Tree Rings Research Articles

Mercury in tree rings close to emission sources in Austria.

Mercury in wood is an important pool of this heavy metal in forest ecosystems because of its relatively high proportion in the biomass compared to other pools. This paper describes the successful application of a modified methodology for stem disk sampling based on wood particles from stem disks from Donawitz (Styria, Austria; pig iron production), from Brixlegg (Tyrol; former copper and silver mining, copper ore processing and copper recycling), and from Gmunden (Upper Austria; cement production). The maximum mercury concentration in the stem disks from Donawitz (Hinterberg: 20.5ppb, St. Peter: 9.3ppb) was recorded in the early 1970s. Several maxima were obtained from the stem disks from Brixlegg: the first was in 1813 (149.9ppb), potentially even earlier, a second (37.6ppb) in the late nineteenth century until the late 1920s, and a third local maximum in the 1970s (9.1ppb), followed by a tendency to decline until the present. A stem disk from Gmunden in Upper Austria showed values of mercury concentrations indicating no increases compared to literature about background sites (≤ 3.2ppb). This method revealed trends in mercury concentrations in tree rings originating from several different mercury emission sources in Austria coinciding with information about industrial history (where available) together with a justifiable effort. We therefore recommend it for further investigations on mercury concentrations in tree rings and their changes over time.

Experience the precision of time: radiocarbon 3.0

Experience the precision of time: radiocarbon 3.0 RESOLUTION aims to achieve an accurate and highly resolved chronology back to 55 000 years BP (Before Present), using some new floating sections of fossil trees. In fact, with tree rings, the resolution will be an order of magnitude higher, and using the most recent advances in the AMS technique, we will obtain confidence intervals of only a few centuries in glacial times. In this way, we can establish in a precise way the timing of when Homo sapiens arrived in Europe, their interaction with Neanderthals and the final cause of the Neanderthal extinction. The project involves fieldwork in the Mediterranean and Southeast Europe to find more glacial trees, study the exist-ing collection of glacial conifers, exceptional 14C precision for 14C dates in the glacial, and the cutting-edge methodolo-gy linking floating tree-ring chronologies to 10Be on the ice core scale.

Reconstructing groundwater and lake level histories in Northern Wisconsin: isolation of groundwater’s influence on tree rings from climatic and environmental drivers

Tree rings can reveal long-term environmental dynamics and drivers of tree growth. However, individual ecological drivers of tree growth need to be disentangled from the effects of other co-occurring environmental and climatic conditions in tree rings to examine the histories of stand- to landscape-level ecological processes. Here, we integrate ecohydrological theory of groundwater–tree interactions with dendrochronological approaches and develop a new framework to isolate water-level effects on tree rings from climate induced variability in tree ring growth. Our results indicate that changing depth to groundwater within 1–2.3 m of the land surface exerts a substantial influence on red pine growth and this influence can be quantified and used to reconstruct long-term groundwater and lake level histories from tree ring patterns in Northern Wisconsin. This research suggests a substantial influence of groundwater on tree growth with implications for improving the mechanistic understanding of climate-induced tree mortality and reduce uncertainty in forest productivity models. Further, this is a transferable approach to isolate and reconstruct strong environmental drivers of tree growth that co-occur with other environmental signals.

The Relation Between Decadal Droughts and Eruptions of Steamboat Geyser in Yellowstone National Park, USA

