Pre-construction Preparations#drilling machine road construction#
1. Technical Preparation: Before construction begins, the project's chief engineer will organize a technical briefing for all construction personnel, outlining specific requirements for key processes, main technical requirements, quality standards, and quality objectives. Pre-job safety training will also be provided to personnel in key positions.
2. Construction Support:
① Before construction begins, complete preparations such as equipment arrival, installation, and commissioning.
② Before drilling, verify the coordinates of each pile. Measurement and layout work can only proceed after verification.
③ Based on the overall site plan for this section, prepare the layout of water supply, power supply, construction access roads, temporary facilities, and material storage areas in advance (see site plan for details).
④ The water consumption for this project is approximately 10 m³/h; the power supply for construction and lighting will meet 100 kW.
V. Construction Technology and Control Methods
Trial drilling should be conducted before construction. The purpose is to adjust various construction technical parameters and verify the feasibility and reliability of the rotary drilling process. Trial drilling should be conducted with a diameter of 1.5m and a depth greater than 50m, with continuous monitoring and timely, accurate recording.
1. Drilling
① Surveying and Setting Out: Surveying and setting out will be completed by the project team's surveyors. Technical personnel should guide the surveying control points according to the pile foundation layout for pile position verification. These control points should be marked with protective markers. The next construction step can only proceed after the supervising engineer's inspection.
After the pile positions are marked, φ8 steel bars are used to mark the four corners as protective pile markers. After re-measurement, protective casings are installed based on these markers. The four corner control piles are then transferred to the protective casings, and the center of the borehole is marked with a crosshair. The drilling rig is then aligned with the borehole position based on these markers.
② Protective Casing Installation: To maintain borehole stability and prevent borehole collapse, protective casings must be installed at the borehole opening. A steel casing with a diameter of 2.2m and a wall thickness of 8mm is used. The length should be greater than 2.2m, and the casing should extend 0.5m above the pile top and ground level. During casing installation, the allowable deviation between its centerline and the pile centerline should not exceed 50mm, and the casing should be ensured to be vertical. The casing should be 1.5m above the groundwater level. The area around the excavated and installed casing should be backfilled with clay in layers and compacted.
Cross-shaped positioning stakes are installed around the casing opening.
③ Drilling: This project uses a rotary drilling rig. The R518 hydraulic crawler drilling rig has a self-weight of 58t, a power of 220KW, an output torque of 176KN·m, a hole diameter of 1.8m, and a hole depth of 66m. It uses a diesel engine for self-powered operation, and the traction system uses a crawler system for easy movement and adaptability to complex site conditions. The drilling system uses a hydraulic power head to drive the drill rod, and the drill bit cuts the soil. The drill rod is telescopic, requiring no installation or disassembly, and features built-in instruments (both electronic and mechanical) to monitor hole depth and borehole inclination at any time.
Before drilling begins, the pile position must be accurately located and a crosshair drawn. After alignment with the pile position, drilling can only commence after on-site technical personnel have inspected and approved the work, and the on-site supervisor has received acceptance. Due to the high groundwater level (1.4~2.4m depth) and thick upper sand layer (27~31.8m), borehole collapse is highly likely. Therefore, PHP chemical drilling mud is required for wall protection during construction,
and the following points must be observed:
a. The mud mix ratio should be determined by testing, with viscosity controlled between 20~22s, sand content <0.5%, and specific gravity <1.10.
b. The mud used for the first time should be thoroughly mixed according to testing, with a mixing time >2 minutes.
c. When drilling begins (within 5m below the surface), advance slowly with light pressure, appropriately extending the drilling time. High-quality PHP chemical mud (made from bentonite, alkali, PHP, and water) should be injected into the hole promptly to balance the formation pressure and form mud around the hole wall to protect it. The drill bit should then be used to rotary excavate and cut the soil, bringing the drill bit out of the hole. The drill bit's bottom cover should be opened to dump the soil into a loader bucket and transport it to the designated location.
d. Due to the loose formation in this project, the drilling speed should be controlled during normal drilling, with gentle lifting and slow lowering. Each pass should not exceed 0.5m. When encountering sand layers, a sand-scooping drill bit should be used, advancing forward and then reversing to seal the bottom opening. When encountering soil layers, a clay drill bit should be used. Mud should be injected into the hole along with the drilling progress to protect the hole wall.
e. Strictly control the mud level in the borehole. Use a mud storage tank connected to the borehole via a mud trench to replenish mud promptly. During construction, the mud level must never be lower than 30cm below the top of the casing.
f. Near the end of the drilling, use a bottom-sealing, sand-removing drill bit to reduce the per-return depth (approximately 30cm), gradually removing the thick mud from the bottom of the hole. Upon reaching the final drilling depth, pause for 20-30 minutes to allow suspended solids in the mud to settle, then remove them with the drill bit.
g. After cleaning the borehole, the mud viscosity should be controlled at 18-20 Pa·s, with a sand content <4%, and a sediment thickness ≤50cm. The mud specific gravity can be determined after a trial drilling.
