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. Type of compacting Weight of equipment Thickness of loose No. equipment. per mtr width not layers of earth. less than. 1

2

Outer diameter of 6000 kgs sheep foot roller/pad foot roller not less than 1.52m Mechanical Compactive effort not compactors less than 4000 kg/m2

25cms to 30 cms

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 premeasured. the quantity so measured should be corroborated with the quantity that has gone into the embankment.

6.7.0

6.7.01

FILTER MEDIA:

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 c) Intermediate layers

Sand Sand

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. filter blanket shall then be placed.

The bottom

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 Thickness of layer

Size of Filter fitter materials

FILTER 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-incharge. 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.