Geology topics

V. Kuksenko

Publications and source records attributed to V. Kuksenko.

3 recordsLinked to original sources

USGS1996

A two-stage model of fracture of rocks

In this paper we propose a two-stage model of rock fracture. In the first stage, cracks or local regions of failure are uncorrelated occur randomly throughout the rock in response to loading of pre-existing flaws. As damage accumulates in the rock, there is a gradual increase in the probability that large clusters of closely spaced cracks or local failure sites will develop. Based on statistical arguments, a critical density of damage will occur where clusters of flaws become large enough to lead to larger-scale failure of the rock (stage two). While crack interaction and cooperative failure is expected to occur within clusters of closely spaced cracks, the initial development of clusters is predicted based on the random variation in pre-existing Saw populations. Thus the onset of the unstable second stage in the model can be computed from the generation of random, uncorrelated damage. The proposed model incorporates notions of the kinetic (and therefore time-dependent) nature of the strength of solids as well as the discrete hierarchic structure of rocks and the flaw populations that lead to damage accumulation. The advantage offered by this model is that its salient features are valid for fracture processes occurring over a wide range of scales including earthquake processes. A notion of the rank of fracture (fracture size) is introduced, and criteria are presented for both fracture nucleation and the transition of the failure process from one scale to another.

Pure and Applied Geophysics↗

USGS1992

Observations of quasistatic fault growth from acoustic emissions

The location of acoustic emission (AE) sources during deformation of rock has proven to be a useful non-destructive analytic technique. We present experimental results,based on AE observations, that show the nucleation and growth of macroscopic fault planes in granite and sandstone samples. By controlling axial stress to maintain constant AE rate rather than more conventional loading conditions such as constant strain rate or constant stress, we have been successful in retarding the failure process in triaxial experiments. As a result, the post-failure stress curve has been followed quasistatically, extending to minutes or hours the fault growth process that normally would occur violently in a fraction of a second. In addition to this novel control system, three-dimensional locations of AE events were determined by analyzing the relative arrival times of AE pulses recorded on a network of transducers attached to the sample. In this manner, as many as 40 000 AE events were located in the course of a single experiment. While the details of fault formation varied from experiment to experiment, a number of features were consistently observed. In all three granite experiments, the fault plane nucleated abruptly at a point on the sample surface soon after reaching peak stress. Prior to fault nucleation, microcrack growth was distributed evenly throughout the granite samples. From the nucleation site, the fault plane grew across the sample, accompanied by a gradual drop in axial stress. AE locations showed that the fault propagated as a fracture front (process zone) with in-plane dimension of 10-50 mm. As the fracture front passed, the AE from a given region would drop to a low level. If allowed to progress to completion, stress eventually dropped to the frictional sliding strength. Sandstone samples showed somewhat different response. In these experiments, a diffuse damage zone appeared prior to peak strength and gradually localized into an incipient fault plane. After passing through peak stress, this plane grew, as in the granite samples, to eventually bisect the sample.

International Geophysics↗

USGS1991

Quasi-static fault growth and shear fracture energy in granite

The failure process in a brittle granite sample can be stabilized by controlling axial stress to maintain a constant rate of acoustic emission. As a result, the post-failure stress curve can be followed quasistatically, extending to hours the fault growth process which normally would occur violently in a fraction of a second. Using a procedure originally developed to locate earthquakes, acoustic emission arrival-time data are inverted to obtain three-dimensional locations of microseisms. These locations provide a detailed view of fracture nucleation and growth.

Nature↗