displays the mast working screen.
The offset of the mast in the x-axis and Y-axis directions can be observed in real-time from the mast working screen. Operate the electric handle of the rotary drilling rig to lift the mast from the transportation state position to the working state position. During this process, the controller of the rotary drilling rig collects signals from the electrical handle and inclination sensor, and through mathematical operations, outputs signals to drive the hydraulic cylinder. The proportional valve realizes closed-loop mast control. Achieve stable and synchronized mast raising. At the same time, the limit switch signal is collected to protect the left and right tilt angle of the drilling mast during the mast raising process. The mast needs to be positioned and set before drilling. Generally, straight-hole operations are required, so the mast needs to be adjusted vertically. There are two methods of sag adjustment: manual sag adjustment and automatic sag adjustment. The automatic vertical adjustment operation can only be carried out through the automatic vertical adjustment button on the display when the mast is within the range of ±5° relative to the zero position; when the mast exceeds the range of ±5° from the relative zero position, the automatic vertical adjustment operation can only be performed through the inching button on the display or the left operation. Use the electric handle on the box to perform manual vertical adjustment. During the vertical adjustment process, the operator can monitor the position of the mast in real-time through the mast working interface of the display, so that the mast finally reaches the set position for drilling. During the construction process, oblique hole operations are sometimes required. The operator needs to self-set the zero position through the automatic positioning button on the display, and then perform the same vertical adjustment operation.
When drilling in Qingshui construction, directly enter the main work interface through the display button, and then perform drilling operations. When drilling, first put the drill bucket on the ground, perform a clearing operation through the clear button on the display, and record the original position of the drill bit. At this time, the display displays the bar and number of the current position of the drilling hole. The operator can use the display to Monitor the actual working position of drilling, the position of each footage, and the hole depth position to operate the drilling operation. During the operation, the operator can monitor the working status of the hydraulic system in real-time through the display of three virtual instruments on the main interface – power head pressure, pressurization pressure, and main roll pressure. Rotate the hole, using the drill bit’s weight and pressure as the drilling power. The short bar column displays the current drilling depth of the drill bit, the long bar column dynamically displays the movement position of the drill bit, and the hole depth number displays the total depth of the hole. When the drill bucket is filled with drilling slag by rotation and squeezing, lift it out of the ground, operate the rotary operating handle to turn the machine to the position of the slag abandonment truck, and load the drilling slag into the slag abandonment truck. After completion, press the automatic return button on the operating display. The machine automatically returns to the drilling operation position with the position alignment button, or the machine manually returns to the drilling operation position by manually operating the rotary operating handle. This working status can be monitored through the return mark in the main interface of the display. After the hole is rotated, the drill bit’s weight and pressure are used as drilling power. When the drill bucket is filled with drilling slag by rotation and extrusion, it is lifted out of the surface and loaded into the slag abandonment truck. At the same time, the geological conditions of the drilling are observed, monitored, and recorded.
(11) Geological conditions records
The geological conditions are recorded in the corresponding geological-related tables; when the rotary drilling machine is drilling, fill in the “Drilling Record Form” promptly. The main contents are work items, drilling depth, drilling speed, and the bottom of the hole. Elevation; the “Drilling Record Form” should be filled in by a dedicated person, and there should be a handover record when handing over a shift; carefully record the geological conditions according to the changes in drilling speed of the rotary drilling machine and soil sampling, and draw the geological profile of the hole piles Each hole pile must be equipped with a soil geological sample box, and the location of each sample in the hole pile and the sampling time are marked in the box; if the geological profile of the hole pile using the rotary drilling machine does not match the design, report it to the supervision site in a timely manner After confirmation, the design unit will determine whether to change the design; when drilling, the slag from the hole must be removed in time to avoid hindering the drilling construction and polluting the environment; after the drilling reaches the predetermined drilling depth, lift the drill pipe and measure the hole depth and Virtual soil thickness (virtual soil thickness is equal to the difference between drilling depth and hole depth).
(12) Hole formation inspection
After the hole reaches the design elevation, check the hole depth, hole diameter, hole wall, verticality, etc., and take measures if it fails. The hole inspection method is determined according to the hole diameter. When the hole is dry, the virtual soil in the hole can be tamped with a heavy hammer, and measured directly with a measuring rope and a hole measuring instrument. If there is groundwater in the hole, a pump can be used. When cleaning holes using reverse circulation slurry pumping, the underwater concrete pouring construction method is used to measure the holes. When cleaning holes, the viscosity and sand content of the mud are reasonably controlled; pile holes that pass the quality inspection are poured in time. Concrete.
(13) Clear holes
Hole cleaning is an important part of bored pile construction and ensures the quality of the pile. Through hole cleaning, it is ensured that the quality indicators of the pile hole, the thickness of the sediment at the bottom of the hole, the amount of drilling slag in the circulating fluid, and the mud on the hole wall meet the quality requirements of the pile hole. Use The hole cleaning method of positive circulation rotary drilling technology is: after the pile hole is finished, raise the drilling tool 20 to 50cm, use a large pump to pump in new mud with performance indicators that meet the requirements, and maintain positive circulation for more than 30 minutes until the hole is cleared. The bottom sediment is reduced and the hole wall is muddy and the sand content of the mud is less than 4%. Because there is a thick layer of loose and easily collapsible soil in the engineering pile hole, the hole cannot be finished immediately after cleaning. Instead, a steel cage is lowered into the hole, and the grouting conduit is installed. After the grouting conduit is installed, a second hole-cleaning operation is performed to ensure that the bottom of the hole is filled before the concrete is poured. The thickness of the sediment meets the requirements to ensure the quality of the concrete columns.
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