March 5, 2020

The Basics of Tunnel Excavation

Tunnels are in many ways unique in the kind of engineering challenges they present. Unlike the vast majority of geotechnics that human beings engage in, tunnels are mostly about removing material to create a structure rather than adding it. Yet, tunnel infrastructure is one of the most ancient kinds, and represents incredible utility in cases where surface infrastructure is undesirable or simply impossible. However, tunnel excavation is highly dangerous, with many horrific tunnel collapse accidents recorded over the years. So what are the basic engineering principles that need to be observed when building a tunnel?

Imagine you have a building in front of you and you are tasked with removing a load-bearing structure in the very middle of the ground floor of it to make way for a corridor. That is essentially what tunnel excavation is. Subterranean infrastructure implies a large, heavy layer of terrain right over it, and removing some soil from underneath it means removing the thing that supported all that earth above. Now the assumption is that the ground is generally hard and can withstand a small cavity no problem. That may be true in situations where you are excavating a monolithic formation of rock, like a cliff, which has a degree of tensile strength if it is uniform. But this is an exceptional scenario, even for rock terrain, which usually has cracks and joints all over. In most other places in the world earth is a loose substance. The density and solidity is due to the pressures that are being put on it from above. Earth isn’t naturally adhesive, but thanks to its coarseness, friction caused by pressure can make it behave like a solid object. By removing soil, pressure in certain sections is removed, potentially creating a chain-reaction of loosening soil.

Tunnel Excavation
Tunnel Excavation

Most tunnels overcome this problem with reinforcing the ceiling and walls with lining. Historically those were stainless steel beams and plates or reinforced concrete that were installed over the entire ceiling and wall surface of the tunnel. The ceilings of tunnels are usually curved into a half circle, allowing for better distribution of pressure around the tunnel. Unfortunately, this relatively simple solution adds an enormous expense to tunnel construction. Many tunnels never got built simply because of how expensive it would be to install these lining systems. Unfortunately there is no easy way around it. The expense for loose soil tunnel excavation can be reduced through economies of scale, where the lining materials are standardised and produced in quantities that make their use economically feasible. Jointed rock is easier to solve, but still requires work. It works in a similar way to the method by which concrete is reinforced by rebar. Jointed rock tunnels are reinforced by rock bolts – long, thick steel bars that are drilled into the tunnel ceilings and walls. These bolts are usually anchored by wedges at their ends. This creates a pattern of steel reinforcement that spreads pressure around the tunnel evenly regardless of the natural join pattern of the rock formation.

Next Post

November 6, 2019

Three of the Largest Mines in the World Today

Ask many people to give examples of geoengineering projects and, sometimes after bridges and dams, you might get mines. Whether open pit or underground, the world’s most extensive mines are among some of the most impressive (if highly functional) engineering projects humanity has ever undertaken. From expensive diamonds to mundane, but possibly more important, commodities…

by Stephanos
Three of the Largest Mines in the World Today
September 10, 2019

The Three Biggest Engineering Projects in the World Right Now

When it comes to mega-engineering projects, not many finish under budget or on time. Many residential house builders come in late and over budget, let alone huge multinational crews working across hundreds of miles over many decades. Untold billions have been put into these projects which, when finished, will show just how far our engineering…

by Stephanos
The Three Biggest Engineering Projects in the World Right Now
July 12, 2019

The Engineers Who Fashioned Today’s World

It is hard to imagine today’s modern world without the great engineering feats that can be seen in every city and dotted around the landscape. From aqueducts to huge hydroelectric dams, skyscrapers and underground transport systems, engineering effects each and every one of us. But who were the forefathers of engineering that helped shape our…

by Stephanos
The Engineers Who Fashioned Today’s World
May 21, 2019

Soil and Geotechnical Engineering

As geotechnical engineering concerns the process of construction methods including rocks, it is imperative that the study of soils is also included. So much so that the highest industry body is now called the International Society for Soil Mechanics and Geotechnical Engineering. The science of geotechnical engineering is highly complex and involves many topics, but…

by Stephanos
Soil and Geotechnical Engineering
March 27, 2019

The World’s Greatest Dams

There are many jaw dropping architectural feats around the world, but surely the engineering brilliance that goes into building a dam must be at the top of the list. The sheer size and dimensions of theses amazing structures is awesome, but the knowledge of what the dam is actually doing makes it even more poignant….

by Stephanos
The World’s Greatest Dams
January 1, 2019

Tips How to Become an Engineer

As an engineer you are probably involved in working out how to build the tallest bridge, design the slickest engine, or how to build the smallest car. And you may be caught up so much in your work that you never pay attention to your career. But today opportunities within engineering are many, and there…

by Stephanos
Tips How to Become an Engineer
June 20, 2018

Architectural Marvels Around the World

There are some amazing buildings and other man-made structures that have been built throughout the world. These are structures that really showcase the talent and creativity of architects. After all, to design and build a structure that is not only aesthetically-pleasing, but also safe and functional, is not an easy task. We will discuss here…

by Stephanos
Architectural Marvels Around the World
June 6, 2018

Top Engineering Firms Around the World

There are several engineering firms throughout the world; some of these have made more impact than others. Here we are going to discuss the top engineering firms that are known today. Well Known Firms The firm 3M  is a well-known company, it is an American company that has expanded into a multinational conglomerate with branches…

by Stephanos
Top Engineering Firms Around the World
May 11, 2018

The Different Types of Jobs in Engineering

There are many types of jobs available in the Engineering field, some of which pay a very high salary. Some of these fields are: mechanical engineering, industrial engineering, electrical engineering, aerospace engineering and petroleum engineering. Within each of these engineering fields are several sub-disciplines in which a person can specialize. To obtain a job in…

by Stephanos
The Different Types of Jobs in Engineering
May 1, 2018

Continuing Education that is Vital for Engineers

Engineering is like many professional fields in that new methods, techniques and approaches are constantly being developed and recommended. This means that it is very important, in fact, essential that an engineer undertake continual learning to stay current within their field and profession. Continuing education thus should be made a priority for workers regardless of…

by Stephanos
Continuing Education that is Vital for Engineers