Post on 22-Nov-2014
description
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