P. JOHN VICTOR
RESEARCH OFFICER
A.P. Engineering Research Laboratories,
Himayatsagar, Hyderabad –500 030.
Site Selection for Dam
i)
Geographical Location – Configuration,
Contours, Gorge Portion, Valley Shape
ii)
Sound Foundation
iii)
Borrow Area Selection – Nearby.
iv)
Spillway Section.
v)
Submergence Consideration
vi)
Facility of Transportation
vii)
Controlled Pollution – Deforestation
Why “Foundation Soil” Studies?
If Foundation Soils are of :
i)
Rock Foundation – Less Problematic,
Grouting to take care of sliding at joints,
Seepage control, Field Permeability
Tests, Geologist’s Report.
ii)
Gravel and Dense Sands – Stability is
not the problem but Seepage.
Contd...
If Foundation Soils are of :
iii)
Fine Sands – Problem of liquefaction due to
sudden stress, earth quakes, ....
Application of sudden shear stress prevents
drainage
Large pore pressures.
Better to Compact or Remove it.
Seepage control measures are to be taken.
iv)
Clay Foundations – High Plasticity, Low Shear
Strength, Slow rate of Consolidation,... Leads to
Stability Problem.
Remedy is flattening of slopes, ground
improvement methods.
Contd...
If Foundation Soils are of :
v)
Mixed Layers – Strata of impervious nature at
top and pervious soils at depths – high seepage
pressures at the toe of the Dam.
Remedy is proper drainage and / or loading berm
to avoid the danger of blow or piping.
vi)
Miscellaneous – Actual conditions at the site can
be more and more complex !!!
EARTHEN EMBANKMENTS
MAIN ZONES (FOR SOIL TESTING):

