Cover Image
close this bookResidential and Non-Residential - Drinking water installations and drainage requirements in Nepal (MTC - SKAT, 1988, 188 p.)
close this folderPART 2 - DRAINAGE REQUIREMENTS
View the document1. SCOPE
View the document2. FIELD OF APPLICATION
View the document3. TERMS AND DEFINITIONS
View the document4. PRINCIPLES OF INSTALLATION
View the document5. PRINCIPAL REQUIREMENTS FOR PARTS OF PIPELINE
View the document6. PRINCIPAL REQUIREMENTS FOR DRAINAGE APPLIANCES
View the document7. PRINCIPLES FOR THE PLANNING AND FITTING OF DRAINAGE PIPES
View the document8. SANITARY APPARATUS (Fixture, Appliance)
View the document9. VENTILATION
View the document10. RAIN WATER
View the document11. MATERIALS
View the document12. PRINCIPLES OF CALCULATION
View the document13. DIMENSIONING
View the document14. INSPECTION AND TESTING

7. PRINCIPLES FOR THE PLANNING AND FITTING OF DRAINAGE PIPES

7.100

PRINCIPLES FOR PLANNING


For planning and execution of building drains (domestic house drainage system) the following marginal requirements are valid. The drainage of premises is as of separate, governmental rule.

7.110

Method of connection - Each plot shall be drained separately and led into the canalization by the shortest way and without using the neighbour's plot.


Where the above is not feasible or not appropriate the drainage of several buildings can be realized by means of a collecting or ground pipe, provided the approval of the concerned government authority has been given.


Where the approval of the authority has been given for such cases of joint sewerage pipes it is suggested that the legality be secured by entering the agreement into the land regisstery.

7.120

Later extension - Where plots are only partially covered with buildings, attention is required that at extension stages the sewer can also be drained by gravity flow.

7.130

Direct drainage in public waters - where premises are situated near public waters the tendency should be for their direct connection to these waters, provided the authorities give their require approval.

7.140

Seepage water - Seepage water shall, if possible, be led to the outfall ditch or in any possible way to the ground water.

7.150

Slope or ground water - Slope or ground water may only be connected into the canalization where permission of the concerned authorities has been granted.

7.160

Seepage of stormwater - where soil conditions are acceptable, a seepage of rainwater can be led directly to the underground, provided permission has been given.

7.200

PRINCIPLES FOR THE LAYING OF PIPES

7.210

Change of direction - Pipe connections may not be utilized for change of direction.

7.220

Reducer fittings - Centric reducers are permissible for connector pipes and branch pipelines, as well as for vertical pipelines (e.g. stacks).


For collector and ground pipelines, as well as in loops, the various diameters may preferably be connected by means of excentric reducers and at parting alignment.



Figure

7.230

Manhole/Inspection Chamber - At each exit of pipes from the house to the pipeline fixed in the ground, there should be a inspection opening, preferably a manhole or a clean out (i.e. branch with tight cover).


On collecting pipes accessible clean outs are required at:



- exit of buildings



- at straight lines after each 40 meters length



- change of direction



Figure

7.300

BUILDING SEWER - as of special governmental rules.

7.400

HORIZONTAL PIPELINES (Ground pipelines).

7.410

Principles - All drains and private sewers have to be of sufficient strength and must be bedded and supported so as not to be damaged by the maximum loads to which they may be subjected. They must be constructed of materials of adequate durability in relation to matter being carried by the drain in relation to the ground and subsoil water outside. Joints must be formed in materials appropriate to the drain itself and in such a way that they remain watertight in all working conditions, including any differential movement that may occur between the pipe and the ground or the structure under which it passes. Joints must not form any obstruction in the interior of the drain.

7.420

Design of pipelines - Drains must be laid in a straight line between points where changes of direction occur. Horizontal pipelines shall be fitted in parallel to the walls of the buildings. The drains have to be of such size and gradient (slope) as to ensure that they are self cleaning and can carry the maximum volume of matter which can be discharged.

