In pile foundation construction, the positioning of reinforcement cages plays a crucial role in engineering safety and quality control, and solving the problem of deviation has always been a challenge. Below, we share two engineering cases to see how on-site construction personnel brainstormed and used simple and practical methods to solve the deviation problem of reinforcement cages!

Two Methods for Positioning Reinforcement Cages

Method 1

Clever Use of "Mineral Water Bottles"

In practical construction, the reinforcement is mostly below the mud, making it impossible to measure and correct visually. To improve pile quality, meet construction requirements, and reduce losses from later quality problem handling, project members from the Ninth Company of CCCC Fourth Highway Engineering Co., Ltd., through continuous practice and active attempts, summarized a positioning guarantee measure for reinforcement cages: the "buoy positioning and lifting bar recheck dual-control method." After using this method, the deviation qualification rate of reinforcement cage quality was controlled at 100%. Technicians who had never seen this method all commented: This is truly an achievement of the working people in practice; this method should be applied in production!

A self-made buoy is hung at the center of the flat cross-section of the reinforcement cage. By adjusting the length of the lead wire, the buoy is adjusted so that after the reinforcement cage is installed, the buoy can be exposed above the mud surface, thereby accurately determining the position of the reinforcement cage. Under the action of gravity, theoretically, the center of the lifting bar and the centroid of the reinforcement cage are in a vertical coincident state, which can verify the accuracy of the buoy. This achieves the purpose of calibrating the reinforcement cage.

1. Making the buoy

The raw materials for the buoy are readily available; mineral water bottles or any floatable object with a findable center point can be used. The buoy can be made from a "CCCC Blue" mineral water bottle, because the exact center of the character "交" on the bottle is the exact center of the bottle cap, and the protruding position at the bottom is the exact center of the bottom. Then drill a hole in the center of the bottle cap, thread the construction line through the hole, mark the center position on the bottle bottom, and the buoy is completed.

2. Calibration of the buoy

After the buoy is made, find a container on site, such as an 18L hydraulic oil drum, place the drum on flat ground, find the center position of the drum opening, then use a plumb bob to mark the center position of the drum opening onto the drum bottom, then fill it with water, adjust the length of the buoy lead wire to match the depth of the drum, then install the buoy lead wire to the mark at the bottom of the drum, and measure the difference from the center line at the top of the drum. If it is less than 5mm, it can be used; if it exceeds the limit, discard it. Since calibration is relative, it is recommended to make and calibrate several spare buoys each time.

3. Installation of the buoy

After the reinforcement cage is connected and lowered to expose the reinforcement that should be exposed, find the pile top position on the reinforcement cage, locate the radial reinforcement, use construction lines to make a cross line, and then connect the buoy lead wire to the intersection of the cross lines. Leave some extra lead wire at the bottle cap for adjusting the buoy. After lowering the reinforcement cage to the design elevation, use a plumb bob (a heavy object can be used) to project the center point recovered from the cross line of the protective piles onto the buoy. If the error is within 10mm, proceed to the next process. If it exceeds the limit, adjust repeatedly with a crane until qualified.

4. When installing lifting bars

Keep the two lifting bars in the same diameter direction. When lowering the reinforcement cage, ensure the lifting bars fall vertically and bear load in pairs. Then measure the center line in the direction of the lifting bar connection line and recheck again. Recheck with the buoy result to avoid human error caused by human operation (wrong cross line hanging).

The application of the buoy method makes it easier to adjust pile foundation deviation problems, making pile foundation quality more controllable. The next construction process can be implemented as planned without affecting the scheduled工期 due to deviation problems. Perhaps there will be more accurate and simpler methods in construction, which requires us to summarize, explore, research, and innovate during construction. Continuous optimization and innovation of technology are the blood of construction; only by continuous updating can it become healthier and higher quality.

Method 2

Self-made "Positioning Tool"

For the positioning of pile foundation reinforcement cages, currently, reinforcement is mostly welded onto the reinforcement cage on site. If the casing is inclined during construction, it will cause the reinforcement cage to deviate with the casing, and in most cases, the positioning reinforcement is below the mud surface, making it difficult to verify the actual deviation.

To further improve the qualification rate of center positioning of pile foundation reinforcement cages and effectively ensure the thickness of the protective layer of the reinforcement cage, Sichuan Road & Bridge Highway Tunnel Company developed a pile foundation reinforcement cage positioning device for the TSEPC-1 section of the G0611 Tongren to Serlong Highway, namely the welded-free hydraulic telescopic positioning device for reinforcement cage installation. It uses welded-free hydraulic telescopic positioning to replace welded positioning of pile foundation reinforcement cages. It not only effectively solves the common problems in traditional reinforcement cage positioning and ensures that the actual center point fully coincides with the theoretical center point, but also guarantees construction quality. It is safe, reliable, simple, and practical.

Inside the positioner and effect diagram

The welded-free hydraulic telescopic positioning device for reinforcement cage installation adopts a hydraulic cylinder system and consists of hinged telescopic rods, handles, double guide tubes, and slider rods. The hydraulic telescopic long rod is fixed to the double guide tubes, and the hydraulic telescopic short rod is hinged to the moving piston. The hydraulic stroke of the jack and the slider form a hydraulic oil circuit. When the jack hydraulic oil is lifted, a seal is formed inside the tube, and the pressure increase inside the tube pushes the slider rod to move up or down, driving the hydraulic telescopic rod to rotate, thereby forming a hydraulic telescopic device. This device is suspended on the casing at the hole opening and uses the three-point positioning method to determine the center plane position of the pile foundation. Therefore, it is suitable for all pile foundation types. Through the hydraulic telescopic rod, it can ensure accurate and precise positioning within a range of 10-30cm, making construction convenient.

Three-point positioning principle

◆Hydraulic telescoping can achieve an adjustment value of 5-30cm, achieving precise positioning;

◆During pile pouring, the reinforcement cage deviation caused by concrete disturbance can be repositioned, achieving dynamic adjustment of positioning;

◆The horizontal bar of the positioning device supports the main reinforcement, achieving multi-point positioning;

◆The welded-free positioning process achieves zero damage to pile foundation reinforcement;

◆Greatly improves the protective layer of pile foundation reinforcement;

◆The device is lightweight, can be lifted and operated with one hand, easy to install, convenient to disassemble, has good durability, and can be reused.

On-site construction assembly and application of the positioner

The welded-free hydraulic telescopic positioning device for reinforcement cage installation has low research and manufacturing costs and is suitable for all types of pile foundations. It not only reduces the installation cost of reinforcement cages but also improves installation efficiency, further achieving cost reduction and efficiency increase.