Download - Earth Dam Construction
EMBANKMENT 1.0.0 SCOPE OF WORK: This specification covers general
requirements for the construction of embankment by providing
and laying homogeneous materials with selected material.
2.0.0 CLASSIFICATION: 2.1.0 Construction of Embankment using useful excavated materials:
includes providing and laying homogeneous materials for
embankment/core of the dam/cut off trench, the material being
selected from the excavated area as per the directions of
Engineer.
2.2.0 Construction of embankment using materials from approved
borrow area:- includes providing and laying homogeneous
materials in suitable layers for embankment/core of the dam/cut
off trench. The homogeneous material has to be transported
from the selected borrow areas as directed by the Engineer.
2.3.0 Materials:
The contractor shall arrange to re-excavate, if necessary, the
useful excavated staff obtained from the foundations of the dam
and convey the same and utilise if in the embankment in
suitable locations as directed.
The impervious materials required for the impervious zones of
the embankment shall be obtained from excavations in the
borrow area or from available useful excavated materials.
The barrow area from where the impervious materials is to be
obtained shall be stripped up to a depth of 1m or any depth as
may be directed and all stumps, roots, top soil, humus and
organic materials shall be removed and dumped as directed. No
separate payment shall be made for this and the unit rate
indicated for providing impervious fill are inclusive of this.
Applicable codes of practice
:
Methods & procedures:
General:
Before commencing the work of embankment, the extremities
of the dam profile, filters etc., shall be marked with reference to
the base line by the Contractor under the direction of the
Engineer. The base line shall have concrete or masonry pillars
with chainage, levels etc., properly inscribed on them.
The embankment shall be constructed only after the approval is
accorded by the Engineer to the various lines as shown on the
approved drawing. The embankment shall be constructed to the
height shown on drawing plus 2.5% to allow for settlement
after consolidation as may be indicated in the drawings. The
construction slopes of the embankment shall be to the lines
formed by joining the upstream and downstream toes of the
design section to the respective outer edges of the intermediate
berms at the top edge of the dam at a height equal to the design
height, plus 2.5%
4.3.1 Placing of materials
The approved materials shall be conveyed and laid in the
appropriate zones of embankment as directed in continuous
layers and thickness of these layers shall be as under:
:
Sl. No.
Type of compacting equipment.
Weight of equipment per mtr width not less than.
Thickness of loose layers of earth.
1 Outer diameter of sheep foot roller/pad foot roller not less than 1.52m
6000 kgs 25cms to 30 cms
2 Mechanical compactors
Compactive effort not less than 4000 kg/m2
10cm
No stones or pebbles having a dimension more than 75mm shall
be permitted to be used in the core of the embankment or with
in the central zone of the saddle. The embankment work shall
be raised as directed by the Engineer.
No materials shall be placed in different zones in the section of
the embankment until the foundation has been de-watered and
suitably prepared therefor. Written permission of the Engineer
shall be obtained before laying the first layer.
The suitability or otherwise of the materials excavated from
stripping of the seat of the embankment and cut off trench for
the embankment work shall be determined by the Engineer.
4.15.2 METHODS & PROCEDURE
The foundation except rock surfaces, for the earth fill shall be
prepared by ploughing leveling and rolling after adding water,
if necessary so that the surface material in the foundation will
be as compact and well bonded with the first layer of the fill as
herein specified for the subsequent layers of the earth fill. The
longitudinal slopes of the soil in the cut off trench excavation
shall not be steeper than 2 horizontal to vertical.
The following precautions shall be taken for bonding the core
of embankment with bed strata.
1. Loose sand, boulders, debris and silt coats, stumps of trees
etc., shall be removed from the entire base of the dam.
2. All decomposed weathered and soft rock shall be removed
up to the levels approved by the Engineer.
3. Fissures and cracks in rocky beds shall be opened to
sufficient depth to facilitate tamping earth. Narrow cracks
shall be filled up with cement mortar (1:3).
4. Sharp projections of the solid rock shall be chamfered.
5. Rocky bed surfaces below the core zone shall be cleaned by
means of high pressure air and water jet.
6. All local leakages shall be sealed confining them to vertical
pipes to be finally plugged with cement mortar of proportion
1;3.
