Directional Drilling Machines

//Directional Drilling Machines

Directional Drilling Machines


© 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:

  1. Soil  strata  through  which  the  pipe  or  cable  is  to  pass.
  2. Diameter  of  the  pipe  or  cable to be laid.
  3. Depth of pipe or cable  below the  ground.
  4. Total length of the pipe or cable.
  5. 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:

  1. Laying of Water supply and Sewerage lines.
  2. Laying of Gas pipelines.
  3. Laying of Telecom cables.
  4. 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.