1. Inspection and correction of steel sheet piles
Steel sheet piles used for temporary support of foundation pits are inspected for surface defects, length, width, thickness, height, end rectangularity ratio, straightness, and lock shape, and welding parts on the piles that affect the installation are removed. (If there are cut holes and section defects, they should be reinforced). If there is severe corrosion, measure the actual thickness of the section and reduce it.
Correction methods include:
1) Surface defect correction: First clean the rust and oil stains on the surface near the defect, then use the welding repair method to fill it up, and then use a grinding wheel to smooth it.
2) Correction of the end rectangularity ratio: Use oxyacetylene to cut the pile end to keep it perpendicular to the axis, and then use a grinding wheel to smooth and repair the cut surface. When the amount of dressing is not large, use the grinding wheel directly for repair.
3) Pile body deflection correction: Ventral bending correction is to fix the two ends of the curved section of the steel sheet pile at the supporting points, and use a jack on the gantry-type top beam frame to perform cold bending correction on the convex part of the steel sheet pile; side Correction of lateral bending is done on a special correction platform. The two ends of the bent section of the steel sheet pile are fixed on the correction platform supports. Jacks are set at a certain distance on the correction platform on the side of the bent section of the steel sheet pile. Use the jacks to press the convex part of the steel sheet pile for cooling. Bend correction.
4) Correction of pile distortion: Depending on the distortion, the method in (3) can be used to correct it.
5) Correction of local deformation of the pile section: local deformation is corrected using a combination of jack pressure, sledgehammer knocking, and oxyacetylene flame heating.
6) Correction of lock mouth deformation: Use standard steel sheet piles as lock mouth shaping molds, and use a slow-speed winch to pull and adjust or use oxyacetylene flame baking and sledgehammer knocking to push the mold for straightening treatment.
2. Guide frame installation
The guide frame is composed of guide beams and purlin piles. It is divided into single-sided and double-sided in plane; single-layer and double-layer in height. This project uses a single-layer double-sided guide frame. The distance between purlin piles is 2.5~3.5m, and the distance between double-sided purlins is 8~15mm thicker than the thickness of the sheet pile wall. The position of the guide frame cannot collide with the steel sheet pile. Purlin piles cannot sink or deform as the steel sheet piles are driven. The height of the guide beam should be appropriate to help control the construction height of steel sheet piles and improve work efficiency. Use a theodolite and a level to control the position and height of the guide beam.
3. Selection of pile-sinking machinery
Use a vibrating hammer to drive steel sheet piles. Set a pile cap between the pile hammer and the steel sheet pile to evenly distribute the impact and ensure that the top of the pile is protected from damage.
4. Steel sheet pile driving
To ensure the accuracy of steel sheet pile driving, the screen driving method is adopted. First, use a crane to lift the steel sheet pile to the pile insertion point for insertion. When inserting the pile, the lock mouth should be aligned. After each piece is inserted, put on the pile cap and hammer gently. During the piling process, to ensure verticality, two theodolites were used to control the pile in two directions. To prevent the plane displacement of the center of the lock, a clamping plate is installed at the lock of the steel sheet pile in the direction of the piling to prevent the displacement of the sheet pile. At the same time, the position of each plate is calculated in advance on the purlin so that it can be checked and corrected at any time. The steel sheet piles were driven several times, the first time from 20m to 15m, the second time to 10m, the third time to the guide beam height, and the fourth time to the design elevation after the guide frame was removed. When piling, start driving the first and second steel plates. The driving position and direction must be accurate and measured every 1m of driving.
1) Requirements
①Steel sheet piles are suitable for supporting structures with shallow burial depths.
②Steel sheet pile driving is suitable for weak strata such as clay soil, sand, and silt.
③ Before constructing steel sheet piles, piles should be tested first, and the number of test piles should not be less than 10.
④ During the setting-out construction of steel sheet piles, the pile heads must be correctly and vertically positioned. During the pile-sinking process, they should be inspected at any time to detect problems and deal with them promptly. The allowable deviation of pile sinking: the plane position is 100mm in the longitudinal direction and -50mm to 0mm in the lateral direction; the verticality is 5.
⑤ Before pile driving, underground, ground, and high-altitude obstacles must be cleared away, and underground pipelines that need to be retained should be dug out and protected.
⑥ After excavation of the foundation pit, the steel sheet piles are vertical and smooth, with no serious distortion, tilt, or splitting, and the lock joints are tightly connected.
⑦ During the construction of the foundation pit earthwork and structure, dynamic observation of the surrounding rock and support system of the foundation pit shall be carried out. Discover problems and deal with them promptly.
2) Impact pile sinking
① For impact pile sinking, pile sinking machinery is selected based on the number of piles driven and construction conditions, and operation and construction are performed according to technical performance requirements.
② Inspect steel piles before use. If they do not meet the requirements, they should be repaired. Holes for hanging plates are drilled behind the reinforcing plate at the upper end of the steel pile. Apply oil to the lock mouth of the steel sheet pile, plug the lower end with a removable object, and conduct a passing test using the 2m standard.
③A single I-shaped steel pile is sunk, and the steel sheet piles are sunk using the purlin method to ensure that the wall surface is vertical and smooth.
④ The purlin piles of the steel sheet pile purlin support must be vertical, the purlin horizontal, and the setting position must be correct, strong, and reliable. The height of the purlin supports should be no less than 5m above the ground; the distance between the lowest purlin and the ground should not be greater than 50cm; the clear distance between purlins should be 8-15mm larger than the combined width of 2 steel sheet piles.
⑤Steel sheet piles are divided into sections of 10-20 pieces. After inserting the purlins one by one, first, drive the positioning piles at both ends and then drive the piles in each group in a stepwise manner in groups of 2-4.
