Key points of construction supervision of high-strength prestressed concrete pipe pile?

PHC Piles of Prestressed Concrete Pipe Piles I. Characteristics and Scope of Application of High-strength Prestressed Concrete Pipe Piles (PHC Piles) Characteristics of PHC Piles 1. 1 PHC Piles have the lowest unit bearing capacity cost among all pile types, and the comprehensive economic benefit index is superior to other pile types. The ability of bamboo piles to penetrate the soil layer is particularly strong, which adapts to the geological conditions with large fluctuation of bearing layer; The quality of finished piles is reliable, which is convenient for supervision and inspection; Short construction period; Low noise, no vibration, no pollution, in line with environmental protection requirements. However, the ductility of PHC piles is poor, and brittle failure will occur when the ultimate load is exceeded. Moreover, there is no professional manufacturer in Guangxi, and it must be ordered from Guangdong. 1.2 scope of application PHC piles have a wide range of applications and are suitable for areas covered by artificial fill, soft soil, cohesive soil, silt, fine sand and medium sand. The bearing stratum is generally coarse sand, gravel sand, round gravel and weathered rock, and the depth of human soil stratum is generally 10m~70m.

Second, the supervision points of high-strength prestressed concrete pipe pile construction 2. 1 Supervision control Check the construction site and adjacent underground pipelines such as high-voltage cables and communication lines before construction; Study the engineering geological report, pile location layout and pile foundation structure construction drawing; Review the qualifications of the main technical personnel of the contractor; Review the contractor's construction organization design or construction technical scheme; Check the certificate of prestressed pipe pile, check the appearance of pipe pile, check the diameter, wall thickness, length and production date of pipe pile; Check the power supply capacity of the standby power supply; Review the layout of surrounding settlement observation points.

2.2 The supervision control in the construction process should review the survey setting-out, pile location and elevation control; When sinking piles, check the welding quality of pile extension. Linearity and verticality control of piles. The welding of the joint should be symmetrical, the weld seam should be full, the welding time should be properly controlled, and the pile sinking can continue only after the welding is completed and it must be naturally cooled for 5min~ 10min; After pile sinking is in place, check whether the number of oil pressure gauges reaches the predetermined value and whether the final pressure times meet the design requirements; Organize the design institute, quality supervision station, Party A and the construction party to confirm the number and pile number of static load test and dynamic load test; Review the construction technical scheme of earthwork excavation; In the process of earthwork excavation, the supervisor must cooperate with the class inspection to deal with the problems in construction in time.

2.3 After pile recompression is completed 15d, conduct controlled static load test and post-construction dynamic test; Review the pile sinking records, concealed works records and pile location layout submitted by the construction party; Organize relevant units to carry out pipe pile acceptance; Organize the quality evaluation of pile foundation engineering.

Three. Technical problems about PHC pile construction 3. 1 Pre-drilling According to the geological conditions in Guangxi, in order to reduce the soil squeezing effect and facilitate crossing the thick sand layer, pre-drilling can be carried out to borrow soil during construction. For pile groups with large pile spacing, holes can be drilled at intervals or not, but pile lifting should be avoided.

3.2 Selection of final pressure value of pile pressing The final pressure value of pile pressing shall be twice the design value of vertical bearing capacity of single pipe pile, but the final pressure of pile pressing can be appropriately increased during construction. Because the final pressure of construction pile pressing is determined according to the lateral constraint of soil under the instantaneous load of construction (the time of final pressure is only the time when the final pressure controls the penetration). The calculation diagram is close to the axial compression member, and the ultimate pressure of pile pressing can be approximately taken as: P=(0.67R-σce)A0, where r is the compressive strength of concrete cube; σce is the effective prestress value of concrete; A0 is the cross-sectional area of PHC pile. In the process of construction, the supervisor should always check whether the final pressure of pile pressing reaches the preset value or exceeds the limit value. Ensure that each pile meets the design requirements and will not be crushed.

3.3 After all recompression pipe piles sink into place. So as to ensure that the pile bottom does not loosen and expand. A certain number of piles (especially large-area pile groups) must be extracted for recompression, and the pile pressing force can be reduced to the static load test value.

3.4 Construction safety: always check whether the crane cable is in good condition and whether the pipe pile is tied and lifted reliably, so as to avoid personal injury and damage; Always check the safety of electricity, including low-voltage lighting and three-phase five-wire system; Always check the limit switch and explosion-proof switch, and replace them in time if they are damaged; Regularly check and urge workers to use safety helmets and safety belts, and it is forbidden to wear slippers to enter the site; Organize Party A and the construction unit to conduct on-site construction safety inspection from time to time to eliminate potential safety hazards.

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