DRAINAGE WORKS



DRAINAGE WORKS

12.1. General Requirements

12.1.1. In designing a drainage system for building(s), the aim shall be to provide self cleansing conduits for the conveyance of soil, waste, surface or sub-surface waters, and for the removal of such wastes speedily and efficiently to a sewer or other outlet, without risk of nuisance and hazard to health.

12.1.2. The discharge of water through a domestic drain is intermittent and limited in quantity and therefore, small accumulations of solid matter are liable to form in the drains between the building and the public sewer. There is usually a gradual shifting of these deposits as discharges take place.  Gradients shall be sufficient to prevent these temporary accumulations building up and blocking the drains.

12.1.3. Normally, the sewer shall be designed for discharging three times the dry weather flow flowing half-full with a minimum self cleansing velocity of 0.75 metre per second.  The approximate gradients which give this velocity for the sizes of pipes likely to be used in building drainage, and the corresponding discharges when flowing half-full are given in Table 1.  The sizes and slopes shall conform to Local Municipal Bye Laws.

12.1.4. In cases, where it is practically not possible to conform to the minimum gradients, a flatter gradient may be used but the minimum velocity in such cases shall on no account be less than 0.61 metres per second.

12.1.5. On the other hand, it is undesirable to employ gradients giving velocity of flow greater than 2.4 metres per second.  Where it is unavoidable, cast iron pipes shall be used.  The approximate gradients which give a velocity of 2.4 metres per second for the various sizes of pipes and the corresponding discharge when flowing half-full are given in Table 1.

12.2. Specifications for materials

12.2.1. Flushing tank (Fig. 1): Subject to the minimum size of 100 mm, the sizes of pipes shall be decided in relation to the estimated quantity of flow and the available gradient.

12.2.2. C. I. Cover: C. I. Cover shall be 560 mm dia and shall be medium duty or heavy duty depending upon the locations of the tank.  It shall conform in all respects to IS: 1726-91 (Part IV and Part II) respectively.  Weight of cover and frame shall conform is IS: 1726-91.

12.2.3. Siphon shall be automatic siphon made of cast iron with trapped outlet for flushing.  The siphon for flushing a sewer line shall be as 65 mm, 80 mm or 100 mm dia as specified.

12.2.2. Manholes

12.2.2.1. C. I. Covers - The covers and frames shall conform to IS: 1726-91 and shall be of the following grades and types:

a)  Heavy duty - These shall be denoted by the letters HD circular solid type for use under heavy vehicular traffic condition and shall conform to IS: 1726-91 (Part-II).

b)  Medium duty - These shall be denoted by the letter MD circular or rectangular solid type for use under light traffic condition such as foot paths, carriage drives and cycle tracks.  These shall conform to IS: 1726-91 (Part – IV & V).

c)  Light duty - These shall be denoted by the letter LD of rectangular size for use in domestic premises or where they are not subjected to wheeled traffic loads.  These shall conform to IS : 1726-91 (Part-IV) – Square types shall conform to IS : 1726-91(Part-VII).  The covers and frames shall be cleanly cast and they shall be free from air and sand holes and from cold shuts.  They shall be neatly dressed and carefully trimmed. All castings shall be free from voids whether due to shrinkage, gas inclusion or other causes. Covers shall have a raised Chequered design on the top surface to provide an adequate non-slip grip.

FLUSHING TANK

The cover shall be capable of easy opening and closing and it shall be fitted in the frame in workmanship like manner.

Table 1 Gradient for sewers

\

Diameter mm

Minimum Gradient

Maximum Gradient

Gradients

Discharge

cum / Min.

Gradients

Discharge

cum / Min.

100

1 in 57 

0.18

1 in 5.6

0.59

150

1 in 100

0.42

1 in 9.7

1.32

200

1 in 145

0.73

1 in 14

2.4

230

1 in 175

0.93

1 in 17 

2.98

250

1 in 195

1.10

1 in 19 

3.60

300

1 in 250

1.70

1 in 24.5

5.30

The cover shall be gas tight and water tight.

The covers used in manholes in sewer lines shall invariably bear the word ‘SEWER’ on the top and those used for storm water drains shall bear the word ‘STORM’.  These markings shall be done during casting of the covers.

The sizes of covers specified shall be taken as the clear internal dimensions of the frame. The approximate weights of the various types of manhole covers and frames shall be as per IS: 1726-91.

Covers and frames shall be coated with a black bituminous composition.  The coating shall be smooth and tenacious. It shall not flow when exposed to a temperature of 63 degree centigrade and shall not be brittle as to chip off at temperature of 0 degree centigrade.

12.2.2. Precast concrete manhole covers & frames - Precast reinforced cement concrete manhole covers intended for use in sewerage and water works shall generally conform to IS : 12592 (Part 1 & 2).  Detailed specifications are as under:

12.3.2.2.1. Grades: Types & Uses - Manhole covers and frames shall be of the following four grades and types.

Grades

Grade   Designation

Type / shape of cover

Light Duty        

LD – 2.5

Rectangular, Square, Circular

Medium Duty

MD – 10

Rectangular, Circular

Heavy Duty      

HD – 20

Circular, Square, Rectangular, (Scrapper Manhole)

Extra Heavy Duty

EHD – 35

Circular, Square, Rectangular, (Scrapper Manhole)

12.4.2.2.2. The different grades and types of manhole covers may be used as follows

a) LD – 2.5 Rectangular, Square or Circular types -These are suitable for use within residential and institutional complexes/areas with pedestrian but occasional LMV traffic. These covers may also be used for Inspection Chambers.

b) MD – 10 - These are suitable for use in service lanes/roads, car parking areas etc.

c) MD – 20 - Suitable for use in institutional /commercial areas/carriage ways with heavy duty vehicular traffic like buses, trucks, etc.

d) EHD – 35 - Circular, square, or rectangular (scrapper manhole) types – These are suitable for use on carriage way in commercial industrial/ port areas/ near warehouses /godowns where frequent loading and unloading of trucks/trailers are common, with slow to fast moving vehicular traffic of the types having wheel loads up to 11.5 tonnes, irrespective of the location of the manhole chambers.

12.2.2.3. Materials

Cement - Cement used for the manufacture of precast concrete manhole covers shall be 33 grade Portland cement conforming to I: 269 or 1489 (part 1 & 2) or IS: 8041 or IS: 8112 or IS: 155.

Aggregates - The aggregates used shall be clean and free from deleterious matter and shall conform to the requirements of IS: 383-79.  The aggregates shall be well graded and the nominal maximum size of coarse aggregate shall not exceed 20 mm.

Concrete - The mix proportions of concrete shall be determined by the manufacturer and shall be such as will produce a dense concrete without voids, honey combing etc. The minimum cement content in the concrete shall be 360 kg/m3 with a maximum water cement ratio of 0.45.  Concrete weaker than grade M-30 (design mix) shall not be used.  Compaction of concrete shall be done by machine vibration.

12.2.2.4. Reinforcement

a)  The reinforcement steel shall conform to IS: 226 or IS: 432 (Part I) or IS: 832 (Part II) or IS: 1566 or IS: 1786 as specified.

Reinforcement shall be clean and free from loose mill scale, loose rust, and mud, oil, grease or any other coating which may reduce or destroy the bond between the concrete and steel. A light film of rust may not be regarded as harmful but steel shall not be visibly pitted by rust.

b)  Fibre steel -  In association with the main steel bars reinforcement steel fibres of appropriate types and forms may also be used as secondary reinforcement  (up to 0.5% by volume).

