1, the water bottle
Water on the outer wall of the casing will cause the foundation to sink and the casing to tilt and displace, causing the pile hole to be skewed or even impossible to construct.
Etiology analysis When the casing is buried, the surrounding soil is not dense, or the water level difference of the casing is too large, or the drill bit collides when it rises and falls.
Prevention measures When burying the casing, the bottom of the pit and the surrounding area should be layered and compacted with the best water content; the hole should be opened at the appropriate height to maintain the head height of 1~1.5m in the casing; The tube is initially found to be filled and reinforced with clay when it is in the water. If the casing is severely sunken or displaced, it should be reworked and re-buried.
2, drilling very slowly or not
Drilling in the hard plastic clay layer is extremely slow, generally 8~10h, accounting for 60%~70% of the single pile drilling.
Etiology analysis The improper selection of the drill bit, the installation angle of the alloy tool is not good, the cutting of the tool is too shallow, the weight of the drill bit is too light, and the drill bit is filled with clay.
Control measures Replace or modify the drill bit, re-arrange the tool angle, shape, arrangement direction, increase the weight, strengthen the slag discharge, reduce the mud weight or switch to the drilling mode, and adopt the reverse circulation drilling method.
3. The wall of the pile hole collapses
After forming into holes or forming holes, the walls of the holes collapse to different extents. The mud discharged from the pores continuously appears bubbles, and sometimes the water level in the casing suddenly drops, which is a sign of collapse.
The cause analysis is mainly due to the loose soil, combined with poor mud protection wall; the casing is not well buried, the water level in the cylinder is not high; the drill bit is drilled; if the drill bit is too fast or the idle time is too long, it will easily cause the lower part of the borehole to collapse; The time to be filled and the time of perfusion are too long after the hole is formed.
Prevention measures: Deeply bury the casing in the loose and easy soil layer, compactly backfill the soil, use high-quality mud to increase the specific gravity and viscosity of the mud, raise the casing, replenish the mud after the final hole, maintain the required head height, and ensure the reinforcement of the cage. Quality, to prevent deformation; to align the hole position when hanging, to straighten and stabilize, to sink slowly, to prevent collision of the hole wall; the time to be filled after hole formation generally does not exceed 3h, and accelerate the perfusion rate and shorten the perfusion time as much as possible; In the case where the steel cage is not in the lower hole, the sand and clay mixture is backfilled to the depth of the collapse hole by 1~2m, or the whole hole is backfilled and compacted, and then the original drill bit and high-quality mud are used to sweep the hole; In the case of slight collapse, use a drill with a diameter smaller than the inner diameter of the cage to sweep the hole with high quality mud or clear the hole with a conduit.
4, the pile hole partial necking
Local necking means that the local aperture is smaller than the design aperture.
Etiology analysis mud performance is poor, large water loss. Causing plasticity, soil layer water swelling, or formation of loose, honeycomb thick layer of mud; improper spacing of adjacent piles, the stress in the soil layer has not dissipated, the new pore wall soft soil rheology; the diameter of the drill bit is excessively worn.
The control measures adopt high-quality mud to control the specific gravity and viscosity of the mud, and reduce the water loss; when the design pile spacing is <4D, the pile should be separated by 1~2 piles; the new pile should be drilled as much as possible after the adjacent piles are piled for 36h; Cage drills with environmentally-friendly diameters; sweep holes with mud and foot-sized drills; pour the sputum as soon as possible after sweeping through the clear holes.
5, the pile hole is inclined
After the hole is formed, the pile hole has a large vertical deviation or bending.
Etiology analysis The rig is not installed properly or there is uneven soil under the drill floor to produce uneven subsidence; the pile frame is unstable, the drill pipe guide is vertical, the rig is worn, the components are loose; the casing is buried, the drill pipe is bent, and the active drill pipe is inclined; Underground obstacles such as the old foundation or the big stone, the soil layer is soft and hard, or the bedrock is inclined.
Prevention and control measures The rig is installed with positive, horizontal, stable, and no-bundle leading edge tangent points. The center of the turntable and the center of the casing are three points. The casing is not skewed, the drill pipe is not bent, the active drill pipe is kept vertical, the guide frame is added, and the control is lifted. Leading faucet, use as much as possible to pressurize and pressurize; remove underground obstacles; except soft and hard interfacial layer adopts light pressure and slow rotation technical parameters, from soft plastic clay layer, especially flow plastic clay layer and sand layer into hard plastic clay layer or When entering the bedrock from the clay layer, the cone-guided small drill bit at the lower end of the cage should be changed to a flat-bottomed guide bit, or directly drilled with a flat-bottomed bit without a guide bit; using a sinking hole or a controlled hole pile to remove Underground obstacles; when the hard plastic clay layer is deflected, the sand and soil mixture are backfilled for 1~2m above the deflection. After being compacted, the flatness alloy bit is used to lightly press the slow tilt; when the bedrock surface is deflected It can be used to inject 20~40mm particle size gravel, which is slightly higher than the deflection point. After impact compaction, it is corrected by flat-bottom alloy drill bit, cone roller drill or flat-bottom steel drill bit.
6, too much sediment at the bottom of the hole
The bottom of the hole is drastically silted, the residual mud sand is too thick or the hole wall soil collapses at the bottom of the hole.
Etiology analysis clear pores are not clean, clear pore mud weight is too small or clear water replacement; steel cage hanging is not vertical alignment, touch the scrap hole wall soil collapsed bottom; after clearing the hole to be filled for too long, mud sediment; sediment thickness The measured bottom height of the hole is not uniform.
After the final hole of the control measures, the drill bit increases the bottom of the hole by 10~20cm, keeps the idling at a slow speed, and maintains the cycle clearing time for not less than 30min; the clear hole is made of high quality mud, the specific gravity and viscosity of the mud are not directly replaced by clean water, and the steel cage is vertically suspended. Into the hole; when using a flat-bottomed bit, the thickness of the sediment is calculated from the bottom plane of the hole reached by the bottom of the drill bit; when the bottom bit with a round hammer is used, the thickness of the sediment is calculated from the bottom plane of the hole reached by the bottom of the drill bit; The punching time is determined by the thickness of the bottom sediment measured in the conduit to meet the specification requirements; the impact force on the bottom of the hole during the initial irrigation is increased, the bottom end of the conduit is controlled at 30~40cm, and the initial irrigation volume must meet the conduit. The bottom end can be buried in the crucible for more than 1.0m, and the residual sediment can be washed by the water blocking plug and the crucible.
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