Tunnelling underground - Melbourne Metro Rail Project

Hoodoos and ironstone rocks - Writing on Stone Provincial Park, AB

A hoodoo is a rock formation which is caused by differential resistance to erosion. This means that some parts of the hoodoo are harder than others and these hard parts last longer. In the hoodoos below, the tops are the hardest part and they protect the soft rock below from wearing away.

The hoodoos in the Milk River valley are made of sandstone which is sand-sized particles cemented together by calcite, silica, or an iron oxide. Some sandstone is quite hard, but sandstone can be so soft that it brushes away when you touch it.

Ironstones are reddish-brown rocks that are very hard. When the sand was being deposited on the ancient beach, living organisms became trapped in the sand. This organic material slowly attracts molecules of iron mineral around it. Slowly, over millions and millions of years, layer upon layer of iron, an ironstone concretion is formed. Ironstones are so hard that when they are exposed on a hoodoo, the soft sandstone around them is eroded away and the ironstone falls out, leaving a hole. The holes in the hoodoos can result in very exotic and curious forms.

Source:http://www.uleth.ca/vft/milkriver/hoodoos.html

Rock Mass Rating (RMR) - Geomechanics Classification

Bieniawski (1976) published the details of a rock mass classification called the Geomechanics Classification or the Rock Mass Rating (RMR) system. Over the years, this system has been successively refined as more case records have been examined and Bieniawski has made significant changes in the ratings assigned to different parameters.

The following six parameters are used to classify a rock mass using the RMR system: 

1. Uniaxial compressive strength of rock material.
2. Rock Quality Designation (RQD).
3. Spacing of discontinuities.
4. Condition of discontinuities. 
5. Groundwater conditions. 
6. Orientation of discontinuities.

Bieniawski (1989) published a set of guidelines for the selection of support in tunnels in rock for which value of RMR has been determined. These guidelines are shown on the table below:

Rock Mass Rating System (After Bieniawski 1989)

The table below shows the guidelines for excavation and support of 10m span rock tunnels in accordance with the RMR system (After Bieniawski 1989).

It should be noted that this table has not had a major revision since 1973. In many mining and civil engineering applications, steel fibre reinforced shotcrete may be considered in place of wire mesh and shotcrete.

Source: Rock mass classification.pdf

Microtunnel calculations with Examine 2D

In 2012 I finished my Master's in Geological Engineering by presenting my thesis entitled Construction of an Outfall with Microtunnel for the Disposal of Brine from a Desalination Plant.

In order to achieve the successful construction of this submarine Outfall, consideration had to be given to environmental impact of the disposal of brine, different methods of construction, and calculations of rock mass to enable the microtunnelling.

Examine 2D was the software used for some calculations, and below are graphs showing tensions, displacements and strength factors:

Sigma 1:

Vertical Displacement:

Total Displacement:


Strength factor: