Showing posts with label Soil Mechanics. Show all posts
Showing posts with label Soil Mechanics. Show all posts

Constant Head Permeability Test

Permeability is the ease with which water can flow through any medium. It is a very important property of soil. Knowledge of permeability is essential to solve many soil engineering problems such as settlement of buidling, yield of wells, seepage through the earth structures etc. Therefore, it is necessary to determine the coefficient of Permeabilty. Several methods can be used to determine this property and one of those tests is Constant Head Permeability Test which is used for granular soil.


Constant head Permeability Test is based on IS: 2720 Part - 36:1987

Equipments:
  1. Constant Head Permeameter
    1. The Permeameter shall have a specimen cylinder with minimum diameter 8 to 12 times than maximum particle size whose covered at bottom with a porous disc and the opening in the disc shall not be more than 10% of the size of the particle to prevent the movement of the particle.
    2. A porous disc or suitable reinforced screen with spring attached to the top or any other device for applying 2 to 4 KG total load when the top plate is placed in place. This arrangement will help in maintaining the placement density and volume of the soil sample during the saturation of the sample and to satisfy the requirement of the test there should not be any change in the volume of the soil sample while performing the test.


    2. Source: IS: 2720 - Part 36

  2. Constant Head Filter Tank - To supply water, shall be fitted with suitable control valves to prevent air bubbles.
  3. Large Funnels - These shall be fitted with special cylinderical spout, 25 mm diameter for 10 mm maximum size particles and 13 mm in diameter for 2 mm maximum size particles. The length of the spout should be greater than the full length of the permeability chamber by atleast 160 mm.
  4. Compaction Equipment - Suitable compaction equipment shall be used.
  5. Vacuum Pump or Water Faucet Aspirator - For evacuating and for saturating soil specimen under full vacuum.
  6. Balance - It should be sensitive to 1 gram.
  7. Scoop - with a capacity of 100 gram of soil.

Sampling and preparation of Specimen
  1. An air-dried granular sample containing less than 10% of particle less than 75 micron shall satisfy the following:
    1. A Sieve Analysis (as per IS: 2720 part - 4) shall be done on the sample prior to permeability test and all the particles greater than 20 mm shall be removed using sieve. These oversized particles shall not be used in the test. The percentage of these particles shall recorded and shall be used in grading of sand or gravel filter to be used at the bottom anda top of the sample in the permeameter.
    2. From the Sample left in the previous step, a sample size of approximately twice the required for filling the permeameater chamber shall be selected by the method of quartering of sample.
  2. The size of permeameter shall be used as:
    Maximum Particle
    Size between IS sieve
    Opening
    (mm)    		 Maximum Cylinder Diameter
    (mm)
    Not More than 35 % of
    Total soil retained on
    sieve opening    		 More than 35% of
    Total soil retained
    on sieve opening

    		2 mm 10 mm 2 mm 10 mm
    2 mm and 10 mm 80 - 120 -
    10 mm and 20 mm - 160 - 230

  3. The following initial measurements shall be made:
    1. The inside diameter, $'D'$, the length $'L'$ between manometer outlets and the depth $'H_1'$ measured at four symmetrically spaced points from the upper surface of the top plate of the permeability cylinder to the top of the upper porous stone or screen temporarily placed on the lower porous plate or screen, this will automatically deduct the thickness of the upper plate or screen from the height measurements used to determine the volume of the soil placed in the permeameter cylinder.
    2. A duplicate top plate containing four larged symmetrically spaced openings through which the necessary can be made, shall be employed to determine the average value for $'H_1'$.
    3. Cross-sectional Area $A$ of the specimen shall be calculated.
    4. A small portion of specimen selected in step 2 and 3 shall be taken for water content determination and weight $'W_1'$ of the remaining air-dried sample shall be recorded for unit weight determination.
  4. If the maximum size of particles is 10 mm or less, place an appropriate size of funnel in the permeability device with the spout in contact with the lower porous plate or screen or previously formed layer, and fill the funnel with sufficient soil to form a layer, taking soil from different areas of the sample in the pan. Lift the funnel 15 mm or approximately unconsolidated layer of thickness to be formed, spread the soil with slow spiral motion, working from the perimeter of the device towards the centre so that a uniform layer is formed. Remix the soil in the pan for each successive layer to reduce the segregation caused by taking soil from the pan.
  5. For soils with a maximum size greater than 10.00 mm, spread the soil from a scoop. Uniform spreading can be obtained by sliding a scoopful of soil in a nearly horizontal position down along the inside surface of the device to the bottom or to the formed layer, then tilting the scoop and drawing it towards the centre with a single slow motion, this allows the soil to run smoothly from the scoop in a windrow without segregation. Turn the permeability cylinder sufficiently for the next scoopful, thus progressing around the inside perimeter to form a uniform compacted layer of a thickness equal to the maximum particle size.
  6. Compact successive layers of soil to the desired relative density by appropriate procedure, as follows, to a height of about 20-mm above the upper manometer outlet.
    1. Minimum Density (Zero percent relative density): Continue placing layers of soil in succession as described until the device is filled to the proper level.
    2. Maximum Density (100 percent relative density): Compact the sample by vibrating tamper, sliding weight tamker or any other approved methods such as deposition under water by vibratory packer equipment where care is taken to obtain a uniform specimen without segregation of particle sizes.
    3. Relative Density Intermediate Between zero and 100 Percent: By trial in a separate container of the same diameter as the permeability cylinder, adjust the compaction to obtain reproducible values of relative density. Compact the soil in the permeability cylinder by these procedures in thin layers to a height of about 20 mm above the upper manometer outlet.
    7. Preparation of Specimen for Permeability Test
  7. Level the upper surface of the soil by placing the upper porous plate or screen in position and by rotating it gently clockwise and anti-clockwise.
  8. Measure and record the final height of specimen, $H_1 - H_2$, by measuring the depth, $H_2$, from the upper surface of the perforated top plate employed to measure $H_1$ to the top of the upper porous plate or screen at four symmetrically spaced points after compressing the spring lightly to seat the porous plate or screen during the measurements; the final weight of air-dried soil used in the test $(W_1-W_2)$ by weighing the remainder of soil $W_2$ left in the pan. Compute and record the unit weights, void ratio, and relative density of the test specimen.
  9. To satisfy no volume change condition, make an airtight seal by pressing down the top plate against the spring and attach it securely to the top of the permeameter cylinder.
  10. To satisfy the condition of laminar flow through saturated soil voids, connect the inlet tube of the top plate of the permeameter to a vacuum pump or suitable aspirator capable of evacuating the air content from the specimen and outlet to the water container as shown in figure below. Close the manometer outlets and the outlet valve at the base plate of the permeameter. Using a vacuum pump or aspirator, evacuate the specimen under 500 mm Hg, minimum for 15 minutes to remove air adhering to soil particles and from the voids. Follow the evacuation by a slow saturation of the specimen from the bottom upward under full vacuum in order to force any remaining air in the specimen. Continued saturation of the specimen can be maintained more adequately by the use of de-aired water, or water maintained at an in-flow temperature sufficiently high to cause a decreasing temperature gradient in the specimen during the test.


