soil mechanics practical final

KATHMANDU ENGINEERING COLLEGE KALIMATI, KATHMANDU

(Affiliated to T.U.)

A

PRACTICAL REPORT ON

SOIL MECHANICS

SUBMITTED BY: SUBMITTED TO: RABINDRA SUBEDI THE DEPERTMENT OF CIVIL BCE ‘C’ ENGINEERING 62109 Er. Renu Biswas

24TH, June, 2008

Submitted by: Rabindra Subedi Soil Mechanics Submitted to: Er. Renu Biswas BCE 62109 ‘C’ Department of Civil

EXPERIMENT NO: 1 25th April,2008

OBJECT: TO DETERMINE THE WATER CONTENT OF THE SOIL SAMPLE BY USING OVEN DRYING METHOD

1. APPARATUS REQUIRED:

• Thermostatically controlled oven at 110 C

• Weighing Balance

• Desiccator

• Container

2. THEORY: The water content of a soil is an important parameter that controls its behavior. It is a quantitative measure of the wetness of a soil mass. The water content of a soil can be determined to a high degree of precision, as it involves only a mass which can be determined more accurately than volumes. The water content of a soil is determined as a routine matter in most of the other tests. The water content of a soil sample can be determined by any one of the following methods:

a) Oven drying method b) Torsion balance method c) Pycnometer method d) Sand bath method e) Alcohol method f) Calcium carbide method g) Radiation method

Oven drying method: The oven drying method is a standard, laboratory method. This is a very accurate method. The soil sample is taken in a small, non‐corridible, airtight container. The mass of the sample and that of the container are obtained using an accurate weighing balance. According to IS: 2720(part I)‐1973, the mass of the sample should be taken to an accuracy of 0.04 percent. The quantity of the sample to be taken for the test depends upon the gradation and the maximum size of the particles and the degree of wetness of the soil. The drier the soil, the more shall be the quantity of the specimen. The drying period of 24 hours has been recommended for normal soils, as it has been found that this period is sufficient to cause complete evaporation of water. The sample is dried till it attains a constant mass. The soils containing gypsum and organic matter may require drying for a period longer than 24 hours. Theoretically the water content of a soil is defined as the ratio of the mass of water to the mass of solids.

It is denoted by (w). Mathematically;

Water content (w) =

The water content is also known as the moisture content (m).

w= 100


Where M1 = Mass of empty container with lid

M2 = Mass of container with wet soil & lid M3 = Mass of container with dry soil & lid The water content of the fine‐grained soils, such as silts and clays, is generally more than that of the coarse grained soils, such as gravels and sands. The water content of some of the fine‐grained soils may be even more than 100%, which indicates that more than 50% of the total mass is that of water. The water content of a soil is an important property. The characteristics of a soil, especially a fine‐ grained soil, change to a marked degree with a variation of its water content.

3. PROCEDURE: The following procedure was adopted for the determination of water content of a soil by using oven drying method.

i. The container was cleaned and dried and then weighed (M1). ii. The required quantity (full of container) of the wet specimen was taken with container and weighed (M2).

iii. Then the container was placed in the oven about 24 hours at 110°±5°C. Then the weight was taken (M3).

4. OBSERVATION:

S.N. Observation Container No.

22 37 16

1 Mass of empty container (M1) 11 7 8

2 Mass of container + Soil (M2) 38 37 44

3 Mass of container +dry soil (M3) 33 31 37

4 Mass of water (Mw) =M2M3

5 6 7

5 Mass of solid (Ms) =M3M1

22 24 29

6 Water Content = 100 100% 22.73% 25.00% 24.14%

Water Content Mean =.=23.957% Total=71.87%

5. RESULT: From the experiment the water content of the soil sample is found to be 23.96%.


6. SUGGESTIONS AND CONCLUSION:

The water content of a soil is an important property of the soil for the determination of other property of soil like liquid limit, plastic limit, dry density etc. water content of the soil sample is found 23.96% which is in normal range, if the water content of the soil is more than 100% we conform that the soil contains more than 50% of the total mass is that of water. This soil has great significance in engineering field. Various methods of water content determination are available but we use oven dry method which is more precise and reliable and is standard laboratory method. For the most accurate result the weight of container with lid and soil must me measured more accurately and the sample should be dried 24 hours more precisely and the temperature of the oven must be 110 5°C. It is conclude that the water content of a given sample of soil can be determined accurately by oven drying method.

SUBMITTED BY :Rabindra Subedi Soil Mechanics SUBMITTED TO: Er. Renu Biswas

62109 BCE ‘C’ Department of Civil

EXPERIMENT NO: 2 25th April, 2008 OBJECT: TO DETERMINE THE FIELD DENSIYY OF THE SOIL

(INSITU-DENSITY) BY USING THE SAND REPLACEMENT METHOD.

1) EQUIPMENT a) Sand pouring cylinder. b) Calibrating container. c) Soil digging tools. d) Glass plate. e) Metal tray. f) Weighing machine. g) Container. h) Oven.

2) THEORY

The dry mass density (ρd) is defined as the mass of solids per unit total volume. i.e. Ρd = As the soil may shrink during drying, the mass density may not be equal to the bulk mass density of the soil in the dried condition. The total volume is measured before drying. The dry mass density is also known as the dry density. The dry mass density is used to express the denseness of the soil. A high value of dry mass density indicates that the soil is in a compact condition. A hole of specified dimensions is excavated in ground. The mass of the excavated soil is determined. The volume of the hole is determined by filling it with clean, uniform sand whose dry density is determined separately by calibration. The volume of the hole is equal to the sand filled in the hole divided by its dry density. The dry density of the excavated soil is determined as, Ρd = (M/V)/ (1+w) Where M= mass of the excavated soil: V =Volume of the hole: w = Water content. The sand pouring cylinder has a pouring cone at its base. The cylinder is placed with its base at the ground. There is a shutter between the cylinder and the cone. The cylinder is first calibrated to determine the mass density of sand. For good results, the sand used should be uniform, dry and clean, passing a 600 micron sieve and retained on a 300 micron sieve.

3) PROCEDURE

a) The volume of calibrating container was determined by measuring its diameter and height. b) The pouring container was filled with sand and its weight was taken. c) Then the container was then placed above the calibrating container and shutter was opened till the

calibrating container and cone was filled. d) Then the pouring container was weighted. e) Again the pouring container was filled with sand and was placed in clean glass plate and shutter

was opened till the cone was filled. f) The sand left behind in the glass plate was weighted.



g) Then the dry density of sand was calculated. h) Then a plane ground surface was selected and a metal tray was placed, then a hole was digged

such that the volume of the hole was equal to the volume of the calibrating container. i) All excavated soil was collected and the weight of the soil was taken. j) The sand filled pouring container was then placed above the hole and sand was allowed to pour in

the hole till the cone was filled.

