Important IS Codes in Civil Engineering

👉 IS: 456 – code of practice for plain and reinforced concrete.

👉IS: 383 – specifications for fine and coarse aggregate from natural sources for concrete

👉 IS: 2386 – methods of tests for aggregate for concrete

👉IS: 456; 10262; SP 23 – codes for designing concrete mixes

👉IS: 800:2007-Code of practice for general construction in steel

👉Geotechnical Engineering

• Determination of water content (moisture content) IS:2720 (Part .II) 1973

• Determination of specific gravity of fine-grained soil IS: 2720 (Part. III) 1980 Sect/1

• Determination of specific gravity of fine, medium & coarse-grained soil. IS: 2720 (Part. III) 1980 Sect/2

•  Grain size analysis IS:2720 (Part.4) 1985

• Determination of Liquid and plastic limit IS:2720 (Part.5) 1985

• Determination of shrinkage factors IS: 2720 (Part. VI) 1987

• Determination of water content - dry density relation using light compaction. IS: 2720 (Part. VII) 198

• Determination of water content - dry density relation using heavy compaction.IS:2720 (Part.8) 1983

• Determination of Unconfined compressive strength IS: 2720 (Part. X) 1991

•  Determination of shear strength parameters(tri-axial) with out measurement of pore pressure parameters IS:2720(Part. XI) 1971

• Direct shear test IS: 2720 (Part. XIII) 1986

•  Determination of Density Index (R.D) of cohesionless soil.IS:2720 (Part.14) 1983

• Determination of consolidation properties IS:2720 (Part.15) 1986

• Determination of permeability IS:2720 (Part.17) 1986

•  Determination of dry density of soils, in place by the sand replacement method. IS:2720 (Part.28) 1974

• Determination of dry density of soils, in place by the core-cutter method.IS:2720 (Part.29) 1975

• Laboratory vane shear test. IS:2720 (Part.30) 1980

•  Determination of the density in place by the ring and water replacement method.IS:2720 (Part.33) 1971

•  Determination of free swell index of soils IS: 2720 (Part. XI) 1977

•  Measurement of swelling pressure of soils. IS: 2720 (Part. XII) 1978

•  Design and construction of pile foundation. IS: 2911:2010

👉 IS codes on Earthquake Resistant Building Design

•  Criteria for Earthquake Resistant Design of Structures: IS:1893

• Code of practice for earthquake design resistant design and construction of building. IS:4326

• Improving Earthquake Resistance of Earthen Buildings. IS:13827  

👉 Cement

• Specification for 33,43,53 Grade ordinary portland cement IS 269 - 2015

• Specification for Rapid hardening portland cement IS 8041 - 1990

• Specification for portland Pozzolona cement IS 1489 (part 1&2) 1991

• Methods of physical test for hydraulic cement IS 4031 - 1988

•  Method of chemical analysis of hydraulic cement IS 4032 - 1985

• Method of sampling for hydraulic cement IS 3535 - 1986

• Standard sand testing of cement IS 650 - 1991

👉Aggregate

• Specification for coarse and fine aggregate IS 383-2016

• Methods of test for aggregate for concrete particle size and shape IS 2386 (Part I) 1963

•  Methods of test for aggregate for specific gravity, density, voids, absorption and bulking IS 2386 (Part III) 1963

• Methods of test for aggregate for Mechanical properties. IS 2386 (Part IV) 1963

• Methods of test for aggregate Soundness IS 2386 (Part V) 1963

👉Bricks

• Method of sampling of clay building bricks IS 5454 - 1978

• Method of test for burnt-clay building bricks. IS 3495 (Parts I to iv) 1976

•  Common burnt clay building bricks. IS 1077 - 1992

👉 Cement Concrete

• Specification for coarse and fine aggregate. IS 383 - 1970

• Specification for compressive strength, flexural strength IS 516 - 1959

• Code of Practices for plain and reinforced concrete etc. IS 456 – 2000

• Recommended Guide Lines for Concrete Mix Design IS 10262 – 1982

Acceptable Values in Geotechnical Engineering

 👉 There is no upper limit of water content (w)

                         i.e.              w ≥ 100%

👉 Void ratio (e) can be greater than unity

                                          e > 1

👉 The value of porosity (η) lies in between 0 to 100%

                           i.e.       0 < η < 100

👉 Degree of Saturation (S)

