Guidelines for Rotary Drilling Rig Construction

1, purpose
The construction technology, operation points and corresponding technical standards of rotary drilling are defined, and the construction of rotary drilling is guided and standardized.
2. Scope of application
It is suitable for the construction of forward drilling in GGGTJ-12 section of Guizhou-Guangzhou Railway.
3. Construction technology and construction parameters
3.1 Drilling Rig Location
The drilling rig can be put in place only when the pile position is checked correctly, the retaining barrel is buried in accordance with the requirements and the elevation of the retaining barrel and the floor has been measured.
The positioning of piling machine should be accurate, horizontal, vertical and stable. The center line of the guide rod, the center line of the cyclone and the center line of the guard barrel of the drilling machine should be kept in the same straight line.
3.2 Mud Preparation
During the construction of bored pile, in order to prevent collapse, stabilize the water level in the hole and facilitate the carrying of drill ballast, the surging soil is used to prepare mud for wall protection. Mud wall protection is to use the pressure difference between mud and groundwater to control water pressure to ensure the stability of the hole wall, so the proportion of mud plays a key role in maintaining this pressure difference. If the proportion of mud in boreholes is too small, the mud wall protection will easily lose its function of preventing soil collapse; if the proportion of mud is too large, it will easily block the mud pump and even make the replacement of concrete difficult, so that the quality of piles can not be guaranteed. To give full play to the role of mud, the selection of its index is very important. This requires that in the actual construction of the project, according to the specific conditions of the project, reasonable control of mud indicators in different soil layers.
3.3 Drilling
Before drilling, it is necessary to check the diameter-keeping device of the bit, the diameter of the bit and the wear of the bit, and to replace the bit in time when the wear exceeds the standard during the construction process.
During drilling, construction is carried out according to the parameters determined by the trial construction. A full-time recorder is set up to record various parameters of the drilling process, such as adding drill pipe, drilling depth, geological characteristics, mechanical equipment damage, obstacles and so on. Records must be careful, timely, accurate and clear.
Rotary drilling rig is equipped with electronic control system to display and adjust the perpendicularity of the drill pipe. At the same time, there are perpendicularity meters on both sides of the drill pipe. During the drilling process, two perpendicularity meters are observed by specialists, and the driller is instructed to adjust the perpendicularity of the drill pipe at any time. The perpendicularity of drill pipe is guaranteed by electronic control and manual observation, thus the perpendicularity of drilling hole is guaranteed.
In the drilling process, the footage speed can be controlled according to geological conditions: when drilling from hard formation to soft formation, the drilling speed can be properly accelerated; when soft formation becomes hard formation, the drilling speed should be slowed down; in the formation with easy shrinkage, the number of sweeping holes should be appropriately increased to prevent shrinkage; in the hard plastic layer, fast speed drilling is adopted to improve drilling efficiency; in the sand layer, slow speed drilling is adopted and the specific gravity and viscosity of mud should be appropriately increased. 。
Mud indicators for import and export must be tested according to requirements, and timely adjustments must be made when excessive standards are found.
When the hole reaches the design depth, it is necessary to measure the footage on the machine. After the supervision engineer has passed the acceptance test, the first hole cleaning can be carried out.
3.4 One Cleaning
Testing mud index, find out that exceed the standard and adjust in time. Then the drill bit is put into the bottom hole to sweep the hole, and the sediment is removed. The hole cleaning must be thorough.
At the end of hole cleaning, after self-inspection is qualified, hole depth measurement is carried out jointly with supervisory engineer as the basis for siltation measurement after the second hole cleaning.
3.5 steel cage fabrication and installation
A remarkable advantage of rotary drilling rig is that it has fast hole formation and little sediment at the bottom of the hole after hole formation. Therefore, as long as reasonable measures are taken in the production and installation of reinforcing cage to avoid scratching the hole wall during installation, the thickness of sediment can be greatly reduced and the occurrence of collapse can be effectively prevented. This requires strict control in the fabrication of reinforcing cage, with emphasis on the outer diameter and straightness of reinforcing cage. The welding quality of the overlap of main reinforcement and the intersection of longitudinal and transverse reinforcement must meet the design requirements. Therefore, it is necessary to check the setting of the protective cushion block of the reinforcing cage. In this project, the cylindrical mortar cushion block is used. A group of cushion blocks is placed along the reinforcing cage at 2 m intervals. Four cushion blocks are set up in each group. The cushion blocks are evenly laid at 90 degrees, which can not only avoid the impact of the cage on the hole wall, but also ensure the uniformity of the concrete protective layer and the correct position of the reinforcing cage in the pile body.
The hoisting of reinforcing steel cage should be lifted at 3 o'clock to keep the axis of the cage coinciding. When entering the hole, it is always necessary to keep the vertical state, and put the hole in the alignment position slowly and lightly, maintain stability, avoid collision with the hole wall, and find out the reason immediately once it is blocked, and prohibit shaking and forced drop.
3.6 inferior catheter
Water tightness test should be carried out regularly for the catheter. Before the catheter is lowered, air leakage, water leakage and deformation should be checked, and "O" sealing rings should be installed.
The catheter should be lowered in turn. After all the catheters enter the hole, they should be placed at the bottom of the hole so as to check the length and depth of the catheter. Then the catheter should be lifted 30-50 cm for secondary hole cleaning.
3.7 Secondary Cleaning
The parameters determined by the design of construction organization are adjusted by testing the indexes of mud in and out, and the values of sedimentation and siltation measured by non-shrinkage hydrological measuring rope and standard measuring hammer are generally controlled within the range of less than 15 cm.
3.8 Underwater Concrete Casting
Underwater concrete pouring is the last key process. The quality of construction will seriously affect the quality of cast-in-place piles. Therefore, the following points should be paid attention to in construction:
(1) The catheter must be tight and moderate in length to ensure that the bottom end is 30-50 cm away from the bottom of the hole.
(2) The mixing of concrete must be uniform and the slump should be controlled between 18 and 22 cm. The first batch of concrete must ensure the success of bottom sealing.
(3) Concrete pouring must be operated continuously and interruption of pouring is strictly prohibited.
(4) During the pouring process, special personnel should record it in order to prevent the pipe from lifting too fast or burying too deep, resulting in pile breakage.
(5) The top elevation of cast-in-place piles should be 50-100 cm higher than the design value to ensure the quality of concrete at the top of piles.
Compared with traditional diving rigs, rotary drilling rig's cylindrical bit will produce "vacuum" in the local space under the drill bit when it puts forward mud level. At the same time, because of the mud's scouring effect on the hole wall at the intersection of the lower part of the protective barrel and the hole when the drill bit is lifted, it is easy to cause the collapse of the bottom hole wall of the protective barrel.