1.FOUNDATIONS AND
BASEMENTS
Foundation
• The lowest artificially prepared parts of the
structures which are in direct contact with the
ground and which transmit the loads of the
structures to the soil below are known as the
foundation.
• It is the lowermost part of the structure that
transfer the super-impose load(live load ), dead
load, wind load, earthquake load, from the super
structure to the soil on which the building rests.
Function of foundation:
• To transmit all superimposed loads (Live,
Dead, Wind, Snow, Vibration etc.)
• To withstand against all kinds of settlements
(against failure of underlying soil)
• To provide stability to the structure so as to
make resistant to the lateral pressure or
thrusts and prevent it from tilting and
overturning.
Characteristic of good foundation
The following are the characteristics of a good
foundation :• Wide enough section to distribute weight
over larger base area within safe bearing
capacity.
• Evenly loaded condition that prevents
unequal settlement.
• Deep enough preventing overturning and
increasing stability.
1.1 TYPES OF FOUNDATION
• Shallow foundations(D/B<=1):
transfers the loads to subsoil at a point near to
the ground floor of the building such as strips
and rafts.
• Deep foundations(Lp /B>=4): transfers the
load to subsoil some distance below floor of
the building such as a pile.
Types of shallow foundation
1.Spread footing
-independent
-combined
-continuous
2.Strip footing
3.Raft(Mat) foundation
4.Grillage foundation
Spread footing
• It is the one which supports either column or
wall.
Independent footing
Combined footing
Continuous footing
Strip footing
• Independent footing of two columns are
connected by beams.
Deep foundation(pile and well)
Uses:
1.In very poor soil condition
2.In water logged soil (high water table)
3.In filling area.
4.In area with heavy load.
5.In the areas where the mat or grillage
foundations are not possible.
Some common problems with
existing foundation.
1.unequal settlement of sub soil.
-non uniform nature of sub soil throughout the
foundation.
-unequal load distribution of the soil strata.
-eccentric loading.
Remedial measures:
-resting the foundation on rigid strata such as rock or hard
bed.
-proper design of the base of footing(age of load from
structure coincides with c.g. of the foundation).
-Loading of foundation should be maintained ie.no
eccentricity.
-pressure on the soil should not exceed the safe bearing
capacity of the soil.
2.unequal settlement of masonry
-mortar used as binding materials in the
masonry construction shrinks and get
compressed when loaded excessively before it
has fully safe set.
Measures:
-using mortar of proper strengths.
-masonry is raised to the same uniform level
through out while excavation of work(not more
than 1.5m high in a day)
3.horizontal movement of the soil
adjoining the structures (sub soil moisture
movement)
-this defect is very common in clay and black
cotton soil such types of soil under go volumetric
changes with the change of atmospheric condition.
-the differential settlement caused by the movement
of subsoil moisture. this alternate swelling and
shrinking of soil results in the formation of cracks in
structure.
Measures:
-raft foundation and pile foundation should be used.
4.Lateral escape of soil below the
foundation.
- These defect is liable to occur when the building
is situated near to river bank where there is
danger of soft or loose soil below the
foundation getting disturbed.
measures:
-in such cases sheet piles of timber or steel should
be driven to confirm the soil and avoid the danger.
Retaining walls
• A retaining wall is a structure designed and
constructed to resist the lateral pressure of
soil when there is a desired change in ground
elevation that exceeds the angle of repose of
the soil.
• A basement wall is thus one kind of retaining
wall.
Types of retaining walls
Water proofing of basement:
Water proofing of basement refers to technique
used to help prevent water from penetrating
the basement of home.
Water proofing is done by:
1.Application of sealants(substance used to
block the passage of water to the surface of
joint or openings)
2.Installation of drains.
3.Providing sump pump to pump out water.
Use of sealants
Methods of water proofing:
1.Monolithic structure
the water proofing is achieved through monolithic
construction of walls and floors by the use of dense
reinforcement concrete which acts as moisture barriers.
2.Drained cavities water proofing.
The moisture that penetrates the external structure of
walls is drained off by the cavity.
3.Membrane water proofing.
Thin membrane is used for waterproofing on the internal
and external face of wall.
Earthquake effects on foundation
An earthquake is the result of a sudden release
of energy in the earth crust that create the
seismic wave. earthquake are caused mostly by
rupture(break) geological faults ,volcanic
activities, landslides, mine blast and nuclear
test.
Shaking and ground rupture are the main
effects caused by earthquake resulting more or
less damage to the building.
Some common effects are:
-Visible cracks in the foundation walls, exterior
brick walls, plaster wall.
-Unequal Settlement of foundation.
Damp proof course
Damp proofing in construction is a type of
moisture control applied to building walls and
floors to prevent moisture from passing into the
interior spaces. Damp problems are one of the
most frequent problems encountered in homes.
Causes of dampness
1.Incorrect or improper design.
2.Use of sub-standard and incorrect materials.
3.sub-standard and faulty workmanship.
4.Ground water table and rains.
Effect of dampness
1.efflorescence of materials.
2.Softening and crumbling of plasters.
3.Blistering and flacking of paints.
4.Corrosion of metals.
5.Deterioration of electrical fittings, wires
leading short circuiting.
6.Creates unhealthy living condition for
occupants.
Properties of effective DPC material
1.Completely impervious.
2.Strong and durable.
3.Flexible
4.Free from salts like sulphates chlorides etc.
Materials commonly used to check
dampness:
1.Flexible materials like hot bitumen, plastic
sheets, bituminous felts, etc.
2. Semi-rigid materials like mastic asphalt.
3. Rigid materials like impervious bricks, stones,
slates, cement mortar or cement concrete
painted with bitumen, etc.
4. Mortar with waterproofing compounds
5. Coarse sand layers under floors
Types of DPC
1.Horizontal DPC
provided in plinth, basement, floor, roof,
parapet wall covers.
2.Vertical DPC
provided in basement wall outer exposed wall
of super structure.
Membrane damp proofing
This consists of introducing a water repellent
membrane or DPC between the source of
dampness and the part of building adjacent to
it.
Damp proofing course may consist of flexible
material, bitumen mastic asphalt, bituminous
felt.
Integral damp
it consists of adding certain water proofing
compounds of materials to the concrete, mixed
so that it becomes impermeable.
Surface treatment
The surface treatment consist of application of
layer of water ,repelling substance or
compounds on these surface through which
moisture enters.
Guniting
This consist of depositing under pressure and
impervious layer of rich cement mortar over the
expose surface for water pressure 1:3 cement
sand mixed which shot with the help of cement
gun under a pressure of 2 to 3 kg/cm2 is
guniting.
Cavity wall construction
This is an effective method of damp prevention
in which main wall of building is shielded by an
outer skin wall, leaving a cavity between two.
Polythene DPC