| Construction
of Buried Plant
UNITED STATES DEPARTMENT OF
AGRICULTURE
Rural Utilities Service
BULLETIN 1751F-641
SUBJECT: Construction of Buried Plant
TO: All Telecommunications Borrowers
RUS Telecommunications Staff
EFFECTIVE DATE: Date of Approval
EXPIRATION DATE: Seven years from effective
date
OFFICE OF PRIMARY INTEREST: Outside Plant
Branch, Telecommunications Standards Division
PREVIOUS INSTRUCTIONS: This bulletin replaces
REA Telephone Engineering & Construction Manual (TE&CM)
Section 641, Construction of Buried Plant, Issue 4, dated
April 1973.
FILING INSTRUCTIONS: Discard REA Telephone
Engineering & Construction Manual (TE&CM) Section
641, Construction of Buried Plant, Issue 4, dated April 1973,
and replace it with this bulletin. File with 7 CFR 1751 and
is available to RUS staff on RUSNET.
PURPOSE: This bulletin provides RUS borrowers,
consulting engineers, contractors and other interested parties
with information concerning the construction of buried plant
facilities.
Adam Golodner 06/30/95
______________________________ __________________________
Administrator Date
TABLE OF CONTENTS
1. General ................................................
6
2. Supervision of Construction ............................
7
3. Characteristics of Tractors ...........................
13
4. Characteristics of Plowing Equipment ..................
15
5. Capabilities of Tractors and Plows ....................
17
6. Handling and Care of Materials During Construction
.... 18
7. Repair of Cables or Wires Damaged During
Construction . 19
8. Preparation for Splicing or Termination
............... 20
9. Installation Procedures for Filled Cables
in
Cold Weather ..........................................
21
10. Assembly Units ........................................
22
11. Directional Boring ....................................
22
12. Figure Eighting Cable .................................
22
13. Aerial Inserts ........................................
23
14. Numbering and Identification ..........................
23
15. Acceptance Testing ....................................
23
TABLES & FIGURES
Figure 1 Typical Cable or Wire Plowshare with
Fixed Feed
Tube..............................................
25
Figure 2 Plowshare with Vertical Shin .....................
26
Figure 3 Plowshare with Shin Angled Back From
Plow-Point .. 27
Figure 4 Plowshare with Shin Angled Toward
Plow-Point ..... 28
Figure 5 Plowshare with Hinged Feed Tube ..................
29
Figure 6 Plowshare with Floating Feed Tube
................ 30
INDEX:
Outside Plant
Construction
Telecommunications
ABBREVIATIONS
AWG American Wire Gauge
BFC Buried Filled Cable Assembly Unit
BFO Buried Filled Fiber Optic Cable Assembly
Unit
°C Degrees Celsius
CATV Community Antenna Television
CFR Code of Federal Regulations
°F Degrees Fahrenheit
LD Loan Design
NESC National Electrical Safety Code
R/W Right-of-way
REA Rural Electrification Administration
RUS Rural Utilities Service
TE&CM Telecommunications Engineering and
Construction Manual
DEFINITIONS
BFC: A buried filled cable assembly unit which
includes all the material and labor costs to place, plow,
and/or trench and backfill 1,000 feet (304.8 meters) of filled
buried copper cable.
BFO: A buried filled fiber optic cable assembly
unit which includes all the material and labor costs to place,
plow and/or trench and backfill 1,000 feet (304.8 meters)
of filled buried fiber optic cable.
Construction Drawings: The drawings developed
through the staking process and used to guide the construction
of outside plant facilities.
Drawbar Pull: The effective pulling force
delivered.
Feed Tube: A tube attached to the blade of
a plow which guides and protects the cables or wires as they
enter the earth. There are several types of feed tubes.
Figure Eighting: A method of removing cable
or wire from a reel and forming the removed cable or wire
in the shape of the numeral eight.
Fixed Feed Tube: A feed tube permanently attached
to the plow; it may have a removable back plate.
Floating Feed Tube: A feed tube attached to
a plow so relative motion may occur between the feed tube
and the plow around axes that are essentially vertical and
horizontal (perpendicular to direction of travel).
Fuse Link: A fine gauge section of cable or
wire that serves as a fuse (that is, open-circuits to interrupt
the current should it become excessive) that coordinates with
telecommunications cable and wire plant, and telecommunications
protective devices.
Hinged Feed Tube: A feed tube attached to
a plow so relative motion may occur between the feed tube
and the plow around an essentially vertical axis.
Loan Design: A comprehensive engineering plan
for a project used to support a loan application to the Rural
Utilities Service (RUS).
Static Plow: A plow that depends upon drawbar
pull only for its movement through the soil.
Type H Outside Plant Housing: A housing consisting
of an upper cover and a base cover. The upper cover consists
of a top, front and back plate with the front cover removable
to permit entry. The base cover consists of a front and back
plate. The base cover back plate can be an extension of the
upper back plate cover.
Type M Outside Plant Housing: A housing consisting
of a one piece upper sleeve designed to fit over the base
cover trapping air to prohibit water from entering the splice
area.
Resident Engineer: The representative of the
Engineer who is delegated full-time "on-site" engineering
responsibilities for construction administration.
Right-of-Way: The strip of land over which
facilities such as highways, railroads, power lines, other
utilities, or telecommunication lines are constructed.
