1. INTRODUCTION:

M/S. SUB SOIL INTERNATIONAL has been awarded the opportunity to work at the proposed site for sub soil investigation including necessary laboratory tests to prepare this report. The soil condition of the area corresponding to bearing capacity, shearing resistance and settlement characteristics. This report contains relevant data in the form of drawing, bore- logs, curves & graphs for necessary case in addition to the abstract of the test results. Discussion and recommendation about the appropriate type of foundation for the probable load has been made with the results obtained in the field & in the laboratory. In the present report, a brief description of the techniques employed during the field works and the methods used in the laboratory test have been presented with significance.

2. PURPOSE:

Sub- soil investigation is predominant feature for designing foundation of important structure in an intelligent, economic and satisfactory manner. Both the result of field & laboratory tests are essential to obtain in formation require by the structural engineer to design the appropriate type of foundation. The purpose of the investigation was to ascertain depth Sequence and thickness, shearing resistance & settlement characteristics of sub- soil and eventually to establish their physical properties for safe and economic design of foundation.

3. SCOPE OF WORK :

The main scopes of the investigation work were:a) Reconnaissance survey of the site and fixing the exact points for boring holes.b) Drilling of exploratory borings the proposed depths determine the sequence of

strata and the depth of each strata.c) Execution of standard penetration test at 1.5m (5ft.) intervals of depth to

ascertain Relative state of compaction and to closely evaluate allowable bearing capacity.

d) Collection of representative disturbed and undisturbed samples of the soil for Laboratory tests and visual classifications.

e) Measuring ground water table in all bore holes.f) Execution of various laboratory tests with some selected samples to determine

Mechanical and physical characteristics of the soil.

4. FIELD WORK:4.1 Execution of boring by percussion method :

The exploratory borings has been executed at the fixed points by the percussion method in the following way. First and 4’diameter-casing pipe was driven vertically into the ground to a sufficient depth a chopping bit attached to the lower end of a drill rod was lowered into the casing pipe and moved up and down with the help of a rope. The other end of the drill rod was fitted with a swivel head, which was connected to a water pump through high-pressure hospice. The up and down movement of the drill rod held the chopping bit to disintegrate the soil and make it loose. The water circulated through the swivel head into the drill rod and was emerged through the process of the chopping bit at a high pressure. Water then rose

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up the annular space between the drill rod and the casing and carried the loose soil out of the drill hole witch was advance in this way. The hole was always kept full with water. As a result the excess hydrostatic pressure above the formation water pressure prevented the uncased wall of the hole from collapsing. In case of loose sandy soil, special type of drilling mud is used which firms a thin lining on the wall of the boring and prevents the hole from collapsing. The number of blows (N) necessary to produce the penetration was recorded in three different stages at six inches interval.

4.2 EXECUTION OF STANDARD PENETRATION TEST:The standard penetration test was performed at 5ft intervals in all the borings. The test were executed by using a split spoon sampler of 1.75 inches inner and 2 inches outer diameter having an over all length of 2’-6’’ and a 140 Ib. hammer failing freely from a constant height of 30 inches on the drill rod. The number of blows (N) necessary to produce the penetration was recorded in three different stages at six inches interval. The N-values were taken as summation of the number of blows required in 2nd and 3rd six inches. For executing the test, the sampling spoon was attached to the lower end of the drill rod and the rod was lowered into the bore. The upper end of the drill was fitted with a socket on which a 140 Ibs. Hammer was allowed to fall freely from the required height of 30 inches.

4.3 COLLECTION OF UNDISTURBED SAMPLES:

Undisturbed sampling is very important in soil investigation for determination of some important soil properties, such as shear strength, unit weight, void ratio, compression index Cc. Unconfined compressive strength, angle of internal friction etc. The soil samples are collected from cohesive layers in thin walled sampler having 1/16th inch wall thickness. The length of the tubes is usually 18 to 24 inches. Before collection of a sample the hole is pressed down into the ground from the top is filed with soil sample. After the Shelby tube is taken out of the hole the ends are cleaned and sealed by paraffin wax in order to prevent any change in moisture content.

4.4 COLLECTION OF DISTURBED SAMPLES:Disturbed soil sample were extracted at every 5ft interval or at every change of strata examined the changes in the color and type drill water returned with cuttings of soils from the borehole during operation.The samples were collected by means of split spoon sampler. This sampler was attached to the bottom of the drilling rod in place of the cutting bit and lowered into the hole at the desired depth. It was then driven into soil up to, a measured depth by means of hammering in a prescribed manner and then removed from the holes. 4.5 GROUND WATER TABLE (GWT):The ground water table was recorded in each hole. Measurement for ground water table was taken after an over height stabilization on completion of boring of a hole and followed by another measurement after 24 hours. The last measurement was taken final for ground water table and recorded. During this period the borehole was protected from any physical disturbance of casing.

