Highway Engineering

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👉The highway planning surveys consists:

    (i) Economic studies (Population and distribution in each village, trend of population growth, per capita income)

    (ii) Financial studies (Source of income and estimated revenue from taxation on road transport, living standards, future trends in financial aspects)

    (iii) Traffic or road studies (Traffic volume, traffic flow pattern, O and D studies)

    (iv) Engineering studies (Road location and alignment studies, Classification, Types of road in use, Maintenance problems)

👉 The stages of engineering surveys for highway locations are:

   (i) Map study

   (ii) Reconnaissance

   (iii) Preliminary surveys

   (iv) Final location and detailed surveys

👉 The following drawing are usually prepared in a highway project:

(a) Key map (Should show the proposed and existing roads and important places to be connected, the size of the plan should not exceed 22 x 20 cm.)

(b) Index map (Should show the general topography of the area, size being 32 x 20 cm)

(c) Preliminary survey plans (details of various alignment, scale: 10 cm = 1km to 25 cm = 1km)

(d) Detailed plan and longitudinal section 

(e) Detailed cross-section

(f) Land acquisition plans

(g) Drawings of cross drainage and other retaining structures

(h) Drawings of road intersections

(i) Land plans showing quarries

👉 Typical Flexible Pavement Failures:

(a) Alligator (Map) cracking

• Most common type of failure and occurs due to relative movement of pavement layer materials.
• caused by repeated application of heavy wheel loads resulting in fatigue failure or due to moisture variations resulting in swelling and shrinkage of subgrade.

                                             

(b) Consolidation of pavement layers

• Formation of ruts are mainly attributed to the consolidation of pavement layers.

(c) Shear failure and cracking

• Shear failure causes upheaval of pavement materials by forming  a fracture or cracking.

(d) Longitudinal cracking

• Due to frost action and differential volume changes in subgrade 

(e) Reflection Cracking

• observed in bituminous overlays over existing cement concrete pavements

👉Typical Rigid pavement failures:

(a) Scaling of cement concrete:

• scaling is observed in cc pavement showing overall deterioration of the concrete.

(b) Shrinkage cracks

(c) Spalling of joint

(d) Warping cracks

(e) Mud Pumping

• Mud pumping is recognized when the soil slurry ejects out through the joints and crack of cc pavements during the downward movement of slab under the heavy wheel load.

 

Foundation Engineering

 👉 The Primary objective of soil exploration is:

• Determination of the nature of the deposits of soil, depth and thickness of various soil strata.
• Location of Ground water table and obtaining soil and rock samples from the various strata.
•  The determination of the engineering properties of the soil and rock strata that affect the performance of the structure.
• Determination of the in-situ properties by performing field

Methods: Test Pits

                 Boring

                 Standard Penetration Test (SPT) [N Value]

                Cone Penetration Test (CPT): Static cone penetration test (SCPT)[qc value]

                 Dynamic cone penetration test (DCPT)

                 Pressuremeter Test (PMT)

                 Dilatometer Test (DMT)

                 Vane Shear Test (VST)

                Geophysical Exploration: Seismic reflection survey

                                                         Seismic refraction survey

                                                         Seismic Cross-hole survey

                                                         Resistivity Survey

              Plate Load Test

              Pile Load Test

  

👉 Standard Penetration Test (SPT): IS 2131-1981

• The Standard Penetration Test (SPT) is widely used to determine the parameters of the soil in-situ. The test consists of driving a split-spoon sampler into the soil through a bore hole at the desired depth.
•  The split-spoon sampler is driven into the soil a distance of 450 mm at the bottom of the boring
• A hammer of 63.5 kg weight with a free fall of 750 mm is used to drive the sampler.
• The number of blows for a penetration of last 300 mm is designated as the “Standard Penetration Value” or “Number” N.
• The test is usually performed in three stages. The blow count is found for every 150 mm penetration.
• The blows for the first 150 mm are ignored as those required for the seating drive.

• Number of blows for the first 150 mm penetration is disregarded due to the disturbance likely to exist at the bottom of the drill hole
• The test can be conducted at every 1m vertical intervals (Not more than 1.5 m)

👉The refusal of test when

• 50 blows are required for any 150 mm increment.

• 100 blows are obtained for required 300 mm penetration.

• 10 successive blows produce no advance.

👉Two corrections due to:

(a) Overburden pressure (granular soil)

(b) Dilatancy (for saturated fine sands and silts)

👉The corrected N value is given by (overburden correction)

                  

                                   N′ = (CF). N

                 where N′ = corrected value of observed N

                CF = correction factor for overburden pressure

👉Dilatancy Correction

                         

                            N′′= 15+0.5(N′-15)       if N′ > 15

Cone Penetration Test (CPT)

There are two types of CPT

(i) Dynamic cone penetration test (DCPT)                 (ii) Static cone penetration test (SCPT)

Static Cone Penetration Test

• The Static cone penetration test, which is also known as Dutch Cone test, has been standardized by “IS: 4968 (Part-III)-1976 - Method for subsurface sounding for soils - Part III Static cone penetration test”.

• The equipment consists of a steel cone, a friction jacket, sounding rod, mantle tube, a driving mechanism and measuring equipment.

• The cone have an apex angle of 60° ± 15′ and overall base diameter of 35.7 mm giving a cross-sectional area of 10 cm2.