RUS accepted (material and equipment): Material
and equipment which RUS has reviewed and determined that:
a. Final assembly is conducted within the
United States, Mexico, or Canada or any of their respective
territories and the cost of United States, Mexican, or Canadian,
manufactured components, in any combination, is more than
50 percent of the total cost of all components utilized in
the material or equipment, and
b. The material or equipment complies with
pertinent RUS or industry standards and field experience has
demonstrated that the material or equipment is suitable for
use on systems of RUS telecommunications borrowers.
RUS technically accepted (material and equipment):
Material and equipment which RUS has reviewed and determined
that:
a. Final assembly is not conducted within
the United States, Mexico, or Canada, or any of their territories,
or the cost of components within the material or equipment
which are manufactured within the United States, Mexico, or
Canada, or any of their territories, cost 50 percent or less
than the total cost of all components utilized in the material
or equipment, and
b. The material or equipment complies with
pertinent RUS or industry standards and field experience has
demonstrated that the material or equipment is suitable for
use on systems of RUS telecommunications borrowers.
Supervision: The responsibility of the resident
engineer or the resident engineer's assigned inspector to
observe the contractor's employees installing cable, outside
plant housings, splices, clean-up, and other related work
items associated with the construction project.
Vibratory Plow: A plow utilizing induced periodic
motion of the blade in conjunction with drawbar pull for its
movement through the soil.
1. GENERAL
1.1 This bulletin discusses construction of
buried plant facilities using filled copper cables or wires,
and filled fiber optic cables. The information and recommendations
in this bulletin are advisory.
1.2 Some of the work items associated with
buried plant construction are as follows:
a. Pre-installation inspection of copper cables
and wires
and fiber optic cables;
b. Plowing or trenching of copper cables and
wires and
fiber optic cables;
c. Lateral trenching of copper cables and
wires and fiber
optic cables to outside plant housings or
poles;
d. Installation of outside plant housings;
e. Installation of serving area interface
cabinets;
f. Tamping of trenches;
g. Installation of direct buried filled splice
cases for
copper cables and wires and fiber optic cables;
h. Splicing of copper cables and wires and
connection of
shield bonds and related grounding;
i. Splicing of fiber optic cables and connection
of armor
bonds and related grounding;
j. Installation of filled buried service wires;
k. Terminating of filled buried service wire
directly to
cable conductors;
l. Construction of aerial inserts;
m. Placement of filled terminal blocks in
outside plant
housings in high service order activity locations;
n. Placement of load coils (See Note);
o. Placement of digital carrier repeater housings,
and
lightwave repeater housings;
Note: When loaded lines are determined by
RUS to be economically feasible and the overall system design
complies with the Modernization Plan (7 CFR 1751, Subpart
B).
p. Placement of directional route and warning
markers,
and route and terminal numbers on outside
plant
housings; and
q. Conducting acceptance tests.
1.3 Information for the design, staking, splicing,
acceptance testing, and construction of direct buried plant
can be found in the following Rural Utilities Service (RUS)
documents:
a. RUS Form 515, RUS Telephone System Construction
Contract
(Labor and Materials);
b. RUS Bulletin 345-150, Specifications and
Drawings for
Construction of Direct Buried Plant (RUS Form
515a);
c. RUS Bulletin 345-153, Specifications and
Drawings for
Construction of Pole Lines, Aerial Cables
and Wires
(RUS Form 515f);
d. RUS Bulletin 345-63, RUS Standard for Acceptance
Tests
and Measurements of Telephone Plant (PC-4);
e. RUS Bulletin 1751F-640, Design of Buried
Plant -
Physical Considerations;
f. RUS Bulletin 1751F-642, Construction Route
Planning of
Buried Plant; and
g. RUS Bulletin 1753F-401(PC-2), RUS Standard
for Splicing
Copper and Fiber Optic Cables (codified under
7 CFR
1755.200).
2. SUPERVISION OF CONSTRUCTION
2.1 The construction of buried plant facilities
should be closely supervised because of the rapid rate at
which plowing or trenching proceeds and because the cable
or wire cannot be visually inspected after installation. This
close supervision should be accomplished by having the resident
engineer or resident engineer's assigned inspector present
at all times during the buried plant construction operation.
The resident engineer or the resident engineer's assigned
inspector also has the responsibility to ensure that the correct
pair sizes, gauges, and types of copper cables or wires, and
the correct number of optical fibers, type of optical fibers
and types of fiber optic cables are placed at the correct
depths and locations within the right-of-way (R/W), and are
free of damage during the buried plant construction operation.
2.2 When more than one plowing or trenching
operation is being performed at the same time, each plowing
or trenching operation should be supervised. During the installation
of the cables or wires, construction may be stopped pending
the resident engineer's decision concerning proposed changes
in the construction route from that shown on the construction
drawings. Undue delays in making such decisions are costly
to the borrower and should be avoided.
2.3 Cables or wires should be inspected for
damage after installation. In order to perform this inspection,
the plow should be advanced 10 feet (3.05 meters) past an
outside plant housing location and stopped. A length of cable
or wire should then be pulled through the plow's feed tube,
back through the slot and over to the outside plant housing.
This procedure provides an opportunity to inspect short lengths
of cables or wires for damage. Particular care should be exercised
in bending the cables or wires during this inspection procedure.
2.4 The minimum bending radius for copper
cables and wires should not be less than 10 times the outside
diameter of the copper cable or wire. The minimum bending
radius for fiber optic cables should not be less than 20 times
the outside diameter of the fiber optic cable. If cables or
wires are bent too sharply, damage could occur to the copper
conductors, optical fibers, shields, armors, and/or jackets
of the cables or wires.
