Automated Design and Production for Linear Schemes Using AutoCAD Civil 3D, Revit, and Dynamo

By Jerome Chamfray, Peter Houlston, and Ian McGregor for Autodesk University

A linear structure is related to and controlled by a 3D alignment. Atkins has developed a solution for automated linear structure design and drafting. This futuristic digital engineering approach delivers significant design efficiency, and it reinforces Atkins’ leading status in the field of digital engineering. This article will share the processes adopted for the solution using AutoCAD Civil 3D software, Revit software, and Dynamo software.

We will cover some typical design elements such as gabion walls and tunnel cross passages that may need to be incorporated to deliver the scheme design. We will discuss the problems that Atkins has had to overcome, and the various approaches chosen to achieve the goal of programming rule-based algorithmic geometry selection and placement, from guidelines for the linear structures, in response to iterative design alterations.

Discovery of Business Challenge

Background
Atkins has a long history in ground engineering and many current linear infrastructure projects that incorporate linear structures such as tunnels, retaining walls, bridges, and viaducts. Examples include Crossrail and the High Speed 2 projects. Our senior leadership has given a mandate to the design teams to embrace digital design methodologies. This means going beyond electronic drafting and CAD and is now being interpreted as needing a degree of automation and an algorithmic approach to design.

Atkins’ analysis of current design practice showed that there were many areas of the design process that involved a lot of manual input of data typically involving inefficient exchanges of information. Often these exchanges required manual interpretation and transformation of information into a suitable format for the next step.

We had heard about the linear structures class at AU in 2016 and decided to initiate a project with Autodesk to explore developing both processes and technology for the coordinated design of tunnels, viaducts, and retaining walls across our ground engineering design disciplines involving highways, structures, and tunnelling teams. This article presents some of the results of that project and things we learned along the way.

Discovery Process
We held two-day workshops with Autodesk to explore our existing business processes. These workshops centred around two typical problems we had already identified as having opportunity for innovation and automation due to involving a lot of manual design processes. The problems were especially impacted by changes to the highway/railway alignment.

The two design processes we explored were gabion wall design and tunnel cross passage design. Each of these design processes is detailed here. In the interactive workshops, we listed each of the following:

• Design criteria and parameters

• Stakeholders in the process

• Inputs to each step

• Outputs from each step

• Deliverable requirements

• Approval flow

We then mapped these into a flow diagram and identified the steps that were slow, difficult, and repeated often.

Training
Autodesk presented the Dynamo CivilConnection package and whilst our engineers are generally experienced in programming or scripting tools (especially Python), they had no knowledge of either Dynamo or Revit within the ground engineering team. Before undertaking an attempt to solve our challenges some Dynamo and Revit basics were taught in a Dynamo upskilling workshop.

The team also took themselves through basic Dynamo tutorials online. Given the team’s proficiency with Python, they adapted to the upskilling more quickly than anticipated and by the third day they were ready to start trying to integrate Civil 3D with Dynamo and solving the real-world problems rather than the hypothetical training examples.

Challenge 1 — Gabion Wall Design

Gabion Wall Design — Highways Example
Atkins has a good process for the first stage of preliminary design in place already. This approach in Civil 3D solves for a generic location problem of where gabion walls are needed by utilizing corridor modelling techniques with a custom subassembly. This process does not do the precise engineering logic of where to provide the gabion baskets; rather, it just provides an indicative location. The design of gabion walls at multiple locations becomes a tedious manual task with no chance for optimization or data to support the final engineering design.

This gabion design is then susceptible to changes in the highway alignment potentially leading to redesign and starting over. Tasks like quantification and drawings production become disconnected, which has meant that much of the detail design has been delegated to the contractor.

Design Parameters
Below are the design steps discussed in the workshop for each cut and fill scenario that we would like to test with a Dynamo design. The gabion basket models will be created as parametric basket objects for various types defining the range of baskets available.

