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.

A geochemical investigation of the free and carbonate-bound organic matter in the clay-sized fraction of argillaceous source rocks and its significance for biogenic interpretation

The molecular composition and biomarker distribution of various occurrences of organic matter in argillaceous source rocks developed in fresh and saline lacustrine environments were revealed by successive treatments of solvent extraction followed by acid hydrolysis using gas chromatography–mass spectrometry. The free fraction obtained by solvent extraction provided abundant geochemical information concerning the sedimentary environment, thermal maturity and biogenic origin, and obvious differences existed between fresh and saline lacustrine source rock samples. Our research results indicate that the carbonate-mineral-bound(CM-bound) fraction released by successive acid hydrolysis could also serve as a significant biogenic indicator, as the bicyclic sesquiterpenoids, indicative of Botryococcus braunii origin, were specifically detected in quite high abundance in the acid-soluble fraction. In addition, the light end hydrocarbons were much better preserved in the acid-soluble fraction, and elemental sulfur was only detected in the CM-bound fraction, suggesting a relatively confined environment for the CM-bound fraction, which thus could preserve additional geochemical information compared to that of the free fraction. The CM-bound fraction also exhibited discernable differences between fresh and saline lacustrine samples. Therefore, it can be concluded that comprehensive analysis of free and CM-bound fractions in the argillaceous source rocks can provide a more authentic and objective interpretation of geologic conditions.

Simulation of coupled THM process in surrounding rock mass of nuclear waste repository in argillaceous formation

To investigate and analyze the thermo-hydro-mechanical(THM) coupling phenomena of a surrounding rock mass in an argillaceous formation, a nuclear waste disposal concept in drifts was represented physically in an in-situ test way. A transversely isotropic model was employed to reproduce the whole test process numerically. Parameters of the rock mass were determined by laboratory and in-situ experiments. Based on the numerical simulation results and in-situ test data, the variation processes of pore water pressure, temperature and deformation of surrounding rock were analyzed. Both the measured data and numerical results reveal that the thermal perturbation is the principal driving force which leads to the variation of pore water pressure and deformations in the surrounding rock. The temperature, pore pressure and deformation of rock mass change rapidly at each initial heating stage with a constant heating power. The temperature field near the heater borehole is relatively steady in the subsequent stages of the heating phase. However, the pore pressure and deformation fields decrease gradually with temperature remaining unchanged condition. It also shows that a transversely isotropic model can reproduce the THM coupling effects generating in the near-field of a nuclear waste repository in an argillaceous formation.

Modeling the complex and long term swelling behavior of argillaceous rocks

The swelling behavior of argillaceous rocks is a complex phenomenon and has been determined using a lot of indexes in the literature. Determining the required modeling indexes that need to be performed requires expensive tests and extensive time in different laboratories. In some of the cases, it is too diffi- cult to find a relation between the effective variables and swelling potential. This paper suggests a method for modeling the time dependent swelling pressure of argillaceous rocks. The trend of short term swelling potential during the first 3 days of the swelling pressure testing is used for modeling the long term swelling pressure of mudstone that is recorded during months. The artificial neural network (ANN) as a power tool is used for modeling this nonlinear and complex behavior. This method enables predicting the swelling potential of argillaceous rocks when the required indexes and also correlation between them is unattainable. This method facilitates the model of all studied samples under a unique formulation.

Mechanical properties and microscopic failure process of exemplary argillaceous interlayer from east China

The landslide disaster caused by the argillaceous interlayer not only destroys buildings,cultivated land,and roads but also seriously endangers human life and safety.This study concerns the mineral composition of selected argillaceous interlayer and their strength characteristics.To study the mineral composition of argillaceous interlayers,8 kinds of samples in the southern Jiangsu region of China were analyzed utilizing X-ray diffraction(XRD).The repeated direct shear strength tests(RDST)were carried out on the undisturbed specimens of the argillaceous interlayer.The results show that the argillaceous interlayer with high content of kaolinite shows ductile failure mode,which means that there is no obvious residual strength in the shear process.The arrangement of mineral particles on the shear surface of the specimens after different shear displacements was observed under the scanning electron microscope(SEM).It was observed that mineral particles on the shear surface showed a more directional arrangement with the increase of shear displacement.Furthermore,the influence of shear direction on the argillaceous interlayer with completely oriented mineral particles was studied through numerical experiments with four shear strength mechanisms proposition proposed.The influence of the mineral arrangement on the action occasion and magnitude of dilatancy component of shear strength is clarified in the shear mechanism.

