What is Method of Construction of Gravel Roads?

Construction of Gravel Roads

Gravel roads are considered superior to Earthen Roads as they can carry heavier traffic.

this type of road can take about 100 tonnes of Pneumatic tyred vehicle or 60 tonnes of iron tyred vehicles per day per lane. 

the camber provided on this type of road is between 1 in 25 and 1 in 30.

Two types of Construction methods are given below.

(I) Feather Edge Type

it is Constructed over the Subgrade with varying thickness, so as to obtain the desired cross slope for the pavement surface.

(II) Trench Type

in the trench type, the Subgrade is prepared by excavating a shallow trench. 

Figure:-(1) Types of gravel road sections

The Construction of Gravel Roads may be divided into following steps.

(I) Construction Material

Hard variety of crushed stone or gravel of specified gradation is used. 

Rounded stones and river gravel are not preferable as there is poor interlocking. 

Gravel to be used for the construction is stacked along the sides of proposed road.

(II) Alignment Location

the central line and Road ages are marked on the ground along the alignment with the help of reference pegs.

(III) Pavement Structure

the layer is rolled using smooth wheel rollers starting from the edges and proceeding towards the centre with an overlap of atleast half the width of roller in the longitudinal direction.

 (IV) Opening to Road Traffic 

A few days after the final rolling and drying out, the road is opened  to the traffic. 

What is Construction of Earthen Roads,Types of Highway Construction

Types of Highway Construction

the highway construction types are various given below.

(1) Earth roads.    (2) Gravel road

(3) Soil Stabilized Roads 

(4) Water Bound Macadam (WBM) Roads

(5) Bituminous Roads

(6) Cement Concrete Roads

Construction of Earthen Roads 

an earthen road is the cheapest type of road prepared from natural soil. 

the pavement Section is totally made up of the soil available at site.

the maximum cross slope 1 in 2 is recommended to avoid erosion due to rain water and formation of cross ruts. the steep cross slope helps to keep the pavement surface free of standing water, otherwise the soil being previous the water would damage the pavement Section by softening.

the Construction of Earthen Roads  may be divided into following steps.

(a)  Construction Material

the pavement Section is totally made up of the soil available at site or nearby which is free from organic substances.

(b) Alignment Location

the centre line and road edges are marked on the ground along the road alignment by dividing wooden pegs .

the spacing of reference pegs depends on the estimated length of road Construction in a day.

(c) Preparation of Sub- Grade

the various operations involved in the Construction of sub Grade are clearing site, Excavation and Construction of soil fills to bring the road to a desired grade and shaping of sub grade.

(d) Construction of Pavement Structure

the soil is mixed, spread and rolled in Layers such that the Compacted thickness of each layer does not exceed 10 Centrimeter.

At least 95% of maximum dry density (MDD) is considered desirable

(e) Opening to traffic

The Compacted earth road is allowed to dry out for a few days before opening to traffic.

Design Elements in Highway Embankments

The Design Elements of highway embankment are following points.

(1) Height:- the height of embankment depends on the desired grade line of the highways, topography, stability of foundation and the soil Profile.

(2) Embankment Material:- Granular Soil is generally preferred as Highway Embankment Material.

The best of the soils existing locally is often selected with a view to keep the lead and lift as low as possible.

(3) Settlement of Filling Material:-

If the embankment foundation consists of compressible soil with high moisture content, the consolidation can occur due to increase in the load. 

To accelerate the rate of consolidation of saturated foundation clay, vertical drains are Constructed.

(4) Stability of Foundation:-

Stability of Foundation is required in case of weak soil just beneath or at a certain depth below of embankment foundation and in case of high Embankments.

(5) Stability of Slope:- 

The Embankment slopes should be stable enough to eliminate the possibility of a failure under adverse moisture and other conditions.

Often much flatter slopes are preferred in Highway Embankment due to aesthetic and other reason.

Why is the pile intregity test is done? What do you mean by PIT Test of Piles?

PIT :- "Piles Integrity Test"

A pile integrity test is done to ensure such defects are not there. 

A defective pile would not carry the desired load, and may lead to catastrophic failure of the superstructure. each and every piles tested. But that is costly.

Hence 5–10% of the total number is tested, at critical locations. 

If a failure is detected. More tests are done.

If a pile fails in this test, load testing is done to ascertain the load bearing capacity, and the pile layout is amended accordingly. 

New piles are made of required. 

this is done before casting the pile cap.

Note:-Piles being underground, visual inspection for flaws in concrete like honeycomb, gaps, fissures etc. cannot be done.

What is design of base plate?, What is required size of Base plate for Steel Structure?

Design of Base Plate :

Grade of steel used                                             fy  =  250 MPa

Grade of concrete used,       

For  M25                              fck =  25 MPa Bearing strength of concrete,=0.45 x fck                               

As per Cl.34.4 of IS :456:20000

=0.45  x  25   =  11.25 N/mm²

Max. bearing pressure should not exceed the bearing strength equal to 0.6 x f_c as per Cl.7.4.1 of IS 800 :2007

0.6  x  25  = 15 N/mm²

partial safety factor                                     γm0   = 1.1

Sectional Properties of column  2 NB TUBE 150  x  4.85 THIK. 

b     =  168 mm    

A  =   24.90 cm²
d    = 150 mm

Maximum support reaction at each leg  =   316 KN

(Ref : " Design of Trestles" in design notes )     =  316000 N

Required area of slab Base           

=  316000  X /          11.25  

=28088.89 mm^2

provide size of base plate more than                              = 28088.9 mm^2                                      =167.5974012 mm^2

proposed section for Base plate    280  x  280  mm
Thickness of plate provided = 22 mm

