Schistosity Planes Research Articles

Mineralization processes in the Bainaimiao Cu-Au deposit in Inner Mongolia, China: Constraints from geology, geochronology, and mineralogy

The Central Asian Orogenic Belt underwent complex tectonic processes and is one of the most intensely accretionary areas globally. Porphyry copper deposits within the belt were likely subjected to deformation during tectonic processes. The Bainaimiao Cu-Au deposit is a typical example of a deformed porphyry deposit whose formation processes include a porphyry emplacement (Event I), a greenschist facies metamorphism (Event II), and a brittle deformation (Event III). Geochronology and trace element geochemistry of zircon, volatiles of magmatic apatite, along with the assemblages, textures, abundances, and compositions of phyllosilicates from these three events were investigated to unveil the physicochemical conditions under which the key geological events relevant to the deposit formation took place. LA-ICP-MS zircon U-Pb dating shows that the granodiorite porphyry in the northern and southern zones formed at 447.4 ± 1.6 to 445.8 ± 3.6 Ma and 436.1 ± 3.8 to 434.1 ± 3.3 Ma, respectively. The granodiorite porphyry in the northern zone has higher oxygen fugacity and Clmelt content but similar Smelt and Fmelt contents compared to the granodiorite porphyry in the southern zone. Microscopic and mineralogic observations point to Event I to be of high plagioclase (22–67 vol%) and quartz (6–40 vol%) content with a range of hydrothermal minerals related to potassic, phyllic, and propylitic alterations. Event II features high amphibole (38–83 vol%) or epidote-chlorite (up to 77 vol%) content with minerals precipitating along the schistosity planes. Event III is characterized by wide veins (3–80 cm) and the highest quartz (61–65 vol%) and calcite (12–19 vol%) content. Geothermometry results show the temperature of potassic and phyllic alterations of Event I to be ∼622 °C and ∼288 °C, respectively. Based on geothermometry and P-T pseudosections, the temperatures of metamorphism and metallic precipitation of Event II were ∼271–634 °C and 297–328 °C, respectively. Both mechanical and chemical mobilization of metallic elements results in Cu mineralization during Event II. The metallic precipitation temperatures of Event III spanned from 297 to 328 °C according to chlorite geothermometry. The ratios of Fe3+/Fetotal and Mg/(Mg + Fetotal) of biotite, chlorite Fe/(Fe + Mg), and white K-mica composition show the mineralizing fluid of Event III to be the most oxidized while that of Event II is the most reduced, F-rich and features the lowest water/rock ratio. This study suggests that deformation processes can increase the Cu mineralization grade of the deformed porphyry deposits through mobilization and re-precipitation of metallic elements.

Surface flaking mechanism of stone components of ancient building complex in Wudang Mountain, China

Surface flaking, a deterioration pattern widely existing in stone components of the ancient building complex in Wudang Mountain, has significantly compromised its historical value. However, a comprehensive investigation into the mechanisms underlying surface flaking of stone components in this region has not been conducted thus far. This study aims to address this gap by employing a range of techniques, such as X-ray diffraction and scanning electron microscopy, to explore the factors contributing to the observed surface flaking. Petrographic analysis revealed that chlorite schists is widely used in ancient buildings as a natural building material, containing clinochlore, actinolite, albite, muscovite, quartz, and various clay minerals. Comparative analyses of mineral composition and microstructure of the samples exhibiting varying degrees of deterioration suggested that the water–rock interaction played a crucial role in surface flaking. It is proposed that this interaction potentially altered the physicochemical and structural characteristics of the stones through the hydration swelling effect of clay minerals (illite, clinochlore, and vermiculite) and dissolution effect of soluble minerals (muscovite, albite, and zeolite). Consequently, an increase in secondary porosity and a weakening of cohesiveness occurred, leading to a reduction in the overall strength of the stone and eventual flaking along the schistosity plane. Furthermore, this deterioration mechanism was validated by comparing strength and deformation of samples under different dry and wet conditions. The findings of this study will not only guide the comprehensive conservation of the ancient building complex in Wudang Mountain but also provide theoretical and methodological support for the preservation of substantialstone cultural relics located in the high-humidity climate zone of southern China.