Source and Enrichment Mechanism of Lithium in the Triassic Argillaceous Marine Sediments from Huangjinkou, Sichuan, China

In the Triassic marine sediments, an obvious enrichment of lithium has been found. The source and enrichment mechanism of lithium is unknown. Here, we report trace and rare earth element and isotope analyses for Triassic sedimentary samples from core ZK601, recovered from the Huangjinkou anticline in the Xuanhan basin. Lithium concentrations from the Leikoupo and Jialingjiang formations are much higher than the average concentrations in the crust of eastern China and in other marine sediments. Lithium concentrations are highest at depths of 3300–3360 m(in argillaceous marine sediments), and Li is positively correlated with Rb, Ga, Zr, Nb and other trace elements. The range of δ^(7)Li values in our samples is consistent with that in other Triassic marine carbonate rocks. Lithium concentrations and isotope ratios are negatively correlated in the argillaceous dolomite samples at depths of 3300–3360 m. We compared the results in this study with trace and rare earth elements in the clay from Sichuan and Chongqing, and propose that the clay in the argillaceous marine evaporites from Huangjinkou formed via the hydrolysis of volcanic ash during Early–Middle Triassic volcanic eruptions into brine basins, during which clay adsorbed Li from the brine and formed Li-rich argillaceous dolomites. The addition and hydrolysis of volcanic ash in the evaporative brine is also related to the formation of a new type of polyhalite.

A thermo-hydro-mechano-chemical formulation for modeling water transport around a ventilated tunnel in an argillaceous rock

Argillaceous rocks are being considered as potential host rocks for deep geological disposal. For the research work in DECOVALEX-2011, 5 participant research teams performed simulations of a labora- tory drying test and a ventilation experiment for Mont Terri underground laboratory built in argillaceous rock formation. Our study starts with establishing a coupled thermo-hydro-mechano-chemical （THMC） processes model to simulate water transport in rock around the ventilated tunnel. Especially in this THMC formulation, a three-phase and two-constituent hydraulic model is introduced to simulate the processes which occur during tunnel ventilation, including desaturation/resaturation in the rock, phase change and air/rock interface, and to explore the Opalinus clay parameter set, It can be found that water content evolution is very sensitive to intrinsic permeability, relative permeability and capillary pressure in clay rock. Water loss from surrounding rock is sensitive to the change of permeability in clay which is induced by excavation damaged zone. Chemical solute transport in the rock near ventilation experiment tunnel is simulated based on the coupled THMC formulation. It can be estimated that chemical osmotic flow has little significance on water flow modeling. Comparisons between simulation results from 5 teams and experimental observations show good agreement. It increases the confidence in modeling and indi- cates that it is a good start for fully THMC understanding of the moisture transportation and mechanical behavior in argillaceous rock.

Evaluation of Risk Sechage-Humidification of a Clay Soil of Algiers： The Case Study of the Argillaceous Marnes

Consecutive differential movements of ground to the dryness and the rehydration of the sols are irregular movements of ground related to the phenomenon of withdrawal-swelling. By risk of withdrawal-swelling, one understands the phenomenon ＂natural＂ likely to occur, with a probability of more or less large occurrence. For the phenomenon of withdrawal-swelling of the argillaceous grounds, one will speak about strong, average or weak risk. This article returns within the framework＇s study of risk withdrawal-swelling or dryness-humidification of the argillaceous Mames of the area of Ouled Fayet and Cheraga of Algiers.

