Rangeview Sanitary Trunk Project Challenges and Mitigation Measures

Yihun Negash, AECOM Canada Ltd, Calgary, AB

Zulfiqar Khowaja, The City of Calgary, Calgary, AB

Abstract

Trenchless technology has been increasingly a preferred method of construction for deep underground utilities particularly where crossing involves existing major infrastructures and environmental features.

Rangeview Sanitary Trunk (RST) Project falls under this category. The project involves micro-tunnelling of 1,800 mm (72 in) trunk for a total length of about 3.3 km (2 mi). The trunk conveys sanitary flow from the future development areas of the southeast corner of the City of Calgary, AB. It connects to the existing siphon chamber at the predetermined elevation which

Project Description

RST project is a 4.4 km (2.7 mi) sanitary trunk project designed to convey sanitary flows from the new development areas in the southeast portions of The City of Calgary to an existing collection chamber which eventually discharges to the Pine Creek Wastewater Treatment Plant via the existing Siphon. The 1, 800 mm (72”) diameter trunk has a design capacity of 3,320 L/s (877 gpm) and it is projected to service about 3,788 ha (9,360 acre) of future developed communities with a projected population of 246,000 people. Out of the 4.4 km (2.7 mi) length of the trunk, about 3.3 km (2 mi) was designed to be installed through trenchless technologies and later reduced to 2.5 km (1.6 mi) during construction through a change order from the Contractor to install the shallower depth, less than 13 m (43 ft) through open-cut construction.

restricts the trunk profile to the minimum allowable slope while crossing hills and valleys.

One of the major challenges of the project is the route crosses a major highway and Environmental Reserve land that consists of wetlands and rare plant species. The crossing at the highway is located at the longest micro-tunnel drive, about 936 m (3,080 ft) and the trunk profile is shallow at that location and frac-out is a concern during micro-tunnelling. Similarly, the soil condition below the wetland is unsuitable for construction and it has a high degree of settlement properties. Securing a regulatory permit to cross the wetland took a long time that impacted the project schedule. In addition, the entire tunnelling sections of the trunk are below the high groundwater level that created challenges during the construction of shafts. This paper presents the challenges encountered during construction and measures taken to mitigate the challenges.

This article will present the challenges encountered on RST project during tunnel and shaft construction and measures are taken to mitigate the challenges.

The rest of the trunk is installed through an open-cut construction.

The revised tunnel alignment consists of the three long drives, three deep shafts, and two exit portals. The summary of the shafts and exit portals is shown in Table 1 and a summary of the tunnel drive lengths is shown in Table 2.