Model Based Design Civil3D Wp

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www.autodesk.com/civil3d

AUTODESK

CIVIL 3D

2005

True Model-Based Design withAutodesk Civil 3D

Autodesk commissioned this white paper written by Karl Fuls. Fuls is a Professional LandSurveyor with more than 20 years experience in civil engineering and surveying software. Fulsis an Autodesk Certified Instructor at the Pennsylvania College of Technology in Williamsport,PA. In addition, Fuls conducts independent training for civil, surveying, and architectural firmsacross the Eastern United States.

Executive Summary ......................................................................................................................2Statement of Purpose ...................................................................................................................2Overview of Model-Based Road Design .......................................................................................3Advantages of the Model-Based Approach ..................................................................................4

Advantages of the Data Model..................................................................................................4Advantages of the Output Model...............................................................................................5

Caveats of the Model-Based Approach ........................................................................................5Autodesk Land Desktop Versus Autodesk Civil 3D ......................................................................5

Using Autodesk Land Desktop with Autodesk Civil Design ......................................................5Using Autodesk Civil 3D ...........................................................................................................7

A Model-Based Case Study..........................................................................................................9Project Planning........................................................................................................................9

Gathering Project Data..............................................................................................................9Designing the Horizontal Alignment ........................................................................................10Designing the Vertical Alignment ............................................................................................11Designing Typical Cross Sections...........................................................................................13Designing Horizontal Transitions ............................................................................................14Designing Vertical Transitions ................................................................................................15Creating the Corridor ..............................................................................................................21Creating the Output Model ......................................................................................................24Use in the Field .......................................................................................................................25Output Model Characteristics..................................................................................................29

Conclusion ..................................................................................................................................31Benefits of the Model to Contractors and Clients....................................................................31

Benefit of the Model to Designers...........................................................................................31Time Savings in Model Creation Using Autodesk Civil 3D......................................................32Time Savings of Model-Based Design ....................................................................................32


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True Model-Based Design with Autodesk Civil 3D


Executive Summary

This paper compares the methods used in AutodeskLand Desktop to those in AutodeskCivil

3D software in performing model-based design. Specifically, this paper demonstrates how themodel-based approach of Civil 3D enables designers to create designs efficiently andaccurately. Using Civil 3D, creating the design model becomes the core design process. Civil3D eliminates time-consuming design sequences, such as data naming, data loading, andregenerating output. Civil 3D reflects changes in the design instantly in the design object and inthe formatted output so designers need not perform tedious checking of output. Using Civil 3Deliminates publication errors and makes identifying design errors a part of the design anddisplay process.

Statement of Purpose

The purpose of this paper is to illustrate the benefits of model-based design over traditional

methods, and to show the advantages of using Autodesk Civil 3D software in performing model-based design. This paper first examines the model-based design process using two different

tools, Autodesk Land Desktop (used with Autodesk

Civil Design) and the more advanced Civil3D. The paper then presents a case study of a model-based design that the author performedusing Civil 3D.

Recent advances in construction technology enable contractors to robotically control gradingoperations from digital models of the project. These models define entities such as roadways,parking lots, graded areas, or building sites. The models consist of data files that the contractorloads into the control equipment to directly control the physical grading operations. Using thistechnology, a contractor can begin construction earlier, control the grading operations more

efficiently, eliminate stakeout errors, and deliver a finished site to the client more economically.

Using digital output models, a contractor no longer needs paper-based construction documentsand line/grade stakeouts to create the final project. Designers must be able to create thesemodels efficiently and provide the contractor an accurate model of the site. The definition of theproject should go directly from the design model to the finished site without the need for plotteddrawings, stakeout calculations, and other steps associated with manual grading. Eliminatingthese intervening steps saves time and reduces human error.

Coming from a paper-based background, many designers believe that what is plotted is whatgets built, regardless of how the plotted documents were produced. Whether the design processconsists of all manual calculations or sophisticated automated design, the published

construction documents never reflect how the data is compiled. Thus, from the contractors pointof view, there is no compelling reason to avoid model-based design.

To move to true model-based design, designers must change their way of thinking and theprocesses used to define a site. Plotted construction documents will always be necessary, butthese should reflect the model, not define it. The model supplied to the contractor is what thecontractor will build. Designers must be able to produce this model accurately and economically,and to respond quickly to design decisions that affect the final product.


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Autodesk Land Desktop does not support true model-based design. Rather, Land Desktopsapproach reproduces the manual design process with automated tools. This approachsegments the design process into separate steps. When you have completed all the steps, youhave the data to produce a set of construction documents or a model. These steps consist ofdiscrete operations that are like links in a chain: each operation depends on the operations thatcame before and feeds the operations that follow. Land Desktop provides no live links

between operations to automatically propagate changes in one link to other links in the chain.

In contrast, the Autodesk Civil 3D package is a model-based system that projects the designmodel onto paper through the use of display and labeling styles. Civil 3D plots what the designdictates, so it is impossible to get the plotted product out of sync with the design. If the designchanges, replotting the drawings guarantees conformance with the design, and the updatedmodel supplied to the contractor automatically agrees with the updated drawings.

Overview of Model-Based Road Design

Model-based road design is a two-part process consisting of data model design and outputmodel design.

In the data-model design process the data becomes a cohesive mathematical definition of thedesign object. This data includes the existing terrain, the horizontal and vertical alignment, thegeometry of the road structure, roadside ditching (if required), and the cut and fill slopes. Theoutput model of a design is the delivered product. Historically, the output model has consisted ofa set of drawings that graphically depicted the location of the road, the vertical profile, typicaland atypical standard design sections, and numerous sheets of cross sections at specificintervals that showed how the road design interacted with existing conditions. These crosssections have comprised the heart of the design definition. To keep this paper-based output atrealistic levels, designers have usually prepared these plotted cross sections at 50-foot (or 25meter) intervals. Designers have annotated these sections with crucial information needed toconstruct the roadway, and contractors have converted this graphical information into hard

location data to be staked in the field for construction.