Plastics - Plastic fibre of polypropylene fibrillated film of suitable type and form (0.55 by weight) may also be used as reinforcement in line of steel reinforcement.

Shapes and Dimensions

Shapes - The shapes of precast concrete manhole covers shall be square, rectangular or circular as specified.

Dimensions - Dimensions of precast concrete manhole covers shall be as given in Table 2, the minimum clearance at top between the frame and cover shall be 5 mm.

Table - 2

Sl. No

Description

Heavy / Extra Heavy duty HD / EHD

Medium duty    M.D.

Light duty   L. D.

1

Clear opening matching the top opening of anhole           

560 mm dia or 600 mm dia or square or 560 mm                       

450 mm dia. 480 mm dia. 500 mm dia. dia or square           

600x450 mm (rectangular) 450 mm dia or350 mm dia or square

2

Precast slab with Integral frame (D/T)           

900mm dia x 180mm or square corners cut1000mm dia x 200 or square corner cut                          

800 mm. dia x 130 mm 800 mm dia x 150 mm                       

850 mm x 700mm x 100 mm 625 mm dia x100 mm or575 mm dia x100 mm or square

3

Thickness of cover depth of frame (TI)

100 mm or110/120 mm

70/80 mm

50 mm

4

Matching manhole cover (B)                                  

685/660 mm or 735/710 mm dia or square                     

585 mm dia or 645 mm dia or square                                               

685 x 535mm 515 mm dia or square 435 mm dia or square

5

Edge protection oF covers/ lifting facility

Precast manhole covers are designed and provided with MS rims of 2.5 mm thickness welded around with provision of two lifting hooks welded at appropriate locations.

6

Chequered pattern on operative surface           

The MS rims along with the edges of precast manhole covers and their operative surface are suitably coated/ finished using corrosion resistant paint.

7

Marking on the covers

Precast manhole covers/precast slabs are suitably marked on the operative surface with the following letters, unless specified otherwise Name of the Department/Sewer or SWD/ Grade /Date of MFR/ Trade Name etc.

8

Performance requirements  When tested for ULTIMATE breaking load using 300 mm dia block as per the method described in IS : 12592 (Part1) manhole covers shall be within the following range :

9

Test Load Light – duty 2.5 tonnes (L. D. – 2.5) Heavy Duty – 20 tonnes (HD –20) Medium duty: 10 tonnes (MD-10) Extra heavy duty : 35 tonnes (EHD-35).

12.2.5. Lifting Device: The minimum diameter of mild steel rod used as lifting device shall be 10 mm for light and 12 mm for medium duty covers and 16 mm for heavy and extra heavy duty covers.  The lifting device shall be protected from corrosion by not galvanising or epoxy coating or any other suitable.

12.2.2.6. Finishing & coating - To prevent any possible damage from corrosion of steel the underside of the covers shall be treated with anticorrosive paint.  The top surface of the covers shall be given a Chequered finish.

In order to protect the edges of the covers from possible damage at the time of lifting and handling it is necessary that the manhole covers shall be cast with a protective mild steel of minimum 2.5 mm thickness around the periphery of the covers. Exposed surface of mild steel sheet shall be given suitable treatment with anticorrosive paint or coating.

12.2.2.7. Physical requirements

a) General - All units shall be sound and free from cracks and other defects which interface with the proper placing of the unit or impair the strength or performance of the units.  Minor chipping at the edge/surface resulting from the customary methods of handling during delivery shall not be deemed for rejecting.

b) Load Test - The breaking load of individual units when tested in accordance with the method described in IS: 12592-91 shall be not less than the values specified in Table 3.

12.2.2.8. Fixing - The frames of manhole shall be firmly  embedded to correct alignment and level in RCC slab or plain concrete as the case may be on the top of masonry which shall be paid as extra unless specified otherwise.

12.2.2.9. Measurements - The manhole covers shall be enumerated under relevant items.

12.2.2.10. Rates - The rate shall include the cost of materials and labour involved in all the operation described above except fixing of frames and covers which shall be paid as extra unless specified otherwise in the item.

12.2.3. Foot Rests - Foot rests shall be of 20 mm M. S. square or round bars as specified.

12.2.3.1. Pipes and Specials - Cast iron (centrifugally cast) pipes and specials shall conform to the specifications as described in 12.2.13.

Table 3.

Grade of cover

Type

Load in Tonnes

Diameter of Blocks in mm

EHD – 35

Circular, square or Rectangular

35

300

HD – 20

Circular, Square or Rectangular

20

300

MD – 10

Circular or Rectangular

10

300

LD – 2.5

Rectangular, Square or Circular

2.5

300

12.2.3.2. Cement Concrete Pipes (with and without reinforcement) - The pipes shall be with or without reinforcement as required and shall be of the specified class.  These shall conform to IS: 458-88. The reinforced cement concrete pipes shall be manufactured by centrifugal (or spun) process while un-reinforced cement concrete pipes by spun or pressure process. All pipes shall be true to shape, straight, perfectly sound and free from cracks and flaws.  The external and internal surface of the pipes shall be smooth and hard. The pipes shall be free from defects resulting from imperfect grading of the aggregate mixing or moulding.

Concrete used for the manufacture of un-reinforced and reinforced concrete pipes and collars shall not be leaner than 1:2:4 (1 cement: 2 coarse and 4 graded stone aggregate).  The maximum size of aggregate should not exceed one third of the thickness of the pipe or 20 mm whichever is smaller.  The reinforcement in the reinforced concrete pipes shall extend throughout the length of the pipe.  The circumferential and longitudinal reinforcements shall be adequate to withstand the specified hydrostatic pressure and further bending stresses due to the weight of water when running full across a span  equal to the length of pipe plus three times its own weight.

Table 4 Concrete pipes

Class

Description

Test Pressure (Hydrostatic)

Conditions where normally used.

NP1

Unreinforced concrete non pressure pipes       

0.7 Kg/sq.cm. (7meter head)

For drainage and irrigation 8520/ use, above ground or in shallow trenches.

NP2

Reinforced concrete light duty, non-pressure pipes                       

- do -

For drainage and irrigation use, for culverts carrying light traffic.

NP3

Reinforced concrete, medium-duty non- pressure pipes 

- do -

For drainage and irrigation use, for culverts, carrying heavy traffic.

NP4

Reinforced concrete, heavy duty non-pressure pipes   

- do -

For drainage and irrigation use for culverts carrying very heavy traffic, such as railway loading.

P1

Reinforced concrete pressure pipes

2.0 Kg/sq. cm. (20 metre head)

For use on gravity mains, the design pressure not exceeding two-third of the test pressure.

P2

Reinforced concrete Pressure pipes.

4.0 Kg/sq. cm. (40 metre head)

For use on pumping mains, the design pressure not exceeding half of the test pressure.

P3

Reinforced concrete Pressure pipes.

6.0 Kg/sq. cm. (60 metre head)

- do -

The dimensional requirements of concrete pipes are given in Annexure 12-A.1

The minimum cover for reinforcement of spun pipes and for all other pipes shall be as given in Table 5.