7.430

Sizes - The size and method of construction for pipes which carry soil and waste water, including their ventilation system, must be appropriate to their function. In the direction of flow, pipes are to be of the same or larger diameters, and must not be reduced.

7.431

Minimal diameter - For ground pipelines the internal diameter at any point must not be less than the outlet diameter of any appliance, pipe or drain discharging its contents through it, and in any case should never be less than 100 mm i.d.

7.440

Water seals - Provision has to be made in the system to ensure that in normal working conditions the water seal in any siphon (trap) in the system is maintained.

7.450

Ventilation - Each house connected to a drainage system requires at least one main ventilation of not less than 100 mm 0 (whether connected to a septic tank or to the canalization mains).

7.460

Means of access - All drains and private sewers shall have such means of access as may be necessary for inspection and cleaning, as indicated below. Inspection chambers etc., may be of brickwork, concrete or other suitable materials so as to properly sustain any loads imposed, to exclude subsoil water, and to remain water tight.



Figure

7.470

Manholes/outside buildings - at every change of alignment, gradient or diameter of drain, there shall be a manhole or inspection chamber. Bends and junctions in the drains shall be grouped together in manholes as far as possible. The maximum spacing of manholes in any ground pipelines, for diameters up to 300 mm, may not exceed 40 m.

7.471

Sizes of manholes - Chambers shall be of such size as will allow necessary examination or clearance of drains. Size of manholes shall be adjusted to take into account any increase in the number of entries to the manhole. The minimal internal sizes of chambers (between brick faces) shall be as follows:



a) for depth of 1 m or less 0.8 x 0.8 m



b) for depths between 1 m and 1.5 m 1.2 x 0.9 m


In adopting the above sizes of chambers, it should be ensured that these sizes accord with full or half bricks and with standard thickness of mortar joints so as to avoid wasteful cutting of bricks.

7.473

Manholes/Inside buildings - Inspection chambers on drains (= manhole on sewers) inside buildings are to comply with the following construction requirements:



a) to be fitted with cover having an airtight seal, fixed down with bolts of non-corrodible material. The chamber is to be watertight under the maximum pressure which could be created by a blockage at a point below the chamber, or



b) contain a drain equipped with fittings having water-tight inspection covers.

7.474

Sample of a manhole, inside building:


Figure

NOTE THAT CHAMBER SHOULD BE OF ADEQUATE SIZE TO PERMIT READY ACCESS TO DRAINS FOR CLEANING AND RODDING

COVERSIZE

DEPTH

60x60 CM

60 CM

80x80 CM

80 CM

80x80 CM OR 100x100

100 CM

7.475

Separate Manholes - For drainages with divided systems joint manholes for any kind of waste waters are not permissible, except where passages are fully enclosed and incorporate approved cleaning openings.

7.510

Slopes of pipelines - Horizontal pipelines shall be fitted with an even slope gradient. The optimal slope for soil and/or waste water pipes is 3%. The acceptable minimal slopes are shown in the following table.

Minimal slope

in %

Storm sewer

1

Soil/waste water drainage


Ground pipelines and collecting pipes

2


- up to i.d. 200 mm



- above i.d. 250 mm

1.5

Branch- and connecting pipelines

2

Vent pipes

1

7.520

Connections to collection and ground pipelines



- Connections to the collecting pipes have to be made with a fitting of up to 60° (e.g. open installation on ceilings).



- Connections to the ground pipeline have to be made with a fitting of up to 45°.



- As a rule the connection in ground pipelines and collector pipes must be made in the upper half of the pipe (e.g. above horizontal axis).



Figure



Figure

7.521

Change of direction - Ground pipelines and collecting pipes shall be fitted with bends up to 45°.

7.522

Example of 90 degree change of direction



Figure

7.530

Trenches for drains - Where trenches for drains are constructed adjacent to the foundations of a building, precautions must be taken to ensure that the drainage trench in no way impairs the stability of the building. Therefore sufficient distance from the building foundation to the sewer pipes and trenches is required.