A true output model is a digital file that contains basic geometric entities (such as 3D faces) andthat defines the finished product of the entire design process. Using the road example, a digitaloutput model usually contains a set of 3D faces that define the surfaces of the lanes, shoulders,cut/fill slopes, and gore areas. Unlike the plotted cross sections, these faces typically reflect thedesign at much closer intervals of 5 feet (or 2 meters).

A designer can create an output model from a data model with varying degrees of ease,depending on the architecture of the data model and the tools used to process the data.Typically, if you have a data model, you can also generate design drawings with little additionaleffort. In contrast, if you start with the paper-based output of a design, you cannot easily create

an output model without first creating a data model.

The example here started out as a paper-based design definition supplied to a local highwaycontractor for a section of four-lane bifurcated highway. I agreed to create an output model of3D faces for use in robotic control of grading activities for subgrade installation. I received theusual construction documentsplan sheets, profile sheets, typical and atypical road and rampsections, bifurcation tables, and plotted cross sections at 25 m intervals. I also received anAutoCADdrawing that defined alignments as polylines and coordinates based on NAD 27,Zone 18 meters, so all data would be georeferenced. Having georeferenced data was crucial for


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GPS (global positioning system) control but was not a factor for robotic control.

Without the tools in Autodesk Land Desktop, Autodesk Civil Design, or Autodesk Civil 3Dsoftware, without robotic or GPS control, and without a contractor who was willing to use newtechnology, I would have done this project the old school waywith grade stakes every 25meters, string lines, and equipment operators smoothing grades between staked sections. Thenew tools and a forward-thinking contractor enabled us to move from manual to automated

grading control.

Robotic control of grading requires a surface model that accurately defines the surface to beconstructed. Since all grading control works directly from the model, and the equipment operatordoes not interact with the grading controls, robotic graders do not perform the typical smoothingfrom one section to the next that occurs with manually controlled grading. In areas ofsuperelevation transition and areas that traverse horizontal and vertical curves, we must createenough data to represent these transitions as smoothly as possible. At the same time, we mustnot create a data set that overwhelms the memory of the equipment. Typical mainline areas ofthis example use 4 m data and problematic areas (transitions, and so forth) use 2 m data.

As technology evolves, contractors and design clients evolve as well, and what designers

supply to them has to meet their new requirements. As more contractors move to roboticgrading, the demand for an output model will become more common, and designers must beable to provide an accurate model. Model-based design helps make this possible.

Advantages of the Model-Based Approach

The model-based approach produces two models, the data model and the output model. Theadvantages that these models present over paper-based designs are as follows.

Advantages of the Data Model

The data model provides a single source of definition for the output model. Everything

that defines the output model resides in the data set; the data model does not requiremanual additions or alterations of specific portions.

Since the data model creates the output model, designers can avoid laborious, sheet-by-sheet checking of plotted information. If the data model is correct, the output model willbe correct as well, whether the output model consists of digital data or drawings plotteddirectly from the data model. Creating a comprehensive data model and viewing theoutput model clearly shows any errors in design. Creating 0.1 m or 0.2 m contours onthe output model quickly shows any surface anomalies that need to be addressed.Viewing the output model in 3D with vertical exaggeration applied also shows areas thatmay need attention. Since each part of the output model is based on the data model, thisapproach provides no opportunity for human error, such as transposing numbers,

slipping decimal points, or pressing the wrong buttons on the calculator.

When designers revise the design concept, they can propagate this change quickly andaccurately through the data and output models. The more such dynamic links thesoftware provides between parts of the data set, the easier this process becomes.

No matter how sophisticated clients become, plotted output will be with us for a long timeto come. Plotting revised drawings based on a revised data/output model requires little


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or no manual input if designers adhere to a strict data model approach. On the otherhand, if designers do any manual tweaking, they will have to correct these tweakswhenever they make changes to the data set.

Advantages of the Output Model

Using the model-based approach, an output model conforming to the clients needs

becomes immediately available for use. In several instances the contractor was able tofeed requested changes I made in the model into the robotics just minutes after Iemailed them to the job site.

The digital format of the output model is more efficient to transport and use. Designersand contractors can email files, place them on memory sticks, and plug them directly intothe control equipment.

Since output models are based on mathematical data models, you can generate detaileddata in the output model that would be impractical by any other method. As mentionedearlier, my example project typically consisted of sections as small as 2 meters. Theadditional time required to process this amount of data was negligible.

An accurate output model is all the contractor needs. The output model should defineevery nuance of the design and should not require any subsequent calculations on thepart of the contractor to implement the design on the ground.

Caveats of the Model-Based Approach

Using a model-based approach requires precise definitions at every step in the designprocess. This approach does not preclude preliminary type designs, but you mustestablish a threshold of required information before you can produce a complete model.What-if scenarios may require defining more information than you normally would in theconceptual stage of the design.

The recipient must test your output model to ensure complete compatibility. Justbecause the contractors software accepts 3D faces does not mean that the 3D facesyou supply will work every time. The beauty of the model-based approach is that youcan alter the output data format without having to change modeling techniques.

You may have to be creative in formatting your model-based output for presentation onpaper. The Autodesk Civil 3D package provides most of the plotting tools that exist inAutodesk Land Desktop, but it requires that you do extra front-end formatting.

Autodesk Land Desktop Versus Autodesk Civil 3D

As stated previously, Autodesk Land Desktop does not directly support model-based design, butyou can use Land Desktop to create a data model and an output model. This section comparesthe steps required in Land Desktop (in combination with Autodesk Civil Design) with the stepsrequired in Autodesk Civil 3D software.

Using Autodesk Land Desktop with Autodesk Civil Design

When using Autodesk Civil Design, you manually create each component of the data model and


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manually link it to the next step in the design process. When you have completed your datamodel, it is segmented; if you change any part of the data chain, you must propagate thechange manually through the rest of the data to update its definition.