Element Response to the Ancient Lake Information and Its Evolution History of Argillaceous Source Rocks in the Lucaogou Formation in Sangonghe Area of Southern Margin of Junggar Basin

With the analysis of the element geochemistry characteristics, the ancient lake infor- mation evolution history of the argillaceous source rocks in Lucaogou 0~/~＇~） Formation in San- gonghe area is reconstructed. According to the ancient lake information and total organic matter （TOC） characteristics of argillaceous source rocks, the study section is divided into 6 Subsec- tions. Subsection I mainly developed low-quality source rocks. This is because of the arid climate, high salinity, low lake productivity, unstable preservation conditions in this Subsection. Subsection II mainly developed high-quality source rocks. This is because of the humid climate, low salinity, high lake productivity, stable preservation conditions in this Subsection. Though the paleoclimate was humid and preservation conditions were stable. Lake productivity and the water salinity changed frequently. So Subsection III mainly developed medium-quality source rocks. Because of the humid climate, high lake productivity, medium sedimentary rate and stable preservation conditions, high-quality source rocks were developed in Subsection IV. The preservation conditions were stable, but other ancient lake information changed frequently. Therefore, the quality of the formed source rocks in Subsection V was different. Subsection VI mainly developed high-quality source rocks be- cause of the humid climate, medium sedimentary rate, high lake productivity, low salinity and good preservation conditions. In summary, the ancient lake information parameters and TOC characteris- tics of each Subsection are different from each other.

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.

Discovery of shale oil in alkaline lacustrine basins:The Late Paleozoic Fengcheng Formation,Mahu Sag,Junggar Basin,China

A new type of shale oil in alkaline lacustrine sediments has been discovered in the Late Paleozoic Fengcheng Formation,Mahu Sag,Junggar Basin,China.The fine-grained sedimentary rocks deposited in this alkaline lacustrine environment can be divided into four types and eight sub-types:mudstone(with no alkali minerals),including massive dolomitic mudstone,and massive and laminated calcareous mudstone;dolomite,including massive argillaceous dolomite(with alkali minerals),and massive and laminated argillaceous dolomite(with no alkali minerals);evaporites;and pyroclastic rocks.The massive argillaceous dolomite(with alkali minerals)and pyroclastic rocks have the highest shale oil potential,with average oil saturation index(OSI)values of 344.67 and 124.65 mg HC/g TOC,respectively.Shale oil exploration in the representative well MY1 indicates that the Fengcheng Formation is thick and contains abundant natural fractures,brittle minerals,and mobile oil.The entire Fengcheng Formation is oilbearing and contains three concentrated stratigraphic intervals of shale oil(i.e.,sweet spots).Well MY1 indicates that,compared with source rocks developed in marine and sulfate-type saline basins,the fine-grained sedimentary rocks deposited in alkaline lacustrine environments can also have high shale oil potential.The co-existence and regular distribution of conventional and unconventional reservoirs in the Fengcheng Formation indicate that it is an ideal exploration target for multiple resource types.

The Origin of Bedded Cherts of the Early Permian Gufeng Formation in the Lower Yangtze Area, Eastern China

Bedded cherts occurring in the Early Permian Gufeng Formation in the Lower Yangtze region, eastern China, are nearly 20-80 m in thickness and contain varying amounts of radiolarians and sponge spicules. There are three types of section for the Gufeng Formation: chert, carbonate and chert-carbonate mixing types. Bedded cherts mainly occur in the first and third types of section. The depocentres of silica are marked by some small (not larger than a few thousand square kilometres in area) rhombic or elliptic hollows and their formation was controlled by faults. Argillaceous volcanic rocks in cherts occur as numerous thin layers. Bedded cherts are characterized by higher Fe and lower Al contents, enrichment in such trace elements as As, Sb, Bi, Ga, Au, Ag and Cr, lower total REE abundance, negative Ce anomaly and varying degrees of HREE enrichment. These characteristics are important evidence for hydrothermal cherts. Minor amounts of substances of non-hydrothermal origin are mixed in the cherts. The temperatures of sea water range approximately from a few tens of degrees to over 160℃. during the deposition of siliceous sediments.