AbstractIn the past century, most eruptions of Steamboat Geyser in Yellowstone National Park's Norris Geyser Basin were mainly clustered in three episodes: 1961–1969, 1982–1984, and ongoing since 2018. These eruptive episodes resulted in extensive disturbance to surrounding trees. To characterize tree response over time as an indicator of geyser activity adjustments to climate variability, aerial and ground images were analyzed to document changes in tree coverage around the geyser since 1954. Radiocarbon dating of silicified tree remnants from within 14 m of the geyser vent was used to examine geyser response to possible variations in decadal to centennial precipitation patterns. We searched for atypical or absent growth rings in cores from live trees in years associated with large geyser eruptions. Photographs indicate that active eruptive phases have adversely affected trees up to 30 m from the vent, primarily in the dominant downwind direction. Radiocarbon dates indicate that the geyser formed before 1878, in contrast to the birthdate reported in historical documents. Further, the ages of the silicified trees cluster within three episodes that are temporally correlated with periods of relative drought in the Yellowstone region during the 15th–17th centuries. The discontinuous growth of trees around the geyser suggests that changes in eruptive patterns occur in response to decadal to multidecadal droughts. This inference is supported by the lack of silicified specimens with more than 20 annual rings and by the existence of atypical or missing rings in live trees during periods of extended geyser activity.

Central European Agroclimate over the Past 2000 Years

Abstract Central Europe has experienced a sequence of unprecedented summer droughts since 2015, which had considerable effects on the functioning and productivity of natural and agricultural systems. Placing these recent extremes in a long-term context of natural climate variability is, however, constrained by the limited length of observational records. Here, we use tree-ring stable oxygen and carbon isotopes to develop annually resolved reconstructions of growing season temperature and summer moisture variability for central Europe during the past 2000 years. Both records are independently interpolated across the southern Czech Republic and northeastern Austria to produce explicit estimates of the optimum agroclimatic zones, based on modern references of climatic forcing. Historical documentation of agricultural productivity and climate variability since 1090 CE provides strong quantitative verification of our new reconstructions. Our isotope records not only contain clear expressions of the medieval (920–1000 CE) and Renaissance (early sixteenth century) droughts, but also the relative influence of temperature and moisture on hydroclimatic conditions during the first millennium (including previously reported pluvials during the early third, fifth, and seventh centuries of the Common Era). We conclude that Czech agricultural production has experienced significant extremes over the past 2000 years, which includes periods for which there are no modern analogs. Significance Statement As temperatures increase, droughts are becoming a growing concern for European agriculture. Our study allows recent extremes to be contextualized and helps to better the understanding of potential drivers. Stable carbon and oxygen isotopes in oak tree rings were analyzed to reconstruct year-to-year and longer-term changes in both temperature and moisture over central Europe and the past 2000 years. We combine these proxy-based climate reconstructions to model how well crops were growing in the past. The early fifth and the early sixteenth centuries of the Common Era were most likely characterized by extreme conditions beyond what has been experienced in recent decades. Our reconstructions of natural variability might be used as a baseline in projections of future conditions.

A stepwise multidisciplinary approach to determine the date and provenance of historical wooden objects

We present a stepwise multidisciplinary approach combining woodworking expertise, dendrochronology, DNA genotyping and radiocarbon dating to determine when, where and how historical wooden objects were made. The effective implementation of this approach is demonstrated with a set of wooden stocks from the Rijksmuseum collections in Amsterdam (the Netherlands). In 2019, preceding an exhibition about slavery, stocks made of oak (Quercus sp.) were donated to the Rijksmuseum. The history of the object was unknown, and a stepwise approach was devised to determine the date and potential place of its manufacture, and whether they were made in the context of Dutch colonial slavery. Pencil marks and tool traces found on the surface of the wood are characteristic of traditional woodworking techniques and indicated that the stocks were processed after 1800 C.E., from fresh wood, shortly after the felling of the tree, and in one go. The tree-ring analysis revealed that the beams originate from the same tree, and that the tree grew in a dense forest. However, it failed to return an exact date for the wood and, consequently, also to determine its provenance. Therefore, we decided to employ DNA-genotyping and radiocarbon dating. The retrieval of DNA was successful, and the results placed the provenance of the wood in an area covering a broad latitudinal transect in central Europe. Radiocarbon wiggle matching, modelled with sapwood statistics for central Europe, revealed that the tree was likely cut between 1791 and 1824 C.E. These results combined suggest that the stocks were produced in the first quarter of the 19th century, using local wood, at a small rural town somewhere in Italy, the Pyrenees, eastern France, Belgium, the Netherlands, Germany or even further north (Denmark, Sweden). While their association with slavery in colonised territories seems unlikely, their production in the context of the Dutch colonial system cannot be ruled out. Therefore, they are valuable historical objects worth being curated and exhibited at a national museum. The stepwise approach here presented can be applied to other large objects at museum collections. We encourage curators, conservators and restorers to consider its implementation to maximise knowledge acquisition and appreciation of wooden cultural heritage.