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5. LABORATORY TEST :

The following laboratory test was done to know the characteristics:

a. Natural moisture content testb. Specific gravity test.c. Atterbarg limits tests.d. Wet &dry density test.e. Complete grain size analysis test.f. Unconfined compression tests.g. Consolidation tests &h. Direct shear tests.

a. Natural moisture content test:

Natural moisture content is one of the most important index properties of fine grained soil witch is used to determine degree of saturation, compressibility, void rate dry unit weight of soil, porosity of soil etc.

The water content of a soil sample is the ratio of the height of the water in the sample to its dry weight. It is usually expressed as a percentage. The soil sample is weighted both natural state and in oven dry state and moisture content is calculated by divided the loose of weight of the sample by the dry of the sample.

b. Specific gravity test:The specific gravity of solid is defined as the ratio of the unit weight of the solid in air to the unit weight of water. To determine the specific gravity of a soil sample of 25 grams of the oven dried sample is thoroughly pulverized and is placed in a calibrate pycnometer.

Water is poured inside the pycnometer until its top slightly in order to calibrated mark. The mixture is than boiled thoroughly in order to eliminate all the air bubbles. More water is then added to the moisture till it touched the calibrated mark. It is then allowed to feel overnight, the temperature recorded and the bottle weighted.

c. Atterbergs limits:Liquid limit is the minimum water content at which a clay soil just starts behaving like a fluid. It is determined with the help of standard liquid limit device which consists of a brass cup and a standard liquid limit device which consists of a brass cup and a arrangement to impart blows to the cup at an uniform rate a grove of standard dimension is cut into a paste of soil contained in the cup the water content at witch 25 blows are sufficient to close the standard groove is termed the liquid limit of the soil sample.

The plastic limit is the minimum water content at which a soil is just plastic and is determined by rolling out a soil sample at a slowly decreasing water content until that water content is reached at which a thread of 1/8” dia just bearing to crumble. The thread is rolled on a grass plate with hand.

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d. Wet, Dry and relative density:

Density of soil samples means mass of the sample per unit of volume. To find the densities of soil samples in undisturbed state, specimens of regular sizes are trimmed out of the original samples and the same are weighed in both natural and oven dry states. Wet density = weight of sample (gm) Volume of sample (cm)

Dry density = wet density 1+w% Where, w water content when saturated, in percent of dry weight.

e. Grain size analysis:A soil may contain various sizes of grains ranging from large boulders, gravel silt, clay and colloids. These dividing lines between the size limits are arbitrary and very with different systems. According to ASTM classification:

Gravel Larger than 4.75 Coarse sand 4.75 to 2.00mm Medium sand 2.00mm to 0.425mm Fine sand 0.425mm to 0.075mm

Fines 0.075mm

f. Unconfined compression test:Unconfined compression test is a simple method for determination of shearing strength of cohesive soil, which is important to determine the bearing capacity of soil. As the name implies, the lateral confining pressure in an unconfined compression test is kept zero. The load is applied directly on the top of the laterally unsupported specimen and a failure is measured. The specimen is prepared from the undisturbed soil sample by carefully trimming it is a cylindrical shape of 2.8” height and 1.4” dia. The specimen is ten placed on the level pedestal of the unconfined compression apparatus in a vertical position. The load is applied axially on the top of the specimen and is distributed uniformly over the surface of the specimen and is distributed uniformly over the surface of the specimen with the help of double providing ring assembly fitted with a strain gauge, fitted with the apparatus. The load is applied at such a rate that the vertical deformation of the sample is nearly 2% per minute in order to avoid any drainage during compression. The load is kept increasing until the specimen fails along its shearing place. The maximum load at failure known as the unconfined compressive strength of the sample.

g. Consolidation Test:The test is performed on a specimen of circular shape of 2.5” dia and 1” thickness. The specimen is prepared from the undisturbed sample by carefully trimming it to the required dimension with the help of cutting edge and aware saw. The specimen is then place in the consolidation ring and its top and bottom are trimmed off level with that of ring. The specimen along with the ring on the top

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and the other at the bottom of the specimen along with the help of a level arrangement fitted with the apparatus. Decreases in volume of specimen are read from a strain gauge attached to the consolidation unit at specified time intervals. The consolidation unit is always kept full with water in order to avoid evaporating of the specimen.

h. Direct shear test:Direct shear test can be performed for both cohesion less and cohesive soil to determine shear strength, angle of internal friction, cohesion c, volume charge etc.