Geophysical and Geotechnical Investigations of a Landslide in Kekem Area, Western Cameroon

Geophysical and geotechnical surveys were conducted in the Western Cameroon (Kekem area) following a landslide on argillaceous material in order to understand the triggering processes and mechanisms of this landslide and to assess the stability of the slope. The geophysical soundings consisting of vertical electrical soundings with the Schlumberger electrode array configuration were carried out to monitor the behaviour of electrical resistivity in the landslide. Geoelectrical data showed a zone of low resistivity values identified as a clayey sand-filled aquifer. This aquifer played an important role in the triggering process of the landslide. Geotechnical soundings showed that the aquifer had a thickness of 7.0 m. The depth from the landslide crest level to the failure surface reached 3.0 m and 20.6 m. Laboratory tests were then carried out in order to evaluate the cohesion of the soil and the angle of internal friction, and to calculate the safety factor in view of making a stability analysis. The laboratory results exhibited a soil with low consistency, almost doughy. The mean value of the safety factor (1.4) been lower than the slope stability coefficient (1.5), revealed that the slope is unstable, likely to know at any moment a reactivation of the slide. This study showed that electrical soundings coupled with geotechnical surveys are useful tools for the characterization of landslides.

Types, distribution and play targets of Lower Cretaceous tight oil in Jiuquan Basin, NW China

Based on drilling and laboratory data, the formation conditions of tight oil reservoirs in the Jiuquan basin were comprehensively analyzed and the exploration domains were sorted out. The Jiuquan basin underwent three cycles of lake level fluctuation in early Cretaceous, leaving three sets of high-quality source rocks, the Zhonggou, Xiagou and Chijinbao Formations in the Lower Cretaceous. There are two types of reservoir assemblages, source-reservoir in one type and source below reservoir type, and two types of tight reservoirs, argillaceous dolomite and conglomerate. The "sweet spots" control the enrichment of oil and gas. Argillaceous dolomite tight oil reservoirs have the characteristic of "integrated source-reservoir", with fractures connecting the matrix micro-pores, pore-fracture type and fracture-pore type "sweet spots" distributed in large scale. The sandy conglomerate tight oil reservoirs were formed by source-reservoir lateral connection, and can be divided into source below reservoir type, source-reservoir side by side type and "sandwich" type. The overlapping areas of the favorable facies belts of fan-delta front and the secondary pore developing belts are the "sweet spot" sites. The favorable areas for seeking conglomerate tight oil are fan-delta front deposits around the Qingxi, Ying'er and Huahai sags, with an exploration area of 550 km^2; while the area to seek argillaceous dolomite tight oil is the NW fracture developed belt in Qingxi sag, with an exploration area of 100 km^2.

Hydro-mechanical fault reactivation modeling based on elasto-plasticity with embedded weakness planes

In this paper,an elasto-plastic constitutive model is employed to capture the shear failure that may occur in a rock mass presenting mechanical discontinuities,such as faults,fractures,bedding planes or other planar weak structures.The failure may occur in two modes:a sliding failure on the weak plane or an intrinsic failure of the rock mass.The rock matrix is expected to behave elastically or fail in a brittle manner,being represented by a non-associated Mohr-Coulomb behavior,while the sliding failure is represented by the evaluation of the Coulomb criterion on an explicitly defined plane.Failure may furthermore affect the hydraulic properties of the rock mass:the shearing of the weakness plane may create a transmissive fluid pathway.Verification of the mechanical submodel is conducted by comparison with an analytical solution,while the coupled hydro-mechanical behavior is validated with field data and will be applied within a model and code validation initiative.The work presented here aims at documenting the progress in code development,while accurate match of the field data with the numerical results is current work in progress.