Late Quaternary fluvial environments at Abo Arroyo, New Mexico, U.S.A.: response to millennial-scale climate change

ABSTRACT Abo Arroyo is a tributary of the Rio Grande in central New Mexico. Its alluvial sequence is made up of four informal units, their age defined by 44 AMS radiocarbon dates from 12.8 ka to 0.85 ka. The earliest, unit 1, is terminal Pleistocene to early Holocene (12.8 ka to 9.0 ka), including the Scholle wet meadow (12.3 ka to 11.1 ka) related to the Younger Dryas. After an erosional gap in the record from 9 ka to 6 ka, coarse gravel (unit 2) was deposited in the channel (5.8 ka and 4.3 ka) during the middle Holocene period of aridity. Subsequently, the late Holocene wet period is characterized by fine-textured alluvium (unit 3) (3.5 ka to 0.945 ka) with shells of an aquatic snail, indicating persistent stream flow. An upper 2-m zone of dark-colored clayey silt beds with high amounts of organic carbon and carbonate accumulated from 1.7 ka to 0.945 ka. A record of C4 signatures, previously interpreted to indicate dry conditions 1.4 ka to 0.945 ka, is reinterpreted as an interval of exceptionally wet floodplain conditions with C4 grasses and sedges. Abo Arroyo and other studies indicate three major episodes of late-Quaternary channel entrenchment: 1) from the full-glacial to late glacial-Bølling/Allerød (6.1 ky), 2) during the middle Holocene (2.5 ky), and 3) during the late Holocene Medieval Warm Period (0.4 ky), each erosional event less severe and shorter duration than the preceding one, and all three represent a significant change from wet to dry climate. During the Medieval Warm Period (A.D. 900 to 1300), a shallow channel formed in unit 3 alluvium, bracketed by AMS dates A.D. 1005 in unit 3 alluvium and A. D. 1100 in unit 4 channel fill. The channel cutting occurred with the shift from wet to dry climate, although the downcutting event was preceded by 100 years of landscape adjustment to the long drought. The canyon fill was entrenched again, deep and wide, by arroyo cutting in the late nineteenth and early twentieth centuries. The regional 83-year second-century drought (A.D. 100 to A.D. 182), documented by tree rings, shows up in the stable-carbon-isotope record from Abo Arroyo alluvium. The drought was more severe than the 400-year warm period but had little effect on the preserved alluvial record. The less severe but longer-duration Medieval Warm Period resulted in channel cutting at Abo Arroyo and elsewhere in the broad region at that time, but the second-century drought did not. Finally, the similarity of Abo Arroyo and Rio Grande late Holocene alluvial records with parallel stratigraphy, sedimentology, and geochronology illustrates that tributaries and main valleys respond alike and in concert to climate and climate change.

Moisture stress limits radial mixing of non-structural carbohydrates in sapwood of trembling aspen.

