Group members

Burhan (2012-GE-16)

Aqib (2012-GE-03)

Awais (2012-GE-21)

Asad (2012-GE-18)

Yasin (2012-GE-54)

Tariq (2012-GE-55)

Shoaib (2012-GE-56)

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) Drill rod 4) 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

Standard Penetration Test, SPT, involves driving a standard thick-walled sample tube into the ground at the bottom of a borehole by blows from a slide hammer with standard weight and falling distance. The sample tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded. The sum of the number of blows required for the second and third 6 in. of penetration is reported as SPT blow count value, commonly termed "standard penetration resistance" or the "N-value

PROCEDURE of SPT

The N-value provides an indication of the relative density of the subsurface soil, and it is used in empirical geotechnical correlation to estimate the approximate shear strength properties of the soils.

Hammer rod showing markings @ 150mm

Correlation between SPT-N value and friction angle and Relative density (Meyerhof 1956)

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

Relatively quick and simple to perform.Provides a representative soil sample.Provides useful index of relative strength and

compressibility of the soil.Able to penetrate dense layers, gravel, and

fill.The SPT is an in situ test that reflects soil

density, soil fabric, stress and strain history effects, and horizontal effective stress

Advantages

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