4) OBSERVATION & CALCULATION:

Mass of mould (a) =1635 gm Mass of mould + Sand (b) =3405gm Mass of sand= b-a = (3405-1635) =1770 gm Dia. Of mould (d) =10 cm Height of mould (h) = 15 cm Volume of mould (V) = 2 1.1781 10-3 m3

Density of sand (ρsand) = = 1502419.149 gm/m3 = 1502.419 kg/m3 Mass of cone jar + sand (m1) =6500 gm Mass of cone jar + sand after removing sand from cone is equals to mass of sand in a jar (m2) = 6142 gm Mass of sand in a cone (m3) = m1-m2 =358 gm Mass of jar + sand after filling hole (m4) = 5500 gm Mass of sand in a hole = (m2-m4-m3) = m5 = 284 gm Volume of the hole (V) =

=

. = 0.1890284 10-3 m3

Mass of soil taken from hole digging (m) = (1200-904) = 296 gm Density of soil (in-situ) i.e. (ρsoil) = =

. ^ = 1565.9023 kg/m3

= 1.566 gm/cc

5) RESULT: Hence form the laboratory experiment the field density of the soil (insitu –density) is found to be 1565.9023 kg/m3 or 1.566 gm/cc.

6) SUGGESTION AND CONCLUSION: Hence from the experiment the field density of the soil is found to be 1.566 gm/cc, this value of density is moist density of field soil but for practical cases we should measure the dry density of the soil i.e. ρd which is given by the formula ρs/(1+w), where w is the water content of the field soil. For the WBM road construction dry density of the soil i.e. ρd has vast application. This method is used for soils of various particle sizes, from fine-grained to coarse- grained. For accurate result the height of sand column in the cylinder is kept approximately the same as that in the calibration test. The depth of the hole should also be equal to the depth of the calibrating container. The observed density of the soil is bulk density of the soil. For the dry density of the soil we should measure the water content of the field soil and we can calculate the dry density of the soil by applying the above mention formula.

Submitted by: Rabindra Subedi Soil Mechanics Submitted to: Department of civil BCE 62109 ‘C’ Engineering

EXPERIMENT NO:3 9th May,2008

OBJECT: TO DETERMINE PARTICLE SIZE DISTRIBUTION OF A SOIL BY SIEVING.

1. APPARATUS REQUIRED: Set of fine sieves 4.75mm,2mm,1mm,600µ,425µ,212µ,150µ, and 75µ ,pan Weighing balance with accuracy of 0.1% of mass of sample Oven Mechanical shaker Trays

2. THEORY: Particle size analysis is a method of separation of soils into different fractions based on the particle size. It expresses quantitatively the proportions, by mass, of various sizes of particles present in a soil. The sieve analysis is meant for coarse‐grained soils (particle size greater than 75 micron) which can easily pass through a set of sieves. The sieve analysis is also known as dry analysis. For the particle size less than 75 micron sedimentation analysis is used which is also known as wet analysis. As a soil mass may contain the particles of both types of soils, a combined analysis comprising both sieve analysis and sedimentation analysis may be required for such soils. In sieve analysis the soil is sieve through a set of sieves. According to IS: 1498‐1970, the sieves are designated by the size of square openings, in mm or microns. Sieves of various sizes ranging from 80 mm to 75 microns are available. The diameter of the sieve is generally between 15 to 20 cm. The soil is sieved through a set of sieves. The material retained on different sieves is determined. The percentage of material retained on any sieve is given by;

Pn = 100 Where, Mn = mass of soil retained on sieve ‘n’, And M = total mass of the sample. The cumulative percentage of the material retained, Cn = P1+P2+……….+Pn Where P1,P2, etc, are the percentage retained on sieve ‘1’, ‘2’, etc. which are coarser than sieve ‘n’. The percentage finer than the sieve ‘n’, Nn=100‐Cn

3. PROCEDURE: The following procedure was done for the particle size analysis of fine grained soil:

First the soil mass was sieve through the IS sieve of 4.75 mm and passing soil of 1 kg mass was taken by accurately measuring from the weighing machine.

Then the sieves was prepared by stacking 4.75mm sieve at top and 75 micron sieve at bottom and others as decreasing size order from the top & finally pan at the bottom.

Then the soil sample was placed at the top sieve i.e. 4.75 mm sieve and it was covered by the top cover.

Then the sample was sieved by using mechanical shaker for 10 minutes. Then the soil fraction retained on each sieve was collect in a separate container. The mass retained in each sieve was weighted accurately.

Then the percentage retained, cumulative percentage retained, and the percentage finer was calculated.


4. OBSERVATION & CALCULATION: Total mass of dry soil = 1000 gm

5. RESULT: From the experiment and observation from the graph following result is found for fine aggregate: D60 =0.845 mm D30 =0.22mm D10 =0.072mm

Cu = = ..

=11.736

Cc =

= .

. . =0.796

Where, D60 = particle size such that 60% of the soil is finer than this size, and D30 = particle size such that 30% of the soil is finer than this size.

6. SUGGESTION AND CONCLUSION: The larger the numerical value of Cu, the more is the range of particles. Soils with a value of Cu less than 2 are uniform soils. Sands with a value of Cu of 6 or more are well graded. Gravels with a value of Cu of 4 or more are well graded. In another conditions the value of the coefficient of curvature lies between 1 and 3 for a well graded soil. From the graph we found that for the fine grained soil Cc= 11.736 & Cu= 0.796, which shows that on considering coefficient of uniformity only the soil is well graded but on considering coefficient of curvature the soil in not well graded. For the accurate result the soil should be oven‐dry. It should not contain any lump. If the soil contains organic matter, it can be taken air‐dry instead of oven dry. During the vibration the specified time should be maintained. There should not be any loss of mass during the mass measurement. The cap should be perfectly fitted on the top of the set of sieves. Pan should be put at the bottom. Dry sieve analysis is suitable for cohesionless soils, with little or no fines. If the sand is sieved in wet conditions, the surface tension may cause a slight increase in the size of the particles and the particles smaller than the aperture size may be retained on the sieve and the results would be erroneous.