    11. Source: IS: 2720 - Part 36

  11. After the specimen has been saturated and the permeameter is full of water, close the bottom val?ze on the outlet tube (See above Fig) and disconnect the vacuum. Care should be taken to ensure that the permeability flow system and the manometer system are free of air and are working satisfactorily. Fill the inlet tube with water from the constant-head tank by slightly opening the filter tank valve. Then connect the inlet tube to the top of the permeameter, open the inlet valve slightly and open the manometer outlet cocks slightly, to allow water to flow, thus freeing them of air. Connect the water manometer tubes to the manometer outlets and fill with water to remove the air. Close the inlet valve and open the outlet valve to allow the water in the manometer tubes to reach their stable water level under zero head.

Procedure:
  1. Open the inlet valve from the filter tank slightly for the first run, delay measurements of quantity of flow and head until a stable head condition without appreciable drift in water manometer level is attained. Measure and record the time $'t'$, head $'h'$ (the difference in level in the manometers), quantity of of flow $'Q'$, and water temperature $'T'$.
  2. Repeat the test runs at heads, increasing by 5 mm in order to establish accurately the region of laminar flow with velocity $'u'$ (where $u = Q/At$), directly proportional to hydraulic gradient $'i'$ (where $i = h/L$). When departures from the linear relation become apparent, indicating the initiation of turbulent flow conditions, 10 mm intervals, of head may be used to carry the test run sufficiently along in the region of turbulent flow to define this region if it is significant for field conditions.

    3. NOTE - Much lower values of hydraulic gradient h/l. are required than generally recognized, in order to ensure laminar flow conditions. The following values are suggested:
    Loose compactness ratings $h/L$ from $0.2$ to $0.3$ and
    Dense compactness ratings $h/L$ from $0.3$ to $0.5$; the lower values of $h/L$ apply to coarser soils and the higher values to finer soils.
  3. At the completion of the permeability test, drain the specimen and inspect it to establish whether it was essentially homogenous and isotropic in character. Any light and dark alternating horizontal streaks or layers are evidence of segregation of fines.

Calculations:
Permeability $K_T$ at temperature $T$ is calculated by:

$K_T = \frac {Q}{A \times i \times T}$


and permeability at 27°C by using the expression,

$K_{27}= K_T - \frac {\mu_T}{\mu_{27}}$


where,
$\mu_T=$ Coefficient of viscosity at $T°C$, and
$\mu_{27}=$ Coefficient of viscosity at $27°C$.

Void ratio $e$ is calculated as

$e= \frac {G_s \times \gamma_w}{\gamma}-1$


where,
$\gamma_w =$ density of water $= 1 g/cm^3$
$\gamma=$ dry unit weight of specimen
$\gamma_s =$ specific Gravity.





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Heavy Compaction Test

This test is performed as per IS:2720, Part - 8

  Procedure:
  1. A 5 Kg air dry sample of soil passing through 20 mm IS sieve is taken and thoroughly mixed with suitable amount of water depending upon the type of soil (3 to 5 % for sandy and gravely soils and 12 to 16 % below the plastic limit for cohesive soil).
    Note: The removal of small amounts of stone ( up to 5 percent) retained on 20-mm IS Sieve will affect the density obtainable only by amounts comparable with the experimental error involved in measuring the maximum dry density. The exclusion or a large proportion of stone coarse than 20 mm may have a major effect on the density obtained compared with that obtainable with the soil as a whole, and on the optimum moisture content. There is at present no generally accepted method of test or of calculation for dealing with this difficulty in comparing laboratory compaction test results with densities obtained in the field. For soils containing larger proportions of gravel, the use of a bigger mould (2250 ml) will avoid major errors.

  2. The Mould (Conforming to IS:10074-1982) with base plate attached is weighed to 1 gm ($m_1$)


  3. Place the Mould on a solid base such as a concrete base, with the extension attached and fill the mould in 5 Layers , approximately of equal mass and compact each layer by giving it 25 nos of blows with a 4.9 Kg Hammer by dropping it from a height of 450 mm above the soil sample.

  4. Remove the extension and level off the soil and weigh the mouth with the soil to 1 gm ($m_2$).

  5. Remove the compacted soil from the mould and determine its water content.

  6. Broke the remaining soil specimen and pass it through the 20 mm IS sieve and mix it with the original soil sample. Add suitable amount of water, greater than what was added previously, and repeat the whole procedure as described above for atleast 5 times. The range of moisture content should be such that the optimum moisture content (OMC) at which Maximum dry density occurs, is within that range.
Note:
  1. If the soil is susceptible to crushing during the compaction, five or more air dried sample with weight 2.5 Kg passing through 20 mm IS sieve is taken and each sample is mixd with different amount of water and follow the procedure as described above.

