Common problems and solutions in the process of drilling holes and piles of rotary drilling rigs

Sep 17, 2022

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1. Protect the Jane with water


The water on the outer wall of the protective tube will seriously cause the foundation to sink, the inclination and displacement of the protective tube, resulting in the deflection of the pile hole, and even the construction cannot be carried out.


Cause analysis: The surrounding soil is not dense when the casing is buried, or the water level difference of the casing is too large, or the drill bit collides when it rises and falls.


Prevention and control measures: When burying the casing, the bottom and surrounding areas of the pit should be layered and compacted with the most correct water content: holes should be opened at the appropriate height of the casing. Keep a water head height of 1-15m in the casing; prevent the casing from colliding when the drill bit is lifted and lowered: when the casing is initially found to be out of water, it can be filled with clay around it for reinforcement. If the casing is seriously sinking or displaced, it should be reworked.


2. Extremely slow or no footage


Drilling is extremely slow in the hard plastic clay layer, generally 8-10h, accounting for 60%-70% of the drilling time of a single pile


Cause analysis: improper selection of the drill bit, improper installation angle of the alloy tool, too shallow soil cutting by the tool, too light counterweight of the drill bit, and the drill bit is covered with clay.


Prevention and control measures: replace or modify the drill bit, rearrange the angle, shape and arrangement direction of the tool, increase the counterweight, strengthen the slag discharge, reduce the specific gravity of the mud or change the drilling method, and adopt the reverse circulation drilling method.


3. Pile hole wall collapse


During or after the hole is formed, the hole wall collapses to varying degrees. Bubbles constantly appear in the mud discharged from the hole, and sometimes the water level in the casing drops suddenly, all of which are signs of hole collapse.


Cause analysis; mainly due to loose soil and poor mud retaining wall; poor embedding of the retaining tube, low water level in the tube; lifting the drill bit and drilling: the drilling speed of the drill bit is too fast or the idling time is too long, it is easy to cause the lower part of the borehole to collapse ; The waiting time and perfusion time are too long after the hole is formed.


Prevention and control measures: Properly protect the casing in the loose and easily slumpable soil layer, backfill the soil densely, use high-quality mud, increase the specific gravity and viscosity of the mud, raise the casing, replenish the mud after the final hole, maintain the required water head height, and ensure the reinforcement cage. Production quality to prevent deformation; when hoisting, it should be aligned with the hole position, hang upright and stabilize, and slowly sink to prevent collision with the hole wall; after the hole is formed, the waiting time for filling is generally not more than 3h, and the filling speed should be accelerated and shortened as much as possible. : In the case that the reinforcement cage is not in the hole, backfill the mortar sand and clay mixture to 1-2m above the collapsed hole depth or backfill and compact the whole hole, and then use the original drill bit and high-quality mud to sweep the hole; when the reinforcement cage touches the hole wall, In the case of slight collapse, use a drill bit with a diameter smaller than the inner diameter of the steel cage to sweep the hole with high-quality mud or clear the hole with a pipe.


4. Partial necking of the hole


Local necking means that the local aperture is smaller than the design aperture.


Cause analysis: poor mud performance and large water loss. Causes plasticity, the soil layer swells with water, or forms a loose, honeycomb-like thick layer


Mud skin: improper construction spacing between adjacent piles, stress in the soil layer has not been dissipated, soft soil rheology of the new hole wall; the diameter of the drill bit is too large


Prevention and control measures: use high-quality mud, control the specific gravity and viscosity of mud, and reduce water loss; when the design pile distance


5. Pile hole offset and tilt


After the hole is formed, there is a large vertical deviation or bending of the pile hole.


Cause analysis: uneven installation of drilling rig or uneven subsidence caused by virtual soil under the drilling floor; unstable pile frame, vertical drill pipe guide, drilling rig wear, loose parts; buried casing deflection, drill pipe bending, active drill pipe tilt; When encountering underground obstacles such as old foundations or boulders, the ten layers of soft and hard are uneven or the bedrock is inclined.


