Serving professionals in engineering, environmental, and groundwater geology
since 1957

MONTHLY DINNER MEETING

Date: Tuesday, May 9th, 2006
Location: Stevenís Steak House, 5332 Stevens Place, Commerce, California

Time: 6:00 p.m.-Social Hour; 7:00 p.m.-Dinner; 7:45 p.m.-Presentation

Cost: $30 per person with reservations, $35 at the door, $15 for students with a valid Student ID

Reservations: Please call (323) 889-5366 or email rmunro@mactec.com

SPEAKER: Dr. Jeffrey R. Keaton
TOPIC: Consensus Definition of Earth Fissures and Overview of AEG Shlemon Specialty Conference

ABSTRACT

Fissures are fractures or cracks in earth materials along which distinct separations exist. The common image of an earth fissure is a relatively long, curvilinear pattern of discontinuous, relatively narrow, open, steep-sided cracks on gently sloping alluvial ground. Horizontal extension is implied by open cracks, and cracks will form under small tensile stress because earth materials are weak in tension. Distinctive patterns of ground cracks are not associated with different formation processes, and descriptive classifications should not be expected to lead deductively to determination of earth fissure cause. Classification schemes developed for landslides and rock defects may be useful for earth fissures, particularly with respect to age or time since the most recent rejuvenation of cracking or collapse. From a practical standpoint, the term Earth Fissure probably should be reserved for ground cracks on relatively gently sloping topography where certain local processes can be clearly ruled out as the cause. Candidate local processes to be ruled out might be fault rupture during earthquakes, landslides, and collapse into solution cavities and underground mines.

Consensus came with difficulty in the Shlemon Conference, and the agreed upon definition of Earth Fissure was: A crack at or near the ground surface with an opening mode that is predominantly perpendicular to the orientation of the crack, generally occurring in unlithified or geologically unconsolidated earth material (soil in the engineering sense).