  2. If the soil contains coarse material of size upto 37.5 mm, the 2250 cc mould is used and 30 Kg sample passing through 37.5 mm IS sieve is used to perform the test with number of layers 5, each layer given 55 numbers of blows from 4.9 kg hammer.

Calculation of Bulk and Dry Density:
Bulk density in $g/cc$ can be calculated from the following relation:

$\gamma_m=\frac{{m_2}-{m_1}}{V_m}$


And dry density can be calcuated from the following relation:

$\gamma_d=\frac{100 \times {\gamma_d}}{100+w}$


Where, $w=$ moisture content of soil in percent.

The dry densities determined from the above calculations is plotted against the corresponding water content of the soil and a curve is obtained. The value of water content on which the dry density is maximum is the OMC of the soil.



Note: OMC is not an inherent property of a soil, it depends upon the compactive effort applied during the test, that means the more the applied force is, more will the dry density and less will be the OMC.






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Light Compaction Test (Standard Proctor Test)

There is a definite relationship betweeen the moisture content and the dry density of the soil. The moisture content at which a soil reaches the maximum value of dry density is called Omptimal Mositure Content or OMC.

To calculate the value of OMC and corresponding value of Dry Density, a test was developed by Ralph R. Proctor in 1933, known as Proctor Test.

There are two types of Proctor Test as given in the table below along with the other details:


Standard Proctor Test Modified Proctor Test
Weight of the
Hammer		 2.494 Kg or 5.5 lb 4.54 kg or 10 lb
Height of Fall 304.8 mm or 12"
 457.2 mm or 18"
Volume of Mould 944 cc or (1/30 cft) 944 cc
Layers 3 5
Blows per Layer 25 25


The proctor test was modified for Indian conditions and they are as follows:




 Light compaction Test Heavy Compaction Test
Weight of the
Hammer		 2.60 Kg 4.90 Kg
Height of Fall 310 mm
 450 mm
Volume of Mould 1000 cc
 1000 cc
Layers 3 5
Blows per Layer 25 25


Light Compaction Test


This test is performed as per IS:2720, Part - 7

  Procedure:
  1. A 5 Kg air dry sample of soil passing through 20 mm IS sieve is taken and thoroughly mixed with suitable amount of water depending upon the type of soil (4 to 6 % for sandy and gravely soils and 8 to 10 % below the plastic limit for cohesive soil).
    Note: The removal of small amounts of stone ( up to 5 percent) retained on 20-mm IS Sieve will affect the density obtainable only by amounts comparable with the experimental error involved in measuring the maximum dry density. The exclusion or a large proportion of stone coarse than 20 mm may have a major effect on the density obtained compared with that obtainable with the soil as a whole, and on the optimum moisture content. There is at present no generally accepted method of test or of calculation for dealing with this difficulty in comparing laboratory compaction test results with densities obtained in the field. For soils containing larger proportions of gravel, the use of a bigger mould (2250 ml) will avoid major errors.

  2. The Mould (Conforming to IS:10074-1982) with base plate attached is weighed to 1 gm ($m_1$)


  3. Place the Mould on a solid base such as a concrete base, with the extension attached and fill the mould in 3 Layers , approximately of equal mass and compact each layer by giving it 25 nos of blows with a 2.6 Kg Hammer by dropping it from a height of 310 mm above the soil sample.

  4. Remove the extension and level off the soil and weigh the mouth with the soil to 1 gm ($m_2$).

  5. Remove the compacted soil from the mould and determine its water content.

  6. Broke the remaining soil specimen and pass it through the 20 mm IS sieve and mix it with the original soil sample. Add suitable amount of water, greater than what was added previously, and repeat the whole procedure as described above for atleast 5 times. The range of moisture content should be such that the optimum moisture content (OMC) at which Maximum dry density occurs, is within that range.
Note:
  1. If the soil is susceptible to crushing during the compaction, five or more air dried sample with weight 2.5 Kg passing through 20 mm IS sieve is taken and each sample is mixd with different amount of water and follow the procedure as described above.

  2. If the soil contains coarse material of size upto 40 mm, the 2250 cc mould is used and 6 Kg sample passing through 40 mm IS sieve is used to perform the test with 3 numbers of layer and each layer given 55 numbers of blows from 2.6 Kg hammer.

Calculation of Bulk and Dry Density:
Bulk density in $g/cc$ can be calculated from the following relation:

$\gamma_m=\frac{{m_2}-{m_1}}{V_m}$


And dry density can be calcuated from the following relation:

$\gamma_d=\frac{100 \times {\gamma_d}}{100+w}$


Where, $w=$ moisture content of soil in percent.

The dry densities determined from the above calculations is plotted against the corresponding water content of the soil and a curve is obtained. The value of water content on which the dry density is maximum is the OMC of the soil.



Note: OMC is not an inherent property of a soil, it depends upon the compactive effort applied during the test, that means the more the applied force is, more will the dry density and less will be the OMC.






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Shrinkage Limit of Soil


Maximum water content at which further reduction in water content does not cause any reduction in the volume of the soil sample. When the water content is reduced below ${w}_{s}$, the particles are so closely packed that volume reduction will not take place and the void space starts getting occupied by air instead of water.

The test for the determination of Shrinkage Limit of Soil is as per IS 2720 Part-6. The test is performed using Evaporating Dish, Spatula, Shrinkage Dish (flat base, 45 mm in diameter and 15 mm in height), Straight Edge (~15 mm in length), Glass cup (50 to 55 mm in diameter and 25 mm in height), Glass plate ( in numbers, 75 X 75 mm and 3 mm thick) and Mercury.