2.5 All reels of filled copper cable and wire
and all reels of filled fiber optic cable should be inspected
before installation for visual signs of damage. In addition,
filled copper cable and wire ends and filled fiber optic cable
ends should be sealed to prevent moisture entry into the cores
of copper cables and wires and fiber optic cables during transportation,
in storage, and during placement.
2.6 The buried plant construction route should
be inspected before beginning the plowing or trenching operation.
When selecting the buried plant construction route, the convenience
and ease of installation should be considered providing the
quality of construction, which would affect future operation
and maintenance of the telecommunications system, is not decreased
and construction costs to the borrower are not substantially
increased.
2.7 Cables and wires, as well as, the equipment
and procedures should be continuously inspected during the
installation to prevent damage to the cables and wires and
to ensure that proper depths are maintained at all times.
Caution should be exercised to prevent damage to the cables
and wires because of cable or wire slippage in the ground
as the plow or trencher leaves the starting pit. Cables and
wires should be checked for damage at sudden or severe changes
in grade or where the plow or trencher is violently impaired
in movement (such as striking a large rock). Generally, buried
plant facilities are more susceptible to damage during trenching
operations and backfilling than they are when being plowed
into the ground. The resident engineer should make certain
that the cables or wires are properly installed in open trenches,
that the trenches are properly backfilled, and that the surfaces
of the ground are restored to the previous conditions. Lateral
trenches should be backfilled and tamped where necessary to
provide solid bases for the cables or wires to rest upon between
the plow slots and the outside plant housings. At outside
plant housing locations, the soil should be properly tamped
so that it will conform to the cables or wires bending radii.
If this procedure is not followed, the cables or wires may
sag downward from the attachments within the outside plant
housings as the soil settles resulting in possible damage
to the copper conductors, optical fibers, and/or loss of cable
or wire shield or armor continuity. All trenches should be
promptly backfilled with soil and mechanically tamped so that
the soil is restored to its original grade to ensure that
future settlement does not result in a hazard to vehicular,
animal, or pedestrian traffic. In areas where experience indicates
that water added to the backfill (flooding) does help achieve
compaction, (usually in sandy soil), the flooding method may
be used as an alternative method to mechanical tamping. Unprotected
and unmarked trenches should not be left open overnight.
2.8 Construction work should be organized
so that plowing and/or trenching operations, together with
the placement of cables or wires, service wires, outside plant
housings, and other associated functions are be done concurrently.
In this manner, the interval from start to completion of any
section of the project is held to a minimum. The resident
engineer assigned to each buried plant construction operation
may not have time to inspect all the details of related work
being performed along the construction route. Therefore, the
resident engineer should have additional personnel to supervise
and inspect all such construction. The number of supervisory
personnel required to inspect all aspects of construction
depends on the amount of proposed construction and on the
number of different operations being performed simultaneously.
2.9 Installation of reel-end splices which
may change proposed digital carrier or lightwave repeater
locations should be considered for re-routing. Because of
the limited deviations allowed in digital carrier or lightwave
repeater spacings, all repeatered lines should be constructed
first, starting at the central office and advancing in the
direction of the repeatered line with a continuous operation
to the last repeater point on each repeatered section unless
otherwise specified in the contract. Deviations from this
procedure should be approved in lieu of holding up the construction
project in the event of late cable or wire deliveries, or
R/W difficulties, etc.
2.10 Installation of reel-end splices on loaded
lines (See Note on Page 6) which may change proposed load
coil locations should be considered for re-routing. Because
of the limited deviations allowed in load coil spacings, all
loaded lines should be constructed first, starting at the
central office and advancing in the direction of the loaded
line with a continuous operation to the last load point on
each loaded section unless otherwise specified in the contract.
Deviations from this procedure should be approved in lieu
of holding up the construction project in the event of late
cable or wire deliveries, or R/W difficulties, etc.
2.11 Sequential markings on the outer jackets
of cables and wires are provided to facilitate proper spacing
of digital carrier or lightwave repeater housings, load coils
(when loaded lines are determined by RUS to economically feasible
and the overall system design complies with the Modernization
Plan [7 CFR 1751, Subpart B]), and inventory of cable and
wire units. The resident engineer and the contractor should
agree on the inventory of buried plant units as they are installed.
Construction drawings should be appropriately marked so they
can be used as permanent records of all plant items.
2.12 Road and ground surfaces should be inspected
to determine if the surfaces have been damaged by the plowing
or trenching equipment. If the surfaces have been damaged,
the surfaces should be repaired and reinspected to determine
that the surfaces have been properly repaired. If repairs
are necessary, the repairs should be performed in accordance
with Federal, State, or local codes, and as set forth in RUS
Form 515, RUS Telephone System Construction Contract.
2.13 Outside plant housings should be inspected
during construction to determine that:
a. The correct size and sealer have been properly
installed;
b. Copper cable or wire conductors have been
correctly
terminated;
c. Shields and/or armors of copper cable or
wire have been
bonded and grounded;
d. Cables or wires tags have been marked with
the proper
information per RUS Bulletin 1753F-401(PC-2);
e. Correct routes and outside plant housing
numbers, and
warning decals have been installed;
f. Stakes or stub poles have been installed
at the
proper depths; and
g. Rodent protection has been properly installed,
as required.
