Rotary drilling rig is a construction machinery suitable for drilling operations in building foundation engineering, widely used in municipal construction, highway bridges, high-rise buildings and other foundation construction projects. With different drilling tools, it is suitable for dry (short spiral), wet (rotary bucket) and rock (core drilling) drilling operations. Rotary drilling rig has the characteristics of high installed power, high output torque, large axial pressure, flexibility, high construction efficiency and multifunctionality. The rotary drilling rig is suitable for the soil and geological conditions in most parts of China, with a wide range of applications, and can basically meet the needs of bridge construction, high-rise building foundation and other projects. Currently, the rotary drilling rig has been widely promoted in various drilling and grouting pile projects. Therefore, it is of great significance to explore the technical aspects of construction preparation for rotary drilling rigs and commonly used clean water construction techniques.
1, Construction preparation
1. Data preparation
(1) Before starting construction, the site engineering geological data and necessary hydrogeological data, pile foundation engineering construction drawings, and drawing review minutes should be available.
(2) Survey data on underground pipelines (pipes, cables), underground structures, hazardous buildings, precision instrument workshops, etc. within the site and adjacent areas.
(3) Technical performance data of the main construction machinery and its supporting equipment, inspection and mix ratio testing of required materials, physical property testing of required materials must be conducted, and qualified laboratories must be commissioned to conduct concrete mix ratio testing based on the raw materials used.
(4) Effective construction organization design or construction plan for pile foundation engineering, and reference materials for load and construction technology testing.
2. Joint review of drawings
Conduct detailed safety technical disclosure, fully promote democracy before construction, mobilize the enthusiasm and creativity of employees, enable all workers involved in construction to participate in discussions on construction plans, increase attention to safety production quality assurance, and evaluate various departments.
2, Construction machinery and equipment
The measuring instruments used, such as theodolites, level gauges, steel tape measures, rotary drilling machines, welding machines, and other mechanical equipment, must have factory certificates of conformity.
3, Requirements for small and medium-sized machinery
(1) Blender
The installation of the machine body is solid and stable, with a rainproof operating shed; All types of clutches, brakes, wire ropes, and protective covers must be safe, reliable, and effective; Operators should hold certificates before taking up their posts; There must be a good separate grounding.
(2) Handheld electric tools
A separate leakage protector must be installed; The protective cover is safe and effective; The shell must have a grounding or neutral connection; The rubber wire must not be damaged.
(3) Electric welding machine
Reliable rainproof measures are in place; Have good grounding or neutral protection; 1, There should be complete protective covers at the secondary wire connection points; The secondary line should use a wire nose; Wiring must not be randomly arranged or pulled, and the insulation of the welding handle must be good; Welders must hold certification before taking up their posts.
(4) Gas cylinder
All types of gas cylinders have clear color codes and shock-absorbing rings, and are not allowed to be exposed to sunlight outdoors; The distance between acetylene gas and oxygen cylinders should be greater than 5m; Acetylene cylinders must be equipped with flashback arresters during use; Leather tubing should be fastened with clamps; Operators must hold a certificate before taking up their posts.
4, Install drilling tools
Drilling tools have a certain degree of rigidity and do not move or shake during drilling or other operations. The installation of drilling tools should comply with the manufacturer's standards. During construction, various specifications of drill bits such as short spiral drill bits, rotary buckets, core drill bits, and core rotary drill bits can be used. During construction, different drill bits for rotary drilling machines should be selected according to the following regulations based on different soil and geological conditions: short spiral drilling tools, suitable for cohesive soil, silt, and fill above the groundwater level, medium dense or above sandy soil, and weathered rock layers. Spiral turning head, using mud wall protection, suitable for cohesive soil, silt, sand, fill soil, gravel soil and weathered rock layers above the groundwater level. Core spiral drill bit, suitable for gravel soil, medium hardness rocks, and weathered rock layers. Core drill bit, suitable for weathered rock layers and rocks with cracks. The specifications of the drill bit are selected and matched by the user according to the actual engineering situation.
5, Common clean water construction techniques
The rotary drilling process of drilling machine: The rotary drilling process first breaks the rock and soil by rotating a bucket drill bit with a valve at the bottom, and directly loads it into the drill bit. Then, the drilling machine lifting device and telescopic drill rod lift the drill bit out of the hole to unload the soil. This process repeats in a loop, continuously taking and unloading soil until the design depth is reached. For rock and soil layers with good adhesion, dry or clean water drilling techniques can be used without the need for mud wall protection. For loose and prone to collapse formations, or with groundwater distribution and unstable borehole walls, static mud wall protection drilling technology must be used to inject wall protection mud or stabilizing fluid into the borehole for wall protection. The following is only a discussion on the construction process of rotary excavation dry soil drilling method.