Dynamics in non-structural carbohydrate (NSC) pools may underlie observed drought legacies in tree growth. We assessed how aridity influences the dynamics of different-aged NSC pools in tree sapwood at two sites with differing climate conditions ('wet' vs. 'dry') that also experienced widespread regional drought five years earlier. We used an incubation method to measure radiocarbon (Δ14C) in CO2 respired from Populus tremuloides (aspen) tree rings to evaluate NSC storage and mixing patterns, coupled with measurements of NSC (soluble sugars, starch) concentrations and respired δ13C-CO2. At a wet site, CO2 respired from rings formed during 1962-1967 was only ~ 11years old, suggesting deep sapwood mixing of NSCs as starch. At a dry site, total NSC was about one-third of wet site totals, maximum ages in deep rings were lower, and ages more rapidly increased in shallow rings then plateaued. These results suggest historically shallower mixing and/or relatively higher consumption of NSCs under dry conditions. Both sites, however, had similar aged NSC (<1yr) in the most recent six rings, indicative of deep radial mixing following relatively wet conditions during the sampling year. We suggest significant differences in NSC mixing among sites are driven by moisture stress, where aridity reduces NSC reserves and restricts the depth of radial mixing. However, dynamic climate conditions in the southwestern US resulted in more complex radial patterns of sapwood NSC age than previously described. We suggest a novel conceptual framework to understand how moisture variability might influence the dynamics of NSC mixing in the sapwood.

Availability of Annual Tree Rings for Determining Cr Concentration in Air

Availability of Annual Tree Rings for Determining Cr Concentration in Air

Relationship between the Radial Growth of Two Dominant Coniferous Species and GPP in the Arid Region of Northwest China

Radial growth of trees is closely related to canopy activity. Revealing the relationship between radial growth and canopy activity is of great significance for forest protection under climate change. In this study, we built tree-ring chronologies for two tree species, spruce (Picea aspruceerata) and Chinese pine (Pinus tabuliformis), from the Helan Mountains in the arid region of northwest China. Correlation coefficients were then calculated to reveal the relationships among tree rings, two kinds of gross primary productivity (GPP) indices, and climate data. The results demonstrated that the radial growth of both spruce and Chinese pine was positively correlated with GPP from late February to early March, and moisture conditions may be the driving factor of tree growth. However, radial growth of Chinese pine was also correlated with GPP from the end of March to the end of August. This study aimed to further supplement the relationship between trunk radial growth and canopy dynamics in the arid zone of northwest China and to provide theoretical guidance for vegetation restoration and forest conservation in the arid zone of northwest China under climate change.

Experimental study on fracture damage and seismic performance of loose through-tenon joints in ancient timber structures

A looseness is typical damage of mortise-tenon joints in ancient timber structures. Brittle fractures of loose joints are likely to occur, leading to joint failure during earthquakes. This study conducts pseudo-static tests on three groups of full-scaled through-tenon joints to examine the fracture damage and seismic behavior of the loose mortise-tenon joints and determines fracture damage modes of through-tenon joints with different looseness. It uses the acoustic emission method to measure the ring count on the tenon surface, along with each joint's critical load and critical energy release rate and then analyzes the fracture damage performance of different tenon joints. In addition, this research investigates the hysteretic and skeleton curve, stiffness degradation curve, and tenon pulling quantity of the joint under various fracture damage states. The results showed that the fracture failure mode of the through-tenon joint is a fracture in the variable cross-section and along the local tenon neck. During the loading process, the critical energy release rate initially increases and then decreases as the looseness grows. In addition, with the increase of crack mouth opening displacement (CMOD) and crack length, the bending moment of the joint firstly increases and then decreases. When the variable cross-section breaks and the tenon neck partially cracks, the joints' bending moment and stiffness reduce with increasing looseness. With the increase in local embedment compression in the lower side of the beam end and the mortise, the amount of tenon pull-out of loose joints decreases under positive and negative loading.

Growth Response of European Beech (Fagus sylvatica L.) and Silver Fir (Abies alba Mill.) to Climate Factors along the Carpathian Massive

European forests are becoming increasingly threatened by climate change and more frequent droughts. The likely responses of species to climate change will vary, affecting their competitiveness, their existence, and consequently, forest management decisions and measures. We determined the influence of climate on the radial growth of European beech and silver fir along the Carpathians to find similarities between the two species and the main differences. Along the Carpathian Mountains, seven sites with mature fir–beech stands above 800 m above sea level were selected and analyzed. Our study confirmed different responses depending on species and location. A more pronounced response of tree growth to climate was observed on the eastern side of the Carpathians, while it was less expressed or even absent on the southern sites. Both beech and fir show better radial growth with higher precipitation in July and slower growth with higher average and maximum temperatures in June of the current year. Fir demonstrates a positive correlation between radial growth and temperature in winter, while beech demonstrates a negative correlation between radial growth and temperature in summer. In the 1951–1960 decade, the average tree ring widths in fir and beech were largest at the southern sites compared to the other sites, but since 2011, the southern sites have had the lowest increase while northern sites have had the largest. Both species respond differently to climate and are likely to follow different competitive paths in the future.

