Failure mechanism and infrared radiation characteristic of hard siltstone induced by stratification effect

The deformation in sedimentary rock induced by train loads has potential threat to the safe operation of tunnels. This study investigated the influence of stratification structure on the infrared radiation and temporal damage mechanism of hard siltstone. The uniaxial compression tests, coupled with acoustic emission(AE) and infrared radiation temperature(IRT) were conducted on siltstones with different stratification effects. The results revealed that the stratigraphic structure significantly affects the stress-strain response and strength degradation characteristics. The mechanical parameters exhibit anisotropy characteristics, and the stratification effect exhibits a negative correlation with the cracking stress and peak stress. The failure modes caused by the stratification effect show remarkable anisotropic features, including splitting failure(Ⅰ: 0°-22.50°, Ⅱ: 90°), composite failure(45°), and shearing failure(67.50°). The AE temporal sequences demonstrate a stepwise response characteristic to the loading stress level. The AE intensity indicates that the stress sensitivity of shearing failure and composite failure is generally greater than that of splitting failure. The IRT field has spatiotemporal migration and progressive dissimilation with stress loading and its dissimilation degree increases under higher stress levels. The stronger the stratification effect, the greater the dissimilation degree of the IRT field. The abnormal characteristic points of average infrared radiation temperature(AIRT) variance at local stress drop and peak stress can be used as early and late precursors to identify fracture instability. Theoretical analysis shows that the competitive relationship between compaction strengthening and fracturing damage intensifies the dissimilation of the infrared thermal field for an increasing stress level. The present study provides a theoretical reference for disaster warnings in hard sedimentary rock mass.

Composition and Provenance of Sandstones and Siltstones in Paleogene,Huimin Depression,Bohai Bay Basin,Eastern China

This study was conducted to distinguish the compositions and provenance of sandstones and siltstones in the Ek1-Es3 members of Huimin （惠民） depression. The samples have been analyzed for petrographic, major element and selected trace element compositions （including REE）. The results show that the sandstones from the first member of Kongdian （孔店） Formation （Ek1） have higher quartz compositions than those from the fourth member （Es4） and the third member （Es3） of Shahejie （沙河街） Formation. The alkali feldspar/plagioclase ratio in the A-CN-K diagrams decreases in the order Ek1〉Es4〉Es3, which suggests that the Ek1 member had a more alkali feldspar-rich granitoid source and more intense weathering of the source than the Es4 and Es3 members. The mineral distributions in the A-CN-K diagrams also indicate that the sandstones and siltstones in the three members underwent K-metasomatism. Extrapolation of the sandstones and siltstones back to the plagioclase-alkali feldspar line in the A-CN-K diagram suggests a high average plagioclase to alkali feldspar ratio in the provenance （tonalite to granite）. In addition, the chemical index of weathering （CIW） and chemical index of alteration （CIA） parameters of the sandstones and siltstones suggest that the weathering of the first cycle material was intense, and the CIW decreases in the order Ek1〉Es4〉Es3 Trace element ratios suggest all the sedimentary rocks were mostly derived from granitoids. Elemental ratio plots （e.g., Th/Sc vs. Eu/Eu^＊） of sandstones and siltstones suggest a mix of a granodiorite-tonalite source as a source of the sandstones and siltstones. The sandstones and siltstones of Es3 and Es4 members also contain higher Eu/Eu＊ and lower Th/Sc ratios than the sandstones and siltstones of Ek1 member. As is consistent with the petrography, it suggests that the sandstones and siltstones of Es3 and Es4 members are derived from a source with less granite and more granodiorite-tonalite than the sandstones and siltstones of Ek1 member.

