© 2009 Er. Jagvir Goyal
Note: This highly informative and elaborate paper was written by the Author many years back and holds valuable information. Readers should update themselves with the latest developments that might have occurred after the presentation of this paper.
A few years back, when the directional drilling machines were being promoted by their manufacturers, doubts were expressed by many over their capability and success. These doubts however were soon dispelled. With time, DDMs have gained more and more ground and popularity. A major reason behind that is the increasing awareness for environment friendly and cleaner technologies. As the Directional drilling machines promote trench-less technology, these are finding quick acceptability for ‘no dig sites’.
Trench-less technology allows laying of pipes or cables along or under the roads without disturbing the road surface. The work continues below ground while the traffic runs as usual. Digging out trenches for laying pipe-lines or cables along or under the roads already open to traffic is a nuisance –making exercise but an unavoidable part of construction jobs. The traffic gets diverted leading to frequent jams and impatient blaring of horns. In most of the cases, the back-filling of soil after the laying of pipes or cables is not done in a proper manner. Resultant pits and bumps make the vehicles jump and leave the drivers cursing under their breath. Even the cool breeze gets laced with the dust left on the roads. In nut-shell, the journey doesn’t remain a pleasant one. Under such circumstances, DDMs prove quite useful and help in eliminating all these problems.
Directional Drilling Machines (DDMs) : A DDM mainly consists of three parts: a boring unit, an electronic tracking equipment and a drill component. The boring unit is a rig whose capacity is to be decided by considering the site conditions. To determine the pull force, torque and pump pressure of the boring rig, the following items are considered:
- Soil strata through which the pipe or cable is to pass.
- Diameter of the pipe or cable to be laid.
- Depth of pipe or cable below the ground.
- Total length of the pipe or cable.
- Unforeseen increases in pull load due to ground conditions.
The electronic tracking equipment plays an important part in execution of the job. It enhances the trencher’s ability by automatically adjusting track speed and force with respect to the ground conditions. An electric stroke limiter increases his control and doesn’t allow the engine to stall whenever tough conditions are encountered in the course of work.
The machine is made to operate at low speed and high torque. This helps the drill component, a cutting bit, to penetrate even the toughest rocks. Numerous boom options are available with different types of cutters and drill-bits. Right choice can be made depending upon the soil conditions and the job to be handled. The diameter of the bore hole is based on the diameter of the pipe or cable to be laid and enough annular space needs to be given to accommodate bends, curves and removal of soil.
Working of a DDM: DDMs are either hydraulic or pneumatically driven. These drive a soil-displacement-hammer through the soil and toe the pipe or cable along the underground directional bore thus created. The hammer has a moving chisel head that makes its way through the soil along the designed alignment. A small pit is required at the point of commencement of laying the pipe-line or cable. This is called launching pit. The DDM begins its work from this pit. Similarly an exit pit is required at the point of termination of cable or pipe. The entry angle and exit angle of the pipe or cable are carefully decided keeping the stress parameters and bending radius in view.
Areas of application: Cables and pipes of polyethylene or steel of diameter varying from 75 mm to 2 metre can be laid below ground, rivers, canals, roads and buildings using DDMs. For the laying of PVC pipes, a soil displacement hammer is used. When a steel pipe is to be laid, a steel pipe ramming hammer is used. Underground drilling can be done even through a solid rock. Not only the laying of new pipes and cables but replacement of existing but damaged pipelines laid for supply of water or gas or to discharge sewage can also be done by this technology and that too without digging these pipes out. For this, heavy duty steel rods of about 3 feet length are thrust into the old pipe until these create a full string of rods. A force is then applied to fracture old pipe into small pieces. The machine also toes along a new pipe which keeps on occupying the position of old pipe being broken. Thus the dismantling of old pipe as well as the laying of new pipe is done as a single activity. This brings in a lot of saving in time and money. The areas which can be immensely benefited by Directional Drilling Machines are:
- Laying of Water supply and Sewerage lines.
- Laying of Gas pipelines.
- Laying of Telecom cables.
- Laying of Electricity cables.
Preparatory works for using DDMs: It is always better to examine certain aspects relating to a job before deciding to use DDMs for the execution of the job. Once the feasibility of using DDMs is ascertained, any problem during execution of work does not arise. The following aspects should be studied:
Soil and area conditions: Carrying out soil investigations of the area to be drilled before a job is taken in hand is very important. The soil strata and individual physical properties of each stratum, the particle size distribution curve and the position of water table are important to be known. In addition, the cone penetration test to find out the details of erratic soft clay deposits should also be done. In case of rivers, the scour level needs to be known. The entry and exit angles for the DDM should be decided after these studies are completed. In most cases, these angles are kept between 6 degree and 15 degree to the horizontal. However, the final decision should be made when the soil studies are available. Additional parameters to be decided are the minimum bending radius, the drill-trace-axis and the distance between entry or exit point.
