SCOPE OF WORK
The Contractor shall perform excavation in
accordance with this Specification and as shown on the approved drawings or as
directed by the Owner.
Excavation shall include incidental clearing,
grading, compacting, leveling, excavation and disposal of excavated materials,
protection, sheeting, shoring, bracing and cofferdams, dewatering of excavation
and work areas and preparation of bearing areas as required to properly install
and complete the work, regardless of portion of the work for which dewatering
is required and regardless of the nature of materials encountered in excavation,
including construction of temporary diversion ditches, culverts, temporary
access road etc. where required.
GENERAL EXECUTION OF EXCAVATION
The Contractor shall notify the Owner in writing
at least three working days prior to the start of any excavation, the beginning
of the work in any working area, to enable the Owner to verify all necessary
levels and cross-sections of the original ground surface. The Contractor shall, prior to starting
excavation in any area, submit to the Owner a plan of operation with complete
details of the method of excavation, type of equipment to be used, proposed
method of diversion of drainage, safety measures to be used, etc.
The Contractor shall set out Works as shown on
the 'approved drawings, utilizing the established benchmarks and coordinates.
The Contractor is responsible for the correct
setting- out of Work. Any additional
work caused by his negligence in setting-out will be at his expense and
corrective action must be carried out without delay as directed by the Owner.
The Contractor is responsible for all necessary
safety measures from the commencement of work until it is completed. The Contractor shall strictly follow safety
regulations in order to prevent accidents.
The Contractor must take every precaution and
use the most appropriate methods of excavation and equipment to avoid the
loosening of material or the breaking of rock beyond the lines and grades shown
on the drawings or as directed by the Owner. If for any reason whatsoever
excavation is carried out beyond the lines and grades shown in the approved
drawings, the Contractor shall, at his own expense, restore the required lines
and grades with mass concrete.
Bottoms of all excavations must be trimmed to
line and grade, the final 20 cm of excavation in any loose geological formation
where concrete is to be placed shall be excavated by hand tools to avoid
disturbance of the bottom, which will then be well rammed, all immediately
prior to the placing of concrete.
Particular care shall be exercised when
excavating in the vicinity of existing and partially or fully completed
structures. The Contractor shall repair or replace, at his own expense, any
structures or equipment damaged by his actions.
It will be the Contractor's responsibility to
utilize to the fullest extent all materials from excavations which are approved
and deemed suitable by the Owner as backfill or other construction. The Contractor shall make his best efforts to
comply with the above requirements.
Where possible, suitable materials shall be
excavated separately from materials to be wasted and shall be placed in the
designated final locations directly from the excavation or shall be stockpiled,
if the immediate placement in the designated location is not possible.
PROTECTION AND SUPPORT
The Contractor shall provide protection and
support required to properly installing work, for protection and support of
adjacent structures and improvements as required for the safety of traffic and
life.
Protection and support includes temporary sheeting,
bracing and shoring and where indicated, permanent sheeting, bracing and
shoring. Temporary sheeting, bracing and shoring shall be removed by the
Contractor when their use is no longer required, unless otherwise directed by
the Owner.
Excavation slopes shall be protected and
supported, where required or when directed by the Owner, so that the slopes and
bottom will be maintained for depth, width and condition indicated and so that
adjacent structures or other construction will be protected from damage caused
by any earth movement.
Protection and support shall be arranged for
minimum interference with pipe laying, electrical installation and other
similar work.
DEWATERING AND DIVERSION OF WATER
General
The Contractor shall furnish install and operate
necessary incidental dewatering equipment as required to do all excavation in
the dry.
Except where specifically permitted by the
Owner, no surface run-off shall be pounded or restricted to a greater degree
than would have occurred naturally either before the beginning of construction
or after completion of the Work.
Diversion of Surface run-off
During the excavation and backfill work, the
Contractor shall construct temporary drainage ditches, culverts and other
structures as required and as directed by the Owner to divert/drain the work
areas.
The Contractor's plan for diversion of the
surface run-off are subject to review by the Owner. Before commencement of the
Work, the Contractor shall submit to the Owner for review, drawings and data
indicating his proposed plans for diversion and care of surface run-off.
The Contractor shall not place any fill across
routes of natural drainage channels until the Contractor has made provisions to
drain the surface run-off into a new diversion ditch.
No surface run-off shall be pounded or
restricted to a greater degree than would have occurred naturally either before
the beginning of construction or after construction of the work, unless
approved by the Owner. Any damage to any
property, equipment or materials as the result of noncompliance to the above
shall be the sole responsibility of the Contractor.
Dewatering
The excavation shall require installation of a
dewatering system consisting of cofferdam/ cut-off walls, sumps and pumps of
adequate capacities and other associated works.
The Contractor shall design, furnish and install a complete dewatering
system and maintain the dewatering system in operating condition until the
completion of his work.
The Contractor shall submit a design for the
dewatering system proposed to be installed by him prior to carrying out the
work.
The Contractor shall be responsible for the
safety and functioning of the dewatering system installed by him.