Table 5

Pipe Thickness

Cover for

Spun Pipes(mm)

Other than spun pipe (mm)

Less than 30 mm

9

12

30 mm to 75 mm

12

16

75 mm and over

18

18

12.2.4. Road gully grating (Fig. 2)

12.2.4.1. Horizontal gully grating - The casting of the grating and frames shall be the same as that of manhole covers as described.  The gully grating cover shall be hinged to the frame to facilitate its opening for cleaning and repairs.  A typical grating is shown in Fig. 2 & 3.  The weight of grating shown in Figure shall be minimum 75 kg.  In case of R. C. C. horizontal gully grating it shall be in cement concrete 1:1:2 (1 cement : 1 coarse sand : 2 graded stone aggregate 20 mm nominal size) as shown in Fig. 3

12.2.4.2. Vertical gully grating - The chamber shall be of brick masonry, 12 mm dia, round bar shall be fixed in cement concrete block at the bottom.  The bars at the top shall be welded or riveted to M. S. flat 40 x 6 mm as shown in Fig. 3

12.2.4.3. Horizontal and vertical gully grating - The details of typical road gully chamber of brick masonry with horizontal and vertical grating shall be as given in Fig. 3

12.2.5. Stone ware pipes and fittings - All pipes with spigot and socket ends and fittings shall conform to IS: 651-92.  These shall be sound, free from visible defects such as fire cracks or hair cracks.  The glaze of the pipes shall be free from crazing.  The pipes shall give a sharp clear tone when struck with a light hammer.  There shall be no broken blisters. The thickness of pipes shall be as given in the Table 6. 

Table 6 Stoneware pipes

Internal diameter mm  

Thickness of the barrel and socket mm

100

12

150

16

200

17

230

19

250

20

300

25

350

30

400

35

450

38

 

R.C.C. ROAD GRATING

The length of pipes shall be 60, 75, 90 cm exclusive of the internal depth of the socket.  The pipes shall be handled with sufficient care to avoid damage to them.

12.2.6. S. W. Gully trap (Fig. 4) - Gully traps shall conform to IS: 651-92.  These shall be sound, free from visible defects such as fire cracks, or hair cracks. The glaze of the traps shall be free from crazing.  They shall given a sharp clear tone when struck with light hammer.  There shall be no broken blisters.

Each gully trap shall have one C. I. grating of square size corresponding to the dimensions of inlet of gully trap. It shall also have a water  tight C. I. cover with frame inside dimensions 300 x 300 mm the cover weighing not less than 4.50 kg and the frame not less than 2.70 kg.  The grating, cover and frame shall be of sound and good casting and shall have truly square machined seating faces.

12.3. SPECIFICATIONS FOR CONSTRUCTING FLUSHING TANK.  

Where it is not practicable to obtain gradients in the sewers, steep enough to give a self cleansing velocity of not less than 75 cm per second, it is necessary to provide flushing water tanks at suitable points in a sewer line to help the flow of sewage.  For pipes under 600 mm dia the quantity of flushing water should be sufficient to fill the sewer at least half bore over the whole length of sewer to be flushed or from one flush point to the next.  The head at which the flush is discharged should give an initial velocity much higher than the self cleansing velocity so as to ensure that solids already deposited will be removed.  The approximate quantity of flushing water per flush over a length of 75 mm to 90 m are given in Table 7. See Fig 1.

Table  7 Water required per flush

Diameter of pipe mm   

Quantity of water litres

 

1400 to 1700

 

1700 to 2700

 

2700 to 3600

 

3600 to 4500

12.4. SPECIFICATIONS FOR CONSTRUCTING MANHOLES (Fig. 5 TO 10)

At every change of alignment, gradient or diameter of a drain, there shall be a manhole or inspection chamber.  Bends and junctions in the drains shall be grouped together in manhole as far as possible.  The maximum distance between manholes shall be 30 m. Manholes of different types and sizes as specified shall be constructed in the sewer line at such places and to such levels and dimensions as shown in the drawings or as directed by the engineer.  The size specified shall include the inside dimensions between brick faces of the manholes.

Where the diameter of the drain is increased, the crown of the pipes shall be fixed at the same level and necessary slope given in the invert of the manhole chamber.  In exceptional cases and where unavoidable, the crown of the branch sewer may be fixed at the lower level but in such cases the peak flow level of the two sewers shall be kept the same.

W - Width of wall

H  - Height of spring of arch above the benching level

T - Thickness of foundation concrete

Sewers of unequal sectional area shall not be jointed at the same invert in a manhole.  The invert of the smaller sewer at its junction with main shall be at least 2/3 the diameter of the main above the invert of the main.  The branch sewers shall deliver sewage in the manhole in the direction of main flow and the junction must be made with care so that flow in main is not impeded. No drain from house fittings, e.g., gully trap or soil pipe, etc. to manhole shall normally exceed a length of 6 m unless it is unavoidable.

Manholes 90 x 80 cm are generally constructed within compound for house drainage only and near the buildings for house drainage.  Manholes 1.2 m x 90 cm are generally constructed for main drainage work for depths less than 1.5 m. Manhole 1.4 m x 90 cm is of the arched type and is generally constructed for main drainage works where depth is 1.50 m or more.  The width of manholes shall be increased more than 90 cm on bends or junctions or pipes with diameter greater than 450 mm and that the benching width on either side of the channel is minimum 20 cm.

Manholes 1.4 m internal diameter are generally constructed for main drainage works where depth is 2.45 m or more as an alternative to manholes of arch type.  The diameter shall be increased suitably, for pipes with diameter greater than 450 mm in the same manner as in the case of rectangular manholes. Before deciding size of manholes, Local Municipal Bye Laws shall be consulted. As a general guide some typical type designs of manholes followed in Delhi have been shown in Fig. 5 to 10.  When manholes are constructed on foot path, these shall be provided with cover of medium duty casting and when built within the width of the road under vehicular traffic, these shall be provided with cover of heavy duty casting.

12.4.1. Excavation - The excavation for manhole shall be true to dimensions and levels shown on the plans or as directed by the engineer.

12.4.2. Bed concrete - The manhole shall be built on a bed of cement concrete 1:4:8 (1 cement : 4 coarse sand : 8 graded stone aggregate 40 mm nominal size)  unless required by local authorities.  The thickness of the bed concrete shall be 20 cm for manholes up to 4.25 m depth and 30 cm for depths beyond 4.25 m unless otherwise specified or directed by the engineer.  In bad ground, special foundations as suitable shall be provided.

12.4.3. Brick work - The brick work shall be with class 75 bricks in cement mortar 1:4 (1 cement: 4 coarse sand).  The external joints of the brick masonry shall be finished smooth, and the joints of the pipes with the masonry shall be made perfectly leak proof.  For arched type and circular manholes, brick masonry in arches and arching over the pipes shall be in cement mortar 1:3 (1 cement: 3 fine sand).  In the case of manholes of circular type the excess shaft shall be corbelled  inwardly on three sides at the top to reduce its size to the cover frame to be fitted.

The walls shall be built of one brick thickness for depths up to 4.25 m.  Below a depth of 4.25 m in ordinary subsoil the wall thickness shall be increased to one and half brick and at 9.75  m below ground two brick thick walls shall be built.

12.4.4. Plaster and Pointing - The walls of the manholes shall be plastered inside with 12 mm thick cement plaster 1:3 (1 cement: 3 coarse sand) finished smooth.  In the case of arched type manhole the walls of the manhole shall be plastered inside all-round  only up to the crown level, and flush pointed for the shaft with cement mortar 1:2 (1 cement : 2 fine sand).  Where the saturated soil is met with, also the external surface of the walls of the manhole shall be plastered with 12 mm thick cement plaster 1:3 (1 cement : 3 coarse sand) finished smooth up to 30 cm above the highest sub-soil water level with the approval of the engineer. The plaster shall further be water proofed with addition of approved water proofing compound in a quantity as per manufacturer’s specifications. In case Local Authorities / By Laws specify richer specifications, the same shall be adopted.

