Unit 3 – Lesson 1: Basic Grading Civil 3D 2010 Student Workbook ▪ 1 Basic Grading Overview In this lesson, you learn the basic concepts of grading a site. More advanced concepts and methods involving roadway corridors and bulk grading of entire blocks are covered in a subsequent lesson. From the previous unit, you now have the ability to collect and import survey data, create points and surfaces, and import images as background information. Using this knowledge, it is easy to comprehend the basic issues involved in manipulating the terrain using techniques such as spot elevations, feature lines, and a special feature of Civil 3D called grading objects, which are contained in grading groups. Feature lines and grading groups are contained within a site and these objects interact with one another when they are in the same site. A fundamental aspect of projects that involve site grading is that a proposed surface representing design conditions must be created. The existing ground surface created from survey data and breaklines is the starting point; the design surface interacts with the existing ground surface. As the designer, you are responsible for developing one or more design alternatives that fits the needs of the client and the applicable regulations. There are many aspects of a project that are affected by grading decisions including stormwater drainage and low impact development methods, slope stability, sound barriers, applicable vegetation, visual impact of a site, and the cut and fill volume balance on the site. This lesson focuses on the use of feature lines, spot elevations, and grading objects. A feature line is similar to an AutoCAD 3D polyline, but offers powerful functionality for setting grades and vertex elevations. Spot elevations are simply design points inserted to control the position and elevation of a particular spot in the final design. Grading objects consist of a set of components that are most often used for projecting a feature line along a cut or fill slope to a surface. These objects are used to model the grading for the site, and are combined together to form the final grading surface. The final surface is important for a variety of reasons, Lesson 1 AutoCAD Civil 3D 2010 Education Curriculum Student Workbook Unit 3: Land DevelopmentUnit 3 – Lesson 1: Basic Grading Civil 3D 2010 Student Workbook ▪ 2 including 1) quantity calculations, 2) generation of construction staking data, and 3) 3D modeling and visualization. While this lesson covers basic grading concepts, many of these techniques are used in final, detail grading. The introduction of these techniques at this early stage reflects their relative simplicity, as well as their importance in visualizing the final product. Objectives After completing this lesson, you will be able to: - Explain the function of sites. - Explain the basic concepts of grading. - Create spot elevations and feature lines. - Edit grading criteria. - Create grading objects and grading groups. - Calculate cut and fill volumes for grading objects. - Create a design surface. - Use styles and labels to create a basic grading plan.Unit 3 – Lesson 1: Basic Grading Civil 3D 2010 Student Workbook ▪ 3 Exercises The following exercises are provided in a step by step format in this lesson: 1. Create Feature Lines and Spot Elevations 2. Create a Grading Object 3. Create a Design Surface About Sites A site contains design objects such as alignments, parcels, feature lines, and grading groups. Using Prospector, you can organize design objects into different sites. In many cases, this site is also the initial parcel from which all subsequent parcel design is generated. You create and maintain relationships among objects by grouping them together in a site. The following illustration shows a site and the objects that make up a typical site. When you create any of these objects, you must specify the site to which it belongs. If you create these objects before you create a site, a site with a default name (for example, Site 1) is created automatically, and the objects are assigned to it. Sites are most often used to organize data. Sites also recognize topology, which refers to the spatial relationships among objects. Objects that are in the same site interact with each other. More than one site can reside in the same geographic location, but the objects contained in the different sites do not interact. These are some general guidelines to use when working with sites: When working with large amounts of data in a site, use representative naming conventions to help you organize your data. For good data management practices, use sites to organize parcel, alignment, feature line, and grading group data either geographically or by project phase. If you want design objects to interact with each other, assign them to the same site.Unit 3 – Lesson 1: Basic Grading Civil 3D 2010 Student Workbook ▪ 4 About Grades and Slopes This lesson introduces the concept of designing the grading to work within the limits of the existing terrain to develop a final design surface. Working with the existing terrain is vital when considering how best to achieve your design goals. Surfaces are often evaluated at different locations with regards to their slope for a variety of reasons. For example, steep slopes are undesirable from a geotechnical perspective due to stability, and flat areas tend to accumulate water. There are regulations and ordinances in place in most localities that control the slope, or grade, in certain areas of a development. The terms grade and slope are synonymous; both are used to express the slope of the land along a line. Common uses of the terms can differ, but grade is often represented as a percent. Percent grade refers to the number of vertical units of drop along the line divided by 100 units (ft/100 ft or m/100 m). Slope is often used as a ratio of the number of horizontal units to vertical units of drop along the line (3H:1V, or 3:1). The importance of knowing the controlling regulations cannot be overemphasized. Using the capabilities of Civil 3D, you can control the slopes and grades of the final surface along any line or face, in any direction. About Feature Lines A feature line is a Civil 3D object that represents a three-dimensional polylinear element. Feature lines connect a series of geometry and elevation points. You can draw
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