The area under operation should be studied to know the likely obstacles in work. Suppose a river needs to be crossed or the cables or pipes are crossing a highway. In such cases, adequate depth of the DDM below the highway or water level has to be checked.
License to work: It is very important to acquire necessary permits where required before taking the job in hand. Trespassing charges are to be avoided. The permit to work may have to be obtained from the River authority, Buildings & Roads department, Pollution control department, National highway authority, district administration, irrigation department or even individuals before taking a job in hand. Some traffic diversions may sometimes be felt necessary. Cutting of some trees along the alignment may be required as their roots might be interfering with the boring plan. For this, forest department may come in to picture. Once the alignment plan is decided, the authorities to be approached for getting the license to work become known.
Preparation of work plan: It remains very convenient to get prepared a drawing of the work area showing location of drilling machine, method of anchoring it, setting of drill fluid preparation unit, storage of pipes or cables to be laid, office cabin, generator and entry pit before starting a job. Minutest details should be shown on this drawing to make the operator’s job smooth. The method of anchoring the machine should be finalized. Drill fluid shall be required during the drilling operation. Its arrangement should be ensured. The pulling head needs to be fabricated and the crew is to be mobilized for the decided period of operation as the job once taken in hand should not be left unfinished. After the drilling operation is over, the ground should always be restored to original finish. Normally, elation over completion of the job makes the crew lax and due care in finishing the entry and exit pits to original ground level is not taken.
Execution of a job: To run a machine, generally a crew of two to three persons is sufficient. One person acts as the boring operator, one as the track equipment operator and third, if required, helps these two in carrying out their activities. Drill fluid is an essential requirement of all drilling operations. Normally, it consists of a suspension of water and bentonite. It makes the job of hydraulic cutting with the jet easier and stabilizes the bore hole, avoiding its collapse. Bentonite is a sort of clay having high contents of silica and alumina. Addition of the drilling fluid is regulated carefully as over release of it may rather hamper the operation besides wastage of fluid. Noise is to be kept low when the machine is working and the vibrations have to be minimal. In case of working below a road, expertise lies in not allowing the overhead traffic to know that a pipe or cable laying operation is going on below the road or highway the traffic is riding.
Availability of DDMs in India : Vermeer manufacturing company of USA, the top name for DDM production has already stepped in India and opened an unit in Ajmer, Rajasthan under the name, Worldwide machinery solutions. This firm produces many models of DDMs that operate in narrow areas where space is a constraint. Marketed under the brand name ‘Navigator’, these DDMs are ideally suited for gas, electricity, water and telecommunication lines. Presently, as many as 13 models of DDMs are being produced by Vermeer, the spindle torque varying from 745.7 Nm to 67791 Nm and the pull back force ranging between 2495 kg to 453592 kg. The largest DDM model D 1000×900 is suitable for extreme drilling under tough conditions and for large diameter trenchless excavation. Equipped with twin CAT C-27 diesel engines of 1600 hp, it has manually operated hydraulic controls and operates at high torque of 453592.4 kg and low spindle speed of 58 rpm.
Some International firms are producing machines of different sizes, equipped with a variety of hammers and bits as the choice of hammer is decided with respect to the type of job, quantum of work and the working conditions i.e. whether a fluid or drilling medium can be used or dry conditions are to be maintained. Sensing the great potential in Trenchless technology, Indian manufacturers are also taking up production of directional drilling machines. One company in India has already set up a large unit in Rajasthan and is now producing such machines of different capacities. Terra Macs limited, a New Zealand manufacturer produces many models of DDMs for mini to mighty jobs and even customizes machines as per requirements of the buyer. However Vermeer is ruling the DDM scene so far.
Use of DDMs in India: DDMs can prove a boon for laying cables and pipes in congested areas like metros. In metros, we just can’t put the daily life and traffic to a halt. So many jobs are being handled in India by using DDMs. Companies have procured high capacity DDMs from abroad and added to their equipment fleet. A 400 metre wide and 15 metre deep river in Thane near Mumbai, having hard rock strata at its base was crossed using DDMs for laying three layer polyethylene coated pipes of 450mm diameter, 10 metre below the base of the river. In West Bengal, laying of 457mm dia HDPE conduits imported from China below river Harohar and river Rupnarayan crossing more than 350 metre length in each case was done. In New Delhi, MTNL now uses DDMs for the cabling work wherever feasible.
There exists an Indian Society for Trenchless Technology in India. This society keeps a tab on the various trenchless jobs going on in the country. The society may prove helpful to interested contractors and firms in providing guidance on directional drilling and sharing experience especially the bottlenecks faced during execution of jobs. Such interactions may help in achieving perfection in trenchless technology.