7. The rock surfaces on which impervious core/hearting zone is
to be laid shall be soaked and coated with a moisture content
3% to 5% more than optimum moisture content. Bentonite
will be supplied by Employer free of cost. The Contractor
shall provide all necessary labour for mixing and applying at
his cost.
8. Wherever rolling is not possible, the thickness of layer shall
be reduce to 75 mm and compaction shall be done by
pneumatic tampers.
4.15.3 PLACING OF IMPERVIOUS FILL:
The finished fill shall be free from lenses, pockets streaks and
layers of materials differing substantially in texture or gradation
from the material prescribed. Materials in each successive
layers shall be placed on the earth fill so as to produce best
practicable distribution of the material subject to the approval
of the Engineer. Normally, the earth fill all over the surface
should be kept at the same level during construction with the
outer edge slightly higher than the inside so as to ensure safety
for working of the vehicles. However, before closure of the
works for the monsoon, the top may be kept slightly sloping
towards outer edges to avoid pools of water forming due to
rain. The compaction shall be done by movement of rollers
parallel to the axis of the dam and shall generally be done only
in part lengths (i.e. the whole section from u/s to d/s between
convenient chainages) and not in part widths.
Before a new layers is deposited, the surface of the pervious
layer shall be scarified and roughened by disc harrowing or
ploughing so directed by the Engineer, so that a good bond may
be obtained with the materials to be super imposed. The
materials shall be deposited, starting from the lowest portion of
the foundation, in rows approximately parallel to the axis of the
dam and spread in uniform layers.
With a view to attaining the same degree of compaction near
the outer most edges as in the entire section of the dam, the
sections shall be laid for 0.6m width more than the prescribed
width on either side of the embankment and after the required
degree of compaction has been attained, the extra widths shall
be dressed to the required sections.
4.15.4 MOISTURE CONTROL:
The Moisture content of earth fill materials prior to and during
compaction shall be distributed uniformly throughout each
layer of materials. the ranges of placement moisture content
shall be as determined by the Engineer from time to time. the
placement moisture content, shall be as a general guide + 3 or –
3 percent of the optimum moisture content of the soil, as
determined by the standard proctor’s compaction test. If the
placement moisture content be greater than the required
moisture content, the materials shall be spread and allowed to
dry up to the required moisture content before starting of the
rolling. If additional moisture is required, water shall be added
by sprinkling of the layer.
Water shall be added to embankment through nozzle,
embankment materials shall be placed only when the weather
conditions are satisfactory to permit accurate control of the
moisture content on the embankment material. During the
construction period if rains occur causing cessation of work, the
top surface shall be graded and rolled with a smooth wheeled
roller to facilitate easy run off, prior to resuming the work, the
top surface should be properly scarified and moistened before
the next layer is laid.
4.15.5 COMPACTION:
i) COMPACTION OF FINE MATERIALS.
The required compaction of cut off core material and hearting
material shall be done by using sheep foot rollers/pad foot
rollers. Pervious zones shall be compacted by power
rollers/vibratory compactors as directed by the Engineer.
In each layer, no individual density test result be less than 98%
of the optimum density obtained by the standard proctor density
test. Average of all tests shall not be less than 99% of the
optimum.
ii) COMPACTION OF GRANULAR/PERVIOUS
MATERIAL:
In respect of zoned embankment power/vibrator rollers shall be
used to obtain the required degree of compaction in the
pervious zones which encase the impervious core. For the
compaction of impervious core material, only sheep foot rollers
shall be employed.
4.15.6 COMPACTION:-
When each layer of material has been conditioned so as to have
proper moisture content uniformly distributed through the
material it shall be compacted by adequate number of passes of
the roller till the required density is obtained. Density test shall
be made after rolling is completed.
In case of soils containing gravels, the optimum moisture
content and the maximum dry density shall be determined for
the total material in the manner prescribed under designation E
38 in the U.S.B.R. Earth Manual. Each layer shall be got
approved from the Engineer before placing the next layer.
4.15.7 TAMPING:
In those parts of the structure which are inaccessible to the
specified rolling equipment, and in close proximity to structure,
where the rolling equipment will not be permitted to operate,
compaction shall be accomplished by mechanical compactors.