Prevention and control measures: The drilling rig is installed in a straight, horizontal, stable, and no-beam tangent point of the leading edge, and the center of the turntable and the center of the protective tube are in a line at three points: the protective tube is not deflected, the drill pipe is not bent, the active drill pipe is kept vertical, the guide frame is added, and the control Lift the faucet, use the drill to pressurize as much as possible; remove the underground obstacles; except that the soft and hard interlayer adopts the technical parameters of light pressure and slow rotation, enter the hard plastic clay layer from the soft clay layer, especially the fluid clay layer and the sand layer. Or when entering the bedrock from the clay layer, the tapered guide drill bit at the lower end of the caged drill needs to be changed to a flat-bottom guide drill bit, or directly drilled with a flat-bottom drill bit without a guide drill bit; Remove underground obstacles; when the hard plastic clay layer is deflected, backfill 1-2m above the deflection with a mixture of sand and material soil, and after compaction, use a flat alloy drill to gently press and slowly turn the tilt; deflection occurs on the bedrock surface When crushed, 20-40mm grain size crushed stone can be put in, slightly higher than the deflection, and the deflection can be corrected with a flat-bottom alloy drill bit, a roller hob drill or a flat-bottom steel grain drill bit after the impact is compacted.


6. Too much sediment at the bottom of the hole


The bottom of the hole is silted, the residual mud and sand are too thick or the soil of the hole wall collapses at the bottom of the hole.


Cause analysis: the hole is not cleaned, the specific gravity of the cleaning mud is too small or replaced by water; the steel cage is not vertically aligned, and the soil of the hole wall slumps to the bottom of the hole; the time for irrigation after cleaning is too long, and the mud settles; The hole bottom elevation for thickness measurement is not uniform.


Prevention and control measures: after the final hole, the drill bit is raised to the bottom by 10-20cm, keep idling at a slow speed, and maintain a cycle cleaning time of not less than 30 minutes. Use high-quality mud to clear the hole, control the specific gravity and viscosity of the mud, do not directly replace it with water, and release the steel cage vertically and slowly Entering the hole; when using a flat-bottom drill bit, the thickness of the sediment is calculated from the bottom plane of the hole reached by the bottom of the drill bit: when using a bridle drill bit with a round hammer at the bottom, the thickness of the sediment is calculated from the bottom plane of the hole reached by the bottom of the drill bit; or use conduit for secondary clean water , the punching time is subject to the thickness of the sediment at the bottom of the hole measured in the conduit reaching the standard requirements; to improve the impact force on the bottom of the hole when the concrete is initially poured, the distance between the bottom of the conduit and the bottom of the hole is controlled at 30-40cm, and the amount of concrete for initial irrigation must meet the The bottom end of the conduit can be buried in the concrete for more than 1.0m, and the residual sediment is washed away by the water blocking plug and the concrete.


7. Duct blockage


During the perfusion process, the concrete cannot fall in the conduit, which affects the smooth progress of the perfusion work.


Cause analysis; water-blocking pipes during initial irrigation; excessive coarse bone particle size; unsatisfactory concrete slump, poor workability and fluidity, uneven mixing and segregation; Water leakage occurs, and a water plug is formed in the pipe; when the concrete in the pipe is not full and contains air, the whole bucket of concrete is poured into the pipe, resulting in the formation of high-pressure air-cold in the pipe, or the air-cold squeezes the heat between the pipe joints and causes the pipe to leak; mechanical failure, The concrete in the duct has initially set, increasing the falling resistance.


Prevention and control measures: The diameter of the water blocking plug should match the inner diameter of the conduit, and it can be discharged smoothly from the pipe. The water blocking rubber pad should be installed on the top surface of the water blocking plug, first store and fill 02-03m3 cement mortar, and then pour concrete to prevent bone particles from growing. Water blocking plug, choose coarse aggregate with particle size less than 25mm, and its maximum particle size is not greater than 1/4 of the inner diameter of the conduit and the minimum clear distance of the main reinforcement of the steel cage: strict concrete mixing ratio, slump is controlled at 16-22cm, slump Generally, the time for reducing the temperature to 15cm should not be less than 1h: the concrete is mixed evenly, and the mixing time of the mixer is more than 90s; to ensure the tightness of the connection part of the pipe and the welding seam, the pipe should be pressure-tested at a pressure of more than 0.5-0.7MPa, and the time is more than 15min. Do not leak, so as not to form a water village in the conduit; during the pouring process, the concrete should be slowly poured into the conduit of the funnel to prevent the formation of high-pressure air locks in the conduit: in order to ensure the normal operation of the machine, there must be a spare mixer, which can be mixed with the concrete if necessary. Retarder: Use a long rod to pound, shake the conduit strongly, or install a vibrator on the upper end of the conduit to force the water-blocking village or concrete to fall.


