Measurement of in-situ strength using projectile penetration: Tests of a new launching system
The Lawrence Livermore National Laboratory has a continuing need to measure rock strength in situ, both for simple prediction of cavity size, and as input to computational models. In a previous report we compared two methods for measuring formation strength in situ: projectile penetration and a cone penetrometer. We determined that the projectile method was more promising for application to our large-diameter (2-4-m) hole environment. A major practical problem has been the development of a launcher and an apparatus for measuring depth of penetration that would be suitable for use in large-diameter holes. We are developing a gas-gun launcher system that will be capable of measuring both depth of penetration and deceleration of a reusable projectile. The current version of the launcher is trailer-mounted for testing at our Nevada Test Site (NTS) in tunnels and outcrops, but its design is such that it can be readily adapted for emplacement hole use. We test the current launcher on 60-cm cubes of gypsum cement, mixed to provie a range of densities (1.64 to 2.0 g/cc) and strengths (3 to 17 MPa). We compared depth of penetration of a 84-g projectile from a ''Betsy'' seismic gun - traveling on the order of 500 m/s - with the depth of penetration of a 13-kg projectile from the gas gun - traveling on the order of 30 m/s. For projectiles with the same nose size and shape, impacting targets of approximately constant strength, penetration depth was proportional to projectile kinetic energy. The ratio of kinetic energy to penetration depth was approximately proportional to target strength. Tests in tuffs with a wide range of strengths at NTS gave a similar linear relationship between the ratio of kinetic energy to penetration and target strength, and also a linear relationship between deceleration and strength. It appears that penetration can indeed be used as a semiquantitative measure of strength.
- Research Organization:
- Lawrence Livermore National Lab., CA (USA); Dynasen, Inc., Goleta, CA (USA)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5515908
- Report Number(s):
- UCRL-96317; CONF-8710196-3; ON: DE88001882
- Resource Relation:
- Conference: Minerals and Geotechnical Logging Society symposium, Golden, CO, USA, 6 Oct 1987; Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
42 ENGINEERING
COMPRESSION STRENGTH
MEASURING METHODS
EARTH PENETRATORS
PERFORMANCE TESTING
TUFF
BOREHOLES
CAVITIES
MECHANICAL PROPERTIES
PENETRATORS
TESTING
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
422000 - Engineering- Mining & Underground Engineering- (1980-)