SETTING OUT
PROPOSING A HOUSE FOR A LAND
v Dimensions
of the land were taken by using given Land separation drawings.
v By
using Wooden pegs the corners of the lands were marked.
v Then
by using leveling machine reduce levels at 3m grids were taken.
v Longitudinal
section of the land were drawn by using reduce levels of the land.
v There were 5 types of houses and according to the drops most suitable house type is selected for the land.
SETTING OUT OF A PROPOSED HOUSE
AT GIVEN LAND
To construct a House
or any other structure, first setting out process should be carried out. The
necessity of the setting out is to identify the locations of structural parts
of the buildings. Mainly setting out work must be carried out with higher
accuracy and the instruments should be free from defects (errors). Theodolite
is the main instrument used in most places where the construction works proceed.
At “Digana housing project” site theodolite was main instrument which used to
setting out the boundaries of houses. By using theodolite 900 angles
marked on the land by using wooden pegs and also when do this task following
things considered.
v Front
face of the house
v Dimensions
of the land
v Dimensions
of the house type “ width and length”
v Costumer
requirements
Then by using marked reference line (900 angle pegs) boundary of the houses were marked and this case steel tape and theodolite was used. Steel tape was used to measure the horizontal distance between each pegs. Then by using string and pegs all the parts of the foundation were marked (Pythagoras theorem (3:4:5) used) and then excavation was done.
EXCAVATION AND FOUNDATION WORK
EXCAVATION
Excavation is an
important process, in a building construction to have certain depth on earth
for a foundation of column and wall. The depth of the excavation depends on
some factors.
They are;
➢
The bearing strength of soil
➢
The size of building to be built over
➢
the uniform ness of soil
EXCAVATION FOR FOUNDATION
The selection of the type of excavation depends on various
factors like,
v Nature
of the Project
v Type
of Sub Soil
v Depth
of Excavation
v Types
of Available Machinery
After selecting a type of excavation, excavation was done
according to the drawings.
Figure3.1: Excavated Trench for Foundation
SOIL TEST FOR EXCAVATED
FOUNDATIONS
Before start any construction activity, it
is essential to investigate about the existing soil, because the entire load
from the structure is transferred to the soil beneath the foundation. From the
result of soil test we can decide whether the soil is suitable for the
construction or any improvement required for the existing soil.
The soil which we find at
the site is a sandy soil and the ground water table is slightly higher than the
normal situation. All the houses and building of the project are two storey or
single storey. Regarding above factors, Mackintosh Test have been recommended
as the soil test (to find allowable baring capacity of soil) of this site and
it is preceded by quality unit of the site. The Mackintosh equipment consists
of a rod and a hammer. One, two and three feet distances have been marked in
the rod to determine penetration of the rod into the ground when proceed the
test. The minimum depth which we should penetrate the rod into the ground is
depend on the zone of influence.
Figure3.2: Zone of Influence
According to above diagram it is obvious
that zone of influence depends on dimensions of the foundation. The following
table shows influence zones for different type of foundations of the houses in
the project.
Table3.1: Influence zones for different type of
foundations
|
Type of Foundation |
Width, B (mm) |
Influence Zone 1.5B (mm) |
Influence Zone 1.5B (ft) |
|
Single Storey |
350 |
525 |
1’ 7” |
|
Two Storey |
500 |
750 |
2’ 5” |
|
Column Footing of Two Storey |
750 |
1125 |
3’ 8” |
According to the
table, for a foundation of two storey house which has B value of 500 mm the
test should be proceed up to 3 feet depth but for a foundation of single storey
house which has B value of 350 mm up to 2 feet of penetration is sufficient.
The test was done on the
excavated foundation trench before placing the screed layer. In this test, the
bearing capacity of a particular soil was determined and then the results will
be compared with the allowable one.
First of all the points
which the soil test to be done was decided so that the points where the load
bearing walls, columns exist according to the plan. Then blows were applied on
the soil by using a steel rod and no of blows were counted to penetrate the rod
into the ground up to 1st feet. Readings were recorded. Like that
the no of blows required for the 2nd feet was counted &
recorded. (For single storey house it is sufficient to precede the test up to 2
feet) Then required minimum number of blows was determined from the chart of
allowable bearing capacity vs. Mackintosh value (blows/feet).
v Single
storey house : 75 kN/m2
v Two
storey house : 200 kN/m2
Finally the value of
blows per feet from the chart was compared with the recorded value and decided
whether soil is capable to bear the structure. If the test is not satisfied,
soil can be improved by following ways and tested again.
v Compact
the ground
v Remove
the existing soil layer and fill with ABC (Aggregate Base Coarse) and Compact.
v Increasing
the width of the foundation
FOUNDATIONS
Foundation is the lowest part of the structure which
provides a base for the supper structure properly. This term includes the
portion of the structure bellow the ground level as well as the artificial
arrangement of concrete blocks, piles and etc. provided to transmit the load of
the structure including the dead weight of the structure itself to the soil
bellow. In fact, it is a device to transmit the load of the structure to the
soil bellow. Foundation is provided for the following four main purposes.