S.No. Observations calculations IS Sieve Size of

openings(m)

Mass of soil retained (gm)

Adjusted wt. Retained (gm)

Percentage Wt. retained

Cumulative % wt. retained (a)

% finer= (100‐a)

1 4.75 mm 4.750 0 1 0.1 0.1 99.9 2 2.00 mm 2.000 175 176 17.6 17.7 82.3 3 1.00 mm 1.000 172 173 17.3 35 65 4 425 µ 0.425 237 238 23.8 58.8 41.2 5 300µ 0.300 68 69 6.9 65.7 34.3 6 150µ 0.150 138 139 13.9 79.6 20.4 7 75µ 0.075 132 133 13.3 92.9 7.10 8 Pan ‐ 70 71 7.1 100 0 Sum = 992 gm 1000 gm

Submitted By: Rabindra Subedi Soil Mechanics Submitted to: Department of BCE 62109 ‘C’ Civil Engineering

EXPERIMENT NO: 4 16th, May, 2008

OBJECT: TO DETERMINE THE LIQUID LIMIT OF A GIVEN SOIL SAMPLE

1) APPARATUS REQUIRED: a) Casagrandes liquid limit device b) Grooving tools of both standard and ASTM types c) Oven d) Evaporating dish or glass sheet e) 425 µ IS sieve f) Weighing balance

2) THEORY: The liquid limit of a soil is the water content at which the soil behaves practically like a liquid, but has small shear strength. It flows to close the groove in just 25 blows in Casagrandes liquid limit device. Liquid limit is the minimum water content at which the soil is still in liquid state but has a small shearing strength against flowing. In the standard liquid limit test, it is the minimum water content at which part of soil cut by a groove of standard dimensions, will flow together for a distance of 12 mm under an impact of 25 blows falling from a height of 10 mm. As it is difficult to get exactly 25 blows in a test 3 to 4 tests are conducted and the number of blows (N) required in each test is determined. A semi‐log graph is plotted between logN and the water content (w). The liquid limit is the water content corresponding to N=25 as obtained from the plot.

3) PROCEDURE i. Adjusted the drop of the cup of the liquid limit device by releasing the two screws at

the top and by using the handle of the grooving tool or a gauge .The drop should be exactly 1cm at the point of contact on the base .Tighten the screw after adjustment.

ii. About 120gm of the air dried soil sample passing 425 µ IS sieve was taken. iii. The sample was thoroughly mixed with distilled water in an evaporating dish or a glass plate

to form a uniform paste. Mixing should be continued for about 15 to 30 minutes, till a uniform mix is obtained.

iv. The mix was kept under humid conditions for obtaining uniform moisture distribution for sufficient period. For some fat clay this moisturing time may be up to 24 hrs.

v. A portion of the matured paste was taken and remixes it thoroughly. Place it in the cup of the device by a spatula and level it by a spatula or a straight edge to have a maximum depth of the soil as 1 cm at the point of the maximum thickness. The excess soil, if any, should be transferred to the evaporating dish.

vi. A groove was cut in the sample in the cup using the appropriate tool. Draw the grooving tool through the paste in the cup along the symmetrical axis, along the diameter through the center line of the cam. Hold the tool perpendicular to the cup.

vii. The handle of the device was turned at a rate of 2 revolutions per second. Count the number of blows until the two halves of the soil specimen come in contact at the bottom of the groove along a distance of 12 mm due to flow and not by sliding.

viii. A representative specimen of the soil was collected by moving spatula width‐wise from one edge to the other edge of the soil cake, at right angles to the groove. This should include the portion of the groove in which the soil flowed to close the groove. Place the specimen in an air‐tight container for the water content determination. Determine the water content.

ix. Remove the remaining soil from the cup. Mix it with the soil left in the evaporating dish. x. Change the water content of the mix in the evaporating dish either by adding more water if

the water content is to be increased or by kneading the soil, if the water content is to be decreased. In no case the dry soil should be added to reduce the water content.


xi. Repeated steps to x and determine the number of blows (N) and the water content in each case.

xii. The flow curve between logN and w was drawn and the liquid limit corresponding to N=25 was determined.

4) OBSERVATION AND CALCULATIONS:

S.No Observations Determination No.

1 2 3 4

1 No of blows(N) 30 13 18 23

2 Container No 39 43C B1 D

3 Mass of wet soil (M1) 25 17 24 19

4 Mass of container (M) 5 5 6 5

5 Mass of container with dry soil (M2)

21 14 20 16

6 Mass of dry soil (M3)= (M2‐M)

16 9 14 11

7 Mass of water (Mw)=M1‐M3

4 3 4 3

7 Water

content(w)= 100 25% 33.33% 28.57% 27.27%

5) RESULT The flow curve between LogN and water content ‘w’ is plotted. Now from the graph of liquid

limit (corresponding to N=25), liquid limit (WL) =27%. 6) SUGGESTION AND CONCLUSION:

Hence from the experiment of liquid limit we found that the liquid limit of the soil sample is 27%. It shows that the sample soil changes from the liquid state to the plastic state only when the water content in the soil sample is 27%. At this stage the shearing strength to the soil is smallest value. The value of liquid limit is directly used for the classification of the fine grained cohesive soils according to Indian Standard on soil classification. Once the soil is classified, it helps a lot in understanding the behavior of soils and selecting the suitable methods of design, construction and maintenance of the structures made up or resting on soils. The liquid limit of a soil is an indicator of the compressibility of a soil. The compressibility of a soil generally increases with an increase in liquid limit. Following precautions are necessary for the exact value of liquid limit: 1. Distilled water should be used in order to minimize the possibility of ion exchange

between the soil and any impurities in the water. 2. Soil used for liquid limit should not be oven dried prior to testing.


3. In liquid limit test the groove should be closed by a flow of the soil and not by slippage between the soil and the cup.

4. After mixing distilled water to the soil sample, sufficient time should be given to permeate the water throughout the soil mass.

5. Wet soil taken in the container for moisture content determination should not be left open in the air even for some time; the containers with the soil samples should either be placed in desiccators or immediately by weighted.

6. For each test the cup and grooving tool should be clean.

Submitted by: Rabindra Subedi Soil Mechanics Submitted to: Department of BCE 62109 ‘C’ Civil Engineering

EXPERIMENT NO: 5 16th, May, 2008

OBJECT: TO DETERMINE THE PLASTIC LIMIT OF THE SOIL SAMPLE.

1) EQUIPMENT: a) Weighing machine b) Two containers c) Oven d) Glass plate

2) THEORY: The plastic limit of a soil is the water content of the soil below which it ceases to be plastic. It begins to crumble when rolled into threads of 3mm diameter. Or in other words, it is the water content at which soil changes from plastic to semi solid state. Or the moisture content at which soil has the smallest plasticity is called the plastic limit. Just after plastic limit the soil displays the properties of a semi‐solid. Change in state at these limits is shown in fig. below:


For the determination purpose, the plastic limit of the soil is defined as the water content at which a soil will just begin to crumble when rolled into a thread of 3 mm in diameter. The difference in moisture contents or interval between the liquid and plastic limits is termed as the plasticity index. Knowing the liquid limit and plasticity index, soil may be classified with the help of plasticity chart according to Indian standard on the soil classification (Is 1498‐1970).

