A new face drilling rig for narrow tunnels and ... - Advanced Mining

EDUCATION
Basics of Geo-Mechanics and Hydrology
by Univ.-Prof. Dr.-Ing. habil. H. Tudeshkil
Surface Mining and International Mining | TU Clausthal | Germany
In addition to the main task of exploration, which is to determine the exact form and extent,
as well as the quality distribution of raw material in the underground, another goal of this
examination phase is to obtain information about geo-mechanical and hydro-geological
characteristics of the underground.
The geo-mechanical characteristics of the overburden
and the raw material, in combination with the tectonic
composition of the underground, have direct influence on
the design of an open cast mine and the selection of the
mining technology. The hydro-geology of the target area,
in which an open cast mine is to be planned, together
with geo-mechanical characteristics of the rocks, directly
influences the stability of benches The water inflow from
the surrounding mountains into an open cast mine must
technically be stopped, so that a smooth, secure and
effective raw material extraction can be ensured. One
exception is the so-called wet mining, where raw material
extraction is done under the water-level.
This brief introduction already points out the fact, that
capturing the rock-mechanical and hydro-geological
composition of the underground is a basic pre-requisite for
a technically and economically optimized open cast mine
planning.
Due to the fact that deposits of mineral raw material
have to be distinguished on the basis of their formation in
soil and hard rocks, they display different geo-mechanical
and hydrological characteristics. Following, the geomechanical
characteristics of soil and consecutively the
characteristics of hard rocks will be described.
Elementary Soil Properties
In principle, soil is not composed homogeneously, but
it is composed of a solid, a fluid and a gaseous phase.
The solid particles, which consist of minerals or organic
material, can be found in different grain sizes (boulders,
blocks, rocks, gravel, sand, silt, clay) in any mix ratio. Apart
form the different grain forms, which have an influence on
interactions between the grains, the charge and electrical
linkage forces (repelling, pulling) are of importance,
particularly in small particles. The individual components of
the solid phase can furthermore be agglutinated, whereby
clay or lime plays an important role. The fluid phase usually
consists of water with dissolved minerals, the gaseous
phase in most cases consists of air.
The portion V T describes the solid material volume (dry
solids). The portion of soil volume which is not filled with
solid substance (in Picture 1 is called VP and is divided
into gas volume V G und liquid volume V F ) is defined as
porosity n.
The porosity n of soil and the void ratio e have a functional
connection and can be converted into each other with the
following terms:
Term 1:
Term 2:
e
n =
1+
e
n
e =
1−
n
The higher the porosity of the soil, the higher is its
permeability.
Issue 04 | 2010 www.advanced-mining.com
4