The distinction between inflow and reservoir elevation is central to the case. Project records identify a peak inflow of 3,440 m³/s, 530 m³/s or 18.2% above the reported reference inflow of 2,910 m³/s for a 1,000-year event. The reservoir reached 160.29 metres at 14:00 on 22 May, 0.29 metres above the design flood level of 160.00 metres but 0.13 metres below the check flood level of 160.42 metres. It was also 1.21 metres below the reported historical maximum of 161.50 metres. Inflow magnitude describes the hydrological challenge, whereas reservoir elevation provides the hydraulic boundary condition governing part of the load on the dam. The researchers therefore characterize the episode as an extreme inflow event with a near-check reservoir level, not as an over-check hydrostatic condition or a probable maximum flood. The supplied archive did not include synchronized rainfall, inflow and outflow series, so the causes and rates of the subsequent reservoir recession could not be quantified.

The structure is a 71.50-metre-high, double-curvature concrete arch dam classified in its design documentation as a Class III water-resources structure. Its crest is at elevation 162.00 metres and its lowest foundation elevation is 90.50 metres. The project includes a surface hydropower-plant intake, a water-conveyance tunnel and two generating units rated at 10 MW each. Its monitoring programme combined manual surface surveys with automatic measurements of hydraulic and structural variables. Seven crest control points, two downstream gate-pier points and four upstream thrust-block points were included in the surface network. Three piezometers on each downstream abutment represented left- and right-abutment conditions, while four additional piezometers covered the downstream thrust-block and foundation zone. Electronic workbooks contained stress-cell, structural-strain, stress-free strain and concrete-temperature channels. The investigators separated values reported in the manuscript from engineering values and timestamps extracted from the workbooks, preserving their original identifiers, units, chronological order and sign conventions. Missing observations were neither interpolated nor smoothed.

Manual surveys indicated that the largest radial differences were concentrated near the central crest and gate-pier region. Survey-to-survey differences at D1, BD4 and D2 ranged from 5.65 to 5.99 millimetres and generally decreased toward the abutments, while tangential differences were visibly smaller in the source plots. In the final before-and-after interval, vertical survey increments ranged from −0.15 millimetres at BD1 to +0.87 millimetres at BD5; D2 and BD6 had the next-largest positive differences, at +0.79 and +0.77 millimetres, respectively. These are interval differences between two manual surveys, not continuous measurements or a directly observed value at 14:00 on 22 May. The archive did not preserve the exact dates of the flood-related surveys, measurement uncertainty or the transformation used to resolve radial and tangential components. It therefore cannot isolate a flood-induced component or determine peak, residual and recovered deformation.

The central position of the radial differences is qualitatively compatible with deformation of an arch dam under changing reservoir head, but the records do not demonstrate that hydraulic loading caused the observed pattern. The surveys were not corrected for temperature or time-dependent behaviour, and monthly vertical increments ranged from settlement to uplift, including −0.89 millimetres in February and as much as +1.52 millimetres in March. Because the table contains neither regularly spaced repeated observations nor an uncertainty model, the study makes no claim of statistical significance, elastic recovery, permanent deformation or foundation consolidation. Statistical and data-based approaches used to separate hydrostatic, seasonal, thermal and time effects require long, synchronized and quality-controlled records. Those prerequisites were absent, so the researchers did not fit a hydrostatic–seasonal–time regression or another event coefficient that would have depended on interpolation across missing data.

Foundation-zone measurements nevertheless provided one quantitative comparison that could be retained from the project archive. Project-derived uplift-pressure coefficients at P1–P4 were 0.15, 0.21, 0.07 and 0.13 when the upstream reservoir level was 160.29 metres. All four were below the project-specific design reference of 0.25, with relative margins calculated as (0.25 − α)/0.25 ranging from 16% to 72%. P2 had the largest coefficient and smallest margin within the four-point set. At the second reported reservoir condition of 158.02 metres, the coefficients were 0.15, 0.20, 0.07 and 0.13, with relative margins of 20% to 72%. The coefficient is a dimensionless head ratio based on piezometric pressure head, upstream water-surface elevation and instrument elevation, rather than a direct measurement of foundation movement. Missing sensor elevations, downstream reference head and calibration records prevented independent reconstruction of the values, so the comparisons do not constitute a standalone structural-safety assessment. P2 was identified as a priority for continued trend review, not as evidence of abnormal uplift or damage.