3) PROCEDURE: a) About 30 gm of air dried soil passing from 425µ sieve was taken. b) The soil was mixed with water and was made plastic enough to shape into a small ball. c) Then the plastic soil was rolled with hand in a glass plate into a thin thread. When the

crumbling occurred when the thread was just above 3mm diameter the sample was then taken for the calculation of plastic limit.

d) The sample so made was then kept in two containers of known weights, and combined weights of sample and container was taken.

e) Then the sample was left in oven for 24 hours for complete drying. f) After 24 hours the weights of each containers containing samples were weighted g) And then the plastic limit was calculated.

4) OBSERVATION:

S.No. Observations and calculations. Sample

Water Content

(%) (added in lab test)

Result

1 Weight of empty container (M) 7 gm 15% No thread formation

2 Weight of wet soil (M1) 6 gm 20% No thread formation

3 Weight of container + dry soil (M2)

12 gm 21.5% Thread formation 3mm diameter i.e.

Plastic limit

4 Weight of dry soil (Ms)=(M2‐M)

5gm

4 Weight of water (Mw)=M1‐Ms 1 gm

5 Water content (w) = 100 %

20%

6 Plastic limit 20% 20% Which is the correct plastic limit of the soil


5) CALCULATIONS &RESULT: Plastic limit (Wp) =20% Liquid limit (Wl) =27% (from experiment no 5 where the sample was same) Plasticity index (Ip) = (Wl‐Wp) = (27‐20) % =7% Plasticity index by the formula (p.I.) =0.73(w.l.‐20) = 0.73*(27‐20) =5.11% adopt the higher of two value i.e. plasticity index =7%. Hence from the experiment we found that the plastic limit of the soil sample is 20%.

6) SUGGESTION AND CONCLUSION: Hence from the experiment we found that the plastic limit of the soil is 20%. From this observed value of plasticity index we conclude that the soil is silts of low plasticity (observed from the plasticity chart) which lies in the range of ML and is partly cohesive soil. The liquid limit of the soil sample is 27% which is less than 50% and the plasticity index is 7% which lies in the range of ML from the chart. The shear strength of the soil at the plastic limit is about 100 times that at the liquid limit. For the exact value of plastic limit following precautions are necessary: 1. Distilled water should be used in order to minimize the possibility of iron exchange between the soil and any impurities in the water.

2. Soil used for plastic limit should not be oven dried prior to testing. 3. After mixing distilled water to the soil sample, sufficient time should be given to permeate the water throughout the soil mass.

4. Wet soil taken in the container for moisture content determination should not be left open in the air even for some time; the containers with the soil samples should either be placed in desiccators or immediately by weighted.

Submitted by: Rabindra Subedi Soil Mechanics Submitted to: Department of Civil BCE 62109 ‘C’ Engineering

EXPERIMENT NO: 6 13Th May COMPACTION TEST OBJECT: TO DETERMINE THE OPTIMUM MOISTURE CONTENT AND MAXIMUM DRY DENSITY OF A SOIL BY

PROCTOR TEST & TO PLOT THE CURVE OF ZERO AIR VOID.

1. APPARATUS REQUIRED: a. Compaction mould of 1000 ml capacity internal dia. 100 mm effective ht. 127.3 mm b. Rammer of 2.6 kg free drop 310 mm c. Detachable base plate d. Collar, 60 mm height e. IS sieve of 4.75 mm f. Oven g. Desiccator h. Weighing balance of 1 gm accuracy i. Large mixing pan j. Straight edge k. Spatula l. Graduated jar m. Mixing tools, spoons, trowels, etc.

2. THEORY:

Compaction is the process of densification of soil mass by reducing air voids. The dry density is maximum at the optimum water content. This process should not be confused with consolidation which is also a process of densification of soil mass but by the expulsion of water under the action of continuously acting static load over a long period. The degree of compaction of a soil is measured in terms of its dry density. The degree of compaction mainly depends upon its moisture content, compaction energy and type of soil. For a given compaction energy every soil attains the maximum dry density at a particular water content which is known as optimum moisture content.


In the dry side, water acts as a lubricant and helps in the closer packing of soil grains. In the wet side, water starts to occupy the space of soil grains and binders in the closer packing of grains. At water content lower than the optimum, the soil is rather stiff and has lot of void spaces and, therefore, the dry density is low. As the water content is increased, the soil particles get lubricated and slip over each other, and move into densely packed positions and the dry density is increased. However, at water content more than the optimum, the additional water reduces the dry density, as it occupies the space that might have been occupied by solid particles. For given water content, theoretical maximum density, (ρd) theomax, is obtained corresponding to the condition when there are no air voids (i.e. degree of saturation is equal to 100%). The theoretical maximum dry density is also known as saturated dry density (ρd) sat. . In this condition, the soil becomes saturated by reduction in air voids to zero but with no change in water content. The soil could also become saturated by increasing the water content such that all air voids are filled.

Dry density i.e. (ρd) = / where, M= total mass of soil, V = volume of soil & w = water content

The condition of zero air void line is a condition where all air is expelled from the voids such that the soil is fully saturated. This condition is idealistic, which cannot be achieved through compaction in actual practice. In practice never brings the soil to zero air void condition. Thus all compaction curves fall at the left hand side of the zero air void line.

I.e. Гd = Г

3. PROCEDURE:

The following procedure was done: a. About 20 kg soil sample was taken for the mould of 1000 c.c. b. The soil was sieve through 20 mm and 4.75 mm sieves. c. The percentage retained on 20 mm and 4.75 mm sieves and passing from 4.75 mm sieves was

calculated. The soil retained on 20 mm sieve was not used. d. Mould of 100 mm dia. was used so that the percentage retained on 4.75 mm sieve was less

than 20. e. The soil was mixed according to retained on 4.75 mm sieve and passing from 4.75 mm sieve

thoroughly in the proportion obtained in step c. f. 2.5 kg of the prepared soil sample was taken for 1000 cc mould for light compaction. g. Water was added to it to bring its moisture content to about 4% in coarse grained soils and 8%

in fine grained soils. h. The mould & base plate was cleaned, dried and grease lightly. The mould with base plate was

weighted. i. The collar was fitted and placed the mould on a solid base. j. The wet soil was compacted in three equal layers by the rammer of mass 2.6 kg and free fall of

31 cm with 25 evenly distributed blows in each layer. k. The collar was removed and trimmed off the soil flush with the top of the mould. In removing

the collar it was rotated to break the bond between it and the soil before lifting it off the mould.

l. The outside of the mould and the base plate was cleaned and weighted the mould with soil and the base plate.

m. The soil from the mould was removed and a representative soil sample from the bottom, middle and top was taken for the water content determination of the compacted soil.

n. The weight of the sample for water content with the container was taken and the sample with the container was placed to the oven at temperature 105˚C to 110˚C for 24 hours.


o. The above procedure was repeated by increasing the water content 7, 10,13,16,19 and 22% until the weight of the soil decreases.

p. The weight of the container with dry soil sample and the weight of container were taken in the nest day.