For earth work excavation, bed concrete brick work, plaster and pointing, RCC work and refilling of earth, respective specifications shall be followed.

12.4.5. Benching - The channels and benching shall be done in cement concrete 1:2:4 (1 cement: 2 coarse sand: 4 graded stone aggregate 20 mm nominal size) and rendered smooth with neat cement.  The depth of channels and benching shall be as given in Table 8.

12.4.6. Foot Rests (Fig. 8) - All manholes deeper than 0.8 m shall be provided with M. S. foot rests.  These shall be embedded 20 cm deep in 20 x 20 x 10 cm blocks of cement concrete 1:3:6 (1 cement : 3 coarse sand : 6 graded stone aggregate 20 mm nominal size).  The concrete block with M. S. foot rest placed in its centre shall be cast in situ along with the masonry and surface finished with 12 mm thick cement plaster 1:3 (1 cement : 3 coarse sand) finished smooth.

Table 8 Depth of Channel and Benching

Sizes of drain

mm

Top of channel at the centre above bed concrete Cm

Depth of benching at side walls above bed concrete cm

100

15

20

150

20

30

200

25

35

250

30

40

300

35

45

350

40

50

400

45

55

450

50

60

Foot rests which shall be of 20 x 20 sq. M. S. bars as shown in Fig. 8 shall be fixed 40 cm apart vertically and staggered laterally and shall project 10 cm beyond the surface of the wall. The top foot rest shall be 45 cm below the manhole cover.

Foot rests shall be painted with coal tar, the portion embedded in the cement concrete block being painted with thick cement slurry before fixing.

12.4.7. Manhole covers and frames - The frame of manhole shall be firmly embedded to correct alignment and levels in R. C. C. slab or plain concrete as the case may be on the top of the masonry.  After completion of the work, manhole covers shall be sealed by means of thick grease.

12.4.8. Measurements - Manholes shall be enumerated under relevant items.  The depth of the manhole shall be reckoned from the top level of C. I. cover to the invert level of channel.  The depth shall be measured correct to a cm.  The extra depth shall be measured and paid as extra over the specified depth.

12.4.9. Rate - The rate shall include the cost of materials and labour involved in all the operations described above but exclusive the cost of (I) excavation, (ii) M. S. foot rests and (iii) 12 mm thick cement plaster with water proofing material applied at the external surface of the manhole if required.  These items shall be paid for separately under relevant items of work.

Payment for extra depths of manholes shall be made separately under relevant items of work.

12.5. SPECIFICATIONS FOR CONSTRUCTING DROP CONNECTION (FIG. 10)

In cases where branch pipe sewer enters the manhole of main pipe sewer at a higher level than the main sewer, a drop connection shall be provided. The work shall be carried out as per Fig. 8, S. C. I. pipes and special conforming to IS: 1729 shall be of the same size as that of the branch pipe sewer.

For 150 and 250 mm main line, if the difference in level between the water line (peak flow level) and the invert level of the branch line is less than 60 cm, a drop connection may be provided with in the manhole by giving suitable ramp.  If the difference is level is more than 60 cm, the drop shall be provided externally.

The main lines up to 350 mm dia, are designed for half depth of flow, from 350 mm to 900 mm for 2/3 depth of flow and beyond 900 mm for ¾ depth of flow.

Excavation - The excavation shall be done for the drop connection at the place where the branch line meets the manhole the excavation shall be carried up to the bed concrete of the manhole and to the full depth of the branch line.

Laying - At the end of branch sewer line S. C. I. cross shall be fixed to the line which shall be extended through the wall of the manhole by a horizontal piece of S. C. I. pipe to form an inspection or cleaning type.  The open end shall be provided with chain and lid.  The S. C. I. drop pipe shall be connected to the cross at the top and to the S. C. I. bend at the bottom.  The bend shall be extended through the wall of the manhole by a piece of C. I. pipe which shall discharge into the channel.  Necessary channel shall be made with cement concrete 1:2:4 (1 cement: 2 coarse sand: 4 graded stone aggregate 20 mm nominal size) and finished smooth to connect the main channel.  The joint between S. C. I. pipe and fittings shall be lead caulked as described. The joint between S. C. I. cross and S. W. branch line shall be made with cement mortar 1:1 (1 cement : 1 fine sand). The exposed portion of the drop connection shall be encased all-around with minimum 15 cm thick concrete 1:5 :10 (1 cement : 5 fine sand : 10 graded stone aggregate 40 mm nominal size) and cured. For encasing the concrete around the drop connection, the necessary centering and shuttering shall be provided.  The holes made in the walls of the manhole shall be made good with brick work in cement mortar 1:4 (1 cement : 4 coarse sand) and plastered with cement mortar 1 : 3 (1 cement : 3 coarse sand) on the inside of the manhole wall.  The excavated earth shall be back field in the trench in level with the original ground level.

Measurements - Drop connection shall be enumerated. The depths beyond 60 cm shall be measured in running metres correct to a cm under relevant items.

Rate - The rate shall include the cost of labour and materials involved in all the operations described above but excluding the cost of excavations and refilling.

12.6. SPECIFICATIONS FOR LAYING AND JOINTING CEMENT CONCRETE PIPES AND SPECIALS

12.6.1. Trenches - Trenches shall be excavated as described.  Where the pipes are to be bedded directly on soil, the bed shall be suitably rounded to fit the lower part of the pipe, the cost  for this operation being included in the rate for laying the pipe itself.

12.6.2. Laying - 12.2.1 Loading, transporting and unloading of concrete pipes shall be done with care.  Handling shall be such as to avoid impact.  Gradual unloading by inclined plane or by chain pulley block is recommended. All pipe sections and connections shall be inspected carefully before being laid.  Broken or defective pipes or connections shall not be used. Pipes shall be lowered into the trenches carefully.  Mechanical appliances may be used.  Pipes shall be laid true to line and grade as specified.  Laying of pipes shall proceed upgrade of a slope.

12.2.2. If the pipes have spigot and socket joints, the socket ends shall face upstream.  In the case of pipes with joints to be made with loose collars, the collars shall be slipped on before the next pipe is laid.  Adequate and proper expansion joints shall be provided where directed.

12.2.3. In case where foundation conditions are unusual such as in the proximity of trees or holes, under existing or proposed tracks manholes etc. the pipe shall be encased all-around in 15 cm thick cement concrete 1:5:10 (1 cement : 5 fine sand : 10 graded stone aggregate 40 mm nominal size)  or compacted sand or gravel.

12.2.4. In cases where the natural foundation is inadequate the pipes shall be laid either in concrete cradle supported on proper foundations or on any other suitably designed structure.  If a concrete cradle bedding is used the depth of concrete below the bottom of the pipe shall be at least 1/4th of the internal dia  of the pipe subject to the min. of 10 cm and a maximum of 30 cm.  The concrete shall extend up the sides of the pipe at least to a distance of 1/4th of the outside diameter of pipes 300 mm and over in dia.  The pipe shall be laid in this concrete bedding before the concrete has set.   Pipes laid in trenches in earth shall be bedded evenly and firmly and as far up the haunches of the pipe as to safely transmit the load expected from the backfill through the pipe to the bed.  This shall be done either by excavating the bottom of the trench to fit the curve of the pipe or by compacting the earth under around the curve of the pipe to form an even bed.  Necessary provision shall be made for joints wherever required.

12.2.5. When the pipe is laid in a trench in rock hard clay, shale or other hard material the space below the pipe shall be excavated and replaced with an equalising bed of concrete, sand or compacted earth. In no place shall pipe be laid directly on such hard material.