All materials to be so compacted shall be spread in layers of
75mm to 100mm thick when loose and the moisture content of
the material and the amount of compaction shall be such as to
produce a degree of compaction equal to that specified for
rolled fill portion Special care shall be exercised to obtained
good contact and bond with surfaces of concrete rock surfaces
which shall include (i) presmearing the surfaces with a slurry of
Bentonite or clay plus bentonite and (ii) using extra moisture
for the fill from 3% to 5% above optimum moisture content.
4.15.8 QUALITY CONTROL:
a) Contractors shall keep close check on the materials and
moisture content and compaction depending upon the test
results supplied by the field laboratory.
b) The density test shall be conducted for each layer of
embankment to ascertain whether the compaction is attained
to the required standards.
All tests on density and penetration will be conducted by the
Employer. Occasional tests shall be carried out to determine
the insitu permeability of the impervious material by taking
holes for depths not more than 1.5 metres in the compacted
embankment.
The Contractor or his representative shall be present and extend
his co-operation at the time of collecting the sample for testing.
The absence of the Contractro or his representative at the time
of collecting the samples shall be deemed as his acceptance for
the samples thus collected. The discretion of taking samples
viz., method and selection of locations for core samples,
conducting tests etc., shall always rest with the Engineer.
4.15.9 RESUMPTION OF WORK AFTER TEMPORARY --------
When the work is stopped at the end of working season and is
to be started in the beginning of next season, any other
stoppages, the top surfaces shall be stripped of all loose and
cracked material to the satisfaction of the Engineer, before
resumption of work. When the work on the embankment is
resumed, the stripped surface shall be roiled adequately and
necessary bond shall be provided between the old and new
surfaces by adequate watering etc.,. No extra payment shall
made for such stripping scarifying, rolling or watering
involved. The minimum levels of the embankment over the
entire length shall be at least four metres above the maximum
water level in the flood disposal arrangements made in the
gorge, as may be specified by the Engineer.
4.15.10 FINISHING OF EMBANKMENT:
The work shall be given a neat finish as regards lines and
grades and top of the dam. The entire work and working space
and borrow areas shall be left neat and clean.
All the humps and hollows from the neat lines of embankment
shall be graded. Materials used to fill depressions shall be
maintained until final completion and acceptance by the
Employer. any material that is lost by weather or other causes
shall replaced by the Contractor at his own expense.
4.15.11 JUNCTIONS:
Junctions of earth works shall be avoided as far as possible. If
such junction are found inevitable and ordered, then special
care to be taken as regards materials to be placed, moisture
content, bond between old and new sections, compaction and
finishing. This shall apply in case of curves and kinks in dam
alignment. Junctions of earth work shall be carried out as
directed by the Engineer.
4.15.12 JOINING OF THE OLD AND NEW EMBANKMENT:
When the embankment is raised to different heights along the
axis of the dam at the end of a working season the longitudinal
slopes (along the axis) shall be trimmed to at least 2H to 1V
prior to starting the fresh work in the next season. The old
slope (previous seasons work) shall be trimmed to the slope
mentioned above and all loose material shall be removed and
thorough bond shall be established between the old and new
embankment by scarifying/raking, moistening before laying the
fresh layers.
4.15.13 TREATMENT FOR EXISTING TRIAL PITS:
All trial pits that are existing at the dam site shall be treated as
specified as below. Before laying the embankment these trial
pits shall be cleaned of any debris of any objectionable
material. The longitudinal slopes (parallel to axis) shall be
trimmed to neat stable slopes.
All the trial pits below the core/hearing zones and cutoff
trenches shall be filled up with compacted material. the trial
pits below all other zones shall be filled back with compacted
material similar in nature to the surrounding material.
4.15.14 MEASUREMENT AND PAYMENT FOR
EMBANKMENT MATERIALS:
The work shall be measured on the basis of cross-section. The
cross-sections will be taken at intervals of 30 metres or closer
as may be considered necessary by the Engineer. The gross
quantity of embankment will be worked out on the basis of
those cross-sections. In the case of curves the quantities will be
evaluated along the centroid of each zones of the cross-sections
and quantities worked out accordingly. The rate indicated for
the embankment items are inclusive of the cost of all plant,
material and labour etc., required for completing the work as
specified in these specifications.
Payment for embankment work will be on the cross sectional
area of the finished embankment. The dam shall be constructed
to the height shown in the drawing ------2.5% height to allow
for settlement after completion. The construction slope shall be
obtained after increasing the top level of the design section by
2.5% of the height and joining the top edges to the heel and toe
points of the design section. The top level of the embankment
in the deposit portion shall be increased by 2.5% of the height
above the design top level and linearly brought to the design top
level at the ends of the dam.