                       0 ≤ S ≤ 100%

👉 Sum of air content (A.C) and degree of saturation (S) should be unity or 100%

               i.e.         A.C + S = 100% or 1

👉 Comparison between Unit weight of solid (Ys), Saturated unit weight (Ysat), Bulk unit weight (Yb), Dry unit weight (Yd) and Submerged unit weight (Ysub)

                     Ys > Ysat > Yb > Yd > Ysub

👉Approximate value of Ys, Ysat, Yb, Yd and Ysub

      Ysub ⋍ 10 kN/m^3

     Yd ⋍ 14 - 15 kN/m^3

      Yb ⋍ 17 - 18 kN/m^3

       Ysat ⋍ 20 kN/m^3

       Ys ⋍ 26-29 kN/m^3

👉For inorganic solid Specific gravity of solids (Gs) is in the range of 2.6 to 2.9 (generally 2.65).

👉 For organic solids Specific gravity of solids (Gs) is in the range of 1.0 to 2.0 (generally 1.2).

👉 Higher value of Gs for fine grained as compare to coarse grained solids

👉 With increase in organic content in the soil Gs decreases (↓)

👉 With increase in mineral content like Iron or Mica, Gs increases (↑)

👉  Specific gravity of solids (Gs) > Mass specific gravity (Gm)

👉 In India Specific gravity is reported at 27 ℃ and if it is required at any other temperature the corresponding change in the unit weight of the water is to be considered.

              Gs (T ℃ ) = Gs (27 ℃) x [ Yw(27 ℃)/Yw (T ℃)]

👉 The value of Density Index / Relative density / Degree of density (Id) lies in between 0 to 100% including 0 and 100%.

               i.e.                    0 ≤ Id ≤ 100%

👉                     Id (%)                          Degree of denseness 

                           0-15                                Very Loose Soil

                           15-35                                 Loose Soil

                           35-65                                Medium Dense Soil

                           65-85                                  Dense Soil

                            85-100                                Very Dense Soil

👉  Relative compaction (Rc) indicates the compactness of both cohesive and cohesionless soil.

                                      Rc = Yd (in field) / Ydmax (in laboratory)

                                      Rc = ( 1 + emin) / (1 + e ) 

                                      Rc = 80 + 0.2 Id

👉 If  e = emax , Id = 0% , Rc = 80%

👉 If  e = emin , Id = 100% , Rc = 100%

👉For uniformly graded soil coefficient of uniformity (Cu) is 1. For well graded sand  Cu > 6 and for well graded gravel Cu > 4.

👉 For well graded soil Coefficient of curvature (Cc) is in the range of 1 to 3, for gap graded soil Cc <1 and  > 3.

👉                Types of soil                           Liquid Limit (%)

                           Gravel                                        Non-plastic

                          Sand                                            Non-plastic

                           Silt                                                   30-40

                      Clay (Alluvial Soil)                             40-150

                      Clay (Black Soil)                                 400-500

👉                  Types of soil                               Plastic limit (%)

                        Gravel                                        Non-plastic

                          Sand                                            Non-plastic

                           Silt                                                   20-25

                      Clay (Alluvial Soil)                             25-50

                      Clay (Black Soil)                                 200-250

 👉              Types of soil                               Plasticity Index (%)

                        Gravel                                          Non-plastic

                          Sand                                            Non-plastic

                           Silt                                                   10-15

                      Clay (Alluvial Soil)                             15-100

                      Clay (Black Soil)                                 200-250

👉                 Designation                              Plasticity Index (%)

                        Non-plastic soil                                     0

                        Low plastic soil                                     < 7

                        Medium plastic soil                              7 - 17                    

                          Highly plastic soil                                > 17  

👉         Sensitivity                                          Description  

                   1                                       Insensitive soil (Coarse grained structure)

                2 - 4                                      Normal/less sensitive soil (Honey Comb Structure)     

                4 - 8                                     Sensitive soil (Honey comb/ Flocculant structure)

                8 -16                                    Extra Sensitive soil (Flocculant/ Dispersed structure )

                  > 16                                                  Quick / Unstable Soil

👉 Sensitivity is inversely proportional to Good quality of soil.

👉Coarse grained soil are less sensitive as compare to Fine grained soil.