Lithostratigraphic analysis and characterization of the upper miocene deformation of the Beni Bou Ifroure massif (Jbel Harcha Unit) eastern Rif Morocco

In the eastern Rif the unit of Jbel Harcha which is part of Beni Bou Ifroure massif, the latter belongs to the Rif chain which was formed during the Alpine orogeny. Lithostratigraphic analysis of the geological map and field investigations shows that this unit is constituted by carbonate facies of limestone attributed to the lower and middle Jurassic. At the level of upper Jurassic and Cretaceous we observe metamorphic terms presented by schists. The structural examination allows to distinguish two types of deformation the first one is penetrative which is materialized by a metamorphism of the formations of upper Jurassic and Cretaceous whose direction of the planes of schistosity varies between N125 and N140. This type is linked to a NE-SW shortening, attributed to the Tortonian and materialized by a set of open and normal faults of direction N040 to N045. The second type is generally characterized by brittle structures presented by dextral strike-slip faults of direction N120 to N140 that intersect the ancient accidents. This episode linked to a N-S to NW-SE shortening is responsible for the N070 thrusting of the Jurassic rocks in the study area.

Petro-structural Evaluation of the Toulepleu-Guéya Section on the Toulepleu-Ity Gold District, West Côte d’Ivoire

The Birimian furrow of Toulépleu-Ity located in the Archaen domain of Côte d'Ivoire is at the heart of various mining projects. Thus, this study is initiated in three localities namely Toulepleu, Zogouiné and Guéya in order to elucidate the petrography and deformations. The data analysis and interpretations undertaken at the University of Man allow to learn deeply this Birimian furrow. Petrographically, two main groups of rocks are identified: (i) magmatic comprising granodiorite, microgranodiorite, tonalite and dolerite, (ii) metamorphic composed of gneissisified granodiorite, metatonalite, metaargilite, metadolerite and various schists (chloritoschists). Argillite is the main sedimentary rock. The metamorphism evolves from greenschist to amphibolite facies overprinted by the chlorite - green hornblende association. Eburnean magmatic event has been ended with the settlement of dolerite which appears metamorphosed and fractured suggesting the reactivation of the Eburnean event. Pervasive hydrothermal alteration is marked by mylonitized quartz veins. Structurally, three main orientations are expressed : N-S, NE-SW and NW-SE. Ductile deformations are observed in schists, metatotalites and metasediments. The schistosity planes have a dip of 44°S. Brittle deformations have a preferential NE-SW orientation and are associated with quartz plus tourmaline veins showing by that their auriferous potentiality. These structures are part of a shearzone of N080° that can serve as a target for gold exploration in the area.

Effectiveness and durability of chemical- and laser-based cleanings of lichen mosaics on schists at archaeological sites

Lichen mosaics on different-textured schists located in the Coa Valley (Portugal) and Siega Verde (Spain) archaeological sites were cleaned using different chemicals, namely ethanol (50% v/v in distilled water), benzalkonium chloride (3% v/v) or Biotin T® (3% v/v), and different Nd:YAG laser wavelengths (1064 nm or 266 nm). The surfaces were evaluated 24 h and 4 years after cleaning to determine its durability using colour spectrophotometry and Raman spectroscopy. Unlike lasers, chemicals achieved overall satisfactory results. Cleaning effectiveness, harmfulness and durability of chemicals were highly influenced by the orientation of the schistosity planes of the stone; in Siega Verde samples, the schistosity planes parallel to the surface contributed to a low impact of the methods on the surface colour and absence of lichen recolonization. Cleaning carried out upon the devitalization of lichens with benzalkonium chloride and Biotin T were maintained longer in both sites.

Characterization of an exhumed high-temperature hydrothermal system and its application for deep geothermal exploration: An example from Terre-de-Haut Island (Guadeloupe archipelago, Lesser Antilles volcanic arc)

We present integrated structural, petrological, mineralogical and geochemical investigations conducted on an exhumed hydrothermal system identified in Terre-de-Haut Island (Guadeloupe archipelago). This work demonstrates, for the first time, the occurrence of ductile shear zones, marked by the development of spaced schistosity planes generated by pressure-solution processes. We unravel first that the development of spaced schistosity is coeval with high-temperature hydrothermalism (approximately 350 °C) and second that this hydrothermal alteration occurred at a depth of less than 2 km. We highlight, at shallow crustal depths, the record of both vertical and lateral fluid pathways in the studied volcanic arc. Finally, combining this new dataset with the large number of published surface data obtained in the active geothermal system of Bouillante, we propose a conceptual scheme for the studied fossil reservoir to document the roots of magmatic arc-related active geothermal systems and to introduce new perspectives for deep geothermal exploration.