Figure 1. Plan, section, elevations. SMP gabion wall design. Cut and fill situations.

Key points to note:

  • Red dots indicate Civil 3D feature lines
  • ‘H’ is maximum height of gabion wall
  • ‘Width’ indicates maximum width to boundary line of site
  • There is an embedded depth value of the gabion wall below bottom of bank
  • There is a maximum height at top of bank the embankment slope can over top the top gabion
  • Want to maximise the size of gabion basket used
  • Minimum number of gabion baskets in a wall
  • Minimum distance to boundary now at foot of wall in fill situation
  • Slope definitions differ slightly in the fill situation
  • There are minimum and maximum values that gabion baskets can deviate from plan boundary defined by C3D FLs
  • Earthworks slope definitions are provided by Civil 3D
  • There is a cost efficiency preference to place larger baskets
  • Would like to build a Civil 3D surface of the final array design by extracting an array of points into a C3D surface object which allows for volume calculations in Civil 3D later

Design Process
1) Civil 3D provides feature line inputs for top/bottom of slope and boundary line

2) Parametric gabion baskets controlled by Dynamo (likely 10 types)

3) Civil 3D provides the cut/fill case

4) Decision to use gabion wall or some other construction method (e.g., sheet pile)

5) Place array of baskets in available space based on:

a) Available width

b) Maximum height

c) Embedment in base

d) Maximum surcharge and batter slope values

e) Maximum height of surface above the top cage

f) Maximum height of basket above surface

6) Export setting out data in appropriate format for on-site placement of cages (Civil 3D feature lines)

7) Obtain surface area of gabion wall

8) Enable drawings production (place 3D solids of gabions) in Civil 3D

9) Enable QTO

a) Basket schedule

b) Volume of stone

c) Volumes of infill/cut

d) Area of geotextile blanket across the back of the gabion wall baskets

Business Value
Why we wanted to explore automation of the design of gabion retaining walls:

  • Automates decision on when to place gabion vs. other retaining wall solutions
  • Optimise the gabion wall geometry and placement
  • Provision of a precise gabion schedule would be a new service Atkins could provide in the design delivery
  • Minimise cost
  • Creation of Civil 3D surface for more precise volume calculations
  • Speed of response to design change
Figure 2. Wireframe of gabion wall array placed in AutoCAD by Dynamo.

Challenge 2 — Tunnel Cross Passages

Cross passages provide points of access between two parallel running tunnels. They are utilized for purposes of maintenance, emergency, and ventilation. In general, the challenge is to set out the geometry of the cross tunnel between two related main running tunnels.

The spacing of cross passages is defined by business rules and will be project specific. The geometry of the cross passage has some specific parameters and is governed by its relationship to each of the running tunnels. Usually it will be defined by an alignment (2D horizontal plane) and profile (2D vertical plane).

Each cross passage will be unique due to its relationships to the running tunnels and other cross passages as well as geology at that location. Planned construction method will also have an impact on geometry.

Design model geometry is non-trivial to solve by current methods and prevents significant optimization of design due to time constraints.

Reinforcing rock bolts around the entrance to the cross passage from the main tunnels are especially complex to design and install due to possibilities of them clashing. There would be added value in being able to design these and produce schedules of hole location and drill angle. Steel reinforcing design is also similarly complex and would benefit from some automation.

Figure 3. Sectional views of tunnel cross passage design.

Design Parameters
Cross passage design should meet the following requirements:

  • Minimise length of tunnel
  • Maintain slope for water egress back to running tunnel
  • Be related to walkways in main running tunnels
  • Maintain space requirements defined by cross section
  • Contractors need a schedule of drill locations
  • Drilling is imprecise so a tolerance cone is needed
  • Clash avoidance is better than clash detection; solution should avoid or advise of clashes and allow for redesign
Figure 4. Rock bolt design related to cross passage.

