What is the subgrade layer?
In transport engineering, subgrade is the native material underneath a constructed road, pavement or railway track (US: railroad track). It is also called formation level. The term can also refer to imported material that has been used to build an embankment.
What is considered subgrade?
Subgrade is that portion of the earth roadbed which after having been constructed to reasonably close conformance with the lines, grades, and cross-sections indicated on the plans, receives the base or surface material. In a fill section, the subgrade is the top of the embankment or the fill.
What is subgrade in asphalt?
Subgrade is the top surface of an embankment or cut section that is shaped to conform to the typical section upon which the pavement structure and shoulders will be constructed.
What are the basic requirements for a subgrade layer?
The subgrade must be able to support loads transmitted from the pavement structure. This load bearing capacity is often affected by degree of compaction, moisture content, and soil type. A subgrade that can support a high amount of loading without excessive deformation is considered good.
How is subgrade prepared?
The foundation of the pavement structure is known as subgrade. Preparation of subgrade consists of all operations before the pavement structure could be placed over it and compacted. The subgrade may be situated on an embankment or excavation or at the existing ground surface.
How do you calculate subgrade?
It is expressed as k=p/s. Here, k = modulus or coefficient of subgrade reaction; p = applied pressure and s = deformation of soil settlement. The coefficient of subgrade reaction is expressed in load intensity per unit of displacement.
How is subgrade improved?
Normally, subgrade material is improved by installing geotextiles. They are used to prevent mixing of soft or inadequate soil that might affect the structural capacity of the subgrade.
How do you prepare subgrade for roads?
Other Subgrade Preparation Practices
- Ensure the compacted subgrade is able to support construction traffic.
- Remove all debris, large rocks, vegetation and topsoil from the area to be paved.
- Treat the subgrade under the area to be paved with an approved herbicide.
What is the subgrade modulus?
The Subgrade Modulus, also known as the Modulus of Subgrade Reaction, is a stiffness parameter typically used in defining the support conditions of footings and mat foundations, such as that shown on Figure 1. The parameter is expressed in units of [Force]/[Length]3. Mat foundation for a building under construction.
When to use subgrade or fine grade elevation?
Subgrade Elevation After final grading (often called fine-grading), the subgrade elevation should generally conform closely to the construction plan subgrade elevation. Large elevation discrepancies should not be compensated for by varying pavement or base thickness because; HMA, PCC and aggregate are more expensive than subgrade; and
When does a subbase go on top of a subgrade?
A slab on ground and pavements normally are designed to be supported by a solid subbase, which needs to be uniform by nature to support the structure above it. A subbase will go on top of the subgrade, which typically is native soil or improved soil that has been compacted.
What can be done to prepare sub grade pavement?
Preparing the subgrade and granular base course for new pavement. This can involve such activities as subgrade stabilization (e.g., with lime, cement or emulsified asphalt), over-excavation of poor subgrade, applying a prime coat or compacting the subgrade.
What do you need to know about subgrade soil?
It is a layer required in many structures such as pavements and slabs, although it needs to have certain characteristics. A subgrade might need special drainage structures to let water if it is composed of impermeable soil, and it should be graded to within plus or minus 1.5 inches of the specified elevation.