All payments both of intermediate and final will be made
subject to 2.5% deductions the quantities of embankments
actually constructed.
SECTION
HORIZONTAL SAND DRAINS
The specification given here refers to item No.2.9 in the Schedule ‘B’.
4.20.1 SAND DRAINS:
These shall be provided as per the drawings or as directed by
the Engineer. Sand shall be well graded and shall conform to
the general specifications for sand (IS:383-1970 or latest
revision) and in particular to the filter criteria as determined in
the field laboratory. Sand shall be laid in layers of 30cms.
Adequately watered and compacted with suitable equipments as
approved by the Engineer.
4.20.2 MEASUREMENT AND PAYMENT:
Measurement and payment shall be as per section 4.14 –
‘Embankment’.
Materials going into the embankments shall be stacked and pre-
measured. the quantity so measured should be corroborated
with the quantity that has gone into the embankment.
6.7.0 FILTER MEDIA:
6.7.01 GENERAL: Filter-media shall be laid as shown in the drawing
and as ---------- by the Engineer-in-charge. The number of
layers in the filter media and the thickness of each layer shall be
as specified and or as directed by the Engineer-in-charge.
The gradation of the filter materials shall generally be as
indicated in the table below;
Position of the layer Size of filter material
I. Horizontal filter:
a) Central layer 50cm thickness. 40mm and downsize aggregate from crushed rock.
b) Outermost layers Top 25 cms. Bottom 25 cms
Sand Sand
c) Intermediate layers
Top 25 cm. Bottom 25 cm.
20mm and down size aggregate from crushed Rock.
II.
Vertical Chimney:
Drain: a) Central layer
60cm thickness 40mm and down size aggregates from crushed rock.
b) Outermost layers U/S 40cm thickness D/S 40cm thickness
Sand Sand
c) Intermediate layer 40cm thickness.
20mm and downsize aggregate from crushed rock.
The Engineer-in-charge may at his discretion modify the gradations to match
the embankment materials to satisfy the filter criteria. The contractor shall
do the necessary ------- of sand at his own cost. The requirements and
gradation for filter shall be established by the corporation field laboratory on
the basis of mechanical analysis of foundation and embankment materials.
The mechanical analysis shall be performed on samples which have been
compacted by methods equivalent to compaction by rollers, so that
individual particles of rock fragments are broken down to their final
condition in the embankment.
No particles of decomposed or weathered rock or soft rock shall be
permitted in the filter, as also wood, vegetable matter or other deleterious
materials. 40mm and downsize and 20mm and downsize metal shall be
crushed from rock obtained from approved quarries and shall be free from
rock dust.
6.7.02: PLACING OF THE FILTER MEDIA:
(a) Horizontal filter blanket: The horizontal filter blanket connecting
vertical chimney drain, Rock toe, and toe drain shall be provided with
graded material as directed by the Engineer-in-charge as per drawings.
Before placing the filter layers, the foundation there for shall be cleaned
and brought to level by filling in depressions (if any) with selected
impervious materials compacted at optimum moistures. The bottom
filter blanket shall then be placed. Each layer shall be adequately
watered and compacted by moving the hauling and spreading equipment
over it or by other means approved by the Engineer-in-charge. The
variation in thickness in each layer shall not exceed 25mm above or
below in the thickness specified in the drawing or as directed. The rock
too shall be laid over it in such a way so as not to damage the filter
blanket in any way. The ----- quoted shall include the provision of
graded filter material of approved quality.
(b) Vertical chimney drain: Filter material shall be so placed that it conforms
to the position as indicated in the drawings. The thick ness and location
of each individual filter layer shall be maintained by placing the material
between temperately placed mild steel sheets or wooden boards which
shall be maintained as directed by the Engineer-in-charge. The
compaction of the filter media shall be done after watering, by vibratory
rollers or by other means approved by the Engineer-in-charge to obtain a
density of atleast 1750 kg/cum. Further specifications issued in this
regard from time to time shall be complied with. The embankment over
the filters shall also be done in such a way so as not to damage the filter
in any way. Sand shall be well graded and shall conform to the general
specification for sand (IS 383-1970 or latest revision) and in particular to
the filter criteria as determined in the field laboratory.
