Introduction
The Mont Royal Tunnel is built through a 700 feet high volcanic intrusion of igneous rock in a geological position with limestone, breccia, and other minerals. The tunnel also extends to a length of 4.97 km through the hill from the St. Lawrence River to Mount Royal. This tunnel is specifically important for a geotechnical analysis due to the fact that the hill is located on a geographical position where there are volcanic intrusions and rocks. These rocks cause a structural irregularity of the hill making the excavation and drilling of the tunnel a difficult and dangerous process (Hugh and Durand 49). Specifically, the Mont Royal Tunnel is situated in a location that has a geological composition of Igneous Dykes of Trenton Limestone and Camptonite Breccia. The igneous dykes are as a result of the volcanic action that formed the hill
Assessment of the Engineering Properties of the Rocks
As has been earlier stated the area has a geological composition of Igneous Dykes of Trenton Limestone and Camptonite Breccia. The engineering properties associated with these rocks are as is listed below.
- Effective stress of upto 5kg/cm2
- Strength of upto 2000kg/cm2
- Shear Stress of upto 140kg/cm2
- Compressive strength of upto 2000 kg/cm2
- Porosity of upto 20%
- Permeability of upto 10%; and
- Bulk density of upto 2.6g/cm3
However due to the discontinuities caused by the crystalline nature of the volcanic rocks on the tunnel tend to have an impact on the uniformity of the engineering properties of the rocks making it necessary for slopes to be stabilized or reinforced (Akis and Satici 161).
Evaluating the Stability of Rock Slopes
The geological composition of the hill as having both limestone and breccia make the hill a perfect point for tunneling because of the crystalline and hard structures of these rocks. The discontinuities within the rock structure however require the slopes of the rock to be stabilized as they pose a major risk during the drilling and excavation processes. The rock slopes have been stabilized in the following ways:
- The Tunnel utilizes breccia as the building stone in this tunnel making it stable.
- It also aids to incorporate steel and concrete beams and columns to improve the stability of the rock slopes and keep them in place. (The Internet Archive n.p).
Determining Stability of Underground in Rocks
The presence of breccia on the hill brings a serious problem during tunneling and excavation as breccia is highly crystalline thus breaking and cracking in the process. This presents the need for the underground to be stabilized during the process to prevent a collapse of the tunnel as the rock is being drilled through. The stability of the underground excavation in the rock is determined by:
- Ensuring that alignment is conducted during excavation
- Cutting the tunnel at the angle the tunnel is presently taking
- It also helps immensely to use the right equipment to maintain the stability of the underground rock (The Internet Archive n.p).
Support Systems for the Rock
The irregularity of the system caused by the limestone and breccia geological compositions called for a need for supporting the rock to prevent a collapse or weakening of tunnel during excavation. The presence of large dykes required more energy drilling meaning that the rock would have to be supported to prevent a collapse of the tunnel in the process. Some of the support systems for rocks that can be installed include:
- Installing steel columns that form a center wall which rest on the rock
- Using pneumatic concrete lining at the back of the mountain where the steel column shields cannot be used (The Internet Archive n.p)
References
Akis, Ebru and Ozgur Satici. "Underground Structures, Rock Structures and Rock Mechanics from Ancient Era to the Modern Age." Journa;l of Geological Engineering (2017): 155-172. Document. 5th March 2018. <https://dergipark.gov.tr/jmd>.
Grice, Hugh and Marc Durand. "Contribution of Discontinuous Rock mass Failure." Journal of Glaciology (2016): 41-55. Web Page. 5 March 2018. <https://www.cambridge.org/core/journals/annals-of-glaciology/article/div-classtitlethe-contribution-of-discontinuous-rock-mass-failure-to-glacier-erosiondiv/76A97583C001406D3F6F81015EE22BE0>.
The Internet Archive. "Full Text of the Mont Royal Tunnel." Journal of Geotechnical Engineering (2015). Web Content. 5th March 2018. <https://archive.org/stream/mountroyaltunnel00moun/mountroyaltunnel00moun_djvu.txt>.