The basic sequence of events to create a road design data model is as follows:

1. Create a terrain model representing existing surface conditions.

2. Draw a horizontal alignment and define it by name.3. Use the alignment to sample the surface to produce profile data.4. Create a profile of existing conditions for the alignment.5. Draw a vertical alignment and define it on the profile.6. Draw and define a road template.7. Sample the surface at specific intervals to produce cross sections.8. Use the Design Control command to apply the design templates and to specify the cut/fill

slopes.9. View the templates to confirm the design.10. Create a 3D grid and display it for the purpose of design confirmation.11. Calculate road volumes for cut/fill balance or estimating.12. Create a road surface and display the contours in the drawing.

Each of these steps is a separate task, none of which are dynamically linked to steps thatprecede or follow. If you modify the vertical alignment, you must manually reprocess thesections in design control. If you change the horizontal alignment, you must repeat steps 3through 5 and 7 through 12 to reflect the change in the finished sections.

Another important factor in the Autodesk Land Desktop/Civil Design approach is that the datacreated resides in an external project file. The entities shown in the drawing are, at best, looselylinked to this data. Every graphical change you make in the drawing (for example, changing thevertical alignment) you must propagate back into the project data before you can calculate theremaining steps.

When designers have to adjust the width of lanes, apply ditching, or change cross slopecharacteristics of the road design, they must also produce transition alignments, profiles, orboth. This task adds to the list of required data and becomes part of the sequence shownearlier. Each template can potentially include eight transition points to the left of centerline andeight to the right. The rules for correctly using these transitions are strict, and managing multipletransitions within an alignment can be challenging. As with most of the data items in AutodeskLand Desktop/Civil Design, these transitions reside in external files. You must add them to thedesign through design control.

One of the least understood aspects of the Autodesk Land Desktop/Civil Design method is howto apply data through design control. You enter design control with a list of sampled sections,say, every 25 meters. When you apply a cut/fill slope, the software applies it to each of the

sampled sections in the list, not to the alignment. The same holds true for ditching, transitions,and template selection.

If you add another sampled section to the list, the software may or may not apply the runningcontrols to it, depending on where it falls in the list. This is particularly significant with respect totransitions. When you apply a transition alignment/profile through design control, the softwarestores it as an offset distance (alignment) or an elevation (profile) for a specific section. If youadd a sampled section, you must reapply all transition alignment and profile data in designcontrol to have it take effect on added sections.


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This process is laborious and requires extreme diligence during the design process. You mustmaintain a strict naming convention for your transition alignments. To ensure the integrity ofyour processed sections, you must reapply them whenever the data set changes. Addingsampled sections to a design is a common occurrence. Making sure they are properly controlledby your design constraints is tedious.

Once the design process is complete in Autodesk Land Desktop/Autodesk Civil Design, youreready to create your output model. Again, you manually craft the output model from theprocessed sections. Once created, the output model contains just a set of 3D faces, a set ofpoints, or a surfacenone of which are directly connected to the design model, and none ofwhich are connected to each other. Any change in the design model requires you to manuallyre-create all parts of the output model.

Using Autodesk Civil 3D

The Autodesk Civil 3D system uses a radically different approach to model design. Each pieceof the design chain resembles its counterpart in Autodesk Land Desktop/Autodesk Civil Design,but in Civil Design the links between pieces of the chain are live, meaning that if you make a

change in one part of the chain, it propagates automatically to the other parts. Also, in Civil 3Dyou follow a slightly different sequence from that in Land Desktop/Civil Design. The followingdescribes the process for a simple corridor design in Civil 3D:

1. Create a terrain model representing existing surface conditions.2. Create a named horizontal alignment.3. Create a profile of existing conditions for the alignment.14. Create a vertical alignment on the profile.25. Create a corridor assembly (typical section) from subassemblies.6. Link the assembly to the corridor and display the resulting processed design.3

Although the sequence of steps resembles that of Autodesk Land Desktop/Autodesk CivilDesign, in Autodesk Civil 3D the links between the data used in the various steps are live. Thus,users need not update all dependencies when they make a change to the data. The softwaredoes this automatically.

The process of changing a horizontal alignment illustrates the advantage of Autodesk Civil 3Dsoftware over Autodesk Land Desktop/Autodesk Civil Design in achieving true model-baseddata (and ultimately model-based output). Using Land Desktop/Civil Design requires thefollowing steps to reprocess a horizontal alignment edit:

1. Edit the horizontal alignment.2. Resample the horizontal alignment for profile data.

3. Re-create the profile.4. Edit the finish grade vertical alignment to agree with the new centerline geometry.5. Resample the alignment for sections (due to stationing change).4

1Sampling occurs automatically as part of the profile creation process. The profile is now dynamically linked to the

alignment and the surface.2 A separate definition step is not required. The vertical alignment is also dynamically linked to the alignment.3 Autodesk Civil 3D software immediately displays the road grid, daylight boundary, and finish contours in the

drawing.


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6. Edit the design control for the revised data.57. View the templates to confirm the design.8. Re-create the 3D grid and display it for design confirmation.9. Recalculate road volumes for cut/fill balance or estimating.10. Re-create the road surface and display the contours in the drawing.

In contrast, Autodesk Civil 3D software requires the following steps to reprocess a horizontal

alignment edit:

1. Edit the horizontal alignment.2. Edit the finish grade vertical alignment to agree with new centerline geometry.6

Unlike with Autodesk Land Desktop/Autodesk Civil Design, if you dont like the edit in theAutodesk Civil 3D system you can simply undo until the old horizontal alignment displays (orreopen the original drawing that you saved before you made the edits) and the software revisesall pertinent dependent corridor data to reflect the current state of the data set. In LandDesktop/Civil Design, you must edit the horizontal alignment back to its original state andreprocess all the dependent data accordingly. Civil 3D contains the entire model (data andoutput) in the drawing; you do not have to update or reapply external definition files when you

make a change. For alternative design analysis, save each version as a separate drawing, andwhen you make the final decision on the corridor, simply use the corridor from the correctdrawing.