⑥ The steel sheet pile purlin is adjusted and closed within the axis of 10 piles of each of the two pile walls at the corner. If it cannot be closed, the two piles at the corner can be overlapped, and the backside must be waterproofed.
⑦ Before sinking the pile, first stand the steel pile upright and fix it in the pile cap bayonet of the pile hammer, then pull up the pile hammer and hit the I-beam pile into a vertical position or insert the steel sheet pile lock into the adjacent pile lock, and drive 2-3 times Use an empty hammer once, and then lightly hammer to stabilize the pile. Only after checking that the pile position and verticality are correct can the pile be sunk.
⑧ During the pile sinking process, the verticality of the pile should be detected and corrected at any time. The penetration of steel pile sinking shall not be less than 10mm every 20 times. Otherwise, stop the machine for inspection and take measures.
⑨ During the pile sinking process, if the center line of the pile driver guide frame is found to be deflected, it must be adjusted in time.
3) Vibration pile sinking
① The vibration frequency of the vibrating hammer is greater than the natural frequency of the steel pile. Before vibrating the pile, the pile clamp of the vibrating hammer should clamp the upper end of the steel pile, and the center of gravity of the vibrating hammer and the steel pile should be in the same straight line.
② The vibrating hammer clamps the steel pile and lifts it so that the I-beam pile is vertically positioned or the steel sheet pile lock is inserted into the adjacent pile lock. After the pile is stable, in the correct position, and vertical, it vibrates and sinks again. Every time the steel pile sinks about 1 to 2 mm, the vibration is stopped to detect the verticality of the pile, and if any deviation is found, it can be corrected in time.
③ The number of vibration-sinkable steel sheet pile test piles shall not be less than 10.
④ If the sinking speed of the steel pile suddenly decreases during pile sinking, pile sinking should be stopped, the steel pile should be pulled up 0.6 to 1.0m, and then sink rapidly again. If it still cannot sink, other measures should be taken.
4) Static pressure pile
① When the pile driver drives the pile, the center lines of the pile cap and pile body must coincide.
② Check the verticality of the pile body at any time during the pile pressing process. During the initial pressing process, if it is found that the pile body is displaced or tilted, and the pile body suddenly tilts during the pressing process or the equipment reaches the rated pressure and continues for 20 minutes, but still cannot sink, take timely measures. measure.
5. Removal of steel sheet piles
When backfilling the foundation pit, pull out the steel sheet piles, trim them, and reuse them. Before removal, pay attention to the removal sequence, time, and pile hole treatment method of steel sheet piles. Certain vibrations will occur when pulling out piles. For example, pulling out piles and then carrying too much soil will cause soil displacement and ground settlement, which will cause harm to the constructed underground structures and affect the normal use of adjacent buildings, roads, and underground pipelines. The steel sheet piles are removed using a vibrating hammer and a crane. The latter is used for steel sheet piles that cannot be pulled out by the vibrating hammer. A hanger is installed on the steel sheet pile, and the crane pulls it upward while the vibrating hammer vibrates. The vibrating hammer generates forced vibration, destroying the bonding force between the sheet pile and the surrounding soil, and relies on the additional lifting force to overcome the resistance of the pile to pull out the pile. When pulling out piles, first use a vibrating hammer to vibrate the lock mouth to reduce the bond with the soil, and then pull out while vibrating. For piles that are difficult to pull out, you can use a diesel hammer to vibrate first, and then use a vibrating hammer to vibrate and pull out alternately. To backfill the pile hole in time, when the pile is pulled out to a height slightly higher than the foundation floor, stop pulling out and use a vibrating hammer to vibrate for a few minutes to fill the soil hole. The pile holes produced by pile extraction can be backfilled in time using the vibration method, squeezing method, and filling method to reduce the impact on adjacent buildings.
1) Pile extraction construction shall include as-built drawings of pile-sinking plane layout; pile-sinking records; as-built drawings of underground pipeline restoration and original pipeline distribution drawings near pile locations.
2) Before pulling out piles, remove and relocate high-altitude obstacles, and level and consolidate the working site. Build temporary transportation roads, set up power and lighting lines, remove piles of soil near pile heads, overhaul machinery and equipment, and formulate construction plans.
3) To extract piles, use a vibrating pile extractor and a crane, and comply with the following regulations:
① Before pulling out the pile, use the chuck of the pile puller to tighten the pile head so that the pulling line coincides with the center line of the pile;
② Loosen the hook slightly when pulling out the pile. After the vibration machine vibrates for 1-1.5 minutes, tighten the hook as the amplitude increases and slowly lift;
③ When the steel sheet pile reaches its height and can be lifted directly by a crane, the vibration will stop. When several steel sheet piles vibrate at the same time, use a falling hammer to break them up;
④ Lift out the vibrated steel pile in time, and the lifting point must be more than 1/3 of the pile length;
⑤ During the process of pulling out piles, observe the lift of the crane’s tail at any time to prevent overturning;
⑥Try pulling out the steel sheet piles one by one, and pull out the easy-to-pull piles first. When pulling out, use the falling weight to vibrate downward a little, and then pull out again after the lock is loose;
⑦ After the steel plate is pulled out, the pile hole should be filled with sand in time.
4) During pile extraction, if the operation method is correct, the amplitude of the pile extraction machine reaches the maximum load, and the pile cannot be pulled out after 30 minutes of vibration, stop the vibration and take other measures.
5) When pulling out piles near underground pipelines, the pipelines must be protected, and machinery must not operate on them.
6) The pulled-out steel piles are trimmed and straightened by the cold bending method before use.
Post time: Apr-30-2024