This test is the most common used in-situ test,

especially for cohesion less soils which cannot be easily

sampled. The test is extremely useful for

determining the relative density and angle of

shearing resistance of cohesion less soils. It can

also determine the unconfined compressive

strength of cohesive soils..

STANDARD PENETRATION TEST

1) Tripod stand 2) Standard split-spoon sampler. It consists of three parts:- (a) Driving shoe, about 75 mm long. (b) Steel tube about 450mm long, split longitudinally

in two halves having inner diameter as 38mm & outer diameter as 50mm.

(c) Coupling at the top of the tube about 150 mm long.

3) Guide pipe 4) Drill rod 5) Drop hammer weighing 63.5kg.

APPARATUS of SPT

• The drop hammer is attached to the rope of tripod hoist. By operating winch the weight is lifted.

TRIPOD HOISTTRIPOD HOIST

The drop hammer is attached to the rope of tripod hoist. By operating winch the weight is lifted.

Split spoon sampler

Coupling 150mm long

Driving shoe 75mm long

Split Tube,450mm long

Hammer with a weight of 63.5 kg falling from a distance of 750 mm (30 in)

Drop hammer

It is used to keep the bore hole of 150 mm, 300mm, 450 mm upto

desired depth at which sample is taken

Equipment making bore hole

Driving head Lifting bailIt is screwed on sampler & the hammer is fallen on it to driven the sampler in ground.

It is used to lift up the sampler from the ground after driven it to 30 cm

The bore hole is to be drilled up to the desired depth.The drilling tools are removed & sampler is lowered to the

bottom of the hole.Three markings @ 15o mm are made on the rod of sampler.The sampler is driven into the soil by drop hammer falling

through the height of 15o mm @ 30 blows/min.The number of blows required to drive each 150mm of the

sampler is counted.The number of blows recorded for the first 150mm is

disregarded.The number of blows recorded for the last two 150mm intervals

are added to give the standard penetration number(N)Likewise, the another samples of soil are collected at the

interval of 1.67 m or where the soil profile or strata changes (IS 6403:1981).

PROCEDURE of SPT

DILATANCY CORRECTION:- Silty fine sands & fine sands below the water table develop pore pressure which is not easily dissipated. The pore pressure increases the resistance of the soil & hence the penetration. The following correction is applied when the observed value of N exceeds 15. The corrected penetration number, Nc = 15 + 0.5(Nr-15), where Nr is the recorded value of N.

If Nr is less than or equal to 15, then Nc = Nr.

CORRECTIONS

OVERBURDEN PRESSURE CORRECTION:- If the two soils having same relative density but different confining pressure one with a higher confining pressure gives a higher penetration number.

NC = Nr *0.77*log10(2000/)

where, NC = corrected penetration number = effective overburden pressure Nr = recorded value of N.

Hammer rod showing markings @ 150mm

Index Properties • Atterberg’s limits • Grain size distribution • Specific gravity • Density • Porosity • Void ratio • Unit weight

Atterberg’s Limits What are we talking about? Fine-grained soil can behave as a liquid,

plastic, semi-solid or solid depending how much water is in it

The water contents at which behavior changes from one state to the other are referred to as the Atterberg’s limits

These limits are: liquid limit, plastic limit and shrinkage limit

Water Content Laboratory determination of water (moisture)

content of soil and rock by mass wc = Ww/Ws

Ww = Weight of water in the soil

Ws = Weight of solid particles in the soil

Water content determination procedure

Clean and dry the water content container Mark the container with an identification

number and weigh it (record it as W1) Place some wet soil sample in the container

and weigh it (record this as W2) Oven dry the sample at 110⁰C for 24 hours Weigh the container with the dry soil sample

(record this as W3 ).

Calculate the water content ‘wc’ as the ratio of weight of water to weight of dry soil

wc = Ww/Ws Ws = (W3-W1)

Ww = (W2-W3)

LIQUID LIMITLiquid limit: water content at which soil shifts

from plastic to liquid state or vice-versa .

LL is the water content at which the soil flows to close a groove, of a standard width, when jarred in a specified manner for 25 times

Casagrande’s Liquid limit device grooving tool Is sieve of size 425µm.Water content containers Balance Spatula Spray bottle Evaporating dish Drying oven set to 105⁰C

Apparatus for LL Test

Apparatus for LL Test

Grooved soil pat in liquid limit device

Procedure for Liquid Limit Test Thoroughly mix the soil sample with water

using a spatula Place portion of the prepared soil in the cup

of the LL device Spread the soil into the cup with about 10

mm thickness at the deepest point of the cup Make the soil surface horizontal with the

spatula .

Remove air bubbles (if any) from the soil Draw the grooving tool through the middle of

the soil pat maintaining the tool perpendicular to the soil surface .

Turn the crank at a rate of 2 blows/second until the groove closes for a distance of ½ inch and record the number of blows .

Take a slice of soil from the cup and obtain its water content

Return the remaining soil from the cup and remix the entire soil sample adding water to increase the water content

Perform at least 2 more trials

Make sure that in the trials, you have one blow count value between 15-25 blows, one between 20-30 blows and one between 25-35 blows

Determine the water content of the soil sample in each of the trials.

Draw flow curve by plotting the obtained water content on the Y-axis on linear scale and the associated number of blows on the X-axis on a logarithmic scale (a semi-log graph will be provided in labs)

Draw a best fit straight line along the points and determine the corresponding water content for 25 blows

Sample Calculation for Liquid Limit Test

TEST NO, 1 2 3 4

MASS OF TARE(W1) 16.2 16.5 15.9 15.7

NO. OF BELOW 'N' 17 24 28 32

W1 + WET SOIL (W2) 25.2 25.6 24.9 25.3

W1 + DRY SOIL (W3) 21.5 22.7 22.3 22.7

MASS OF DRY SOIL(Ws) 5.3 6.2 6.4 7

MASS OF WET SOIL (Ww) 3.7 2.9 2.6 2.6

WATER CONTENT, Wc 69.8 46.8 40.6 37.1

PLASTIC LIMITPlastic Limit is defined as the water content

at which soil shifts from plastic to semi-solid state or vice-versa

It is the water content at which the soil starts to crumble when rolled into a thread of diameter of 3.2 mm

Procedure for Plastic Limit Test Take about 20 g of soil from the soil prepared

for the LL test and make an ellipsoidal mass Roll the soil mass between palm or fingers

and the glass plate Apply sufficient pressure to roll the soil mass

into a thread of uniform diameter Roll the thread to a diameter of 3.2 mm

within 2 min (use the comparison rod for diameter reference

Break the thread into several pieces, squeeze them together, re-form into ellipsoidal mass and re-roll into a thread of 3.2 mm in diameter

Continue this re-rolling process until the soil starts to crumble .

Determine the water content of the crumbled soil (make sure you use more than 6 g of soil when you do the water content estimation)

Repeat the test one more time .Find plasticity index (PI) by subtracting

PL(Plastic Limit) from LL (Liquid Limit ).

Bore hole Log