12.2.6. The method of bedding and laying the pipes under different condition are illustrated in Fig. 9.

12.6.2.7. When the pipes are laid completely above the ground the foundations shall be made even and sufficiently compacted to support the pipe line without any material settlement.  Alternatively the pipe line shall be supported on rigid foundations at intervals. Suitable arrangements shall be made to retain the pipe line in the proper alignment, such as by shaping the top of the supports to fit the lower shall in no case exceed the length of the pipe.  The pipe shall be supported as far as possible close to the joints.  In no case shall be taken to see that super imposed loads greater than the total load equivalent to the weight of the pipe when running full shall not be permitted.

Suitably designed anchor blocks at change of direction and grades for pressure line shall be provided where required.

12.6.3. Jointing - Joints are generally of rigid type. Where specified flexible type joints may also be provided.

1) Rigid spigot and Socket Joint (Fig. 11) - The spigot of each pipe shall be slipped home well into the socket of the pipe previously laid and adjusted in the correct position. The opening of the joint shall be filled with stiff mixture of cement mortar in the proportion of 1:2 (1 cement: 2 fine sand) which shall be rammed with caulking tool.  After a day’s work any extraneous material shall be removed from the inside of the pipe and the newly made joint shall be cured.

2) Rigid Collar Joint (Fig. 11)- The two adjoining pipes shall be butted against each other and adjusted in correct position. The collar shall then be slipped over the joint, covering equally both the pipes.  The annular space shall be filled with stiff mixture of cement mortar 1:2 (1 cement : 2 fine sand) which shall be rammed with caulking fool.  After a day’s work any extraneous materials shall be removed from the inside of the pipe and the newly made joint shall be cured.

3) Semi flexible spigot and socket joint (Fig. 11) - The joint is composed of specially shaped spigot and socket ends on the concrete pipes.  A rubber ring shall be placed on the spigot which shall be forced into the socket of the pipe previously laid.  This compresses the rubber ring as it rolls into the annular space formed between the two surfaces of the spigot and the socket, stiff mixture of cement mortar 1:2 (1 cement : 2 fine sand) shall then be filled into the remaining annular space and rammed with a caulking tool.  After day’s work any extraneous materials shall be removed from the inside of the pipe and newly made joint shall be cured.

4)Semi-Flexible Collar Joint ( Fig.11 )- This is made up of a loose collar which covers two specially shaped pipe ends as shown in the Fig. 10.  Each end shall be fitted with a rubber ring which when compressed between the spigot and the collar, seal the joint.  Stiff mixture of cement mortar 1:2 (1 cement : 2 fine sand), shall then be filled into the remaining annular space and rammed with a caulking tool. After day’s work any extraneous materials shall be removed from the inside of the pipe and newly made joint shall be cured.

5) Internal Flush Joint (Fig. 11) - This joint is generally used for culvert pipe of 60cm dia and over.  The ends of the pipe are specially shaped to form a self centering joint with an internal jointing space 1.3 cm wide the finished joint is flush with both inside and outside with the pipe wall as shown in Fig. 10.  The jointing space is filled with cement mortar 1:2 (1 cement: 2 fine sand) mixed sufficiently dry to remain in position when forced with a trowel or rammer. After day’s work any extraneous materials shall be removed from the inside of the pipe and newly made joint shall be cured.

6) External Flush Joint (Fig. 11) - This joint is suitable for pipes which are too small for jointing from inside.  This joint is composed of specially shaped pipe ends as shown in Fig. 10. Each end shall be butted against each other and adjusted in correct position. The jointing space shall then be filled with cement mortar 1:2 (1 cement : 2 fine sand)  sufficiently dry and finished off flush.  Great care shall be taken to ensure that the projecting ends are not damaged as no repairs can be readily affected from inside the pipe.

12.6.3.7. In all pressure pipe lines the recess at the end of the pipe line shall be filled with jute braiding dipped in hot bitumen or other suitable approved compound.  Pipes shall be so jointed that the bitumen ring of one pipe shall set into the recess of the next pipe.  The ring shall be thoroughly compressed by jacking or by any other suitable method. The number of pipes that shall be jacked together at a time shall depend on the diameter of the pipes and the bearing capacity of the soil, for small pipes up to 25 cm diameter, six pipes can be jacked together at a time.

The quantity of jute and bitumen in the ring shall be just sufficient to fill the recess in the pipe when pressed hard by jacking or by any other suitable method.  Before and during jacking care shall be taken to see that there is no offset at the joint.

12.6.4. Testing - For pressure pipes, the completed pipeline shall be tested for pressure (Known as site test pressure) which shall not be less than the maximum pipeline operating pressure plus the calculated surge pressure, but in no case shall it exceed the hydrostatic test pressure.  For non-pressure pipes the joints shall be tested as per procedure laid down under para 12.7.4.

12.6.5. Refilling of Trenches - The specification as described shall apply.  In case where pipes are not embedded on concrete special care shall be taken in refilling, trenches to prevent the displacement and subsequent settlement at the surface resulting in uneven street surfaces and dangers to foundations etc.  The back filling materials shall be packed by hand under and around the pipe and rammed with a shovel and light tamper.  This method of filling will be continued up to the top of pipe.  The refilling shall rise evenly on both sides of the pipe so as not to disturb the pipe.  No tamping shall be done within 15 cm of the top of pipe.  The tamping shall become progressively heavier as the depth of the backfill increases.

12.6.6. Measurements - The lengths of pipes shall be measured in running metres nearest to a cm as laid or fixed, from inside of one manhole to the inside of the other manhole.  The length shall be taken along the centre line of the pipes over all fittings such as bends, collars, junctions, etc. which shall not be measured separately.

Excavation, refilling, shoring and timbering in trenches, and cement concreting wherever required shall be measured separately under relevant items of work.

12.6.7. Rate - The rate shall include the cost of materials and labour involved in all the operations described above.

12.7. SPECIFICATIONS FOR LAYING AND JOINTING STONE WARE PIPES

12.7.0 For all sewers and drains, glazed stoneware pipes shall be used as far as possible in preference to other types of pipes. These are suitable, particularly where acid effluents or acid sub-soil conditions are likely to be encountered.

12.7.1. Trenches

12.7.1.1. Specifications as described in 12.6.1 shall apply, as far as possible.

12.7.1.2. The trench shall be so dug that the pipe can be laid to the required alignment and at the required depth.  When the pipe line is under a roadway, a minimum cover of 90 cm is recommended for adoption, but it may be modified to suit local conditions.  The trench shall be excavated only so far in advance of pipe laying as specified by the engineer.  The trench shall be so shored and drained that the workmen may work therein safety and efficiently.  The discharge of the trench de-watering pumps shall be conveyed either to drainage channels or to natural drains.

12.7.1.3. The excavation shall be carried out with manual labour or with suitable mechanical equipment as approved by the engineer.

12.7.1.4. Unless otherwise specified by the engineer, the width at bottom of trenches for different diameters of pipes laid at different depths shall be as given below

(a)  For all diameters, up to an average depth of 120 cm, width of trench in cm = diameter of pipe + 30 cm. (b)  For all diameters for depths above 120 cm, width of trench in cm = diameter of pipe + 40 cm.

(c)  Notwithstanding (a) and (b) the total width of trench shall not be less than 75 cm for depths exceeding 90 cm.

The width of trench in the upper reaches shall be increased as described in para above sub-head ‘Earthwork’.