2.14 Direct buried filled splices and cases
should be inspected during construction to ensure that:
a. Cable or wire jackets have been properly
prepared;
b. Copper cable or wire conductors have been
properly
spliced;
c. Optical fibers have been properly spliced;
d. Buffer tubes containing the optical fibers
have a
sufficient amount of slack;
e. Shields and/or armors of cables or wires
have been
bonded and grounded;
f. Encapsulating compounds have been properly
mixed and
applied; and
g. The direct buried filled splice cases have
been
properly installed.
2.15 When direct buried filled splice cases
are required to be protected from mechanical damage, protection
of the splice cases should be accomplished either by placing
treated planks approximately 6.0 inches (152 millimeters)
above the splice cases or by placing the splice cases in handholes.
2.16 Construction drawings should be accurately
marked to indicate the following:
a. Routing of cables or wires;
b. Lengths, pair sizes, gauges, and types
of copper cables;
c. Lengths, number and types of optical fibers,
and types
of fiber optic cables;
d. Locations of direct buried filled splice
cases and
splice warning signs;
e. Locations of handholes;
f. Locations of outside plant housings;
g. Locations of warning and route signs;
h. Locations of load coils (See Note on Page
6);
i. Locations of digital carrier repeater and
serving area
interface cabinets;
j. Locations of lightwave repeater housings;
and
k. Locations of other buried utilities and
obstacles.
This should facilitate future reinforcements
which may be required on the project. If depths greater than
normal depths in the Loan Design (LD) have been specified
to facilitate future reinforcing or to provide a greater degree
of mechanical protection to the buried plant facilities, the
resident engineer should make certain that such depths are
achieved.
2.17 For copper cable buried construction
projects, direct buried filled splice cases, trenching, labor,
and other materials associated with the installation of reel-end
splices are included in the BFC assembly unit. Therefore,
such splice cases are not covered in the final inventory for
compensation purposes. Although the splice cases are not inventoried,
all splices cases and cable or wire lengths should be shown
on the construction drawings for future reference. For ease
of future location, all direct buried filled splices should
be located at a measured distance with respect to the center
of the road or from some other permanent marker such as a
locating ball, etc. Construction drawings should also indicate
the location of all outside plant housings or direct buried
filled splice cases that were installed for the purpose of
repairing cable or wire damage that occurred during construction.
2.18 For fiber optic cable buried construction
projects, the BFO assembly unit does not include direct buried
filled splice cases, trenching, labor, and other materials
associated with the installation of reel-end splices. Therefore,
such splice cases should be covered in the final inventory
for compensation purposes. All splice cases and cable lengths
should be shown on the construction drawings for future reference.
For ease of future location, all direct buried filled splices
should be located at a measured distance with respect to the
center of the road or from some other permanent marker such
as a locating ball, etc. Construction drawings should also
indicate the location of all outside plant housings or direct
buried filled splice cases that were installed for the purpose
of repairing cable damage that occurred during construction.
2.19 Where rock conditions exist that make
the plowing of cables or wires impractical or inadvisable,
trenching, aerial inserts, or re-routing should be considered
as construction options along that particular section of the
route. The decision as to what option should be used is normally
made during the construction period by the resident engineer.
2.20 The buried construction route should
be cleared only to a width that will allow for the passage
of the cable or wire placing equipment. The responsibilities
in regards to obtaining, operating on, clearing obstructions
(trees, brush, etc.), disposal of debris and restoration of
public and private R/W, including any compensations are defined
in RUS Bulletin 345-150, Specifications and Drawings for Construction
of Direct Buried Plant (RUS Form 515a).
2.21 Special care should be exercised to avoid
damage to fences, trees, lawns, and shrubs. Disturbance of
ground surfaces by heavy construction equipment should be
kept to a minimum. All fences removed or cut for access of
the equipment should be repaired promptly in accordance with
RUS Bulletin 345-150, Specifications and Drawings for Construction
of Direct Buried Plant (RUS Form 515a). When installing cables
or wires in pasture and/or range lands, gates should be closed
and fence openings should be repaired as soon as possible.
2.22 Plowing or trenching operations within
the area of subsurface structures should be carried out in
a manner that will avoid accidental contact of the digging
tools with such structures. The equipment which may be used
for such operations should be operated only by qualified personnel.
When foreign structures are encountered such as buried power
cables, Community Antenna Television (CATV) cables, gas lines,
etc., the installation of the buried telecommunications cables
or wires should be performed in accordance with the requirements
of the latest edition of the National Electric Safety Code
(NESC) or Federal, State, or local codes. Where Federal, State,
or local codes are more stringent than the NESC, the installation
of the buried telecommunications cables or wires should be
performed in accordance with the more stringent codes.
2.23 The minimum depth requirements for buried
cables or wires are given in RUS Form 515 and RUS Bulletin
345-150 (RUS Form 515a). In certain situations it may be desirable
to bury cables or wires at depths greater than the minimum
depths given in RUS Form 515 and RUS Bulletin 345-150 (RUS
Form 515a). These greater depths need to be approved by RUS
prior to bidding.
2.24 Portions of the filled buried service
wires that are exposed to possible subscriber damage should
be protected by placing the exposed portions of the wires
in nonmetallic conduits or split "U" guards.
3. CHARACTERISTICS OF TRACTORS
3.1 The resident engineer should be familiar
with the characteristics and capabilities of the tractors
and plowing equipment used in the construction of buried cable
or wire plant facilities. The equipment used on the construction
project should be subjected to the requirements listed in
RUS Form 515 and RUS Bulletin 345-150 (RUS Form 515a) and
approval of the public authorities having jurisdiction over
highway and road R/W. The size and maneuverability of the
equipment should also be considered in the selection of the
cable or wire construction route.
