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Smt. Vasundhara Raje
Hon'ble Chief Minister, Rajasthan

Dr. Rampratap
Hon'ble W. R. Minister, Rajasthan
Right to Information Presantation on RTI Act The Act No 22 2005 RTI Directory IGNB

Soil Properties and their Influence on Design of Dams



Many dams fail due to improper assessment of effect of soil properties of borrow area and foundation soils on the stability of dams and appurtenant works. In this paper, an effort has been made to high light the different soil properties such as dispersivity and swelling pressure and their effect on dam design. This will help in safe design of dams and will reduce the number of dam failures. FIVE Annexes have been enclosed explaining soil classification including description, average properties for different type of soils, suitability of soils for construction of dams, degree of expansion of fine-grained soils and general guidelines for embankment sections.
Generally the following soil tests are conducted before designing an earthen embankment. These tests should be conducted on soils in the borrow area, foundation and existing embankment (if any).

  1. Particle size distribution
  2. Atterberg limits
  3. In situ moisture content and density test
  4. Proctor maximum dry density and optimum moisture content
  5. Total soluble solids with EC, pH, carbonates, bicarbonates, and sulphates
  6. Specific gravity
  7. Permeability of disturbed samples and field permeability
  8. Triaxial shear test for cohesion and angle of internal friction
  9. Dispersivity by
    (a) Pin hole test
    (b) Crumb test
  10. Free swell index
  11. Swelling pressure
  12. Compressibility
  13. Ionic concentration of river water
  14. Organic matter
  1. Particle size Distribution:
    Particle size distribution by sieve analysis (for particle size greater than 0.075 mm) and by hydrometer analysis (for particle size smaller than 0.075 mm) is carried out in order to determine percentage of components (Table 1) present in the soil.
    Table 1. Grain size classification of soils:
    S. No.
    Soil Type
    Partical size
    Less than 0.002 mm
    0.002 to 0.075 mm
    Fine sand
    0.075 to 0.425 mm
    Medium sand
    0.425 to 2.000 mm
    Coarse sand
    2.000 to 4.750 mm
    Fine gravel
    4.750 to 20.00 mm
    Coarse gravel
    20.00 to 80.00 mm

    Grain shape varies with particle size and mineralogy. Soil grains are classified in three categories.

    1. Bulky Grains: If the dimensions of the soil particles are about the same, as in sand and gravel, the soil grains are described as being of a bulky shape. Coarse-grained soils are bulky (except for mica).
    2. Flaky or scale like grains: These resemble a piece of paper and are extremely thin compared to their length and breadth.
    3. Needle like grain shape:
      • Fine grained soils: These are soils more than 50% of which pass through 75 micron IS Sieve.
      • Coarse grained soils: These are soils 50% or less of which pass through 75 micron IS Sieve.

    Clay (Particle size less than 0.002 mm)
    Clays are plastic fines. They have low resistance to deformation when wet, but when dry they are hard, cohesive masses. Clays are virtually impervious, difficult to compact when wet and impossible to drain by ordinary means. Large expansion and contraction with changes in water content are characteristics of clays. The small size, flat shape and type of mineral composition of clay particles combine to produce a material that is both compressible and plastic. The clays having higher liquid limit are more compressible. At the same liquid limit, the higher the plasticity index, the more cohesive is the clay.
    Small amount of organic matter in colloidal form in clay will result in appreciable increase in liquid limit without increasing plasticity index. Clays with high organic matter create voids through decay.
    Silts (Particle size 0.002 to 0.075)
    Silts are the non-plastic fines. They are inherently unstable in the presence of water and have a tendency to become quick when saturated. Quick silts are often called bull's liver by construction people. Silts are fairly impervious, difficult to compact and are highly susceptible to frost heaving. Silt masses undergo change of volume when distorted or strained in shear (the property of dilatancy). The dilatancy property together with the "quick" reaction to vibration affords a means of identifying typical silt in the loose, wet state. When dry, silt can be pulverised easily under finger pressure (i.e. very slight dry strength)
    Silts differ among themselves in size and shape of grains, which are reflected mainly in the ability to compress. Higher the liquid limit of a silt, more compressible it is. The liquid limit of a typical bulky- grained, inorganic silt is about 30 percent, while highly micaceous or diatomaceous silts (so called elastic silts) consisting mainly of flaky grains may have liquid limit as high as 100 percent.
    Soils containing large quantities of silt and clay are the most troublesome to the engineer. These materials exhibit marked changes in physical properties with change of water content. Dry clay is hard and suitable as a foundation for heavy loads, but may turn into a soft, highly compressive material when wet. Many of the fine soils shrink and crack on drying and expand on wetting, which may adversely affect structures founded upon them or constructed of them.
    Coarse Grained Soils ( Gravel & Sand)
    Gravel and sand have essentially the same engineering properties, differing mainly in degree. Well-graded compacted gravel or sands are stable materials. The coarse grained soils, when devoid of fines are pervious, easy to compact, little affected by moisture and not subjected to frost action. Gravels are generally more pervious, more stable and less affected by water or frost than are sands, for the same amount of fines.
    As sand becomes finer and more uniform, it approaches the characteristics of silt with a corresponding decrease in permeability and reduction in stability in the presence of water.
    The soil classification based on particle size distribution and Atterberg limits have been given in Annex 1.

