Mitigating Potential for Rig Overturn - Industry Practices, Design and Evaluation of Working Platform

Scott Jacobs, PE, D.GE, Senior Engineer, Keller

Introduction
With development projects moving into less suitable land, Keller and key leaders in the geotechnical design and construction industry continue to address how to navigate increasingly difficult site access conditions safely. Once the contracts are signed and the solution is selected, the working platform evaluation should begin in parallel with evaluating the subsurface conditions.  Early-stage evaluations of soil type, bearing capacity, and the anticipated equipment types are key to a safe working platform program implementation. 

In 2018, the Industry Wide Working Platform Working Group made up of ADSC, DFI, and PDCA, published a position statement that states, “the responsibility for providing a safe working platform should be acknowledged by controlling entities (general contractors, construction managers, and owners) as being an integral cost for every project. Specialty subcontractors should not be left with the unknown risk and cost of creating safe working platforms without due consideration.”

Working platform failure

In December 2020, the Working Group published the Recommended Industry Practices for Safe Working Platforms for Construction Equipment, a recommendation document highlighting aspects of establishing an effective working platform program, including administration, design and installation, and inspection.  The project team can work together using the program to reduce risk and safely construct a project.  

Engineering Industry’s Opportunity to Help
During the design phase, the project team has a unique opportunity to highlight risks to the owner, including working platform concerns.  By using the Recommendation Document, the project team can identify the working platform stability risk early on for the owner/GC to address during preconstruction.  For example, when deep foundations are identified as the appropriate solution, it can become evident that the equipment required to install the recommended foundation may result in high ground pressures.  While the exact equipment type or how the equipment will be used may not be known, some general guidance can be provided to allow Owners to budget and plan for future costs, such as the design and construction of a working platform. Historically, these concerns have been addressed during the construction phase, sometimes resulting in health and safety, schedule, and/or cost implications.  Identifying the risk early allows specialty contractors to build the evaluation into the bid and allows Owners/GCs to account for these costs accordingly.  

Assessment & Evaluation 
If the working platform risk has not been addressed at the point of construction, the recommendation document can help finalize the working platform assessment and evaluation.  

First, identify a designated representative who is responsible for all aspects of the working platform program.  Assigning this role is critical for proper communication during the project. The designated representative will perform an initial site assessment followed up by one or more of the following: no working platform needed, empirical evaluation, engineering evaluation, and finally, certification as required. A basic pre-construction site evaluation can be performed by assessing the boring logs along with a site visit and visual inspection.  The equipment planned for the work, or similar, can be observed, and soil reaction can be monitored in real-time.  The use of probe rods/penetrometers is helpful to confirm boring log assumptions, including areas between borings or any areas disturbed during construction (e.g., utility installation or pre-excavation).  

A site evaluation does not have to require sophisticated equipment and can be simple and quick;  however, there are obvious issues to consider:  

• Site conditions can change as the site is developed throughout a project.  
• It can be difficult to confirm what is happening between borings at depth.
• How deep does the probe rod “feel” and/or penetrate, and is it enough to evaluate?
• Does the equipment onsite equate/relate to the equipment you are evaluating for?

Empirical evaluation and platform design would include using available data, experience, and established practices; however, an engineering evaluation would also include a full engineering analysis backed up by established methods such as BRE 470. A working platform certification can be used to identify all pertinent aspects of the working platform design, and requirements can then be provided and transmitted to all parties.  

Working platform example - crane mats

Construction Phase
This assessment and evaluation process will get most projects to the construction phase. The design and construction teams can then work together during installation and oversight. The  Recommended Industry Practices for Safe Working Platforms for Construction document highlights installation, inspection, and maintenance of the working platform, including the demarcation of working platform limits.  Daily jobsite safety meetings such as JHAs and Tool Box talks are a great opportunity to share Working Platform topics with the onsite design and construction teams.

Working platform example – gravel platform constructed
for heavily loaded equipment

Effective and Timely Evaluation of Working Platform 
The ability to evaluate the installed working platform is often difficult to assess as oftentimes there is limited information available on the platform itself.  The DFI/EFFC working platform task group has been actively analyzing four tests to help with working platform evaluation. The goal is to identify portable equipment/tests for the field that would improve data quality and timing of working platform evaluation/maintenance. 

• Stitz Hammer- is a pneumatic Dynamic Cone Penetrometer that can be used to measure penetration resistance of both the platform and the subgrade.   
• Panda DCP – is a automatic version of the Stitz Hammer.
• Lightweight Deflectometer (LWD) – is a device used to measure the bearing capacity and stiffness of the working platform. 
• Plate Load Testing – A plate load test to directly measure the bearing capacity of the working platform. 

The group’s analysis is focusing on the usability of the tests in the field and has worked with over 40 sites worldwide on this testing program.  

Scott Jacobs testing platform
with Stitz Hammer

Conclusion
Working platform safety is a critical component to project and requires more attention from all parties in the design/construction industry.  Identifying the risk early allows Owners to understand true costs of the projects and to reduce the potential for rig topple during early-stage construction.  These surprises can sometimes lead to long delays or added cost that might stop a project completely.  Preconstruction teams have an opportunity to identify risk and reduce cost and schedule overruns.  

No matter the stage of the project, a working platform evaluation often can be performed using qualified personnel and simple tools. Establishing an effective working platform program is essential to completing a project on time, on budget, and most importantly, safely. 

If you want to learn more about the Industry Wide (ADSC/ DFI / PDCA) Working Platform Working Group and how to implement working platform design/evaluation into in geotechnical design and construction, please contact Scott at  Scott.Jacobs@keller-na.com.

References:
ADSC, DFI, PDCA. Recommended Industry Practices for Safe Working Platforms for Construction.  December 2020. 
WPWG_Recommended_Industry_Practices_Working_Platforms-2020.pdf (xcdsystem.com)

Federation of Piling Specialists (FPS).  Working platform Guidance. Accessed May 2019.  https://www.fps.org.uk/guidance/working-platform-guidance/

Building Research Establishment (BRE), 2004.  BR470 Working Platforms for Tracked Plant.  Bucknalls Lane, Watford