4. OBSERVATIONS AND CALCULATIONS: The following observation was taken from the experiment: Diameter of mould = 100 mm height of mould = 127.3 mm Volume of mould, V =π/4 (10.0)2 12.73 = 999.81 ≈1000 ml Specific gravity of solids, G = 2.67 (taken) S.No Observations and calculation Determination No.

1 2 3 4 5 1 Mass of empty mould + base

plate 3895 gm

3895 gm

3895 gm

3895 gm

2 Mass of mould + base plate +compacted soil

5825 gm

5950 gm

5995 gm

5875 gm

3 Mass of compacted soil, M =(2)‐(1)

1930 gm

2055 gm

2100 gm

1980 gm

4 Bulk density, ρ= 1.93 g/cc

2.055 g/cc

2.100 g/cc

1.980 g/cc

5 Container no G 43 B F3 39 6 Mass of container + wet soil (a) 23 gm 22 gm 38 gm 32 gm 7 Mass of container + dry soil (b) 21 gm 20 gm 33 gm 27 gm 8 Mass of water (Mw) =(a)‐(b) 2 gm 2 gm 5 gm 5 gm 9 Mass of container (c ) 5 gm 6 gm 5 gm 6 gm 10 Mass of dry soil (Ms)= (b)‐(c) 16 gm 14 gm 28 gm 21 gm 11 Moisture content (w) = 12.5 % 14.285% 17.857% 23.809%

12 Dry density (ρd) = 1.716 g/cc

1.798 g/cc

1.782 g/cc

1.599 g/cc

Sample calculation: ρd = =..

=1.716 gm/cc

Water content at optimum water content = 16% and maximum dry density ρd max. = 1.80 gm/cc The dry density at 100% saturation is, ρd =

=

. . . =1.87 gm/cc. I.e. S =1 and for ρd=1.80 gm/cc, S

=0.884 i.e. degree of saturation is = 88.4%.

Gs = specific gravity of soil grains W = water content at o.m.c. ρw = unit mass of water (1g/cc) S= degree of saturation (one for fully saturated soils).

5. RESULT: Hence from the experiment we found that the maximum dry density of the soil is 1.80 gm/cc. And the Optimum water content is 16 %. The degree of saturation at optimum water content is 0.884 i.e. 88.4 %.


6. SUGGESTIONS & CONCLUSION: Following precautions are necessary for the exact determination of O.M.C. and maximum dry density of the soil:

a. Adequate period is allowed for mixing the water with soil before compaction. b. The blows should be uniformly distributed over the surface of each layer. c. Each layer of compacted soil is scored with a spatula before placing the soil for the succeeding layer. d. The amount of soil used should be just sufficient to fill the mould i.e. at the end of compacting the

last layer surface of the soil should be slightly (5 mm) above the top rim of the mould. e. Mould should be placed on a solid foundation during compaction.

Compaction of soils increases soil density, shear strength, bearing capacity but reduces their void ratio, porosity, permeability and settlements. The results of this test are useful in the stability of field problems like earthen dams, embankments, roads and airfields. In such constructions, the soils are compacted. The moisture content at which the soils are compacted in the field is controlled by the value of optimum moisture content determined by the laboratory proctor compaction test. The compaction energy to be given by the field compaction unit is also controlled by the maximum dry density determined in the laboratory. In other words, the laboratory compaction tests results are used to write the compaction specification for field compaction of soils. From the experimental value of the test soil the optimum moisture content of the soil is found to be 16% which is the maximum value of water that can be added to the soil so that we can achieve the maximum dry density from the soil.


EXPERIMENT NO: 7 30th May, 2008

GRAIN SIZE ANALYSIS BY HYDROMETER METHOD

OBJECT: TO DETERMINE THE PERCENTAGES OF VARIOUS SOIL GRAINS (FINER THAN 75 MICRON) BY HYDROMETER METHOD.

1. APPARATUS REQUIRED: 1. Hydrometer (calibrated at 27 ° C, range 0.995 to 1.030 g/cc). 2. Cylinder or Jars (two, volume of 1000 cc, graduated, dia.. about 7 cm, height 30 cm ) 3. Dispersing agent solution (containing 33 gm of sodium hexameta‐ phosphates and 7 gm of sodium carbonate in

distilled water to make one liter of solution) 4. Mechanical stirrer (high speed greater than 5000 rpm) 5. Balance (accuracy 0.01 gm) 6. Thermometer (accuracy 0.5 ° C) 7. Stop watch 8. Sieve 75 micron 9. Centimeter scale 10. Distilled water 11. Soil weighing dish.

2. THEORY: The hydrometer analysis is based on strokes law, which defines the rate of free fall of a sphere through a liquid it is given as: V= (2γs‐γ1) r2/9η ……………………………………………………… (1) Where, V = velocity of sphere (also known as terminal velocity, (cm/sec)) γs = density (unit mass of sphere), gm/cm3 γ1 =density of liquid, gm/cc r = radius of sphere, cm η = Viscosity of liquid, gm/sec cm2 If the above equation is used for hydrometer analysis, γs is taken equal to average specific gravity of soil grain assuming unit mass of water equal to 1 and if viscosity is taken in dyne sec/cm2, it becomes:

V = D2 …………………………………………………………………… (2)

Where Gs = average specific gravity of grains (solids) D = equivalent diameter of grains (mm)

Hence D =

If particles of diameter D travel through a distance h (cm) in time t minutes

Then, D =

…………………………………………………… (3)

In the above equation h is determined by the equation, h = h1+ (h0 ‐

) …………………………………….. (4)

Where, h1= distance from the lowest graduation to the graduation mark (R) of the stem at the top surface of soil water mixture, h0 = distance from the lowest graduation to the centre of volume of the bulb. Vh = volume of hydrometer A1= cross‐sectional area of the jar. A calibration table is prepared between h and the hydrometer reading on the stem.