  2. Atterberg Limits:
    The behaviour of all soils with fines and particularly clays varies considerably with water content. Clay may be almost like a liquid or it may be very stiff depending upon its water content.
    If a fine-grained soil is mixed with a large quantity of water, it is in a liquid state.
    If the water content is gradually reduced, then the following apply:
    1. Liquid limit: The limit of water content, at which soil water suspension passes from zero strength to an infinitesimal strength, is the true liquid limit.
    2. Plastic limit: The moisture content at which the soil has a small plasticity, as determined by a standard test, is called the plastic limit.
    3. Shrinkage limit: The moisture content, at which its further reduction will not cause a further reduction in the volume of soil, is called shrinkage limit. At shrinkage limit, voids in soil are completely filled with water.
      In between plastic and shrinkage limits, the soil displays the property of semi solid. Between the plastic and liquid limits, the soil exhibits plastic behaviour.
      Table 2. Moisture content variation and Atterberg limits:
      Liquid state Liquid limit

      Plastic limit

      Shrinkage limit

      Plastic state
      Semi solid state
      Solid state
      The liquid limit is indicative of the compressibility of the soil. Soils having a liquid limit above 45 are compressible in nature. Small amount of organic matter in colloidal form in clay will result in an appreciable increase in liquid limit without increasing the plasticity index. Liquid limit of bulky grained inorganic silt is about 30%, which may be increase to 100% for elastic silts consisting mainly of flaky grains.
      If the shrinkage limit is less than 15, it is likely to develop cracks in the embankment. If it is less than 10, the soil should not be used in embankments, as the section is likely to develop extensive cracks. Soils having shrinkage limit more than 25 are also not suitable for dam construction.
      The shrinkage limit should be higher than the optimum moisture content (OMC), otherwise dam section will develop cracks on moisture reduction (drying).
      If the shrinkage limit of the soil is lower than the OMC, then the soil should be used for the inner core only. Outer shell should consist of soils having a shrinkage limit higher than OMC.
    4. Plasticity index: It is the difference between the liquid and plastic limits. For non-plastic soils, the plasticity index is zero. For clayey soils, the plasticity index is higher. It indicates the moisture contents over which the soil is in plastic condition. The plasticity index depends upon the clay present in the soil. The information regarding the type of clay in the soil may be obtained by considering the plasticity index in relation to the liquid limit.
    5. Shrinkage index: The numerical difference in between plastic limit and shrinkage limit, is called shrinkage index.
      In Annex 2 the suitability of soils for construction of dams based on soil classification is available for general guidance.
  3. In Situ Moisture Content and Density:
    These values indicate whether the natural/embankment soil is dense or not, and if the natural moisture content is near the OMC or not.
    Extract from 'Earth Maual' by U.S.B.R.: Various criteria for quality control have been proposed. Table 3 lists suggested limits of density and moisture control based on experience gained in compacting 44 cohesive soils and 18 cohesionless soils in Bureau of Reclamation earthfill dams. In the absence of instructions to the contrary, the criteria given in this table should be used. It is recognised that the normal frequency distribution curve for any desired average value permits a small percentage of very low tests. However, because of the relatively small samples recommended to be tested, the values listed in the table as " minimum acceptable" are suggested as a basis for requiring recompaction of the area represented by lower test values.
    The effect of gravel content in cohesive soils must be taken into account in control. Available data indicate that lesser percentages of density on the 4.76mm fraction basis are required for gravelly cohesive soils than for soils containing little or no gravel. This fact is reflected in Table 3.
    Table 3. Criteria for control of compacted dam embankments
    Type of material % of 4.75mm & above by dry weight of total material retained
    Percentages based on 4.75 mm fraction
    15 m or less in height
    Greater than 15 m height
    Minimum acceptable density Desirable average density Moisture limits Wo-Wt Minimum acceptable density Desirable average density Moisture limits Wo-Wt
    Cohesive soils controlled by the Proctor test 0-25 95% of MDD 98% of MDD -2% to +2% 98% of MDD 100% of MDD 2% to 0% (note 2)
    26-50 92.5% of MDD 95% of MDD 95% of MDD 98% of MDD
    more than 50 (note 1) 90% of MDD 93% of MDD 93% of MDD 95% of MDD
    Cohesionless soils controlled by the relative density test Fine sands with 0-25 Dd=75 Dd=90 Soils should be very wet Dd=75 Dd=90 Soils should be very wet
    Medium sands with 0-25 Dd=70 Dd=85 Dd=70 Dd=85
    Coarse sands and gravels with 0-100 Dd=65 Dd=80 Dd=65 Dd=80

