Filing activity in this dataset is spread across a mix of Chinese state infrastructure groups, research universities and a smaller number of international specialists, with no single assignee dominating the full 98-family set. China Railway Tunnel Group No.2 Engineering and Shandong University are among the few still filing in the most recent tracked year, while larger historical filers such as China Railway Engineering Equipment Group and Shimizu Corporation show no filings in that same window. Because the ranking is family-based rather than raw document counts, it reflects distinct inventions rather than continuation filings inflating any one holder's totals.

The trend data shows filings peaking at 11 in 2017 and falling to 3 by 2022 and 2 in the latest partial year, a pattern typically seen once the core mechanical claim space — cutter head geometry, face pressure control, segment lining methods — has been substantially staked out. New activity tends to narrow into specific operational refinements, such as grouting sequencing or wear monitoring, rather than broad machine architecture. It is also worth noting that publication lags filing by roughly eighteen months, so the last one to two years in any chart will understate true filing volume.

A patent family groups together all the related filings — continuations, divisional applications and equivalent filings in multiple jurisdictions — that stem from a single underlying invention. Counting families rather than individual published documents avoids overstating an assignee's actual inventive output when they file the same invention in several countries or through multiple continuations. This dataset ranks 98 families, which is a fairer basis for comparing assignees than a raw count of published records would be.

The clearest under-claimed territory sits at the overlap between core E21D tunneling claims and digital or AI-adjacent subclasses: G06F, G06N and G06Q each carry only 3 records in this dataset, far below the near-total concentration in E21D itself. Specific opportunities include AI-assisted advance-rate prediction, real-time cutter head wear sensing, and automated face pressure control loops — areas referenced by only a handful of filings despite the operational importance of these functions. A first claim in these areas would need to tie the software or sensing method concretely to a physical TBM control loop to avoid pure business-method rejections, particularly given the small G06Q footprint.

Start with the highest-cited records in the dataset: US5890771A on general tunnel boring machine method and structure, and US5106163A on forward-end inspection, both carry heavy citation counts and represent foundational claim territory in the US. On the Chinese side, CN207620797U (shield tunnel lining load simulation and testing) and CN110566233A (post-segment grouting method for hard rock shield tunnels) are the most-cited domestic filings and are directly relevant to segment lining and grouting claims. Citation volume favours older filings, so also check recent Chinese filings in the same technical area even where citation counts are still low.