Factors to Consider in Foundation Design, Footing Depth and spacing, Location Considered for Footing , Soil Settlement, Net vs Gross pressure(Design soil pressure),EROSION/SCOURING PROBLEMS FOR STRUCTURES ADJACENT TO FLOWING WATER,Corrosion Protection, Water table fluctuation, Foundation in sand and silt deposit ,Foundation on loess and other collapsible soils,Foundation on clays and clayey silts, IS code Method,

1. FACTORS TO CONSIDERED IN
FOUNDATION DESIGN AND
NUMERICAL BASED ON BIS
METHOD
SUBMITTED BY
ABHISHEK KUMAR(202301)
ABDUL NASHITH (202302)
ANKAJ KUMAR(202304)

2. Factors to Consider in Foundation Design
a) Footing depth and Spacing
b) Location considered for footing
c) Soil Settlement
d) Net vs Gross soil pressure
e) Erosion problems for structure adjacent to flowing water
f) Corrosion protections
g) Water table fluctuation
h) Foundation sand and silt
i) Foundation on clay and clayey silt
j) Foundation on loess and other collapsible soils

3. Footing Depth and spacing
• The frost line
• Zones of high volume change due to moisture fluctuation
• Topsoil of organic materials
• Peat and muck
• Unconsolidatedmaterials such as abandoned garbage dumps and similar filled in areas.
• Scour Depth
• Root holes
• Underground defects

4. Location Considered for Footing
• Load of structure
• Soil bearing capacity
• Soil types
• Ease of construction
• Water table level
• Natural Disaster and Exreme
• Economic design

5. Soil Settlement
The soil might get settled after installing a foundation. Settlement is time
dependent and results from gradual reduction of volume of saturated soils. If
the foundation is placed on loose soil, there is possibility that the foundation
would be settled overtime gradually.
A geotechnical engineer shall verify the bearing capacity of soil to ensure that
load will not have any negative effect on soil to settle. Prior to foundation
installation, the soil shall be compacted to a degree recommended by
geotechnical report.

6. Net vs Gross pressure(Design soil pressure)
• The bearing capacity equation are based on gross soil pressure qult which is
everything above the foundation level. If the allowable pressure is based on
the bearing equation, the pressure is a gross pressure.
• Settlement are caused only by net increase in pressure over the existing
overburden pressure , if the allowable pressure is based on settlement
consideration, it is a net pressure.

7. EROSION/SCOURING PROBLEMS FOR
STRUCTURES ADJACENT TO FLOWING WATER
• Bridges, piers, abutments, bases for retaining walls and footings for other structures adjacent
to or located in flowing water must be located at a depth that erosion or scour does not
undercutthe soil and cause a failure.
• An accurate predictionof scour depth is necessary as to use the shortest possible pile lengths.
Approachesto avoid Scouring
• Scour is accelerated if the foundation creates, channels, obstruction; to reduce scour, the
foundationshould create a minimum obstructionto normal stream flow patterns.
• Determine the foundationtypes
• Estimate the probabledepth of scour effect etc

8. Corrosion Protection
• In polluted ground areas such as old sanitary landfills, shorelines, near sewer
outfalls line from older industrial plants or backwater areas where water stands over
dead vegetation, there can be corrosion problem with metal foundation members as
well as concrete. Concrete is generally resistant to corrosion.
• However, if sulphates are present, it may be necessary to use sulfate resistant
concrete.
• It may occasionally be necessary to use air-entrained concrete for foundation
members.
• Use of treated timber piling instead of metal piling may be required where the soil
has a PH much above 9.5 or below 4.0

9. Water table fluctuation
A lowered water table increases the effective pressure and may cause additional
settlements. A raised table may create problem for the owner from the
following:
• Floating the structure i.e. making it unstable or tilting it
• Reducing the effective pressure creates excessive settlement
• Creating a wet basement if the basement walls are not watertight

10. Foundation in sand and silt deposit
Foundation on sand and silt require consideration of the following:’
• Bearing capacity
• Densification of loose deposits to control settlement
• Placing the footing at a sufficient depth that the soil beneath the footing is
confined. If the silt or sand is not confined, it will roll from the footing
perimeter with a loss of density and bearing capacity

11. Foundation on loess and other collapsible soils
Collapsible soils are generally wind-blown (aeolian) deposits of silts dune
sands and volcanic ash. Typically they are loose but stable, with contact points
well-cemented with water-soluble bonding agent so that certain conditions of
load and wetting produce a collapse of the soil structure with a resulting
settlement.

12. Foundation on clays and clayey silts
Clay and clayey silts may range from very soft, normally consolidated, to very
stiff, highly over consolidated deposits.
Major problem are often associated with the very soft to soft, deposits from
both bearing-capacity consideration and consolidated settlements.

13. IS code Method
IS 6403:1981 gives the net ultimate bearing capacity of soil which is similar to
vesic method
qnu = c Nc sc dc ic + q (Nq-1) sq dq iq + 0.5 B ɣ Nɣ sɣ dɣ iɣ W’
Where q= effective pressure at the base
W’ – take into account the effect of water table.
Nc ,Nq, Nɣ are bearing capacity factor and can be find out with the help of IS
6403:1982 in Table 1 clause 5.1.1.
Shape factors sc , sq, sɣ are give in IS 6403:1982 of table 2 of clause 5.1.2

14. Depth factor can be calculated with the help of IS 6403:1982 clause 5.1.2.2
Inclination factor can be calculated with the help of IS 6403:1982 clause
5.1.2.3

16. Numerical based on IS Code method