7.531

Trenches for drains near a building



Figure



trenches filled with concrete to levels shown, expansion joints at spacing not excedding 9 m centres along trench.

7.540

Drains passing through outer walls - Where a drain passes through a wall (including the wall of an inspection chamber or septic tank) precautions must be taken to prevent damage or loss of watertightness by differential movement. This also applies if a drain passes under any other structure which may exert stress. Note: Where within the range of the ground-water table, a watertight passage is indispensible.

7.550

Inlets to drain - Inlets to ground pipelines and collector lines are to be made as indicated below.



Figure

7.560

Series of rainwater pipes - Collected, with siphon and with connection to sewer, as indicated below.



Figure

7.570

Waste connection to gully - In divided drainage systems, where waste waters are discharged separately from soil waters, there exists the possiblity of joined drainages by use of a gully.

Such waste water pipes in a building can be taken through an external wall of the building by the shortest practicable line, and shall discharge below the grating or surface box of the chamber but above the grating of a properly trapped gully.

The waste pipes shall be brought to the gulley without any reduction in diameter. A straight pipeline with few bends is preferable.



Figure


Note: The outlet of a gulley (floor drain with siphon) may be led into a soil and/or waste water sewer system.

7.580

Connections of appliances into horizontal pipelines near to (vertical) stacks - Where stacks are over 10 m in height, connections of appliances for drainage are to be inserted into collector or ground pipeline no closer than 1.5 m from the vertical stack.



Figure

7.590

Septic Tank design - The principal factors to be considered in deciding on the capacity of a septic tank are the average daily flow of sewage, the rentention period and adequate sludge storage to suit the frequency of cleaning (desludging).

7.591

It is important that the tank capacity be sufficient to permit reasonably long periods of trouble-free service and prevent frequent progressive damage to the effluent absorbtion systems due to discharge of sludge by overloaded tanks.

7.592

Depending on local circumstances preferred methods of disposal of septic tank effluent are:



a) by dilution, if there is adequate flow in the receiving watercourse,



b) by a soakpit, if the ground is sufficiently porous and the water table is sufficient low,



c) by sub-surface irrigation where the ground is less porous,



d) by surface irrigation over a grass plot where ground conditions are unsuitable for sub-soil irrigation. An area of about 1 m2 per person is required, or



e) by evapo-transpiration up to 100 m2 per person may be required where the ground is of heavy clay.


In connection with (c) above, the WHO publication “Excreta Disposal for Rural Areas and Small Communities” sets out the percolation test procedure and, based on the results, the size and minimum spacing requirements for disposal trenches.

7.593

Note: In principle septic tank designs are to be provided by civil engineers/architects, as they are not part of sanitary building installations.

7.594

Example of a septic tank design



Figure

7.595

Kitchen connections - In certain cases it might be advisable to have a simple grease arrestor fitted near to the kitchen sink (e.g. covered gully). This helps to avoid blockages in the drainage pipe, leading from the house to the mains or to the septic tank.

7.600

LEADERS (Stacks)

7.610

Principles - drainage pipes, such as leaders, branch and connector pipelines, etc., shall be situated inside the building. If this is not possible then they can be situated outside the building, provided easy access is maintained after completion of construction works.

7.611

Leaders (Stacks) - shall have the approved diameter and be continued upwards without any reduction in diameter, without any bends or angle being formed (except where this is unavoidable), to such a height and position as to afford by means of the open end a safe outlet for foul air.

7.612

Layout of pipes - Pipe work and appliances should be so arranged as to allow close grouping of connections preferably with the water closet near to the leader.

7.613

Siphon - All appliances directly connected to leaders (stacks) are to be fitted with a siphon.