    Wo -Wt is the difference between optimum water content and fill water content in percent of dry weight of soil MDD is the Proctor's maximum dry density.
    Dd is relative density
    (note 1) Cohesive soils containing more than 50 percent gravel sizes should be tested for permeability of the total material if used as a water barrier
    ( note 2) For high earth dams special instructions on placement moisture limits will ordinarily be prepared
  4. Proctor Maximum Dry Density and Optimum Moisture Content
    Soil compaction refers to the process of obtaining increased density of soil in a fill by reduction of its pore space by the expulsion of air. The bearing capacity of any soil usually increases with increasing dry density and decreasing moisture content. High density assures high shear strength and greater imperviousness. When a soil is submerged, its effective density is reduced and with this it's bearing capacity.
    The moisture content of a soil is defined as the ratio of the weight of water present in the soil to the dry weight of solid soil particles. The moisture content at which the weight of soil grains obtained in a unit volume of the compacted soil mass is maximum is called the "optimum moisture content" and the dry density so obtained is called "Maximum Dry Density" (MDD). As coarse-grained soils do not absorb the water and are not appreciably amenable to lubrication, they do not display distinct Optimum moisture content. For coarse and fine-grained soils, average values are 8 to 15 and 17 to 36 respectively as given in Annex 3. At OMC, the soil is broadly 90% saturated depending upon type of soil, meaning that about 10% of the void space is occupied by air.
    Warning: The OMC should always be less than the shrinkage limit. Otherwise on exposure to sun, cracks will develop in such soil. If such soil has to be used in embankments, then it should be covered with good suitable soil, so that moisture reduction in such soils is avoided.
  5. Total Soluble Salts, E.C., pH, Carbonates, Bicarbonates and Sulphates
    Total Soluble Salts: These consist of sodium, calcium, magnesium, and potassium. The suitability of soil depends upon the percentage of sodium in comparison to other cations. In dispersive soils, the increased salt concentration (without an increase in sodium salt) reduces the dispersivity of the soil. A very high percentage of total soluble salts may cause failure of an embankment by formation of cavities caused by removal of salts with seeping water.
    Electrical Conductivity: This measures the ability of the solution to conduct electricity and is expressed in millimhos/cm or micromhos/cm. E.C. value in millimhos/cm at 250 c can be converted to salt concentration in parts per million or milligram per litre with reasonable accuracy by multiplying by 640.
    Table 4. Electical Conductivity showing severety of salt content
    E.C. in miili-mhos/cm Severity
    Less than 1 Normal
    Between 1 and 2 Fairly good
    Between 2 and 3 High
    Between 3 and 4 Very High

