Technology and Technique Demonstration Day Horizontal
reading this section and attending this lecture the attendee will have an increased
Trenchless Excavation Construction Methods (TEC).|
Horizontal Earth and Rock Boring methodology. |
Environmental Well material installation techniques.|
Boring equipment used in small diameter well installations.|
following section presents an overview of Horizontal Boring process as it pertains
to the installation of horizontal remediation wells and other underground utilities.
is a brief introduction to basic horizontal equipment, site setup and general
procedures followed during a typical horizontal bore. Some of the references to
Line and Grade may or may not be of major concern to the remediation specialist.
However, in cases of watermain or gravity flow aqueducts it represents a critical
factor in the success or failure of the project. Furthermore, it is important
to know were the bore is heading to avoid hitting underground hazards and utilities.
excavation construction (TEC) methods include all methods of installing utility
systems below grade without direct installation into an open cut trench. These
methods are broken down into three main categories; Horizontal Earth Boring (HEB),
Pipe Jacking (PJ) and utility Tunnelling (UT). The method most commonly used in
the installation of environmental remediation wells is the Horizontal Earth/ Rock
HORIZONTAL EARTH BORING
Auger Horizontal Earth Boring is a process of simultaneously jacking casing through
the earth while removing the spoil inside the encasement by means of a rotating
flight auger. The auger is a flighted tube with couplings at each end that transmit
torque to the cutting head from the power source located in the bore pit and transfers
spoil back to the machine. The casing supports the soil around it as the spoil
is removed. However, in the case of standard 2" environmental remediation well
installations, Marathon Drilling has adapted it's vertical hollowstem auger system
to their Horizontal Boring Machines which eliminates the need for casing to keep
the hole open as the well is installed. In many respects, horizontal well installation
procedure is similar to its vertical counterpart in both protocol, and material.
The geotechnical conditions of the site, together with design requirements of
the field programme will dictate the specifications and type of well material
that should be used.
TYPE AUGER HEB METHOD
track type auger boring machine consists of a track system, the boring machine,
casing pipe, cutting head and augers as the main components. The optional components
consist of variations of bentonite lubrication systems, a grade control head,
a casing leading edge band, and a water level indicator or electronic indicator.
main factors that effect auger boring are the torque and thrust. Every effort
is made to control these two forces. The torque is created by the power source
which can be a pneumatic, hydraulic or internal combustion engine working through
a mechanical gear box. The torque rotates the augers which, in turn, rotates the
cutting head. The casing (if required) does not rotate while it is jacked through
the hole. One end of the rams is attached to the boring machine while the other
end is attached to the lugs that lock into the track system.
cases where the torque or thrust exceed the machines capacity then all forward
advancement is halted. Since actual conditions to be encountered are not known
until the boring operation commences every effort should be made to minimize torque
and thrust and both should be closely monitored during the operation.
the project to be successful, soil test borings, unit weight of soil, soil classification,
groundwater level determination, standard penetration test (SPT) value, unconfined
compressive strength of soil, etc. should be available. It is in the interest
of all contractors to excavate test pits prior to bidding a project. However this
does not mean that changed conditions and/or obstacles will not be encountered
during the boring program. Every effort should be made therefore to ensure that
unexpected conditions can be handled safely.
jobsite should be surveyed for overhead powerlines and other obstructions, water
job access and working space. All utilities should be contacted , located, marked
and if necessary exposed to positively identify and locate any potential underground
obstruction in the bore path. Utility lines damaged beneath a road way by the
boring operation would most likely result in open cutting of the roadway at a
substantial expense and great inconvenience to the public. In most instances an
entrance pit is required on the approach side of the bore. The site should allow
adequate room for a boring pit excavation plus the subsequent stockpiling of excavated
material if it is not being removed from the job site. Natural water drainage
should also be considered. It should be ensured that in case of heavy rain the
pit, equipment and material is not flooded.
possibility of building a temporary drainage system to route water away from the
job site should be investigated.
PIT EXCAVATION AND PREPARATION
beginning and end of the bore should be located far enough away from existing
structures to allow adequate safety for the structure and the public. The distance
of the bore pit to the roadway should allow for safe sloping of the pit walls
if necessary. If sloping of the pit walls cannot be accomplished, sheeting of
the pit walls should be considered. Local codes and OSHA manuals should be consulted
concerning the specifications and requirements for pit wall sloping and sheeting.
all the utilities located and marked, excavation can begin. All cuts, grades and
slopes should conform with the construction plans. The boring pit should be offset
slightly to the side of the bore line on the side that the spoil exits from the
machine. This allows for more access for spoil removal. Any utilities in the pit
must be supported. If groundwater is expected or encountered a dewatering system
must be utilized.
boring pit bottom must be firm enough to support the boring machine tracks, boring
machine, casing, and the augers. in most cases, the pit will have to be excavated
below grade and then filled with crush stone to the required specifications. Wooden
planking is then placed under tracks for support. A concrete floor may be poured
if the bore is of considerable length, size and duration or if soil conditions
boring machine applies thrust to the back of the boring pit. To withstand this
thrust, a backing plate should be installed against the back wall of pit, square
with the line of thrust. For low to medium thrust pressures, steel sheeting, a
steel plate or wooden timbers have been found to be adequate. However, on long
and large diameter bores, a concrete backstop in addition to steel plate is desirable.
