Environmental Sciences Seminar Series Presents:

ENGINEERING GEOLOGY OF EXPANSIVE SOIL AND BEDROCK: A CASE STUDY FROM COLORADO

Jerry D. Higgins, Ph.D., P.G.

2006 Richard Jahns Distinguished Lecturer in Engineering Geology

Department of Geology & Geological Engineering

Colorado School of Mines

Golden , CO 80401

Tuesday, February 21, 2006

Smittcamp Alumni House, CSUF, Fresno

(reception at 5:00 pm , followed by seminar at 5:20 pm )

Abstract

The Colorado Piedmont, adjacent to the Rocky Mountain foothills, is mostly underlain by soils derived from the weathering of underlying sandstone, claystone and shale bedrock. The many claystone and shale units contain varying amounts of expansive (smectite) clays. Foundation problems in expansive colluvial and residual soils have been recognized by the engineering community, and appropriate investigation techniques, foundation design, and site grading strategies are practiced routinely with reasonable success.

Relatively recently, development has intensified along the steeply dipping bedrock belt directly east of the Front Range . The steeply dipping sandstones, claystones, and shales are typically covered by very thin soils. Differential ground heave has occurred at many locations within the steeply dipping belt shortly after an area has been developed. Extensive damage to buildings, utilities, and roads results, and financial losses in excess of several tens of millions have been reported.

Investigations revealed that individual beds display a different potential to expand due to varying clay mineralogy. These bedrock units are highly weathered and fractured near the ground surface, which allows deep infiltration of water. Irrigation of gardens and lawns by homeowners in this semi-arid climate introduce additional water sources and make the problem worse.

Research conducted by the Colorado School of Mines and the Colorado Geological Survey (CGS) developed conceptual models of the heave mechanisms. Once the cause was understood, the CGS and county planners designated a “swelling bedrock overlay district” that identified the at-risk areas separately from expansive soils hazards. Within this district, counties require developments to incorporate specified methods of investigation and foundation design. Over-excavation and backfilling with inert material is required at most construction sites, and has proven very successful.

All members of the professional, educational, and research communities are welcome. For additional information, please contact the Earth & Environmental Sciences department office at (559) 278-3086 or vengieb@csufresno.edu .

Parking restrictions will be relaxed in Lot V (Shaw and Woodrow Avenues) between 4:30 and 7:00 pm for seminar participants. An online campus parking map is available at: http://www.csufresno.edu/univrelations/map.