HEARTING

CASING

COT

FILTERS
TESTS ON SOILS FOR
IRRIGATION PROJECTS
• Pre Construction
• During Construction
• Post Construction
WHY PRE CONSTRUCTION SOIL
EXPLORATION?
• Determination of Site Characterization
• For bringing out deficiencies / evaluating
strength
• For arriving at Suitability / Improvement
• To provide design inputs in an unambiguous
manner - more realistic
• To evolve a proper and adequate design avoiding assumptions
PRE CONSTRUCTION
TESTS
a) Along Proposed Axis (Foundations)
b) Borrow Area Soils
c) Spillway Location
d) CM & CD Works
e) CNS Soils for Canals
f) Filters
a) ALONG PROPOSED AXIS
(FOUNDATIONS)
• CLASSIFICATION TESTS:
– Mechanical Analysis
• Sieve Analysis
• Hydrometer Analysis
– Atterberg Limits
• Liquid Limit
• Plastic Limit
• Shrinkage Limit
a) ALONG PROPOSED AXIS
(FOUNDATIONS) Contd..
•
•
•
•
LABORATORY / INSITU PERMEABILITY TEST
DIFFERENTIAL FREE SWELL TEST
FIELD DENSITIES & MOISTURE CONTENT
SHEAR PARAMETERS
– TRIAXIAL SHEAR TEST
– DIRECT SHEAR TEST
– UNCONFINED COMPRESSION TEST
• CHEMICAL ANALYSIS
• BEARING CAPACITY COMPUTATIONS
b) TESTS ON BORROW AREA
SOILS
• CLASSIFICATION
• LABORATORY PERMEABILITY TEST
• DIFFERENTIAL FREE SWELL TEST
( IF DFS > 50% , BETTER TO CONDUCT SWELL
PRESSURE TEST )
• PROCTOR’S COMPACTION TEST
• SHEAR PARAMETERS
– TRIAXIAL SHEAR TEST
– DIRECT SHEAR TEST
– UNCONFINED COMPRESSION TEST
• CHEMICAL ANALYSIS
• EFFECTIVE STRESS PARAMETERS
c) TESTS FOR SPILLWAY
CONSTRUCTION
• INSITU PERMEABILITY TESTS
– SINGLE PACKER METHOD
– DOUBLE PACKER METHOD
(TO DECIDE ABOUT THE GROUTING)
• FIELD ROCK SHEAR TEST
(TO ASCERTAIN THE BOND BETWEEN
THE NATURAL ROCK AND CONCRETE)
• GEOLOGIST’S REPORT
d) TESTS FOR CM & CD WORKS
• COLLECTION OF UNDISTURBED SOILS
(TO COMPUTE THE SAFE BEARING
CAPACITY)
• DIFFERENTIAL FREE SWELL
• PLATE LOAD TEST
e) TESTS ON CNS SOILS
• MECHANICAL ANALYSIS
– SIEVE ANALYSIS
– HYDROMETER ANALYSIS
• ATTERBERG LIMITS
– LIQUID LIMIT
– PLASTIC LIMIT
• SWELL PRESSURE TEST
REQUIREMENTS TO USE AS
CNS SOIL
•
•
•
•
•
•
•
GRAVEL ( > 2 MM )
0 – 10%
SAND ( 2 - 0.06 MM )
30 – 40%
SILT ( 0.06 – 0.002 MM ) 30 – 40%
CLAY ( < 0.002 MM )
15 – 20%
LIQUID LIMIT
30 – 50%
PLASTIC LIMIT
20 – 25%
SWELL PRESSURE
< 0.10 Kg/Sq.Cm.
IS 9451-1994
f) TESTS FOR FILTERS
• MECHANICAL ANALYSIS
– SIEVE ANALYSIS
– HYDROMETER ANALYSIS
– GRADATION CURVE
FILTERS
(IS 9429 – 1980)
Need of Filters:
Transition filters are required between
impervious zones of fine grained soils, and
pervious zones or drains of coarse material to
prevent migration of soil grains from the former
to the latter. As the direction of seepage is
towards the upstream face at the time of
drawdown, such filters are needed both on the
Upstream and downstream side of the core.
FILTERS
Requirement of a Filter:
a)
Its voids should not permit the
migration of the particles from the
protected zone.
b)
It should be sufficiently more
pervious than the protected zone to
induce a sharp reduction in
hydraulic gradient.
Contd...
Requirement of a Filter:
D15 of filter
D85 of protected soil
D15 of filter
D15 of protected soil
D50 of filter
D50 of protected soil
<5
> 4 & < 20
< 20
FILTERS
Thickness of Filter:
a) Horizontal Filter – 15 to 30 Cm.
b) Vertical Filter – 1.00 to 1.50 m.
INSITU
TESTING PROCEDURES
& THEIR IMPORTANCE
TYPES OF INSITU
PERMEABILITY TESTS
IN ROCKY STRATA :
• SINGLE PACKER METHOD
• DOUBLE PACKER METHOD
IN SOILS :
• JAPANESE METHOD
• PUMPING IN TEST
• PUMPING OUT TEST
IMPORTANCE OF PERMEABILITY DATA
• CORE LOGGING OF A BORE HOLE
PROVIDES INFORMATION ON THE PHYSICAL
CONDITION OF THE ROCK MASS
• WATER PERCOLATION TESTS –
PERMEABILITY RESULTS OF A STRATA
SUPPLEMENTS INFORMATION ON THE
DRILL HOLE DATA
• WHAT CAN BE THE LOSS DUE TO FEATURES
SUCH AS THESE IF STORAGE STRUCTURES
CONTEMPLATED?
PERMEABILITY
• THE STATE OF WATER MOVEMENT BELOW THE
SURFACE THROUGH A MEDIUM IS CALLED
PERCOLATION AND THE MEASURE OF MOVEMENT
CALLED PERMEABILITY
DARCY’S LAW
