Sonia Sorabella Swift, PE, VP of Engineering & Development, Menard
The 10th edition of the Massachusetts State Building Code (MSBC) went into effect in July of 2025 and became the first official code to contain language for ground improvement in the US. The MSBC addresses ground improvement overall and, in more detail, rigid inclusions (RIs). Neither ground improvement nor RIs had officially been codified in the US.
Codification of RIs is a controversial topic, as the main benefit of RIs is flexibility and optimization of designs. Unlike deep foundations, the behavior of RIs is heavily dependent on soil conditions. The resistance against codification comes from a desire to respect the inherent flexibility of ground improvement systems, and specifically RI systems. However, the call for codification came from recognition that the use of RIs had evolved over the past 20 years and some guidelines were necessary to create minimum standards within the ground improvement industry. While Massachusetts was the first, the Connecticut State Building Code also issued provisions to codify RIs in 2025, and the International Code Council is reviewing a proposal to add ground improvement generally and RIs specifically to upcoming issues of the International Building Code.
Why Has the Evolution of RIs Created a Need for More Structured and Standardized Designs?
RI columns are significantly stiffer than the surrounding soils and are used to mitigate settlement and increase bearing capacity of the soil. RIs were initially introduced as an alternative to stone columns on ground improvement sites with a layer of soft soil that would not be able to provide sufficient lateral confinement of the stone column through the soft soil (ASIRI, 2012, Masse, 2020).
As RIs came into use, they were typically designed conservatively as settlement mitigation elements. Designs were highly redundant and allowed for the use of shallow foundations designed for uniform bearing. Load transfer platforms (LTPs) separated the RIs and the superstructure, allowing for the load to engage with the in-situ soils. Load sharing results in optimization of the RI system and makes the design and installation of the LTP critical. As the importance of the LTP was recognized; LTPs were robust and carefully designed. (Swift and Pearlman, 2024)
As the industry overall became more comfortable with RIs, the industry recognized that RIs were underutilized. It became common to use RIs more strategically with higher allowable stresses (e.g. 7 MPa or 1000psi) and to maximize foundation sizes, increasing the bearing pressure of footings. RIs became more commonly used on sites with poor soils near the ground surface and at depth, so the RIs were providing bearing capacity and mitigating settlement. With high applied loads and poor soil conditions, the behavior of the RIs becomes more ambiguous, and design considerations need to be more rigorous. (Swift and Pearlman, 2024)
Similarly, owners and general contractors saw potential savings in the LTPs, frequently requesting the approval of alternate materials and thinner platforms, which has often led to more rigid support of the system with less redundancy, especially in cases where thin or no LTPs are used under footings, floors. or mats. (Swift and Pearlman, 2024)
Through this evolution, we have traveled the spectrum of applicability of RIs. Figure 1 shows a spectrum of applicability for RIs including the key distinctions between designs on the left and right sides of the spectrum. RIs can, have, and should be used at any point along the spectrum, provided that all parties acknowledge a project’s place on the spectrum and consider its impacts and understand the design. (Swift and Pearlman, 2024)
How Does Codification Change the Use of RIs?
The risk associated with codification is that developing rules for the design and installation of such an adaptable system may create requirements that minimize risk but hamper flexibility. However, the code language in the 10th edition of the MSBC incorporates flexibility and allows for interpretation. This accommodates projects along the spectrum and provides some minimum guidelines for RI designs. With careful application and a comprehensive understanding of the purpose and behavior of RIs, optimization is still possible with the current code provisions. Additionally, we now have minimum requirements for RI designs that owners and reviewers can use to evaluate proposed RI solutions. Understanding RI system behavior is critical for the entire project team so that reasonable and realistic project performance criteria can be developed. Criteria should be optimized and consider the risk associated with a project’s place on the spectrum to reduce costs when compared to deep foundations. The use of RIs instead of deep foundations may be the difference between a project that is economically viable and one that is not. Let’s use the code requirements to make more projects successful without increasing costs to owners.
References
ASIRI, Multiple authors (2012), “ASIRI 2012, Recommendations for the design, construction and control of rigid inclusion ground improvements”, Presses des Ponts et Chaussées, ISBN 978-2-85978-462-1.
Masse, F., Potter-Weight, A, Swift, S, and Buschmeier, B. 2020. Rigid Inclusions: Current State of Practice in North America, GeoCongress, Minneapolis, Minnesota, February, 2020.
Swift S. and Pearlman S. (2024, May 10). Rigid Inclusions: A Spectrum of Applicability [Conference presentation], IFCEE 2024, Dallas, Texas, USA.