Growth rate estimation by 210Pb chronology in precious corals collected off the southern coast of Japan

The Lead 210 (210Pb) concentrations were determined to estimate the skeletal growth rates in the four species of precious corals including Japanese red coral (Corallium japonicum), pink coral (Pleurocorallium elatius), white coral (P. konojoi), and a deep-sea coral (Coralliidae sp.), and in a bamboo coral (Keratoisis sp.). Colonies were collected from the southern coast of Japan, western North Pacific margin. The 210Pb concentrations typically showed the exponential decrease with distance from the edge to the center of the skeleton axis in a cross section of main stem of colonies. The mean radial growth rates for colonies were estimated from the slopes of the best fit curves for exponential decrease in 210Pb concentration along the multiple transects. The obtained mean and standard deviation of radial growth rates in the diameter (the number of transects, n) for three colonies of C. japonicum were 0.31 mm/y (n = 1), 0.21 ± 0.05 mm/y (n = 2), and 0.36 ± 0.13 mm/y (n = 2), respectively, which were broadly comparable to the previously reported growth rates obtained by growth ring counting. Those obtained for three white coral colonies were 0.52 mm/y (n = 1), 0.60 mm/y (n = 1), and 0.36 ± 0.25 mm/y (n = 2). The radial growth rate for the bamboo coral colony was 0.13 mm/y in radius. The linear growth of the main steam of some colonies was analyzed from several cross sections. The linear growth rates of colonies could be estimated from the slope of the best fit curve (1) for increasing mean 210Pb concentration along the cross transects of the axis and (2) for increasing center 210Pb concentration of the skeleton axis. The linear growth rates calculated from the mean and center concentrations for two C. japonicum colonies were 8.5 and 6.1 mm/y, and 1.8 and 1.4 mm/y, respectively. Those for a P. elatius colony were 4.7 and 3.4 mm/y. The difference between the two estimates may reflect the morphological structure of the skeleton. The growth rates measured for the radial increase and linear extension of the main stem of the colonies could provide basic information for the demographic study of these coral species thereby fostering a rational exploitation of their populations.

Basic Nitrogen (BaN) Is a Key Property of Antimalarial Chemical Space.

Most antimalarials are based on basic N-heterocycles and possess amine functionalities. Despite this, the role of basic nitrogen (BaN) in antimalarial drug design has not been studied systematically. Our cheminformatics analysis indicates that BaN is an important feature of antimalarial space. We show that potent research antiplasmodials (RAP) and advanced-stage antimalarials (ASAMs) consistently show a higher BaN count (#BaN) compared to oral drugs. Similarly, BaN is often a vital feature of the hits obtained from phenotypic screenings despite the use of varied assay conditions. The literature review demonstrates that in several unrelated scaffolds, the addition of BaN results in enhanced antiplasmodial activity. In addition, potent antiplasmodials and HTS hits are bulky, lipophilic, and less polar and have a high aromatic ring count (#AR). This characterization of antimalarial space may be used to collate a focused compound collection to achieve higher hit rates in HTS, as shown retrospectively in this perspective.

