Trenchless Installations Preserve Pavement Integrity

Horizontal directional drilling (HDD) has been successfully used to perform trenchless pipeline installations under highways, roads, waterways, and various other situations where traditional open cut-and-cover methods will results in significant traffic disruptions and/or environmental damage. In the case of pavements, utility and pipeline cuts have been shown to accelerate pavement deterioration and create significant user delays. Initially trenchless pipeline construction bids were higher than open cut-and-cover methods. However, if full life cycle costing methods are used trenchless construction methods are more cost-effective than the low bid open cut. This is the first known study that investigates the comparative impacts of directional drilled and conventional open cut and cover pipeline installations on pavement integrity and performance. Obtaining such comparisons under the same levels of subgrade type, pavement structure, traffic, and environmental conditions is unique and will provide field data that will be important to both the trenchless and pavement industries. This paper reports on a joint effort between The Centre for Advancement of Trenchless Technologies (CATT) and The Centre for Pavement and Transportation Technology (CPATT), both located in the University of Waterloo Department of Civil Engineering, to carry out the foregoing comparisons. CPATT’s test site at The Regional Municipality of Waterloo’s waste management facility (reported at TAC’s 2003 Conference) was used for the research. The trenchless and open-cut installations were placed in a clayey till subgrade about 2m from the surface, which is overlain by 300mm of granular B subbase, 150mm of granular A base and 100mm of hot mix asphalt. The open-cut installation was restored to pre-cut conditions using current best practices. During trench re-instatement field instrumentation was installed to measure soil backfill and pavement response to traffic loading. Strain gauges were installed at the bottom of the asphalt layer to measure the pavement response to traffic loading and environmental changes. The pipes, 200mm SDR-17 high-density polyethylene (HDPE) were instrumented to measure pipe short and long-term behaviour (strains and deflections). Other data collected includes the construction progression and comprehensive materials characterization data that includes the slurry used for the directional drilled pipe installation. This paper provides an overview of the University of Waterloo Centre for Pavement and Transportation (CPATT) research program and test track facility. It also discusses the research program designed to quantify pavement deterioration and polyethylene pipe performance when pipes are installed under flexible pavements using a directional drill and open cut-and-cover construction methods. Details of the construction and instrumentation are presented. Directionally drilled and open cut pipe construction induced pipe deflections are also discussed as an example of the quality of data being collected in this study.