Generally the chimney filter and the impervious materials adjacent to it shall
be raised together with a maximum differential height of 0.6m between the
filter and the adjacent embankment. The filter shall be higher than the
adjacent embankment.
6.7.03: Measurement and payment: all filter materials going into the filter
media shall be stacked and pre-measured before it is placed in the quantity
that has gone into the embankment. Measurement shall be for the entire
graded filter media and not separately for individual layers of graded
materials and payment shall be made on the lines and thickness as specified
or as directs by the Engineer-in-charge on the basis of unit rate for such item
quoted by the contractor. Measurement and payment shall be as per para
6.3.04.
6.8.00 PROVIDING AND PLACING OPEN JOINTED PIPE: (Item
No.10 Schedule ‘B’)
6.8.01: These pipes shall be provided in the toe drain of the rock toe. The
pipes shall be pipes of 30cm dia and 2 meters length or less, if available. An
oversized collar should be provided at the junction to allow ------ of water.
The pipes shall be laid with open joints with uniform grade between any two
man holds. The pipes shall be embedded in concrete walls of the manholes,
as directed by the Engineer-in-charge. Before lay8ing the pipes the filter
layer below it shall be laid perfectly, adequately watered and compacted to
avoid any further settlement of pipes laid there on. The aggregate amount
the pipe should be hand packed.
6.8.02: MEASUREMENT AND PAYMENT: The measurement shall be
made at the unit rates quoted for the item by the Contractor in Schedule ‘B’
which unit rate shall be inclusive of the cost of all material, machinery
labour etc.,
6.9.00 (Item No. 12 of Schedule ‘B’)
6.9.01 The rock toe of the dam embankment shall consist of suitable
draining mixture of rock fragments, boulders and quarry spalls
obtainable from excavations, borrow pits of quarries as the case may
be. The material shall be fairly well graded consisting principally of
rock fragments, ranging in volume from 0.0033 to 0.04 cum. The
dumping shall be done in layers of about 0.60M and such as to have
larger fragments placed near the outer slopes and finer materials
adjacent to the inside slopes. Sufficient materials such as rock spalls,
stone chips, etc., shall be hand packed as directed in to the rock
material. The fill shall be dense and well graded with no larger voids
or cavities and surface of the outer and inner slopes as shown in the
drawings, or as directed in the Engineer-in-charge. The stones on the
out face shall be hand packed so as to bring up the plane face of rock
to form the rock toe facing. Rock fragments and spalls shall be
tightly driven into the interstices to prevent the aggregate of the filter
behind the rock toe form passing through the interstices.
6.9.02 Measurement and Payment: Measurements of rock toe in Dam
embankment shall be taken as per the quantity of rock fill placed in
Dam embankment to the lies and grades shown in the drawings or as
established by the Engineer-in-charge. Payment for this items shall
be made on the basis of the unit rate quoted.
SECTION -
8. ROUGH STONE REVETMENT
The specification given here refers to the item No. 2.11 in the
Schedule ‘B’
4.19.1The slope to receive the stone revetment shall be first prepared by
scraping the slope of embankment to the required lines and grades and the
revetment laid on the filter bed of 45cm thick. The earth slopes to receive
the filter shall be properly formatted. The thickness of the revetment shall
be 60 cms and is should be formed of two layers of stones. The stones on
the face shall not be less than 25 cms x 20 cms and 30 x 40 cm deep at right
angles to the slopes of dam. The total thickness of 45 cm shall be made of
not more than two stones i.e. there shall be one more stone of 10 cm to 20
cm thickness being the facing stones. Through stones of 40 cm depth and
not less than 30 cm x 40 cm on the face shall be provide at the rate of two
from every sqm. 25% of the same shall project 15 cm from finished
surface. Cashew should be taken to stagger the headers. The layer of
revetment shall be constructed as per IS:8237-1976 or its latest revision.
4.19.2 The stones used for the revetment shall be perfectly sound, durable
and clean. The stones shall be taken from the approved quarries.