Variations of deep water uptake and water use efficiency indicated divergence in tree growth stability

Insights into forest growth stability in response to intensified climate change and disturbances is critical to maintain the continued flow and stability of forest services. However, the underlying drivers for tree growth stability remain poorly understood. In this study, we quantified the spatiotemporal pattern in tree growth stability of Chinese pine (Pinus tabulaeformis) plantations and its relationship to diverse driving factors (climate, stand structure, ecophysiological traits, soil properties, and topography) across a great climatic gradient in northern China in the period of 1979–2018. We calculated the coefficient of variation of tree ring chronology (TRIcv) to characterize tree growth stability and revealed that the TRIcv increased significantly with increasing multiyear mean aridity index (MAI) and vapor pressure deficit (VPD) spatially. Temporally, TRIcv displayed increasing trend in 25 of 40 study sites. Constrained redundancy analysis revealed that TRIcv was strongly mediated by water availability, water uptake from different soil layers, wood density, tree height, leaf stable carbon isotope discrimination (δ13C), and leaf nutrients. The ratio of water uptake from 60 to 80 cm soil layer and leaf δ13C were the two most important ecohydrological-related factors determining TRIcv, highlighting that the water uptake strategy and leaf water use efficiency play critical role in reshaping the tree growth stability of Chinese pine to cope with the intensifying climate change.

Acoustic emission characteristics and failure prediction of defective cemented gangue-fly ash backfill under seepage-stress coupling

ABSTRACT Aiming at the problem of seepage-stress coupling failure instability of cemented gangue-fly ash backfill (CGFB) with defects, the triaxial compression test and acoustic emission (AE) monitoring test of the CGFB were carried out in this paper. The strength characteristics of defective CGFB under seepage-stress coupling were analysed，the variation rules of AE parameters (ring count, b-value and entropy value) in the failure process were systematically studied. It is found that the AE parameters (ring count, b-value, and entropy value) of backfill with defects under seepage-stress coupling have a ‘mutation’ phenomenon, which can be used as a precursor feature of failure instability of backfill. Combined the grey-cusp catastrophe theory, a failure prediction model of backfill based on AE parameters (ringing count) was established, and the seepage-stress coupling fracture of backfill with defects was effectively predicted, indicating that the model is feasible to predict the seepage-stress coupled failure of backfill with defects. The research results can provide a theoretical basis for stability monitoring and failure prediction of backfill in deep water-rich mines in China.

Coupling dendroecological and remote sensing techniques to assess the biophysical traits of Juniperus virginiana and Pinus ponderosa within the Semi-Arid grasslands of the Nebraska Sandhills

Woody species encroachment is occurring within the semi-arid grasslands of the Nebraska Sandhills U.S., primarily driven by native Juniperus virginiana and Pinus ponderosa, altering ecosystems and the services they provide. Effective, low cost, and cross-scale monitoring of woody species growth and performance is necessary for integrated grassland and forest management in the face of climate variability and change. In this study, we sought to establish a relationship between remote sensing-derived vegetation indices (VIs), tree dendrochronological (raw and standardized tree ring width) measurements, and the abiotic environment [(precipitation, temperature, Palmer Drought Severity Index (PDSI), and soil water content (0–300 cm depth)], over a 30-year period (1984–2013), to assess the performance of encroaching woody J. virginiana and P. ponderosa within the Nebraska Sandhills. We also investigated whether VIs can be used as an effective alternative tool to replace or complement ground measurements. Our results indicate that precipitation, temperature, and PDSI were significant (p < 0.05) predictors of J. virginiana and P. ponderosa growth based on dendrochronological measurements and VIs, while soil water content from 40 to 300 cm depth was a significant predictor of J. virginiana performance. Out of the six VIs that were investigated, four were significant predictors of tree ring growth. R2 values between grassland VIs and growing season climate were greater than those of J. virginiana or P. ponderosa, while grassland performance was decoupled from soil water content. Additionally, climatic conditions in the previous year were significant determinants of current year growth of tree species but did not affect current year grassland performance. This study provides evidence for the efficacy of remote sensing-based VIs in monitoring interannual variation in the growth of woody species, while determining abiotic factors impacting the growth of grassland vegetation, J. virginiana, and P. ponderosa in the Nebraska Sandhills.