• THE FLOW RATE IS PROPORTIONAL TO THE CROSS
SECTIONAL AREA OF A MEDIUM THROUGH WHICH THE
WATER FLOWS
• FOR UNIT CONDITIONS THE EQUATION CAN BE WRITTEN AS
Q= KA h/l where
K= Co-efficient of permeability
Q= quantity of water discharge per unit area of time
A= cross sectional area through which it flows
h= hydraulic head variation
l= the distance in which the head is lost
• The Eqn can be re-written as K= Q/A . L/h
• Temp and viscosity although affect they are not considered because
the effect on flow of water is insignificant
WHAT IS LUGEON VALUE?
• THE UNITS ARE NORMALLY EXPRESSED IN
feet/year; cm/sec; m/sec; feet/day etc.
• Another unit commonly used is Lugeon named after a
French Engineer M.Lugeon who conceived carrying out
water pressure tests
• One lugeon is defined as the quantity of water lost in
litres/min per metre cross sectional area of bore hole at a
pressure of 10 bars
• Because of adoptability water tests in river valley
projects use this unit which is equivalent to 10 feet/year
or 10-5 cm/sec or 10-7 metre/sec
PACKER TESTS OR PUMP IN METHOD
• SINGLE PACKER METHOD AS THE
BORE HOLE PROGRESSES
OR
• BY DOUBLE PACKER METHOD AFTER
COMPLETION OF BOREHOLES
• EQUIPMENT REQUIRED ARE DRILLING
EQUIPMENT, PRESSURE GAUGE,
PUMP, WATER FEEDER LINES, DRILL
ROD, PERFORATED ROD AND OTHER
FITTINGS WATER METER ETC
METHODOLOGY
• A MEASURED QUANTITY OF WATER IS PUMPED
INTO THE BOREHOLE UNDER KNOWN PRESSURE
FOR A UNIT LENGTH OF SECTION
• WATER LOST OBSERVED FOR 3 CONTINUOUS
READINGS FOR SPECIFIC TIME DURATION.
• LUGEONS CALCULATED
PRECAUTIONS
• SATURATION OF THE TEST SECTIONS FOR A
SPECIFIED PERIOD
• CALIBRATION OF PRESSURE GAUGES, WATER
METRES ETC
• USE OF CLEAN WATER TO PREVENT CLOGGING OF
THE FEATURES- USE OF SETTLING TANKS
• OTHERWISE PERMEABILITY CALCULATIONS CAN
BE GROSSLY MISLEADING
PROCEDURES
• TESTS TO BE PERFORMED UNDER UNCASED
SECTIONS AND UNGROUTED SECTIONS AND
WHERE DRILLING MUD USED TO BE AVOIDED
• PRELIMINARY DRILLING DATA SUCH AS CORE
LOSS, COLLAPSED SECTIONS, CHANGE IN
LITHOLOGY THEREORE CHANGE IN PERMEABILITY
CHRACTERISTICS, POSSIBILITY OF PACKER
GETTING STRUCK OR WIDER SECTIONS WHERE
PACKER WILL NOT BE SEATED PROPERLY TO BE
GATHERED
• SINGLE PACKER TESTCAN BE PERFORMED IN
HOLES CASING NOT REQUIRED EVEN FOR SOFT
SANDSTONE ETC OR WHERE HIGHLY
FRACTURED/SHEARED SECTION OF BORE HOLE
• IN DOUBLE PACKERS THOUGH EFFICIENT LEAK
THROUGH THE LOWER PACKER CAN GO
UNNOTICED LEADING TO ERRONEOUS RESULTS
• TEST SECTIONS IN ANY CASE SHOULD NOT BE
LESS THAN FIVE TIMES THE DIAMETER OF THE
BOREHOLES
• CYCLIC TESTS ARE PERFORMED TO DETERMINE
WASHABILITY AND GROUTABILITY OF JOINTS
• PRESSURES TO BE APPLIED IS EITHER GOVERNED
BY THE COVER OF ROCK
• OR THE FOUNDATION THAT CAN WITHSTAND
WITHOUT HEAVING SUBJECT TO MAXIMUM HEAD
OF THE RESERVOIR TO BE IMPOUNDED
LUGEON CALCULATIONS:
Lugeon Value = Intake water in Lt/min/mt X 1MPa
Test Pressure (MPa)
1 Kg/cm2 = 10 m head
Q = 1.25 Lt/5 min or
= 0.0833 Lt/min/mt for 3 m test section
H1 = 8.68 m or 0.868 Kg/cm2
H2 = 10 m or 1.00 Kg/cm2
Test Pressure = 1.868 Kg/cm2
= 0.1868 MPa
Lugeon Value = 0.833/0.1868 = 0.45 Lugeons
H1 = Distance between centre of test section & swivel
H2 = Applied Pressure
SIZES OF DRILL HOLES
Size of Casing
Dia. of hole in mm.
EX
38.1
AX
48.4
BX
60.3
NX
76.2
JAPANESE METHOD:
2 ft X 4 ft pit
¼ : 1 slope
Leave first two readings for one hour each. Then take
another minimum of 3 – 4 readings hourly.
4 ft X 4 ft …. Repeat same procedure.
BUT….
DEPTH = 1 ft 9 inches and @ 3 inches, tie
thread to measure water.
Find difference in discharge
Difference X 21.2 = k X 10-6 cm/sec
GROUTABILITY VS PERMEABILITY
• MEDIA INDICATING LESS THAN ONE LUGEON
NORMALLY COULD NOT BE GROUTED
• BETWEEN ONE TO FIVE LUGEONS USE OF
APPROPRITAE PRESSURES AND DETERMINATION
OF POST GROUT PERMEABILITY TESTS REQUIRED
FOR CROSS CHECKING
PLATE LOAD TEST
INSITU ROCK SHEAR TEST
LABORATORY
TESTING PROCEDURES
SOIL CHARACTERISATION