Spatial distribution, controlling factors and failure mechanisms of the large-scale landslides in the urban area of Azazga city (northern Algeria)

The city of Azazga is facing extensive and damaging landslide hazard. The aim of this study was to investigate the inventory mapping, the deformation characteristics, the controlling factors and the failure mechanisms of the landslides in the urban area of Azazga based on field surveys, aerial photographs/satellite images interpretation and the exploitation of available data including rainfall database, boreholes, piezometers, inclinometers and laboratory tests. The prepared landslide inventory map indicates that the unstable urban perimeter covers an area of 281.6 ha which represents about 31% of the urban area. Analysis of the inventory data highlighted the action of two types of conditioning factors: (i) susceptibility factors represented by the presence of clay, marl deposits with low mechanical resistance characteristics, the presence of shallow aquifers, the morphology and steep slope, the tectonic features network and a dense hydrographic network; (ii) the triggering factors corresponds to the high intensity rainfall and the uncontrolled human activity. Statistical analysis of the relationship between the landslide occurrence and the landslide-conditioning factors shows that the highest density of landslides occur in quaternary scree and cretaceous clay flysch located on slopes ranging between 5° to 20°. The statistical results indicate that the highest concentration of landslides occurred in the highest rainfall classes ranging between 950 to 1050 mm. Additionally, the results showed the important role of the fluvial incision with more of the landslides occur at a distance of 50 m from the nearest rivers. These data also indicated that the high density of the landslides is concentrated in the farming and urban zones. The inclinometer measurement results reveal a deep rupture surfaces between 4 and 28 m located at the scree–flysch bedrock interface. According to the mechanism modes, landslides are controlled by the following: (i) the dip of the flysch formation layers, the schistosity planes and fractures downward slope direction; and (iii) the interface contact between the quaternary scree and flysch substratum. This work presents an exhaustive understanding of the causes, deformation characteristics and failure mechanisms of the large-scale landslides as a useful information for landslide hazard and risk mitigation.

Kinematic process and mechanism of the two slope failures at Baige Village in the upper reaches of the Jinsha River, China

On Oct. 10 and Nov. 3, 2018, two landslides, i.e., the “10.10” and “11.3” rockslides, occurred successively at Baige Village, Jiangda County, Tibetan Autonomous Region, P. R. China. The two landslides are located in the upper reaches of the Jinsha River and both dammed the river. Immediately since the slides, the authors have been working on the slides and help disaster reduction. Based on the data collected by April 2020, this paper is aimed at clarifying the geological condition of the slides and at explaining why the slides occurred and what the whole sliding process was. Conclusions are summarized as follows. First, the two landslides occurred in the suture belt of the Jinsha River and the rocks are composed of tectonic melange slices of mainly gneiss intermingled with carboniferous slate and marble and with intruded serpentine and granite porphyry. The gneiss generally bears a schistosity plane with an averaged attitude of N47° W/47°, dipping into the slope. Secondly, long-term geomorphological evolution of the bank slope due to river incision contributed to the progressive slope deformation for the development of the “10.10” rockslide. No preferential joints exist in the slope, but alteration and weathering played important roles in its occurrences. Rainfall and earthquakes may also accelerate its deformation. Thirdly, the “10.10” rockslide is of high-speed wedge-like slope failure with a high-position and a high-shear outlet. Its sliding and deposition process demonstrate special features as initial speed, collision between debris, surging waterjet, and second slipping. Fourthly, the whole process of the “10.10” rockslide can be divided into 6 steps, i.e., startup of the major sliding and sliding resistance zones, sliding initiation of the trailing zone, formation of debris-eroded zones, collision of debris and triggering waterjet and mist, secondary slip of the landslide dam, and surface flush in the deposition area. The estimated speed may reach as high as 67 m/s. Fifthly, the “11.3” rockslide follows a different mode, i.e., wedge cleaving effect. And finally, the cracked zones still have the risk to constitute a potential landslide and to dam the river again.

