Trenchless Construction Methods
Introduction
Among the main challenges facing most municipalities and cities today is the modernization of public infrastructure. As a consequence, the application of trenchless technology to modern construction engineering is on a steady increase, as it is now being applied for the repair or replacement and installation of underground infrastructure systems. According to Pitroda, Bhavsar and Belani (2014), the use of trenchless technology is gaining more popularity because it ensures that there fewer disruptions to business, homes and roadways infrastructures compared to the traditional underground construction methods. Trenchless technology can be described as the science for renewal or repair and installation of underground cables, pipes and ducts using methods that eliminate or minimize the need to undertake excavations (Pitroda, Bhavsar & Belani, 2014). This technology helps to reduce the environmental damage associated with a given underground construction as well as the social associated with it. As such, this technology is often preferred during the installation of various utilities that pass under highways, rivers, or other obstacles with a very minimum distribution of the normal flow of operations or damage to the ecosystem. This paper seeks to describe the different methods of trenchless technology and its applications.
Trenchless Construction Methods
Different trenchless construction techniques can be implemented either for renewal purposes or new constructions (Pitroda, Bhavsar & Belani, 2014). Some of the common factors considered when choosing the most appropriate trenchless construction method to be used in a particular site include issues like the overall soil condition of the boring site, the level of groundwater, and the unanticipated obstructions, among others. Moreover, the personal health and safety of workers have to be maintained during the construction process, and among the considerations that should be made includes factors such as ensuring that the minimum pipe diameter has to be maintained at all conditions during the boring process while over-excavation should also be avoided. Pitroda, Bhavsar and Belani (2014) suggest that each construction purpose requires the use of unique trenchless construction methods. As such, trenchless construction techniques can be classified into three broad categories. As shown in the figure below;
Figure 1: Fig.1: Trenchless Construction Methods
Based on the classification described in the figure above, trenchless construction techniques are categorized under three main classes;
A. The horizontal earth boring method
B. The Pipe jacking method, and
C. The Utility Tunneling method
The basis of this classification relies on the type of work and workers required to execute it. For example, from the chart above, the horizontal earth boring technique doesn’t require workers to go ahead with the work inside or within the borehole drilled. However, the pipe jacking technique and utility tunneling method require workers to be inside the borehole being drilled. The difference between the pipe jacking technique and the utility tunneling method is in the support structure employed by both techniques. The pipe jacking technique makes use of prefabricated structures for support, while the utility tunneling method uses the equipment applied for excavation as its support structure temporarily.
The Horizontal Earth Boring Technique
The horizontal earth boring technique is broken down further into several different methods which include;
a) The Horizontal auger boring method
b) The Horizontal directional drilling method
c) The Pipe ramming methods
d) The Compactions methods
e) The Pilot-tube micro tunneling method and,
f) The Micro tunneling methods
When implementing the horizontal earth boring method, several considerations have to be put in place. For example, during the horizontal auger boring method, uncased boring has to be avoided to minimize the likelihood of an accident or collapse on the personnel drilling. Pitroda, Bhavsar and Belani (2014) add that during the micro tunneling methods, a 42 inches minimum pipe diameter has to be maintained at all conditions to ensure that the personal health and safety of works are maintained. Other factors that have to be considered when applying the pipe jacking method is the overall shaft design features. The categorization of each of these methods has been depicted in the diagram below.
Figure 2: The Horizontal Earth Boring Methods
A detailed explanation of each of the above categories of the horizontal earth boring techniques has been given below.
The Horizontal Auger Boring Method
This method is commonly applied in the installation of steel cast pipes across busy areas such as highways or railroads because it is considered to be a more economical and effective technique compared to others. The boring auger method involves the drilling of a horizontal bore through a barrier that starts from the drive and ends up at the reception shaft. The anger string used in this technique is made up of a cutting head located on the leading end. The spoil is later taken back onto the shaft, being driven into the drill.
In this case, uncased boring is often avoided to minimize the likelihood of an accident or collapse on the personnel drilling. During the drilling process, the auger string is used to rotate the cutter head, and the boring machine is used to rotate the auger string. As the drilling hole advances, a casing occupies the borehole. The machine is fitted with a hydraulic jack that facilitates the case moves into the hole, and this is achieved by pushing it as the boring signs of progress. From this description, it is quite evident that the soil excavation process and removal, alongside the insertion of the machine’s casing, should all be done as one continuous operation.
Figure 3: Horizontal Auger Boring Across the Roadway without Disturbing It
Retrieved from Arjun (2017)
Horizontal Directional Drilling
This technique is a two-stage process, where the first stage involves a pilot hole with a small diameter that is drilled along the desired centerline or proposed line. The second stage of this process is usually concerned with the enlargement of the drilled pilot hole. By enlarging the drilled pilot hole, it allows for the accommodation of a utility line that is later pulled through the enlarged hole. Najafi (2012) indicates that the enlargement process can sometimes be undertaken at different stages until the desired hole diameter hole is obtained. This technique is commonly applied during the installation of conduits or pipelines.
Figure 4: Horizontal Directional Drilling
Retrieved from Arjun (2017)
Pipe Ramming Methods
This technique involves the use of trenchless construction methods mainly applied for road crossings and railroad utility installation. In this technique, the steel casing is usually hammered in the earth using an air compressor. Depending on the overall diameter of the hammered pipe, it may be the open or close end. Using air pressure, the soil is usually pushed out of steel when there are large diameters employed (Pitroda, Bhavsar & Belani, 2014). The diagrams below demonstrate the main characteristics of this method and how the procedure is undertaken.
