Download standard penetration test

PREPAID BY :
(1) LAD PARTH J:130500106022
(2) PATEL RIYA K:130500106034
(3) RATHWA AARTI : 130500106041
(4)TANDEL HETAL J: 13050010051
GUIDANCE:
(1) VIKRANT SIR
(2) RATAN SIR
REFERANCE:
RANGWALA ,
B C PUNMIYA
SITE INVESTIGATION & SUB – SOIL EXPLORATION
(a) FOR NEW STRUCTURES
1.
THE SELECTION OF TYPE AND DEPTH OF FOUNDATION.
2.
THE DETERMINATION OF BEARING CAPACITY OF THE SELECTED FOUNDATION.
3.
THE PREDICTION OF SETTLEMENT OF THE SELECTED FOUNDATION.
4.
THE DETERMINATION OF THE GROUND WATER LEVEL.
5.
THE EVALUATION OF THE EARTH PRESSURE AGAINST WALLS, BASEMENTS, ABUTMENTS ETC.
6.
THE PROVISION AGAINST CONSTRUCTIONAL DIFFICULTIES.
7.
THE SUITABILITY OF SOIL AND DEGREE OF COMPACTION OF SOIL.
(B) FOR EXISTING STRUCTURES
1. THE INVESTIGATION OF THE SAFETY OF THE STRUCTURE.
2. THE PREDICTION OF SETTLEMENT.
3. THE DETERMINATION OF REMEDIAL MEASURES IF THE
STRUCTURE IS UNSAFE OR WILL SUFFER DETRIMENTAL
SETTLEMENT.
SITE EXPLORATION
THE OBJECT OF SITE EXPLORATION IS PROVIDE RELIABLE, SPECIFIC AND DETAILED INFORMATION
ABOUT THE SOIL AND GROUND WATER CONDITIONS OF THE SITE WHICH MAY BE REQUIRED
FOR A SAFE AND ECONOMIC DESIGN OF FOUNDATIONS. FOR THIS PURPOSE, AN EXPLORATION
OF THE REGION LIKELY TO BE AFFECTED BY THE PROPOSED WORKS SHOULD YIELD PRECISE
INFORMATION ABOUT THE FOLLOWING:
i.
THE ORDER OF OCCURRENCE AND EXTENT OF SOIL AND ROCK STRATA.
ii.
THE NATURE AND ENGINEERING PROPERTIES OF THE SOIL AND ROCK FORMATION, AND
iii.
THE LOCATION OF GROUND WATER AND VARIATION.
METHODS OF SITE EXPLORATION
1. OPEN
METHODS
2. BORINGS
3. SUB SURFACE
EXCAVATION
4. GEO
PHYSICAL
SOUNDINGS
Boring :
The various boring methods adopted for soil exploration are
as follows:
1.
2.
3.
4.
5.
Wash boring
Auger boring
Rotary drilling
Percussion drilling
Auger and Shell boring
Auger Boring
This type of augers are commonly used
for clayey or sandy soils or soft soils. It
can be operated manually or
mechanically. The hand operated augers
are used up to 6 meter depth and the
mechanically operated augers are used
for greater depth up to 15 meter.
The auger is vertically driven into the
ground by roating its handle and is
pressed down during the process of
rotation.
At every 30 cm. depth of penetration,
the aiger is drawn out and the samples
of soils are collected separately for
testing.
Wash boring
 This boring is used for testing of depth
3 meter soft to stiff cohesive and sandy
soils.
 In this method, the casing pipe is driven
into the ground for a certain, through
which a hollow drilled rod with a sharp
chisel or chopping bit at its lower end
is inserted.
 The water is forced with pressure
through the drill rod, which is
alternatively raised, dropped and
rotated.
 The chopping and jetting action of the
bit and water disintegrates the soil.
STANDARD PENETRATION TEST
THE STANDARD PENETRATION TEST IS THE MOST COMMONLY USED IN-SITU TEST, ESPECIALLY FOR
COHESIONLESS SOIL WHICH CANNOT BE EASILY SAMPLE.
THE TEST IS USEFUL FOR DETERMINING
• THE RELATIVE DENCITY OF SOIL
• THE ANGLE OF SHEARING RESISTANCE OF COHESIONLESS SOILS
• UNCONFINED COMPRESSIVE STRENGTH OF COHESIVE SOILS
THE STANDARD PENETRATION TEST IS CONDUCTED IN A BORE HOLE USING A STANDARD SPLIT
SPOON SAMPLER . THE SAMPLER IS DRIVEN INTO THE SOIL BY A DROP HAMMER 65 KG MASS
WITH A FREE FALL OF 750 MM.
THE TEST PROCEDURE IS STANDARDISED AND SET OUT IN THE IS : 2131-1981 – ‘ STANDARD
PENETRATION TEST’.