New sources of biological data supporting environmental history of a tropical forest of south-eastern Brazil

The Tijuca Forest results from a reforestation project executed in the second half of the nineteenth century, with native and exotic species planted in the mountains of Rio de Janeiro, Brazil. Aiming at a theoretical reflection, the use of integrated methodologies from different areas of knowledge was evaluated to expand the research of the environmental history of a tropical forest in south-eastern Brazil, using everything from the search for historical documents to the counting of tree growth rings. It was possible to find some of the trees from the initial reforestation efforts, to circumscribe the locations of the first plantations, hitherto unknown, as well as the original intentions of tree selection: a reflection of the silvicultural model of the period that incorporated the tropical identity of the forest without giving up the market demand. The project area indicates that the planted forest would cover approximately 330 ha, prioritizing restoration by micro basins. In the 33 years analysed, about 155,000 trees were planted (110,000 with success) from a repertoire of at least 107 species, prioritizing the native ones. The quality of the wood, mainly for the naval segment, was prioritized, but other purposes were also met. The model and selection criteria for planting areas and species characterize a strategic plan that foresaw the recovery of water sources simultaneously with the generation of wealth in the medium and long term, diversifying the use of the soil and inaugurating a cycle of silvicultural exploitation in the country. This study re-signifies the understanding of the Tijuca Forest ecology, not only in space but mainly in time, revealing the subtle relationships between tropical nature and society in formation.

Mechanical Behavior and Crack Evolution of Goaf Surrounding Rock with Different Roof-Contacted Filling Rates.

The goaf formed by mining is filled and treated, which greatly improves the safety and stability of the surrounding rock. During the filling process, the roof-contacted filling rates (RCFR) of goaf were closely related to the stability control of the surrounding rock. The influence of the roof-contacted filling rate on the mechanical characteristics and crack propagation of the goaf surrounding rock (GSR) has been studied. Biaxial compression experiments and numerical simulation experiments were conducted on samples under different operating conditions. The results were as follows: (1) The peak stress, peak strain, and elastic modulus of the GSR are closely related to the RCFR and the goaf size; they increase with the increase of the RCFR, and decrease with the increase of the goaf size; (2) In the initial loading stage, a small number of cracks are generated, and the acoustic emission ringing count increases slowly. The mid-loading stage is the crack initiation and rapid expansion, and the cumulative ring count curve shows a "stepwise" growth. In the later loading stage, cracks continue to propagate and form macroscopic fractures, but the number of rings significantly decreases; (3) Shear cracks are prone to occur in the rock part of the GSR; tensile cracks are prone to occur in the backfill; and the crack propagation speed in the rock is faster than in the backfill. Stress concentration is the direct cause of GSR failure. The maximum concentrated stress of rock mass and backfill is 1~2.5 times and 0.17~0.7 times of the peak stress of the GSR, respectively.

Evolution Law of Acoustic–Thermal Effect of Freeze–Thaw Sandstone Failure Based on Coupling of Multivariate Monitoring Information

The instability and failure of rock that has been frozen and thawed cause serious rock engineering accidents in cold regions. Exploring the precursor information of freeze–thaw rock failure is of great theoretical value and engineering significance. Real-time uniaxial compression acoustic thermal monitoring experiments were conducted on freeze–thaw sandstone, and non-contact rock fracture precursor warning indicators were proposed. According to the coupled analysis of acoustic–thermal monitoring information, a precursor information chain for freeze–thaw rocks was established in time and space, and the spatiotemporal evolution of damage and acoustic thermal effects of freeze–thaw sandstone under compressive load was studied. The freeze–thaw cycle enhances the sensitivity of acoustic–thermal precursor information. Significant synchronous changes in ring count often occur during the rapid expansion period of damage, which can provide an essential reference for the occurrence and intensification of damage. The sequence of precursor warning information during the process of freeze–thaw sandstone compression failure is in the order of thermal infrared temperature → acoustic emission ringing count → acoustic emission energy → infrared thermal image. Thermal infrared temperature and acoustic emission precursor information can help in prioritizing early warning of rock damage in terms of time. At the same time, thermal image anomalies can predict potential fracture areas of rocks.