👉 Skempton defined a parameter referred as Activity (Ac) which is used to indicate the compressibility of the soil (Swelling, Shrinkage of the soil with change in water content). 

👉 Ac defined as the ratio of Plasticity index of the soil to the % age of the particle finer than 2 μ (Clay size).

👉           Activity (Ac)                               Description

                   < 0.75                                        Inactive Soil

                 0.75 - 1.25                                  Normal Active soil

                  > 1.25                                            Active soil

👉 A linear relationship exist in the plot of Plasticity index (Ip) on the y-axis and % of particle finer than 2 μ (% clay particle, C) on the x-axis. Slope of Ip Vs C gives the activity (Ac).

👉 Compressibility = fn ( Activity, Liquid limit)

👉                Type of Minerals                           Activity (Ac)

                          Kaolinite                                        0.40 - 0.50

                           Illite                                               0.50 - 1.0

                         Montmorillonite                                1 - 7

                     Na-Montmorillonite                              4 - 7

                      Ca-Montmorillonite                             1- 5                           

👉 Collapsibility of soil is the property by the virtue of which it shows large decrease in volume with increase in water content without any increase in pressure being applied over it.

👉 Collapsibility of the soil is measured in terms of the parameter referred as Collapse Potential that can be determined by performing plate load test.

👉 Collapse potential is defined as the ratio of decrease in the volume of soil with increase in water content expressed in terms of original volume of soil.

                      Collapse Potential (Cp) = △V / Vo  = △H / Ho = △e / (1+eo)

👉      Collapse Potential (Cp)                            Effect on Structure 

                  0 - 1 %                                                        No effect

                  1 - 5 %                                                       Less effect

                  5 - 10 %                                                    Moderate effect

                 10 - 20 %                                                      Severe effect

                  > 20 %                                                       Very Severe effect

👉 The height of capillary rise (hc) in fine grained soil is comparatively more than the height of capillary rise in coarse grained soil as hc is inversely proportional to D10.

👉           Types of Soil                             hc (cm)

                   Gravel                                       2-10

                   Sand                                          10 - 100

                    Silt                                            100 - 1000

                   Clay                                           1000 - 3000

👉 Permeability (k) of coarse grained soil is more than the permeability of fine grained soil.

 👉       Type of soil                     k (cm/sec) 

               Gravel                              > 1

              Sand                               1 - 10^-3

              Silt                                 10^-3 - 10^-7

             Clay                                   < 10^-7

👉    Property                        Dry of Optimum               Wet of Optimum   

   1. Structure                                  Flocculant                              Dispersed 

   2. Permeability                             More (↑)                                  Less (↓)

   3. Pore Water Pressure                 Less (↓)                                  More (↑) 

   4. Swelling                                   More (↑)                                 Less (↓)

   5. Shrinkage                                  Less (↓)                                  More (↑) 

   6. Compressibility

     At low stress                                Less (↓)                                  More (↑) 

    At high stress                               More (↑)                                 Less (↓)

  7. Strength                                      More (↑)                                 Less (↓)

  8. Young's Modulus of Elasticity    More (↑)                                 Less (↓)

👉   Type of Soil                             At-rest Earth pressure Coefficient (Ko)     

         Dense Sand                                                        0.40 - 0.45

         Loose sand                                                         0.45 - 0.50

       Normally consolidated Soil (OCR = 1)                0.50 - 0.60

      Over Consolidated Soil (OCR > 1)                          1 - 4

👉 For Active Stage strain required is in the order of 0.2 to 0.5 % 

👉 For Passive stage strain required is in the order of 5 to 15 %

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MATURITY of CONCRETE

 👉 The strength of concrete depends upon both the time as well as temperature during the early period of gain in strength.

👉 The maturity of concrete is defined as the summation of product of time and temperature 

                                                 Maturity = ∑ (time x temperature)

👉 Its units are ℃ hr or ℃ days.

👉The temperature is reckoned from -11 ℃ as origin in the computation of maturity, since hydration continues to take place up to about this temperature.

👉 Example 1: A sample of concrete cured at 18℃ for 28 days is taken to be fully matured which is equal to ?

      Maturity (M28 days) = 28 x 24 x [ 18 - (-11)] = 19488 ℃ hr.

                                         OR

     Maturity (M28 days) = 28 x [ 18 - (-11)] = 1092 ℃ days.