Procedure (Remoulded Soil):


  1. Take a sample weighing about 100 gram from the thoroughly mixed portion of soil passing through 425 microns IS sieve.
  2. Place about 30 gram of soil from the soil sample already taken in step 1, in an evaporating dish and thoroughly mixed with distilled water in an amount sufficient to fill the soil voids completely and to make the soil paste enough to be readily worked into the shrinkage dish without entrapping the air bubble.
  3. Determine the clean empty Shrinkage Dish.
  4. Determine the Volume of Shrinkage Dish by filling it to overflowing with mercury, removing the excess by pressing the plain glass plate firmly over the top of the shrinkage dish in such a way that the plate is flush with the top of the dish and no air is entrapped.
    Weigh the mercury held in the dish and divide it by the unit weight of mercury to obtain the Volume of the Dish.
  5. Coat the inside of the shrinkage dish with a thin layer of grease or vaseline or some other heavy grease.
  6. Place soil paste equal to 1/3rd of the volume of the dish (approx) and allow it to flow to edges of the dish by tapping the dish on a firm surface.
    Add a similar amount of soil paste and repeat the step until the dish is completely filled. Strike off the excess soil using a straight edge.
  7. Weigh the Shrinkage Dish filled with Soil paste immediately and allow the soil pat to dry in the air until its colour changes from dark to light.
  8. Oven dries the soil pat in the shrinkage dish at $105-110{}^\circ C$ and cool it down in a Desiccator and weigh it immediately after removing from desiccator.
  9. Fill the glass cup with mercury and remove the excess mercury by pressing the glass plate with prongs firmly over the top of the cup and collect the excess mercury in a suitable container. Place the cup filled with mercury in evaporating dish carefully and then place the oven-dried soil pat on the surface of the mercury in the glass cup by means of the glass plate with same prongs and press the plate firmly over the top of the cup. Weigh the displaced mercury in the evaporating dish and obtain the volume of the soil pat.

Procedure (Undisturbed Soil):


  1. Take undisturbed Soil sample pats approximately 45 mm in diameter and 15 mm in height. Round off their edges to prevent the entrapment of air during mercury displacement.
  2. Take the sample in a small dish and air dry it.
  3. Oven dry the sample at $105-110{}^\circ C$
  4. Remove the sample from the oven and smoothen the edges of the pat by sandpapering. Brush off the soil dust from the specimen with a soft paintbrush.
  5. Place it on a clean dish and over dry it again.
  6. Cool the oven-dry specimen in a desiccator and determine the weight of the oven dry specimen.
  7. Determine the Volume of the specimen by displacing mercury as done for the remoulded soil (Step 9).
  8. Determine the Specific Gravity of the soil as per IS 2720-Part 3.

Moisture Content,

$w=\frac{W-{{W}_{0}}}{{{W}_{0}}}\times 100$

$W=$ Weight of wet soil pat obtained by dish.
${W}_{0}=$ Weight of the dry soil pat.

Shrinkage Limit (Remoulded Soil),

${{w}_{s}}=w-\left( \frac{V-{{V}_{0}}}{{{W}_{0}}} \right)100$

$V=$ Volume of wet soil pat
${V}_{0}=$ Volume of oven Dry soil pat

Shrinkage Limit (Undisturbed Soil),

${{w}_{su}}=\left( \frac{{{V}_{os}}}{{{W}_{os}}}-\frac{1}{G} \right)100$

${V}_{os}=$ Volume of oven dry sample
${W}_{os}=$ Weight of oven dry sample

Shrinkage Index,

${{I}_{S}}={{I}_{P}}-{{w}_{s}}$

${I}_{P}=$ Plasticity Index

Shrinkage Ratio,
$R=\frac{{W}_{0}}{{V}_{0}}$

Volumeteric Shrikage(Volumetric change),

${{V}_{s}}=({{w}_{1}}-{{w}_{s}})R$

${w}_{1}=$ given moisture content







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Plastic Limit of Soil


The minimum water content at which soil is in the plastic stage is called plastic limit water content. If a soil sample has water content equals to its plastic limit then it will crumble when rolled into a 3 mm diameter thread. The method to find the plastic limit of soil is based on IS 2720 Part 5.

Procedure:


  1. Take soil sample of 20 gram from the thoroughly mixed portion of material passing through 425-micron sieve.
  2. Mix the soil sample with distilled water thoroughly in an evaporating dish on the glass plate (20 X 15 cm) till the soil mass become plastic enough to be easily moulded with fingers.
  3. Form a ball with about 8 gm of this plastic soil mass.
  4. Roll this ball between fingers and the glass plate with sufficient pressure to roll the mass into a thread of uniform diameter throughout its length.
    Rolling shall be done till the threads of 3 mm diameter.
  5. Form the ball from these 3 mm diameter threads.
  6. Repeat the process of alternate kneading and rolling until the thread crumbles and it can no longer be rolled into a thread.
  7. Collect the crumbled pieces of soil in an airtight container for its water content determination.

The plastic limit shall be determined for at least 3 portions of the soil passing 425 microns IS sieve and the average of these 3 will be the plastic limit of the soil.

Plasticity Index


Plasticity index is the difference of liquid limit and plastic limit.

${I}_{P}={W}_{L}-{W}_{P}$


This property is due to the presence of clay minerals.