12.7.2. Laying - All pipes shall be laid on a bed of cement or lime concrete with thickness and mix as specified, projecting on each side of the pipe to the specified width of the trench.  The pipes with their crown level at 1.20 m depth and less from ground shall be covered with 15 cm thick.  Concrete above the crown of the pipe and sloped off to meet the outer edges of the concrete, to give a minimum thickness of 15 cm all-around the pipe (Fig. 12).  Pipes laid at a depth greater than 1.20 m at crown of the pipe and sloped off from the edges to meet the pipe tangentially (Fig. 12).

12.7.2.2. The pipe shall be carefully laid to the alignments, levels and gradients shown on the plans and sections.  Great care shall be taken to prevent sand etc. from entering the pipes.  The pipes between two manholes shall be laid truly in a straight line without vertical or horizontal undulation.  The pipes shall be laid with socket up the gradient.  The body of the pipe shall for its entire length rest on an even bed of concrete and places shall be excavated in the concrete to receive the socket of the pipe.

12.7.2.3. Where pipes are not bedded on concrete, the trench floor shall be left slightly high and carefully bottomed up as pipe laying proceeds, so that the pipe barrels rest on firm and undisturbed ground.  If the excavation has been carried too low, the desired levels shall be made up with concrete 1:5:10 (1 cement : 5 fine sand : 10 graded stone aggregate 40 mm nominal size) for which no extra payment shall be made.

12.7.2.4. If the floor of the trench consists of rock or very hard ground that cannot easily be excavated to smooth surface the pipe shall be laid on a levelling course of concrete as desired.

12.7.2.5. When S. W. pipes are used for storm water drainage, no concreting will normally be necessary.  The cement mortar for jointing will be 1:3 (1 cement: 3 fine sand). Testing of joints will also not be done.

12.7.3. Jointing

12.7.3.1. Tarred gasket of hemp yarn soaked in thick cement slurry shall first be placed round the spigot of each pipe and the spigot shall then be slipped home well into the socket of the pipe previously laid.  The pipe shall then be adjusted and fixed in the correct position and the gasket caulked tightly home so as to fill not more than 1/4th of the total depth of the socket.

W = D+X, where D is the external diametre of the pipe.  

X = 300 upto trench depth of 1200

         400 trench depth more than 1200

T = 100 for pipes under 150, ¼th internal dia

         Subject to a min. of 150 and max. 300 for

        Pipes more than 1500 dia.

MWL = Maximum water level

12.7.3.2. The remainder of the socket shall be filled with stiff mixture of mortar in the proportion of 1:1 (1 cement: 1 fine sand).  When the socket is filled, a fillet shall be formed round the joint with a trowel forming an angle of 45 degree with the barrel of the pipe.

12.7.3.3. After day’s work any extraneous material shall be removed from the inside of the pipe. The newly made joint shall be cured for at least seven days.

12.7.4. Testing of joints

12.7.4.1. Stoneware pipes used for sewers shall be subjected to a test pressure of 2.5 m head of water at the highest point of the section under test.  The test shall be carried out by suitably plugging the lower end of the drain and the ends of the connection if any and filling the system with water.  A knuckle bend shall be temporarily jointed in at the top end and a sufficient length of vertical pipe jointed to it so as to provide the required test head, or the top may be plugged with a connection to a hose ending in a funnel which could be raised or lowered till the required head is obtained and fixed suitable for observation.

12.7.4.2. If any leakage is visible, the defective part of the work shall be cut out and made good. A slight amount of sweating which is uniform may be overlooked, but excessive sweating from a particular pipe or joint shall be watched for and taken as indicating a defect to be made good.

12.7.4.3. Any joint found leaking or sweating, shall be rectified or embedded into 15 cm layer of cement concrete (1:2:4) 30 cm in length and the section retested.

12.7.5. Refilling - In cases where pipes are not bedded on concrete special care shall be taken in refilling trenches to prevent the displacement and subsequent settlement at the surface resulting in uneven street surfaces and dangers to foundations etc.  The backfilling shall be packed by hand under and around the pipe, and rammed with a shovel and light tamper.  This method of filling will be continued up to the top of pipe.  The refilling shall rise evenly on both sides of the pipe continued up to 60 cm above the top of pipe so as not to disturb the pipe.  No tamping should be done within 15 cm of the top of pipe.

12.7.6. Measurements - The lengths of pipes shall be measured in running metres nearest to a cm as laid or fixed, from inside of one manhole to the inside of the other manhole.  The length shall be taken along the centre line of the pipes over all fittings such as bends, junctions, etc. which shall not be measured separately.

Excavation, refilling, shoring and timbering in trenches, and cement concreting wherever required shall be measured separately under relevant items of work.

12.7.7. Rate - The rate shall include the cost of materials and labour involved in all the operations described above excluding the cost of concrete which shall be paid for separately.

12.8. SPECIFICATIONS FOR FIXING STONEWARE GULLY TRAP  

12.8.1. Excavation -  The excavation for gully traps shall be done true to dimensions and levels as indicated on plans or as directed by the engineer.

12.8.2. Fixing - The gully traps shall be fixed on cement concrete foundation 65 cm square and not less than 10 cm thick. The mix for the concrete will be 1:5:10(1 cement: 5 fine sand : 10 graded stone aggregate 40 mm nominal size).  The jointing of gully outlet to the branch drain shall be done similar to jointing of S. W. pipes.

12.8.3. Brick masonry chamber - After fixing and testing gully and branch drain, a brick masonry chamber 300 x 300 mm (inside) in brick work of specified class in cement mortar 1:5 (1 cement: 5 fine sand) shall be built with a half brick thick brick work round the gully trap from the top of the bed concrete up to ground level.  The space between the chamber walls and the trap shall be filled in with cement concrete 1:5:10 (1cement: 5 fine sand: 10 graded stone aggregate 40 mm nominal size).  The upper portion of the chamber i.e., above the top level of the trap shall be plastered inside with cement mortar 1: 3 (1 cement: 3 coarse sand), finished with a floating coat of neat cement.  The corners and bottom of the chamber shall be rounded off so as to slope towards the grating. C.I. cover with frame 300 x 300 mm (inside) shall then be fixed on the top of the brick masonry with cement concrete 1:2:4 (1 Cement : 2 coarse sand : 4 graded stone aggregate 20 mm nominal size) and rendered smooth.  The finished top of cover shall be left about 4 cm above the adjoining ground level so as to exclude the surface water from entering the gully trap.

12.8.4. Measurements - The work shall be enumerated. Excavation shall be measured separately under relevant item of earth work.

12.8.5. Rate - The rate shall include the cost of materials and labour involved in all the operations described above, except earth work which shall be paid for separately.

12.9. SPECIFICATIONS FOR CONSTRUCTION OF OPEN SURFACE DRAIN (Fig 13)

12.9.0. The open drains shall be of the size, as specified in the item and laid to such gradients and in such locations as may be shown in the relevant drawing or as directed by the engineer.

The size of the drain as specified shall be the width of the drain at the top, measured between the masonry walls.  The drain shall be given, as far as possible, uniform slope from the starting point to the discharge point.

The average depths of the various sizes of drains shall be as follows

Drain size

Depth

10 cm

20 cm

15 cm

20 cm

25 cm

30 cm

12.9.1. Measurements - The drains shall be measured in running metres, correct to a cm.

12.9.2. Rate - The rate shall include the cost of labour and materials required for all the operations described above, suitable deduction or extra payment, per cm basis shall be made in case there is a variation in average depths from those as stated.

