What is Tunnel Surveying? Application of Tunnel Surveying

What is tunnel surveying?

Tunnel surveying is a process in which qualified personnel use tools to direct the construction of tunnels and underground structures.

The process is usually done underground, using vertical measurement techniques, but may also take place through water-filled passages with the help of surface circulation.

Surveying is a process that involves separating out different elements or objects, such as rock and dirt, from the aggregate or mixture.

The process of tunnel surveying is all about creating accurate models, in some cases of underground structures, that are used by the construction industry to expedite the design as well as to ensure a safe and efficient, and economical construction project.

Tunnel surveying equipment

There are a number of different kinds of the tunnel surveying equipment that can be used to map tunnels and underground structures.

The best kind of equipment for the job depends on the complexity and size of the task as well as on the needs of the surveyor.

Some typical types of tunnel surveying equipment include:

Magnetometers

These are usually used to detect magnetic fields and can be used to find objects that are buried deep in the ground.

Electromagnetic Equipment

This is the equipment that is used to measure the resistivity of the ground, a technique that can be used to determine if there are mineral deposits or even underground water sources within rocks.

Borehole equipment and monitoring instruments

These are the instruments for studying the surface features at a particular location, as well as for the assessment of surface geology and groundwater levels and condition.

Ground-Penetrating Radar Systems

These are the equipment of tunnel surveying that is used to measure the thickness of various materials such as rock, soil, and other materials.

Piezometers

They are instruments used to measure water pressure below ground level.

Descent drilling instruments

These are equipment that is used when the surveyor needs to go deeper into the ground than usual, he uses descent drilling tools and techniques (also known as auger boring) that allow him to reach or even go below the water table.

Other Equipment

other equipment used by the surveyor can include things such as a level and measuring tape to take levels and measurements of tunnels, and also includes a compass, or a clinometer (for taking angles or topographical bearings).

Tunnel surveying methods

The tunnel surveying methods used by surveyors depend on the type of underground structure that is being surveyed.

There are three classifications:

Continuous tunnels – these tunnels don’t have any cross-sections.
Segmented tunnels – these tunnels can be broken into smaller segments.
Complex tunnel intersections – this type of tunnel includes complex intersections and junctions with other passages, and needs to be mapped precisely for construction purposes.

How it works

Once the surveyor has made his measurements, he can do calculations to determine the dimensions and dimensions of different underground structures or structures that are submerged in water.

He then uses models to design and draw the underground structure, in a very precise way so that it becomes easier for construction workers to set up their equipment and conduct excavation works.

From simple models to complex models, the process is similar – a model is created, and then it is used to plot the underground structure.

Application of Tunnel Surveying

Tunnel Surveying can be applied in various areas. They include:

Speed up the design and construction process.
Make the design process more efficient and allow for earlier completion of the project.
Ensure the safety of the construction workers by providing detailed information about how to safely construct or excavate different parts of a tunnel or underground passage.
Reduce the costs involved in designing complex structures that include tunnels, underground passages, and other structures that are located deep underground or even underwater.
Ensure that work is conducted according to the plan, thus ensuring that all aspects of the project are being completed in a timely manner with minimal or no snags or problems.

Types of tunnel surveying

The different types of Tunnel Surveying are:

Site investigation – this type of tunneling is used to determine the ground conditions in an area, including the depth, hardness, and thickness of the ground.
Boring and excavation – this type of tunneling is usually done to construct mines, tunnels or other underground structures; it includes methods such as auger boring, conventional mining or even tunnel boring machines.
Ground-penetrating radar – this type of surveying is used to measure the thickness of materials and other underground features.
Perished concrete or rock – this type of surveying is used to determine the depth and height of structures that have deteriorated due to fire or other natural disasters; it can even be used to locate buried structures and archaeological sites.
Open hole type surveys – these types of surveys are best suited for large industrial manufacturing plants where tunnels need to be constructed with the proper specifications; these surveys are usually done in areas where there is heavy traffic.
Manholes and shafts – these types of surveys are used to determine the location of underground structures such as manholes, subway tunnels, and other similar structures.