Abutment piezometric plots raised a separate data-verification problem. The April 2025 plots report left- and right-abutment piezometric elevations of 132.69–151.54 metres, with changes of −4.04 to +0.07 metres relative to the local series reference. For the flood-period plots, the stated combined range was 131.70–165.28 metres. The upper plotted value stood 3.28 metres above the 162.00-metre dam crest and 4.99 metres above the reported reservoir peak. It could reflect a different elevation datum, a conversion problem or a sensor anomaly, but the raw abutment-seepage workbook contained only headers, and sensor elevations and datum-conversion records were unavailable. The researchers consequently retained 165.28 metres only as a value transcribed from the original plot and assigned it no physical interpretation. Although the plotted series varied with reservoir level over parts of the record, synchronized raw observations were unavailable for correlation, lag or change-point analysis. The archive does not establish 150 metres as a threshold, identify a preferential seepage path or demonstrate bypass seepage, internal erosion or piping.

Automatic monitoring supplied the study’s most consequential limitation. Stress-cell, strain and temperature records generally stopped at 08:00 on 21 May and resumed at 08:00 on 8 June, creating an approximately 18-day interval that included the reservoir peak and early recession. Most structural-strain channels resumed on 8 June, while four S01 directions and all stress-free gauges resumed on 23 June. None of the automatic series sampled the 22 May peak, and the pre-gap and post-gap observations therefore could not be treated as a before–peak–after recovery sequence. At 08:00 on 21 May, the signed E01–E07 stress-cell outputs ranged from −17.1912 kilopascals at E02 to +41.1092 kilopascals at E05. At 08:00 on 8 June, they ranged from −15.1412 to +59.3157 kilopascals. Across the same common endpoints, 14 active temperature channels changed by −1.2993 to +1.5815°C. Because both the peak and the intervening thermal history were missing, these endpoint differences could not be attributed uniquely to hydraulic loading or used to test recovery. Stress-free strain channels recorded free deformation rather than load-induced stress and could not be converted to stress without a validated constitutive model and the required thermal and material parameters.

Quality control also flagged a discontinuity in stress cell E08. Its output changed from −84.6223 kilopascals on 21 May to +6.0923 kilopascals on 8 June, a step of 90.7146 kilopascals, and its temperature field on 8 June was blank. The retained metadata could not distinguish structural behaviour, recalibration or instrument error, so E08 was excluded from the representative E01–E07 range. That exclusion was a quality-control decision, not evidence of abnormal behaviour at the instrument location. More broadly, the archive lacked complete manufacturer and model information, nominal resolution and accuracy, calibration coefficients and dates, maintenance logs, detailed installation elevations, measured concrete properties, and site-specific geological and grout-curtain sections. It therefore could not support metrological revalidation, formal uncertainty propagation, strength-based safety evaluation or generalization to other arch dams. This was a descriptive, single-event case study based on records collected for operational monitoring, not a prospectively designed experiment.

The case identifies specific ways in which future event-focused monitoring could preserve evidence that the May 2025 archive lost. Event-triggered acquisition should synchronize reservoir level, rainfall, inflow, outflow, concrete temperature, deformation, piezometric head, structural strain and stress-cell output to a common clock, supported by redundant power, local buffering, communication-status logs and explicit missing-data flags. Manual surveys should retain exact timestamps, benchmark checks, coordinate transformations, instrument precision and environmental conditions. Abutment piezometers require verified datums and sensor elevations before plotted elevations can be interpreted, while E08 requires comparison with calibration, maintenance, power and acquisition records before it can rejoin a representative stress-cell range. The available evidence supports these verification priorities but not claims of piping, permanent damage, elastic recovery or overall dam failure. Its central lesson is that an exceptional inflow can leave the most informative structural response unobserved when acquisition, metadata and survey documentation are not prepared before the event.