12.10. SPECIFICATIONS FOR CONSTRUCTING ROAD GULLY CHAMBER WITH GRATING.

12.10.1. Road gully chamber and horizontal grating (Fig. 3 & 2 ) - The chamber shall be of brick masonry of specified class and shall have a C. I. grating with frame fixed in 15 cm thick cement concrete 1:2:4 (1 cement : 2 coarse sand : 4 graded stone aggregate 20 mm nominal size) at the top.  The size of the chamber shall be taken as the clear internal dimensions of the C. I. frame. The chamber shall have a connection pipe, the length of which in metre between the road gully chamber and the manhole of the drain shall not be less than one by forty (1/40) times the nominal diameter of pipe in mm (i.e., for 150 mm connection pipe, length shall not be less than 3.7 m and for 250 mm connection pipe length shall not be less than 6.25 m).  The chamber shall be built at a location fixed by the engineer.  Generally the spacing of the chambers shall be 18 to 36 m depending upon the

grading of the road channel and the area of the drainage.  R. C. C. gully grating shall be fixed in cement mortar 1:2 (1 cement: 2 coarse sand) as shown in Fig. 2.

12.10.2. Road gully chamber with vertical grating (Fig. 3) - The chamber shall be of brick masonry 12 mm dia round bar shall be fixed in cement concrete block at the bottom.  The bars at the top shall be welded or riveted to M. S. flat 40 x 6 mm as shown in Fig.3.  The specifications shall be same as described. 

12.10.3. Road gully chamber with horizontal and vertical grating - The details of typical road gully chamber of brick masonry shall be same as shown in Fig. 3.

12.10.4. Measurements: Road gully chambers shall be enumerated.

12.10.5. Rate - The rate shall include the cost of materials and labour involved in all the operations described above except the cost of excavation and connection pipes.

12.11. SPECIFICATIONS FOR CONSTRUCTING BRICK MASONRY GREASE TRAP (Fig 4)

12.11.0. The internal size of the trap shall be 80x40x46 cm. The height shall be measured from the top of the floor to the top of the cover,  40 mm thick stone baffles shall be fixed 50 mm deep in masonry with cement mortar 1:4 (1 cement : 4 fine sand), as shown in the Fig. 2.  The connection of open surface, drain with a soak pit shall be invariably through a grease trap.

12.11.1. Measurements - Grease traps shall be enumerated.

12.11.2. Rate - The rate shall include the cost of labour and materials required for all the operations described above.

12.12. SPECIFICATIONS FOR CONSTRUCTION OF SEPTIC TANK (FIG. 14 & 15)

12.12.0. In unsewered area, every house shall have arrangements for its sewage being treated in septic tank, effluent from which should be given secondary treatment either in a biological filter or on the land, or in a sub-surface disposal system.

12.12.1. Surface and sub-soil water should be excluded from finding way into the septic tank.  Waste water may be passed into the septic tank provided the tank and the means for effluent disposal are designed to cope up with this extra liquid.  Depending on the location of the water table and the nature of the strata, the type of disposal for the effluent from the septic tank shall be decided.

12.12.1. Dimensions - Septic tanks shall have minimum width of 75 cm, minimum depth of one metre below water level and a minimum liquid capacity of the one cubic metre. Length of tanks shall be 2 to 4 times the width.  Suitable sizes of septic tanks for use of 5,10,15, 20 and 50 persons based on certain assumptions are given in Annexure 12-A.2

12.12.2. Cover and frame - Every septic tank shall be provided with C. I. cover of adequate strength.  The cover and frames shall be 500 mm dia.  (M. D.) Minimum or 610 mm x 455 mm (LD).  The specification for frames and cover as given shall apply.

12.12.3. Ventilating pipe - Every septic tank shall be provided with C. I. ventilating pipe of at least 50 mm diameter.  The top of the pipe shall be provided with a suitable cage of mosquito proof wire mesh.

The ventilating pipe shall extend to a height which would cause no smell nuisance to any building in the area.  Generally the ventilating pipe may extend to a height of about 2 m, when the septic tank is at least 15 m away from the nearest building and to a height of 2 m. above the top of the building when it is located closer than 15 metres.  The ventilating pipe may also be connected to the normal soil ventilating system of the building where so desired.

12.12.4. Disposal of sludge - The sludge from septic tanks may be delivered into covered pit or into a suitable vehicle for removal from the site.  Spreading of sludge on the ground in the vicinity shall not be allowed.

12.12.5. Testing - Before the tank is commissioned for use, it shall be tested for water-tightness by filling it with water and allowing it to stand for 24 hours.  It shall then be topped up, if necessary, and allowed to stand for a further period of 24 hours during which time the fall in the level of the water shall not be more than 1.5 cm.

12.12.6. Commissioning of septic tank - The tank shall be filled with water to its outlet level before the sewage is let into the tank.  It shall, preferably, be seeded with small quantities of well digested sludge obtained from septic tanks or sludge digestion tanks.  In the absence of digested sludge a small quantity of decaying organic matter, such as digested cow dung, may be introduced.

12.12.7. Sub-surface absorption system - The effluent from septic tank shall be disposed of by soak pit or dispersion trench depending on the position of the sub-soil water level, soil and sub-soil conditions and the size of the installation.

12.12.8. Measurements - Septic tank shall be enumerated.

12.12.9. Rate - The rate shall include the cost of materials and labour involved in all the operation, except Sub-Surface absorption system which shall be paid for separately.

12.13. SPECIFICATIONS FOR SOAK PIT 2.5 M DIA X 3 M DEEP (FIG. 16)

12.13.1. Construction - The earth excavation shall be carried out to the exact dimensions as shown in the figure.  In the soak pit shall be constructed a honey-comb dry brick shaft 45 x 5 cm and 292.5 cm high.  Round the shaft and within the radius of 60 cm shall be placed well burnt brick bats.  Brick ballast of size from 50 to 80 mm nominal size shall be packed round the brick bats up to the radius of 90 cm.  The remaining portion shall be filled with brick ballast of 40 mm nominal size.  The construction of shaft and filling of the bats and the ballast shall progress simultaneously.

12.13.2. Cover and Drain - Over the filling shall be placed a single matting which shall be covered with minimum layer of 7.5 cm earth.  The shaft shall be covered with 7.5 cm earth.  The shaft shall be covered with 7.5 cm thick stone or R. C. C. slab 10 cm wide and 10 cm deep brick edging with bricks of class designation 75 shall be provided round the pit.  The connection of the open surface drain to the soak pit shall be made by means of 100 mm diameter S. W. pipe with open joints.

12.13.3. Measurements: Soak Pit shall be enumerated.

12.13.4. Rate - Rate shall include the cost of labour and material involved in all the operations.

12.14. SPECIFICATIONS FOR SOAK PIT 1.2 X 1.2 X 1.2 m

12.14.1. Construction - The earth excavation shall confirm to the general specifications for earthwork.  After the excavation is complete the soak pit shall be filled with brick bat.  The brick bats shall be   obtained from properly burnt bricks of size 10 cms wide and 10 cms deep brick edging with bricks of class designation 75 shall be provided round the soak pit.

12.14.2. Measurement - Soak pit shall be enumerated.

12.14.3. Rate - Rate shall include the cost of labour and material involved in all the operations.

12.15. SPECIFICATIONS FOR DISPERSION TRENCH (FIG. 17)

12.15.0 It shall be provided when the sub-soil water level is within 180 cm from the ground level.  Dispersion trenches are not recommended in areas where fibrous roots of trees or vegetation are likely to penetrate the system and cause blockages.

