TUTORIALS
Abstract of quantities for Manhole
Comprises excavation, RCC work, Concrete work (PCC), Brickwork, Plaster work within or outer, Iron steps / stairs.
Let’s assume a sketch of the manhole [all the data is supposed]
The base of PCC which is 6” thick. The brick wall with 9” thickness
RCC slab that is 6” thick
The slab has a manhole that has 18” diameter
Assume 3” thick PCC in floor
Assume iron steps below the man hole
Pipe is at the middle of the triangular portion
The dimension of the manhole is 3’ x 2.5’
Compute the subsequent items quantities:
a) Excavation with regard to manhole construction
b) Concrete work in the foundation and superstructure
c) Brickwork in the walls
d) Inside plaster work
e) Iron steps
Summary of quantities:
a) Direct calculation method
b) To utilize table for inputs
Excavation = Excavation depth x Area in plane
Excavation = Breadth x Length x Depth
Excavation = 5 x 5.5 x 3.5 = 96.25 cft
Length = 3’ + 9” + 9” (2 times the wall thickness) + 6” + 6” (bearing portion) = 5.5’
Breadth = 2.5’ + 9” + 9” (2 times the wall thickness for one side and another side) + 6” + 6” = 5’
Depth = 3’ (wall depth below the ground level) + 6” thickness of PCC work in the bed = 3.5’
PCC in bed = Excavation depth x Area in plane
PCC in bed = length x breadth x depth
PCC in bed = 5.5 x 5 x 0.5 = 13.75 cft
a) Overall excavation = 96.25 cft
b) PCC in bed layer = 13.75 cft
PCC [concrete] in floor = Length x breadth x average depth
PCC [concrete] in floor = 3 x 2.5 x [0.25 + 0]/2 = 0.9375 cft
RCC in slab = Length x breadth x thickness – π D2/4 x T [because there is a manhole in the slab]
RCC in slab = (4.5 x 4 x 0.5) – π (1.5)2/4 x 0.5
RCC in slab = 9 – 0.884 = 8.12 cft
PCC [concrete] in floor = 0.9375 cft
RCC in slab = 9 – 0.884 = 8.12 cft
Brickwork for walls [long wall method, short wall method, centreline method, etc]
Brickwork for walls = external box volume – internal box volume
Brickwork for walls = [4.5 x 4 x 4] – [3 x 2.5 x 4] = 72 – 30 = 42 cft
Brickwork = 42 cft
Compute inside plaster
Inside plaster = inside parameter x height = [(3 x 2) + (2.5 x 2)] x 4 = 44 ft2
Inside plaster = 44 ft2
Iron steps = 3 @ 12” c/c
Manhole covers = 1 cover having 18” diameter
Get through the subsequent video lesson to obtain additional information.
Lecturer: SL Khan