TECHNICAL | SHAFTS, CAVERNS
design and construction considerations. 3 - Ground Conditioning and Improvement Options - three sub-sections; pp 14-19 Topics include: the same methodology is used again, considering the following - description, applicability, suitability geotechnically, advantages and disadvantages, and some options have discussion of and design and construction considerations. The techniques covered are - compaction grouting, deep soil mixing, and this time AGF has more coverage.
4 - Lining Options - three sub-sections, but with further sub-divisions; pp 19-40 Topics include: initial discussion on temporary versus permanent lining, then each is explored in the following pages through different methods, following the same methodology as before. Methods discussed includes: for soft ground - piles (tangent, secant), sheet piling, trenched/diaphragm walls, caisson (open, pneumatic), segmental underpinning, ribs & boards & liner plates; and, for rock - bolts, shotcrete, steel ribs & mesh, cast insitu concrete, and steel segmental lining. Note is made of the emerging trend, for final lining design and construction, of using spray-applied waterproofing membranes. 5 - Excavation Options - ; pp40-48 Topics include: boring & raise boring, roadheader, and vertical shaft sinking machines (also for soft ground), and drill & blast. Discussion includes use of techniques in mining as well as applicability to civil engineering tunnels. Note that some excavations options will have crossover with lining methods, such as piling, D-Walls, caisson, and segmental.
6 - Mucking and Hoisting - two sub-sections; pp48-53 Topics include: methods discussed are primarily grabs and crane systems.
7 - Decision Chart and Diagrams One sub-section; pp53-62 8 - Summary - very brief; pp62 References; pp62-63
ILLUSTRATIONS AND CHARTS The chapter sections are very well illustrated; the images are highly effective additions to support the well-structured information. In total, there are 77 figures, including a few large tables. Although there is less labelling than may be preferable
for a book-style focus on a subject, the information structure has a repeated pattern which helps to negotiate the narrative flow. The similarities in such labelling can though, without beneficial numbering, require some extra checks on location within the report. The arrangement supports dipping into the report as a ready reference to brief, specific areas. Fuller, closer reading throughout is, like most reports, likely only to be closer for early or initial familiarisation with the information, in full, and which of course will help later navigation. The report concludes with, in journal style, 1.5-pages
of References. As noted, there is no Index, but certainly having a series of extensive flow charts on shaft selection - albeit from case study examples, and while noting they have specific data - is a constructive way to
30 | April 2026
bring the ideas discussed together. As listed above they are gathered together and constitute chapter section 7 - which is over 10 pages, and is dominated by its six large flow charts and two large tables. The principal other table in the report is in the chapter
section 6, immediately before, and provides a general approach and recommendations for selecting the shaft construction method. Thereafter, the tables in the report work with the
flow charts to focus on application to two case studies discussed - a sewer tunnel and a transport tunnel, respectively, both from the US Pacific North West. They are: Case 1: West side combined sewer overflow (CSO) tunnel project in Portland, Oregon. Case 2: Sound Transit’s Northgate Link Extension project, in Seattle, Washington. The first case study is discussed with four flow charts, the second case using two flow charts and two large tables.
CONCLUSION The report emphasises that shaft construction is an integral part of tunnelling works to develop different kinds of underground spaces. Yet, being so important it “remains under-developed” for the most part, it says, and “Hence, proper selection of the construction method is critical”. As such, the reports points to the value of decision
trees and charts as “valuable tools” to negotiate the information matrix in a structured way and so “improve the selection process” for shaft construction methods. “Therefore, integrating these tools into the planning
and execution phases of shaft construction is highly recommended for any engineering team,” it says. The summary cautions, though, that the guidance
“does not replace direct experience with the design and management of shaft construction.” It points to the uniqueness of each project and, consequently, discussions required on management and allocation of risk, of ‘What If’ scenarios, the contents of the risk register, and value engineering.
The look of a journal paper comes from how the information was first published. Although the contents originate from work undertaken within ITA-AITES by WG23, the information came out first elsewhere - as a long paper in the Elsevier journal Tunnelling and Underground Space Technology (TUST), under an open access facility. Inside, the ITA-AITES report presents the information as a reproduction of the TUST journal’s long paper, as permitted under the particular open access facility. For citation purposes, ITA-AITES points to the TUST publication - as below * - but it labels its own version of the guidance as Report 36, issued in July 2025, from WG23. *For citation, the details are: TUST 164 (2025) 106654, and
https://doi.org/10.1016/j. tust.2025.106654.
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