Currently, Japan has about 400,000 km of sewer pipes in its vast underground utility system. Approximately 10,000 km, or 2.5 percent, of these have exceeded the expected 50-year lifespan of underground pipes.
The amount of deteriorating sewer lines in place that are over their 50-year life will continue to increase over time. Additionally, the need to change pipe diameters and gradients of existing lines is often required due to increased wastewater emissions and changes in drainage districts. Thus, the need for techniques for upgrading and reinstalling existing urban pipes without open-cut excavation is rapidly expanding.
Rebirth Ace System is a system for upgrading deteriorated and damaged pipes and for reconstructing pipes lacking flow capacity by increasing their diameter and reinstalling new pipes along the existing horizontal trajectory. The technique is done without open-cut excavation and with the sewer system remaining in service.
This paper covers the latest reconstruction driving method that can be used on reinforced concrete, polyvinyl chloride (PVC) and stoneware pipes used as utility pipes. The method features the ability to cut reinforcing bars of up to 5.0 mm to around 3 cm in length when simultaneously crushing reinforced concrete pipes. In the first onsite construction using the Rebirth Ace System in March 2007, it sufficiently demonstrated its capability, with pipe replacement being completed in a short time at low cost.
Rebirth Ace Systems Techniques and Functions
Rebirth Ace System is comprised of four major techniques: 1) techniques for investigation in and around pipes without open-cut excavation; 2) main pipe reconstruction driving; 3) lateral pipe refurbishing without open-cut excavation; and 4) dewatering for shifting sewage flow in construction area by bypassing.
Development was completed in 2005 for this total solution system for upgrading pipes.
During reconstruction, a driving machine with a special cutter head that crushes and removes existing pipe is driven while simultaneously replacing it with a new pipe. Existing pipe structure and function are restored, and the new pipe diameter is increased to improve flow capacity. The major functions for reconstruction driving with the Rebirth Ace System are as follows:
- Drives and replaces pipe regardless of the amount of existing pipe slack and displacement.
- Reconstructs existing pipe of diameters from 200 to 700 mm; and installs new pipes up to 700 mm.
- Finely crushes and removes reinforced concrete, polyvinyl chloride, and stoneware pipe and various bases.
- Conducts reconstruction driving of up to 150 mm through existing manholes.
Development and Introduction
Existing methods for reconstruction driving by crushing and removing small-diameter (700 mm or less) reinforced concrete pipes and replacing with new pipes, pose several problems listed below:
- Cutting reinforcement of larger pipes may be difficult.
- Length of cut reinforcement may be long, making intake into driving machine, transport, and expelling difficult.
- Driving efficiency decreases with poor expelling.
A special high-capacity crushing and cutting head was developed with the Rebirth Ace System to solve those problems. Figure 2 illustrates an exterior view of the Rebirth Ace System’s reconstruction driving system.
Cutter Head Reinforcement Cutting Mechanism and Pipe Upgrading The method for using the Rebirth Ace System is described as follows:
- The reinforcing steel is placed circumferentially and the distribution bars are placed in the tube axis of the reinforced concrete pipes requiring to be cut along with the concrete that shapes the pipe. The rotation of the special cutter head (Figure 3) crushes the concrete pipe into fine pieces, and the crushed surface of the pipe becomes uneven due to the shape of the gear at the cutter head.
- The distribution bars exposed at the cross-section of the pipe are then bent by the rotation of the cutter head. Those and the reinforcing steel are wedged between the head of the cutter and the concrete at the concave portion of the cross-section of crushed pipes and the surface of the reinforcing steel is gradually reduced and cut by the synergetic effect of the rolling action (Figure 4).
- The special cutter equipped to the jacking machine has a maximum torque of 14.0 kNm and the rotating speed can be adjusted to 4 levels. In order to prevent the rolling of the machine during the reconstruction drive, inverse rotation is also available. Reinforced concrete pipes are crushed most efficiently when the driving speed of the jacking machine is 4 cm/minute and the rotating speed of the cutter is at 25 revolutions/minute. Under this condition, the thrust force underground reaches 150¬200 kN, and by the synergetic effect of the thrust and the rotating cutter, the reinforced concrete pipe is crushed at the most effective rate.
- Any point on the cutter head can crush the existing pipe. Subsequently, pipes can be upgraded and the required shape restored without constraints; even in the event of large slack or displacement, no matter where the pipes are ocated in the excavated cross-section.
Reinforced concrete pipe crushing capability of special cutter head
Reinforced concrete pipes were set on base materials such as railroad ties, crushed stones, and un-reinforced concrete as test specimens approximating the conditions of buried pipe.
Experiments were then conducted to validate the crushing ability of the special cutter head. In the reinforced concrete crushing experiment, the concrete was crushed into pieces that could not be distinguished from the surrounding soil. More than 90 percent of the reinforcing steel could be cut into pieces less than 9 cm long, with an average length of 3 cm. Figures 5 and 6 illustrate the condition and length distribution of the cut reinforcing steel.
It should be noted that most of the older pipes were originally laid by open excavation. For 700 mm or smaller reinforced concrete pipe, the reinforcing steel is at most 5 mm in diameter. The special cutter head has sufficient crushing capability to handle this situation.
Actual construction with the Rebirth Ace System was conducted in February and March 2007 in Tokyo. Reconstruction driving was done in two sections of 39.3 m and 33.5 m, respectively. Both sections had existing reinforced concrete pipes 250 mm in diameter with 3.2 mm reinforcing steel and 2.8 mm distribution bars. The pipes were installed on railroad tie bases. After reconstruction driving, pipes were replaced with new reinforced concrete pipes of 400 mm in diameter (original pipe was 250 mm) to relieve the lack of flow capacity. Existing pipe reinforcement, concrete and the railroad tie bases were finely crushed and cut as shown in Figures 7 and 8 and then removed. Driving progressed at a rate of about 8 to 10 m per day. Subsequently, construction could be completed in a short time, greatly reducing inconvenience on the living environment and traffic disruption.
The ability of the Rebirth Ace System to handle various installation conditions and stages of pipe deterioration was evaluated in field trials. In the year since development and practical application, the system has been introduced to actual construction projects and achieved the expected success. In terms of economy, we have confirmed that it can be introduced with construction costs only slightly higher than traditional reconstruction driving methods.
Maintaining utility pipes is a common issue worldwide and the Rebirth Ace System looks to be an optimum no-dig solution that can meet needs in pipe upgrading and reinstalling.
Hidenori Hino is with AIREC Engineering Corp., based in Tokyo. This article was submitted by the Japan Society for Trenchless Technology.