7.614

Placing of pipes - Pipes should be placed, fixed and jointed so as to avoid risk of damage through variations in temperature. Unless suitable precautions are taken, the jointing of pipes exposed to unduly high temperatures may become unsatisfactory. Small drainage pipes are particularly liable to damage caused by the freezing of water from a leaking tap in places where freezing normally occurs.

7.615

Access - Sufficient provision should be made for access to all pipework. The embedding of joints in walls should be avoided as far as possible. Pipes should remain readily accessible for the complete height of the building both during erection and after completion for maintenance works. Where fitted inside the house and in shafts access must be possible from each floor. Where fitted on to the outside wall, permanent platforms are to be provided for access.



Figure



It is recommended that leaders and branch and connector pipelines remain accessible, where possible, and are not concealed in masonry (to be fitted in shafts, ducts, etc.).

7.616

Clean out - At the footing of each leader and at easily accessible sites, installation of lockable, airtight gastight “clean outs” is required. This is in order to secure cleaning of these pipelines. However, they may not be situated in living rooms, and if possible also not in workshops.



Figure



Note: clean-out's to be the same dimension as the horizontal ground pipeline (min. 100 mm i.d.): reduction only above the clean out.

7.617

Change of direction - The transition of the leaders into the horizontal pipeline or into a loop, and the transition of the horizontal pipeline into the leader is to be made with two bends of between 30° and 60° (max.) and with a straight piece of pipe between (M ³ 2d).



Figure

7.618

Offset - To shift the fall line of leaders up to 1 m distance offset bends with pointed edges from 15° up to 45° shall be utilized.



Figure

7.620

Loops - Where loops of leaders are unavoidable the influence on the drainage function shall be compensated by appropriate measures.

7.621

Loop with bypass - Where the leaders have a height of over 10 m the drainage appliances in the storey above the loop have to be connected to a bypass. Where there are no drainage appliances in the storey above the loop, a vent pipe shall be made.



Figure

7.622

Connections of bypass loop to stack - The connections to the stack must be made at least 2 m above and 1 m below the stack loop. Connections must be made using fittings having angles of between 45° (min.). and 60° (max.), as shown above.

7.623

Dimensioning of loop pipes - The diameter has at least to correspond to the connected S-values. The loop can be made one dimension smaller than the corresponding leader.

7.624

Loop without bypass - No stalk bypass is required where the height of the leader between the top-most inlet and loop is less than 10 m. In such a case there may be no insertion of a connector or branch line into the leader within 1 m either side of the loop bend.



Figure



7.630

Connection of appliances into horizontal pipelines near to vertical stacks - Where leaders are less than 10 m in height (Height between the top-most inlet and the collection pipe or ground pipeline) no apparatus may be connected within 1 m either side of the easy bend (as shown above)

7.640

Pipe fixings - All drainage pipes need to be securly fasted to the building structure in order to remain in their proper place and not to change shape or direction (e.g. plastic pipes). A proper, open installation has pipes fixed approx. 5 cm clear of the finsihed surface of the wall by means of suitable clamps.

7.641

Brackets/Clamps - Pipe clamps are to be appropriately designed so as to withstand applied loads. They are to be coated to resist corrosion.


Note that branches from leaders are not to be regarded as fixings, since such “clamping” could harm the branch fittings (especially on plastic pipes) and therefore clamps are still required. There are principally two types of brackets:



a) Guide bracket and hangers: they serve as pipe guides and enable contraction and expansion in the desired directions.



b) Anchor bracket: A strong bracket fitted firmly to the building structure and the pipe. It serves to hold the pipes and to resist possible movement of pipes (i.e. fixpoint). All sockets normally should be secured with such a strong bracket.

7.642

Number of brackets - Leaders shall be secured with a minimum of two brackets in each floor. One anchor bracket just below the socket, and one guide bracket at the middle point.

7.700

BRANCH AND CONNECTOR PIPELINES

7.710

Principles - The pipework in branch and connector pipes should always be arranged to allow free drainage of the system. Connections to main or branch pipes should be so arranged as to prevent cross flow from one appliance to another.