Ø To distribute
the load of the structure over large area
so as to overloading of the
Soil beneath.
Ø To load sub
stratum evenly and thus prevent unequal settlement.
Ø To provide
a level surface for building operations
Ø To take the
structure deep in to the ground and thus increase stability preventing over
tuning.
SETTING UP THE SCREED TOP LEVEL
After proceeding soil test, pegs were
placed on trenches to mark screed top level. The screed top level of all houses
in the project was independent each houses from the land and peg tops were
adjusted to this level from TBM by using dummy level and staff. This is very
important because the finished floor level of the house depends on the accuracy
of screed top level.
Elevation of the TBM =
z
Initial Reading =
x
Level of the Line of Collimation = x + z
Screed Top Level =
99.670 m
The Final Reading =
(x + z) – 99.670
RANDOM RUBBLE MASONRY
Rubble is built over
the concrete foundation in a specified shape that it will not create tensile
force with stones from approval quarry. Rubble masonry strength depends on:
v The
stone should be laid in their well balanced position
v Stones
should be offset in specified interval vertically and horizontally to have
homogeneous bond.
v All
stones should be well watered before build.
Rubble masonry is many types such as
Random Rubble Masonry, Coursed Rubble Masonry etc.
In my work site Random Rubble Masonry was
done for foundations. In this type of masonry, Rubble or irregular sizes are
used to build. The stones are put in irregular way and bonded with mortar 1:6
cement: sand. The foundation make up to 230mm below the DPC level. Then infill
blocks were laid on foundation and it
wall thickness. These blocks were filling Grade 15 concrete.
Figure3.4: Infill Block Layer on Foundation
SETTING OUT FOR SUPERSTRUCTURE
After finishing the foundation work, using
the Theodolite two lines with perpendicular to each other (grid lines) was
marked on foundation. It was done by using the pegs which were used for the
foundation setting out. The setting out of the houses was carried out by using
these two grid lines. Then blocks are placed on these two grid lines and after
that by using them other walls are marked by putting blocks and also in this
case used given drawings. After placing all the blocks, 1st block layer was
checked for diagonals in the each room to make sure that corners are at 900.
BOUNDARY WALL
The boundary wall was constructed for a
separation of two lands. It was constructed by using random rubble masonry.
Boundary walls also constructed as same as retaining wall construction.
RETAINING WALL
Retaining walls are constructed to stop
falling down of soil in embankments. The dimensions of the retaining wall are
depending on the height of the embankments. Initially the soil was excavated to
designed depth for retaining wall foundation. If the soil was loose, the
excavating depth should be increased. Then the gage 250 polythene is laid on
top of soil in order to prevent the absorption of water from the concrete to
soil. Then 1:3:6(150mm) cement concrete (screed) was placed and compacted. If
the soil was loose, reinforcement also provided. In After one day, water was
poured on the concrete for curing and random rubblework was started. The rubble
used for retaining wall was 150mm to 225mm and it was constructed with 1:6
cement sand mortar. When constructing, some 75mm diameter weep holes also
constructed. Then 25mm aggregate filter media was placed in front of the weep
holes as shown in figure…. The filter media is to filter the water without soil
and prevent soil from entering through the weep holes. After the construction
of rubblework, 20mm thick rendering was applied on the retaining wall with 1:3
cement sand mortar. The dimensions of a retaining wall were given below.
Figure3.5: Detail of a Retaining Wall
BLOCK WORKS
Ø 1:5
cement sand mortar were used.
Ø Before
starting block workers, blocks should be wetted.
Ø Mortar
layer thickness should be 10 mm and not exceeding 15mm.
Ø First
the Connor blocks are placed and plumb the blocks and then with the help of
string other blocks are laid on a line.
Ø After
lying the Blocks the vertical joints must be filling with mortar very well to
keep the proper bonding between Blocks.
Ø The
number of Blocks that can be laid for day is maximally up to eight. (5”)
Ø When
continuance the Block work there are two tie beams available at the forth layer
of the Block work and lintel level.
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