Care must be taken to ensure that the developed thrust pressures do not disturb
any existing utilities in and around the bore pit area. Each bore pit should be
constructed as if it were to be in use for a much longer time than anticipated
to allow for unforeseen problems and delays. Doing it right the first time will
save both time and money.
an exit pit is required at the end of the bore. The safety requirements for the
exit pit are the same as for the entrance pit. Unless absolutely necessary no
personnel should be allowed in the exit pit during the boring operation. The unexpected
entry of the boring head into the pit can catch the person and cause serious injury
or death. As the casing pipe approaches the exit pit care should be taken to prevent
different types of equipment may be required on or around the boring site. Excavated
and /or cranes are needed to dig the boring pit and set the equipment. Boring
machine and tracks appropriate for the job are required. Augers must be placed
in the casing sections . A cutting head is selected depending on the ground conditions
and is installed on the front of the first auger section. The cutting head type
that is selected for a particular project should be compatible with the anticipated
most critical part of the boring operation is the setting of the machine track
on line and grade. If the alignment is not right when the bore is started, it
is not likely to improve during the boring process. The master track is placed
in the pit with the push plate against the backstop. It is then aligned with the
proposed bore and the machine is set on the master track. The push bar dogs are
engaged at the rear most holes in the tracks and the slide rails, the master casing
pusher and the casing adapter are installed. A grade control head may be used
to mechanically adjust the grade of the auger bore crossing from the bore pit.
may be needed in the boring operation on some soil conditions to help facilitate
spoil removal, for use with bentonite lubricants, and for monitoring grade with
the grade control head.
addition to the above mentioned equipment, the optional components include the
discussed previously, controlling torque and thrust are two major concerns of
the auger boring operation. Application of a bentonite lubricant to the outer
skin of the casing reduces the friction between the casing and the soil which,
in turn, reduces the thrust requirements. There are two basic types of lubricants.
One is a bentonite which is an expansive montmorillonite, colloidal material which
when mixed with water becomes an excellent lubricant and sealant. It is the best
lubricant for sand and porous soils because of its sealing properties. The second
type of lubricant most commonly used is some form of polymer agent. In some cases
they work better than bentonite. They ease the problem of separation when they
get in the casing. The polymers such as Baroids EZ Mud works better than bentonite
in certain types of soil such as clay, where the encapsulation of the clay by
the polymer reduces their sticking and balling tendencies. Either method improves
the thrust capabilities in all types of soils. The complete lubrication system
consists of a mixing tank, a pumping method and a distribution system. The lubricant
is transferred to a point of application near the leading edge of the casing through
a steel pipe generally 0.5 inch (12mm) to 1.5 inch (38) mm).
water level is a device to measure the grade of the pipe casing as it is being
installed. It permits the monitoring of grade by using a water level sensing head
attached to the top of the leading edge of the casing. The level operates in the
same way as a sight tube on a boiler. Both ends of the system are vented to ambient
pressure. A pit mounted control and indicator board is located at some convenient
point in the pit near the operator. A hose connects the bottom of the indicator
to tube to a water pipe running along the top of the casing. Water is used to
fill the system. The level of water in the pit indicator will then show the level
of the valve at the end of the casing as it is pushed into the ground. One should
be careful when using this system to ensure that the system is full so that an
incorrect reading is not taken.
grade control head is used for making minor corrections in the grade.
can be used to make vertical corrections only. During the boring process, the
actual grade can be monitored with the water level and the necessary adjustments
can be made with the grade control head. If the grade control head is used, then
the leading end of the casing must be properly prepared. When water is injected
in the casing to facilitate spoil removal, the point of injection is located behind
the garde control head to prevent the water from contacting the excavation face.
For this, a 0.5 inch (12mm) diameter steel pipe , tack welded to the top of the
casing, injects water through a 3 inch (75mm) slot approximately 24 inches (60mm)
behind the grade control head.
cases of large diameter well installations casing may have to be used to prevent
the collapse of the borehole. The casing should be of good quality and should
be well prepared. Machine cut bevelled edges assure casing alignment., exact lengths
keep the head at the correct location relative to the casing, and the smooth walls
reduce the thrust required and the tendency to yard prior to its transport to
the jobsite and arrives at the jobsite with the auger inside and the cutting head
attached to the leading end of the auger. All casing are usually loaded with the
augers at the yard and arrive at the jobsite ready to use. It is recommended that
all bores be done with a string of full size auger sections. However, under conditions
where auger loading is light and the spoil moves easily in the casing, lead sections
of full size augers can be followed by smaller diameter auger sections. As a general
rule, smaller diameter augers should never be used in the lead section of the
casing. The smallest auger used should not be less than three forths the diameter
of the casing.
this recommendation is neglected, problems normally occur. This decreases the
efficiency as the spoil is not removed from the casing -where the smaller diameter
auger is being used- at the rate of excavation. This results in the augers rotating
more revolutions to remove the volume of spoil being excavated at the face which
results in the rotation of the auger without forward advancement.
factors in the use of smaller augers are bending and torque. The undersized auger
creates bending which results in stresses in the auger stem. Also the smaller
auger will have more wind up from the same torque loading than the full size auger.