If the above methods are ineffective, the pipe should be removed immediately for cleaning, and the concrete in the hole should be re-irrigated or piled up. Water through the water stopper; when the concrete in the hole has not yet coagulated, clean the conduit as soon as possible, go down to the concrete surface again, turn on the pump to flush the floating slurry, and then lower the water stopper for watering. After the water stopper is flushed out, insert the conduit down as far as possible. In the originally poured concrete, the conduits are inserted up and down in situ to make the concrete mix and compact, and then continue to pour; after the initial setting of the concrete, a drill bit with a slightly smaller diameter than the steel cage can be drilled to the depth of the bottom end of the original conduit to re-clear the hole. It is better to add a section of steel cage with a smaller diameter and bury it in the new hole, and pour the concrete according to the normal procedure.


8. The steel cage floats or sinks


Refers to the phenomenon that the position of the reinforcement cage is higher or lower than the design position. When the floating is large, the horizontal shear resistance of the pile is reduced; the excessive subsidence brings trouble and loss to the civil construction.


Cause analysis: the initial position of the reinforcement cage is too high or too low, the fluidity of the concrete is too small, the depth of the conduit embedded in the concrete is too large (above 6m), the reinforcement cage is floated by the concrete top; the conduit is buried too long, and it is easy to be lifted. Shaking, it is difficult to align the center of the cage, and the phenomenon of hanging cage is easy to occur: the concrete sinks too fast during the lifting of the pipe, and the instantaneous recoil force makes the steel cage float; the steel cage is deformed due to poor quality or improper installation; or the pile hole is inclined, The steel cage is deformed along with it, which increases the lifting force of the concrete; the steel bars at the bottom of the cage are bent inward and hooked to the conduit; the steel cage and the orifice are fixed, and the wire is stretched and sunk under its own weight and pressure; or the steel cage has its own weight. It is too light and will be lifted by concrete.


Prevention and control measures: The initial position of the steel cage rotation is accurate and fixed firmly with the orifice. In order to prevent the wire from stretching and sinking or resisting the lifting force, methods such as hoisting and casing can be used to withstand the upper opening of the steel cage; speed up the pouring speed, shorten the pouring time or add a retarder to prevent the top layer of concrete from flowing into the steel cage. When the concrete is close to the bottom of the cage, control the buried depth of the conduit at 15-2m to minimize the penetration of the conduit, and use the rotating conduit to compact concrete; every bucket of concrete is poured, check the buried depth, measure the depth, and remove the pipe until the reinforcement cage is reached. After burying, restore the normal embedding depth, generally controlled at 2-4m, and the maximum is not more than 6m, which is convenient for rotation and displacement; when the steel cage rises, stop pouring concrete, check the management depth, remove the local conduit, and keep the 1.5-2m conduit for management. When hooking the cage, the catheter should be lowered, and then lifted up after rotating and shifting the hook.


9. Broken pile


After the concrete is solidified, it is discontinuous, and the intermittent piles filled with loose vegetables such as washing liquid and mud in the middle affect the integrity of the pile itself, reduce the strength and bearing capacity of the pile, and even fail to meet the design requirements.