Length of the base plate = 280 mm

Width of the base plate  =280 mm

Area of base plate            

Abp =  280  x   280    
                                        

  = 78400 mm^2

        Hence Safe/  Design Ok        

Yield strength of the steel                                                  =   250 N/mm²

Stress on base plate                                                               w = 4.031 N/mm²

Check for Base plate thickness

Depth of column section                                                            = 168 mm

Total width column section                                                         =150 mm

Smaller projection  b = ( 280  -  150)  /  2     =65 mm 

Larger  projection  a  = (280 - 168)/   2    = 55.85 mm

Thickness of the base plate required,  T  =   2.5 x  4.03 x (65  x  65

-  0.3  x ( 5.85 x 55.85 ) x  1.1/250 

T    =   12.0762 m

Provided thickness of base  plate                                             =    22 mm

        HENCE  SAFE      



Durability of structure , Factors affecting durability of Building , Requirements for durability, Exposure Condition

DURABILITY - a durable steel structure is one that platform satisfactorily the desired function in the working environment under anticipated exposure condition during its service life, without deterioration of the cross-sectional area and loss of strength due to corrosion.
the material used, the detailing, fabrication, erection and surface protection measures should all address the corrosion protection and durability requirements.
                                   Requirements for Durability
As per Cl. 15.2.1 of IS-800-2007 Shape, Size ,Orientation of Members Connections and details
The design, fabrication and erection details of exposed structures should be such that good drainage of water is ensured. standing pool of water , moisture  accumulation and rundown of water for extended duration shall be avoided.
the details of connections should ensure that:
a) All exposed surfaces are easily accessible for inspection and maintenance;
b)All surfaces, not so easily accessible are completely sealed against ingress of moisture.
As per Cl. 15.2.2 of IS-800-2007 Exposure Condition
The general environment , to which a steel structure is exposed building its working life is classified into five levels of severity.
Sn.          Environmental classifications                  Exposure Conditions

i)  mild                            Surfaces normally protected against exposure                                                          to weather or aggressive condition as in interior of                                                building, except when located in coastal areas

ii) Moderate                               Structural Steel  Surfaces:

                                                   a) exposed to condensation and rain   

                                                  b)Continuously under water

                                                 c) exposed to non-aggregate soil/underwater

                                                 d) Sheltered from saturated salt air in coastal areas

iii) Severe                    Structural Steel  Surfaces:

                                              a) exposed to severe frequent rain

                                              b) exposed to alternate wetting and drying

                                               c) severe condensation

                                               d)Completely immersed in sea water

                                                e) exposed to saturated salt air in coastal area

iv) very severe                      Structural Steel  Surfaces exposed to:

                                                                     a) sea water spray

                                                                      b) corrosive fumes

                                                                      c) aggressive subsoil or groundwater

v) Extreme                              Structural Steel  Surfaces exposed to:

                                                           a) tidal zones and splash zones in the sea

                                                           b) aggressive liquid or solid chemicals

                                   
                        Factors affecting durability of the Building/ Structure 

factors that affect the durability of the buildings under condition relevant to their intended life are listed below.
a) Environment
b) Degree of exposure
c) Shape of the member and structural detail
d) Protective measure
e) Ease of Maintenance

Camber/ Cross Fall,Geometric Design and Alignment of Camber or Cross Fall

Camber/ Cross Fall
The reason for that is because most roads have a camber to them that helps water drain off of them rather than pooling up in the center of the road. 
The camber is any curve on a surface, and in this case refers to upward curve from the edge of a road towards the center.

As per IRC SP:73:2015 Clause; 2.8.1 - The crossfall on straight sections of road carriageway, paved shoulders and paved
portion of median shall be 2.5 percent for bituminous surface and 2.0 percent for cement
concrete surface.

 

As per IRC SP:73:2015 Clause; 2.8.2 - The cross fall for earthen shoulders on straight portions shall be at least 0.5 percent steeper than the slope of the pavement and paved shoulder subject to a minimum of 3.0 percent. On super elevated sections, the earthen portion of the shoulder on the outer side of the curve shall be provided with reverse crossfall of 0.5 percent so that the earth does not drain on the carriageway and the storm water drains out with minimum travel path.

As per IRC SP:73:2015 Clause; 2.8.3 -The two-lane roads shall be provided with a crown in the middle. On horizontal curves, the carriageway shall be super elevated.

                                          Image Source:engineeringdiscoveries



Geometric Design and Alignment
As per IRC SP:73:2015 Clause; 2.9.1 -Geometric design shall conform to IRC:73 except as otherwise indicated in this Manual. While designing the horizontal alignment, the following general principles shall be kept in view:
i) Alignment should be fluent and it should blend well with the surrounding topography.
ii) On new roads, the curves should be designed to have largest practical radius,
but in no case less than ruling value corresponding to ruling design speed.
iii) As a normal rule, sharp curves should not be introduced at the end of long tangent since these can be extremely hazardous.
iv) The curves should be sufficiently long and they should have suitable transitions to provide pleasing appearance.
v) Reverse curves shall be avoided as far as possible. Where unavoidable,sufficient length between two curves shall be provided for introduction of requisite transition curves.
vi) Curves in the same direction, separated by short tangents known as broken back curves, should be avoided as far as possible.
vii) To avoid distortion in appearance, the horizontal alignment should be coordinated carefully with the longitudinal profile.
viii) Hair pin bends on hilly terrain should be avoided as far as possible.