Before laying, it is necessary to thoroughly remove grease, paint, sealing materials, water stains and dirt that may affect the bonding strength between the geogrid and the bottom layer to make the laying surface clean and dry. The pressure-sensitive back of the plastic geogrid is a water-soluble substance. If there is water on the road, it must be watered after the road is dry. Before laying the grid, the adhesive layer of oil must be sprayed. If emulsified asphalt is used as the adhesive layer oil, the grill should be placed after the emulsifier is fully emulsified and dried.
1. Sinking pipe: After the pile driver is in place, the verticality of the sinking pipe must be stabilized and adjusted to ensure that the deviation of verticality does not exceed 1%. Start the motor and start sinking the pipe. Pay attention to adjusting the stability of the pile driver when sinking. Tilting and dislocation are strictly prohibited, and remember to make construction records during the soaking period.
2. Feeding: After sinking the pipe to the design height, feed it as soon as possible until the surface of the mixture in the pipe is flush with the inlet of the steel pipe. If the amount of the above-mentioned materials is insufficient, the material must be poured into the hollow when the pipe is pulled out to ensure that the height of the pile top meets the design requirements. The mixing ratio should strictly abide by the design regulations, and the thickness of the pile top floating slurry after pile driving should generally not exceed 200mm. Stir evenly, and the stirring time is not less than 2 minutes.
3. Construction sequence: Before construction, the original surface and slope should be cleaned and leveled. After excavation, backfill and compaction, roll to the original surface, and then carry out ordinary concrete pile construction. The elevation of the pile top is 25cm lower than the ground, which is convenient for platform construction. The construction of ordinary concrete piles should start at the foot of the old slope, and then tilt the pile outwards until the roadbed is filled to the height of the pile top. The pile driver is used for pile driving row by row. During the construction period, the interval between two adjacent piles shall not exceed the initial solidification time of the mixture, so as not to affect the strength of the mixture.
4. Broken neck pile: When pile driving in soft soil, the vibration force of pile driver is small. When using continuous pile driving, the main effect of the new pile on the pile is squeezing, and the geogrid makes the pile squeeze into an oval or irregular shape, which seriously causes the pile neck to shrink and break. In order to avoid this phenomenon, whether it is piling in saturated soft soil, hard soil or in the foundation between hard soil layers, appropriate piling sequence should be selected.
5. Uneven pile strength: the pile crane hoisting system raises the sinking pipe too fast, which may cause the neck to break. Extrusion is too slow or the vibration holding time is too long, resulting in a decrease in the cement content of the pile tip, excessive floating of the pile top, and easy separation of the mixture, resulting in uneven strength of the pile body. During the construction process, the drawing speed should be strictly controlled within the range of 1.0~1.2m/min, always maintain uniformity, and the vibration retention time should be well controlled.
6. Key points of construction inspection:
① Process inspection: The quality inspection of the construction process mainly checks construction records, mixture slump, pile number, pile position deviation, pile top elevation, and pile compressive strength. Allowable deviation of the pile position: 0-50mm, the pile inclination is not more than 1%, and the effective diameter of the pile is not less than the design value.
②Quality inspection after construction: During pile inspection and pile formation, samples are taken to collect mixed test blocks, and each pile machine is manufactured by the team
③150mm×150mm×150mm test block, standard curing, compressive strength test for 28 days. Take no less than 10% of the total number of piles to conduct a low-strain dynamic test to check the integrity of the pile.
7. Pile foundation detection method.
When the strength of the ordinary concrete pile meets the test load conditions, the low strain reflected wave method is used to test the quality of the pile. Analyze the integrity of the pile body, determine the location and influence of the pile body defects, and judge the pile end embedding.