Field observations in a thin colluvium landslide complex along the Ohio River near Cincinnati, show that measurable, late winter and spring pore water pressure increases occur when several centimetres of rain fall over a period of one or more days. Average pre-storm fillable porosity of 9% suggests that the colluvium was near saturation during the period of record. Dimensional analysis of flow through a sloping homogeneous layer of uniform thickness shows that short-term pore pressure fluctuations in very nearly saturated soils can be approximated by a one-dimensional linear diffusion equation. The concept of slope-parallel and slope-normal characteristic times is also introduced to determine the conditions under which slope-parallel and slope-normal flow will predominate. Analytical solutions to the diffusion equation are then used to investigate the effects of storm frequency and magnitude on pore pressure fluctuations. Comparison of solutions for layers of finite and infinite thickness shows that an impermeable substrate nearly doubles pore pressures along the substrate for storms of short duration; however, the effect of an impervious boundary vanishes with increasing duration. Finally, measured rainfall values are incorporated into a finite-difference simulation of the observed pore pressures, with good results.
|Number of pages||26|
|State||Published - Oct 1991|
Bibliographical noteFunding Information:
Much of this work was funded by a research grant from The Hillside Trust, Cincinnati, Ohio. In addition, Robert Fleming, U.S. Geological Survey, provided equipment and data. Andrea Haas, Robert Olson, and Mary Reistenberg assisted with field work, which the Sisters of Charity kindly allowed take place on their property. Lawrence Murdoch explained the use and installation of tensiometers. Computer facilities for some of the theoretical analysis and text processing were provided by the New Mexico Bureau of Mines and Mineral Resources. Arvid Johnson, Robert Fleming, Richard Iverson, David Nash, and Shirley Dreiss all provided invaluable comments during the course of this study. Debi Mancione checked the text for spelling and grammar, and critical reviews by Rex Baum, Jeff Keaton, William Judd, and two anonymous reviewers further improved the clarity of this paper.
ASJC Scopus subject areas
- Geotechnical Engineering and Engineering Geology