At this time’s’ all particles greater than diameter ‘D’ would have settled below the depth h. But the concentration of the particles of sizes smaller than ‘D’ remains the same at this depth. This concentration is measured by the hydrometer in terms of specific gravity of the suspension. If Wd is the mass of soil particles finer than ‘D’ per unit volume of suspension at time’s’, it can be calculated by the equation:

Wd = …………………………………………………………… (5)

Where Rc2 = correct hydrometer reading = Rh+Cm C1 –Cd = Rh±C ……………………………………………. (6) Where, Rh =hydrometer reading Cm = correction due to meniscus C1 = correction due to temperature Cd = correction due to dispersing agent C = composite correction If Wd is the total mass of soil taken in the original 1000 cc of suspension, the percentage finer than ‘D’ is obtained from equation:

Percentage finer, N = 100 ………………………………….. (7) Hence at any time t, the size of particles is calculated from above equation (3) and (4) and the corresponding percentage finer from equation (7). Hydrometer method is used to determine the particle size distribution of fine‐grained soils passing 75 µ sieves. The hydrometer measures the specific gravity of the soil suspension at the centre of its bulb. The specific gravity depends upon the mass of solids present, which in turn depends on the particle size. In a given soil the percentage of different soil particles up to 75 micron is determined by sieve analysis, but the percentage of various soil particles finer than 75 micron is determined by hydrometer analysis. Hence the hydrometer analysis is useful in knowing the percentage of silt and clay. Activity of clays may also be estimated if clay fraction is known.

Activity =

Activity helps in classifying the soils as follows: Activity Classification <0.75 Inactive 0.75‐1.25 Normal >1.25 Active

In short form D =M / where M = .

3. PROCEDURE: The following procedure was done for the hydrometer analysis: a. First 50 gm of pretreated dry soil passing from 75 micron sieve was taken. b. Then the soils was placed in an evaporating dish and cover it up with 100 cc of dispersing solution and warmed

gently for about 10 minutes. c. The sample was transferred to the cup of mechanical stirrer using distilled water until the cup is three fourth

full and operated the mixer for about four minutes. d. Then the clean hydrometer was kept in a 1000 cc. jar filled with distilled water and 100 cc dispersing agent

solutions. e. After stirring, the specimen was washed into a 1000 cc jar and enough water was added to bring the level to

1000 cc mark. f. Then mixed thoroughly the specimen in the jar by placing the palm of the hand in the open end and turning

the jar up side down and back. g. Then the jar was placed on the table and inserted the hydrometer. The stop watch was started

simultaneously. h. Then the reading at the top of the meniscus at 0.5, 1, 2 and 4 minutes was observed. i. The temperature of the suspension was recorded.


j. Then the further reading at 8, 15, 30 minutes and 1, 2, 4, 8 and 24 hours after the start of the test was taken. For each of these readings, the hydrometer was inserted just before the reading.

k. For determining the hydrometer corrections the readings on the top and bottom of the meniscus formed on the stem of the hydrometer was taken when it was floating in the second jar containing the distilled water and dispersing agent only. For calibration of hydrometer the following procedure was done:

l. The cross‐sectional area of the jar was measured for which measure the distance between two graduations on the jar by the scale and recorded the volume between the two.

m. For determining the volume of the hydrometer, 1000 cc graduated jar was taken and filled about 700 cc of distilled water in it, and recorded the exact reading. Inserted the hydrometer and the reading on the graduation jar was taken. The difference of readings before and after insertion of the hydrometer gives the volume of hydrometer.

n. The centre of the volume of the hydrometer from the lowest graduation mark on the stem was measured. o. The distances from the lowest graduation mark to the other marks on the stem of the hydrometer was

measured.

4. OBSERVATIONS AND CALCULATIONS: The observation and calculation are given in the table below: Hydrometer – Calibration: i. Hydrometer no. =1 ii. Sedimentation Jar No. = C2 iii. Volume of hydrometer, VH, = 880‐800 =80 cm

3 iv. Volume between any two graduations =850‐320 =530 cc v. Length between two graduation =14.9 cm vi. Cross‐sectional area of jar, Aj =530/14.9 =35.57 cm

2 vii. Distance between lowest graduation and neck = 1 cm viii. Distance between neck and center of volume of bulb = 8 cm ix. Distance between lowest graduation and centre of the bulb (h0) = 1+8 = 9 cm

x. Constant, K =(h0 ‐ ) = (9 ‐ .

= 7.8754

Table no: 1

Time Hydrometer reading Rh

(Rc1) (1) Distance from lowest graduation to Rh i.e. h1

(cm) (2)

Effective depth h(cm) (3)

h =h1+(h0 ‐ )

Temperature (4)

0.5 minute 1.022 3.6 11.4754 24˚C 1 minute 1.022 3.6 11.4754 ‘’ 2 minute 1.017 3.9 11.7754 ‘’ 4 minute 1.014 4.8 12.6754 ‘’ 8 minute 1.0105 5.9 13.7754 ‘’ 16 minute 1.0065 7.05 14.9254 ‘’ 30 minute 1.005 7.80 15.6754 ‘’ 1 hour 1.0045 7.70 15.5754 ‘’ 2 hour 1.004 7.80 15.6754 ‘’ 4 hour 1.003 8.10 15.9754 24.5˚C 24 hour 1.003 8.10 15.9754 24.5˚C


Table No.2: Mass of dry soil (passing from 75 µ sieve) taken=50 gm Specific gravity of the soil grains (Gs) = 2.67 Top meniscus reading on hydrometer stem =1.0265 Bottom meniscus reading on hydrometer stem =1.0270 Meniscus correction, Cm = (1.0270‐1.0265) =0.0005 (+ve) Hydrometer reading (Rh) = (reading‐1)*1000 = (1.022‐1)*1000 =22 and so on. At 24˚C viscosity = 9.16 milli poise from table = 9.3374*10‐6gm‐sec/cm2

At 24.5 ˚C viscosity = 9.055 milli poise = 9.055 10‐3N‐S/M2 /10=9.055*10‐4*1/9.81kg‐S/104 cm2 = 9.2304*10‐6gm‐ sec/cm2

Factor M =

Diameter of particle D = D =

= M /

Composite correction C = top meniscus reading on hydrometer stem when floating in jar containing distilled water and dispersing agent only ‐1.000 =1.0265‐1.000= +0.0265 correction is –ve i.e. ‐0.0265.