Atterberg Limits for soils
Soil Type ${W}_{L}$ ${W}_{P}$ ${I}_{P}$
 Sand  non-plastic
 Silt $ 30-40$ $ 20-25$ $ 10-15$
 Clay $ 40-50$ $ 25-50$ $ 15-100$

Consistency of Soil
${I}_{P}$ Consistency
$ 0$  Non Plastic
$ <7$  Low Plastic
$ 7-17$  Medium Plastic
$ >17$  Highly PLastic


Consistency Index or Relative Consistency


${{I}_{C}}=\frac{{{W}_{L}}-w}{{{I}_{P}}}$


Liquidity Index


${{I}_{L}}=\frac{w-{{W}_{P}}}{{{I}_{P}}}$



Consistency of Soil on the basis of ${I}_{C}$ and ${I}_{L}$
${I}_{C}$ ${I}_{L}$ Consistency
$ >1$ $ <0$  Very Stiff
$ 1-0.75$ $ 0-0.25$  Stiff
 $0.75-0.5$ $ 0.25-0.5$  Medium Stiff
$ 0.5-0.25$  $0.5-0.75$  Soft
$ 0.25-0$ $ 0.75-1$  Very Soft
$ <0$ $ >1$  Liquid State








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Liquid Limit of soil

Liquid limit is defined as that minimum water content at which it has a tendency to flow. All soil at liquid limit possesses similar shear strength which is negligible.


Determination of Liquid Limit

  1. Casagrande's Tool

    Casagrande tool to be used in the determination shall conform to IS 9529 and test procedure is as per IS 2720 Part 5.
    Source: MATHalino

    Procedure:


    1. Take soil sample of 120 gram from the thoroughly mixed portion of material passing from 425-micron sieve.
    2. Mixed it thoroughly with distilled water in an evaporating dish or on a flat glass plate to form a uniform paste.
      In case of clayey soil, left it for 24 hours so as to ensure uniform distribution of moisture throughout the soil mass.
    3. Remix the soil mass just before the test and place the paste in the cup and squeezed it down as shown in the figure.
    4. Turn the crank at a rate of 2 revolutions per minute until the two halves of the soil cake come in contact with the bottom groove along a distance of about 12 mm.
    5. Record the number of drops at which this 12 mm distance is covered.
    6. Take a representative slice of soil for determination of water content.
      At least two consistent consecutive closures shall be observed before taking the sample for the determination of water content.


    Water content at which 25 blows closes the groove is called liquid limit. It is obtained from the semi-log curve between water content and number of blows and this curve is known as flow curve

             Flow Index, ${{I}_{f}}=\frac{{{W}_{1}}-{{W}_{2}}}{{{\log }_{10}}{{N}_{2}}-{{\log }_{10}}{{N}_{1}}}$



  2. Cone Penetration Method


    This method is also based on IS 2720 Part 5 and its apparatus shall conform to IS 11196.

    Procedure:


    1. Take soil sample of 150 gram from the thoroughly mixed portion of material passing from 425-micron sieve and mixed it with distilled water to make a uniform paste.
    2. Put the wet paste in the cylindrical cup of penetration apparatus ensuring no air is trapped in the process.
    3. Adjust the penetration cone such that it just touches the top of the soil paste.
    4. Release the vertical clamp and let it penetrate under its own weight for 5 seconds and reading shall be noted to the nearest millimetre.
    5. If the difference in penetration is between 14 and 28 mm, the test shall be repeated with suitable adjustments to moisture content either by adding some water or exposure of the spreading paste on a glass plate for a reduction in moisture content. And the test shall be repeated to have at least 4 sets of values of penetration in the range of 14 to 28 mm.


      6. A graph representing water content on the y-axis and cone penetration on the x-axis is prepared and the best fitting straight line is drawn. The water content corresponding to cone penetration of 20 mm shall be taken as the liquid limit.





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Sieve Analysis

Sieve analysis is carried out for the determination of particle size distribution in the soil and performed as per IS 2386 Part-1

Apparatus:
Sieves of various sizes are shown below and shall conform to IS 460-1962


Type Sieve Designation

Square hole,
Perforated Plate
80 mm, 63 mm, 50 mm, 40 mm, 31.5 mm,
25 mm, 20 mm, 16 mm, 12.5 mm, 10 mm,
6.3 mm, 4.75 mm

Fine mesh,
Wire Cloth
3.35 mm, 2.36 mm, 1.18 mm, 600 microns,
300 microns, 150 microns, 75 microns

Sample:
The weight of the sample available shall not be less than the weight given below.


Maximum size present
in substantial
proportions
(mm)
Minimum weight
of sample
(KG)
63 100
50 100
40 50
25 50
20 25
16 25
12.5 12
10.5 6
6.3 3


Procedure
  1. Dry the sample, if necessary at room temperature or by heating them at a temperature of $100^\circ C$ to $110^\circ C$ and clean the sieves if required.

  2. Weigh the sample and sieve it successively on the appropriate sieves starting from the largest.
    Each sieve shall be shaken separately over a clean tray until not more than a trace passes through it but in no case less than 2 minutes.

  3. Break the lumps of fine materail, if any, by gentle pressure with a finger against the side of the sieve.

  4. Clear the sieve opening with a light brushing on the underside of the sieve.

  5. After the completion of sieving process, wiegh the aggregates retained on each sieve.

Note: Mechanical Sieving may be used but care should be taken to ensure that sieving is complete and the time for sieving should not be less than 10 minutes.

Result
  1. The cumulative percentage by weight of the total sample passing each of the sieves, to the nearest whole number.
  2. The percentage by weight of the total sample passing one sieve and retained on the next smaller sieve, to the nearest 0.1 percent.
  3. The results of sieve analysis may be recorded graphically on the chart for recording sieve analysis as shown below.


Wet Analysis
This method of test deals with the procedure for determining the total quantity of material finer than 75-micron IS Sieve in aggregates by washing.

Apparatus
  1. Balance
    The balance or scale shall be of sufficient capacity and sensitivity and shall have an accuracy of 0.1 percent of the weight of the test sample.
  2. Sieve
    A nest of two sieves, the lower being 75-micron IS Sieve and the upper approximately 1.18-mm IS Sieve (see IS :460-1962).
  3. Container
    A pan or vessel of a size sufficient to contain the sample covered with water and to permit of vigorous agitation without inadvertent loss of any part of the sample or water.
  4. Oven
    An oven of suflicient size capable of maintaining an uniform temperature of $110 \pm 5^\circ C$.