12.15.1. Construction - Dispersion trenches shall be 50 to 100 cm deep and 30 to 100 cm wide, excavated to a slight gradient and shall be provided with 15 to 25 cm of washed gravel or crushed stone.  Open jointed pipes placed inside the trench shall be made of unglazed earthenware clay or concrete and shall have minimum internal diameter of 75 to 100 mm.  Each dispersion trench should not be longer than 30 m and trenches should not be longer than 30 m and trenches should not be placed closer than 1.8 m.

The covering for the pipes on the top shall be with coarse aggregate of uniform size to a depth of approximately 15 cm.  The aggregate above this level may be graded with aggregate 12 to 15 mm to prevent ingress of top soil while the free flow of water is no way retarded.  The trench may be covered with about 30 cm of ordinary soil to form a mound and turned over.  The finished top surface may be kept at least 15 cm above ground level to prevent direct flooding of the trench during rains.

12.15.2. Measurements - The length of dispersion trench shall be measured in running metres nearest to a cm.

12.15.3. Rate - The rate shall include the cost of materials and labour involved in all the operations described above.

12.16. SPECIFICATIONS FOR DESLUDGING OF SEPTIC TANKS

Septic tanks shall be de-sludged periodically, the intervals of de-sludging, depending upon the design of the septic tanks and the capacity in relation to its users.  De-sludging may be done when the sludge level reaches a predetermined level.  A portion of the sludge may be left in the tank to seed the fresh deposits.

Annexure 12-A.1

DIMENSIONAL REQUIREMENTS OF CONCRETE PIPES

A.  Class NP1 – unreinforced non pressure pipes

Internal Diameter of Pipes mm

Barrel   Wall Thickness

mm

Collar Dimensions

Minimum Caulking

Mm

Minimum Thickness mm

Minimum Length mm

80

25

13

25

150

100

25

13

25

150

150

25

13

25

150

200

25

13

25

150

225

25

13

25

150

250

25

13

25

150

300

30

16

30

150

350

32

16

32

150

400

32

16

32

150

450

35

19

35

200

 

B.  Class NP2 – Reinforced concrete light duty, non pressure pipes

Internal  Diameter

of Pipes   Nominal   (mm)

Barrel   Wall Thickness

(mm)

Collar Dimensions

Minimum  Caulking (mm)

Minimum  Thickness (mm)

Minimum  Length

(mm)

80

25

13

25

150

100

25

13

25

150

150

25

13

25

150

200

25

13

25

150

225

25

13

25

150

250

25

13

25

150

300

30

16

30

150

350

32

16

32

150

400

32

16

32

150

450

35

19

35

200

500

35

19

35

200

600

45

19

40

200

700

50

19

40

200

800

50

19

45

200

900

55

19

50

200

1000

60

19

55

200

1100

65

19

60

200

1200

70

19

65

200

1400

75

19

75

200

1600

80

19

80

200

1800

90

19

90

200

2000

100

19

100

200

2200

110

19

110

200

Note 1: The effective length of barrel shall be 2 m up to 250 mm nominal diameter pipes and 2.5, 3.0, 3.5 or 4.0 m for pipes above 250 mm.

C. Class NP3 – Reinforced concrete medium duty, non pressure pipes

Internal  diameter of Pipes (mm)

Barrel Wall Thickness (mm) 

80

25

100

25

150

25

200

30

225

30

250

30

300

40

350

75

400

75

450

75

500

75

600

85

700

85

800

95

900

100

1000

115

1100

115

1200

120

1400

135

1600

140

1800

150

2000

170

2200

185

2400

200

2600

215

Note:

1)  The effective length of barrel shall be 2 m up to 250 mm nominal diameter pipes and 2.5, 3.0, 3.5 or 4.0 m for pipes above 250 mm.

2)  The actual internal diameter is to be declared by the manufacturer and the tolerance is to be applied on the declared diameter.

3)  Minimum thickness and minimum length of collars shall be the same as that for the next higher size available in NP2 class pipes corresponding to the calculated inner diameter of collars.

D. Reinforced concrete pressure pipes class p1 tested to 20 m head,  Class P2 tested to 40 m head and class p3 tested to 60 m head

Internal diameter of pipes(mm)

Barrel dimension

Class P1 (mm)

Class P2 (mm)

Class P3 (mm)

80

25

25

25

100

25

25

25

150

25

25

25

200

25

30

35

225

25

30

35

250

25

30

35

300

30

40

45

350

32

45

55

400

32

50

60

450

35

50

70

500

35

55

75

600

40

65

90

700

40

70

105

800

45

80

120

900

50

90

-

1000

55

100

-

1100

60

-

-

1200

65

-

-

Note:

1)  The effective length of barrel shall be 2 m up to 250 mm nominal diameter pipes and 2.5, 3.0, 3.5 or 4.0 m for pipes above 250 mm.

2)  Collar dimensions will be same as specified for class NP2 pipes.

Annexure 12-A.2

Recommended sizes of septic tanks

Recommended sizes of septic tanks for 20 users

No. of

Users

Length M

Breadth m

Liquid depth (Cleaning interval of)

1 year m

2 year m

5

1.5

0.75

1.0

1.05

10

2.0

0.90

1.0

1.40

15

2.0

0.90

1.3

2.00

20

2.3

1.10

1.3

1.80

Note:  (1) The capacities are recommended on the assumption that discharge from only WC will be treated in the septic tank. (2)  A provision of 300 mm should be made for free board.

(3)  The sizes of septic tanks are based on certain assumptions, while choosing the size of septic tank exact calculation shall be made.

Recommended sizes of septic tanks for residential colonies

No. of Users

Length (m)

Breadth (m)

Liquid depth (Cleaning interval of)

1 year (m)

2 year (m)

50

5.0

2.0

1.0

1.24

100

7.5

2.65

1.0

1.24

150

10.0

3.0

1.0

1.24

200

12.0

3.3

1.0

1.24

300

15.0

4.0

1.0

1.24

Note: (1) A provision of 300 mm should be made for free board. (2) The sizes of the septic tank are based on certain assumptions while choosing the size of septic tank, exact calculation shall be made.

3)  For population over 100, the tank may be divided into independent parallel chambers for ease of maintenance and cleaning.

Recommended sizes of septic tanks for hostel and boarding schools

No. of Users

Length (m)

Breadth (m)

Liquid depth (Cleaning interval of)

Once in a year (m)

Once in 2 years (m)

50

5.0

1.6

1.3

1.4

100

5.7

2.1

1.4

1.7

150

7.7

2.4

1.4

1.7

200

8.9

2.7

1.4

1.7

300

10.7

3.3

1.4

1.7

Note: 1) A provision of 300 mm should be made for free board. (2)  The sizes of the septic tank are based on certain assumptions while choosing the size of septic tank exact calculation shall be made.

3)  For proportion over 100, the tank may be divided into independent parallel chambers for ease of maintenance and cleaning.

Annexure 12-A.3

LIST OF BUREAU OF INDIAN STANDARDS (IS)

Sl. No

IS. No

Subject

1

458-2003

Precast concrete pipes (with and without reinforcement) (3rd Revision) (Amendment 2)

2

651-1992

Specification for salt glazed stoneware pipes and fittings(5th revision)

3

1726-1991

Specification for cast iron manhole covers and frames(3rd revision)

4

1729-2002

Specification for sand cast iron spigot and socket soil waste and ventilating pipes, fitting and accessories1st revision) (Amendments 4) (Reaffirmed 19

 

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