• The friction sleeve should have an area of 150 cm2 as per standard practice.
• The sounding rod is a steel rod of 15 mm diameter which can be extended with additional rods of 1 m each in length.
• The driving mechanism should have a capacity of 20 to 30 kN for manually operated equipment and 100 kN for the mechanically operated equipment.

Dynamic Cone Penetration Test

• The dynamic cone penetration test is standardised by “IS: 4968 (Part I) – 1976 - Method for Subsurface Sounding for Soils-Part I Dynamic method using 50 mm cone without bentonite slurry”.

• The equipment consists of a cone, driving rods, driving head, hoisting equipment and a hammer.

• The hammer used for driving the cone shall be of mild steel or cast-iron with a base of mild steel and the weight of the hammer shall be 640 N (65 kg).

• The cone shall be driven into the soil by allowing the hammer to fall freely through 750 mm each time.

• The number of blows for every 100 mm penetration of the cone shall be recorded.

• The process shall be repeated till the cone is driven to the required depth.

Environmental Engineering

 👉Fluctuations in water demand:

• In India  the maximum daily demand of water is generally taken as 180% of the annual average daily demand of water ( peak factor = 1.8 ) 
• In India the maximum hourly demand of water is generally taken as 150 per cent of the hourly demand on the day of maximum use of water ( or the maximum day for the year). [Peak Factor = 1.5]
• Average Daily per capita Demand = Quantity required in 12 months / (365 x population)
• Maximum daily demand = 1.8 x average daily demand.
• Maximum hourly demand of maximum day i.e. Peak demand = 1.5 x average hourly demand on a maximum day

                                                              =     2.7 x annual average hourly demand

👉 Water Quality Parameters

 1.Conductivity or Electrical Conductivity (EC): is the ability of water to carry an electrical current. Pure water is a poor conductor of electricity and water shows significant conductivity when dissolved salts are present (generally, directly proportional to the amount of salts dissolved in the water). It is measured using conductivity sensors, and is expressed as siemens/meter (S/m).

 2.Colour: It is an important from the standpoint of aesthetics. Colour in water is often caused by organic substances such as algae or humic compounds. The colour could be Apparent (caused by suspended matter) or True (caused by dissolved or colloidal solids).

For measurement purpose, the colour produced by 1 mg/L of platinum (as K2PtCl6) and 0.5 mg/L of

cobalt (as CoCl2•6H2O) is taken as the standard one unit of colour, and a sequential dilution method

may be followed to determine the colour in standard colour units. Spectrophotometric determination of colour in the form of absorbance at select wavelength is also getting popular.

2. Odour: in water is objectionable. Pure water is odourless, but water may acquire odour when some

substances are dissolved. Decayed organic substances give fouling smell while inorganic substances

give earthy smell. 

• Odour is measured through Threshold Odour Test, where dilution factor is determined to make the water odourless.
• Threshold Odour Numbers (TON) can be computed as:

            = (Volume of Sample + Volume of Pure Water needed to remove any odour)/Volume of Sample

3. Turbidity: is an optical property, describing the clarity, or haziness of the water caused by the presence of very fine suspended or colloidal particles (typically not filterable by routine methods). Turbid waters are unacceptable to consumers. Turbidity may also affect the treatability of waters.

• Turbidity is measured through passing a beam of light through the sample, and recording its scattering. The quantity of light scattered is dependent upon the concentration and size distribution of the particles.

a) In turbidimetry, the intensity of light transmitted is measured.

b) In nephelometry the intensity of the light scattered at 900 is measured.

4. Hardness: in water is caused by the presence of Ca2+ and Mg2+ ions as Hydrogencarbonate ‐ Ca(HCO3)2, Mg(HCO3)2 ; Sulphates‐ CaSO4, MgSO4 ; Chloride ‐ CaCl2, MgCl2 etc. Bicarbonates of Ca and Mg leads to Temporary Hardness, while sulphates/chlorides/nitrates of Ca and Mg leads to Permanent Hardness.

• Hardness is most commonly measured by titration with an EDTA solution, however test strips or

instruments separately measuring Ca and Mg are also being used. Hardness can also be collocated

using ion balance where equivalence of Ca2+ and Mg2+ are estimated after converting each ion as mg/L of CaCO3.

5. Solids : refers to the mass of solids present in the water. The Total Solids (TS) mass present in the water could be in suspended or dissolved state, and could be volatile or fixed by nature. Based on these different measures of solids are estimated. The measurements are done using gravimetric analysis.

• Inorganic salts in water often remains in dissolved state and are non‐volatile even at high temperatures, therefore contributes to Fixed Dissolved Solids (FDS). While, Fixed Suspended Solids (FSS) are inorganic particles suspended in the liquid; such as undissolved salt crystals and silt particles.
• Organic compounds are often volatile at high temperature. The dissolved organics e.g. sugars, fatty acids etc. constitutes Volatile Dissolved Solids (VDS), while suspended organics and microorganisms constitute Volatile Suspended Solids (VSS).
• Sum of FDS and VDS forms Total Dissolved Solids (TDS), while sum of VSS and FSS is called Total Suspended Solids (TSS).  

6. Most Probable Number (MPN) : is most commonly applied parameter for microbial quality testing of water. Fecal coliforms act as an indicator for fecal contamination of water.