Sample
The test sample shall be selected from the material which has been thoroughly mixed and which contains sufficient moisture to prevent segregation. A representative sample, sufficient to yield not less than the appropriate weight of the dried material, as shown below, shall be selected:


Maximum nominal
size of aggregate (mm)
Minimum weight
of sample
(KG)
4.75 0.5
10 2
20 2.5
40 or over 5

Procedure
  1. Dry the sample at a tempeature of $110 \pm 5^\circ C$ and weigh it to the nearest 0.1 percent.

  2. Place the dried sample in a container and add water to cover it agitate it vigorously.
    The agitation shall be sufficiently vigorous to result in a complete separation of fine aggregates (smaller than 75-micron) from coaser particles and bring the fine aggregates to suspension.
    Care should be taken to avoid decanatation of coarse aggregate. This process is repeated until the wash water is clear.

  3. Immediatley pour the wash water over the nested sieve arranged with the coarser siever on the top.

  4. Dry the washed aggregate retained on the nested sieve at a temperature not more than $110 \pm 5^\circ C$ and weigh it to the nearest 0.1 percent.


Calculation
The amount of material passing 75-micron sieve is calculated from ,

$A=\frac{B-C}{B} \times 100$

Where
$A=$ Percentage of material finer than 75-micron
$B=$ Original dry weight
$C=$ Dry weight after washing





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Unit weight of Soil

The bulk Unit weight of soil is defined as the ratio of the total weight of the soil sample and its total volume.

                                            ${{\gamma }_{t}}=\frac{W}{V}=\frac{{{W}_{s}}+{{W}_{w}}}{{{V}_{s}}+{{V}_{w}}+{{V}_{a}}}$



Unit weight of soil solids is defined as the weight of soil solids per unit volume of solids alone.

                                            ${{\gamma }_{s}}=\frac{{W}_{s}}{{V}_{s}}$



The dry unit weight of soil is defined as the weight of soil solids (or dry soil) per unit volume of soil.

                                            ${{\gamma }_{s}}=\frac{{W}_{s}}{V}$



The saturated unit weight of soil is defined as the bulk unit weight of soil mass in the saturated condition.

                                            ${{\gamma }_{sat}}=\frac{\text{Weight of saturated soil}}{\text{Volume of soil}}$



The submerged unit weight of soil is defined as the submerged unit weight of soil solids per unit Volume. When soil exists below groundwater, the buoyant force acts on the soil solids and reduces its unit weight.

                                            ${{\gamma }_{sub}}=\frac{{{W}_{sub}}}{V}={{\gamma }_{sat}}-{{\gamma }_{w}}$


Different methods to find unit weight of soil


  1. Core Cutter Method


    It is field method which is based on IS 2720 Part 29. A core cutter is a cylindrical seamless steel tube of internal diameter 100 mm and 130 mm long with 3 mm thick wall. Steel Dolley has 25 mm height with an internal diameter of 100 mm and a wall thickness of 7.5 mm with a lip to enable it to be fitted on the top of the core cutter.



    Procedure:

    1. Weigh the empty core cutter accurately, say ${W}_{c}$
    2. Remove the top layer of soil of an area of approximately $30 {cm}^{2}$.
    3. Place the dolly on the soil and rammed it down vertically into the soil layer until only 15 mm of the dolly protrudes above the surface.
    4. Dug out the cutter of the surrounding soil carefully and trim flat the soil core.
    5. Weigh the cutter containing soil, say ${W}_{s}$
    6. Remove the soil core from the cutter and take a representative soil sample in an airtight container for its water content determination $w$.

                          $\text{Bulk unit weight, }{{\gamma }_{t}}=\frac{{{W}_{s}}-{{W}_{c}}}{{{V}_{c}}}$
                          $\text{Dry unit weight, }{{\gamma }_{d}}=\frac{{{\gamma }_{t}}}{1+w}$


  2. Water Displacement Method


    In this method Volume of the soil specimen is determined. The soil mass is coated with paraffin wax to make soil specimen impervious to water as when soil comes in contact with water it disintegrates.

    Procedure:


    1. Trim the soil specimen into a more or less regular shape and weigh it, say $W$
    2. Coat the specimen with thin layer of paraffin wax by dipping it in molten wax and weigh it after it cools down, say ${W}_{t}$
    3. Immerse the waxed specimen in a water displacement container. And the volume of water that comes out of the flow tube will be the volume of the waxed specimen, say ${V}_{t}$.
    4. Peel off the wax out of the specimen for determination of its volume from its mass and its density ${\rho}_{p}$
    5. Take a representative soil sample in an airtight container for its water content determination $w$.

                          $\text{Volume of soil specimen, V}={{V}_{t}}-\frac{{{W}_{t}}-W}{{{\rho }_{p}}}$
                          $\text{Bulk unit weight of soil,}{\gamma}_{t}=\frac{W}{V}$
                          $\text{Dry unit weight, }{{\gamma }_{d}}=\frac{{{\gamma }_{t}}}{1+w}$


  3. Sand Replacement Method


    This is a field method based on IS 2720 Part 28.

    Procedure:


    1. Excavate a small area and weigh the excavated soil precisely.
    2. Place a calibrated cylinder containing sand over the excavated area and fill the pit with sand.
    3. Find the volume of the pit from the calibrated cylinder.
    4. Take a representative soil sample in an airtight container for its water content determination $w$.

    Once the volume and water content is known, bulk unit weight and dry unit weight is calculated as shown in the core cutter method.




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Specific Gravity of Soil

The specific gravity of soil solids is defined as the ratio of the unit weight of solids (absolute unit weight of soil) to the unit weight of water.