Design,construction and mechanical behavior of relics of complete large Longyou rock caverns carved in argillaceous siltstone ground

This paper presents a comprehensive summary of data, analyses and findings from the investigations over the past twelve years about the relics of large Longyou rock caverns carved about 2 000 years ago at shallow depths in argillaceous siltstone. The paper presents the typical features associated with the rock caverns. They include structures, large spans, portals, extreme shallow-buried depths, imprints, drainages, inclined ceiling, inclined sidewalls, slender rock pillars, rock staircases, site and strata selections, caving lighting, carving method, and underground construction surveying. They are used to reconstruct and highlight the design and construction methods adopted by the ancients. The paper further demonstrates that the relics of the complete large rock caverns are a consequence of coincidental combinations of ancient human effort and natural factors. The full occupation of water with weak acidity in the large rock caverns with the soft surrounding rocks of weak alkalinity is found to be the main factor ensuring and preserving the caverns to have been stable and integral over 2 000 years. However, the five unwatered complete rock cavern relics have been experiencing various deteriorations and small failures including cracks, seepage, small rock falls and delaminating ceiling rocks. Although these deteriorations have been repaired and stabilized effectively, the paper demonstrates that an entire roof collapse failure is highly possible in the near future to each of the five unwatered rock cavern relics. The findings presented in this paper are also invaluable both to the long-term protection and preservation of the large rock cavern relics of national and international interests and importance, and to extend and enrich our experience and knowledge on the long-term stability and integrity of man-made underground rock cavern engineering projects.

The Firstly Discovered Cosmic Spherules in Carbonaceous Siltstone from the Taizi Formation of the Mesoproterozoic Shennongjia Group,Central China

Objective Spherical micro-particles are often preserved in Precambrian sedimentary rocks. Finnish and Chinese scholars have previously discovered carbonaceous, siliceous or ferruginous spherules of out-space origin in the 1.6 Ga and 1.4 Ga sequence, respectively. The presence of spherules can record possible cosmic impact events. Also, cosmic spherules provide important information on the evolution of planets from outer space.

Siltstone Geochemical Compositions: Applications for Event Size and Correlation

Thinly laminated siltstone and sandy siltstone are major components of the Upper Permian Brushy Canyon Formation, west Texas and south New Mexico. These rocks have been variously interpreted as the deposits of low-density turbidity currents or as windblown sediment deposited over water. Nevertheless, all models agreed that this lithology was deposited without subsequent reworking by bottom currents or burrowing organisms. These siltstones, thus, are ideal test units for quantitatively estimating hydraulic properties of the flows that formed them. In particular, the Zr/Ti ratio was tested as a geochemical proxy for flow size and transport distance. In situ geochemical abundance and grain size of particles with contrasting susceptibility to erosion—Zr- and Ti-rich particles—were mapped and measured by X-ray fluorescence analytical microscopy, μXRF. Lamination thickness was measured from Fe fluorescence intensity, which increased sharply at the top of each layer. Within the same sample, zircon grains were systematically finer than rutilated quartz grains. Zr/Ti fluorescence ratio positively correlated with lamination thickness, not particle sizes. In other words, Zr/Ti fluorescence ratio fluctuations resulted from variations in mineral abundance. Therefore, variations of Zr/Ti fluorescence ratio in these siltstones are likely caused by fluctuations in the intensity of erosional events rather than transport distance. High Zr/Ti ratios and thick laminations reflect periods of enhanced erosion. The average wind velocity during typical events was estimated to be at least 150 km?hr?1, or the equivalent of a Category 1 hurricane. The method used here could be applied to both outcrop and subsurface strata correlation.

A hypothesis for crack free interior surfaces of Longyou caverns caved in argillaceous siltstone 2000 years ago

Five complete caverns were discovered in Longyou in 1992.They were manually caved in argillaceous siltstone at shallow depths more than 2000 years ago.When they were un-watered,their integrity was maintained completely,and their interior rock surfaces were free of old cracks.Since then,however,the rock's interior faces have initiated and propagated more and more cracks.This paper attempts to address the question of why the rock interior faces were free of old cracks once they were unearthed.To address this question,this paper proposes a hypothesis that the argillaceous siltstone has the ability of self-healing its cracks over a short period of time under weak acid water environment.Data and evidence are presented herewith to prove the hypothesis.They include observations and measurements in the field and test results in the laboratory.Specifically,a three-point bending test is used to form a tensile crack in a rectangular rock specimen and a deadload test for the specimen immersed in initially weak acid water is used for self-healing its crack.The results have shown that the argillaceous siltstone is in a state of weak alkalinity and the rain water at the site is in a state of weak acidity.Therefore,when it is immersed in weak acid water for some time,the argillaceous siltstone would be able to make chemical reactions to generate new minerals such as calcite.The new minerals would be able to infill the cracks and then heal the crack within a few years.Once the crack is self-healed,the rock can regain its strength and integrity.Consequently,the rock interior surfaces could be free of old cracks when the water was pumped out of the caverns.