4You need to reenter noninterval sampling stations.

5 If you use transition alignments or profiles, you must individually reattach them since the software calculates the

offsets and elevations from the horizontal alignment geometry and profile data.6 Autodesk Civil 3D software updates the profile data, profile labeling, corridor processing, corridor surface,

drawing display, and volumes automatically.


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A Model-Based Case Study

Nearly every design tool assumes that the project involves perfect design tasks, for whichevery aspect of the design follows common engineering rules. In such tasks, for example, allchanges in centerline grade occur with a vertical curve, all superelevations have classicproportions, and multilane roadways are symmetrical about the design centerline. Its when you

wander off the typical design path that software makes your task easier or more difficult. Thesubject of this case study posed some atypical challenges that illustrate the benefits of model-based design.

In this case study I used the Autodesk Civil 3D package to create a detailed surface model forrobotic-controlled grading of the subgrade of a four-lane bifurcated highway. A total roboticstation controlled placement and final grading of the subbase. The robotic station communicatedwith the grading equipment (dozer with stone box for placement and grader for final grading)and tracked the exact location of the equipment, including the elevation of the stone box andblade. A display showed the operators the location of the equipment and the edges of theproposed lanes. Using this display, the operators controlled only the location, direction, andspeed of the equipment. The system constantly communicated the exact location and elevation

of the device to the robotic station occupying a known control point. The total station had asurface model of the project loaded in its memory and continuously compared the deviceelevation (box/blade) to that of the design surface at the equipments location. The station sentcontrol signals to the hydraulics to adjust the box/blade to the correct design elevation. Thiseliminated the need for grade staking and grade lines for equipment control.

Project Planning

During the planning portion of this modeling project, it became clear that 25 m spacing of thesections yielded insufficient data to properly define the surface for robotic control. After someexperimentation, I decided to model the tangent portions of the main roadway with 4 m sectionsand spiral/curve portions at 2 meters. I decided to model all access ramps at 2 m intervals.

The project encompassed about 10.5 km of roadway, but for brevity in this case study I showhow I modeled the portion extending from station (Sta.) 109+000 to 110+380. This segment alsocovers the most complicated portion of the project.Gathering Project Data

The original project designers used CADD software only for producing (drafting) theconstruction documents. I received one CAD file (containing the centerlines and edges ofpavement), one set of 11x17 plan/profile drawings, one set of 11x17 typical sections, and oneset of 11x17 design sections done every 25 m. When I requested the design data used, Ireceived the superelevation data in spreadsheet form and learned that this data, coupled withthe sections, comprised the entire definition of the project. The designers had calculated all the

design sections manually and had drafted them accordingly. Elevation data between the plottedsections existed only at specific design stations (points of curvature, points of tangency, and soon) based on the superelevation data.

The design parameters for this section of roadway are far from typical. While the designcenterline profile does use tangents and vertical curves, the opposing southbound (SB) lanesare bifurcated (separated horizontally and vertically). I modeled the range where the bifurcationwas waning based on a design table of vertical/horizontal offsets from the design centerline.The vertical grade/alignment in this transition region is purely graphical for the SB lanes.


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While working on the actual project (which had originally been designed in Autodesk LandDesktop 2004), I discovered several areas where the plotted design data in the sectionsconflicted with the vertical alignments and other supplemental information. I also discovered thatmany changes occurred in the pavement structure between the supplied 25 m stations.Transitions for shoulder rollover occurred over an 8 m distance, and none of these wereaccurately reflected in the provided 25 m sections. Crucial horizontal and vertical changes in the

alignment/profilethe inclusion of which was mandatory for accurate modelingoften occurredat non-25 m stations. Effective robotic control required roadway surface data at an interval farsmaller than 25 m to construct a smooth road surface that adhered to the overall designscheme. To fill in the gaps between the 25 m stations, I had to secure the superelevationspreadsheets from the design firm to accurately model what was happening in the curves. Thefirm did not supply this data as part of the construction documents. I dont know how thecontractor could have manually set grades for data he did not have. I suppose this is where theequipment operator would have smoothed the areas between staked sectionsdefinitely not anaccurate method when it comes to high-speed highways.

Designing the Horizontal Alignment

I received the design horizontal alignment in the form of graphics and a definition. Using thegraphics, I created an alignment named CL Rte 15 Partial starting at Sta. 109+000 and endingat 110+380 (1.38 km).7 The following diagram shows the graphical representation of the designcenterline with travel lanes:

7 As mentioned earlier, the actual modeling project ran over 10.5 km, but I am using only a portion of the overall

model for this presentation.


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Designing the Vertical Alignment

To control the roadway vertically, I needed to create profiles, starting with the design centerline

for the CL Route 15 Partial alignment. The supplied design data for this portion of the project isas follows:


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Applying this definition to the alignment, I got the following profile view:

Because this roadway is bifurcated, the inside edge of the northbound (NB) lane follows thedesign centerline profile and the SB lanes are offset vertically from the design centerline basedon the bifurcation chart supplied by the designers:

The following partial profile shows this bifurcation transition graphically:

Bifurcation Table

Sta NB SB Diff Sta NB SB Diff

109+000 370.508 366.820 3.688 109+360 362.588 360.570 2.018109+020 370.068 366.380 3.688 109+380 362.148 360.271 1.877

109+040 369.628 365.940 3.688 109+400 361.708 359.972 1.736

109+060 369.188 365.500 3.688 109+420 361.273 359.672 1.601

109+080 368.748 365.060 3.688 109+440 360.875 359.386 1.489

109+100 368.308 364.621 3.687 109+460 360.521 359.150 1.371

109+120 367.868 364.216 3.652 109+480 360.209 358.968 1.241

109+140 367.428 363.867 3.561 109+500 359.940 358.839 1.101

109+160 366.988 363.562 3.426 109+520 359.715 358.764 0.951

109+180 366.548 363.261 3.287 109+540 359.532 358.742 0.790

109+200 366.108 362.961 3.147 109+560 359.393 358.774 0.619

109+220 365.668 362.662 3.006 109+580 359.297 358.860 0.437

109+240 365.228 362.363 2.865 109+600 359.244 358.979 0.264

109+260 364.788 362.064 2.724 109+620 359.233 359.098 0.135

109+280 364.348 361.766 2.582 109+640 359.266 359.218 0.048

109+300 363.908 361.467 2.441 109+660 359.342 359.337 0.005

109+320 363.468 361.168 2.300 109+680 359.457 359.457 0.000

109+340 363.028 360.869 2.159 109+700 359.577 359.577 0.000


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Designing Typical Cross Sections

The following schematic shows the required cross section for this model. I needed the variouspoints in the cross section to address lane and shoulder width changes and to accommodatevariations in shoulder cross sections in superelevations.