3.2 The power capabilities of static type
tractors may be stated in either terms of drawbar horsepower
or drawbar pounds pull. Direct gear drive tractors are normally
rated in terms of drawbar horsepower and tractors with torque
converters are normally rated in terms of drawbar pounds pull
at a given forward speed. The terms drawbar horsepower and
drawbar pounds pull refer to the reserve tractive horsepower
and the reserve tractive force, respectively, available beyond
that required to move the tractor itself. Crawler and rubber-tired
tractors are two types of static tractors.
3.3 In crawler tractors, the factors which
influence traction are the width and length of the track and
the design of the grousers. Grousers are metallic ribs which
are attached to the tracks to penetrate and grip the soil.
The grousers are attached to the tracks at right angles to
the tracks and to the direction of motion. Grousers are used
to ensure that traction is obtained by shearing the soil and
not by friction of the metal on the soil alone. In general,
crawler tractors with long, wide tracks and high grousers
obtain greater traction than crawler tractors with short,
narrow tracks and low grousers.
3.4 Factors influencing the traction of rubber-tired
tractors include the weight and weight distribution of the
tractor, tire size, inflation pressure and tread pattern,
and wheel base.
3.5 For traction in various soils, a choice
of various widths, lengths, and depths of track may be obtained
on crawler tractors. For rubber-tired tractors, the traction
in various soils will depend on sizes and inflation pressures
of the tires. Both crawler and rubber-tired tractors may be
operated in surface conditions varying from solid rock to
swamp-like soils and weather conditions varying from droughts
to floods and from frosts to summer sun.
3.6 Manufacturers of both crawler and rubber-tired
tractors should be contacted to determine the tractive forces
of their respective equipment in various soil conditions.
3.7 Rubber-tired tractors are more difficult
to keep on straight courses, particularly on slopes, than
crawler tractors. Factors which can influence the steering
of rubber-tired tractors are the tractor's transmission type
and steering mechanism. Rubber-tired tractors can be manufactured
with clutch-brake, differential and limited slip differential
transmissions. Steering of clutch-brake rubber-tired tractors
is accomplished by the skidding of the wheels. Steering rubber-tired
tractors with differential drive transmissions is accomplished
with steerable wheels at the front, at the back, or all around.
3.8 If rubber-tired tractors are used for
the construction project, all-wheel drive tractors with all
wheel steering and limited slip differential transmissions
should be the preferred rubber-tired tractor types because
the oblique steering properties tend to offset any tendency
of the tractors to slip sideways on the slopes. It should
be noted that rubber-tired tractors having rear wheel steering
are difficult to keep on straight courses when the plow is
in the ground.
3.9 Cables or wires are usually installed
along the most feasible route, whether it is along public
R/W, private R/W, or across farming or grazing lands. Farming
or grazing landowners are usually reluctant to consent to
the use of crawler or rubber-tired tractors on farming or
grazing lands because of the surface damage that can be done
to the farming or grazing lands as a result of these type
tractors. Since crawler tractors do far less surface damage
than rubber-tired tractors, crawler tractors should be the
preferred tractors for buried plant construction projects
involving private R/W across farming or grazing lands.
3.10 Department of transportation officials
frown upon surface damage done to hard highway or road surfaces
as a result of track slippage. Since track slippage can result
from the crawler's insufficient power and traction (weight),
either rubber-tired tractors or crawler tractors with rubber
pads should be the preferred tractors for buried plant construction
projects involving hard surfaces because the rubber-tired
tractors and the rubber padded crawler tractors do not damage
the hard surfaces of the public or private R/W.
3.11 The drawbar pull characteristics of static
type tractors are not entirely applicable to vibratory tractors.
The vibratory tractor's principle of cutting and vibrating
can reduce the drawbar pull, as related to static type tractors,
as much as 80 percent in some soil conditions. In addition,
since the vibratory tractor's weight is dictated by drawbar
requirements and not engine size, a significant reduction
in the vibratory tractor's weight and size can be achieved
through plow vibrations. However, drawbar requirements for
vibratory type tractors increase as the plowing speeds increase
and, therefore to obtain full advantage of plow vibrations,
plowing speeds are relatively low. Thus for a vibratory tractor's
drawbar capability, a vibrating plow should settle to a speed
that depends on the soil conditions.
4. CHARACTERISTICS OF PLOWING EQUIPMENT
4.1 The soil properties such as hardness,
friction, adhesion, cohesion, and abrasion should be evaluated
before selecting the type of plow for the construction project.
Soil hardness is the resistance to penetration. Soil hardness
is at a minimum for sandy soil and at a maximum for dry clay.
Friction is the force at the plow/soil interface that resists
the motion or tendency to motion of the plow to the soil.
Friction is affected by the amount of moisture and natural
lubricants in the soil. Adhesion is the sticking of the soil
to the plow being used. Cohesion is the resistance of the
soil to tearing apart and it is at its maximum in clay soil.
Abrasion is the property of wearing away of the plowing equipment
by the soil particles.