Cause analysis; formulas with large slump loss and discontinuous pouring process are important reasons for broken piles. During the pouring process, buried pipes, stuck pipes and other situations will cause piles to break; 1) Buried pipes: the pipes are buried in the concrete If the middle burial is too long, the reinforcement cage is deformed, the pouring time is too long, the concrete has initially set, the internal resistance has doubled, and the conduit is stuck in the concrete; the flange plate is against the lower end of the reinforcement cage. Due to the large inclination of the hole, the frictional resistance between the cage and the hole wall is too large, and there is a certain height of concrete in the cage, so that the catheter cannot be lifted; ② stuck pipe: the aggregate gradation is unreasonable, containing large-sized pebbles and boulders; The time or transportation distance of the concrete mixing machine is too long, and the partial initial coagulation phenomenon of segregation has occurred and it is directly used for perfusion, the conduit is poorly sealed, and local water leaks.


10. Collapse


During the pouring process, if it is found that the mud level in the wellbore casing slurry suddenly rises and overflows the casing, and then plummets and bubbles emerge, it should be suspected that it is a sign of hole collapse, which can be detected with a sounding hammer. If the sounding hammer was originally suspended on the surface of the concrete and has not been taken out, it is buried and cannot be lifted up, or the sounding hammer cannot reach the original depth when detecting the concrete surface, and the difference is very large, which can be confirmed as a collapsed hole.


The cause of the collapsed hole may be water leakage around the foot of the casing, the water level in the hole decreases or in tidal rivers, the water level difference in the hole decreases when the tide rises, the original hydrostatic pressure cannot be maintained, and due to the stacking of heavy objects around the casing or the vibration of the machine etc. can cause collapse. After the collapse of the hole, the cause should be identified, and corresponding measures should be taken, such as maintaining or increasing the water head, removing heavy objects, eliminating vibration, etc., to prevent the hole from continuing to collapse, and then use a suction dredge to suck out the soil that has collapsed into the hole. Continue to collapse the hole to restore normal perfusion. When the collapsed hole is not serious, it can be backfilled to the position above the collapsed hole, and measures such as improving the mud performance, increasing the water head, and burying the deep casing can be taken to continue drilling. When the hole collapse is serious, all the drilled holes should be backfilled with sand or small gravel sandwiched with clay immediately. When the collapsed hole is not deep, the method of deep burying of the casing can be adopted, and the surrounding area of the casing can be re-drilled.


11. The hole body is skewed


When the hole body is deflected or bent, the reasons should be analyzed and dealt with. Generally, the drill cone can be hung at the deviation to sweep the hole repeatedly to make the hole straight: when the deviation is serious, the clay soil should be backfilled to the deviation, and then drilled after the sediment is compacted.


12. Holes, shrinkage holes


In case of reaming and shrinking, measures should be taken to prevent the collapse of the hole and prevent the drill cone from swinging too much. The shrinkage hole is caused by excessive wear of the drill cone, untimely welding and repairing, or due to the soft ten and stick seven mudstones that expand in contact with water in the formation. The former should pay attention to welding and repair the drill cone in time, and the latter should use high-quality mud with a small water loss rate. retaining wall. When shrinkage has occurred, it is advisable to use a drill to sweep the hole up and down repeatedly to expand the hole diameter.


13. Paste drilling, buried drilling


Paste drilling and buried drilling often occur in rotary drilling and percussion drilling in positive circulation (including submersible drilling rigs). In this case, the mud consistency, the inlet and outlet of drilling slag, the inner diameter of the drill pipe, and the slag discharge equipment should be checked and calculated, and the appropriate footage should be controlled.


14, stuck drill


Sticking often occurs in percussion drilling. After sticking, it is not advisable to lift it only lightly. When the light lift does not move, it can be impacted with a small impact drill cone or the drilling slag around the drill cone can be loosened by means of punching and suction before lifting.


15. Drop the drill


When the falling objects are dropped, it is advisable to use fishing forks, hooks, rope sets and other tools to salvage quickly. Assuming that the falling objects have been buried by sediment, the sediment should be removed first according to the above-mentioned items, and the salvage tools should be brought into contact with the falling objects before salvaging. In any case, it is strictly forbidden for construction personnel to enter the borehole without a casing or other protective facilities to deal with the fault. When it is necessary to drill down the protective tube or other protective facilities, check that there is no harmful gas in the hole, and prepare safety facilities such as anti-virus, anti-drowning, anti-slump and burial before action.

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