IN-PIPE GROUND PENETRATING RADAR FOR NON-DESTRUCTIVE. EVALUATION OF PVC LINED CONCRETE PIPE
Samuel T. Ariaratnam1 and Noel Guercio2
1DEWSC, Ira A. Fulton School of Engineering, Arizona State Univ., P. O. Box 870204,
Tempe, AZ, 85287-0204, USA; E-mail: ariaratnam@asu. edu
2Project Engineering Consultants, 2310 W. Mission Lane, Suite 4,
Phoenix, AZ, 85021, USA; E-mail: noel@pecaz. com
Underground utility services play an essential role in sustaining urban life. The majority of these utility services are delivered through pipeline networks, which are mostly buried underground and are interconnected through other urban systems to distribute or collect basic sustainable needs such as treated water, waste water, gas, communication, and power. Deterioration of underground infrastructure systems occurs due to ineffective maintenance management practices. Because new installation can be very costly and disruptive, the best course of action is to maintain the present infrastructure in a more effective way to maximize life span and prevent catastrophic failures. The accurate evaluation of current underground infrastructure must be done before any crucial decisions including lifecycle, rehabilitation and replacement intervals, and appropriate remedial methods can be made. Unfortunately, traditional technologies and management approaches have been limited by the use of insufficient data in the evaluation of the structural integrity of an aged infrastructure. This paper describes the testing, development, and application of a novel assessment technology, which combines in-pipe Ground Penetrating Radar (GPR) with Digital Scanning and Evaluation Technology (DSET) robotics to collect accurate information about the condition of the inside wall of concrete sewer pipes. A case study applying this innovative technology to sections of large diameter PVC-lined concrete pipe in the City of Phoenix is presented. The study and adoption of innovative pipeline assessment methods provide better information to improve the decision-making process, thereby making economical decisions to optimize resources in more efficient ways.
The recent Infrastructure Report Card produced by the American Society of Civil Engineers (ASCE) assigned the U. S. infrastructure an overall average grade of D (ASCE, 2005). Within the overall infrastructure, both water and wastewater systems were giving grades of D-. This is alarming as the nation struggles to maintain the integrity of its buried network. The project cost for fixing this problem is estimated to be in the trillions of dollars. Municipalities are trying adopting fiscally responsible strategies for minimizing the impact of their failing water and wastewater systems. A situation analysis must first be performed through the review and assessment of Closed Circuit Television (CCTV) records of the current state.
Back in the 1950’s the City of Phoenix, Arizona searched for a feasible solution to the problem of hydrogen-sulfide attacks on reinforced concrete sewer lines. Due to elevated temperatures in the Southwestern United States, Phoenix, along with other cities such as Los Angeles, Las Vegas, and Sacramento, turned to adopting a PVC liner to provide a protective barrier inside concrete pipe. The lined concrete pipe of choice for the City of Phoenix was Ameron’s T-LockTM pipe. T-Lock pipe is a
M. Pandey et al. (eds), Advances in Engineering Structures, Mechanics & Construction, 763-772. © 2006 Springer. Printed in the Netherlands.
reinforced concrete pipe lined with a polyethylene sheet. As illustrated in Figure 1, the liner is fixed to the concrete with imbedded “Tees” that run the length of the pipe section. This prevents the liner from detaching itself from the pipe. The degree of lining varies depending on what has been specified and is intended to protect the concrete from harmful sewer gases including hydrogen-sulfide.
The City of Phoenix wastewater collection system is comprised of approximately 6,400 km (4,000 miles) of pipeline ranging in diameter from 200 mm (8 in) to 2,250 mm (90 in) and including over 72,000 manholes. Of the Phoenix system, approximately 98 km (61.4 miles) are composed of lined concrete pipe. In addition to its own system, the City operates and maintains two systems from the Sub-Regional Operating Group (SROG). These systems convey wastewater from the Cities of Phoenix, Mesa, Tempe, Scottsdale, Glendale, Peoria and Tolleson to the 91st Avenue Wastewater Treatment Plant located at 91st Avenue and Southern Avenue. These two SROG-owned systems include the Southern Avenue Interceptor (SAI) and the 99th Avenue Interceptor. The SAI includes approximately 30 km (19.1 miles) of PVC lined concrete pipe and 99th Avenue system includes approximately 10 km (6.5 miles) of PVC lined concrete pipe.
Figure 1. Cross-sectional view of reinforced concrete sewer pipe with T-Lock liner (Ameron 2001)
The City of Phoenix was the first municipality to initiate a major assessment program on the lined – concrete system. The program consists of a condition assessment of all lined concrete sewer pipe 750mm (30 in) in diameter and larger that are maintained and operated by the City, including those portions owned by the SROG. This also included the condition assessment of the associated manholes. The project was divided into two phases. Phase 1 included a condition assessment of all lined concrete sewer pipe constructed prior to 1990. Phase 2 included a condition assessment of all lined concrete sewer pipe constructed after 1989. Phase 2 also included an evaluation of the pipe erosion due to sediment and debris transportation within the sewage flow.