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New Document: Recommended Procedures for Implementation of DMG Special Publication 117: Guidelines for Analyzing and Mitigating Landslide Hazards in California
With the implementation of the Seismic Hazards Mapping Act in California, general guidelines for evaluating and mitigating seismic hazards in California were published by the California Department of Conservation, Division of Mines and Geology (CDMG; now the California Geological Survey (CGS)) in 1997 as Special Publication 117. This publication presents guidelines for evaluation of seismic hazards other than surface fault-rupture and for recommending mitigation measures. The guidelines in SP 117 provide, among other things, definitions, caveats, and general considerations for earthquake hazard mitigation, including a summary overview of analysis and mitigation of earthquake induced landslide hazards. The document also provides guidelines for the review of site-investigation reports by regulatory agencies who have been designated to enforce the Seismic Hazards Mapping Act.
In 1997 building officials in the Department of Building and Safety of the City of Los Angeles and the Department of Public Works of the County of Los Angeles requested assistance in the development of procedures to implement the requirements of the DMG SP 117 guidelines and the Seismic Hazards Mapping Act for projects requiring their review. Specifically, both agencies sought assistance in the development of recommendations for dealing with earthquake-induced liquefaction and landslide hazards. Cooperation was sought from other agencies in southern California and officials from the Counties of Riverside, San Bernardino, San Diego, Orange, and Ventura agreed to participate. In addition, the Division of Mines and Geology lent support to this effort.
A group of practicing geotechnical engineers and engineering geologists was assembled to form a committee to develop implementation procedures. It was decided to deal with liquefaction and landslide hazards separately. The liquefaction implementation committee was organized under the auspices of the Southern California Earthquake Center (SCEC) and completed its work in March 1999 with the publication of a set of recommended implementation procedures by SCEC. Two workshops were organized by SCEC to provide further explanation of the procedures.
The landslide hazard analysis implementation committee began its work in August 1998. The landslide hazard analysis implementation committee had the following members:
The over 3-1/2 years effort of the committee members to study, evaluate, discuss, and formulate these guidelines is greatly appreciated. The summation of those consensus efforts is presented in a document titled "Recommended Procedures for Implementation of DMG Special Publication 117: Guidelines for Analyzing and Mitigating Landslide Hazards in California." This document explains recommended procedures for implementing landslide guidelines, and is available via download or mail through SCEC. Although the document has been peer reviewed, the information and opinions presented are those of the committee and have not been endorsed by ASCE, SCEC, or the City or County of Los Angeles.
The purpose of this document is two-fold. The first objective is to present information that will be useful and informative to building officials so that they can properly and consistently review and approve geologic and geotechnical reports that address slope stability hazard and mitigation. The second objective is to provide a broad-brush survey of some of the most common methods of analyses and mitigation techniques that will be useful to geotechnical engineers, engineering geologists, building officials, and other affected parties.
The report presents practical guidelines for static and seismic slope stability evaluations that blend state-of-the-art developments in methodologies for such analyses with the site exploration, sampling, and testing techniques that are readily available to practicing engineers in the southern California area. Accordingly, the intent is not necessarily to present the most rigorous possible procedures for testing the shear strength of soil and conducting stability evaluations, but rather to suggest incremental rational modifications to existing practice that can improve the state-of-practice. It should be noted that the committee by no means intends to discourage the use of more sophisticated procedures, provided such procedures can be demonstrated to provide reasonable solutions consistent with then-current knowledge of the phenomena involved.
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