Design Process
1) Alignments and profiles from C3D

2) Track, train, and tunnel design data inputs

3) Pedestrian walkway geometry located

4) Locate cross passage by chainage

5) Minimise length of cross passage

6) Main running tunnel low point is a consideration (sumps and pumping)

7) Consider geology in location

8) Automate profile geometry? With minimum/maximum profile grade (e.g., min. 2.5%)

9) Apply a C3D subassembly for cross passage size (clash checking)

Business Value

Why we wanted to explore automation of the design of tunnel cross passages:

  • Optimizing the placement and number of cross passages is of high value. They are expensive to design and construct.
  • Automated production of sectional drawings related to cross tunnels would be a win for this project. That is a non-trivial manual task at present.
  • Ability to test tunnel geometry with short response times should support engineering decision making and optioneering due to increased data availability. Some high-level decisions today are made based on engineering judgement because modelling takes too long or is seen as impractical due to high manual effort or skill level.
  • Better space planning for utilities in cross passages.
Figure 5. Tunnel cross passage geometry in Dynamo, with rock bolt design.

Solution Approach
A perception exists that Dynamo is part of Revit but due to low understanding of the value that Revit could bring to the modelling challenges it was worth explaining the modelling environment architecture. Dynamo is just an environment that is initiated from Revit in order to access the Revit API. In reality, what the system provides is a dynamic modelling environment of its own that can read/write from many sources, Civil 3D and Revit are just two special cases.

Figure 6. Comparison of Civil 3D to Dynamo to Revit software architecture and in-use modelling architectures.

The Autodesk CivilConnection Dynamo package is a custom package that loads into Dynamo and provides a live connection to Civil 3D via the Civil 3D API. Dynamo provides a visual, interactive programming environment in which to prototype design. It is not constrained to working just with Revit data.

A key feature of the installed nodes is to allow the loading of Civil 3D corridor model information into Dynamo in such a way as to establish a usable linear coordinate system in the Dynamo and Revit environments. This means that location can be expressed in terms of an Alignment, Station (Chainage), Feature Line reference, offset, and elevation in addition to the rectangular Cartesian and polar systems.

For example, the location of any gabion basket can now be expressed in terms of a location relative to the main road alignment, or associated feature line, and if that alignment changes then the basket location can be reset but maintain the already established relationship.

This location-based relationship is fundamental to solving the design challenge. Civil 3D provides the bounding space in which gabion baskets are required. The Dynamo toolkit provides the ability to explore, prototype, and optimize the 3D array of baskets.

Jerome Chamfray is BIM manager at Atkins. He has 17 years of experience leading 3D design and engineering drawing preparation for major projects involving earthworks, tunnelling, infrastructure, and building projects. His current focus is on the further development of BIM and Digital Engineering approaches for Atkins Ground Engineering and Tunnelling projects. His expertise is centred on BIM, data management, drawing production and ground modelling using AGS geotechnical data combined with 3D spatial information. His wide range of expertise and valuable knowledge have led him to be identified as a technical expert on large multidisciplinary projects in South Africa, Middle East, and the UK. He is also Atkins’ technical authority on subsurface digital engineering.

Peter Houlston is a geotechnical engineer based in the Birmingham office of Atkins Ground Engineering team. Peter has a wide variety of experience, from numerical modelling of cutting heave in new build railways projects to specification and interpretation of advanced laboratory testing to characterise the response of driven piles in chalk. Recently, his focus has turned to application automated design processes to geotechnical engineering design.

Ian McGregor is senior implementation consultant within the BIM service line at Autodesk. He is focused on assisting customers deliver BIM transformation within the infrastructure industry. He has extensive experience managing requirements for large and complex projects and delivering across multiple engineering standards and languages. He also provides consultancy on BIM process definition and standardization for transportation, airports, and water industries.

Want more? Read on by downloading the full class handout at Autodesk University: Automated Design and Production for Linear Schemes Using AutoCAD Civil 3D, Revit, and Dynamo.

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