Tunnel Surveying Advantages

The advantages are as follows:

It can be used to determine the location of underground structures that are built underwater.
The tunnel surveying equipment is easy to use and relatively inexpensive.
The process of surveying is quite simple, thus making it an excellent tool for those who don’t have much knowledge about the intricacies of architecture, engineering or construction work.

Tunnel Surveying Disadvantages

Some of the disadvantages are:

It cannot be used to accurately determine the depth of underground structures that are built underwater.
The process of surveying varies from worksite to worksite and can also have problems; thus, it can sometimes lead to a lot of time wasted and many problems for the project.
The results obtained by tunnel surveying are not guaranteed; thus, the accuracy of the results is not guaranteed or 100% accurate.

Tunnel Surveying Example

Construction of the Panama Canal

The construction of the Panama Canal is one of the most famous examples of how tunnel surveying was used to design and construct an underground structure.

The project was started by France in 1880, but after 10 years, it became a failure; most structures collapsed, and more than 22,000 people died during the construction project.

When the United States took over in 1904 to finish what France had started, they first used aerial photography to survey all parts of the canal that was located underwater.

In 1909, the military engineers used these images to create an accurate plan of the canal that was then used in designing and constructing the final structure.

The first stage of construction began in August 1914; by November of that same year, the U.S. Army Corps of Engineers completed and opened the canal.

The total cost of this project was $375 million ($8.2 billion today); by comparison, a similar sized tunnel project that included roads and bridges had a budget set at $1 billion ($23.7 billion today).

The Panama Canal is still considered one of the most complicated tunnels ever built; it is fifty-five kilometers long, with a width and depth of up to sixty meters and a height of twenty meters.

The main factors that allowed the U.S. engineers to complete this project were that they had accurate mapping for the project and a simplified process for surveying the underground structure.

The Proportion of Tunnel Survey

Every engineering project has a proportion of tunnel survey. It is the most practical way of surveying and designing a tunnel.

The following are 5 important elements for the purpose of tunnel survey. They are abbreviated as:

1) Geology: (Geo): it includes information on the nature, structure and composition of the ground through which a tunnel is to pass.

2) Coordinates: (Co): it is the location of the station at which a survey is to begin and end; it determines the starting point of the tunnel, and it also determines where a dividing line will be drawn between two segments.

3) Direction: (Dir): it describes the longitudinal or transversal direction of a tunnel. It is measured in degrees.

4) Profile: (Pro): it includes drawings and measurements of specific portions of the tunnel such as its length, height, diameter, and gradient slope. It is also known as a profile drawing.

5) Cross section: (Sec): it refers to the cross-section of the tunnel, which can be tensile, transverse or longitudinal.

Tunnel Surveying Procedure

You will come across the following procedure for tunnel surveying, which is described below.

The geologist will decide on the way to proceed by stating the depth, direction, and nature of the tunnel that is to be created. This can be done with a computer-generated mapping or by using a measuring device.
The geologist will use lasers and radar to survey underground features or features that cannot be seen using standard surveying equipment such as cameras, trucks or bulldozers.
The surveyor will then determine a starting point and the length of the tunnel from that point; they will measure the height, diameter, and gradient slope of the proposed tunnel using a mapping device and a coordinate machine.
The surveyor will then determine the surface features such as topography, water features, roads, and buildings; they will then calculate the height above sea level to ensure that it is safe for all aspects of construction.
The surveyor will then determine the direction of the tunnel and draw a plan of the entire tunnel.
The surveyor will then establish the direction, profile, cross-section, and slope to create a detailed plan that is accurate.

Post-Surveying

After completion of the surveying process, you will have to go through several steps that are necessary after surveying is completed. Below is a checklist of these steps:

After the completion of tunnel surveying, the surveyor will have to send his information to the authority who created a contract for the project.
After receiving this information, the authority will then convert this into a plan and create contracts for all aspects of construction that are necessary for building the tunnel.
The contractor will then complete all aspects of the project and send reports to ensure that it meets all stated requirements for specific details and measurements.
After the tunnel is complete, the authority will then start inspecting what has been built; they will then send a final report in order to ensure it meets all of the stipulations.

Benefits of Tunnel Surveying

Tunnel surveying is an effective way to survey and design underground structures for construction purposes.

It helps improve productivity and efficiency, which benefits all parties involved in a project. Tunnel surveying can also increase safety by reducing the chance of an accident that could be caused by human error or unforeseen conditions underground.

