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Republic of the Philippines
TECHNOLOGICAL UNIVERSITY OF THE PHILIPPINES
COLLEGE OF ARCHITECTURE AND FINE ARTS
Ayala Boulevard cor. San Marcelino St., Ermita Manila
Egenias, Arboy M.
Ganacia, Jemica G.
• A large sewer that receives flow from
a number of trunk sewers and
transports the flow to the wastewater
treatment plant. These sewers do not
connect to homes, buildings or
• In a storm, they allow some of the
sewage to flow directly into a
receiving stream, thus keeping it from
overflowing onto the streets.
• The interceptor sewer has a
minimum of 15 feet in diameter.
• Also used in separate systems to
collect the flows from main and trunk
sewers and carry them to treatment
• An interceptor could be 36-48 for
sanitary and 60+ for storm. In terms
of flow, that is highly dependent on
the pipe size, material and slope...
• Also known as Grease traps
are plumbing devices designed to
intercept most greases and solids
before they enter a wastewater
• It is usually used in restaurants.
• They only have kitchen waste water
flowing through them and are not
served by any other drainage system
such as toilets. They can be made
from a number of different materials;
e.g. stainless steel, plastics, concrete
& cast iron.
• Effectively they are boxes within the
drain run that flows between the
sinks in a kitchen to the sewer system.
• They range from 35 litre capacity to
45,000 litres and above capacity.
They can be located above ground,
below ground, inside the kitchen or
outside the building.
• Grease trap sizing is based on the size
of the 2 or 3 compartment sink,
dishwasher, pot sinks, and mop
Sizing for Multiple Fixtures:
1. Determine the flow rate for each fixture to
be serviced by the interceptor.
2. Add together 100% of the largest flow rate,
50% of the second largest, and 25% of all
3. Result is the recommended flow rate of the
Types of Connections
• How drainage fixtures and fittings are connected to
an existing system via manholes and/or inspection
• There are 4 ways to connect new drainage to an
1. - via a new branch junction or access chamber to
an existing pipeline
2. - via a saddle onto an existing sewer
3. - via an existing manhole or existing inspection
4. - via a new inspection chamber or new manhole
Methods 3 and 4 are the main focus.
Types of Chambers
• Access chambers are intended to provide
simple access for cursory inspection and access
for drain rods or other maintenance equipment.
They are not intended to provide access for a
maintenance operative and are generally not
more than 600mm deep.
• Inspection chambers (often abbreviated to
IC) are larger than access chambers, typically a
minimum 450mm diameter. Again, they provide
access for maintenance equipment, but tend to
have more branches/spurs feeding into them
and are often up to 1000mm deep.
Manholes tend to have iron covers
ICs can be circular, usually 450 or
....or they can be rectangular, usually with
a concrete cover
• A manhole (alternatively utility hole, cable
chamber, maintenance hole, inspection
chamber, access chamber or confined space) is
the top opening to an underground vault used to
house an access point for making connections or
performing maintenance on underground and
buried public utility and other services
including sewers, telephone, electricity, storm
drains and gas.
• Manholes (MH) are the largest chambers
providing access to a sewer or drain for
maintenance equipment, and, in some cases, for
operatives to enter the system itself. The
minimum internal dimensions of a manhole are
600x900mm and they can be of any depth,
although most modern manholes tend to be at
least 1 metre deep with inspection chambers
used for shallower depths.
Access and inspection chambers are used when
the depth to the drain is a meter or less; for
anything deeper, something more robust is
required. The most common forms of manhole
• sectional pre-cast concrete
• sectional plastic
• cast in-situ concrete around a plastic
• For depths up to 2.7m, the minimum internal
dimensions for a rectangular manhole are
1200x750mm, although manholes with more
than 3 branches may be even bigger. Anything
deeper than 2.7m is a major project best left to
professional drainage contractors.
• Circular manholes are commonly used for main
sewers; for depths up to 1.5m, they must have a
minimum diameter of 1050mm and for anything
deeper than 1.5m, the diameter has to be
• This cross-section shows a typical construction
for a manhole in a residential setting, such as
beneath a driveway. It depicts the two most
common constructions, using, on the left, pcc
(Plain Cement Concrete) chamber sections, and
on the right, Engineering brickwork.
• The cover detail may be different for a manhole
within a trafficked area, or if recess tray
cover for block paving was to be used.
• The number of branches entering a manhole will
determine the length dimension. A manhole
with more than 4 branches may need to be
longer to fit them all in. Similarly, manholes
utilising 150mm diameter channels may need to
Plan view of typical manhole with a single branch oblique junction,
again illustrating two construction types.
Sectional concrete inspection chamber with crown unit and cover
• There are several different types of manhole to
suit a variety of purposes and conditions, but an
idealized manhole construction is shown here to
illustrate the basic concepts and components.