Self-siphonage of traps through drainage in the branch and/or connector pipeline shall be avoided by means of the following installation technologies.

7.720

Horizontal Connection - The appliances should be grouped as closely as possible round the main stack so as to keep the branch and/or connector pipes short and reduce noise.

7.721

Gradual slope - Pipes should have a gradual and continuous slope in the direction of flow.

7.722

Minimal distance - In order to prevent siphonage, the distance of the leader's fall line and the angle of the next 88.5° bend may not be less than 0.25 m.



Figure



Note: A direct horizontal connection between the siphon exit and leader is prohibited.

7.723

Minimal slope of connector- and branch pipelines - The minimal slope has to be equal to the measurement of the internal diameter of the connector or branch pipeline, as shown below.



Figure

7.730

Branches from the leader - The branch of a horizontal connector pipeline from the leader has to be made at an angle of between 87° and 88.5°. In the case of a connector pipeline with secondary ventilation the connection to a leader can be between 45° and 88.5°.



Figure

7.731

Connector tilt-line -. Single devices for drainage can be connected to a leader with a straight tilt-line of between 45° and 60° (max.).



Figure

7.732

Adapters and connections - The adapter to a connector on to a branch pipeline or collector pipe, has to be made with a fitting of up to 60°.



Figure

7.740

Cross flow - The insertion of a connector pipeline into a leader has to be made so that no disturbing cross-flow may occur into another connector pipeline. The following shows some examples of this.

1

4

2

5

3

6

7.741

Opposite drainage appliances - Connector pipelines of opposite, equally loaded drainage appliances may be joined by the use of permitted special fittings, provided they are located in the same appartment or where it is possible to have a round-the-clock access to the drainage appliances (e.g. in hotels, schools, etc.). Opposite WC-arrangements are to be connected vertically.



Figure

7.742

Dimensioning - Branch and connector pipelines of max. 4 m effective length, having max. 1 fall line or tilt line in a branch pipeline of max. 1.5 m in height are to be dimensioned according the table: “Branch and connector pipelines without vent.” (Fig. 13.420)

7.743

Increased loadings with secondary vent - Where the above conditions may not be realized, a branch- or connector pipeline can be ventilated at it's end. Such pipes with secondary vent, pipes may have increased loadings, as of table: “Branch and connector pipelines with ventilation.” (Fig. 13.430)

7.760

Principle of installation for connector and branch pipelines - Variant 1: The connector pipeline with an effective length of up to 4 meters, may have only one tilt-line or fall line up to max 1.5 m measured after the elbow of the apparatus connector. The dimensioning follows the table: “SV-values” (13.300)



Figure


Variant 2: The connector or branch pipeline of the SV-groups o.5 and 1.0, with an effective length of between 4 and 8 meters, may have only one fall line or one tilt-line of up to 1.5 m if adjacent to the elbow of the apparatus connector, provided the diameter of the pipeline is made larger by one dimension as in table: “SV-values”, Fig. 13.300 (i.e. to increase indicated SV-values by one dimension).



Figure


Variant 3: The connector or branch pipeline, with an effective length of up to 4 meters and with one or several tilt-lines or fall lines within 4 meters, has to be made one dimension larger as indicated in table: SV-value (= increase indicated diameter of table by one dimension), except for WC



Figure


Variant 4: All other connector or branch pipelines are to be made with a connector or branch vent, as mentioned in table: SV-values.

7.770

Branch pipeline with ventilation - Stacks normally require a ventilation pipe to be of the same dimension as the stack. Provided there is at least one ventilation pipe of 100 mm 0 within the house installation, the following exception for reduced ventilation is applicable.



Figure


Both of the drainage appliances closet and service sink or wash basin fitted in the first floor may be connected as a joint pipeline to a ventilated collector pipeline or ground pipeline. The dimension of the corresponding vent pipe above roof level may be reduced to i.d. 50 mm.