Rapports

The life extension capabilities of CIPP for pipe rehabilitation are well established. The measured long-term flexural modulus creep retention factor (CRF) of CIPP has been employed to design numerous installations where the actual life extension has later been demonstrated. The CRF is determined by the CIPP system manufacturer through type testing of the resin/felt material.

Accepted industry consensus is that field prepared CIPP samples can exhibit lower short-term flexural properties than the short-term flexural properties which are determined by CIPP system suppliers during type testing. Factors such as installation conditions or crew experience can contribute to flexural properties of field samples occasionally falling below the specified design minimums. This characteristic of CIPP field installations has been referred to as natural variation.

One commonly observed anomaly which can be related to lower short-term flexural properties in CIPP field samples is ineffective resin saturation of the needled felt. Since in needled felt CIPP systems, the resin itself is responsible for achieving the ultimate flexural properties, failure to fully saturate the voids within the felt with resin can result in lower flexural performance.

Current design practice assumes that CIPP field samples which exhibit short-term flexural properties lower than those determined during type testing will nonetheless exhibit long-term creep performance which is similar to the creep behavior originally determined by the system supplier during type testing.

This paper describes the findings of a research project examining the relationship between resin saturation effectiveness of needled felt CIPP field samples and short-term and long-term flexural properties.

Cured-place-pipe (CIPP) has demonstrated that it can be an effective rehabilitation technology when implemented within an appropriately managed project. Numerous specifications have been written to describe the processes which are required to ensure that the Owner is left with rehabilitated assets which will deliver the expected life extension of the asset. The processes included in these specifications typically reflect a balance between, on one side, the risk of a failure to meet design objectives and on the other, the cost, both in direct dollars and indirectly in administration and management, to minimize that risk.

While the first CIPP installation was completed in 1971, the first industry standard practice, ASTM F1216 was not published until 18 years later. Even though the standard has seen regular revisions since then, the recommended inspection practices have largely remained the same even while anecdotal evidence to support more rigorous practices has accumulated. Only very recently has published research based upon actual data from installations demonstrated the prevalence and magnitude of natural variation (lower mechanical properties and/or wall thickness) in CIPP installations.

In this vacuum, the content of owner specifications has come to reflect the individual specification writers experience or lack thereof with CIPP and their perception of the risk of not meeting design objectives. Using statistical and economic analysis of actual project experiences, this paper will demonstrate the risks and costs of a CIPP quality assurance process which has been informed by five decades of research and industry experience.

Creep is a time-dependent phenomenon wherein a material experiences continually increasing strain under a constant load. ASTM D2990 is the test method employed when investigating the creep properties of plastics and has been applied in industry to the study of cured-in-place pipe (CIPP) material. In the application of D2990 to CIPP material, several situations may be encountered where subjective interpretation of the standard is required. Such situations include determining loading conditions to provide data relevant to real-world CIPP design and selecting the appropriate curve-fitting equations to accurately predict long-term properties. In long-term creep testing, loading conditions should be set below the yield point of the material while being greater than the expected working load.

This would be to ensure that the majority of recorded strain is creep-related and that experiment durations remain practical. Under ASTM D790 and ASTM D638, the yield point is defined as the end of the linear portion of the stress-strain curve where the material exhibits an increase in strain without an increase in stress. Issues arise when trying to determine the yield point of composite materials such as watermain CIPP because their stress-strain curves do not typically show an initial linear region or a point of zero slope.

This paper seeks explore other methods for determining an effective yield point of CIPP watermain which can be used as a reference for future long-term creep tests.

The American Society for Quality defines quality assurance as “all the planned and systematic activities implemented within the quality system that can be demonstrated to provide confidence that a product or service will fulfill requirements for quality”. Requirements for quality in sewer CIPP projects typically revolve around achieving a minimum design life of 50 years and are defined within the Owners construction specification or tender documentation.

Research has demonstrated that the physical properties of installed sewer CIPP liners measured in laboratory tests can vary to a greater degree than more traditional pipe materials. To incorporate this characteristic of sewer CIPP installations, many owner’s quality requirements have been evolving to ensure that their CIPP projects achieve design life with an acceptable degree of confidence. Unlike the ASTM and ISO standards and specifications which are incorporated within owner specifications, there are no industry-wide universal approaches employed by owners to define their sewer CIPP quality assurance best practices.

This paper examines the quality assurance tests and the sewer CIPP quality assurance best practices employed by four Canadian municipalities, Edmonton, Montreal, Toronto and Winnipeg in current sewer CIPP projects and describes the quality assurance outcomes of the different approaches.