a) What four (4) pieces of udormation awe protection at a culvert oulet? b) Why

Question

a) What four (4) pieces of udormation awe protection at a culvert oulet? b) Why is the "new MEPDG pavement analyis design guide method that ODOT uses? method dfrnt from the ASHTO c) Under what used? design conditions should the rigid pavement joint factor () of 27b d) Underdrains are provided in pavement cross-sections to keep the pavement dry f what reason? e) What condition causes a culvert to awaxs operate under outlet contro 1) What should be the maximum spacing of contraction joints for a 6 rigid pavemet

Explanation / Answer

a) The four pieces of information required for rock channel protection are

>> Apron length

>> Apron width, which is based on diameter of discharge pipe

>> Alignment, where there should be no bends

>> Thickness.

b)

>> AASHTO method did not consider the variation of moisture and temperature on the mechanical properties of the pavement layers while, MEPDG do it.

>> MEPDG design procedure incorporates mechanistic principles, including calculations of pavement stress,strain and deformation responses using site-specific climatic,material, and traffic characteristics.

c)

>> Several dowel load transfer system features are critical to ensure the long-term effectiveness of the dowel load transfer system. So the rigid pavement joint factor of 2.7 is used.

>> It is based on the condition that Larger diameter dowel bars substantially reduce dowel bearing stresses and subsequent joint faulting.

>> Also dowels should be coated with a corrosion inhibitor to ensure the long-term effectiveness of the bar.

>> Additionally, the underlying base or subbase courses also contribute to the load transfer capabilities of transverse joints.

>>  In particular, stabilized and lean concrete bases provide greater slab edge support and thereby reduce deflections.

d)

>> Water has a damaging effect on most of the materials used in road construction. In the summer months heavy rainfall can cause water infiltration into the cracks and joints of road pavement, with resulting weakening of the pavement structure, which can develop into deformation, cracking and potholes.

>> Likewise, saturation of the pavement sub-layers due to a high water table will reduce the moduli of elasticity of the sub-layers giving rise to early rutting and cracking and requiring early maintenance.

>> It is therefore important that efficient permanent under drainage is provided to prevent the level of the water table rising to formation level and to drain water which may have penetrated through the edge or cracks and joints in the road pavement into the road structure.

>> The installation of adequate under drains allows the designer to use higher soil strength in assessing the pavement thickness.

e) Culverts to always operate under outlet control that,

>> The flows are regulated, or if not regulated, they can be predicted with certainty.

>> The channel is stable in both vertical and horizontal alignment.

>> There will be no hydraulic drops or jumps within the barrel or near the ends.

>> Clearance can be provided between the culvert crown and the water surface during the maximum predicted discharge.

>> Flow contraction into the culvert barrel is minimal and contraction scour is not a concern.

f)

For a 6" rigid pavement, as per IRC recommendation, the maximum spacing of contraction joints is 4.5m.

THANK YOU

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