(1) The pore forming process flow of clear water construction technology:
During the drilling process, there is no need for mud wall protection. Instead, the mud produced by the drill bit during slow rotary drilling plays a certain stabilizing role on the hole wall. During rotary drilling, the drill bit travels back and forth between the bottom of the hole and the surface, resulting in a relatively rough hole wall. The interlocking effect between the pile and soil of rotary drilling and grouting 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, qualified survey and layout personnel shall be organized to release all pile positions, nail cross protection piles, conduct survey review, and record the layout data for filing; When planning the driving route, keep a certain distance between the access road and the drilling location; To avoid affecting the stability of the hole wall; When the construction site is dry land and the groundwater level is below the original ground level during the construction period, the site should be leveled and compacted, and debris should be removed; When the site is located in shallow water, a drilling machine is installed on the top surface after island construction, and the top surface of the island is about 1.0m above the construction water level; The drilling machine chassis should not be directly placed on unstable soil to avoid uneven settlement; The placement of the drilling machine should consider the convenience of excavating and transporting the borehole during drilling construction.
(3) Pile position layout
Pile position layout shall be carried out according to the principle of "from overall to local". When conducting elevation layout of drilling holes, the elevation of the layout shall be reviewed in a timely manner. Use a total station to accurately layout the positions of each pile point, ensuring that the error is within the specified range.
(4) Drilling machine in place
When the drilling machine is in place, it is necessary to check the performance status of the drilling machine in advance. Ensure that the drilling machine is working properly.
(5) Burial steel casing
(6) Under the premise of accurate layout, 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 excavation method is generally used, which is relatively simple and feasible.
(7) The burying of steel casing is the beginning of the construction of rotary drilling machine. The plane position and verticality of the steel casing should be accurate, and the surroundings and bottom of the casing should be tight and impermeable.
(8) When burying steel casing, the position of the drilling machine should be marked at the bottom of the pit through the positioning control pile layout. Lift the steel casing into the pit again, find the center position of the steel casing, use a cross line at 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 center position of the drilling machine. At the same time, use a level or plumb bob to check and make the steel casing firm and straight. Afterwards, symmetrically and uniformly backfill the optimal moisture content clay around the steel casing, and compact it layer by layer to achieve the best 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, it should be excavated deep or replaced with soil. After backfilling and compacting 300-500mm thick clay at the bottom of the pit, the casing should be placed to prevent leakage and collapse at the bottom of the casing. During compaction, the steel casing should be prevented from tilting. The upper opening of the casing should be tied with wooden blocks and symmetrically suspended to prevent downward movement.
(9) Principles for the production and installation of steel casing
Steel casing with a length of less than 4m shall be made of steel plates with a thickness of 4-6mm, while steel casing with a length greater than 4m shall be made of steel plates with a thickness of 6-8mm; When the steel casing is buried deep, multiple sections of steel casing are used for connection, and the connection form is welding. During welding, the joint is ensured to be round and smooth, while meeting the requirements of rigidity, 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 requirements of the design and relevant specifications. If the pile hole is in a river, the steel casing should be buried at a depth of at least 0.5m in a harder and denser soil layer; The top of the steel casing is 1.5-2.0m higher than the construction water level or groundwater level, and 0.3m higher than the construction ground; Before burying the steel casing, accurate measurement and layout should be carried out to ensure that the deviation of the top position of the steel casing is not more than 5cm, and the slope of the steel casing should not exceed 1% during burial; Before burying the steel casing, a larger diameter drill bit should be used to pre drill to the elevation position at the bottom of the casing, and then the drilling bucket should be removed and used to press the steel casing into the predetermined position. Fill the outer perimeter of the casing with coarse-grained soil and compact it tightly.
(10) Drilling construction
The drilling process of a drilling machine is generally carried out with clean water, without the need for mud wall protection; If there is groundwater distribution and the borehole wall is unstable, protective mud or stabilizing fluid can be injected into the borehole for wall protection. The following are the basic operations for drilling with a rotary drilling rig:
When carrying out construction with clean water, turn the key switch to the power mode, and the display of the rotary drilling rig will show the rotary drilling rig marking screen. Press any key to enter the work screen. Firstly, the drilling mast of the rotary drilling rig is erected and adjusted vertically, that is, the rotary drilling rig is moved to the position where the drilling operation is carried out, and the display of the rotary drilling rig shows the working screen of the mast.
