Highway (Road Work) Interview Questions and Answers

Project report should contain information such as

1. General detail of the project.
2. Purpose of the project.
3. Features of the road including selection of route, traffic, alignment etc.
4. Drawings related to road and specifications.
5. Drainage system and cross drainage structures.
6. Material, labour and equipment estimates
7. Cost of the project and rates of the individual items.
8. CPM, PERT details
9. Other miscellaneous items like diversion roads, road site amenities, lodging sites, traffic control etc.

Camber is a transverse slope provided to the road to drain off surface water (rain water) from the pavement and it is provided by raising the middle of the road surface.

Camber is important due to following reasons –

1. To prevent the entry of surface water in the subgrade which adversely affect the surface condition and life of the pavement.
2. Bituminous roads are very much affected by water. It causes stripping of bitumen from the aggregates and results in deterioration of the pavement layer. Therefore, camber is important.
3. Also, camber allow the pavement to get dry soon after the rain as the skid resistance of the pavement gets considerably decreased under wet condition and makes it slippery and unsafe for vehicles.

The main function of the traffic separators is to protect head-on collisions between vehicles moving in opposite directions on the adjacent lane. It also helps in channelize the traffic into streams at intersections, shadow the crossing and turning traffic, segregate slow traffic and to protect pedestrians.

Kerb is a separator between pavement and footpath. It also provides lateral support to the pavement.

According to this theory the time taken by the driver or the total reaction time of the driver is split into four parts:

1. Perception – it is the time required in perceiving any object.
2. Intellection – it is the time required in analyzing the situation
3. Emotion – it is the time lost due to emotion of driver like anger or fear.
4. Volition – it is the time taken for the final action (applying the brake)

Horizontal curve without superelevation imparts centrifugal force in outward direction of curve. Due to that pressure on outer wheel of vehicles increases, it imparts more pressure on outer edge of pavement, due to which consolidation occurs at one or more than one layer of pavement, which is called ruts and the process is known as rutting.

To counter balance the centrifugal force and to reduce the tendency of vehicle to overturn or skid, the outer edge of the pavement is raised with respect to the inner edge, thus providing a transverse slope throughout the length of the horizontal curve. This transverse inclination is to the pavement surface is known as superelevation.

Transition curve is provided to change horizontal alignment from straight to circular curve gradually. This curve has a radius equal to infinite at straight road and gradually changes to designated radius at circular curve. Objective of transition curve are

1. To gradually introduce the centrifugal force between straight and circular.
2. To avoid sudden jerk.
3. To introduce superelevation gradually.
4. To introduce extra widening gradually.

At higher elevations lesser gradient is provided because at higher elevations, availability of oxygen is less due to which less fuel burnt by vehicles and hence it reduces the pulling power of vehicles.

Valley curves are designed taking headlight sight distance (HSD) into account. We use HSD for valley curve because at day time there is no restriction to sight distance but during night in absence of street light, the only source of visibility is head light. The visible distance through headlight is known as HSD.

In India rate of growth of traffic is approximately 5 to 7.5% per year.

Following are the important charts:

1. Trend Chart – trend chart shows the traffic volume trend over a period of year. This chart is used for the calculation of rate growth of traffic and also used for planning and future expansion.
2. Variation Chart – this chart shows hourly, daily and seasonal variation. Variation chart helps in deciding the facilities and regulation needed during peak traffic period. Ex. During peak flow a particular class of vehicle is restricted to one road and diverted to another road.
3. 30th Highest hourly volume – As per Indian Road Congress (IRC), 30th highest hourly volume is considered as design hourly volume. This volume is exceeded only 29 times in a year and all other traffic volume will lie lesser than that. Generally, this volume is 8% to 10% of average daily traffic (AAT). It is observed that 30th highest hourly volume gives a satisfactory result in terms of performance and it is economical in nature.

Following are the accident types:

1. A moving vehicle collides with a park vehicle.
2. A moving vehicle collides with an object like tress, polls etc.
3. Head on collision of vehicles.
4. Two vehicles approaching from different direction collide at an intersection.