I needed horizontal and vertical control for six transition points to the left and six to the right inthe final assembly to enable accurate modeling of the supplied design. I named these L8L3(SB) and R3R8 (NB). Following Autodesk Land Desktop conventions, I numbered mytransitions from centerline out and prefixed them with L (left) and R (right) as appropriate. Sincethis modeling project started in Land Desktop, I kept the same naming convention to eliminateconfusion.

The assembly (template in Autodesk Land Desktop terms) I needed required multiplesubassemblies to address the various horizontal and vertical controls being applied. Forsimplicity, I show generic subassemblies here since I was modeling only the top surface of theroadway. Since the project had a constant 370 mm pavement thickness, I was able to lower thefinal surface for placement of the subbase material.

The following shows the assembly used with the corresponding control locations for horizontaland vertical transitions:


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Designing Horizontal Transitions

I defined the horizontal transition alignments from the existing polylines that represented thespecific features of the roadway: edges of shoulder (L3, L8, R3, R8), edges of pavement (L5,L6, R5, R6), and shoulder rollovers (L4, L7, R4, R7). The following is a portion of the road planshowing the various transitions, with the defined alignment name in parentheses:

Creating alignments from polylines, the alignment list for this project now appeared as follows:


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Designing Vertical Transitions

The superelevations used were not symmetrical about the point of intersection of thecurve/spiral, and the built-in superelevation routines could not adhere to the supplied design, soI modeled these from the superelevation spreadsheets provided by the designer. To furthercomplicate the superelevation issue, the original designers applied runout and runoff differentlyto the NB and SB portions of the curve to account for the bifurcation transition and difference in

circular curve radius

The following is a typical superelevation chart from the project:

SOUTHBOUNDPAVEMENT

NORTHBOUNDPAVEMENT

REMARKS TRANSITION ORDINATE WIDTH e STATION e WIDTH ORDINATE TRANSITION REMARKSRATE (m) (m) RATE RATE (m) (m) RATE

109082.439000 -0.020000 7.200000 -0.144000 0.000741 BEGIN SE TRANS0.000000 -0.144000 7.200000 -0.020000 109090.4920000.000000 -0.144000 7.200000 -0.020000 109100.000000

109100.000000 -0.006992 7.200000 -0.050341 0.000741109109.439000 0.000000 7.200000 0.000000 0.000741 LEVEL SECTION

0.000000 -0.144000 7.200000 -0.020000 109117.4920000.000000 -0.144000 7.200000 -0.020000 109120.000000

109120.000000 0.007823 7.200000 0.056325 0.000741109128.439000 0.014074 7.200000 0.101333 0.000741 Begin Roll-over109136.439000 0.020000 7.200000 0.144000 0.000741

0.000000 -0.144000 7.2000 -0.020000 109140.000000109140.000000 0.022638 7.200000 0.162992 0.000741BEGIN SE TRANS -0.000741 -0.144000 7.200000 -0.020000 109144.492000

-0.000741 -0.226709 7.200000 -0.031487 109160.000000109160.000000 0.037453 7.200000 0.269659 0.000741109163.439000 0.040000 7.200000 0.288000 0.000741

-0.000741 -0.288000 7.200000 -0.040000 109171.492000-0.000741 -0.333376 7.200000 -0.046302 109180.000000

109180.000000 0.052267 7.200000 0.376325 0.000741109182.439000 0.054074 7.200000 0.389333 0.000741 Begin Roll-over109190.439000 0.060000 7.200000 0.432000 0.000741

-0.000741 -0.432000 7.200000 -0.060000 109198.492000-0.000741 -0.440043 7.200000 -0.061117 109200.000000

109200.000000 0.067082 7.200000 0.482992 0.000741109217.439000 0.080000 7.200000 0.576000 0.000741 END SE TRANS

-0.000741 -0.546709 7.200000 -0.075932 109220.000000END SE TRANS -0.000741 -0.576000 7.200000 -0.080000 109225.492000

As is evident in the preceding table, applying standard superelevation parameters based on the

design centerline would not work because the superelevation applied asymmetrically on the NBand SB curves. Also notice that the design applied a rollover type shoulder at specific points inthe alignment. Not to be confused with the rollover rate, a rollover shoulder indicates where thehigh side shoulder takes on a positive slope for a portion of its cross section and a negativeslope for the balance. I discuss this below when I introduce shoulder rules.

To address this atypical superelevation, and to provide exact modeling data for crucial stationsnot depicted on the 25 m design cross sections, I had to build a MicrosoftExcel worksheet thatwould calculate and organize the data for this design. With the design grade and thesuperelevation data, I could calculate the edge of pavement elevations for the NB and SBcartways at standard intervals and at crucial horizontal and vertical design stations (points ofcurvature, points of tangency, PVCs, PVTs, and so on).


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The shoulder rules applied to this design specified that on the low side of superelevations, thenormal 4 percent shoulder slope would acquire the superelevation slope (E value) when itreached 4 percent, and would follow the E value through the curve and then descend with the Evalue until it reached the normal 4 percent slope. On the high side, I applied a two-step rule. ForE values of 2 to 4 percent, the normal shoulder slope of 4 percent transitioned to 2 percent overa distance of 8 m prior to the superelevation station. For E values of 6 percent or more, theshoulder transitioned from 2 percent to a crowned shoulder of 1.2 m at 3 percent and 3.0 m at

2 percent over a distance of 8 m prior to the station where E equals 6 percent. The following is aschematic of the shoulder rules as applied to the left horizontal curve in the data set.