👉 The relationship between maturity and strength of concrete is shown in figure below:

👉 The maturity concept is very useful for estimating the strength of concrete at any other maturity as a percentage of strength of concrete of known maturity by using the formula:

  Percentage of strength at maturity of 19800 ℃ hr = A + B log maturity/1000

👉Plowman has given the following values of constants A and B

     28 day strength at 18 ℃                                             Coefficients

   ( M = 19800 ℃ hr/kg/cm^2)                                       A              B

                < 175                                                              10             68

          175 - 350                                                              21             61

          350-525                                                                32             54

          525- 700                                                               42            46.5

Example 2: The strength of a fully matured concrete sample is found to be 500 kg/cm^2. Find the strength of identical concrete at age of 7 days when cured at an average temperature of 20 ℃ in day and 10 ℃ in night?

Solution: Maturity of concrete at the age of 7 days = ∑ (time x temperature)

                                     = 7 x 12 x [ 20 - (-11)] + [ 7 x 12 x (10-(-11)]

                                     = 4368 ℃ hr

 Now A = 32 , B = 54

Percentage of strength of concrete at maturity of 4368 ℃ hr = A + B log (4368/1000) 

                                                                                                = 32 + 54 x log (4368/1000)

                                                                                                 = 66.5%

Strength at 7 days = 500 x (66.5/100) = 332.5 kg/cm^2

STAFF SELECTION COMMISSION TENTATIVE CALENDAR OF EXAMINATIONS FOR THE YEAR 2021-2022

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Standard Penetration Test (SPT Test) and Split Spoon Sampling

 1. Aim:

• To conduct the SPT test as per specification
• Collect and identify soil samples in the split spoon sampler
• Record and interpret the test data   

2. Introduction:

In the standard penetration test (SPT), a standard split spoon sampler is driven into the soil by a hammer weighing 65 kg, with a free fall of 75 cm. The number of blows of the hammer required to penetrate 300 mm of the sampler (Last 150 mm + 150 mm) is recorded as N-value. This N-value gives the idea of the relative density of granular soils and the consistency of cohesive soil . It may also be used for determining the approximate bearing capacity needed in foundation design.

                                                   The split spoon sampler is used for obtaining disturbed representative samples of soil which are needed for visual classification and certain laboratory tests.

3. Apparatus Used:

(i) Split spoon sampler with a drive shoe, and sampler head.

(ii) Drill rod 

(iii) Drive weight assembly consisting of

(a) Guide rod with driving head

(b) Hammer of 63.5 kg

(iv) A tripod assembly with a pulley, hoisting and lowering arrangement

(v) Boring equipment-Post hole auger

(vi) Centering guide for keeping drill rod vertical

(vii) Spanners, Wrenches, Measuring tape, Chalk for marking.

4. Procedure:

(i) Locate the exact position on the ground where the test has to be conducted.

(ii) Make a bore hole using the auger

(iii) Stop boring at the depth where the penetration test has to be conducted. Record this depth. Penetration tests are usually conducted at intervals of 1.5 m or change of stratum which ever occurs earlier.

(iv) Centre the tripod over the bore hole such that plumb line attached to the pulley passes through the center of the bore hole.

(v) Inspect the split spoon sampler, clean it and assemble.

(vi) Connect the sampler head of the sampler to a rod using coupling in between.

(vii) Lower the sampler with the drill rod into the bore hole so that the drive shoe just touches the bottom of the bore hole.

(viii) Keep the drill rod vertical and insert the centering guide through the drill rod till the guide is placed on the ground.

(ix) Connect the top portion of drill rod to the driving head of the guide rod using a coupling.

(x) Link the hammer chain with the hook provided on the pulley.

(xi) Raise the hammer by operating the hoist line and insert its hole to the guide rod so that the hammer rests on the driving head.

(xii) Replace the top cap of guide rod. The distance between bottom of top cap and base is 75 cm. This ensures a free fall of 75 cm.

(xiii) Mark the drill rod at heights 15 cm, 30 cm and 45 cm above the ground level.

(xiv) Raise the hammer and allow it to drop freely through a height of 75 cm.

(xv) Count the number of hammer blows. Observe whether the sampler is going down or not with every blow.

(xvi) Do not record the number of blows required to cause first 15 cm of penetration (Seating drive)

(xvii) Record the number of blows required to penetrate the sampler for the remaining 30 cm . This gives the N-value (Field value). Raise the sampler to the surface and open the sampler, measure the length of the sample.

