Kajima Corporation (President: Hiromasa Amano) is proceeding with the development of the next-generation mountain tunnel automated construction system 'A 4 CSEL for Tunnel' by dividing it into six construction steps.

Of these, the spraying work requires a reliable spraying thickness and smoothness of the finish, and the skill makes a big difference in the work time and quality. This time, we have applied the 'automatic spraying system' to the complex uneven bedrock surface of an actual tunnel (Hida City, Gifu Prefecture). As a result, it was demonstrated that the technology for automatically spraying concrete smoothly with a high accuracy of +/-20 mm on the sprayed surface between shorings was established.

Development background

We are promoting technological development with the aim of fundamentally solving the pressing problems of the construction industry, namely the shortage of skilled workers, frequent occupational accidents, and low productivity compared to other industries. 'A 4 CSEL for Tunnel' is used for six construction steps in excavation work for mountain tunnel construction: 1. Drilling 2. Charge/blasting 3. Slide out 4. Deburring 5. Spraying 6. Rock bolting It automates and remotes each heavy machinery, generates work plans that match the site environment in real time, and builds the most efficient work algorithms. Regarding the 5. spraying work, in June 2021, we will develop an 'automatic spraying system' that can set the spraying thickness and finish it smoothly as planned in a simulated tunnel in Shizuoka Prefecture. bottom.

However, the actual bedrock has a surface to be sprayed with complex irregularities. Therefore, it was necessary to demonstrate the technology to ensure the finishing accuracy in uneven ground that could not be reproduced in the simulated tunnel.

Outline and result of automatic spraying system

In experiments in a simulated tunnel, a basic nozzle work (nozzle separation distance and nozzle angle with respect to the spraying surface) was constructed to spray the desired spraying thickness on a smooth finished surface with minimal bounce of the sprayed concrete. Did.

On the other hand, it is important to determine the optimum spraying pattern to ensure a smooth finished surface from the shape measurement results by scanning before spraying, which is important for the actual bedrock spraying surface with complex unevenness of the ground. It is a spraying plan to be used and a control program for the machine to perform work according to the plan. The flow from scanning to the start of automatic spraying is as follows.

Scan the area to be sprayed before spraying and measure uneven surfaces

In order to ensure a smooth finished surface, the spraying area is zoned according to the size of uneven steps, and a spraying plan is created.

Input the created plan into the control program of the automatic spraying machine

Start automatic spraying

In the spraying plan, the spraying work is divided into optimal small blocks based on the shape of the target surface, and the spray nozzle movement speed, nozzle angle, and number of sprays are set for each block. By adding a program that can mechanically control these spraying plans, we have made it possible to perform highly accurate automatic spraying even in tunnels under construction.

This time, in an actual tunnel, automatic spraying was performed on the uneven ground shape (red line in the graph), and the sprayed finish surface (green line) between the shoring was sprayed with a standard deviation of +/- 20 mm (blue line). I have confirmed that it is done.

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