To address all the required control points in the roadway, I needed a total of 12 vertical controlpoints (L8L3 and R3R8) in the final template. The R3 point in the NB lane followed the designcenterline profile, and the L3 point in the SB lane followed the values contained in thebifurcation table. These two points also followed the design centerline alignments for the NBand SB lanes, which varied in offset from the design centerline based on bifurcation distance.


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The edges of shoulders transitioned horizontally in specific areas to accommodate entrance andexit ramps. I controlled the horizontal transition with transition alignments gleaned from thesupplied drawing. I calculated the elevations in the Excel spreadsheet following the varioussuperelevation and shoulder rule parameters (discussed earlier) that may have been in effect.

The following is a portion of the spreadsheet used to create transition control profiles for eachsegment of the SB roadway. The L designations (L8L3) refer to transition points in the

template and correspond to the points on the preceding shoulder rule schematic. The NBportion of the roadway uses similar notation (R3R8).

To identify the areas where each of the design parameters is in force, I have applied thefollowing color-coding scheme to the preceding worksheet:

Design grade dataShoulder slope transitionlow side of superelevation (SE)

Rollover transitionhigh side of SE (24 percent)

Rollover transitionhigh side of SE (rounded to 2 percent)

Width transitionsNormal sectionSuper transitionGraphical grade section


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Concatenating station/elevation for each of the six control points (L8L3) for the SB lane gaveme the format for a profile that I could bring into the drawing (via the Create From Filecommand) and add to the design alignment profile. I generated the following data from theportion of the worksheet shown above:

SB L8 SB L7 SB L6 SB L5 SB L4 SB L3

Profile Profile Profile Profile Profile Profile

109000 366.481 109000 366.616 109000 366.664 109000 366.820 109000 366.772 109000 366.772109012.174 366.205 109012.174 366.349 109012.174 366.397 109012.174 366.553 109012.174 366.505 109012.174 366.505

109014.5 366.153 109014.5 366.297 109014.5 366.345 109014.5 366.501 109014.5 366.453 109014.5 366.453

109014.6 366.163 109014.6 366.283 109014.6 366.331 109014.6 366.499 109014.6 366.451 109014.6 366.451

109020 366.043 109020 366.163 109020 366.211 109020 366.380 109020 366.332 109020 366.332

109040 365.597 109040 365.717 109040 365.765 109040 365.940 109040 365.892 109040 365.892

109060 365.151 109060 365.271 109060 365.319 109060 365.500 109060 365.452 109060 365.452

109080 364.706 109080 364.826 109080 364.874 109080 365.060 109080 365.012 109080 365.012

109097.145 364.323 109097.145 364.443 109097.145 364.491 109097.145 364.683 109097.145 364.635 109097.145 364.635

109100 364.261 109100 364.381 109100 364.429 109100 364.621 109100 364.573 109100 364.573

109115.516 363.938 109115.516 364.058 109115.516 364.106 109115.516 364.302 109115.516 364.254 109115.516 364.254

109120 363.851 109120 363.971 109120 364.019 109120 364.216 109120 364.168 109120 364.168

109136.492 363.556 109136.492 363.676 109136.492 363.724 109136.492 363.924 109136.492 363.876 109136.492 363.876

109140 363.498 109140 363.618 109140 363.666 109140 363.867 109140 363.830 109140 363.830

109144.492 363.426 109144.492 363.546 109144.492 363.594 109144.492 363.796 109144.492 363.772 109144.492 363.772

109160 363.067 109160 363.187 109160 363.235 109160 363.562 109160 363.538 109160 363.538

109171.492 362.795 109171.492 362.915 109171.492 362.963 109171.492 363.389 109171.492 363.365 109171.492 363.365

109180 362.566 109180 362.705 109180 362.761 109180 363.261 109180 363.237 109180 363.237

109190.492 362.282 109190.492 362.444 109190.492 362.509 109190.492 363.104 109190.492 363.080 109190.492 363.080

109198.492 362.063 109198.492 362.243 109198.492 362.315 109198.492 362.984 109198.492 363.008 109198.492 363.008109200 362.022 109200 362.205 109200 362.278 109200 362.961 109200 362.985 109200 362.985

109220 361.481 109220 361.709 109220 361.800 109220 362.662 109220 362.686 109220 362.686

109223.516 361.387 109223.516 361.623 109223.516 361.717 109223.516 362.610 109223.516 362.634 109223.516 362.634

109225.492 361.335 109225.492 361.575 109225.492 361.671 109225.492 362.580 109225.492 362.604 109225.492 362.604

109240 361.115 109240 361.355 109240 361.451 109240 362.363 109240 362.387 109240 362.387

109260 360.816 109260 361.056 109260 361.152 109260 362.064 109260 362.088 109260 362.088

109280 360.518 109280 360.758 109280 360.854 109280 361.766 109280 361.790 109280 361.790

109300 360.199 109300 360.439 109300 360.535 109300 361.467 109300 361.491 109300 361.491

109320 359.885 109320 360.125 109320 360.221 109320 361.168 109320 361.192 109320 361.192

109340 359.564 109340 359.804 109340 359.900 109340 360.869 109340 360.893 109340 360.893

109360 359.242 109360 359.482 109360 359.578 109360 360.570 109360 360.594 109360 360.594

109380 358.921 109380 359.161 109380 359.257 109380 360.271 109380 360.295 109380 360.295

109400 358.600 109400 358.840 109400 358.936 109400 359.972 109400 359.996 109400 359.996

109417.9 358.313 109417.9 358.553 109417.9 358.649 109417.9 359.704 109417.9 359.728 109417.9 359.728