The pumps, piping and the sumps installed shall
have adequate capacity to keep the excavation dry for the entire construction
period.
If any failure of the dewatering system occurs,
the Contractor shall be responsible for correction of all deficiencies, and
repair of any damages at no additional cost to the Owner.
The Contractor shall make available a standby
electric supply system, or spare diesel pumps and spare parts for quick
replacement for the continuous service of his dewatering system.
DISPOSAL OF EXCAVATED MATERIALS
Excavated materials which are not suitable as
fill materials shall be hauled and disposed of in the designated spoil
area. The materials which are in excess
of the fill requirements for the Contractor's work shall be hauled to the
designated stockpile area.
The spoil area and the stockpile area shall be leveled,
trimmed and graded to drain as directed by the Owner.
LINES AND GRADES
Excavation shall be perform to the lines and
grades shown on the approved drawings or to the depth where suitable foundation
conditions are encountered.
The Contractor must take all necessary
precautions and utilize such methods of excavation that will prevent the
disturbance of material and its possible displacement beyond the required
excavation lines indicated on the approved drawings or as directed by the
Owner.
Any over excavation, no compensation will be
allowed and an approved material for back filling at his own expense.
EARTH EXCAVATION
Earth excavation means general excavation,
including excavation from stockpile areas, of material such as clay, silt,
sand, gravel, crushed or screened rocks, boulders of up to a volume of 0.75 m3,
cemented or weathered rock which may be removed by hand tools, power shovels,
dozers or other earth moving equipment and by ripping without continuous
systematic drilling and blasting. Rippable material shall be defined as such
that the materials can be removed by a properly equipped D8 Caterpillar, or
similar, without excessive wear on the equipment.
Earth excavation may be accomplished by any
method and by the use of any excavation and hauling equipment suitable for the
work. Rock or boulders encountered in the excavation may be drilled and blasted
whenever other methods of loosening such as ripping, crowbarring, or wedging
prove impracticable and shall be removed as required.
In case that earth excavation shall not be
carried out to rock or to specified levels as indicated on the drawings and the
natural foundation material is disturbed or loosened, for any reason, the
foundation shall be improved by compaction, or replaced with approved fill and
compacted, or by other means as directed by the Owner.
TRENCH EXCAVATION
Trenches shall be excavated in hard and soft
material to the limit lines and grades shown on the approved drawings or as
directed by the Owner.
The Contractor shall furnish all labor, material
and equipment required for the proper execution of the work. Correct and adequate bracing and supporting
of the excavation shall also be included.
Excavation performed beyond the lines and grades
shown on the approved drawings, without specific instructions from the Owner,
shall be back filled to grade and lines with approved materials. All additional
work of this nature shall be carried out at the Contractor's expense.
Trenches for pipelines, steel pipes, ducts and
conduits shall be excavated in straight sections and provide a minimum of 20 cm
between the outside face of the pipelines, electrical duct or conduit and the
side of the trench.
Mechanical excavation shall stop not less than 5
cm above the final bottom level and also at an approved distance from permanent
works so that no damage occurs to the same.
The work shall include the excavation of the
remainder, which shall be done and graded manually to provide uniform bearing
on compacted soil immediately before the installation or placing of any
equipment.
If the character of the material at any location
in the bottom of a pipe trench is such that it might cause unequal settlement
or provide unequal bearing for the pipe, or is otherwise unsuitable for the
pipe’s foundation, unsatisfactory materials shall be removed and back-filled
with granular materials and/or concrete and compacted as directed by the Owner
at no extra cost to the Owner.
EXCAVATION FOR THE CONTRACTOR’S CONVENIENCE
This classification shall consist of -all excavation
performed by the Contractor for the purpose of executing the Work, but not
specifically shown, required or mentioned in the Contract Documents, such as
excavation for haul roads, camps, shops, sanitary land fills and other similar
excavation. Permission shall be obtained
from the Owner for the location of borrows areas and eventual spoil areas for
unsuitable material.
The Contractor shall stabilize the slopes of
such excavation in such a manner that they do not represent any danger to the
public or property. Such excavation shall be performed at the Contractor's own
cost and no separate payment will be made for this work.
PREPARATION OF BEARING AREAS
Bearing areas for foundations shall be inspected
and approved by the Owner before any concrete is placed thereon. If bearing areas are not suitable, as
determined by the Owner, The Contractor may be requested to carry on the
excavation deeper to more suitable bearing material. Such additional excavation will be paid for
on the Unit Price basis set forth in the Contract. The Contractor may be requested by the Owner
to make auger borings or other tests in bearing areas to determine thickness of
bearing stratum.
Foundations shall be placed on undisturbed soil
unless otherwise indicated.
Before placing any concrete on soil, the bearing
soil shall be compacted as specified herein for type of fill material
involved. Surfaces shall be relatively
smooth.
Before placing any concrete on soil that will
absorb water, the surface of the soil shall be thoroughly wetted with clean
water immediately before concrete is placed.