The pipe pile foundation is a deep foundation that connects the tops of several piles into a whole through a cap to jointly bear dynamic and static loads, while the pipe pile is a vertical or inclined foundation member set in the soil, and its function is to pass through the weak foundation. The highly compressible soil layer or water transfers the load of the pipe pile to the harder, denser or less compressive foundation bearing layer. We usually refer to the pile in the pipe pile foundation as the foundation pile. With the improvement of production level and the development of science and technology, the type, technology, design theory, calculation method and application scope of pile foundation have been greatly developed, and are widely used in high-rise buildings, ports, bridges and other projects.
In the process of pile driving, the top of the pipe pile is prone to concrete drop angle, cracking, collapse or even the steel bar on the top of the pile is completely exposed and damaged. What are the reasons and preventive measures for this phenomenon?
Reason:
1) Factors such as engineering geological conditions and construction equipment were not considered in the design, the design strength of the concrete was low or the reinforcing mesh on the top of the pile was insufficient, and the distance between the main reinforcement and the top surface of the pile was small. When the pile is prefabricated, the concrete mix ratio is poor, the construction control is not strict, and the vibration is not compact. The concrete curing time is short, and the curing measures are improper, so that the steel bar and the concrete cannot work together under the load, and the top of the pipe pile is prone to rupture.
2) The top surface of the pile is not flat, the plane of the top of the pile is not perpendicular to the axis of the pile, and the protective layer of the pile is too thick.
3) The contact surface between the pile top and the pile cap is not flat, and the pile is not vertical when it sinks, which makes the top surface of the pile inclined, causing the top surface of the pile to be partially broken by concentrated stress.
4) When the pile is driven, the pile top is not lined or the liner is damaged and not replaced in time, so that the pile top directly bears the impact load. If the hammer weight is not selected properly, the pile hammer is small, the pile top is hit many times, and the pile top concrete is prone to fatigue damage.
Precaution:
1) If it is a shallow broken pile and can be treated by simple precipitation, the best and most economical method is to excavate or deal with caisson;
If it is a deep broken pile, there are two solutions. One is to discuss with the design or testing to expand the upper diameter to meet the bearing capacity requirements. This is nothing more than a concrete problem;
2) Use rotary jet pile treatment.
When the pile is made, it is required to be vibrated and compacted, and the main feed should not exceed the first layer of mesh. After the pile is formed, the maintenance should be strictly strengthened. After reaching the strength of the concrete member, a natural curing period of one to three months should be used to increase the resistance of the pile top ability to impact.
3) The pile hammer should be selected reasonably according to the engineering geological conditions, the size and shape of the pile section. When piling, the components should be checked to check whether the top surface of the pile is convex or concave, whether the plane of the top of the pile is perpendicular to the axis of the pile, and whether the tip of the pile is skewed. Check whether the contact surface between the pile cap and the pile and whether the replacement wood is flat, if it is not flat, it should be dealt with. The stabilizing pile should be vertical, the pile top should be added with a pile pad, and the pile pad should be replaced in time if it is damaged.