Clogging of slurry-shield tunnel-boring machine drives in sedimentary soft rock:A case study

This paper presents a case study of the clogging of a slurry-shield tunnel-boring machine(TBM)experienced during tunnel operations in clay-rich argillaceous siltstones under the Ganjiang River,China.The clogging experienced during tunneling was due to special geological conditions,which had a considerably negative impact on the slurry-shield TBM tunneling performance.In this case study,the effect of clogging on the slurry-shield TBM tunneling performance(e.g.,advance speed,thrust,torque,and penetration per revolution)was fully investigated.The potential for clogging during tunnel operations in argillaceous siltstone was estimated using an existing empirical classification chart.Many improvement measures have been proposed to mitigate the clogging potential of two slurry-shield TBMs during tunneling,such as the use of an optimum cutting wheel,a replacement cutting tool,improvements to the circulation flushing system and slurry properties,mixed support integrating slurry,and compressed air to support the excavation face.The mechanisms and potential causes of clogging are explained in detail,and the contributions of these mitigation measures to tunneling performance are discussed.By investigating the actual operational parameters of the slurry-shield TBMs,these mitigation measures were proven to be effective in mitigating the clogging potential of slurry-shield TBMs.This case study provides valuable information for slurry-shield TBMs involving tunneling in clay-rich sedimentary rocks.

An Improved Method of Laser Particle Size Analysis and Its Applications in Identification of Lacustrine Tempestite and Beach Bar：An Example from the Dongying Depression

Grain size analysis is a common method in the study of sedimentology. For the consolidated sedimentary rocks, the traditional methods are rock slice observation and image analysis. In recent years, laser particle size analyzer is used widely in particle size analysis of sedimentary rock. Unlike the pretreatment of loose samples, the rock samples must be crushed, added acid to wipe out cement, and washed. However, in the step of washing, most of the fines component（less than 63 μm） in the suspended state should be inevitably lost. It will significantly affect the accuracy of particle size analysis, especially for siltstone. This paper presents a siltstone sample pretreatment method which core step is washing acid by centrifuge. Compared with traditional decantation method, the results show that the median particle size reduced 33.2 μm on average. Compared with the precipitation method which is commonly used for handling loose samples, the change of solid-liquid separation time is from 12 h to 10 min, while the average reduction of median particle size is about 15 μm. The grain size value corresponded to the cumulative volume of 10%/90% reduced 2.5 μm/20.3 μm on average. The percentage of the clay component less than 2 μm increased 2.88% on average. The fine particle（2–4 μm） and silt component（4–63 μm） increased 1.71% and 5.56% on average. Based on this method, two kinds of similar lacustrine siltstone were analyzed. They are tempestite and beach bar which are difficult to identify in the Lijin sub-depression, Dongying depression, Shengli oilfield, China. The final grain-size probability plot of tempestite is the type of “one saltation component and three suspension components”. The content of suspension components can reach to 80%–90%. The beach bar is the type of “one saltation component and two suspension components”. The content of suspension components can reach to 40%–45%. They both have the characteristics of high slope which means well sorting. But they can be distinguished based on the suspension sedimentary characteristics which were preserved by maximum degree in this kind of sample pretreatment method.

Control of favorable lithology on Jinlongshan micro-fine disseminated gold deposits, southern Qinling Mountains

Jinlongshan gold orebelt, a newly discovered one in sedimentary rock region in southern Qinling Mountains, is mainly located in upper Devonian and lower Carboniferous calcareous siltstone and argillic silty limestone of later Paleozoic era. Typical disseminated gold mineralization occurred in calcareous siltstone, which is major host rock and mainly composed of silt (SiO2 mostly varies from 38% to 73%) and calcite (CaO mostly varies from 10% to 25%). Pyrite created by living beings in Nanyangshan formation may be poor in gold. Faults and favorable layers jointly control disseminated gold mineralization. The significance of this opinion is very great for gold exploration.