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Development and application of a modified rock mass rating system for fault zones

Dosch, John M.
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Advisor
Gutierrez, Marte S.
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Date
Date Issued
2023
Date Submitted
Keywords
clay rich faults
 Eisenhower Johnson Memorial Tunnel
 fault rock
 rock mass classification
 rock mass rating
 tunnel excavation
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2023 - Mines Theses & Dissertations
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Dosch_mines_0052N_12741.pdf
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Dosch_mines_0052N_316/EJMT Fault Width and Clay Fraction Data Used.zip
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Dosch_mines_0052N_316/MATLAB Codes.zip
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https://hdl.handle.net/11124/179102
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Abstract
One of the most problematic geological conditions that can be encountered in a tunnel excavation is a fault zone. Fault zones are zones of sheared discontinuities that can range from tens of meters to hundreds of kilometers in length. When a tunnel excavation is unprepared to deal with these fault zones, a fault has the potential to cause damages to structural support systems, clogging of a tunnel boring machine (TBM), very large deformations, increases to project time and cost, and even total project stoppages. Understanding the characteristic of a fault zone and the expected responses from the excavation can help prevent these issues. This thesis focuses on these steps for a new bore of the Eisenhower Johnson Memorial Tunnel (EJMT), a tunnel about 60 miles west of Denver, Colorado. The EJMT runs through a clay-rich fault zone and experienced significant convergences, problems, and delays during its construction. Avoiding these mistakes of the past for a new bore is key. This thesis first focuses on a qualitative discussion on faults, fault infilling, and excavation methodology effectiveness for fault zones. This thesis then covers the history of the rock mass rating system (RMR) and the system’s deficiencies when evaluating fault zones. It was found that the current RMR system overpredicts the rock quality of fault zones. A modified RMR system is proposed that accounts for the various behaviors of fault zones and this new RMR system is applied to the fault zones of the Eisenhower Memorial Tunnel. With these new RMR values, insights into tunneling through fault zones, and existing correlations to the advance rates of excavation methods of drill and blast and various TBM types, the double shield TBM was selected as the excavation method that will provide the highest overall advance rate and expected stability for a new bore of the EJMT.
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