Meuse/Haute-Marne centre:next steps towards a deep disposal facility

This paper presents the main results obtained during a decade of scientific activities in the Meuse/Haute-Marne Underground Research Laboratory （URL） located on the eastern boundary of the Paris Basin, in the Callovo-Oxfordian clay rock formation. The URL was built in the framework of ANDRA＇s research program into the feasibility of a reversible deep geological disposal of high-level and intermediate-level long-lived radioactive （HL, ILLL） waste. Its underground drifts have been used to study a 160-million-year old clay layer. The 2006 Planning Act adopted this disposal concept as the reference solution for the long-term management of HL and ILLL radioactive waste. Today, research is continuing into the design and sitting of the disposal facility which could be commissioned by 2025 if its license is granted in 2016. Through these programs, the laboratory will help ANDRA develop a concrete approach with a view to proposing suitable architectures and management methods for a deep disposal facility, to allow by 2016 the decision for the start of the construction of the shafts and drifts of the new disposal facility.

A Sand Control System for Light Oil Reservoir

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A Fine Investigation on Geological Conditions for Oil Accumulation in the Paleogene Intersalt Shale Series in the Qianjiang Depression

This study dealt with the rhythmic Qian 3410 of the intersalt shale series in the Qianjiang Depression,in which the geological condition for oil accumulation in the rhythmic shale was investigated by using the basic drilling,core and well logging data,as well as data obtained from the thin section identification,SEM,mercury injection,X-ray diffraction and rock freezing heat analyses.The study result indicated that:1)the intersalt shale series are characterized by TOC in a range of 0.35%-6.38%(averaging 3.19%),Types I and II1 organic matter,and from immature to mature oil,indicative of a potential for generating a great volume of immature oil;2)in the target layer,mineral compositions are complicated,which can divide into argillaceous dolomite facies,argillaceous limestone facies,dolomitic mudstone facies,and calcium-mirabilite-filling dolomitic mudstone facies;and 3)of them,the argillaceous dolomite facies is the most contributory,with reservoir spaces consisting of intergranular pores as dominant,as well as rare dissolution pores and seams.It is characterized by high organic abundance(4.23%-6.38%),high content of brittle mineral(50%-71%),low content of clay mineral(18%-33%),high porosity(10.8%-26.3%)and good oil-bearing properties(S1 distributed in 3.48-5.64 mg/g,and S1/TOC value in a range of 348-564 oil mg/g).Therefore,the argillaceous dolomite facies was considered the key target series to be explored for the intersalt shale oil in the study area in the coming days.

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.

Seismic event, sequence and tectonic significance in Canglangpu Stage in Paleo-Tanlu Fault Zone

The Canglangpu Stage of Lower Cambrian Series is widely distributed along both sides of the Tanlu (Tancheng-Lujiang) Fault Zone in the Jiao-Liao-Xu-Huai regions. In the Liaodong Peninsula, the Canglangpu Stage consists of three formations, i.e. Gejiatun, Dalinzi and Jianchang formations in ascending order (lying on the eastern side of the Tanlu Fault Zone). The Dalinzi Formation, developing in a littoral Sabkha environment, is full of catastrophic event records of violent seism, such as liquefied muddy-sandy veins, hydroplastic folds, hydroplastic micro-faults (three forming an organic whole), liquefied crinkled deformations, liquefied breccia and sandy dikes. Based on such records, the seismic liquified sequence of argillaceous rocks in Sabkha is built up. In northern Jiangsu and Anhui provinces, however, there hardly observe seismic records in the Canglangpu Stage, which consists of Jinshanzhai and lower Gouhou and upper Gouhou formations (lying on the western side of the Tanlu Fault Zone). Even if the Gouhou Formation, developing in a lagoon-dry environment, is in the same climate zone as the Dalinzi Formation, and 4 depositional sequences have been identified in the Canglangpu Stage in Northern Jiangsu and Anhui provinces, however, in the same stage in the Liaodong Peninsula, there exist only 3 ones. Therefore, it is not supported by the above mentioned evidence (such as catastrophic events, sequences stratigraphy and lithologic correlation of formations) that the Canglangpu Stage in the Liaodong Peninsula came from northern Jiangsu and Anhui provinces through a long-distance, about hundreds kilometers, left-hand displacement of the Tanlu Fault in the Mesozoic era.