FAQs

What is the most popular mode of tunneling?

The most popular mode of tunneling is known as tunnel boring machine (TBM). It is a machine that has rotating cutter heads on the front to control the direction of excavation and carry out shaping work.

What are some of the methods used by tunnel surveyors?

Some of the most common methods used by a tunnel surveyor include:

Data collection and processing; includes data on measurements, a grid system, and networking information for database management.
Tunnel design, involves drafting plans that are used to create a design for the tunnel.
Tunnel survey; this includes a survey of the actual tunnel route and measurements as well as the setting out of levels and control points.
Line drawing; this process involves creating a final drawing that can be used by engineers to create a blueprint for the project.
Data management; is an ongoing process that involves collecting and organizing data in order to maintain consistency in all aspects of the project.

What is an important consideration when planning a tunnel project?

It is important to consider the following items when planning a tunnel project:

Local topography and ground conditions, which refers to the topography of the area where the project is being carried out. This can determine factors such as soil characteristics, rock type and ground water flow patterns.
The amount of traffic on a project; could determine where columns will be built for support and what materials will be used.
The size and height of the project; will determine the available space for excavations and the operational aspects such as lighting, ventilation, access, and emergency exits.
The need to connect with utilities under construction; will determine the materials used for foundations, reinforcements and how they will be connected to existing utilities.
Space; refers to the space required in building structures such as buildings, shops or parking lots.

What are the necessary requirements in a very large tunnel project?

There are several requirements for a very large tunnel project:

A need for expert tunnel surveyors; there is a lot of data involved, which include the coordinates of the existing topography, existing tunnel structures, and other underground utilities that might be encountered during the excavation process.
A need for advanced equipment; equipment needs to be enhanced or made more suitable to large tunnels.
Additional personnel.
Longer construction time.

Why do you need a tunnel survey?

“A tunnel is a man-made structure that can be used for transportation or for other purposes. It uses the force of gravity to move people and goods through the ground.”

If a planned project requires the movement of people and materials such as construction materials, food, or water, then it requires a tunnel survey.

why do we need to survey underground structures?

Tunnel surveying is a must for any engineering project. It helps use the most effective designs and methods for building and designing tunnels safely.

A tunnel survey will also help reduce construction costs and avoid unexpected delays.

How many years does it take to get a tunnel survey started?

It can take anywhere from 1 to 3 years for a tunnel survey to be completed. A survey team is usually 1 to 4 people that are trained and experienced in various aspects of surveying.

Why is it important for the designers of a tunnel project to have accurate information about all the underground features?

This information is essential for an effective and efficient design process. Everything must be measured, recorded, mapped and planned in order to complete a successful project.

What are the most common causes of errors and delays in the tunnel surveying process?

The surveyor must be aware of any potential errors or delays during the process. A common cause of errors and delays is not maintaining proper communication between all parties involved in the project.

How accurate will my plan of a tunnel be?

It always depends on how well it is created, but you can expect your plan to be exact. The surveyor will ensure that all information has been provided and that a plan has been made from beginning to end.

How much does it cost to surveil a tunnel?

The cost of surveilling the tunnel depends on how long the tunnel is and how many sides or corners that it has. The following are approximate costs for surveilling a tunnel:

Tunnel survey costs can range from $20,000 to $100,000; surveyors will use a combination of data and manual methods to determine these costs. The length of the tunnel and the number of sides will affect these costs.

How do tunnel surveyors determine the depth of the tunnel?

Tunnel surveyors calculate the depth of tunnels by using a number of different methods. They can be done in one of three ways:

Template surveying – this method involves placing a metal plate in front of the tunnel to serve as a template or guide. The plate will then be used to establish the shape and length of the tunnel by using calculations and drawings.
Cable-mounted camera (CLAM) – this method involves placing a 100-meter cable that is attached to the camera at one end and the tunnel at the other end, along with two instruments. The instruments are used to capture different images of the tunnel that are then used to establish various aspects of it.
Radar (radio detection and ranging) – this method involves using a radar system to find the shape and location of the tunnel. A surveyor will then use calculations and diagrams to determine the length, direction, grade and cross-sectional area of it.