Subject of Research: Evidence-constrained reassessment of deformation, seepage, uplift and stress monitoring during an extreme inflow event at a Chinese concrete arch dam

Article Title: Field-monitored deformation, seepage, and stress response of a concrete arch dam during an extreme inflow event

Article References: Chen, Y., Wang, X., Jiang, C., Liang, J., & Li, W. (2026). Field-monitored deformation, seepage, and stress response of a concrete arch dam during an extreme inflow event. Frontiers in Earth Science, 14, Article 1943967. https://doi.org/10.3389/feart.2026.1943967

Image Credits: AI Generated

DOI: 10.3389/feart.2026.1943967

Keywords: concrete arch dam, extreme inflow, field monitoring, dam deformation, piezometric response, uplift pressure, data completeness, structural monitoring, reservoir hydraulics, monitoring gap, Field-monitored, deformation

His father, apparently a medical doctor, fell into disgrace, and Kudrna used the short opening of the Prague Spring to flee to England. He later recalled leaving with a bag containing only two books on butterflies. After becoming a British citizen, Kudrna completed a master’s degree at Cambridge, where his thesis was developed under the guidance of Brisbane Charles Somerville Warren, whose work on the genus Erebia was particularly remembered.

The thesis provided the basis for Kudrna’s revision of the genus Hipparchia, published by E. W. Classey in 1977.

Kudrna’s later work showed how taxonomic conclusions could emerge from the comparison of specimens collected in different places and from the study of features that were not obvious in external appearance alone. One example arose in 1975, when Giorgio Leigheb collected specimens from a group of Hippparchia on the Aeolian Islands whose wing morphology and behavior appeared unusual to him. He sent the material to Kudrna for examination of the genitalia.

Kudrna responded that it was a new species, which he subsequently named Hipparchia leighebi in 1976. The episode illustrates the combination of field observation, specimen study and formal taxonomic analysis in Kudrna’s work. It also connected him closely with Leigheb, one of the colleagues who later recalled his life in a memorial account.

His interest in the collection of Italian lepidopterist Roger Verity developed after he met Leigheb in Turin in the early 1970s and was shown the five volumes of Farfalle diurne d’Italia. Beginning in about 1976, he made several visits to La Specola in Florence with support from small grants awarded by British societies. There, he selected Verity’s type material carefully and re-boxed it as a separate collection.

Kudrna continued returning to Italy after his Florentine period, staying in Novara, at Leigheb’s house on Lake Orta, or in Genoa with Emilio Balletto. The authors of the memorial regarded these repeated visits as probably the happiest period of his life. Kudrna accompanied Leigheb on field visits to habitats in which he wanted to observe particular butterflies.

These included the rice paddies around Novara, where Lycaena dispar was to be photographed; the heaths of the Piano Rosa, where Coenonympha oedippus remained abundant; the alluvial soils along the lower Sesia River, densely populated at the time by Zerynthia polyxena; the steep slopes of Mount Kastel, where Erebia flavofasciata was sought; and the Laquinthal Alps, where Erebia christi was photographed. The account describes these journeys as physically demanding for Kudrna, but says that he continued with determination and satisfaction. The visits allowed him to see the habitats and living butterflies associated with the specimens and regions central to his work.

Kudrna was a founding member of the Societas Europaea Lepidopterologica and served as editor of its journal, Nota Lepidopterologica, from 1977 to 1980. At La Specola, he prompted Emilio Balletto to become a society member in 1976 and encouraged him to attend the organization’s first congress in Paris in 1978. Kudrna left the editorial position after a series of disagreements, which the memorial does not detail.

A lasting friendship with Balletto and Leigheb continued through frequent correspondence and shared excursions. The memorial also recalls that Warren’s death in 1979 left Kudrna less happy in Britain and contributed to his eventual decision to settle in Germany. In Germany, Kudrna obtained citizenship and secured recognition of his medical degree.

He had already been working on projects connected with the Alexander Koenig Museum in Bonn, where a curator position became available. He applied for it, but it went to someone else, and he subsequently lost a grant he had held with the museum for several years. He then came to Genoa for two visiting appointments, teaching a conservation biology course at the local university during 1983–84 and 1984–85.

A small University of Catania grant supported monitoring of butterflies on the Aeolian Islands, and he also visited Sardinia a few years later. These activities added field monitoring to his taxonomic career and placed him in direct contact with butterfly populations in Mediterranean environments. Kudrna’s publishing plans included an eight-volume work on the butterflies of Europe, for which he was editor.

Only three parts appeared between 1985 and 1990, and the planned taxonomic volumes were not published because of difficulties involving the publisher and its new management. The second volume, Introduction to Lepidopterology, was written in the form of separate articles; the memorial notes that the chapters were not all of the same level. The eighth volume, written entirely by Kudrna and titled Aspects of the Conservation of Butterflies in Europe, introduced several indices, including a Range Affinity Index for evaluating how strongly a species could be regarded as European and therefore relevant to conservation in Europe.

