Stanley J. Vitton

A dynamic damage growth model for uniaxial compressive response of rock aggregates

A model that combines damage evolution theory with dynamic crack growth is developed to investigate the uniaxial compressive response of rock aggregate. A damage parameter that determines the time at which the rock looses its ability to transmit the stress completely is introduced into the model. Flaw distribution in rocks is described by a two parameter Weibull distribution. The model correlates the damage parameter with the dynamic growth of “wing” cracks from the pre-existing microcracks. Influences of model parameters on stress–strain response and failure strength are studied systematically. The results of the dynamic damage evolution model are compared to the experimental observations on three types of rock and a good correlation is obtained.

Tornado Detection Based on Seismic Signal

Abstract At the present time the only generally accepted method for detecting when a tornado is on the ground is human observation. Based on theoretical considerations combined with eyewitness testimony, there is strong reason to believe that a tornado in contact with the ground transfers a significant amount of energy into the ground. The amount of energy transferred depends upon the intensity of the tornado and the characteristics of the surface. Some portion of this energy takes the form of seismic waves, both body and surface waves. Surface waves (Rayleigh and possibly Love) represent the most likely type of seismic signal to be detected. Based on the existence of such a signal, a seismic tornado detector appears conceptually possible. The major concerns for designing such a detector are range of detection and discrimination between the tornadic signal and other types of surface waves generated by ground transportation equipment, high winds, or other nontornadic sources.

Hazard assessment of rainfall-induced landslides: a case study of San Vicente volcano in central El Salvador

The San Vicente volcano in central El Salvador has a recurring and destructive pattern of landslides and debris flows occurring on the northern slopes of the volcano, and in recent memory, there have been at least seven major destructive debris flows. There has been no known attempt to study the inherent stability of these slopes and determine the factors that might lead to slope instability. Past events on the volcano were used to perform a 2D slope stability back analysis and to estimate the unknown model parameters. This analysis confirmed that the surface materials of the volcano are highly permeable and have very low shear strength. Additionally, the analysis provided insight into the groundwater table behavior during a rainstorm. Slope geometry, rainfall totals and initial groundwater table location were found to have the greatest effect on stability. A methodology is outlined for creating a stability chart to be used during rainfall events for monitoring slope stability. This chart could be used by local authorities in the event of a known extreme rainfall event to help make evacuation decisions. Finally, recommendations are given to improve the methodology for future application in other areas as well as in central El Salvador.

APPLICATION OF ANCHORED GEOSYNTHETIC SYSTEMS FOR IN SITU SLOPE STABILIZATION OF FINE-GRAINED SOILS

The use of anchored geosynthetic systems (AGS) was proposed by Koerner et al. for the stabilization of slopes at or near their failure state. AGS provides in-situ stabilization of soil slopes by combining a surface-deployed geosynthetic with an anchoring system of driven reinforcing rods similar to soil nailing. Installation of the system involves tensioning a geosynthetic over a slope’s surface by driving anchors through the geosynthetic at a given spacing and distance. By tensioning the geosynthetic over the slope’s surface, a compressive load is applied to the slope. Benefits of AGS are described to include the following: (a) increased soil strength due to soil compression, including increased compressive loading on potential failure surfaces; (b) soil reinforcement through soil nailing; (c) halt of soil creep; (d) erosion control; and (e) long-term soil consolidation. Following installation of the AGS and 1 year of monitoring, it was found that the anchored geosynthetic system provided only some of the reported benefits and in general did not function as an active stabilization system. This was in part because the system could not provide and maintain loading on the geosynthetic. The geosynthetic, however, did tension when slope movement occurred, preventing the slope from failing. Thus, the system functioned more as a passive restraint system and appeared to function well over the monitoring period.

SOIL PARTICLE SIZE ANALYSIS USING X-RAY ABSORPTION

Low strain dynamic shear modulus property is generally used to subclassify soil strata, determine elastic settlements under geotechnical structures, and characterize the dynamic nature of soils. Several methods to interpret the dynamic shear modulus of sands from in situ friction cone test results have been developed. These methods used calibration chamber test data of clean sands. Therefore, these methods are not valid for interpreting the shear modulus of cemented sands. Introduced here is an interpretation method to estimate the shear modulus of cemented sand. Thirty-seven friction cone penetration tests (CPTs) were conducted on artificially cemented sand specimens of relative densities ranging from 45 percent to 85 percent and confining pressures ranging from 100 to 300 kPa in a laboratory stress-straincontrolled calibration chamber. Cementation levels of 1 and 2 percent were used in preparing cemented specimens. Resonant column tests were also conducted on the same sand with identical cementation lev...