Technical measures to prevent and cure common housing quality problems: foundation foundation
1. Design
1. Before designing the cement-soil mixing pile, the weakest site to be treated should be selected Conduct an indoor mix ratio test on the soil layer to select the appropriate cement content and admixtures.
2. The concrete strength grade of cast-in-place piles should not be less than C20. When pouring concrete underwater, it should not be less than C30. The length of the steel cage of cast-in-place piles should be set strictly in accordance with the specifications, and plain concrete cast-in-place piles should not be used.
3. Prestressed concrete pipe piles should be given priority to prestressed high-strength concrete pipe piles (PIIC) and prestressed concrete pipe piles (PC). Prestressed concrete pipe piles should not be used in soft soil foundations or projects with basements. Condensation: 1: Thin-walled pipe pile (PTC).
4. Buildings with design grades of Class A and Class B should be designed according to foundation deformation. For Class C buildings, when the characteristic value of the foundation bearing capacity is less than 130kPa, buildings with complex shapes, building pile foundations built on weak foundations with eccentric loads, and friction-type pile foundations should be subject to settlement verification. The final average settlement of the foundation of the first-level building shall not be greater than 60mm, and the final average settlement of the pile foundation of the second-level building shall not be greater than 150mm. The uneven settlement value must be controlled within the allowable range of the specification
II. Construction
1. The compaction coefficient of each layer of cushion layer must be tested, fumigated and passed After testing to meet the design requirements, the upper layer of soil will be laid and filled.
2. Before the construction of the cement-soil mixing method, when there are open shores, ponds, hidden ponds, or hidden ditches, water should be pumped and dredged, and viscous materials should be backfilled and compacted in layers. Miscellaneous fill soil or domestic waste should not be backfilled. Rubbish.
3. The over-grouting of the top concrete of cast-in-place piles should be more than 50cm higher than the design elevation of the pile top. When pouring concrete with water, the top concrete elevation of the pile should be 5% higher than the pile length of the design elevation, and it must not be Less than 1.5m, ensure that the strength of the pile top concrete after removing the laitance meets the design requirements.
4. During the underwater pouring of concrete, the initial pouring amount should ensure that the conduit is buried to a depth of o. Above 8m, the buried depth of the conduit should be controlled at 2-6m. It is strictly prohibited to pull out the concrete surface. Concrete pouring must be continuous, and a dedicated person should measure and record it.
5. For pile group foundations of immersed tube cast-in-place piles in soft soil foundations and pile foundations with pile center distances less than 4 times the pile diameter, technical measures such as jump driving should be taken to ensure the quality of adjacent pile bodies.
6. When hoisting the reinforced cage of bored piles, it should avoid collision with the hole wall and should be fixed immediately after being in place; after the sediment at the bottom of the hole is retested and meets the requirements, it should be poured immediately within 0.5 hours. Concrete.
7. No soil should be piled up at the entrance of the human digging pile hole, and no collision with the hole wall when hoisting the steel cage and string tube: when the design elevation is reached, the slag should be cleaned and drained immediately. After acceptance, the Immediately seal the back and pour concrete.
8. The vertical deviation of prefabricated piles shall not exceed 0.5%. When connecting piles, the pile centerline deviation should be less than 5mm, and the node bending sagittal height should not be greater than 1‰; for welded joints, the rest time after welding should be greater than 8 minutes. When sulfur clay piles are bonded, the clay pouring time should be less than 2 minutes, and the rest time after pouring should be greater than 7 minutes.
9. During foundation pit excavation, when encountering unstable soil (trough) conditions such as weak soil, groundwater seepage, or deep excavation, support first and then excavate. It is strictly prohibited to damage engineering piles, supporting structures, etc. during mechanical excavation. The foundation pit must be
10. When cutting piles manually, the pile cutting should be carried out in two steps. A small hammer should be used to repair the pile within a range of about 30cm above the pile top. The anchorage length of the pile top concrete should meet the design requirements on the premise of ensuring that the strength of the pile top concrete meets the requirements.
11. For basement exterior wall panels or structures with waterproofing requirements, if butt-bolts are used for pouring concrete support forms, waterstops should be welded, and on the side formwork: wood blocks with a lining thickness of more than 20mm , remove the wooden pad after removing the formwork, cut off the bolts in this section, and seal it with waterproof cement mortar. The deformation observation of buildings should be entrusted to a professionally qualified measurement unit. Civil buildings should be observed once after each floor is completed, and the settlement rate is ≥ 2. When Omm/d, the loading speed should be slowed down and the number of observations should be increased.
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