Figure 5: The Procedure of Pipe Ramming Method
Retrieved from Arjun (2017)
Figure 6: Final Arrangement after the Piper Ramming method
Retrieved from Arjun (2017)
Compaction Methods (CM)
This method is also referred to as impact moiling, and it is commonly used during the installation of conduits or pipes with a diameter of less than 8-inch. The technique involves the development of a borehole that is done through pulling or pushing a pipe through the compression of the soil. According to Pitroda, Bhavsar and Belani (2014), construction undertaken without requiring any engineering assistance can easily adopt this technique.
Micro tunneling
The Micro tunneling trenchless construction method is a technique that is completely controlled by a remote. According to Pitroda, Bhavsar and Belani (2014), this method is aimed at providing continuous support to the excavation process through the aid of a pipe jacking process that is well guided. This method is commonly applied in sewer line installations. During the boring process, Pitroda, Bhavsar and Belani (2014) indicate that the spoils are usually removed through the help of mechanical augers or pumping. Najafi (2012) adds that this technique tends to be very accurate. Various micro-tunneling machines are often available for the boring process, with the factors considered when choosing the most appropriate machine for this process being issues like the overall soil condition of the boring site, the level of groundwater, and the unanticipated obstructions, among others.
Pipe Jacking Method
This technique involves the installation of a prefabricated pipe through the ground. During this process, the driving happens from the driveshaft to a reception shaft. This driveshaft comprises of jacks with the ability to move the pipe. Pitroda, Bhavsar and Belani (2014) observe that during this process execution, a hydraulic jack utilizes the thrust power to ensure that the pipe is moved forward deep into the ground. The jack’s rams are then retraced once the installation of all the pipes has taken place. Following this procedure is important because it ensures that the preparation of the following pipe happens smoothly in a position that will allow for the repeat of a similar procedure.
Figure 7: Pipe Jacking Work Procedure
Retrieved from Arjun (2017)
During this procedure, Pitroda, Bhavsar and Belani (2014) indicate that soil is transported from the jacket pipe and the driven shaft, simultaneously with the excavation process. The process can be undertaken either manually or mechanically. As earlier stated, the pipe jacking technique involves a worker’s entry method that requires workers to be present during the excavation and soil removal process within the pipe. As such, Pitroda, Bhavsar and Belani (2014) argue that a 42 inches minimum pipe diameter has to be maintained at all conditions to ensure that the personal health and safety of works are maintained. Other factors that have to be considered when applying the pipe jacking method is the overall shaft design features. Pitroda, Bhavsar and Belani (2014) suggest that the design features adopted have to be good and strong to be able to withstand any large thrust that might result from this process. Moreover, over-excavation should also be avoided because it is likely to result in numerous voids developing and in situations where these voids occur, they can only be fixed through the use of grouting techniques. As such, making these considerations is very important for the success of this process while also ensuring that the safety and health of the workers are well maintained.
Utility Tunneling Method
Similar to the pipe jacking technique, the utility tunneling method serves the same purpose. However, the difference between these two methods is in the support structure or lining used. While the pipe jacking method uses special types of steel as supporting structure, the utility tunneling method usually adopts a temporary support structure such as concrete liner plates, still ribs or wood lagging systems (Pitroda, Bhavsar & Belani, 2014).
When applied in the construction of trenches, the utility tunneling procedure involves the installation of liners acting as continuous supporting structures in front of the cutting face, and the soil is usually removed through an excavation process. The diagram below gives a visual description of the utility tunneling technique.
Figure 8: Utility Tunneling Method
Retrieved from Arjun (2017)
From this diagram, it is quite evident that the construction of the tunnel usually happens between the two accessible shafts.
Conclusion
From the preceding, the emergence of trenchless technology has equipped construction engineers with science that allows for the renewal, repair and installation of underground cables, pipes and ducts using techniques that eliminate or minimize the need to undertake excavations. As such, this technology is often preferred during the installation of various utilities that pass under highways, rivers, or other obstacles with a very minimum distribution of the normal flow of operations or damage to the ecosystem. Moreover, this technology helps to reduce the environmental damage associated with a given underground construction as well as the social associated with it. There are different trenchless construction methods with the main differences between them being the basis of their classification, which usually depends on the type of work or the workers required to execute it. For instance, the horizontal earth boring technique doesn’t require workers to go ahead with the work inside or within the borehole drilled. However, the pipe jacking technique and utility tunneling method require workers to be inside the borehole being drilled.
Moreover, the support structure or lining used can also be a key determinant of the type of trenchless constriction method used. For example, while the pipe jacking method uses special types of steel as supporting structure, the utility tunneling method usually adopts a temporary support structure such as concrete liner plates, still ribs or wood lagging systems. Some of the common factors considered when choosing the most appropriate trenchless construction method to be used in a particular site include issues like the overall soil condition of the boring site, the level of groundwater, and the unanticipated obstructions, among others. To ensure that the personal health and safety of workers are maintained, the minimum pipe diameter has to be maintained at all conditions during the boring process, while over-excavation should also be avoided. Making these considerations is very important for the success of any trenchless construction method.
References
Arjun, N. (2017, January 10). Trenchless construction methods and their details and uses. Retrieved from https://theconstructor.org/construction/trenchless-construction-methods/15290/
Najafi, M. (2012). Trenchless technology: Planning, equipment, and methods. McGraw Hill Professional.
Pitroda, J., Bhavsar, J., & Belani, D. (2014). A REVIEW ON TRENCHLESS TECHNOLOGY: STATE OF ART TECHNOLOGY FOR UNDERGROUND UTILITY SERVICES. Conference: National Conference on: “Trends and Challenges of Civil Engineering in Today’s Transforming World”, ISBN: 978-81-929339-0-0.