109418 359.056 109418 359.056 109418 359.078 109418 359.702 109418 359.726 109418 359.726

109420 359.022 109420 359.022 109420 359.048 109420 359.672 109420 359.696 109420 359.696

109440 358.714 109440 358.714 109440 358.762 109440 359.386 109440 359.410 109440 359.410

109460 358.462 109460 358.462 109460 358.526 109460 359.150 109460 359.174 109460 359.174

109480 358.251 109480 358.251 109480 358.344 109480 358.968 109480 358.992 109480 358.992109500 358.089 109500 358.089 109500 358.215 109500 358.839 109500 358.863 109500 358.863

109520 357.960 109520 357.960 109520 358.140 109520 358.764 109520 358.788 109520 358.788

109540 357.866 109540 357.866 109540 358.118 109540 358.742 109540 358.766 109540 358.766

109557.818 357.811 109557.818 358.051 109557.818 358.147 109557.818 358.771 109557.818 358.795 109557.818 358.795


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The final piece of control data I needed consisted of the vertical profiles for each of thetransitions in the assembly. Using the design spreadsheet, I created a set of data thatrepresented station/offset for each component of the roadway. Using this data, I created anASCII file in the format of station, elevation for each transition point. Using Profiles>CreateFrom File in the pull-down menus, I imported these values as a defined profile for the designalignment. My profile list for the design alignment now appeared as follows:

The following diagram shows the right (NB) transitions through a fully superelevated curve tothe left where the rollover shoulder on the high side is in effect:


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A blowup of the R6R7 transition profiles shows how the rollover shoulder was created:

Note that I also added a profile called Median. Since the purpose of this project was to modelthe cartway and shoulder areas only, the median area does not directly concern us. However,using the design grade for the median center created some odd-looking topography in thebifurcated area, so I derived a median profile by averaging the inner edge elevations of the NBand SB shoulders and creating a profile from the averages. This produced an even gradebetween the innermost edges of the shoulders and made viewing the contours less confusing.

So far, I have described how I accumulated the horizontal and vertical control data for eachaspect of the design template, treating NB and SB as separate entities. To complete the model,I brought this data together into a corridor definition that included the 12 vertical controls (L8L3,R3R8) and the corresponding 12 horizontal controls (L8L3, R3R8) calculated from the

various sources of the provided design data (AutoCAD drawing, design sections, designprofiles, and superelevation worksheets).


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Creating the Corridor

I created a corridor using the preceding assembly, the centerline alignment, the 12 horizontalalignments, the 12 vertical alignments, and the median profile for the centerline grade. The firststep in corridor constructions was to specify the baseline (CL Route 15 Partial), region range(109+000 to 110+380), assembly used (Rte 15), and frequency of sampling. The followingshows the parameters applied:

You establish the frequency of sampling by clicking the ellipsis () in the frequency column.The following dialog box appears for user entry:

For robotic control, I had to strike a balancebetween reasonable frequency of data to producea good constructed surface and the memorycapability of the control systems. Using 1 msampling, data for about one-half of the NB lane(Sta. 106+000 to 110+480) completely exhaustedthe memory in the control unit. I switched to 4 msections on tangents and 2 m data on curve andspirals for the NB and SB lanes. On the accessramps I used 2 m spacing on tangents and 1 mon curves and spirals due to the rapidly changing

superelevations and tight horizontal geometry.

The user-specified stations shown reflect uniquelocations on the alignment where horizontalchanges occur in the assembly. Although I couldhave enabled the At Horizontal Geometry Pointsoption, this would have provided only centerlinegeometry points and nothing for the attachedalignments for transitions.


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The last step in modeling the corridor was to attach the transition profiles and alignments to thecorridor definition. Clicking the ellipsis in the Logical Name column for the corridor region takesyou to the Logical Name Mapping dialog box. The software attaches the various alignments andprofiles by name to the corresponding subassembly in the corridor assembly. Whenconstructing the assembly, I used names for the subassemblies that reflected their purpose(median, shoulder, lane) and the transition points that controlled them (L3, R4, and so on). Thismade attaching the profiles and alignments much easier to understand.

I have now described how I applied all the defining data to the corridor design. After processing,the Autodesk Civil 3D software displayed the corridor showing the sampling data, the linksbetween sampled sections, and the corridor contours. The following diagram shows a portion ofthe corridor approaching the first horizontal curve to the left in the vicinity of the bifurcationtransition (left) and a portion in the vicinity of the access ramps where considerable lane width

transitions occur (right):


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Note the superelevation transition on the left snapshot and how the rollover shoulder develops.The right snapshot shows the lane width anticipation of an exit ramp while the main cartway is in

full superelevation. It is interesting to note that the preceding displays represent a singleobjecta corridorand this corridor contains or directly references all the data used in itscreation. If an alignment changes, the corridor reflects the change. If a profile changes, thecontours of the corridor reflect that change. Making a simple change no longer requires tediousreapplication and reprocessing of bits and pieces of data in design control. Its impossible tomiss a step when making changes because the software requires no steps once the corridor isbuilt. If any of the defining data changes, Autodesk Civil 3D reflects those changes in thecorridor display when it rebuilds. You can add more sampling stations and the corridor rebuildsautomatically when you accept the added stations.


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Creating the Output Model

The final product of all this work was a surface that a robotic control unit could use for subgradeplacement and grading. Everything I created above simply became the input to the model. Thecontractor did not need this information except for verification purposes. The only data Itransmitted to the field was the surface.

You create a surface from the corridor using the Corridors>Export>Corridor Surfaces command.In this instance I used the default surface name of Rte 15 Top. The following diagram showsthe same areas viewed previously as a corridor, but now the display shows only the surfacecontours on the left and the surface triangles on the right:


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Use in the Field

When I had previously used Autodesk Land Desktop, the contractor used the 3D faces createdfrom the processed sections to build a surface in TopconOffice-3D, which could import 3Dfaces from AutoCAD drawings. Since Autodesk Civil 3D software currently cannot export the 3Dfaces from the corridor or the triangles from the corridor surface, I output the surface inLandXML format to bridge the gap from Civil 3D to the robotic total station that controlled the

grading process.