The test is a direct shear machine which consists of a normal loading device, 2”x2” two pieces sample, square box etc.

The rate on shearing displacement of approximately 0.05” per minute is offer used for a sample thickness of about 0.05 inch.

The results of a direct shear test on cohesion less & cohesive soil can be presented in a summary table & by a stress-strain curves.

6. PHYSICAL PROPERTIES:

The physical properties of the soil formation particularly the layer stratification, consistency/ relative density, unit weight, moisture content and specific gravity etc. have been performed by executing different types of field and laboratory tests. The evaluated physical properties of the soil formation of the project area may be summarized as follows:

6.1 Stratification:The overall layer of the investigated are cohesive type soil comprising granular soil of very loose to medium dense fine sand with trace to little silt up to the final depth of boring (ref. Bore logs).

6.2 Specific gravity :The specific gravity of the investigated soil very from 2.65 to 2.98.

7. ENGINEERING PROPERTIES:

The engineering properties of the sub-soil formation of the project area have been evaluated by performing confirmatory laboratory tests on the soil samples collected during field investigation. The overall engineering properties of the investigated layers of soil may be summarized as follows:

7.1 Angle of internal friction:The angle of internal friction of the investigated soil by the performance of direct shear test is found 18.

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8. EVALUATION OF BEARING CAPACITY:

8.1 Shallow foundation:

Cohesive soil:For small jobs where a better economy can be achieved by using a conservative design value based on simple test results. The standard penetration resistance, and the allowable bearing capacity as indicated in the accompanying table (tarzaghi and peck, 1948) are very approximate.

(Ref- foundation design by Wayne C. Teng, Twelfth printing, page-120)

Granular soil:

The allowable soil bearing pressure has been established empirically and may be expressed by the equation.

Qult = 2N2 B Rw + 6 (100+N) 2D Rw

(Ref- foundation Design by Wayne C. v Teng, Twelfth printing, page-118)

Where, Rw & Rw`= Correction factor for position of water table (Ref. Foundation design by Wayne C. Teng, Twelfth printing page-119)

B= Width of footing (Assumed=7ft)D= Depth of footing (Assumed=7ft)N=Corrected SPT value (correction due to overburden pressure)

Correction for Standard penetration resistance, N value:For standard penetration tests made at shallow depth, the number of blows is usually too low. At a grater depth, the same soil with same relative density would give higher penetration resistance.

Two types of corrections are normally applied to the observed N values in cohesion less soil. They are,

Correction due to overburden pressure (For shallow foundation ):-

There are many methods by which correction can be applied due to the effect of overburden pressure. The method that is normally used is the one as:- 50Modified eq. Is N = N′ (---------) P+10

Where, N = adjusted value of standard penetration resistance. N′= standard penetration resistance as actually recorded. P = effective overburden pressure, psi not exceeding 40; = Weight of soil above the level at which the standard.

Penetration test is made. Use buoyant weigh for soil below water level.

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It is recommended at the present time that, if the adjusted N to be used in design should be divided by factor of safety, say=2.0

8.2 Mat foundation:

Using MEYORHOF empirical equation and for 2 inch assumed settlement of Mat as follows:

qa ( Ksf) = ( N/ F2 ) Kd

Where, qa = Allowable bearing capacity for 2 inch settlement in ksf.

F2 = 4 for fps unit. N = Average of N – value in a zone 0.5B above to 2B below of foundation. Kd = 1.0495.

(Ref- foundation analysis and design by Joseph E. Bowles, fifth edition, page-263)

8.3 Pile foundation:

Ultimate End Bearing (P pu): For standard penetration test (SPT) data Meyerhof proposed:

Ppu = Ap (40N) Lb/B </= Ap (380N) (KN)

Where, N = statistical average of the SPT N55 numbers in a Zone of about *B above to #B below the pipe point.B = Width or diameter of pile point.Lb = Pile penetration depth into point-bearing stratum.Lb/B = average depth ratio of point into point- bearing stratum.

(Ref- foundation analysis and design by Joseph E. Bowles, fifth edition, page-895)

Ultimate Skin resistance (P s):

In non-cohesive layer, MEYORHOF method (using SPT data) is used.Unit skin friction (Ps) calculation is described below:

Ps = fs x (perimeter x length of a segment)Fs = xm. N (in Kpa).

Where, xm = 1.0 for pile with small volume displacement.

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