Torque windup pulls the cutting head back towards the casing and could cause the
wing cutters to contact the casing, further increasing torque and causing even
more damage. The use of a partial band at or near the head end of the casing is
recommended when boring in most soil conditions. The band compacts the soil and
relieves pressure on the casing by decreasing the skin friction.
banding process is most effectively utilized in unstable soil conditions where
wing cutters are not used. In this case, the casing is pushed forward without
the borehole being over excavated. Therefore the soil compacting benefit is more
pronounced as it relieves the pressure on the following sections. It is also beneficial
in rock or boulders as it strengthens the leading edge of the casing.
cutters are devices that are attached to the cutting head which open and close.
the cutting head is rotated clockwise, the wing cutters open up to provide over
excavation of the bore hole. The over -excavation of the borehole allows the casing
to enter more easily since it minimizes casing skin friction. Wing cutters are
used only in stable soil conditions and are never used with the cutting head inside
the casing. The wing cutters are adjustable to control the amount of over-excavation.
Normally, the standard overcut is 1 inch (25mm) greater than the nominal casing
diameter. When the cutting head is rotated anti- clockwise, the wing cutters close
up so that the cutting head can slide back inside the casing for auger removal
wing cutters must be set so as not to over-excavate at the bottom of the casing.
This causes the bore to drift in a downward direction. Over-excavation of the
bottom can be prevented by keeping the boring head centered. This is accomplished
by using new or built up augers in the lead section of the casing. Worn augers
in the lead section will allow the head too much freedom and the wing cutter pattern
will be erratic.
of Casing: Collaring is the first operation in the beginning a bore. The objective
is to start the cutting head into the ground without lifting the casing out of
the saddle. This is done by rotating at low RPMs and using a slow thrust advance.
When about 4 feet (1.3 meters) of casing has entered the ground, the engine is
shut down, the saddle is removed, and the line and grade of the casing is checked.
If the casing is not on line and grade with the proposed bore, the casing is removed
and the process is repeated. The success of the bore depends to a great extent
upon the line and grade of the first section of the casing.
the first section of casing has been installed in the ground, the casing is cleaned
by rotating the auger until all the spoil is removed. The machine is then shut
down and the auger pin in the spoil chamber is removed. The machine is then moved
to the rear of the track and again is shut down. Then the next section of casing
and auger is lowered into position. The augers at the face are aligned flight
to flight, the hexagonal joint is coupled and the auger pin is installed. Scabs
are welded on the casing to be installed at 11 and 1 O'clock positions. The casing
is the advanced over the auger. The casing is aligned with installed casing by
resting the scabs on top of the installed casing and using 4 foot minimum (1.2
meter) straight edges along the top and sides. If the new casing is in line with
the installed casing and seriously out of line at the machine end, it means the
installed casing is misaligned and must be corrected or else it will result in
unacceptable bore alignment. Once the casing to be installed has been properly
aligned with the casing already in the earth, the two are tacked together then
welded fully. The drive is then coupled to the auger and the casing is secured
to the pusher. the water and bentonite lines, if being used, are added. The machine
is started up and the casing is installed. The process is repeated until the bore
OF AUGERS AT THE COMPLETION OF THE BORE:
the bore is completed, the machine is shut down and the cutting head is removed.
The casing is then cleaned by rotating the augers in the normal direction. The
torque plates are then removed to detach the machine from the casing and the augers
are retracted until the coupling is well outside the casing. The auger section
is uncoupled from the machine and the auger sections and is removed. The machine
is then coupled to the next auger section and the process is repeated until all
the auger sections are removed.
well installation, as mentioned in the opening paragraph, is quite similar to
standard vertical remediation well installation procedures. Once the borehole
has been completed to the required length the well installation can commence.
The Screen is slid into the borehole/ hollow stem auger and fitted with the required
lenght of riser pipe. The Screen may prepacked with filter media guaranteeing
the correct placement of sand along the screen. Additional sand may have to be
blown in around the prepack screen to fill the annulus between it and the borehole.
This is usually done through a tremie line using a compressor fitted with a series
of environmental air filters to prevent oil contamination. The bentonite seal
can then be blown in using the same technique to complete the installation.
all the augers have been removed, the boring machine and the tracks are removed
from the pit. The boring pit and receiving pit are then backfilled to restore
the site to its prior condition. It is important that the pit foundation is properly
restored to prevent any differential settlement.