Date Time (minute)

Elapsed

Time(t)

minute

Hydrometer

Reading (Rh)

Temp‐

erature

T(˚C)

Composite

Correction ±C

Rc1= Rh+Cm

Effec‐ tive depth h(cm)

/ Viscosity η

(gm/sec /cm2)

Factor M

Particle “C’

(mm) (9)

Rc2= Rh±C (4)+(6)

Factor N

% finer w.r.to wt. Wd (13) (14)

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) 30thmay

0.5 0.5 22 24˚C ‐0.0265 22.0005 11.4754 4.7906 9.3374 *10‐6

12.9514*10‐3

0.06204 21.9735

3.1976 70.2625

‘’ 1 1 22 ‘’ ‐0.0265 22.0005 11.4754 3.3875 9.3374*10‐6

12.9514*10‐3

0.04387 21.9735

3.1976 70.2625

‘’ 2 2 17 ‘’ ‐0.0265 17.0005 11.7754 2.4265 9.3374*10‐6

12.9514*10‐3

0.03143 16.9735

3.1976 54.2745

‘’ 4 4 14 ‘’ ‐0.0265 14.0005 12.6754 1.7801 9.3374*10‐6

12.9514*10‐3

0.02305 13.9735

3.1976 44.6817

‘’ 8 8 10.5 ‘’ ‐0.0265 10.5005 13.7754 1.3122 9.3374*10‐6

12.9514*10‐3

0.01699 10.4735

3.1976 33.4901

‘’ 16 16 6.5 ‘’ ‐0.0265 6.5005 14.9254 0.9658 9.3374*10‐6

12.9514*10‐3

0.01251 6.4735 3.1976 20.6997

‘’ 30 30 5.0 ‘’ ‐0.0265 5.0005 15.6754 0.7229 9.3374110‐6

12.9514*10‐3

0.00936 4.9735 3.1976 15.9032

‘’ 1 hr 60 4.5 ‘’ ‐0.0265 4.5005 15.5754 0.5095 9.3374*10‐6

12.9514*10‐3

0.00659 4.4735 3.1976 14.3044

‘’ 2 hr 120 4.0 ‘’ ‐0.0265 4.0005 15.6754 0.3614 9.3374*10‐6

12.9514*10‐3

0.00468 3.9735 3.1976 12.7057

‘’ 4 hr 240 3.0 24.5˚C

‐0.0265 3.0005 15.9754 0.2580 9.2304*10‐6

12.8769*10‐3

0.00332 2.9735 3.1976 9.5081

31th May

24 hr 1440 3.0 24.5˚C

‐0.0265 3.0005 15.9754 0.1053 9.2304*10‐6

12.8769*10‐3

0.00135 2.9735 3.1976 9.5081

5. RESULT:

From the hydrometer analysis the particle size less than 0.075 mm and percentage finer is calculated in the above table. And the particle size distribution curve is plotted in the graph.

6. SUGGESTION AND CONCLUSION: The hydrometer analysis is based on the strokes law of viscosity. The particle size less than 75 micron can not be determined by simple sieve analysis so it needs hydrometer analysis for the particle size determination. The


particle size distribution curve shows that the shape of the curve is approximately well graded nature. The behavior of fine –grained soils depends upon the plasticity characteristic and not on the particle size. For the exact analysis by the hydrometer following precautions are necessary: a. The insertion of the hydrometer should be done carefully without bumping. b. The hydrometer should float at the center of the jar and should not touch the sides. c. The stem of the hydrometer should be dry and clean. d. There must be no vibrations in the vicinity. e. The temperature variations should be minimized by keeping both the jars away from any course of heat and

direct sunlight. The hydrometer analysis is useful in knowing the percentage of silt and clay present in the soil. Activity of clays may also be estimated if clay fraction is known.

Activity =

Activity helps in classifying the soils as follows: Activity Classification <0.75 Inactive 0.75‐1.25 Normal >1.25 Active

The S type curve is the characteristic of well graded soils. From the graph we found nearly S curve so it is classified as well graded for clay, silt and sand.

Submitted by: Rabindra Subedi Soil Mechanics Submitted To: Department of BCE 62109 ‘C’ Civil Engineering

EXPERIMENT NO: 8 6th June, 2008 PERMEABILITY TEST OF SOIL

OBJECT: TO DETERMINE COEFFICIENT OF PERMEABILITY OF GIVEN SOIL SAMPLE BY VARIABLE HEAD METHOD.

1. APPARATUS REQUIRED:

a. Permeater mould , internal diameter = 100 mm , effective height =127.3 mm, capacity=1000cc b. Detachable collar, 100 mm diameter, 60 mm height c. Dummy plate, 108 mm diameter, 12 mm thick d. Drainage base, having a porous disc e. Drainage cap, having a porous disc with a spring attached to the top f. Water supply reservoir g. Vacuum pump h. Stop watch i. Thermometer j. Graduated glass stand pipe, 5 to 20 mm diameter k. Supporting frame for the stand pipe, and the clamp

2. THEORY:

The property of the soils which permits water (fluids) to percolate though its continuously connected voids is called its permeability. Depending upon the value of Reynolds’s number the flow of water through soils may be ‘laminar’ or ‘turbulent’. In laminar flow, a particle of water starting from a given position follows a definite path without crisscrossing the path of other particles. In turbulent flows the particles do not follow any definite path but have random, twisting and crisscrossing path. For laminar steady flow, according to Darcy’s law the rate of water is proportional to the hydraulic gradient in uniform and homogeneous soils. i.e. V α i ………………………………………………………………………………………………..(i) Where v = discharge velocity of water V = k *i If q = discharge of water per unite time q = k*i*A (7‐2) If i= 1 K = v (7‐3) Where, i = hydraulic gradient K = coefficient of permeability A = cross sectional area of the soil for discharge q. In soil mechanics, the coefficient of permeability, k expresses the degree of permeability. It has the velocity dimensions. Factors affecting the coefficient of permeability can be studied by the equation

K= c ds2 Г

Where k = coefficient of permeability C= constant ds = average diameter of soil grains Гw = unit weighted water η = viscosity of the water e = void ratio of the soil Viscosity and unit weight of water depend upon temperature; hence the coefficient of permeability is effected by the climatic conditions also. Constant ‘C’ depends upon arrangement and shape of grains and voids. Thus the soil in‐situ often as smaller permeability in vertical direction as compared to the horizontal due to horizontally stratified structure.


The coefficient of permeability may be determined both in the laboratory and field by direct tests. In the laboratory, constant head method is more suited to coarse grained soils as the quantity of seepage in case of relatively impervious soils is less. Variable head method is suited to fine grained soil as the fall of head is very fast in coarse grained soils. Permeability is the property of soils, which permits water (fluids) to percolate through its continuously connected voids. A soil is called highly pervious if it allows the flow of water through it easily where as impervious soils do not allow the flow of water through it. In constant head test, a steady vertical flow under constant head difference H is maintained throughout the soil sample of length 'L' and x‐sectional area 'A' and the volume of water per unit time passing through the sample is measured. Whereas, in variable head or falling head test, a steady vertical flow under varying head difference dH i.e.( H1 – H2) maintained throughout the soil sample of length 'L' and x‐sectional area 'A' and the volume of water per unit time passing through the sample is measured. As the soil sample taken during the experiment was fine grained, variable head method was adopted.