    1 miili-mhos/cm=1000 micro-mhos/cm
    pH value: The pH value represents the concentration of hydrogen ions (H) in water. It is the logarithm of the reciprocal of the hydrogen ion concentration. A value of pH less than 7 indicates acidic character while pH value more than 7 is indicative of alkaline character, while 7 is neutral. Alkaline soils (pH > 7) are more prone to dispersivity.
    Carbonates: of calcium and magnesium are not soluble in water. Only carbonates of alkali metals like sodium and potassium are soluble in water.
    Bicarbonates: Bicarbonates are generally soluble in water. High concentration of bicarbonates may result in precipitation of calcium and magnesium bicarbonates from soil, increasing the relative proportions of sodium ions, which is harmful for stability of embankments.
    Sulphates: The sulphates (principally soluble sulphates) present in soil or ground water in contact with concrete/masonry works attack the cement paste causing deterioration and disintegration. The free lime of cement acts with sulphates finally forming calcium sulphate aluminate. This compound crystallises on drying causing expansion and ultimate disintegration of concrete. As such, soils having sulphates in appreciable quantity should not be used adjoining concrete/masonry structures. If it is essential to use soils containing sulphates then suitable admixtures should be added to concrete/mortar to save them from the ill effects of sulphates.
    Salt concentration is expressed in parts per million (PPM) or milligram per litre (mg/l) both units being equal.
  6. Specific Gravity:
    This is the ratio of weight in air of a given volume of soil solids to the weight of an equal volume of distilled water, at a given temperature.
    The specific gravity of engineering soils usually varies between 2.6 to 2.8. If it is less than 2.6, it may indicate possible presence of organic matter.
  7. Permeability:
    The rate of movement of gravitational water through soil pores is termed the permeability of soil.
    Permeability of disturbed/undisturbed soil samples should be measured in the laboratory. Permeability of foundation and embankment soils should also be measured in situ. The soils are categorised as permeable, semi permeable or impermeable as per the following limits.
    Impermeable : with permeability less than 1 x 10-6 cm/sec
    Semi permeable: with permeability 1x 10-6 to 1x 10-4 cm/sec.
    Permeable : With permeability more than 1x 10-4 cm/sec.
    The dam embankments should be impermeable. The permeability of the down stream section of embankment should not be less than that upstream.
  8. Triaxial Shear Test
    This is a test in which a cylindrical specimen of soil encased in an impervious membrane is subjected to a confining pressure and then loaded axially to failure.
    1. Unconsolidated Undrained Test (Q test)
      This is a soil test in which the water content of the soil sample remains unchanged during the application of the confining pressure and the additional axial (or shearing) force. No drainage and hence no dissipation of pore pressure is permitted during the application of the confining pressure and then the axial load.
      This test is usually performed on partly saturated soil and is used mostly for analysis of the stability of the earth dam under the "end of construction" condition.
    2. Consolidated Undrained Test (R test)
      Drainage is permitted after application of confining pressure so that the sample is fully consolidated under this stress. No drainage is permitted under the application of the axial load. This test is carried out with pore water pressure measurement, for obtaining effective stress values of cohesion and angle of internal friction.
      The values of C and f obtained from this test, are used to check stability of the upstream slope under the sudden draw down condition, after the soils are fully saturated.
    3. Consolidated drained Test (S test)
      Drainage is permitted after application of the confining pressure and during the axial loading. The values of shear parameters so obtained are almost the same as the effective stress values obtained from undrained tests with pore pressure measurement.
      The values of C and f obtained from this test are used to check stability of the downstream slope when the reservoir is in operation.
      Generally, the 25th percentile strength values are used in the stability analysis of slopes (i.e. 75% of the samples exhibit strength values).
  9. Dispersivity:
    Dispersive soils are clay soils, which are highly susceptible to concentrated leak by a process of colloidal erosion. These clays have a predominance of dissolved sodium cations in the pore water, whereas ordinary erosion resistant clay has calcium and magnesium as the dominating dissolved cations. These are eroded by a process in which the, individual colloidal clay particles go into suspension in practically stilled water. All colloidal particles carry a like electric charge, which prevents the particles from attracting each other.
    Dispersivity of clayey soils is determined by two tests namely:
    1. Sherard's pin hole test
    2. Crumb test

