Geo technical properties of soil by sajid hussain

1. PRINCIPLE OF FOUNDATION

2. TREACHER
Engr. QAMAR ABBAS
Group leader
Sajid Hussain
1409-BTCT-021
Adeal liaqat
1409-BTCT-002
Alamgir khan
1409-btct-003

3.  1) Introduction
 2) Grain size distribution
 3) Sieve analysis
 4) Hydrometer Analysis
 5) Size limits for soil
 6) Weight-Volume relationship
 7) Relative Density
 8) Atterberg Limits
 9) Liquidity Index
 10) Effective stress
 11) Consolidation

4.  Design of foundation of structure requires knowledge
about following factors:
 Load on foundation
 Requirements of local building codes
 Behavior of soil that will support foundation
 Geological condition of soil
Last two are related to the mechanics of soil so
engineer must have a good grasp of the basic
principles of soil mechanics

5.  This presentation primarily a review of basic
geotechnical properties of soil:
 Grain-size distribution
 Plasticity
 Soil classification
 Effective stress
 Consolidation
 Shear strength etc

6.  Grain size of soil vary greatly
 Coarse grained soil distribution by
sieve analysis
 Fine grained soil distribution by
Hydrometer analysis

7.  Using some amount of dry soil
 Stack of progressively finer sieves
with pan at bottom.
Retained soil is measured
 Cumulative % of soil passing is
 determined Which is known as
% finer.
 % finer of each sieve is determined
 Plotted on semi logarithmic
graph paper.

8. Table 2.1 U.S. Standard Sieve Sizes
Sieve No. Opening (mm)
 4 4.75 60
 6 3.350
 8 2.360 40
 10 2.000 % wt
 16 1.180
 20 0.850 20
 30 0.600
 40 0.425
 50 0.300 0
 60 0.25 10 1 0.1 0.01
 Grain size, D(mm)

9.  Two parameters can be determined
 uniformity co-efficient (cu)
Cu=D60/D10
 co-efficient of curvature
Cc=(D30)2/(D60)(D10)
Where D10,D30,D60 are diameters corresponding to
the percent finer then 10,30, and 60% respectively

10.  Hydrometer analysis is based
on the principle of sedimentation
of soil particles in water.
 Test involves the use of 50g
of dry soil.
 A deflocculating agent is added
to the soil.
 Agent is genraly125 cc of 4%
solution of sodium hexametaphosphate.
 Soil is allowed to soak for at least
16 hours in the deflocculating agent.

11.  After soaking period, distilled water is added and
sample is transferred to a 1000-ml glass cylinder
 More distilled water is added to the
 cylinder to fill it to the 1000-ml mark
 Then the mixture is again thoroughly agitated.
 A hydrometer is placed in the cylinder to measure the
specific gravity of the soil–water suspension in the
vicinity of the instrument’s bulb.

12.  Hydrometers are calibrated to show the amount of
soil that is still in suspension at any given time t.
 The largest diameter of the soil particles still in
suspension at time (t)can be determined by Stokes’
law…

13.  Soil particles having diameters larger than those
calculated by above EQ.. with hydrometer readings
taken at various times.
 The soil percent finer than a given diameter D can be
calculated and a grain-size distribution plot prepared.

14.  Several organizations develop the size limits for
gravel, sand, silt, and clay on the basis of the grain
sizes of soils.
Classification system Grain size (mm)
Unified Gravel: 75 mm to 4.75 mm
Sand: 4.75 mm to 0.075 mm
Silt and clay (fines): < 0.075 mm
AASHTO Gravel: 75 mm to 2 mm
Sand: 2 mm to 0.05 mm
Silt: 0.05 mm to 0.002 mm
Clay: < 0.002 mm

16.  In nature, soils are three-phase systems.
 solid
 Water and gas

17.  The void ratio, e, is the ratio of the volume of voids to
the volume of soil solids in a given soil mass.
 The porosity, n, is the ratio of the volume of voids to
the volume of the soil specimen.
or
 The degree of saturation, S, is the ratio of the volume
of water in the void spaces to the volume of voids.
Vs
Vv
e 
V
Vv
n 
e
e
n


