I. Introduction
This article documents the process of demolishing an old dam. Since part of the old structure needs to be retained for use after the demolition, a combination method of diamond wire saw and floating crane was adopted. This plan was reviewed by experts, with the main idea being to ensure that the weight of each dismantled component does not exceed 30 tons.
II. Introduction to the Demolition of the Working Bridge
The working bridge was mainly dismantled using a floating crane with an 80-ton lifting capacity. The working bridge is a simply supported beam, and the method used was direct lifting, as shown in the figure below.
According to calculations using REVIT, the volume of the working bridge is 5.18 cubic meters, with a weight of approximately 12.95 tons, which meets the requirement of not exceeding 30 tons.
During the demolition of the lower structure of the working bridge, a diamond wire saw was used for cutting. The following figure shows the process of lifting the lower structure with a floating crane while cutting is underway. Although the photo is taken from a distance, the diamond wire saw machine can be seen, and water is being poured for cooling during the cutting process. Detailed information on diamond wire saw cutting will be provided later in this article. The volume of the lower structure of the central pier working bridge is less than 1 cubic meter, and the lower structure of the seam pier is even smaller.
The following figure marks the position of the diamond wire saw machine during the lifting of the lower structure of the working bridge.
Due to site access limitations, the dismantled lower structure of the working bridge was placed on a transport ship to be removed from the site.
III. Demolition of Gate Pier Framework
1. Calculation of Lifting Objects in Sections The volume of the central pier structure to be demolished is 35.823 cubic meters, with an estimated weight of 89.558 tons. It is divided into three sections, each controlled to be within 30 tons.
2. Lifting Straps Operators first installed lifting straps on an aerial lift vehicle. Despite the backlight in the photo, the process can still be seen.
The following image shows a clearer view of the strap installation process. Due to the difficulty of operating at height, the method of threading the straps was changed after the first lift.
The following image shows the process of tying and lifting, with the first section of the gate pier framework already removed.
To improve efficiency, lifting holes were later drilled into the structure, as shown below. This method significantly increased threading efficiency.
The image below shows each dismantled section with two lifting holes, making the threading operation much easier.
3. Cutting The following image shows the framework before cutting, with each beam cut into three sections using a diamond wire saw. The diamond wire saw, similar to a saw for wood, can cut through concrete structures without damaging the remaining parts.
The diamond wire saw operates by driving a diamond chain through a machine. The chain is guided by pulleys to ensure directional cutting. The following image compares the size of the diamond wire saw chain to a hand. During the cutting process, the chain is automatically tightened by the machine.
Here, guide wheels are used, fixed to the structure wall with M14 expansion bolts.
The following image shows the cutting process, with all parts labeled. The diamond wire saw machine does not need to be at the same height as the cutting plane; it can be above or below it. Guide wheel installation can also achieve vertical and underwater cutting. If the chain cannot wrap around the structure to be cut, holes can be drilled for threading the wire, allowing flexible handling of various situations.
The image below shows water being sprayed during the cutting process. Spraying water cools the chain and reduces dust, which is essential for maintaining clean cutting operations. If there are requirements for the straightness of the cut surface, additional relay guide wheels can be added.
IV. Conclusion
The demolition process mainly utilized the diamond wire saw and floating crane. Due to site constraints, the floating crane, despite its high cost, was chosen. The following image shows the performance parameters of the 80-ton floating crane.
The efficiency of fili diamond wire saw cutting is generally calculated based on the area of the cutting surface, with a typical rate of 2 to 3㎡/h.