4.2 Static and vibratory type tractors can
be equipped with either direct mounted or towed plows. One
advantage in using towed plows over direct mounted plows is
that the tractors can be of the general purpose type. Towed
plows can also be unhitched for crossing soft patches of soil,
swamps, and streams and winched across these areas with the
tractors standing on firm ground. When undulating terrain
is encountered, towed plows in some instances can do better
jobs of installing the cables or wires at the proper depths
than some of the direct mounted plows. However, direct mounted
plows are considered superior to towed plows for most terrain
and soil conditions. One of the reasons that direct mounted
plows are considered superior to towed plows is that the direct
mounted plows can be easily maneuvered. Another reason is
that direct mounted plows rely on the weight of the tractor
and its hydraulics for positive holddown rather than the dead
weights used for towed plows. The dead weights placed on towed
plows to maintain a 15,000 pound (67,723 newton) downward
force may result in a reduction of the tractor's power necessary
for plowing. With properly designed direct mounted plows,
the proper depths of the cables or wires can be maintained.
4.3 Direct mounted plows are considered more
stable than towed plows because the towbars of the tractors
pulling the separately mounted plows tend to lift the fronts
of the tractors off the ground. For tractors equipped with
towed plows, the stability of the tractor increases as the
tractor's weight is increased but decreases as the drawbar
pull increases. For tractors with direct mounted plows, the
stability of the tractor increases as the drawbar pull increases
and the resistance offered by the earth to the plow increases.
4.4 The ideal plow should be designed so that
the cables or wires exit the plowshare at approximately the
same heights above the bottoms of the plowed slots regardless
of the depths. The disadvantage of these type plows are that
the cables or wires may be damaged because of abrupt changes
in elevation when passing over rocks, etc. One method of overcoming
this type of cable or wire damage is the use of four point
or parallelogram type linkage.
4.5 If hydraulic rams are used to transmit
part of the tractor's weight to the plow for positive holddown,
the hydraulic rams should be double acting and capable of
raising the rear of the tractor with the plow-point resting
on the ground.
4.6 The equipment should be capable of extending
the plow blade to a depth of at least 36 inches (914 millimeters)
when the tractor is angling across and along drainage ditches
or rough terrain. The plow-point, leading-edge (shin), share-shape,
and share-width should be designed to cut a narrow slot through
the earth without excessively disturbing the soil. The broad
"V" shaped leading-edge (shin) equal to the plowshare's
thickness has been found to be satisfactory. Figure 1 depicts
a sketch of a typical cable or wire plowshare. The proportions
and the angles of attack of the plow-points have been shown
to have the greatest effect on drawbar pull and pull-down.
This means that plows designed with vertical shins as shown
in Figure 2 or shins that angle back from the plow-points
as shown in Figure 3 tend to stay in the ground better than
plows designed with shins angled towards the plow-points as
shown in Figure 4. For most soils and rock, the plow-point
penetration angles should range from a minimum of 30°
to a maximum of 50° from the horizontal. In addition to
plowshares with fixed feed tubes as shown in
Figure 1, plowshares are also available with
either hinged or floating feed tubes. Figure 5 shows a plowshare
with a hinged feed tube, while Figure 6 shows a plowshare
with a floating feed tube.
5. CAPABILITIES OF TRACTORS AND PLOWS
5.1 One tractor should be able to pull a plow
through most soil types. A second tractor to assist the prime
tractor should be used when additional traction is needed
in hard to plow soil types, muddy and swampy type soils, or
other difficult areas. Crawler tractors generally provide
better flotation and more positive traction than rubber-tired
tractors. The prime tractor used to pull the plow should be
the larger of the two tractors. The prime tractor should have
a minimum rating equivalent to 55,000 pounds (2.45 x 105 newtons)
drawbar pull at 1.2 miles per hour (1.93 kilometers/hour)
or 130 drawbar horsepower at the rated engine speed at a depth
of 24 in. (61 cm). For burial depths greater than 24 in. (61
cm), tractor manufacturers should be contacted to determine
minimum drawbar pull or drawbar horsepower requirements necessary
to achieve the specified burial depth.
5.2 Plowing should be considered difficult
when the equivalent of at least 250 drawbar horsepower is
applied to the plow. When difficulty in plowing as defined
above is encountered, alternative methods of placing the cable
or wire should be considered for those areas. The alternative
methods for placing the cable or wire in those areas could
be the use of aerial inserts, pre-ripping, rock trenching,
or major re-routing of the construction route. Since the 250
drawbar horsepower is considered to be a very large amount
of power, good judgement should be exercised to prevent damage
to the equipment and unnecessary or undue damage to the terrain
caused by the upheaval of large boulders.
5.3 When a second tractor is needed to assist
in the plowing operation, the second tractor should be equipped
with a winch and a blade. The second tractor containing the
winch and blade may then be used for necessary R/W clearing
and cleanup when it is not required to assist the prime tractor.
5.4 Compaction of plow slots should be performed
after the cables or wires have been plowed-in. The method
of compacting most plow slots should be as follows:
a. Run the tractor track or tire along and
immediately
adjacent to both sides of the plow slot;
b. Fill in any ground depressions which may
have developed
with soil to form a mound over the center
of the plow
slot; and
c. Then run the track or tire over the center
slot.
5.5 A signaling method between the person
riding the reel tender or plow, and the tractor operator should
be developed to:
a. Inform the tractor operator when the plow
or reel
tender is to be stopped at access points along
the
construction route;
b. Prevent damage to the buried cables or
wires; and
c. Minimize the possibility of injury to construction
personnel.
The signaling method chosen should be able
to attract the attention of the tractor operator over the
operating noise of the tractor. One such method could be use
of a loud alarm bell with a flashing light.
