Development and Review of 3D Engineered Models for Construction

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Purpose

The purpose of this guidance is to outline the best practices that should be followed when developing three-dimensional (3D) engineered roadway models for Delaware Department of Transportation (DelDOT) projects. These models will ultimately be utilized in the construction phase of DelDOT projects. At this time, this document does not include best practices for the development of 3D models for bridge structures and appurtenances related to bridge structures.

This document also presents the review criteria being utilized when performing Quality Assurance/Quality Control (QA/QC) reviews of 3D engineered data and 3D models.

Should you have any questions, concerns, or suggestions pertaining to the information contained within this document, please send an email to DOT_CADDSupport@delaware.gov.

Benefits of 3D Engineered Content

DelDOT utilizes various forms of 3D engineered content throughout the lifecycle of projects as the projects progress from conceptual designs to final construction deliverables. This document focuses on the 3D engineered model portion of the 3D engineered content, herein further referred to as 3D Models.

3D models provide numerous benefits in both the design and construction phases of a project, a few of which are listed below.

Design Phase

A more comprehensive design can be developed.
Enables integration of several design processes, resulting in quicker updates during the design phase.
Ability to more accurately detect and address design issues and conflicts during the design phase.
Constructability issues are easier to detect during the design phase.
3D models aid in extracting more accurate quantity estimates.

Construction Phase

Contractors can identify and rectify constructability issues prior to mobilization, saving time and money.
Contractors have a better understanding of material quantities throughout the project site.
Faster construction execution with Automated Machine Guidance (AMG), which has associated efficiency and safety benefits.
Provides the contractor with insight as to the engineer’s design intent.
Enables more efficient workflows for the measurement and payment of material quantities.

3D models are extremely beneficial in analyzing clash detections during the design phase. A clash occurs when different infrastructure elements occupy the same space in the proposed design. Generating a 3D model is extremely beneficial in detecting these clashes so that remedies can be evaluated and considered during the design phase, resulting in reduced construction time delays and additional costs.

Generating a 3D model is also beneficial on large earthwork and paving projects where AMG practices may be considered during the construction phase. Projects which include the following earthwork operations will benefit from the creation of a 3D model:

Large application of sub-base material spreading,
Large application of paving,
Mass earthmoving,
Stormwater management facilities requiring grading, and
Wetland mitigation areas requiring earthwork.

Not all projects will benefit equally from the generation of 3D models. Creating a 3D model during the design phase requires a significant investment of time and resources, which has an associated cost that should be considered individually on each project.

Surveying Considerations

In order to generate an accurate 3D model, one that accurately ties into the original ground surface, it is essential to have a complete ground survey of the existing topographical features.

Due to the levels of accuracy inherent to the various methods of data collection (Total Station Positioning, Aerial Mapping, Real Time Kinematics, etc.) designers need to recognize the potential limitations that each survey method imposes on the ultimate 3D model.

Determination of what electronic file deliverables are going to be provided to the contractor should be considered during the scoping phase of each project. Based on those considerations, the appropriate method of survey data collection should be discussed to assure the survey data accuracy levels are appropriate for the project.

Electronic File Deliverables

Currently, as per DelDOT’s General Note number 2 on the “NOTES” sheet, the following electronic design data files may be made available to the Bidders:

ASCII Data Files with Coordinates and Elevations for Proposed Points as Selected by the Engineer – These files should be made available to the contractor on all projects. The points that are provided should be chosen by the engineer but generally include all the proposed geometric points that are shown on the plans. These points can also include associated elevations at the discretion of the engineer. When provided, these files will be provided in an ASCII text file format.
Design File, in .DGN File Format, That Contains 3D Triangles Representing the Existing Surface. - Where a complete topography survey has been performed in accordance with DelDOT standards, the existing triangulated surface file (DGN) should be provided to the contractor.
Design File, in .DGN File Format, that Contains 3D Feature Lines for the Proposed Design. 3D Feature Lines are for the Proposed Top Surface Elevation Only – Providing the proposed 3D Feature Lines for the Proposed Top Surface should be considered in accordance with the guidance in the “Benefits of 3D Engineered Content” section of this document.

Figure 1: Example of General Notes #2

3D Modeling Applications

The Department currently utilizes the following civil design applications from Bentley Systems, Inc. to create 3D models during the design phase:

OpenRoads Designer - Most Current Version as per CADD Wiki

It is not the intent of this document to detail out the process for creating 3D models through the use of OpenRoads Designer, and the reader is instructed to consult the other “Training Guides” that have been developed by/for DelDOT for additional information regarding 3D model creation.

A simplified, typical workflow for generating 3D engineering content and 3D models is shown in Figure 2.

Figure 2 - Typical Workflow for Creating 3D Engineering Content

3D Model Density Considerations

As indicated in “Figure 2 - Typical Workflow for Creating 3D Engineering Content”, 3D models are generated as templates are assigned to a roadway corridor and then “pushed” along the assigned roadway corridor. The density of the 3D data being generated in an engineered model is controlled by the following factors:

Initial Template Drop Interval (Set by Designer)
Horizontal Curvature Densification Settings (Set by DelDOT CADD Standards)
Vertical Curvature Densification Settings (Set by DelDOT CADD Standards)

During the design stage, template drop intervals are established at the time of initial placement along the roadway corridor. The following guidelines should be considered when initial template drop intervals are being established along the roadway corridor.

