EGL-projecrts-fissures

UNLV Engineering Geophysics Laboratory

Definition and Delineation of Cemented Deposits

Background

In the alluvial deposits on which Las Vegas and other cities in the arid Southwestern United States are built, we encounter lenses of alluvial sands and gravels that have been cemented with calcium carbonate. This rocklike material, commonly known as caliche, is very important to practicing geotechnical engineers. Caliche is valued for the strong bearing surface it provides for shallow foundations. On the other hand, where excavations are required, it presents a nuisance, requiring rippers, "headache balls," or even explosives to dislodge.

These cemented materials tend to occur in discontinuous lenses with thicknesses up to 5 meters. The capacity to detect the presence of caliche in the subsurface during planning stages of a project, and, better yet, to be able to establish its lateral continuity and thickness, would be highly useful. Research Program

We are developing techniques for imaging shallow caliche lenses in desert soils. This research activity includes:

· Characterizing the static and dynamic material properties of caliche and cemented sands and gravels;

· Conducting numerical analyses to predict the effects of the stiff inclusions on seismic data collected at the ground surface;

· Collecting surface wave data at sites containing caliche with well understood stratigraphy and lateral variability;

· Exploring methods to enhance efficiency in the field through muti-channel data acquisition;

· Developing automated inversion procedures to create two-dimensional profiles of laterally varying sites.