6. HANDLING AND CARE OF MATERIALS DURING CONSTRUCTION
6.1 Extreme care should be exercised in handling
materials during the construction process. The plowing operation
should be supervised at all times to ensure that the cables
or wires feed through the plow and into the ground under zero
tension. Under no circumstances should tension be allowed
to develop in the cables or wires. Whenever the plow is stopped,
sufficient lengths of cable or wire should be removed from
the reel to guard against sudden movements when the plow is
restarted.
6.2 Extreme caution should be exercised to
ensure that the plow is never backed up while the blade is
in the ground. The backing up of the plow could cause severe
damage to the cables or wires. If the plow strikes a buried
object or rock during the plowing operation, the plow should
be stopped without backing up and the plow removed from the
soil and the cable or wire inspected for possible damage.
Should it be necessary to back up the plow, the cables or
wires should be uncovered a sufficient distance back from
the plow and inspected for damage. If cable or wire damage
is discovered, the damage should be repaired in accordance
with the construction contract and specifications.
6.3 Care should be exercised to prevent damage
to exposed cables or wires during the construction period.
Construction work should be scheduled to keep such exposure
to a minimum. Where cables or wires are being placed along
the construction route, all trenching and backfilling for
both inline and short lateral trenches should be completed
each day so as not to leave the cables or wires exposed overnight.
Cables or wires left exposed are susceptible to damage. Cables
or wires left exposed are also considered hazards to vehicles,
pedestrians, and animals.
6.4 Where outside plant housings are used,
caution should be exercised to avoid damaging the cables or
wires when:
a. Joining the lateral trenches to the plow
slot;
b. Installing the outside plant housings;
and
c. Forming the cables or wires in the outside
plant
housings.
The stakes or stub poles of outside plant
housings should be installed before the cables or wires are
placed in the lateral trenches.
6.5 Cables or wires should be installed in
outside plant housings as soon as practicable. The installation
work should be completed within one week after the cables
or wires have been plowed or trenched in the ground. However,
no trenches or other excavations should be left open overnight
unless the openings are protected by a method specified in
the contract.
6.6 Buried plant connections using dissimilar
metals should be avoided to eliminate the possibility of galvanic
corrosion. Therefore buried plant connections should be made
using only tinned coated metals.
7. REPAIR OF CABLES OR WIRES DAMAGED DURING
CONSTRUCTION
7.1 Minor damage to the outer jackets, where
the shields or armors of the cables or wires have not been
bent, abraded, or penetrated should be repaired in accordance
with Bulletin
1753F-401(PC-2), RUS Standard for Splicing
Copper and Fiber Optic Cables.
7.2 Where shields or armors have penetrated
the outer jackets of cables or wires, the damaged sections
should be enclosed in direct buried filled splice cases or
outside plant housings. The outer jackets, shields, or armors
of the damaged sections should be removed as though preparing
for splicing. The shields or armors should then be bonded
together. Damage to the copper conductors or their insulations
or optical fibers or their buffer tubes should be repaired
in accordance with Bulletin
1753F-401(PC-2), RUS Standard for Splicing
Copper and Fiber Optic Cables.
7.3 Cables or wires found to be damaged after
installation should be repaired. If the damage is considered
minor, the damage should be repaired in accordance with Bulletin
1753F-401(PC-2), RUS Standard for Splicing
Copper and Fiber Optic Cables. If the damage is considered
major, the damage should be repaired either by replacing the
damaged sections with new cables or wires spliced to the undamaged
sections of the cables or wires or repaired in accordance
with the method specified in the contract.
7.4 All outside plant housings or direct buried
filled splice cases added because of repairs should be numbered
and shown on the construction drawings. However, they should
not be included in the final inventory for compensation purposes
as specified by the RUS 515 Contract and RUS Bulletin 345-150
(RUS Form 515a).
8. PREPARATION FOR SPLICING OR TERMINATION
8.1 Buried filled copper cables or wires should
be spliced in accordance with Bulletin 1753F-401(PC-2), RUS
Standard for Splicing Copper and Fiber Optic Cables and enclosed
in RUS accepted or technically accepted outside plant housings
or direct buried filled splice cases.
8.2 Buried filled fiber optic cables should
be spliced in accordance with Bulletin 1753F-401(PC-2), RUS
Standard for Splicing Copper and Fiber Optic Cables and enclosed
in RUS accepted or technically accepted filled fiber optic
splice cases. These splice cases should then enclosed in either
RUS accepted or technically accepted handholes or outside
plant housings specifically design for fiber optic systems.
8.3 When terminal blocks are used in outside
plant housings, only RUS accepted or technically accepted
filled terminal blocks should be used.
8.4 The front covers of Type "H"
outside plant housings and the dome covers of Type "M"
outside plant housings should be bolted in the closed position
at the time the housings are installed. The covers of both
type outside plant housings should also be kept in closed
position at all times except when work is being performed
within the outside plant housings.
9. INSTALLATION PROCEDURES FOR FILLED CABLES
IN COLD WEATHER
9.1 Flexibility of filled copper cables or
wires and filled fiber optic cables should not be a problem
at normal operating temperatures. However, flexibility may
be affected when the cables are exposed to lower temperatures.
The flexibility of filled copper cables or wires and filled
fiber optic cables could be sharply reduced at temperatures
below 40°F (4.4°C). At temperatures below 40°F
(4.4°C), almost twice the force may be needed to bend
the filled copper cables or wires and filled fiber optic cables.
