According to the Technical Specification for Highway Subgrade Construction, the maximum particle size of the subgrade filler of the first-class highway should be less than 100mm, and the minimum CBR (California Bearing Ratio) of the filler should be 8%. Within 500mm below the top surface of the road bed, the soil that meets the requirements of the road bed shall be filled and compacted in layers to achieve uniformity and compactness.

In order to meet the design requirements of elastic modulus value of subgrade soil foundation, the soil layer 30cm deep below the top surface of subgrade must reach the compactness required by relevant national codes, regulations and standards. According to the actual situation of subgrade, the reinforcement of individual subgrade should be based on soil quality, precipitation, groundwater type and buried depth, and the source of reinforcement materials. After comparison, reinforcement measures such as in-situ rolling, changing or improving soil, strengthening underground drainage and setting geosynthetics can be adopted.

Second, the determination of subgrade:

Generally, the fill in the filling section is 0.5~ 1.0m, of which the cultivated soil section is tentatively 0.8m, and the construction waste removal section is tentatively 1m (the specific thickness of surface cleaning and construction waste removal shall be subject to the actual measurement during construction, and the principle is to remove the expressive plant roots, house foundation and construction waste, so that the soil foundation can be compacted to meet the compaction standards required by specifications and design drawings).

4% quicklime soil shall be replaced within 0.3m of the main road bed of a section of fill, and 15cm of unscreened gravel shall be replaced with the main road bed of general fill.

Third, the determination of pavement width:

The width of pavement only includes the width of roadway and sidewalk, excluding the width of land for urban greening along the street other than sidewalk, which is mainly determined by traffic volume. Does not include kerb width. The width of highway subgrade is the sum of pavement width and shoulder width on both sides. When there are median, emergency stop, climbing lane, speed change lane and wrong lane, the width of these parts is also included. Highway pavement width refers to roadway width, excluding shoulder width.

Extended data:

The materials for subgrade construction, whether filling or excavation, are mainly earth-rock particles. Therefore, subgrade is a kind of geotechnical structure, which is often attacked and destroyed by changes in natural conditions such as geology, water, rainfall, climate and earthquake, and its resistance is poor. Therefore, the subgrade should have sufficient firmness, stability and durability. For high-speed railway, the subgrade should also have reasonable stiffness to ensure the stability and comfort of the train at high speed.

The main function of subgrade is to provide necessary conditions for the laying of track or pavement and the operation of train or traffic, to bear the static load, dynamic load and traffic load of track and locomotive or pavement, and to transmit and disperse the load to the depth of foundation. On the longitudinal section, the subgrade must ensure the elevation required by the line; On the plane, subgrade, bridge and tunnel are connected into a complete through line.

In civil engineering, subgrade plays an important role in engineering quantity, occupied area and investment. Subgrade is connected with bridges and tunnels to form a line together. There are two basic forms of subgrade according to the different terrain conditions: embankment and cutting, commonly known as filling and excavation.

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