A.
Description. The trench shall be excavated to full
depth and grade for a distance of at least 50 feet in advance of pipelaying
but not more than one average day's pipelaying in advance of the work.
The trench shall be so braced and drained that the workers may work
therein safely and efficiently. It is essential that the discharge
from the trench dewatering pumps be conducted to natural drainage
channels, drains or storm sewers.
B.
Width of trench.
(1)
The width of trench shall be ample to permit the pipe
to be laid and jointed properly and the backfill to be placed and
compacted as specified. Trenches shall be of such extra width, when
required, as will permit the convenient placing of timber supports,
sheeting and bracing and the handling of fittings.
(2)
The minimum width shall be sufficient to give clearance
of at least eight inches on either side of the barrel of the pipe.
C.
Bell holes. Bell holes shall be provided at each joint
to permit the jointing to be made properly.
D.
Pipe clearance in rock. Ledge rock, boulders and large
stones shall be removed to provide a clearance of at least six inches
below and eight inches on each side of all pipes and fittings.
E.
Excavation to grade.
(1)
The trench shall be excavated to the depth required
so as to provide a uniform and continuous bearing and support for
the pipe on solid and undisturbed ground at every point between bell
holes. Any part of the bottom of the trench excavated below the specified
grade shall be corrected with approved material and thoroughly compacted
as directed by the inspector. The finished grade shall be prepared
accurately by means of hand tools.
(2)
The subgrade beneath the center line of the pipe shall
be finished to within 0.03 foot of a straight line between pipe joints
or batter boards. All tolerance shall be above specified grade.
F.
Excavation in poor soil or rock.
(1)
Where the bottom of the trench at subgrade is found
to be unstable or to include ashes, cinders, all types of refuse,
vegetable or other organic material, large pieces or fragments of
inorganic material or rock which, in the judgment of the inspector,
should be removed, the contractor shall excavate and remove such unsuitable
material to the width and depth ordered by the inspector. Before the
pipe is laid, the subgrade shall be made by backfilling with an approved
material in three-inch uncompacted layers. The layers shall be thoroughly
tamped, as directed by the inspector, so as to provide a continuous
bearing and support for the pipe at every point between the bell holes.
The finished subgrade shall be prepared accurately by means of hand
tools.
(2)
The subgrade beneath the center line of the pipe shall
be finished to within 0.03 foot of a straight line between bell holes
or batter boards, and all tolerances shall be above the specified
grade.
G.
Special foundation in poor soil. Where the bottom
of the trench at subgrade is found to consist of material which is
unstable to such a degree that, in the opinion of the inspector, it
cannot be removed and replaced with an approved material thoroughly
compacted in place to support the pipe properly, the contractor shall
construct a foundation for the pipe, consisting of piling, timber
or other materials, in accordance with plans approved by the Board
of Public Works.
H.
Blasting. Blasting for excavation will be permitted
only after securing the approval of the inspector and only when proper
precautions are taken for the protection of persons or property. The
hours of blasting will be fixed by the inspector. Any damage caused
by blasting shall be repaired by the contractor at his/her expense.
The contractor's methods of procedure shall conform to state laws
and municipal ordinances.
I.
Braced and sheeted trenches.
(1)
Open-cut trenches shall be sheeted and braced as required
by any governing state laws and as may be necessary to protect life,
property or the work. When close sheeting is required, it shall be
so driven as to prevent adjacent soil from entering the trench either
below or through such sheeting. Where sheeting and bracing are used,
the trench width shall be increased accordingly.
(2)
The inspector reserves the right to order the sheeting
driven to the full depth of the trench or to such additional depths
as may be required for the protection of the work. Where the soil
in the lower limits of a trench has the necessary stability, the inspector,
at his/her discretion, may permit the contractor to stop the driving
of sheeting at some designated elevation above the trench bottom.
The granting of permission by the inspector, however, shall not relieve
the contractor in any degree from his/her full responsibility under
the contract.
(3)
Sheeting and bracing which have been ordered left
in place must be removed for a distance of three feet below the established
street grade or the existing surface of the street, whichever is lower.
Trench bracing, except that which must be left in place, may be removed
when the backfilling has reached the respective levels of such bracing.
Sheeting, except that which has been left in place, may be removed
after the backfilling has been completed or has been brought up to
such an elevation as to permit its safe removal. Sheeting and bracing
may be removed before flushing the trench, but only in such manner
as will ensure the adequate protection of the completed water and/or
sewer structures and prevent the disturbance of adjacent ground.
J.
Care of surface material for reuse. All surface materials
which, in the opinion of the inspector, are suitable for reuse in
restoring the surface shall be kept separate from the general excavation
material, as directed by the inspector.
K.