Filled cables or wires and filled fiber optic cables should
be inspected each morning to determine if the cables or wires
are flexible enough for plowing when night time temperatures
drop below 30°F (-1.1°C). When filled cables or wires
and filled fiber optic cables have been stored outdoors and
subjected to cold nights, considerable time may be lost each
morning waiting for the cables or wires to warm up even though
the day time temperature may be above 40°F (4.4°C).
During the spring and fall of the year, the filled copper
cables or wires and filled fiber optic cables may be stored
in heated warehouses prior to placement in the ground. This
storage in heated warehouses allows the filled copper cables
or wires and filled fiber optic cables to be transported to
the project site as needed and installed while the cables
or wires are still flexible.
9.2 Some filling compounds used in the cores
of filled copper cables or wires may become stiff as the temperature
decreases making it difficult to separate the cable or wire
pairs. In general, filled copper cable or wire installations
below 40°F (4.4°C) could be slow, difficult, and possibly
even halted unless special precautions are taken to offset
the effects of the lower temperatures.
9.3 Filling compounds used in loose tube buffers
of filled fiber optic cables should not become stiff as the
temperature decreases. This should allow the optical fibers
to be easily separated at low temperatures.
9.4 As mentioned in Paragraph 9.2, the copper
cable or wire pairs may become difficult to separate as the
temperature decreases. At temperatures as low as 20°F
(-6.7°C), the copper cable or wire pairs may be separated
by flexing the free ends of the cable or wire cores and separating
a few pairs at a time. It is also interesting to note that
the filling compounds at a temperature of 20°F (-6.7°C)
are more user friendly to work with than at elevated temperatures.
Consequently, the copper cable or wire pairs may be spliced
without wiping the pairs free of filling compound.
10. ASSEMBLY UNITS
10.1 Detailed descriptions of all standard
buried plant assembly units are given in RUS Bulletin 345-150,
Specifications and Drawings for Construction of Direct Buried
Plant (RUS Form 515a).
10.2 Where standard buried plant assembly
units are insufficient to provide for unique buried plant
construction requirements, detailed "nonstandard assembly
units" should be created to meet those requirements.
The buried plant nonstandard assembly units should be approved
by RUS prior to the bidding of the project.
11. DIRECTIONAL BORING
11.1 Directional boring in buried plant construction
should be considered as an alternative method of installing
cables or wires under highways, streets, driveways, across
lawns, etc., to avoid the expensive costs of repairing and
restoring the above mentioned items to their pre-construction
appearances.
11.2 Directional boring should also be considered
for installing cables or wires under streams, lakes, or rivers,
when in the opinion of the borrower or borrower's resident
engineer, the use of aerial inserts are economically or environmentally
cost prohibited.
11.3 When directional boring is used in the
buried construction process, the installation should performed
in accordance with boring equipment manufacturer's recommendations.
12. FIGURE EIGHTING CABLE
12.1 When "figure eighting" of cables
or wires is required during the buried construction process,
the "figure eighting" of the cables or wires should
be performed either manually or mechanically.
12.2 When performed manually, the cable or
wire should be pulled off the reel and "figure eighted"
in a large open area free of obstructions. The bend radius
of the "figure eight" for copper cable or wire should
not be less than 10 times the cable's outside diameter. For
fiber optic cable, the "figure eight" bend radius
should not be less than 20 times the cable's outside diameter.
12.3 When "figure eighting" is performed
by a "figure eighting" machine, the equipment manufacturer's
instructions should be followed.
13. AERIAL INSERTS
13.1 Aerial inserts in buried plant construction
should be used over streams and similar obstructions when,
in the opinion of the borrower or the borrower's resident
engineer, cables or wires cannot be installed either by plowing,
trenching, directional boring, or protected by guard assemblies.
Every effort should be made to avoid using aerial inserts
because the aerial inserts are susceptible to storm damage
and power contacts. When aerial inserts are prone to possible
contact with power conductors operating at 300 volts or higher
or there is a high probability of lightning exposure to the
aerial insert, fuse links should be installed at both ends
of the aerial insert. Fuse links should consist of short lengths
of color matched conductors that are at least two (2) American
Wire Gauge (AWG) sizes finer (numerically higher) than the
finest (numerically highest) gauge size of aerial and buried
cables or wires being installed.
13.2 All assembly units such as poles, guys,
anchors, etc., used for the installation of aerial inserts
in buried plant construction are described in RUS Bulletin
345-153, Specifications and Drawings for Construction of Pole
Lines, Aerial Cables and Wires (RUS Form 515f).
14. NUMBERING AND IDENTIFICATION
14.1 Every outside plant housing installed
along the construction route should be marked with route letters,
housing numbers, warning decals, and, when required, the load
point numbers (when loaded lines are determined by RUS to
be economically feasible and the overall system design complies
with the Modernization Plan [7 CFR 1751, Subpart B]).
14.2 Every direct buried filled splice case
installed along the construction route should be identified.
The identification of the direct buried filled splice cases
should be accomplished by using either above ground warning
signs or electronic locating devices.
15. ACCEPTANCE TESTING
15.1 After installation, buried copper cables
or wires should be tested in accordance with RUS Bulletin
345-63, RUS Standard for Acceptance Tests and Measurements
of Telephone Plant (PC-4) and the RUS Form 515 Contract.
15.2 After installation, buried fiber optic
cables should be tested in accordance with the procedures
listed in the contract.
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