THE NUMBER OF HAMMER BLOWS REQUIRED FOR 150 MM PENETRATION IS COUNTED. THE
SAMPLER IS FURTHER DRIVEN OF HAMMER BLOWS REQUIRED FOR 150MM PENETRATION IS
COUNTED.
THE NUMBER OF BLOWS RECORDED FOR THE LAST TWO 150 MM INTERVALS ADDED TO GIVE
THE STANDARD PENETRATION NUMBER (N).
IN OTHER WORDS,THE ‘ SPT VALUE’ IS EQUAL TO THE NUMBER OF BLOWS REQUIRED FOR
300 MM OF PENETRATION BEYOND A SEATING DRIVE OF 150MM.
THE SPT VALUE (N- VALUE) IS CORRECTED FOR
(1) DILATANCY CORRECTION
(2) OVERBURDEN PRESSURE CORRECTION
1.
DILATANCY CORRECTION
TERZAGHI AND PECK (1967) RECOMMENDAD THE FOLLOWING CORRECTION IN THE CASE OF
SILTY FINE SANDS WHEN THE OBSERVED VALUE OF N EXCEEDS 15.
NC = 15 + 1/2 [NR - 15]
WHERE,
NC = CORRECTED SPT VALUE
NR = RECORDED SPT VALUE
• GEOPHYSICAL METHODS:
THE STRATIFICATION OF SOILS AND ROCKS CAN BE DETERMINED BY GEOPHYSICAL METHODS OF
EXPLORATION WHICH MESSURES CHANGES IN CERTAIN PHYSICAL CHARACTERISTICS OF THESE
MATERIALS,FOR EXAMPLE DENSITY,MAGNETISM,ELECTRICAL RESISTIVITY,ETC.
THE FOLLOWING TWO GEOPHYSICAL METHODS ARE COMMONLY USED:
(I)SEISMIC REFRACTION METHOD
(II)ELECTRICAL RESISTIVITY METHOD
(I)SEISMIC REFRACTION METHOD:
THE SEISMIC REFRACTION METHOD IS BASED ON THE PRINCIPAL THAT SEISMIC WAVES HAVE
DIFFERENT VELOCITIES IN DIFFERENT TYPES OF SOIL.
THE SEISMIC REFRACTION METHOD IS MORE SUITED TO SHALLOW EXPLORATION FOR CIVIL
ENGINEERING PURPOSES.
•
THE ELECTRICAL RESISTIVITY D IS GIVEN BY
ℓ=2*3.14*D*V/I
ℓ=MEAN RESISTIVITY (OHM/M)
D=DISTANCE BETWEEN ELECTRODES (M)
V =POTENTIAL DROP BETWEEN TWO INNER ELECTRODES (VOLTS)
I=CURRENT APPLIED BETWEEN TWO OUTER ELECTRODES (AMPERES)
LIMITATIONS:
(I)THE METHODS ARE CAPABLE OF DETECTING ONLY THE STRATA HAVING DIFFERENT ELECTRICAL
RESISTIVITY.
(II)THE SERVICES OF AN EXPERT IN THE FIELD ARE NEEDED.
• PLATE LOAD TEST:
PLATE LOAD TEST IS A FIELD TEST TO DETERMINE THE ULTIMATE BEARING CAPACITY OF SOIL ,AND THE
PROBABLE SETTLEMENT UNDER A GIVEN LOADING.
THE TEST ESSENTIALLY CONSISTS IN LOADING A RIGID PLATE AT THE FOUNDATION LEVEL, AND DETERMINING
THE SETTLEMENTS CORRESPONDING TO EACH LOAD INCREMENT.
THE SIZE OF SQUARE BEARING PLATE MAY BE 30 CM*30 CM OR 75 CM* 75 CM. THE THICKNESS OF PLATE
SHOULD NOT BE LESS THAN 25 MM.
THE TEST PIT WIDTH IS MADE FIVE TIMES THE WIDH OF THE BASE PLATE BP.
BF=5BP
DP/BP=FOUNDATION OF DEPTH/FOUNDATION OF WIDTH=DF/BF
WHERE,
BP=WIDTH OF PLATE
BF=WIDTH OF FOUNDATION
DF=DEPTH OF FOUNDATION
DP=DEPH OF HOLE
• THE LOADING OF THE TEST PLATE MAY BE APPLIED WITH THE HELP OF A HYDRAULIC JACK.
• THE REACTION OF THE HYDRAULIC JACK MAY BE BORNE BY EITHER OF THE FOLLOWING TWO
METHODS
(I)GRAVITY LOADING PLATFORM METHOD
(II)REACTION TRUSS METHOD
INCASE OF GRAVITY LOADING METHOD , A PLATFORM IS CONSTRUCTED OVER A VERTICAL
COLUMN RESTING ON THE TEST PLATE, AND THE LOADING IS DONE WITH THE HELP OF SAND
BAGS, STONES OR CONCRETE BLOCKS.