Grading in earthworks

Grading in civil engineering and landscape architectural construction is the work of ensuring a level base, or one with a specified slope, for a construction work such as a foundation, the base course for a road or a railway, or landscape and garden improvements, or surface drainage. The earthworks created for such a purpose are often called the sub-grade or finished contouring.

Grading (also known as Leveling) is the creation of flat surfaces with or without a uniform gradient (gradient), for example, for future construction or stable embankments. This involves removing or filling uneven areas. In construction, flat surfaces are referred to as planar.

Soil leveling is done using bulldozers and graders. In this context, demolition and clearing can also be colloquially referred to as leveling if buildings or vegetation are removed.

Regrading

Regrading is the process of grading for raising and/or lowering the levels of land. Such a project can also be referred to as a regrade.

Regrading may be done on a small scale (as in preparation of a house site) or on quite a large scale (as in major reconfiguration of the terrain of a city, such as the Denny Regrade in Seattle).

Regrading is typically performed to make land more level (flatter), in which case it is sometimes called levelling.) Levelling can have the consequence of making other nearby slopes steeper, and potentially unstable or prone to erosion.

Transportation

In the case of gravel roads and earthworks for certain purposes, grading forms not just the base but the cover and surface of the finished construction, and is often called finished grade.

Process

After the existing conditions of the limit of work has been surveyed, surveyors will set stakes in places that are to be regraded. These stakes have marks on them that either give a finished grade to the design of the project, or have CUT/FILL marks which specify how much dirt is to be added or subtracted. All grade marks are relative to site benchmarks that have been established. The regrading work is then often done using heavy machinery like bulldozers and excavators to roughly prepare an area, then a grader is used for a finer finish.

Levelling is the set of operations, both surveying and calculation, aimed at transforming the irregular physical surface of the land into a flat, horizontal or inclined surface. The levelling project of a given area is carried out on the representation of a dimensioned plan or, in the case of very large areas, on that of contour lines.

In many cases, heavy machinery such as bulldozers and excavators are used to roughly prepare the area, and graders are used to perform more detailed finishing. Today, a combination of laser levels and graders can level an area 700m in diameter to within 20mm of elevation difference. It is also easy to plan the movement of the removed soil if the level is surveyed before leveling.

This project requires:

the calculation of the height of earth to be reported or excavated (red levels) in correspondence with characteristic points

the determination of the transition line, if it exists, between the fill area and the excavation area

the calculation of the volumes of earth to be filled and excavated, in order to be able to proceed with the estimated metric calculation of the movement of the earth.

There are different types of flattening:

Levelling with excavation work only.

Levelling with fill work only.

Levelling with excavation and fill works.

Compensatory smoothings.

Excavation-only levelling will occur when the design level is equal to or smaller than the lowest level of the ground.

The project or leveling plan, to which the natural surface of the land must be reported, can be of established position or to be fixed in such a way as to have the compensation between the volumes of the fill and the excavation. In the case that the project plan is of established position, it is sufficient that its height is assigned, or the height of one of its points if it must be horizontal; it is necessary to have the elements to define its line of maximum slope, if it must be inclined.

The red level, for each point considered, is given by the difference between the design level and the ground level (QR = QP - QT). If the sign is positive, there is a red fill level, that is, the design plane passes, at that point, above the ground (fill ordinate); if it is negative, there is a red excavation level, that is, the plane passes below the ground (excavation ordinate). The points of the ground that have a level coinciding with the design level, that is, have a zero red level, are defined as passage points and can be found with the graphic method of overturning or analytically. The broken line that joins the passage points is defined as a passage line and separates the excavation area from the fill area.

If, after completion of a shell, it is necessary to level or level out unevenness on the surfaces of the floor slab, ceilings or already laid screeds and to adjust height differences, then either

a filler is applied,

a self-levelling or self-levelling levelling or filler compound is spread on the subfloor,

a calcium sulphate or cement-based flow screed is applied,

a filling of sand, slag, perlite, expanded polystyrene (Styrofoam), hemp shives or similar, which is often consolidated by binding agents, or

a soft insulating material must be applied.

A load-distributing layer of screed or dry screed must then follow the fill and insulation material.

Environmental design

In the environmental design professions, grading and regrading are a specifications and construction component in landscape design, landscape architecture, and architecture projects. It is used for buildings or outdoor amenities regarding foundations and footings, slope terracing and stabilizing, aesthetic contouring, and directing surface runoff drainage of stormwater and domestic/irrigation runoff flows.

Purposes

Reasons for regrading include:

Enabling construction on lands that were previously too varied and/or steeply sloped.

Enabling transportation along routes that were previously too varied and/or steep.

Changing drainage patterns and rerouting surface flow.

Improving the stability of terrain adjacent to developments.

Consequences

Potential problems and consequences from regrading include:

Soil and/or slope instability

Terrain prone to erosion

Ecological impacts, habitat destruction, terrestrial and/or aquatic biological losses.

Drainage problems (surface and/or subsurface flow) for areas not considered in the regrading plan.

Loss of aesthetic natural landscape topography and/or historical cultural landscapes.

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