The deviation of the mast in the x-axis and y-axis directions can be observed in real time from the working screen of the mast. Operate the electrical handle of the rotary drilling rig to lift the mast from the transport position to the working position. During this process, the controller of the rotary drilling rig collects signals from the electrical handle and tilt sensor, and through mathematical operations, outputs signals to drive the proportional valve of the hydraulic cylinder to achieve closed-loop control of the lifting mast. Realize smooth and synchronized erecting of the mast. Simultaneously collect limit switch signals to protect the left and right inclination angles of the drilling mast during the process of erecting the mast. Before drilling, it is necessary to position and set the mast. Generally, for straight hole operations, it is necessary to adjust the verticality of the mast. Vertical adjustment can be divided into two methods: manual adjustment and automatic adjustment. Automatic vertical adjustment can only be performed through the automatic vertical adjustment button on the display within a range of ± 5 ° relative to the mast's zero position; When the mast exceeds the relative zero position ± 5 ° range, manual vertical adjustment can only be performed through the jog button on the display or the electrical handle on the left control box. During the vertical adjustment process, the operator can monitor the position status of the mast in real time through the mast work interface of the display, so that the mast can ultimately reach the set position for drilling. During the construction process, it is sometimes necessary to perform inclined hole operations. The operator needs to use the automatic positioning button on the display to set the zero position, and then perform the same vertical adjustment operation.
When drilling with clean water, enter the main work interface directly through the display button and then proceed with the drilling operation. When drilling, first land the drill bucket on the ground and use the reset button on the display to reset the drill bit. Record the original position of the drill bit. At this time, the display will show a bar column and a number indicating the current position of the drill hole. The operator can monitor the actual working position, each footage position, and hole depth position of the drill hole through the display to operate the drilling operation. During the homework process, 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 coil pressure. Rotating drilling, using the self weight of the drill bit and pressure as drilling power, a short bar shaped column displays the current drilling depth of the drill bit, a long bar shaped column dynamically displays the movement position of the drill bit, and the numerical value of the hole depth displays the total depth of the hole. After the drilling bucket is rotated and squeezed to fill with drilling slag, it is lifted out of the surface, and the rotary operation handle is operated to rotate the machine to the position of the waste slag truck. The drilling slag is loaded into the waste slag truck. After completion, the machine automatically returns to the drilling operation position by operating the automatic return alignment button on the display, or manually returns to the drilling operation position by operating the rotary operation handle. This working status can be monitored through the return indicator on the main interface of the monitor. After rotating the hole, use the self weight of the drill bit and apply pressure as drilling power. After the drilling bucket is rotated and squeezed to fill with drilling slag, it is lifted out of the surface and loaded into the waste truck, while observing, monitoring, and recording the geological conditions of the drilling hole.
(11) Geological condition record
Record the geological conditions according to the corresponding geological tables; During the drilling operation of the rotary drilling machine, timely fill in the "Drilling Record Form", which mainly includes: work items, drilling depth, drilling speed, and hole bottom elevation; The Drilling Record Form shall be filled out by a dedicated person, and there shall be a handover record during the shift handover; According to the changes in the drilling speed of the rotary drilling machine and the sampling of soil layers, carefully record the geological conditions, draw a geological profile map of the borehole pile, and prepare a soil geological sample box for each borehole pile. The location and sampling time of each sample at the borehole pile must be indicated in the box; When the geological profile of the rotary drilling machine hole pile does not match the design, it shall be promptly reported to the supervisor for on-site confirmation, and the design unit shall determine whether to make changes to the design; During drilling, it is necessary to promptly remove the slag from the hole opening to avoid hindering drilling construction and polluting the environment; After reaching the predetermined drilling depth, lift the drill rod and measure the depth of the hole and the thickness of the virtual soil (the thickness of the virtual soil is equal to the difference between the drilling depth and the hole depth).
(12) Hole inspection
After reaching the design elevation, check the depth, diameter, wall, verticality, etc. of the hole, and take measures to deal with any unqualified ones. The method of hole inspection is determined based on the diameter of the hole. When the borehole is dry, a heavy hammer can be used to compact the loose soil inside the hole, and a measuring rope and hole gauge can be used to measure it directly. If there is groundwater in the hole, the method of pump suction reverse circulation pumping can be used to clean the hole, and the method of underwater concrete pouring construction can be used for hole measurement. During hole cleaning, the viscosity and sand content of the mud should be reasonably controlled; Timely pour concrete into pile holes that have passed quality inspection.
(13) Clear hole
Hole cleaning is an important part of pile construction to ensure the quality of the pile. Through hole cleaning, it is ensured that the quality indicators of the pile hole, the thickness of sediment at the bottom of the hole, the amount of drilling slag in the circulating fluid, and the mud and dirt on the wall of the hole meet the requirements of pile hole quality. The cleaning method using positive circulation rotary drilling technology is as follows: after the pile hole is drilled, the drilling tool is raised by 20-50cm, and a large pump is used to pump in new mud with performance indicators that meet the requirements, and maintain positive circulation for more than 30 minutes until the sediment at the bottom of the hole is removed and the mud and sand content on the wall of the hole are less than 4%. Due to the thick and loose soil layer that is prone to collapse, the engineering pile hole cannot be terminated immediately after cleaning. Instead, a steel cage is inserted into the hole, and a secondary cleaning operation is carried out after installing the grouting conduit to ensure that the sediment thickness at the bottom of the hole meets the requirements before concrete pouring and to ensure the quality of the concrete column.