4.19.3 The stones shall for as possible have fairly large flat surface so as to
obtain a fairly even surface and have minimum voids. The stones shall be
placed on edge normal to the slopes. Beginning at the bottom of the slope
as shown in the drawing, the stone shall be laid compact land flush each
other with maximum joint space of 1.25 cms. Rock spalls shall be tightly
driven into the interstices to the underlying slope. Such filling shall be
carried on simultaneously with the placing in position of large stones and
shall is no cases be permitted to lag behind. The wedging shall be done
with large size chips, each being well driven with a hammer so that no
chip can be picked or removed by hand. The distribution of header stones
shall be uniform and staggered from course. Higher irregular points shall
be knocked off so that the finished revetment shall present a smooth and
uniform surface.
4.19.4 The filter media below the revetment shall be laid as shown in the
drawing or as directed by the Engineer. The filter media for the rough stone
revetment shall conform to the following requirement.
POSITION OF THE
FILTER
Thickness of layer Size of Filter fitter materials
Bottom layer adjacent
to the Earth slope
15 cm.
Sand
Intermediatellayer 15 cm. 20 mm and downsize
Top layer 15 cm 40 mm and down size
4.19.5 The engineer may at his discretion modify the gradation of sand to
match the embankment materials. The Contractor shall do the necessary
processing of sand at his own cost. The required gradations for filters shall
be established by the Employment field laboratory on the basis of
mechanical analysis.
The mechanical analysis shall be performed analysis shall be performed
on samples which have been compacted by method equivalent to
compunction by rollers. So that individual particulars of rock fragments
are broken down to their final condition in the embankment. No particulars
of decomposed or weathered rock or soft rock shall be permitted in the
filter. No debris, wood, vegetable matter or other deleterious materials shall
be permitted in the filter.
4.19.6 MEASUREMENT AND PAYMENT:
Measurement of revetment shall be taken along the U/s slope at 30M or
closure intervals at the description of the Engineer(along the centre line of
the dam) and will be paid on the quantity of revetment as per the unit rate
indicated in Schedules-B. Unit rate indicated for this item is per square
meter and includes the cost of the rough stone revetment and also the cost of
spall backing and the filter media below the revetment stone.
SECTION
9. ROUGH STONE PITCHING
The specification given here refer to the item 2.12 in the Scheduled ‘B’
4.22.1 The surface to receive the pitching shall first be prepared by
scraping the slope of embankment to the required lines and grades as
shown in the drawings or as direct by the Engineer pitching laid over gate
and sand backing. Earth slopes of the excavation and/or the slops of the
embankment to receive the metal l backing and sand shall be properly
formed. The thickness of the pitching shall conspires of 0.30-m thick layer
of stones and 0.45m thick filter basking. The stone layer be formed in a
single layer and the stones on the face shall not be less than 25 cms x 20 cms
and 30 cms deep at right angles to the slopes of the dam. The layers of
pitching shall be done as mentioned in IS –m8237-1976 or it latest revision.
the stones issued for the pitching shall be perfectly sound, durable and as
regular in shape as possible and clean. The stones shall be taken from the
approved quarries.
The stones shall as for as possible have frilly large flat surfaces so as to
obtain a fairly even surface and have minimum voids. The stones hall be
placed on edge normal to the slopes. Beginning at the bottom of the slope,
the stones, shall be laid hand packed with broken joints and so matched
land interlocked ;that they are keyed together with a minimum of joint
space. Rock fragment and spells shall be l tightly driven into the interstices
to wedge the pitching stones so as to close direct opening to the underlying
Slopes. Such filling shall be carried on simultaneously with placing in
position of large stones and shall in no case be permitted to lag behind.
The wedging shall be done with large chips leach chips being well driven
with a hammer so that no chip can be packed or removed by hand. The
distribution of large size stones shall be uniform . High irregular points
shall be knocked off and finished so that the pitching shall present a neat
smooth and uniform surface..
4.22.2 FILTER BACKING BEHIND PITCHING:
A filter backing consisting of 15 cms thick layer of agreement of size 40
downsize, 15 cms layer of aggregates of size 20mm and down size, 15 cms
thick layer of sad shall be provided. The aggregates shall be laid over the
prepared surface of sand which shall be well watered and compact6ed and
hand packed as shown in the drawing and directed by the Engineer. The
sand used shall be as indicated in section 4.21. The aggregate shall be well
graded and shall be free from weathered rock, debris wood vegetable matter
and other deleterious materials and contacted with suitable method approved
by the Engineer.
4.22.3 MEASUREMENT AND PAYMENT
Measurement of pitching shall be taken along the pitched slopes at 30M or
close intervals at the discretion of the Engineer and will be k paid for the
quantity of pitching as per the unit rate indicated.
