Trenchless Construction Methods and Their Details and Uses

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Trenchless Construction Methods

Trenchless construction methods can be implemented for new construction as well as for renewal purpose. Each purpose requires specific trenchless construction techniques.

Classification of Trenchless Construction Methods

The classification flow chart of trenchless construction methods are shown in figure-1.

Fig.1: Methods employed under trenchless construction

From the above figure, trenchless construction methods are classified as:

• Horizontal earth boring,
• Pipe jacking, and
• Utility Tunneling

The classification is based on the requirement of workers. From the above chart, the horizontal earth boring (HEB) do not require workers to proceed the work inside the borehole drilled. While the pipe jacking methods (PJ) and the Utility tunnelling (UT) method involves workers inside the borehole. The pipe jacking differs from utility tunneling in terms of the support structure they employ. Pipe jacking uses prefabricated structures as support and the UT method employs the equipment used for excavation itself as the support structure which is temporary.

Horizontal Earth Boring (HEB)

The horizontal earth boring construction method is further divided into several methods such as:

• Horizontal augur boring
• Horizontal directional drilling
• Pipe ramming methods
• Compactions methods
• Pilot-tube microtunneling
• Microtunneling methods

Each method is described in detail in the following sections.

Fig.2: Classification of Horizontal Earth Boring (HEB) Method

Horizontal Auger Boring (HAB) Method

The installation of a steel cast pipe across a busy area like road, railroad or highway etc. can be done by horizontal auger boring method, as it is found more economical than any other method. In this method, through an embankment (from the drive to reception shaft) a horizontal bore is driven. The auger string consists of a cutting head at its end, that is leading. The spoil is taken back to the driven shaft. Uncased boring is avoided to get rid of collapse or accidents to the personnel working. The cutter head is rotated by the auger string, which in turn is rotated by the boring machine. With this advancement of drilling hole, a casing will occupy the bore hole. The hydraulic jack facilitates the movement of the case into the hole, by pushing it, with the progress of boring. So the soil excavation and removal, the insertion of the casing, all are done as a continuous operation.

Fig.3.Depicting horizontal auger boring without disturbing the roadway

Table.1: Horizontal Auger Boring (HAB) Method Characteristics

Method	Diameter range in inches	Installation height in feet	Material of Pipe used	Application	The degree of Accuracy
Auger Boring	4-60	600	steel	Road, rail crossings	±1% of length of bore
Steered on grade auger boring	4-60	600	Steel	Gravity & pressure pipe	±12in
Steered on line grade auger boring	4-60	600	Steel	Pressure & gravity pipes	±12in

Horizontal Directional Drilling (HDD)

The horizontal directional drilling methods mainly involves two stages or process.

1. In the first stage, a small diameter pilot hole is drilled along the proposed line or center line that is desired.
2. The second stage is to enlarge the drilled pilot hole. This enlargement will help in the accommodation of the utility line which is later pulled all through the hole that is enlarged.

The process of enlargement is sometimes done at different stages, until a desired diameter of hole is obtained. The method is mainly involved in installation of pipelines or conduits. The horizontal directional drilling method can be classified into different categories:

• Small -mini HDD
• Medium -midi HDD
• Large - maxi HDD

Fig.4: The Boring Operation done in Horizontal Directional Boring

Table.2: The Characteristics of Horizontal Directional Drilling Method

Method	Diameter range in inches	Installation height in feet	Material of Pipe used	Application	The degree of Accuracy
Mini-HDD	2-12	>/=600	PVC, Clay, FRP, PE	Cable, Pressure Pipe	Varying
Midi -HDD	12-24	>/=1000H	PE, Steel, Ductile iron	Pressure Pipe	''
Maxi -HDD	24-48	>/=6000H	Steel, PE	Pressure Pipe	''

Pipe Ramming (PR) Methods

Pipe ramming method is a trenchless construction methods used for the installation of utilities for railroad or road crossings mainly. The steel casing is hammered inside the earth by means of an air compressor. The hammered pipe may be opened end or closed end depending on the diameter. The soil is pushed out of the steel with the help of air pressure, when large diameters are employed. The main characteristics of pipe ramming method is shown in table-3.

Fig.5: Pipe Ramming Method - Procedure

Fig.6: Final Arrangement After Piper Ramming method

Table.3: Characteristics of Pipe Ramming Methods

Compaction Methods (CM)

Installation of conduits less than 8-inch diameter can make use of compaction method. This method is also called as impact moiling. The method is proceeded by forming a bore hole by pushing or pulling of pipe, by the compression of the earth(soil). Those jobs that are done with no engineering assistance, make use of these methods. Table.4: The characteristics of Compaction Methods

Method	Diameter in inches	Maximum installation depth in feet	The material of pipe used	Application	Accuracy
Compaction Methods	8 or less	250	Any	Cables or pipes	±1% of the length of the bore

Microtunneling

Microtunneling is a trenchless construction method. This is a complete remote controlled method. It provides continuous support to the whole excavation process with the help of a guided pipe jacking process. Microtunneling method is applied for sewer line installation. The spoils are removed with the help of pumping or by means of mechanical augers. It generally constitutes six independent systems all together:

• A micro tunnel boring machine
• A jacking system
• A spoil removal system
• The guidance system (Laser guidance)
• Remote Control system
• A pipe lubrication system

The microtunneling is very accurate in nature. A wide variety of microtunneling machine are available for boring. The factors that need to identified to choose the best machine is based on the soil conditions of the site, the groundwater level and obstructions that are unanticipated.

Pilot-Tube Microtunneling

This method is an alternative for the microtunneling. It makes use of all the main features of horizontal boring techniques and perform. It gains the accuracy of microtunneling, the spoil removal system property of an auger boring machine, the auger and guidance system as in microtunneling, directional drill method's steering mechanism and also make use of camera mounted theodolite. It is a complete equipped system, even with LED to have a higher accuracy in line as well as grades. For the installation of smaller sewer, water or main line sewers, the method is found very economical. For house water lines or sewer connections to the main lines, this method is a good choice. The pilot tube machines are usually used in soft soil that are relatively in a smaller depth. The distance of jacking can be around 300 feet or less. The main characteristics of the pilot tube tunnelling are mentioned in table 8. Table.8: Characteristics of Pilot-Tube Microtunneling

Method	Diameter in inches	Maximum installation depth in feet	The material of pipe used	Application	Accuracy
PTMT	6-10	300	Steel, PCP, DIP, VCP, GRP	Gravity Pipes with small diameter	±1inches

Read More: Trenchless Technology in Construction Pipe Jacking and Utility Tunneling Methods in Trenchless Construction