In the variable or falling head test, the coefficient of permeability (k) is given by

2H1H

10log AtaL 2.3k =

Where, a = cross sectional area of stand pipe

A = cross sectional area of soil

l = length of soil sample

t = time taken for water to flow from head h1 to h2

H1 = initial water level on stand pipe measured from the lower opening

H2 = final water level on stand pipe measured from the lower opening

Applications:

Water flowing through soil exerts considerable seepage forces which have direct effect on the safety of hydraulic structures. The rate of settlement of compressible clay layer under load depends on its permeability. The quantity of stored water escaping through and beneath an earthen dam depends on the permeability of the embankment and the foundation respectively. The permeability of the soil is the factor for the rate of drainage of water through wells and excavated foundation pits. Shear strength of the soil also depend indirectly on its permeability as the dissipation of the pore pressure is controlled by its permeability. Different soils have different values of permeability. The values of permeability for different types of soils determine the use of the soils for different purposes.

Approximate values of coefficient of permeability for different types of soils are:

Type of soil Value of K (cm/sec) Nature Drainage properties Sand 1.0 – 10‐3 Pervious good Silt 10‐3 – 10‐6 Semi‐pervious fair Clay less than 10‐6 Impervious poor


3. PROCEDURE: Following procedure was done for the determination of permeability coefficient of the soil:

a) At first the cover of the mould was removed and little grease on the sides of the mould was applied.

b) The weight of the mould with dummy plate was weighted.

c) The internal diameter and effective height of the mould was measured and then the collar and the base plate were attached.

d) Soil sample was compacted at given dry density and moisture content into the mould. The mould was then set up with its cover, base, collar and plate.

e) The reservoir or the stand pipe was connected to the bottom inlet of the mould and water was allowed to flow in. This process is done to check whether the soil in the mould is completed saturated or not. The soil is considered to be fully saturated when water is seen to come out from the top opening.

f) Then the reservoir or standpipe was connected to the top inlet and water was allowed to flow down through the soil and out of the bottom opening continuously. This was done to check if the flow is steady and laminar.

g) The bottom opening was then closed and the standpipe was filled with water up to certain level h1. This level was marked and the bottom opening was then opened. The time of flow from h1 to another marked level h2 was recorded. The difference in height between h1 and h2 was taken about 30–40 cm.

h) Step 4 was repeated several times to obtain 10 readings. i) The temperature of water was measured by a thermometer.

4. OBSERVATION AND CALCULATION:

Diameter of stand pipe (d) = 20.4 mm = 2.04 cm

Cross sectional area of stand pipe (a) = π/4 20.42 = 326.851 mm2 = 3.2685 cm2

Diameter of soil sample (D) = 10 cm

∴ Cross sectional area of soil (A) = π/4 102 =78.5398 cm2

Length of soil sample (L) = 127.3 mm =12.73 cm

Temperature of water = 24˚C

Ht. of the base of standpipe to the bottom opening (H) = 48.5cm


Observation Table:

S.NO. INITIAL HEAD

H1 (CM) FINAL HEAD H2 (CM)

TIME T (SEC)

K (CM/S)

MEAN K (CM/S)

1 148.5 138.5 19.1 1.9315 10‐3 2 138.5 128.5 22.2 1.7864 10‐3 3 128.5 118.5 22.5 1.9054 10‐3 4 118.5 108.5 24.4 1.9120 10‐3 5 108.5 98.5 24.4 2.0970 10‐3 1.9576 10‐3

6 98.5 88.5 29.0 1.9535 10‐3 7 88.5 78.5 31.8 1.9953 10‐3 8 78.5 68.5 35.6 2.0255 10‐3 9 68.5 58.5 41.5 2.0122 10‐3

Sample Calculation For 1st observation: We have,

2H1H

10log AtaL 2.3k =

H1 = 100cm

H2 = 90 cm

t = 19.1 sec

cm/sec3-10 x 1.9315 138.5148.5

10log 19.1 x 78.539

12.73 x 3.2685 2.3k ==

∴ Mean k24oC = 1.9576 10‐3 cm/sec

Now,

η27 oC = 8.55 x 10‐3 poise

η 24˚C= 9.16 x 10‐3 poise

k27oC = k24

oC x η24

oC / η27

oC = 1.9576 x 10

‐3 x 9.16 x 10‐3 / (8.55 x 10‐3) = 2.0973 x 10‐3 cm/sec

5. RESULT: From the above experiment, the coefficient of permeability of the soil sample at 24˚C is found to be 1.9576x10‐3 cm/s & the coefficient of permeability at standard temperature 27o C (as IS: 2720) is found to be 2.0973x10‐3 cm/s. The coefficient of permeability of the soil lies between 10‐3 to 10‐6 hence, we classify that the soil is silty and which is semi‐pervious.


6. SUGGESTIONS &CONCLUSION: The permeability of the soil is an important factor regarding the engineering properties of the soil. The stability and safety of the structure standing depends on the permeability of the soil. Excessive seepage can cause the failure of structure. Similarly, the settlement of soil, quantity of water drained, shear strength of the soil etc are governed by the permeability of the soil. All these factors are very significant in civil engineering point of view. For this reason, the permeability of soil is to be determined prior to construction of any structure. For the correct value of permeability coefficient determination of the soil following precautions are necessary:

a) All the possibilities of leakage at the joints must be eliminated. All the joints and washer must be thoroughly cleaned so that there are no soil particles between them.

b) Grease should be applied liberally between mould, base plate and collar. c) Rubber washers must be moisture with water before placing. d) Porous stones must be saturated just before placing. e) De‐aired and distilled water must be used to avoid the choking of flow water. f) Soil samples must be fully saturated before taking the observations. g) In order to ensure laminar flow condition, cohesionless soils must be tested under low

hydraulic gradient. h) Steady flow must be established before taking the observations.

Hence the variable method is suitable for very fine sand and silt with K =10‐2 to 10‐5 mm/sec. permeability has vast application in the seepage analysis of the soil and the drainage property of the soil. Knowledge of permeability is essential in a number of soil engineering problems, such as settlement of buildings, yield of wells, seepage through and below the earth structures. It controls the hydraulic stability of soil masses. The permeability of soils is also required in the design of filters used to prevent piping in hydraulic structures. The coefficient of permeability of the soil in lab is determined generally by two methods: a. Constant head method and b. variable head method.

In field the coefficient of permeability of a soil deposit in‐situ conditions can be determined by the following methods: 1. Pumping‐out tests. 2. Pumping‐in tests.

Rabindra Subedi Soil Mechanics

Casagrandes Liquid Limit Apparatus

soil mechanics practical final

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