1
  100% 
Vv
Vw
S
Vs
Vv
e 

18.  The weight relationships are moisture content:
Moisture content =
 saturated unit weight:
Moist unit weight =
 dry unit weight
Dry unit weight =
 When a soil mass is completely saturated the moist unit
weight of a soil becomes equal to the saturated unit
weight, So = if Vv =Vw
100% 






Ws
Ww
W
V
W

V
Ws
d 
sat

19.  In granular soils, the degree of compaction in the field
can be measured according to the relative density,
defined as: The ratio of the density of a substance to
the density of a standard

20. The denseness of a
granular soil is
sometimes related to the
soil’s relative density.
Table 2.5 shows

21.  When a clayey soil is mixed with an excessive amount
of water, it may flow like a Semi-liquid.
 If the soil is gradually dried, it will behave like a
plastic, semisolid, or solid material, depending on its
moisture content.
 The moisture content, in percent, at which the soil
changes from a semi-liquid to a plastic state is defined
as the liquid limit (LL).

22.  The moisture content, in percent, at which the soil
changes from a plastic to a semisolid state is called
plastic limit (PL).
 Semisolid to a solid state are defined as the shrinkage
limit (SL). Or
 Shrinkage limit is defined as the moisture content at
which the soil does not undergo any further change in
volume with loss of moisture

23.  The liquid limit of a soil is determined by
Casagrande’s liquid device (ASTM Test
Designation D-4318) and is defined as the moisture
content at which a groove closure of 12.7 mm (1/2
in.) occurs at 25 blows.

24.  The plastic limit is defined as the moisture content at
which the soil crumbles when rolled into a thread of
3.18 mm (1/8 in.) in diameter (ASTM Test
Designation D-4318).

25.  The difference between the liquid limit and the plastic
limit of a soil is defined as the plasticity index (PI)
 solid semi-solid plastic state liquid
 increase moist
 volume of mixture
SL PL LL
Moist content

26.  The liquidity index (LI) is used for scaling the
natural water content of a soil sample to the limits.
 It can be calculated as a ratio of difference between
natural water content, plastic limit, and liquid limit:
where “W” is in situ moisture content of soil.
PLLL
PLW
LL




27.  Effective stress is a force that keeps a collection of
particles rigid.
 The total stress at a given point in a soil mass can be
expressed as
where
 = total stress
 ‘= effective stress
 u = pore water pressure
u '



28.  The effective stress( ‘) is the vertical component of
forces at solid-to-solid contact points over a unit
cross-sectional area.


whu 2
21 hh sat 

29.  The total vertical stress at any point
 The pore pressure is
 The effective vertical stress =
Total vertical stress –pore pressure
h 
 ww hhu  
u '

30.  process of making something stronger or more solid.
 In the field, when the stress on a saturated clay layer
is increased for example by the construction of a
foundation, the pore water pressure in the clay will
increase.
 Because the hydraulic conductivity of clays is very
small, some time will be required for the excess
pore water pressure to dissipate and the increase in
stress to be transferred to the soil skeleton.

31. u At time t = 0

32.  Hence, the increase in effective stress at time t = 0 will
be
 Theoretically, at time t= when all the excess pore
water pressure in the clay layer has dissipated as a
result of drainage into the sand layers.
At time =
 Then the increase in effective stress in the clay layer is.
0'  u

0u 






'
0'
' u

33.  This gradual increase in the effective stress in the
clay layer will cause settlement over a period of time
and is referred to as consolidation.
 TEST(ASTM Test Designation D-2435)
 specimen size
2.5 in dai.
1 inch height
 Place inside.
 Reading 24 h.

34.  Load is doubled and more settlement reading are
taken.
 all times during the test, the specimen is kept under
water.
 The procedure is continued until the desired limit of
stress on the clay specimen is reached.

36. ANY QUESTION
?