Following are several photos of the grading and control equipment in operation on Route 15.Notice that you dont see the normal forest of grade stakes, steel stands, or string lines alongthe roadway.

GPS-controlled placement of subgrade material. This method, although accurate enough for materialplacement (+/30 mm), was not accurate enough for final grading. Instead of using two different methods, thecontractor opted to use robotic control for all placement and grading operations.


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The robotic total station used to control the grading operation. Occupying a known point, the total stationcommunicated in real time with the grading equipment, so it had the exact location of the box/blade andinstantly adjusted the elevation to match the loaded roadway surface.

The dozer/stone box with robotic transponder attached


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The grader with the robotic transponder attached. Note the absence of grade stakes and other means ofmanual grade control.

A view of the project looking up-station at the superelevated curve near the ramp area. Note the bifurcationtransition before the curve.


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A view of the project looking down-station at the bifurcated roadway.


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A blowup of the ramp area. This view actually shows three different corridors.

A view of Ramp C entering the main NB lanes. Note how the ramp transitions from full superelevation

to a manual superelevation to match the cross slope of the NB lane.


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Conclusion

Model-based design potentially benefits all parties involved in the design process, fromdesigners to contractors to clients. Model-based design reaches its full potential if you use theproper tools, such as Autodesk Civil 3D software. This section summarizes the benefits todesigners, contractors, and clients.

Benefits of the Model to Contractors and Clients

The compactness of the final model, coupled with the exacting definition used to compile it,gives contractors a data set they can use to accurately and efficiently construct a complexroadway and appurtenant areas, with a minimum of manual stakeout and virtually nopostprocessing of the design data. The contractor applies the output model directly to theground, eliminating layout mistakes and achieving significantly enhanced efficiency. In theactual case study project, the contractor surpassed completion goals for the remainingconstruction season.

Since we reverse engineered this project from plotted documents and other supplied data thatdid not follow classic rules of behavior, we had to do far more work to reflect the supplied design

in the final model than we would have done to model it completely in the design stage. Wespent a lot of time and effort to gather the data, create definitions from the data, transformsparse information into a more verbose format needed to control the vertical transitions withinthe alignment, and compile all this input data into a corridor model. If we had used the AutodeskCivil 3D model-based design techniques from the beginning, the output model would haveemerged as a normal product of the design cycle, which we could have delivered to thecontractor in addition to the plotted drawings. Whether we had used robotic control of grading orconventional line/grade stakeout, we still would have needed to process this data into a usableform that accurately reflected the design intent. We could have saved all this time and effort if adesign model had been available.

Benefit of the Model to Designers

As a side benefit of true model-based design, you discover errors during the design phase. Youcan almost consider the model a digital prototype that makes it easy to see when conflictsarise. The exit and entrance ramps in this project provide a good example of this benefit. Basedon superelevation data and the profiles, the mating edge of one of the exit ramps differed fromthe edge of the NB lane it was mating with by 0.2 m. When I discovered this anomaly from theoffset in the finish contours of my model, I contacted the designers and they supplied me withrevised superelevation data for the ramp that resolved the problem. It appears that they haddiscovered and corrected this anomaly on their end but had failed to update the constructiondocuments accordingly.

Everyone makes errors, and we do everything we can to make sure they never leave the office.

With a large project like this one, the chance of errors becomes greater when many people workon different aspects of the projects. The QA process also becomes complex. The more heavilymethods rely on manual input in creating the construction documents, the harder it is to find andcorrect errors. From the contractors point of view, having a single surface that directly controlsthe grading operation is far simpler and less prone to human error than calculating, setting,labeling, and using grade stakes.


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Time Savings in Model Creation Using Autodesk Civil 3D

Although using Autodesk Land Desktop with Autodesk Civil Design produces identical results tousing Autodesk Civil 3D software, these two approaches involve quite different processes. Civil3D, being model-based, does not require the repeated manual updating of data to reflect

changes. It does not require you to resample when you add stations, then reapply transitions tothe new stations, then reprocess the sections, and then rebuild the surface and contours. Civil3D automatically updates the surface and contours for the current state of the designwhat yousee in the corridor object is the current state of the design.

Since I modeled this project with both the Autodesk Land Desktop 2004 and Autodesk Civil 3Dtools, I can easily see how much time I would have saved creating the model if I had used Civil3D originally did the project. The hours of redefining and reapplying horizontal and verticaltransitions would still be mine. I would not have spent hours redefining and re-creating theroadway surface for visual checking. I would not have wasted hours because I had picked thewrong transitions to apply to design control and then had to correct them. I estimate I couldhave cut my actual modeling time (not counting data acquisition and processing) by 5075

percent using Civil 3D over Land Desktop. I would have realized part of this savings by virtue ofthe model being the data, enabling me to see in real time the exact state of the design. Thebalance of the time savings would have resulted from removing me (and the chance for manualerror) out of the chain of operations required in Land Desktop.

Time Savings of Model-Based Design

Had the original designer used model-based design, all the hours I put into this project couldhave been spent elsewhere. The contractor would have obtained the surface model directlyfrom the design, and I could have passed on the time and cost savings to the contractor andclient.

As we obtain better tools for model-based design such as Autodesk Civil 3D , we must committo truly model in the design stage rather than revert to cartooning the design when things get alittle sticky or deadlines loom. Model-based design does require specific input at specific pointsin the design process, but with a tool like Civil 3D, a design can start simply and evolve asadditional design decisions are made.

Autodesk and Civil 3D are registered trademarks or trademarks of Autodesk, Inc., in the USA and/or other countries. All other brand names, product names, or trademarks belong to

their respective holders. Autodesk reserves the right to alter product offerings and specifications at any time without notice, and is not responsible for typographical or graphical

errors that may appear in this document.

2005 Autodesk, Inc. All rights reserved.

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