Chris van Swaay and Martin Warren later adopted the index when compiling the first Red Data Book of European Butterflies. After the eight-volume project folded, Kudrna turned to an atlas of European butterfly distributions. Three updated editions appeared in 2002, 2011 and 2019, each adding revisions and clarifications to the mapped information.

The final edition, Distribution of Butterflies and Skippers in Europe, was sent to Balletto and Leigheb as a Christmas gift shortly before Kudrna’s death. The authors said that he was very proud of the atlas. The three editions also document the continuing development of his distribution work, although the memorial does not provide quantitative estimates of the atlas’s coverage or changes in species ranges.

Balletto and Leigheb described Kudrna as sometimes a very difficult person, and said they had told him several times that he was his own worst enemy. They nevertheless connected this aspect of his temperament with the psychological strain of leaving occupied Czechoslovakia, separating from family, losing his possessions and spending years away from his roots while seeking acceptance in England and Germany. His employment and financial circumstances were often uncertain, and professional disagreements contributed to the tensions surrounding his career.

The memorial presents these factors as partial explanations rather than excuses, while acknowledging the depth of the friendship shared with him. His work, as summarized by the authors, included taxonomic revisions, the description of Hipparchia leighebi, work on museum type material, butterfly monitoring, conservation writing and three editions of a European distribution atlas.

Subject of Research: Otakar Kudrna’s work on European butterfly taxonomy, distribution and conservation.

Article Title: Otakar Kudrna 1939–2021

Article References: Balletto, E., & Leigheb, G. (2021). Otakar Kudrna 1939–2021. Nota Lepidopterologica, 44, 133-140. https://doi.org/10.3897/nl.44.67734

Image Credits: AI Generated

DOI: 10.3897/nl.44.67734

Keywords: Otakar Kudrna, European butterflies, Lepidoptera, taxonomy, conservation biology, distribution atlas, museum collections, Range Affinity Index, Hipparchia, field monitoring, Otakar, Kudrna

The research team, led by Yongjing Ye and Keqing Li, carried out their investigation at Longshou Mine, where the drift cross-section is hexagonal, with a sidewall width of 6 meters, a floor width of 4 meters, and a height of 5 meters. The load-bearing layer of backfill above the drift is 3 meters thick. Before filling, crews place triangular steel trusses on the drift floor and lay steel mesh above them, lapping the mesh continuously along the floor and up both sidewalls. The longitudinal bars of the mesh, spaced at 300 millimeters, and the main bars of the trusses act together as the tensile reinforcement of the resulting composite slab.

To model this structure, the researchers turned to a classic tool of reinforced concrete theory: the transformed section method. Because steel is far stiffer than cemented backfill, with an elastic modulus ratio of roughly 122 in this case, each bar’s cross-sectional area can be converted into an equivalent area of backfill. This allows the neutral axis position, the moment of inertia, and the stress distribution of the whole section to be calculated with standard beam mechanics. Before cracking, the model treats the backfill as a homogeneous, linear-elastic material obeying the plane-section assumption; after cracking, it assumes the fractured tension zone carries no tensile force at all, leaving the steel to act alone. That second assumption is deliberately conservative, meaning the real capacity of a cracked roof is likely higher than the model predicts.

The roof itself is idealized as a simply supported beam spanning the drift width, loaded by a uniformly distributed overburden pressure. The authors are candid about the limits of this idealization: real drift ends receive some rotational restraint from surrounding rock and adjacent fill, so the simply supported model may slightly underestimate stiffness and overestimate deflection. Self-weight is likewise excluded from the capacity calculations because it is identical for every reinforcement scheme considered, making the results valid comparative indices rather than absolute design loads.

Validation came from an ambitious field monitoring program. Because embedding and fixing sensors in soft backfill is notoriously difficult, the team designed a dedicated fixing device and installed pressure cells at elevations of 1, 2, and 3 meters above the drift floor, concrete strain gauges at four elevations, and rebar stress gauges welded directly into the steel mesh and trusses. All instruments sat at midspan, and convergence monitoring sections were arranged along several drifts to track roof subsidence as mining advanced. The results showed the overburden load on the roof’s load-bearing layer holding steady between 0.11 and 0.16 megapascals, with strain flipping from compression near the top of the section to progressively larger tension near the bottom, exactly the pattern a bending beam should produce.