Piling excavated material. All excavated material
shall be piled in a manner that will not endanger the work and that
will avoid obstructing sidewalks and driveways. Hydrants under pressure,
valve pit covers, valve boxes, curb stop boxes, fire and police call
boxes or other utility controls shall be left unobstructed and accessible
until the work is completed. Gutters shall be kept clear or other
satisfactory provisions made for street drainage, and natural watercourses
shall not be obstructed.
L.
Trenching by hand methods. Hand methods for excavations
shall be employed in locations where obstructions are shown on drawings
or where, in the opinion of the inspector, property can best be protected
by digging by hand. In other locations, the contractor may use trench-digging
machinery.
M.
Barricades, guards and safety provisions. To protect
persons from injury and to avoid property damage, adequate barricades,
construction signs, torches, lanterns and guards, as required, shall
be placed and maintained during the progress of the construction work
and until it is safe for traffic to use the highway. All material
piles, equipment and pipe which may serve as obstructions to traffic
shall be enclosed by fences or barricades and shall be protected by
proper lights when the visibility is poor. The rules and regulations
of the local authorities respecting safety provisions shall be observed.
N.
Maintenance of traffic and closing of streets.
(1)
The contractor shall carry on the work in a manner
which will cause the least interruption to traffic and may close to
travel not more than two consecutive blocks, upon the specific permission
of the city, including the cross street intersected. Where traffic
must cross open trenches, the contractor shall provide suitable bridges
at street intersections and driveways.
(2)
The contractor shall post, where directed by the inspector,
suitable signs indicating that a street is closed and necessary detour
signs for the proper maintenance of traffic.
O.
Structure protection. Temporary support, adequate
protection and maintenance of all underground and surface structures,
drains, sewers and other obstructions encountered in the progress
of the work shall be furnished by the contractor at his/her expense
and under the direction of the inspector. The structures which may
have been disturbed shall be restored upon completion of the work.
P.
Protection of property and surface structures. Trees,
shrubbery, fences, poles and all other property and surface structures
shall be protected unless their removal is shown on the drawings or
authorized by the inspector. When it is necessary to cut roots and
tree branches, such cutting shall be done under the supervision of
the inspector.
A.
Backfill material. All backfill material shall be
free from cinders, ashes, refuse, vegetable or organic material, boulders,
rocks or stones or other material which, in the opinion of the inspector,
is unsuitable. However, from one foot above the top of the pipe to
the subgrade of the pavement, material containing stones up to eight
inches in their greatest dimension may be used, unless specified otherwise
herein.
B.
Use of excavated material as backfill. When the type
of backfill material is not indicated on drawings or specifications,
the contractor may backfill with the excavated material, provided
that such material consists of loam, clay, sand, gravel or other material
which, in the opinion of the inspector, is suitable for backfilling.
C.
Sand or gravel backfill. Where sand or gravel backfill
is not indicated on the drawings or specified herein and, in the opinion
of the inspector, should be used in any part of the work, the contractor
shall furnish and backfill with sand or gravel as directed.
D.
Backfilling under pipe. All trenches shall be backfilled
by hand, from the bottom of the trench to the center line of the pipe
with sand, gravel or other approved material placed in three-inch
layers and compacted by tamping. Backfilling material shall be deposited
in the trench for its full width on each side of the pipe, fittings
and appurtenances simultaneously.
E.
Backfilling over pipe.
(1)
From the center line of the pipe, fittings and appurtenances
to a depth of one foot above the top of the pipe, the trench shall
be backfilled by hand or by approved mechanical methods. The contractor
shall use special care in placing this portion of the backfill so
as to avoid injuring or moving the pipe.
(2)
The backfill material from the center line of the
pipe to one foot above the pipe shall consist of approved excavated
material which shall be placed in three-inch layers and compacted
by tamping.
F.
Backfilling in freezing weather. Backfilling shall
not be done in freezing weather except by permission of the inspector,
and it shall not be made with frozen material. No fill shall be made
where the material already in the trench is frozen.
G.
Backfill sand. All sand used for backfill shall be
a natural bank sand, graded from fine to coarse, not lumpy or frozen,
and free from slag, cinders, ashes, rubbish or other material which,
in the opinion of the inspector, is objectionable or deleterious.
It shall not contain a total of more than 10% by weight of loam and
clay, and all material must be capable of being passed through a three-fourths-inch
sieve. Not more than 5% shall remain on a No. 4 sieve.
H.
Backfill gravel. Gravel used for backfill shall consist
of natural bank gravel having durable particles graded from fine to
coarse in a reasonably uniform combination, with no boulders or stones
larger than two inches in size. It shall be free from slag, cinders,
ashes, refuse or other deleterious or objectionable materials. It
shall not contain excessive amounts of loam and clay and shall not
be lumpy or frozen. No more than 15% shall be finer than No. 200 sieve.
Backfill gravel shall be used in the top 18 inches of backfill of
all ditches in city streets.
