PREVIEW | RETC 2025


NETWORKING EVENTS A number of networking and social events are planned throughout RETC 2025,


including: Monday 9 June 07.00 - RETC Scholarship Recipients Breakfast 07.00 - Women in Tunneling Breakfast, sponsored by Affholder, Delve Underground, and Brierley Associates. Panel talk will focus on ‘Workforce Sustainability - Lessons for the Future’


11.30 - Welcoming Lunch, sponsored by JF Shea. Speaker is Ivan Joseph, a performance coach, leadership and cultural transformation expert


17.00 - RETC Scholarship Recipients Reception 17.00 - Exhibition Hall hosted reception 20.00 - UCA of SME Young Members Reception, sponsored by Affholder and Stantec Monday 10 June 07.00 - UCA of SME Breakfast 11.30 - Exhibition Hall lunch 16.00 - Exhibition Hall hosted reception, sponsored by Frontier-Kemper Constructors


Track 3 - Ground support and final lining The presentations look at four different tunnel projects, the different challenges of which were: First, use of Sequential Excavation Method (SEM) for a


new stormwater drainage tunnel, parallel to the existing tunnel, in weak sandstone and overlying limestone, for a variety of tunnel openings ranging from large flat-back box tunnel to long-span junctions a cathedral-shaped sections. Second, a design-build solution that developed


innovative ground support for weak fractured geology and also Cast-in-Place (CIP) concrete lining to allow construction of an underground stilling basin for discharge improvement at a dam project, in Japan. The project saw a reinforced concrete pillar support used to support the excavated space and concrete forms in the CIP works stage to help constructability and with the program schedule. Third, the engineering of backfill around three steel


and competitive sealed bids; and, last, looking at how


TBM projects in cohesive ground that presents clogging potential have helpful contractual clarity with Geotechnical Baseline Reports (GBR) and this has been increasing in North America.


SPONSORS OF RETC 2025 Overall Conference Sponsor: Jennmar Civil GOLD level: Frontier-Kemper Constructors; Hatch;


Herrenknecht; HNTB; Jacobs; Mott MacDonald; Skanska; and, Traylor Bros. SILVER level: Affholder; Barnard; Jay Dee; JF Shea; Kiewit; and, Turnstone Industrial Solutions. BRONZE level: Aztec (part of Typsa); Dr Sauer & Partners; Black & Veatch; Brierley Associates; Delve Underground; Stantec; Subsurface and Tunnel Engineering, LLC; Wade Trim; and, Walsh.


pipes running through a carrier tunnel constructed by TBM, with challenges that included mix designs, heat of hydration temperature control, steel pipe buoyancy control, water ingress management, and contact and skin grouting. Last, another pipe burial inside a tunnel is discussed


- this time as part of the final lining, though, where Self- Compacting Concrete (SCC) was used for backfilling around the 72-inch steel pipe used and potential remaining voids were grouted.


Track 4 - Grouting and ground modification Also four presentations to begin this track, and they look at:


First, addressing construction risk on a tunnel to be


decommissioned at a dam, with mitigation measures including use of high-pressure tremie grouting to backfill under the main dam structure. Second, another discussion on construction risk,


this time considering how grouting on projects is becoming weighted more to risk management for bids as opposed to anticipating the scope and quantity of grouting. The abstract says “This often leads to grout quantities


which are reflections of the risk allocation process, not the geologic conditions.” Grouting design and specification are to be discussed


along with contracting methods. Third, ground improvement using compacted grouted


columns (CGC), in the case of a microtunneling job - introduced as a construction alternative. The CGC helped to minimize settlement in marsh layers, transfer pipe loads to bearing layers, and maintain slope stability. Last, construction experience is shared on another


type of ground improvement - using Deep Cement Mixing (DCM). DCM was used to improve soft clays. Details will be


shared on the current design code, data from laboratory testing, and recommendations for selecting stiffness to strength ratios for different Unconfined Compressive Strength (UCS) values.


28 | Summer 2025


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