The comparison between theory and measurement was instructive. The model predicted an initial cracking capacity of 0.30 megapascals, comfortably above the measured 0.14 megapascals, confirming the roof stayed uncracked throughout monitoring, which matched field observation. Predicted strains at 0.5, 1.0, and 1.5 meters above the floor matched measured trends with errors of only 18, 38, and 2 microstrain. At 2.0 meters, however, the measured compressive strain of 632 microstrain vastly exceeded the predicted 58, a discrepancy the authors attribute to local stress concentrations, pressure arching, material heterogeneity, and the fact that a single gauge records a local response while the model describes an average. Rebar gauge readings told a similar story: theoretical forces of 6.3 and 6.7 kilonewtons fell within the measured range but below the maximum of 10 kilonewtons, prompting the team to introduce a calibrated adjustment coefficient of 1.7 on the elastic modulus ratio to cover unfavorable stress states with a safety margin.

With the calibrated model in hand, the reinforcement’s contribution became quantifiable. Installing the mesh and truss shifts the neutral axis downward, shrinking the tension zone and cutting the peak tensile stress at the bottom edge, where cracks begin. The result is a 7.6 percent increase in initial cracking capacity, from 0.288 to 0.310 megapascals. More striking is the post-cracking behavior: at the moment the backfill first cracks, the steel carries only about 114 megapascals against a tensile strength of 375 megapascals, leaving substantial reserve. The model predicts the reinforced roof can still sustain 0.102 megapascals of overlying load after cracking, roughly 33 percent of its cracking capacity, with tensile rupture of the reinforcement, rather than crushing of the backfill, governing eventual failure.

Subidence calculations revealed a subtler picture. The classical elastic deflection formula for a simply supported beam predicted a mere 0.28 millimeters of sag, wildly short of the 16 millimeters measured in the field, exposing the inadequacy of ideal elastic theory for absolute prediction. A geometric alternative fared far better: by computing the elongation of the roof’s lower boundary under bending and approximating the sagging profile as a circular arc, the team obtained a theoretical subsidence of 31.5 millimeters, which a field-calibrated adjustment coefficient of 0.49 refined to 15.4 millimeters, closely matching observation. Before cracking, reinforcement barely changes subsidence at all. Its real value emerges afterward: by continuing to carry tensile force, it extends the allowable subsidence from 23.05 to 41.09 millimeters, an increase of about 78 percent, delaying crack propagation and instability rather than preventing initial deflection.

Finally, the team used the corrected model to optimize the reinforcement layout itself, holding truss geometry fixed and varying only bar diameters and spacings within a 200-to-500-millimeter window for the mesh. Evaluating total steel mass, cracking capacity, post-cracking capacity, and limiting subsidence across seven schemes, they identified a preferred configuration using 6-millimeter mesh bars at 200-millimeter spacing with trusses at 1000-millimeter spacing. Compared with the original design, this scheme raises the theoretical post-cracking load-bearing capacity by 22.5 percent while actually trimming material cost by 3.1 percent, with cracking capacity and deformation limits essentially unchanged. A cost-focused alternative cuts steel mass by 17 percent at unchanged performance. Because the schemes alter only spacing and diameter, they require no change to existing fabrication practice. The authors stress that both calibration coefficients are empirical values tied to Longshou Mine’s monitoring data and must be recalibrated elsewhere, and that hangers and other vertical components, whose load-transfer roles differ from horizontal tensile reinforcement, remain outside the model’s scope for future work. Even so, the study delivers something underground engineers have long lacked: a fast, transparent, field-tested formula connecting steel layout to roof survival.

Subject of Research: Mechanical modeling and field monitoring of steel-reinforced cemented backfill roofs in downward drift mining

Article Title: A mechanical model for bottom reinforcement strengthened backfill roofs in downward drifts revised by field monitoring

Article References: Ye, Y., Li, K., Hu, Y., Zhang, B., Guo, R., & Han, B. (2026). A mechanical model for bottom reinforcement strengthened backfill roofs in downward drifts revised by field monitoring. Results in Engineering, 32, Article 113264. https://doi.org/10.1016/j.rineng.2026.113264

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113264

Keywords: backfill roof, downward drift mining, cemented backfill, steel reinforcement, transformed section method, simply supported beam, field monitoring, roof subsidence, cracking capacity, post-cracking behavior, Longshou Mine, mining geotechnics