These two tests should be carried out on a given sample and if the soil is found dispersive by any of the two tests, it should be categorised as dispersive.
Higher values of pH and sodium concentration and lower values of total dissolved salts promote soil dispersivity.
Soils containing the clay mineral montmorillonite, are prone to dispersion. Generally, dispersive clays have been red, brown, grey (some nearly white), yellow and all transitions among them. No black colour soils with obviously high organic contents have tested dispersive. All tested fine grained soils, known to be derived from in situ weathering of igneous and metamorphic rocks, have been found non dispersive as well as soils derived from lime- stone.
Salt, hydrated lime, gypsum, alum and fly ash may be used to treat dispersive soils after observing their effect on the soil in laboratory.
Dispersive soil can be used as fill material by keeping placement moisture content on the wet side (about 1%) of optimum moisture content. Such soil should be compacted in thinner layers using pneumatic tampers to obtain a high degree of density, and permeability less than 1x10-6 cm/sec and good bond with the structure/ foundation rock. As far as possible non- dispersive soils should be used near structures and at rock interface.
With dispersive soils the frequency of density and moisture control tests should be increased.
One should closely observe the compacted soil surface for cracks and take measures for prevention/correction of moisture by appropriate methods.
Effectively seal surface cracks in the foundation rock by slush grouting.

  1. Free Swelling Index:
    This indicates swelling potential of fine-grained soils when water is added to them. If the free swell index of a soil is more than 100, then such behaviour may require special attention. The degree of expansion of fine-grained soils based on their properties is available at Annex 4.
  2. Swelling Pressure:
    The characteristics of swelling and the swelling pressure of black cotton soils are attributed to the presence of montmorillonite or a combination of montmorillonite and illite clay minerals. Clay minerals are made of colloidal particles having diameters less than one micron. The presence of specific clay minerals is determined by an x-ray diffraction test.
    Degree of expansion: The fine-grained soils exhibit low to very high degree of expansion depending upon the presence of clay minerals. Based upon the Atterberg limits and free swell of a soil the degree of expansion and degree of severity is indicated in at Annex 4.
    As per IS 6186 : 1986, Bentonite, a characteristic type of fine- grained clay, is an alteration product of volcanic ash containing not less than 85 percent of the clay mineral montmorillonite.
    Black cotton soils have a predominance of the montmorillonite clay mineral. The grain size distribution and index properties of expansive soils expressed in percentages are in the following ranges.
    Clay (less than 2 micron) 50 to 70%
    Silt (0.075 mm to 0.002 mm) 20 to 35%
    Fine and medium sand (2 mm to 0.075 mm) 30 to 50%
    Coarse sand and Gravel (greater than 2 mm) Less than 10%

    Index Properties:
    Liquid Limit 60 to 100%
    Plastic Limit 30 to 50%
    Plasticity Index 30 to 40%
    Shrinkage Limit 8 to 12%

    If a high liquid limit (greater than 55 %) is accompanied by a low shrinkage limit (lower than 10) swelling pressure and free swell tests should be conducted.
    The swelling pressure is determined by conducting a one dimensional swelling pressure test using either fixed or floating rings on both undisturbed and remoulded soils in the partially saturated condition. Two methods are used to determine swelling pressure.
    • Consolidometer method in which the volume change of the soil is permitted and the corresponding pressure required to bring back the soil to its original volume is measured.
    • Constant volume method in which the volume change is prevented and the consequent pressure is measured. The details of the two methods are available in IS 2720 (Part XLI): 1977.