IDENTIFICATION

MECHANICAL ANALYSIS
 SIEVE ANALYSIS
 HYDROMETER ANALYSIS

ATTERBERG’S LIMITS
 LIQUID LIMIT
 PLASTIC LIMIT
 SHRINKAGE LIMIT

CLASSIFICATION

NOTATIONS: G – S – M – C – W – P – H – I – L – O – Pt
GC – GW – CH – ML .......
SC–SM; GC–SC
SIEVE ANALYSIS
Why? – To know the grain size distribution of
coarse grained soils (gravel & sand)
For gravel
For Sands
40 mm
2.000 mm
25 mm
0.600 mm
12.5 mm
4.75 mm
0.425 mm
0.250 mm
0.150 mm
0.075 mm
ADD DISPERSIVE AGENT
SIEVE SETS
SIEVE SHAKER
HYDROMETER ANALYSIS
Why? – To know the grain size distribution of
fine grained soils (silt & clay)
Grain Size Distribution
Clay
Silt
Particle 0.002
size in
mm
Sand
0.075
Gravel
4.75
Cobbles
75
GRAVEL
4.75
FINE
SAND
0.075
FINE
0.425
2.00
MEDIUM
4.75
COARSE
20
75
COARSE
Boulders
300
ATTERBERG’S LIMITS
Vol.
Cu.Cm.
Solid
SemiSolid
Plastic
SL
PL
Moisture content (%)
Liquid
LL
CASAGRANDE’S LIQUID LIMIT DEVICE
Specific Gravity
It is the ratio of the mass of a given volume of solids to the mass of
an equal volume of water at 4 o C.
DIFFERENTIAL FREE SWELL TEST
Free Swell Index test
IS: 2720 part 40
Graduated glass cylinders100ml
sample passing 425 micron sieve
10mg in each cylinder
kerosene in one and
distilled water in another
FSI in % expansiveness
< 20
low
20-35
moderate
35-50
high
> 50
very high
Free Swell Index: It indicates the Expansive
qualities of soil. It gives the amount of
volume increase of soil on coming in contact
with water
DIRECT SHEAR TEST
SET UP FOR
TRIAXIAL
COMPRESSION TEST
1.5“ DIA.
3.0“ HEIGHT
(–) 4.75 mm SOIL
1.25 mm/min
PROCTOR’S COMPACTION TEST
Why? – To find out the Maximum Dry Density
(MDD) and Optimum Moisture Content (OMC)
of a soil under a particular compactive effort.
Heavy compaction
(5, 25, 45, 4.9)
Dry Density
(gm/cc)
Light compaction
(3, 25, 31, 2.6)
MOISTURE CONTENT (%)
PROCTOR’S COMPACTION
APPARATUS