5. Observation:

Diameter of bore-hole -----------------------

Type of boring -----------------

R.L of Ground surface ------------------

R.L of Groundwater table-----------------------

Observation Table:

Depth below GL (m)           No. of blows per 30 cm penetration               N-value 

From                  To

------                 ------                      --------------------                                     -------------

------                 ------                      --------------------                                     -------------

------                 ------                      --------------------                                     -------------

------                 ------                      --------------------                                     -------------

Unit weight of soil----------------

Effective stress--------------------

Observed N-value ------------------------

State of compaction/consistency: Very loose/Loose/Medium/Dense/Very dense/Very soft/Soft/Firm/Stiff

Corrected for overburden pressure--------------

Dilatancy correction ----------------

Note: For more details about SPT Test and N-value correction please visit:

                                                                     SPT Test  

Direct Shear Test

 1. AIM:

Determination of Shearing Strength of Soils by Direct Shear Test.

2. Apparatus Used: 

(i) Shear box, container for shear box, grid plates (Two pairs: one perforated and one without perforation) porous stones, base plate, loading pad (IS 11229)

(ii) Loading frame for applying shear force at a constant rate of shearing displacement 

(iii) Loading yoke for applying normal loads.

(iv) Weights when applied on the hanger induce normal load intensities of 0.05, 0.10, 0.50 and 1.00 kg/cm^2.

(v) Proving Ring 

(vi) Dial gauges (2 nos.)

(vii) Stop watch, balance, spatula, straight edge.

3. Procedure:

(i) Assemble the two halves of the shear box using the connecting pins.

(ii) Place the shear box inside the container.

(iii) Place the base plate inside the shear box.

(iv) Over the base plate, keep one grid plate without perforations such that the grids ar perpendicular to the direction of shear.

(v) Carefully place the soil sample inside the shear box so that it rests on the grid plate.

(vi) Over the top of the sample another grid plate without perforations such that the grids are perpendicular to the direction of shear.

(vii) Slightly press this grid plate evenly so that the grids are buried in the sample.

(viii) Place the loading pad on the top grid plate.

(ix) Bring the proving ring assembly in contact with U-arm provided for the top half of the shear box.

(x) Place a steel ball on the spherical groove provided on the loading pad.

(xi) Seat the loading yoke on this ball.

(xii) Remove the pins connecting the upper and lower halves of the shear box.

(xiii) Fix two dial gauges, one on the loading yoke to measure vertical displacement and the other on the bracket provided on the shear box container to measure shearing displacement.

(xiv) Apply the required normal load on the hanger of the loading level.

(xv) Apply the shearing force to cause a shearing displacement of 1.25 mm/minute . immediately after applying the normal load.

(xvi) Note the readings on the two displacement dial gauges and the proving ring dial gauge at regular interval of time.

(xvii) Continue applying the shear force, till the specimen fails which is indicated by a kick-back of the pointer in the proving ring dial gauge.

(xviii) If such a failure does not occur, continue till the specimen undergoes a shearing displacement.

(xix) Conduct at least three tests on separate specimens having same density and water content but applying different normal loads.

4. Observation Table:  

Time  Shear dial reading  Shear displacement  Normal dial reading Normal displacement Proving ring 

(minute)                                  (mm) ∊                                                          (mm) 

------         ----------               --------                    -----------                   ------------                       ----------

-----         ----------               --------                    -----------                   ------------                       ----------

-----         ----------               --------                    -----------                   ------------                       ----------

-----         ----------               --------                    -----------                   ------------                       ----------

-----         ----------               --------                    -----------                   ------------                       ----------

-----         ----------               --------                    -----------                   ------------                       ----------

Shear Force (kg) = -------------------

Shear Stress =     Shear Force / Area

5. Plotting the Results:

(i) Draw a graph by plotting the normal stresses as the abscissa and shear stresses as the ordinates corresponding to failure states.

(ii) Join the points corresponding to the state of failure by a line. This line gives the Mohr envelope for the soil.

(iii) Measure the angle which the line (Mohr's envelope) makes the horizontal axis. This gives the angle of shearing resistance (Φ)

(iv) Measure the intercept which the line (envelope) makes with the shear stress axis. This gives the cohesion value c in kg/cm^2.