If the swelling pressure is more than 50 kPa, treatment is necessary. In canals, treatment is provided by a cover of cohesive non-swelling soils over swelling soils as per IS 9451: 1994

  1. Compressibility:
    The decrease in volume per unit increase of pressure is defined as the compressibility of soils. It is measured only for undisturbed samples. Compressibility is a property of a soil pertaining to its susceptibility to decrease in volume when subjected to load. The phenomenon of compressibility is associated with a change in volume of the voids and, to a very limited extent with changes in the soil particles.
    Soils having only air voids will be compressed immediately upon application of load. In saturated soils, the pore pressure will increase significantly with an increase in the soil's compressibility. In general a very compressible cohesive soil will develop high pore pressure when loaded, unless there is an appreciable amount of air present. Compressibility of sand and silt varies with density. Compressibility of clay varies directly with water content and inversely with shear strength.
  2. Ionic concentration in river water:
    Ionic concentration in river water below 1.2 meq/litre is considered low. River water passes through embankment. As such it may dissolve salts present in the embankment and foundation. Small quantities of calcium and magnesium salts in soil may increase dispersivity of soils and thus such reservoir water may aggravate a piping problem.
  3. Organic matter:
    Even a small amount of organic matter in colloidal form in clay, will result, in an appreciable increase in liquid limit of the material, without increase in plasticity index. The tendency for soils high in organic content is to develop voids by decay while this makes them undesirable for engineering use. Soils containing even moderate amounts of organic matter are significantly more compressible and less stable than inorganic soils.
    In Annex 5, general guidance for embankment slope inclination based on soil classification and height of embankment has been provided for guidance.

The inference of soil test result help in designing the earthen embankments/ dams with proper safety measures and economy.
Following inferences need special attention.

    1. S.L.(shrinkage limit) of soil should be higher than its optimum moisture content (OMC), otherwise cracks will develop upon moisture reduction below O.M.C.
    2. Soils having S.L. less than 10 should not be used in dam embankment, as the dam section is likely to develop extensive cracks.
    3. If S.L. is in between 10 to 15, than it is likely to develop cracks in the embankment.
    4. Specific gravity of most inorganic soils is in between 2.60 to 2.80. Values less than 2.60 indicate possible presence of organic matter in appreciable quantity.
    5. Permeability of the downstream portion of an embankment should be higher than the upstream portion; otherwise dam may fail on this account only.
    6. The soils containing appreciable quantities of colloidal particles (less than 0.001 mm in diameter), sodium, the clay mineral Montmorillonite & illite, are prone to dispersion. Higher values of percent sodium in soil make it dispersive.
    7. The dispersive soil may be used safely in dam embankment except near masonry/concrete works and near foundation rock, if the permeability of the embankment may be ensured to be 1x10-6 cm/sec or less.
    8. Soils of high swelling potential are not suitable as embankment material.
    9. The soils containing appreciable quantities of sulphates should not be used adjoining the concrete/masonry works. If it is essential to use, then a suitable admixture should be added to the concrete/mortar to make safe.


1 I.S. 1498: 1970. Classification and identification of soils for general engineering purposes"
2 I.S.12169: 1987. Criterion for design of small embankment dams"Criterion for design of small embankment dams"Criterion for design of small embankment dams"
3 ASTM Special Technical Publication No. 623(1977). "Dispersive clays, Related Piping, and Erosion in Geotechnical Projects"
4 I.S. 6186:1986 Specification for bentonite
5 I.S. 3873: 1993 Laying cement concrete/stone slab lining on canals Code of practice
6 I.S. 9451:1994 Guidelines for lining of canals in expansive soils
7 I.S. 2720(Part XLI:1977) Methods of test for soils-Part XLI Measurement of swelling pressure of soils.
8 'Earth Manual' Publication of United States Bureau Of Reclamation

Soil Classification including Description

  1. Coarse grained soils: These contain more than half materials larger than 75 micron IS sieve size, the smallest particle visible to the naked eye.
    (i) Gravels - More than half of coarse fraction is larger than 4.75 mm IS Sieve size.
    Clean gravels (Little or no fines)
    Well graded gravel, gravel sand mixture, little or no fines
    -- do --
    Poorly graded gravel or gravel sand mixture, little or no fines
    Gravel with fines(Appreciable amount of fines)
    Silty gravel, poorly graded gravel - sand - silt mixture
    -- do --
    Clayey gravel, poorly graded gravel - sand - clay mixtures

(ii) Sands - More than half of fraction is smaller than 4.75 mm IS sieve size.