Unit rate indicated for this item is per square meter of the exposed face of
revetment and includes the cost of aggregates. And backing behind the
pitching stones including necessary surfacing of bed to have correct required
slope etc., complete.
6.13.00 PROVIDING MANHOLE:
6.13.01: PROVIDING MANHOLE IN THE DRAIN:
i) Man holes are to be provided at 90M c/c along the toe drain. The
outer diameter of manhole shall be a minimum of 1.60mtr. with
20cms thick 1:2:4 ( by volume) this concrete wall. The average
height of manhole is 3 mtrs. which varies as per section of rock toe.
The cut off walls as indicated in the drawing shall be provided.
ii) The 60cms dia manhole cover shall be provided with pre-cast concrete
slab. The manhole shall be provided with cold twisted bars of 16mm
dia at suitable intervals as shown in the drawing.
iii) Ladder rungs of 16mm dia, bars at 30cms/c/c shall be provided as
shown in the drawing. The last man hole shall be provided with out
fall d rain to lead --------- safely to further down stream side of the toe
of the dam so that there is no water logging or flooding. For this
purpose a channel shall be excavated with suitable gradient, so that
that the flow from the toe drain and the manhole will not stagnate near
the toe of earthen dam and will be taken safety downstream to the
river course. The rates include providing concrete, pre-cast concrete
cover of 60cms diameter and all items as shown in the drawing.
iv) Measurement and payment: Measurement will be for each manhole.
Payment including all items shall be for each man hole provided.
6.14.00: Surface drainage: Item No. 16 of Schedule ‘B’). The paved cross
drains (chutes) shall be provided at about 90M c/cto drain the rain water
along the sloping surface terminating in the paved longitudinal drain at the
junction of berm and slope or leading into the rock toe. The paved
longitudinal drain and cross drains shall be formed out of stone pitching and
faces plastered with CM 1:4 proportion by w eight. Hume pipes of 150mm
and 200 to 250cm in length (or suitable available lengths)as approved by the
Engineer-in-charge, shall be laid at a grade of 1 in 50 as shown in drawing
over the compacted and watered layers of embankment to avoid further
settlement. If required, the formed embankment shall be excavated to the
required grade and dimensions. Necessary check bunds shall be provided
along the paved longitudinal collecting drain at 90M c/c to divert the water
properly into the cross pipes. The space around the pipe shall be properly
filled with a filter and compacted to the required density. Necessary
cushioning and pavement over the pipes shall be provided in flush with the
respective berm level. The sloping drain on the last slope above the rock toe
shall be suitably connected to the rock toe.
The laying of the pipes and the method of jointing shall be in accordance
with the approved drawings and as per the direction of the Engineer-in-
charge. The pipes shall conform to ISI specification prescribed for hume
pipe IS No.1592 of 1970.
Measurement and payment: The measurement for the paved drains shall be
in running meter. The rate quoted in Schedule ‘B’ shall include the cost of
excavation, re-filling, grading, plastering including the cost of all labour,
materials etc.,. The measurement for pipes shall be made on the basis of
running meter of actual length of pipe embedded including the cost of pipe,
making necessary excavation, grading, jointing, with all materials and
labour.
SECTION
11. OPEN PAVED DRAINS
Specification given here refers to the item No. 1.40 & 2.13 in the Schedule
‘B’.
The drain provided just downstream of the toe of the embankment dam shall
be formed with ---d/s slope of the dam forming the u/s slope of the d rain as
shown in the drawing. The bed --- the downstream slope of the d rain shall
be provided with 30cm thick stone pitching with --- of size 30cm X 40cm on
the face. The interstices shall be packed with rock spall and the joints shall
be pointed with cement mortar or proportion 1:3 by weight to a depth 75mm
-- two stages. The d rains at the toe shall be connected to an out fall drain in
as indicated in the drawings with arrangements for embedding a V-notch for
measurement of seepage.
MEASUREMENT AND PAYMENT
:
The measurement for this item shall be on the basis of running meter of the d
rain constructed. The payment shall be made at the unit rate indicated in
Schedule ‘B’ and this rate includes the cost of all materials, labour required
for laying the stones, packing the joints with rock spalls, pointing the joints
with mortar etc., complete.