Characterizing Controlled Low-Strength Materials (CLSM) for Narrow-Trench Reinstatement

Abstract

Cutting the pavement to install a small diameter utility network, such as flexible pipes, conduits or telecommunication lines, is a common practice in urban areas. The last 200 meters of installation is known particularly difficult to deliver, with obstacles both above and below ground to navigate, and these difficulties increase installation time and cost. Micro-trenching (MT) is a variation of narrow-trenching (NT) in which the trench is as narrow as 25 to 40 mm. Providers have found a considerable saving in project time and cost when MT is employed instead of the traditional open-cut method. Due to its advantages, MT is growing in popularity as a means of quickly, efficiently, and cost-effectively installing the utility networks is in a metropolitan area. Hence, many utility installers are now switching to NT. Despite all the advantages, NT method is not being widely practiced around the world because municipalities are reluctant to accept the risks associated with it, including potential pavement damage, and lack of stability of the buried conduit in shallow depths in freeze-thaw climatic regions. Due to the narrow width of the trench and shallow depth of the installation, the quality of the backfilling plays a crucial role in the durability of the installation. The backfill materials in cold regions are exposed to harsh weather conditions including prolonged winter seasons, short thawing periods and long summer days. This, as well as lack of available knowledge about the performance of the materials inside a narrow trench, resulted in many distress and failures in surveyed MT projects. This research study aims to improve the overall civil work of the NT projects. To serve this purpose, different backfilling materials and methods were investigated and properties of the three most promising alternatives for NT application, i.e cold-mix-asphalt, lightweight cement-based foams, and alkali-activated foams, studied in detail. Subsequently, the performance of the reinstated trench, as well as its response to the different pavement or narrow-trench designs, were evaluated by a series of physical and numerical models. The result showed the satisfactory performance of lightweight foams as a backfilling material. Lastly, a multi-objective optimization model was developed to minimize project cost and time while using the most levelled resources.