Location

Arlington, Virginia

Session Start Date

8-11-2008

Session End Date

8-16-2008

Abstract

A case history of extensive 60-m high excavations in a weak rock mass for a canyon landfill in Northern California is presented. The landfill is underlain by the Panoche Formation, a complex series of sandstones, siltstones, claystones, shales and conglomerates, thought to be dominantly turbidites, deposited as sub-sea fan deposits. As part of the design, kinematic analyses were performed, accompanied by two independent approaches used to evaluate the strength of the rock mass. One approach was based on laboratory rock core testing, while the second approach was based on the Hoek and Brown Criterion using mostly field observations. The two approaches yielded consistent results. Characterization of the rock mass indicated a pronounced improvement in the rock structure and the condition of the discontinuities with depth, resulting in an increasing Geologic Strength Index (GSI) with depth. Subsequent analyses performed using a layered Hoek and Brown Criterion allowed further steepening of rock excavations. Comparisons are also made in the results of the analyses using a layered vs. a more commonly used uniform Hoek and Brown approach. It was observed that the layered approach identified more critical, relatively shallow failure surfaces and eliminated the spurious apparently critical deep-seated rock mass failure surfaces, generated assuming a uniform rock mass.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Sixth Conference

Publisher

Missouri University of Science and Technology

Publication Date

8-11-2008

Document Version

Final Version

Rights

© 2008 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Aug 11th, 12:00 AM Aug 16th, 12:00 AM

Characterization of a Weak Rock Mass and Geoengineering Analyses for a Canyon Landfill in Northern California

Arlington, Virginia

A case history of extensive 60-m high excavations in a weak rock mass for a canyon landfill in Northern California is presented. The landfill is underlain by the Panoche Formation, a complex series of sandstones, siltstones, claystones, shales and conglomerates, thought to be dominantly turbidites, deposited as sub-sea fan deposits. As part of the design, kinematic analyses were performed, accompanied by two independent approaches used to evaluate the strength of the rock mass. One approach was based on laboratory rock core testing, while the second approach was based on the Hoek and Brown Criterion using mostly field observations. The two approaches yielded consistent results. Characterization of the rock mass indicated a pronounced improvement in the rock structure and the condition of the discontinuities with depth, resulting in an increasing Geologic Strength Index (GSI) with depth. Subsequent analyses performed using a layered Hoek and Brown Criterion allowed further steepening of rock excavations. Comparisons are also made in the results of the analyses using a layered vs. a more commonly used uniform Hoek and Brown approach. It was observed that the layered approach identified more critical, relatively shallow failure surfaces and eliminated the spurious apparently critical deep-seated rock mass failure surfaces, generated assuming a uniform rock mass.