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.
In a cut section the subgrade is the bottom of the cut (Figure 7-1). The subgrade supports the subbase and/or the pavement section. To ensure a stable, long-lasting, and maintenance free roadway, the subgrade is required to be constructed using certain proven procedures that provide satisfactory results.

What is a subgrade in construction?

The “subgrade” is the in situ material upon which the pavement structure is placed. Although there is a tendency to look at pavement performance in terms of pavement structure and mix design alone, the subgrade can often be the overriding factor in pavement performance.

Figure 1: Subgrade Preparation on Kaua’i

Figure 2: Subgrade Preparation on SR 528 in Marysville, WA

img class=’aligncenter wp-image-189362 size-full’ src=’https://www.ammacement.in/wp-content/uploads/2022/12/gygaepoxajolo.jpg’ alt=’What Is Subgrade In Road Construction’ /> Figure 3. Subgrade work on SR 97 south of Bend, Oregon.

How important is the subgrade in pavement performance?

The “subgrade” is the in situ material upon which the pavement structure is placed. Although there is a tendency to look at pavement performance in terms of pavement structure and mix design alone, the subgrade can often be the overriding factor in pavement performance.

Figure 1: Subgrade Preparation on Kaua’i

Figure 2: Subgrade Preparation on SR 528 in Marysville, WA

img class=’aligncenter wp-image-189362 size-full’ src=’https://www.ammacement.in/wp-content/uploads/2022/12/gygaepoxajolo.jpg’ alt=’What Is Subgrade In Road Construction’ /> Figure 3. Subgrade work on SR 97 south of Bend, Oregon.

What is pre-preparation of subgrade?

Quality Control: –

The poor soil should be avoided if possible, but when it is required to build over weak soils, several techniques are used to improve subgrade performance, as follows.

Remove poor soil and replace it with higher quality fill material.Soil stabilization using admixtures can increase subgrade stiffness and reduce swelling tendencies of soil.Additional base layers can help to spread pavement loads over a larger subgrade area.

Required maximum laboratory dry unit weight when tested as per IS:2720 (Part 8), and it should not be less than 18 kN/cumRelative compaction as a percentage of maximum laboratory dry density as per IS:2720 (Part 8) is not less than 98%.Construction of subgrade with approved material satisfying a minimum CBR of 5% should be followed.

Also, Read: Site Clearance – Clearing and Grubbing for Highway Construction Loading, Summary Article Name Subgrade – Steps for Preparation of Subgrade Description The subgrade may be situated on embankment or excavation or at the existing ground surface. In all the above cases, Site Clearance -Clearing Grubbing Operation should be done before starting the pavement structure construction. Author WhiteHelmet Publisher Name Construction Civil Publisher Logo

What is the CBR required for construction of a subgrade?

Construction of subgrade with approved material satisfying a minimum CBR of 5% should be followed. Your Opinion Matters: How easy is it to understand the information on our website? The subgrade may be situated on embankment or excavation or at the existing ground surface.