Not all features depicted will be found on all
• Shallow Manhole - a manhole that has a
constant diameter or same cross-section
• Deep Manhole - a manhole with an access
shaft of a smaller diameter or plan size than the
• Cover and Frame - see table for guidance on
strength rating of various covers
• Seating ring - sometimes used in place of
regulating between cover and cover slab
• Brickwork - only engineering brick should be
used, laid to English Bond
• Corbelling - the method of projecting brickwork
outwards to reduce an opening or to carry a load.
Each course should not oversail by more than 50mm
• Cover slab - also known as a 'biscuit'. Best thought
of as a 'lid' for the main shaft, with a single access
opening, minimum 600x600mm
• Reducing slab - used to accommodate a change in
chamber diameter from a larger diameter main shaft
to a narrower diameter entrance shaft
• Straight back tapers - perform the same function
as reducing slabs, ie to accommodate a change in
shaft diameter, but without providing a landing.
Also known as 'Cone Sections'
• Landing Slab - used in Deep Manholes, these
limit the maximum shaft depth to 6 metres, and
may be thought of as shaft dividers, providing a
resting point or 'landing' at convenient intervals
• Chamber sections - the individual sections
used to construct a sectional shaft. Obviously not
present with brick-built shafts
• Soffit - the underside of a cover slab, arch or
other structure. Opposite of Invert
• Benching - a smoothed concrete topping,
usually a granolithic mortar, sloping at not less
than 1:30 and neatly shaped and finished to the
base of a manhole
• Invert - the lowest point on the surface of a
pipe, channel or culvert
• Rocker Pipe - a short length of pipe, usually
less than 1 metre, placed at the inlet/outlet of a
solid structure, such as a manhole or building, to
accommodate differential settlement between
the structure and the drainage system
Idealized Adoptable Deep Manhole
• Cover slabs are the 'lid' for many manholes,
especially the larger ones. They are also known
as 'Reducing Slabs', because they reduce the
opening size or the chamber dimensions, and, on
site, they are affectionately referred to as
'biscuits' because that's the sort of humour that
gets us sent to serve in the trenches.
• The basic role of a cover slab is to provide a firm
platform to both 'cap' the chamber and to carry
the cover along with any regulating brickwork.
They are typically manufactured in a high-strength,
steel-reinforced concrete, and, for
manholes, the minimum opening size of
600x600mm is created within the cover slab
during the casting process. Although the vast
majority of cover slabs are supplied fully-cured
from specialist manufacturers, custom slabs may
be cast on site and lifted into position once
cured, or, in certain cases, cast in-situ atop the
• A secondary role for cover slabs is to reduce the
apparent size of the chamber, so that, for
example, a circular 1800mm diameter chamber
or a rectangular 1200x750mm chamber, can be
fitted with a standard 600x600mm cover at the
• These are heavy items, and they are generally
fitted with two or more 'lifting eyes', which are
steel, loops embedded into the concrete, that
should be used to sling the biscuits from a crane
or excavator during lifting and placement.
• The cover slab is normally mortar-bedded onto
the top of the chamber with the internal face of
the joint tooled smooth. When the surround
concrete is placed around the chamber, it is
brought up to be level with the top of the cover
slab, as shown opposite. The regulating
brickwork can then be built on top of the cover
slab and the cover and frame fitted to suit the
• Covers for manholes come in a wide variety of
shapes, sizes and materials. The specification of
manhole and access covers for public areas is laid
down, which is summarized in the table opposite.
Domestic driveways and patios often have the
appallingly unattractive pre-cast concrete crown
units and covers, and most block paved areas now
feature recessed tray covers, fabricated from
galvanized steel. Over recent years, covers
manufactured from new high-strength composite
materials have started to be used, primarily in
Class Test Load
A15 1.5 Pedestrian areas only
B125 12.5 Car parks, domestic
areas with occasional
C250 25 Carriageways if <500mm
kerb face, car parks,
Must be non-rocking/
D400 40 Carriageways and hard
Must be non-rocking/
E600 60 Loading areas, docks,
F900 90 Exceptionally heavy
loads, ports, airports
Ductile and Cast Iron covers
• are manufactured to conform to but other
materials, such as galvanized steel or pre-cast
concrete are not included within the scope of
that standard. Manufacturers of galvanized steel
covers have formed a Trade Association
(FACTA) in order to impose some standards and
quality into the market, but, at the time of
writing, there is no nationally or internationally
• Most covers actually consist of 2 components;
the cover itself, and a frame. The frame is
typically bedded on mortar to a specified height
set to suit the surrounding paving or ground
level and the cover sits inside the frame, from
where it can be lifted and possibly removed
when access to the manhole is required.
• Many of the heavier units have the cover itself
split into 2 triangles, known as 'double
triangular' format. The two halves can be bolted
together but are often left unattached to
facilitate easier removal. Removal is achieved by
the use of 'keys' which fit into the eyes on the
surface of the cover, are turned through 90° and
then it's down to brute force, although there are
special cover-lifting contraptions now available.
• As mentioned above, many paving projects now
use Recess Tray Covers rather than the types of
covers illustrated above. Recess Trays can be
used with any type of paving, although they are
most commonly associated with Block Paving.
Opening double-triangular cover with MH keys