Drilling records should be meticulously filled out during the drilling process, detailing changes in the formation, any problems encountered, and the measures and effects taken. If any formation anomalies are detected, on-site technical personnel should be notified immediately. The drilling rig operator or foreman must sign the record. Once the borehole depth reaches the designed depth, the project technician will conduct a borehole quality inspection. If the quality meets the design and specification requirements, the supervisor will conduct a second inspection for approval.
2. Reinforcing Cage Transportation and Placement: The reinforcing cage is fabricated in three sections. After passing the supervisor's acceptance inspection, it will be transported to the bored pile construction site using a reinforcing cage transport vehicle. When placing the reinforcing cage, it will be lifted using two or three points (setting lifting points at quarter or fifth points of the cage) using the crane's hooks. After the cage is lifted horizontally, the lifting speed of the crane hooks will be adjusted to ensure it is upright, preventing twisting, bending, and permanent deformation. For horizontal transportation and lifting, long round logs of at least 5.0m should be used to reinforce the lifting points. The cage must be aligned with the borehole position, lifted vertically and stably, and lowered slowly to avoid collision with the borehole wall.
Before lowering the reinforcing cage, the positioning blocks on the cage should be checked to ensure the thickness of the concrete cover. Additionally, during concrete pouring, hooks and jacking pipes must be used to prevent the reinforcing cage from floating or sinking.
When welding the two sections of the reinforcing cage at the borehole opening, single-sided lap welding is used within 20m below the pile top, with an effective weld length of 10d, width of 0.7d, and thickness of 0.3d; tack welding is used below 20m, with a tack length of 28d. Joints are staggered to ensure that the number of joints within the same section does not exceed 50% of the total number of reinforcing bars. The spacing between adjacent joints is ≥35d.
After the reinforcing cage welding is completed, stirrups should be added to the joint areas. The cage can only be lowered after acceptance by the on-site supervisor. The positioning of the reinforcing cage is determined according to the pile formation conditions, using a locator or welding of lifting bars. The length of the lifting bars is determined based on the design elevation of the reinforcing cage and the top elevation of the casing. The allowable deviations in the reinforcing cage fabrication quality are: main bar spacing ±20mm, stirrup spacing 0-20mm, reinforcing cage length ±10mm; reinforcing cage diameter ±5mm, protective layer thickness ±10mm.#drilling machine road construction#
3. Concrete Pouring
① Wire Guide Pipe Lowering and Secondary Hole Cleaning: Underwater concrete pouring in this project will utilize the wire guide method. The wire guide will have an inner diameter of φ250mm, and a sealing test must be performed before use.
Before lowering the wire guide, prepare the required wire guides according to the hole depth, accurately measure and record the length and number of wire guides used. When lowering the wire guide, ensure tight connections. After the wire guide is lowered into the hole, the bottom end should be 0.25~0.4m from the bottom of the hole. The wire guide should be located at the center of the borehole. After the wire guide is lowered, remeasure the hole depth and the thickness of the sediment at the bottom of the hole. If the sediment at the bottom of the hole exceeds the requirements, a secondary hole cleaning should be performed using the wire guide until the sediment thickness at the bottom of the hole meets the requirements.
② Concrete Pouring: Concrete pouring will use the wire guide method. A bladder with a diameter slightly smaller than the wire guide diameter can be used as the water-stop plug. A crane will be used to lift the wire guide for concrete pouring.
a. After hole cleaning, place the bladder-type water-stop plug inside the wire guide, install the initial pouring bucket, and prepare for pouring. a) Concrete slump: 18-20cm; Concrete strength grade: C25.
b) Before pouring, check the slump and workability of the concrete at the borehole opening. Pouring can only begin when the slump meets the requirements for underwater pouring and the workability is good. For the initial pouring, the concrete truck should drive directly to the borehole opening and discharge concrete into the hopper. Once the hopper is full (2m³), pouring should begin. Simultaneously, any remaining concrete from the truck should be added to the hopper. During this process, ensure the hopper is always filled. The initial pouring volume is 6m³. Ensure the grout pipe is buried at a depth >1.5m in the concrete after the initial pour.
c) During the pouring process, measure the rise of the concrete and calculate the pipe embedment depth. Carefully fill out the underwater concrete pouring record. Promptly lift the tremie pipe. The tremie pipe embedment depth in the concrete should be controlled between 3-6m. To ensure the quality of the pile top, a certain amount of concrete should be poured beyond the designed pile top elevation. This over-pouring should be controlled within 0.5~1.0m, and the concrete pouring should be continuous without interruption.
4. Key Points and Measures for Construction Quality Control To ensure the project is completed on time, efficiently, and with high quality, each key construction process should be strictly controlled.#drilling machine road construction#