Normal tangent section template drop intervals are typically 10’.
Detailed modeling section (Intersections, entrances/driveways, etc.) template drop intervals are typically 1’, 5’, and 10’
Template drop intervals should never exceed 25’.

In addition to templates being dropped at the intervals recommended above, templates should also be placed at the following key station points:

Horizontal geometry transition points. (Ex: Shoulder widening from 8’ to 10’ at Station XX+XX)
Superelevation transition points. (Start of tangent runout, Superelevation Runoff, Full Superelevation)
Intersection of all side road alignments.

In general, templates should be spaced at closer intervals at complex locations where grades and geometrics are changing or transitioning. In complex locations, the model density should be increased to ensure that the designer’s intent is accurately captured in the 3D engineered model.

3D Model Content Requirements

Determining the required Level of Development (LOD) of a 3D model requires an understanding of how the 3D model will ultimately be utilized in the construction phase. The table below lists the various components that are required to be included in the 3D models, as well as the DGN file that is included in the Contract Deliverables for DelDOT projects. Some optional components that may be necessary to convey the designer’s intent are included in this table as well.

Finished Grade 3D Model Features	Required / Optional
Pavement Edges	Required
Pavement Cross Slope Break Lines	Required
Curbs, and Curb & Gutter Edges and Break Lines	Required
Channelization Islands Break Lines	Required
Sidewalks and Shared Use Pathway Edges	Required
Pedestrian Connection Break Lines	Optional
Retaining Walls, Barriers, etc. Break Lines	Required
Roadside Slope Break Lines	Required
Guardrail Maintenance Pavement Edges	Required
Guardrail End Treatment Grading Break Lines	Required
Driveway Edges and Grading Break Lines	Required
Drainage Ditches, Berms, etc. Break Lines	Required
Drainage Pipe Outlet Grading Break Lines	Required
Stormwater Management Facility Break Lines	Required

** Pedestrian connections shall be “modeled” to the extent to verify that the pedestrian connection can be built within the existing right-of-way, or within the proposed areas of takings (PE or RW).

Electronic Design Data and 3D Model Cross Checking

As indicated in the “Electronic File Deliverables” section of this document, the following electronic design data files may be made available to the Bidders:

ASCII Data Files with Coordinates and Elevations for Proposed Points as Selected by the Engineer.
Design File, in .DGN File Format, That Contains 3D Triangles Representing the Existing Surface.
Design File, in .DGN File Format, that Contains 3D Feature Lines for the Proposed Design. 3D Feature Lines are for the Proposed Top Surface Elevation Only.

The table below provides a brief overview of where potential electronic design data may be derived within the plan set, and where that design data requires cross checking against the 3D models.

Sheet Description	Design Data Provided	3D Model Cross Check
Title
Index of Sheets
Addenda and Revisions
Legend
Notes
Typical Sections		X
Horizontal and Vertical Control	X	X
Construction Plans	X	X
Profiles		X
Grades and Geometrics	X	X
Construction Details	X
Stormwater Management Plans	X	X
Environmental Compliance Plans
Construction Phasing, M.O.T. and Erosion Control Plans
Detour Plans
Landscaping Plans
Lighting Plans	X	X
Utility Relocation Plans	X	X
Signing, Striping and Conduit Plans
Sign Structures	X
Signalization Plans

Electronic Design Data

If it has been determined by the project designer that electronic design data will be provided for the project, the project designer shall review the information below to determine if the appropriate electronic design data has been generated, and reviewed, prior to inclusion in the deliverables for the Contract.

NOTE – The document entitled “Release for Delivery of Documents in Electronic Form to a Contractor” MUST be signed by all parties prior to the delivery of any electronic project files. This document can be found at the following location on the DelDOT Design Resource Center (DRC): https://deldot.gov/Business/drc/index.shtml?dc=projectmanagement#horizontalTab3

Horizontal and Vertical Control (ASCII Format)

“Horizontal / Vertical Control Data” schedule information.
“Construction Alignment Control” schedule information.

Construction Plan (ASCII Format)

“Right-of-Way Monument Schedule” information.

Grades and Geometrics (ASCII Format)

“Coordinate List” schedule information.

Construction Details (ASCII Format)

If applicable, any design data that contains layout information or point data information shall be provided. This information shall include the Point Number, Station, Offset, Northing, Easting and/or Elevation.

Stormwater Management Plans (ASCII Format)

If applicable, any design data that contains layout information or point data information shall be provided. This information shall include the Point Number, Station, Offset, Northing, Easting and/or Elevation.

Lighting Plans (ASCII Format)

If applicable, any design data that contains layout information or point data information shall be provided. This information shall include the Point Number, Station, Offset, Northing, Easting and/or Elevation.

Utility Relocation Plans (ASCII Format)

If applicable, any design data that contains layout information or point data information shall be provided. This information shall include the Point Number, Station, Offset, Northing, Easting and/or Elevation.

Sign Structures (ASCII Format)

If applicable, any design data that contains layout information or point data information shall be provided. This information shall include the Point Number, Station, Offset, Northing, Easting and/or Elevation.

3D Model Review

When electronic file deliverables are being provided on a DelDOT project, the project designer shall complete and submit the Appendix A : 3D Engineered Model Review Checklist, at the milestone submittals (Initial Review Submission / Final Review Submission) as specified in the checklist.