Clean sands ( Little or no fines)
Well graded sands, gravelly sands, little or no fines
-- do --
Poorly graded sands or gravelly sands, little or no fines
Sands with fines (Appreciable amount of fines)
Silty sands, poorly graded sand - silt mixtures
-- do --
Clayey sands, poorly graded sand clay mixtures
  1. Fine grained soils: These contain more than half of materials smaller than 75 micron IS sieve size. The 75 micron IS sieve size is smallest particle size visible to the naked eye.
    Silts and clays with low compressibility and liquid limit less than 35
    Inorganic silts and very fine sands rock flour, silty or clayey fine sand or clayey silts with none to low plasticity
    -- do --
    Inorganic clays, gravelly clays, sandy clays, silty clays, lean clays of low plasticity
    -- do --
    Organic silts and organic silty clays of low plasticity
    Silts and clays with medium compressibility and liquid limit greater than 35 and less than 50
    Inorganic silts, silty or clayey fine sands or clayey silts of medium plasticity
    -- do --
    Inorganic clays, gravelly clays, sandy clays, silty clays, lean clays of medium plasticity
    -- do --
    Organic silts and organic silty clays of medium plasticity
    Silts and clays with high compressibility and liquid limit greater than 50
    Inorganic silts of high compressibility, micaceous or diatomaceous fine sandy or silty soils, elastic soils
    -- do --
    Inorganic clays of high plasticity, fat clays
    -- do --
    Organic clays of medium to high plasticity
  2. Highly organic soils:
    Pt Peat and other high organic soils with very high compressibility

    (Extract from Table 2 of I.S. 1498-1970

Suitability of soils for construction of dams

Relative Suitability
Homogeneous Dykes
Zoned Dam
Impervious Blanket
Impervious Core
Pervious Shell
Very Suitable GC GC SW, GW GC
Suitable CL, CI CL, CI GM CL, CI
Fairly Suitable SP, SM, CH GM, GC, SM, SC, CH SP, GP CH, SM, SC, GC
Poor -- ML, MI, MH -- --
Not Suitable -- OL, OI, OH, Pt -- --

(Extract from Appendix A of I.S. 12169-1987)

Average properties for different types of soils

S. No.
Soil Group
Maximum Dry Density (Kg/cum)
Optimum Moisture Content (Percent)
Cohesion Kg/sqm

(Extract from Table 2 of I.S. 12169-1987)

Degree of Expansion of fine grain soils

Liquid Limit Plasticity Index Shrinkage Index Free Swell (Percent) Degree of Expansion Degree of Severity
20-35 <12 <15 <50 Low Non Critical
35-50 12-23 15-30 50-100 Medium MArginal
50-70 23-32 30-60 100-200 High Critical
70-90 >32 >60 >200 Very High Severe

(Extract from Table 8 of I.S. 1498-1970)

General guidelines for embankment sections

S. No. Description Height upto 5 m. Height above 5 m. Height above 10 m. and upto 15 m.
1 Type of Section Homogeneous/ Modified homogeneous section Zoned/ Modified homogeneous/ Homogeneous section Zoned/ Modified homogeneous/ Homogeneous section
2(a) Side slopes for coarse grained soils U/S D/S      
GW, GP, SW, SP Not Suitable Not Suitable Not suitable for core, suitable for casing zone
GC, GM, SC, SM 2:1 2:1 2:1 2:1 Section to be decided based upon the stability analysis
(b) Fine Grained Soil      
CL, ML, CI, MI 2:1 2:1 2.5:1 2.25:1 --do--
CH, MH 2:1 2:1 3.75:1 2.5:1 --do--
3 Hearting zone Not required May be provided Necessary
Top Width -- 3 m. 3 m.
Top level -- 0.5 m above MWL 0.5 m above MWL
4 Rock Toe Height

Not necessary upto 3 m height.
Above 3 m height, 1m height of rock toe may be provided.

H/5, where H is height of embankment.

H/5, where H is height of embankment.
5 Berms Not necessary Not necessary The berm may be provided as per design. The minimum berm width shall be 3m.

(Extract from Table 1 of I.S. 12169-1987)

U/S =upstream
D/S = downstream
H = Horozontal
V = Vertical

* Director, Minor Irrigation Schemes, Jaipur -302015

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