                                   $G=\frac{{{\gamma }_{s}}}{{{\gamma }_{w}}}$



Determination of Specific Gravity of Soil Solids by Pycnometer Method

A pycnometer is a glass jar of about 1-litre capacity and fitted with a brass conical cap. This cover has a small hole of 6 mm diameter at its apex.

  1. Weigh the empty pycnometer, say ${W}_{1}$.
  2. Fill the pycnometer with dry soil and weigh it, say ${W}_{2}$.
  3. The remaining volume of pycnometer is gradually filled with distilled water and weighed, say ${W}_{3}$. The entrapped air should be removed either by slight heating or vigorous shaking or by applying vacuum.
  4. Empty the bottle and clean it thoroughly and filled with distilled water and weighed, say ${W}_{4}$.



                              $G=\frac{\text{Weight of solids}}{\text{Weight of equivalent volume of water}}$

                              $G=\frac{{{W}_{2}}-{{W}_{1}}}{({{W}_{4}}-{{W}_{1}})-({{W}_{3}}-{{W}_{2}})}$





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Water Content of Soil

As almost all the properties of soil depend on water content, it is very important to measure the water content very accurately.

Different methods to find water content:

  1. Oven Drying Method

    Oven Drying Method is a standard laboratory method. It is a very accurate method but this method needs 24 hours for its completion so it's a lengthy method. This method is based on IS 2720 Part 2.

    1. A small empty container is weighed, let it be ${W}_{1}$
    2. The soil to be tested is filled in a small airtight container and weighed, let it be ${W}_{2}$.
    3. The container is then dried at a temperature of $105-110^{\circ}C$ for 24 hours in the laboratory
      Above $110^{\circ}C$ water of crystallisation may be lost. It is the water in the molecular structure of soil particles.
    4. If the soil contains a significant amount of organic matter then the soil is dried at a temperature of $60-80^{\circ}C$.
    5. After 24 hours the container is cooled down to room temperature and weighed, let this weight be ${W}_{3}$

      6. Water content, $\frac{W_{w}}{W_{s}}=\frac{W_{2}-W_{3}}{W_{3}-W_{1}}$



  2. Pycnometer Method

    A pycnometer is a glass jar of about 1-litre capacity and fitted with a brass conical cap. This cover has a small hole of 6 mm diameter at its apex. This method for the determination of water content can be used only if the specific gravity (G) of soil solids is known.

    1. Weigh the empty pycnometer, say ${W}_{1}$.
    2. Fill the pycnometer with moist soil and weigh it, say ${W}_{2}$.
    3. The remaining volume of pycnometer is gradually filled with distilled water or kerosene and weighed, say ${W}_{3}$. The entrapped air should be removed either by slight heating or vigorous shaking or by applying vacuum.
    4. Empty the bottle and clean it thoroughly and filled with distilled water or kerosene and weighed, say ${W}_{4}$.



      5. Water Content, $w=\left( \frac{{{W}_{2}}-{{W}_{1}}}{{{W}_{3}}-{{W}_{4}}} \right)\left( \frac{G-1}{G}-1 \right)$


    This method is not suitable for cohesive soil because removal of entrapped air in case of cohesive soil is difficult.

  3. Sand Bath Method

    Sand bath method is a rapid field method but it is not accurate. A Sand bath is a large open vessel containing sand filled to a depth of 3 cm or more. This method is based on IS 2720 Part 2.

    1. Crumble the soil to be tested and place loosely in a tray. Place a few pieces of white papers on it and weighed the whole assembly.
    2. Place the tray on the sand bath and heat it over a stove. Drying will take about 20 to 60 m.inutes, depending upon the type of soil.
    3. Turn the soil specimen with a palette knife.
      Overheating of the sample should be avoided and overheating is occur when white paper turns brown.
      The drying should be continued until the sample attains a constant mass.
    4. When drying is complete, remove the tray from the sand bath, cooled and weighed.

      5. Water Content, $w=\frac{{{W}_{final}}-{{W}_{initial}}}{{{W}_{final}}-{{W}_{tray}}}$

  4. Calcium Carbide Method

    When water reacts with calcium carbide it produces acetylene gas. The water content of the soil is determined indirectly from the pressure of the acetylene gas formed. The instrument used is known as moisture tester. This method is based on IS 2720 Part 2.

    $Ca{{C}_{2}}+2{{H}_{2}}O\to {{C}_{2}}{{H}_{2}}+Ca{{(OH)}_{2}}$


    The instrument used is known as moisture tester.
    The pressure of the acetylene gas produced acts on the diaphragm of the moisture tester. The quantity of the gas is indicated on a pressure gauge. The water content $({w}_{t})$ based on the total mass is determined from the calibrated scale of the pressure gauge.

    The water content based on the dry mass is determined by, $w=\frac{{{w}_{t}}}{1-{{w}_{t}}}$

  5. Radiation Method

    In this method, Radio-active isotopes are used to determine the water content. A device containing a radio-active isotopes materials, such as cobalt-60, is placed in a capsule. It is then lowered in a steel casing A. The steel casing has a small opening on its side through which rays can come out. A detector is placed inside another steel casing B.


    Neutrons are emitted by the radioactive isotope. When these neutrons strike with the hydrogen atom of water, they lose energy and this loss of energy is proportional to the quantity of water present in the soil. The detector is calibrated to give directly the water content.






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Stress Capillarity and Permeability


Stress on soil doesn't depend on the area as long as any external loading is not applied.
Total Stress is a physical parameter which can be measured by pressure cell.
Effective Stress is not a measurable quantity, in fact, it's not even real but many soil properties such as compressiblity, consolidation, settlement, shear stress and bearing capacity depend on it. These parameters do not directly depend on Total Stress.

The soil above the water table is not completely dry but there is water up to a certain height above the water table, this water is called capillary water. It happens because water in the pores is not only subjected to gravitational pull but also to a force of adhesion between the soil particles and water molecules inside the soil pores.

