SUB SURFACE INVESTIGATION

PREPAID BY : (1) LAD PARTH J: (2) PATEL RIYA K: (3) RATHWA AARTI : (4)TANDEL HETAL J: 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 2. BORINGS 3. SUB SURFACE 4. GEO METHODS EXCAVATION PHYSICAL SOUNDINGS

Boring : The various boring methods adopted for soil exploration are as follows: 1.Wash boring 2.Auger boring 3.Rotary drilling 4.Percussion drilling 5.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 : – ‘ 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 = /2 [N R - 15] WHERE, N C = CORRECTED SPT VALUE N R = 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.

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