Circular shape of rotary is preferred when traffic in both the cross roads are approximately equal whereas Elliptical shape generally preferred when traffic on one road is higher as compare to traffic on another road. Tangential and Turbine shape is not preferred because of chances of over-speeding.

1. Transverse joints – Following are the transverse joints:

Expansion Joint – these joints are provided in the transverse direction to the pavement to allow expansion of slab when environment temperature is more than construction temperature.

Contraction Joint – these joints are provided in transverse direction to allow contraction of slab in order to prevent cracking due to tensile stress development as environment temperature is less than construction temperature.

Warping Joint – whenever the top and bottom have different temperatures, the slab tends to warp downward or upward inducing warping stresses. So, to prevent the warping of the slab warping joints are provided along the longitudinal direction of pavement. If expansion and contraction joints are properly designed and constructed, there is no need of providing warping joints.

Construction Joint – this is not a type of joint. Due to discontinuity of work construction joints are created. To avoid this in pavement construction, concreting should be stopped at expansion, contraction and longitudinal joint.

2. Longitudinal Joints – these joints are provided in the direction of traffic and tie bars are used to connect two slabs in lateral direction in order to prevent lateral sliding due to dynamic forces, expansion, contraction etc.

Generally, the CBR (California Bearing Ratio) value at 2.5 mm penetration will be greater than that at 5 mm penetration and in such case the former shall be taken ad the CBR value for design purposes. If the CBR value corresponding to a penetration of 5 mm exceeds that for 2.5 mm, the test shall be repeated. If identical results follow, the CBR corresponding to 5mm penetration shall be taken for design.

Modes of water penetration into road structure:

1. Capillary rise of sub-soil water from beneath the pavement.
2. Penetration of surface water from top of the pavement (percolation) mostly through cracks on the pavement surface.
3. Penetration of sun-soil water from sides of the pavement
4. Interception of water due to flooding of cross drains provided along the pavement.
5. Interception of surface water from sides of the pavement.

Various components of road surface:

1. Sub-grade – the top of the ground on which the foundation of the road rest is called subgrade.
2. Sub-base – when the bearing capacity of the soil is poor and the intensity of traffic is high, then a layer is provided between soling (base) and subgrade, this layer is known as sub-base.
3. Base – the foundation of a road is called base or soling. The thickness of base, in no case, should be more than 30 cm. the base course receives the impact of the traffic through the wearing course.
4. Wearing course – the super structure of a road is called wearing course or road surfacing or wearing layer.

The gradient at which no tractive effort is required to maintain a constant speed by the vehicle, is known as floating gradient. The gradients less than the floating gradient require some tractive effort to maintain a constant speed by the vehicle and the gradients more than the floating gradient result in increase of speed.

It is a progressive loosening or separation of aggregate particles in a pavement surface coarse from the surface downward or from the edge inward.

The causes are;

1. Lack of compaction
2. Construction in thin lift during cold weather
3. Dirty or disintegrated aggregates
4. Too little asphalt in the mix
5. Overheating of asphalt mix
6. Mix is very close to coarse
7. Action of water
8. Sensitive aggregate refuse coating due to special charge (anti-stripping materials must be used)

Modified test have the 5 times greater compactive energy than in the standard test and a higher value of dry density is obtained in the modified Proctor test as compared to the standard proctor test.

Liquid limit is the percentage of water contentin which the soil mass has a capacity to flow as a liquid. It is between the liquid and plastic state of soil.

Plastic limit is the percentage of water content in which the soil mass can be moulded without crumbling. It is in between the plastic and semi-solid state of soil.

C.B.R or California Bearing Ratio: It is a ratio of a force required to penetrate a sample to a certain depth (with 5 cm dia. Piston) to a force required to penetrate the sample of high-quality crushed stone with the same depth and piston

By the following equation

            W = d x V x A

Where,

            W = Actual Surcharge Weight

            A = Area of Mould

            d = Density of Material

            V = Sum of the thickness of Layers