rock characterization

7/30/2019 Rock Characterization

1/26

Rock Mass Characterization

Geological and geotechnical data

collection


2/26

Purpose

To obtain representative and

unbiased information:

Location of major geological

features

Discontinuity orientation,frequency, size, shear strength

Information to carry out a

rock mass classification

Intact rock strength

Ground water

Joint condition


3/26

Concepts Rock mass can be thought of as an assembly of potential

blocks, which can be disaggregated by an excavationprocess

Geotechnical domains: regions of similar engineering

behaviour that can be delineated within a rock mass.

Structural domains: regions comprising similar sets of

geological structures that can be delineated within a rock

mass

Systematic collection of geotechnical information is

essential for accurate characterization


4/26

Concepts

Rock mass behavior is controlled by the nature ofgeological discontinuities and the physical properties ofthe rock material bridges (intact rock bridges)

Large scale geological discontinuities are often low inshear strength and continuous, and can be seismicallyactive. They are often defined during orebody delineation

Minor scale jointing stochastic joint set characteristics,

sampling techniques required


5/26

Types of Data Collected

Rock Name (Type)

Rock Material Properties Colour

Grain size and shape

Texture

Other textural features and fabric

State of weathering

State of alteration

Strength


6/26


Alteration & weathering Affects both rock & discontinuities

Alteration may enhance rock strength

Weathering will always reduce rock strength

Multiple weathering schemes have been suggested including

Dearman (1986) and Stapleton ,1976


7/26



8/26


Strength Via laboratory testing

Uniaxial Compressive Tests

Triaxial Tests

Field Tests Point load Index

Schmidt Hammer

Discontinuity wall strength Grades

See next slide


9/26



10/26

Source of Data

Core Logging Borehole geophysical logging

Outcrop and spot mapping

Systematic face mapping

Scanline mapping

Window mapping

Photographic scanning

Steropsis


11/26

Source of Data


12/26

Geotechnical core log

Comprises:

Header (hole number, project, rig, core size, bit type, plunge andbearing of hole, collar coordinates)

Depth (from - to)

Rock material description

Degree of weathering

Field estimate of rock strength

Graphic log

Defect description and angle relative to core axis

Location of samples taken for testing

Rock Quality Designation

Core recovery

Water return Packer test results

Casing details


13/26

Oriented Core Log

Augments data from the simple geotechnical log and

includes additional information on:

alpha and beta angles for the defect

defect roughness and planarity

infill characteristics (type and thickness)

actual fracture spacing


14/26


15/26


16/26


17/26


18/26


19/26


20/26


21/26


22/26


23/26


24/26


25/26


26/26

rock characterization

Documents