shallow foundation
TRANSCRIPT
GROUP NO.01Name Roll No.
(1) Raktim Barua 10.01.03.123(2) Farjana Akter 10.01.03.140(3) Fatema Sultana 10.o1.03.159(4) Md.Shahadat Hossain 10.01.03.154(5) Raiyan Fardous Ratul 10.01.03.153(6) Sajjad Hossain 10.01.03.152(7) Mehrana Rashid Noor 10.01.03.162(8) Tuhin 10.01.03.156(9) Bushra Tasnim 09.02.03.002
Foundation:Foundation is the lowest part of a structure which
provides a base for the super‐structure and transmit the loads (live load, wing load) on the structure including the dead weight of the structure itself to the soil below.
Types of Foundation:
Foundation can be broadly classified into two types–1. Deep Foundations 2. Shallow Foundations
Shallow foundations:Foundation is placed immediately lowest part of the super structure, is termed as Shallow foundation.
Why we use shallow foundation?
‐ To distribute the structural loads over a wide horizontal area at a shallow depth below the ground level.
The various types of shallow foundations are :
(a) Spread footing(b) Combined footing(c) Mat or Raft foundation.(d) Grillage footing(e) Eccentrically loaded footing
Spread footings
Spread footings are structural members used to support columns and walls and to transmit and distribute their loads to the soil.
Types of spread footing Wall footings Reinforced concrete
footings Inverted arch footing Column footings
Wall Footing
Support walls that may be either bearing or nonbearing walls.
Commonly required to support direct concentric loads.
Why Wall Footing?
Footings carry relatively light loads on well drained cohesive soil.
A wall footing under concentric load behaves similarly to a cantilever beam.
Used in low rise buildings.
Why Wall Footing?
Reinforced concrete footing
Why Reinforced concrete footing?Relatively heavy loading
than wall footing.
Bearing capacity of the
soil is low.
In a reinforced concrete wall footing, the behavior is identical to that of wall footing.
Reinforcing steel is placed in the bottom of the footing in a direction perpendicular to the wall like a reinforced concrete beam or slab.
Why Reinforced concrete footing?
Inverted arch footing
When a wall iscomposed ofisolated piers, itis well tocombine all theirfootings intoone, and to stepthe piers down .
Inverted arch footing
COLUMN FOOTINGS
WHY COLUMN FOOTINGS?
This is one of the most economical types of footings.
Used when columns are spaced at relatively long distances.
WHY COLUMN FOOTINGS? Low bending strength.When bearing capacity of soil is good. Carry heavy loads. Used to support single columns.To distribute the load uniformly.
CHARACTERISTICS OF COLUMN FOOTINGS
Constructed with brick, stone or plane concrete.
Circular, rectangular or square in plan.
PROCEDURE OF COLUMN FOOTINGSEARTHWORK LEVELING
Support
Brick flat soling
9’X9’ Wooded Frame
3”BRICK FLAT SOLING
Joint of rod
Wires
BINDINGTHE RODS
Upper rod
Inner rod
6” interval
POSITION OF RODS
PLAN
3”Clear cover
6”Block
CLEAR COVERS&
BLOCKS
Centering with plumb bob
Ring
Centre point of column
CENTERING THE COLUMN
6” Interval ring
PREPARED COLUMNREINFORCEMENT
Length 17”
Width 9”
LENGTH & WIDTH OF RING
PUTTING THE COLUMN INTO THE FOOTING
Load bearing support
CAVING TENDENCY
LEVELLING THE COLUMN
SUPPORTING THE COLUMN
Vibrating
PORING CEMENT CONCRETE
A COMPLETE COLUMN FOOTING
Combined footings
Combined footingsusually support two columns, or three columns not in a row.
Combined footings are used when tow columns are so close that single footings cannot be used or when one column is located at or near a property line.
When two columns are close together, causing overlap of adjacent isolated footings.When soil bearing capacity is low, causing overlap of adjacent isolated footings.
WHY COMBINED FOOTINGS?
PROCEDURE OF COMBINED FOOTINGS
A COMPLETECOMBINED FOOTING
Foundation which consists of thick reinforced concrete slab covering the entire area of the bottom of the structure like a floor.
This foundation was invented by John Root at Chicago in 19th
century.
Raft Foundation
Why Raft Foundation?
Base soil has low bearing capacity or the column loads are so large that more than 50% of the area is covered by conventional spread footings.
Resist unequal settlement due to earthquake.
Quickness of the construction work.
Figures of the Different Types of Raft
PROCEDURE OF MAT FOUNDATION
PlanShoringExcavation of soilBrick flat soling
or C.C. castingFormwork &
Placing of reinforcement CastingCuring
Before earth can be excavated to make the foundationcertain precaution has to be taken to stop the outside soilfrom caving in the excavated area. These precautions arecalled shoring , the purpose of which is to anyhow retainthe surrounding soil.
Shoring process
Excavation
Excavate earth according to design
specification
Reinforced chair
Bottom rebar
Top rebar
POSITION OF REBARS
PREPARED COLUMN REINFORCEMENT
SUPPORTING THE COLUMN
Extra top rebar
Position of column on foundation
Support
Column
Formwork for casting
Wooden frame
Support
Pouring cement concrete & compacting
Spread footers being installed tooshallow, oftentimes just 2‐3 feet belowa foundation, which does not eliminatethe effects of expansive soils.
Foundation repair will last longerthan a week as the excavations aremade and the concrete will have tobe cured before the holes can berefilled.
Limitations of shallow foundation
A huge amount of earthwork is to bedone in Mat foundation.
If the shoring system can not resistthe pressure of outside land, then thestructure surrounding the area may bedamaged by deflection of soil.
Ground water may come out whenthe earthwork is done.
Limited to dealing with point loads.
Limitations of shallow foundation
It is a quick process compared to others inthe construction work.
This type of foundation is alsoeconomically cheaper than any otherfoundations.
Though there are some limitations in matfoundation still it is economical in somecases.
Advantages of shallow foundation
It can resist ground water absorption.
The damage due to earthquake islesser than any other type offoundation.
It consists of a reinforced concrete slab which is more thicker than footing foundation.
It prevents unequal settlements.
Advantages of shallow foundation
We know shallow foundations are not applicable for high rise structures, but we saw a lot of high rise structures which are building upon raft foundation!Generally Raft is used when the bearing capacity of soil is low, but in some sites, we saw raft foundation is used instead of having a good bearing capacity!
Conflicts of Our Knowledgewith Our Experiences
Questions ? ?