When design a structural elements of a structure, main thing is soil type. Foundation type is depend on soil type. Simply there have many laboratory test has to done.
For
example: One is Triaxial test. This test done for clay type soil. For sand
direct shear test has to be done.
Borehole
test.
For
borehole test normally we do Standard Penetration Test (SPT).
For SPT
used 150mm diameter tube. This tube is driven to the ground using hammer. The
weight of this hammer is 5.9T. The drop height is 1.5m. After 0.5m penetration,
take the sample out and then again place the tube in same place and do the
test. Each 0.5m penetration take out the sample. Count how many drops needed to
penetrate 0.5m depth.
Soil
type classification.
Example graph of SPT
How to
justify the soil type at site.
First
take the soil sample by using hand. Then drop the soil sample freely. If soil
particles are stick in palm, it is sand. If not stick soil type is silt or
clay. For identify whether its clay or silt, there have another trick. Take
that soil sample in to palm and drop water to it. If particles move towards
hand, it is a silt. If not clay.
N = No
of drops
N>50 – Rock
N, 30-50 – Very sense soil
N, 10-30 – Loose soil
N<10 – Not appropriate for
construction
Soil has
to be removed up to N is 30.
If it is
a pad foundation N should be greater than 30 below to 1.5B (B is the width of
the pad)
A= Foot
print
a= Total
foot print
If a
> 50%A, Rafter foundation is needed.
Strength
of soil.
Safe
Bearing Capacity of Different Soil
|
|||
Non-Cohesive
soil
|
Cohesive
Soil
|
||
Type
of Soil
|
Values
in kN/m2
|
Type
of Soil
|
Values
in kN/m2
|
Gravel,
Sand and Gravel Compact offering high resistance to penetration when
excavated by tool
|
450
|
Soft
shale, hard or stiff clay in deep bed, dry
|
450
|
Coarse
Sand Compact and Dry
|
450
|
Medium
clay readily indented with a thumb nail
|
250
|
Medium
Sand Compact and Dry
|
250
|
Moist
clay and sand clay mixture which can be indented with strong thumb pressure
|
150
|
Fine
Sand, Silt (dry lumps) easily pulverized by the fingers
|
150
|
Black
cotton soil or other shrinkable or expansive clay in dry condition (50%
saturation)
|
150
|
Fine
sand, loose and dry
|
100
|
Soft
clay indented with moderate thumb pressure
|
100
|
Very
soft clay which can be penetrated several inches with the thumb
|
50
|
||
Structural
elements planning.
Beam length for each type.
Beam
Type
|
Cantilevers
(meters)
|
Simply
Supported (meters)
|
Fixed/Continuous
(meters)
|
Rectangular
|
3
|
6
|
8
|
Flanged
|
5
|
10
|
12
|
Slab length of each type.
Support
Condition
|
Cantilevers
(meters)
|
Simply
Supported (meters)
|
Fixed/Continuous
(meters)
|
|||
Slab
Type
|
One
way
|
Two
way
|
One
way
|
Two
way
|
One
way
|
Two
way
|
Max.
Span in meters
|
1.5
|
2.0
|
3.5
|
4.5
|
4.5
|
6.6
|