$\overline{\sigma }=\sigma -u$

$h=\frac{0.03}{d}=\frac{0.03}{0.2{{D}_{10}}}$

${{h}_{c}}=\frac{C}{e{{D}_{10}}}$

$Seepage Force ={{\gamma }_{w}}\Delta hb$

$\frac {Seepage Force}{Volume}=i{{\gamma }_{w}}$

$i=\frac{\Delta h}{b}$

${{i}_{cr}}=\frac{{{\gamma }_{sub}}}{{{\gamma }_{w}}}=\frac{G-1}{1+e}$


$\overline{\sigma }=$ Effective Stress
${\sigma }=$ Total Stress
$u=$ Pore Pressure
$i=$ Hydraulic Gradient
$h=$ Capillary Rise
$C=$ Empirical Constant $=0.1-0.5$ ${cm^2}$
${\Delta h}=$ Drop in total Head
${{i}_{cr}}=$ Critical Hydraulic Gradient




Permeability


Permeability is the ease with which water can flow through any medium. It is a very important property of soil. Knowledge of permeability is essential to solve many soil engineering problems such as settlement of buidling, yield of wells, seepage through the earth structures etc.




$q=kiA$

$V=ki$

${{V}_{s}}=\frac{V}{n}$

${{K}_{p}}=\frac{K}{n}$

Constant Head Permeabilty Test
$K=\frac{qL}{Ah}$

Falling Head Pearmabilty Test
$K=\frac{aL}{At}{{\log }_{e}}\left( \frac{{{h}_{1}}}{{{h}_{2}}} \right)$

Unconfined Aquifer Test
$K=\frac{q{{\log }_{e}}\frac{{{r}_{2}}}{{{r}_{1}}}}{\pi (h_{2}^{2}-h_{1}^{2})}$

$R=3000d\sqrt{K}$

Confined aquifer Test
$K=\frac{q{{\log }_{e}}\frac{{{r}_{2}}}{{{r}_{1}}}}{2\pi D({{h}_{2}}-{{h}_{1}})}$

$K=\frac{1}{{{C}_{S}}}\times \frac{{{\gamma }_{w}}}{\mu }\times \frac{1}{S_{A}^{2}}\times \frac{{{e}^{3}}}{1+e}$

$K=CD_{10}^{2}$

$K={{C}_{V}}{{\gamma }_{w}}{{m}_{v}}$

Permeability of Stratified Soil
${{K}_{H}}=\frac{{{K}_{1}}{{H}_{1}}+{{K}_{2}}{{H}_{2}}+{{K}_{3}}{{H}_{3}}...}{{{H}_{1}}+{{H}_{2}}+{{H}_{3}}...}$

${{K}_{V}}=\frac{{{H}_{1}}+{{H}_{2}}+{{H}_{3}}...}{\frac{{{H}_{1}}}{{{K}_{1}}}+\frac{{{H}_{2}}}{{{K}_{2}}}+\frac{{{H}_{3}}}{{{K}_{3}}}...}$


Unconfined Aquifer
Source: NPTEL





$q=$ Dischagre per unit time
$K=$ Permeabilty of soil
$i=$ Hydraulic gradient $=$ loss of head per unit lenth
$V=$ Superficial Velocity of flow
${{V}_{s}}=$ Seepage Velocity
${{K}_{p}}=$ Coefficient of Percolation
${\mu}=$ Coefficient of Viscosity
${{C}_{S}}=$ Shape factor Cofficient
${{S}_{A}}=$ Specific Surface Area
${{C}_{v}}=$ Coefficient of Consolidation
${{m}_{v}}=$ Coefficient of Volume Compressiblity

Confined Aquifer
Source: NPTEL










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Soil Compaction

Compaction of soil is the process of Increasing the unit weight of soil by forcing the soil solids into a dense state and reducing the air voids.
It is done to improve strength, load carrying capacity and to reduce voids, settlement and to control undesirable volume changes.
To find the effort required to compact a soil mass to a desired density we perform protector/compaction test.
According to Protector there is a relationship between compactive effort and mositure content.

For a specfic amount of compaction energy applied on the soil, there is one moisture content termed as optium moisture content(OMC) at which a particular soil attains maximum dry density.


Standard Protector Test

1. Weight of Hammer: 2.495 KG (W)
2. Height of Fall: 304.8 mm = 12inch (h)
3. Volume of mould: 944 cc (V)
 4. Compacted in 3 (n) layers with 25 blows in each layer (N)
Compacted energy (E) applied per unit Volume,

$E=\frac{NnWh}{V}$ 

 

Modified Protector Test

1. Weight of Hammer: 4.54 KG (W)
2. Height of Fall: 457.2 mm = 18inch (h)
3. Volume of mould: 944 cc (V)
          4. Compacted in 5 (n) layers with 25 blows in each layer (N)



Light Compaction Test (IS: 2720, Part-7)

1. Weight of Hammer: 2.6 KG (W)
2. Height of Fall: 310 mm (h)
3. Volume of mould: 1000 cc (V)
          4. Compacted in 3 (n) layers with 25 blows in each layer (N)

Heavy Compaction Test (IS: 2720, Part-8)

1. Weight of Hammer: 4.9 KG (W)
2. Height of Fall: 450 mm (h)
3. Volume of mould: 1000 cc (V)
          4. Compacted in 5 (n) layers with 25 blows in each layer (N)

Compaction Equipment


Type of Equipment Suitablity for soil type Nature of Project
Rammers or Tampers All Soils Confined areas such as fills behind retaining wall
Smooth wheeled rollers Crushed rocks, gravels, sands Road Construction etc
Pneumatic tyred rollers Sands, Gravels silts, clayey soil Base, sub base and embankment compaction
sheepfoot rollers Clayey soil Core of Earth Dams
Vibratory Rollers Sands Embankments for oil storage tanks etc




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