A Modified Engineering Classification Method for Schistose Surrounding Rocks of Tunnel

For schistose surrounding rocks of tunnel, engineering classification of rock masses by the widely used BQ method in China are often inconsistent with the reality. In this study, microtests and uniaxial compression test were performed on three types of quartz mica schist. Microtests reveal that the schist is characterized by natural orientation and interbedded distribution of minerals and microfissures are prone to be distributed directionally along the smooth edge of flaky minerals. Mechanical test shows that the compressive strength of schist samples has U-shaped change with the varied loading direction. Moreover, the strength anisotropy degree of the schist is positively correlated with the development of schistosity planes, and the strength anisotropy increases significantly after saturation. When the direction of uniaxial load applied to the samples changes gradually, the splitting-tensile, shear-slip and shear failure occur respectively, indicating that the dominant factors affecting the strength of schist specimens are not uniform. In particular, the strength of specimens with transverse schistosity planes is less affected by the weak planes. Based on the experimental study, a new model considering the schistosity development degree was constructed, which is served as the evaluation of the basic quality of schistose rock mass. By regression analysis on 168 sets of practical data, an optimized BQ equation was further developed. Then a correction coefficient table was put forward based on numerical simulation, which is helpful to correctly determine the final engineering grade of surrounding rock. Case study shows that the improved BQ method is more reliable for classifying engineering grade of schistose surrounding rock.

Residual lattice strain in quartzites as a potential palaeo-piezometer

SUMMARY If a crystal lattice is subjected to a stress, it becomes distorted and no longer represents the ideal crystal symmetry, and if the stress introduces defects such as dislocations, some of this distortion is preserved after the applied stress is removed. In this study, we investigate lattice distortion in quartz at the micron scale with synchrotron X-ray Laue diffraction. From Laue images the local deviatoric strain tensor is derived and corresponding stresses are calculated based on elastic properties. The method is applied to metasedimentary quartzites from the Bergell Alps that were deformed at conditions of greenschist facies metamorphism. The residual palaeostrain is represented in maps of the deviatoric strain tensor components and with deviatoric strain axis pole figures. Data suggest overall shortening perpendicular to the schistosity plane but with considerable asymmetry relative to foliation and lineation, probably attributed to simple shear. Crystallographic pole figures from Laue diffraction agree with neutron diffraction and EBSD measurements and display quartz c-axes girdle distributions with maxima also perpendicular to schistosity. The method shows promise to be used as a palaeo-piezometer to unravel the stress field during tectonic deformation.

Anisotropy of quartz mica schist based on quantitative extraction of fabric information

In this study, comprehensive laboratory experiments, such as thin-section and optical section analyses and P wave velocity and uniaxial compression tests, are performed on three types of quartz mica schist samples. The thin-section analysis reveals that the schist predominately consists of flaky mica and granular minerals, including quartz, feldspar, and calcite. The two types of minerals, both presenting a certain degree of orientation, are arranged to form a quasi-bedded structure as a whole, which essentially leads to macroscopic physicomechanic anisotropy. By means of optical section observation, directional microfissures are found to mainly be distributed alongside the edge of the oriented mica layer, while defects in other parts exhibit irregular orientation. Moreover, quantitative information is extracted from gray images by Image-Pro Plus (IPP), and then, relevant indicators are proposed to quantitatively analyze the differences in the content, morphology, and distribution characteristics of minerals and defects among the three types of samples. P wave velocity measurements of dry cylindrical specimens with different schistosity angles α show that the minimum value lies in the direction of the transverse schistosity planes (α = 90°) and that the P wave velocity increases with the decrease of the schistosity angle. There is an obvious linear positive correlation between the orientation coefficient of mica, which is adopted to indirectly reflect the orientation degree of microfissure, and the 0.5 power of the velocity anisotropy coefficient. The uniaxial compression test of specimens reveals the anisotropic characteristics of the peak strength, failure mode, and crack initiation and propagation for the schist samples. In particular, with the change of the schistosity angle, the peak strength and crack initiation strength have a U shape, characterized by a minimum value at α = 30° and maximum value at α = 0° or 90°. Directional microfissures and irregular defects with a dominant angle control the crack initiation of the specimens with 0° ≤ α ≤ 45° and 45° < α ≤ 90°, respectively. The weak edge of the directional mica layers has a more or less guiding effect on crack propagation when compressive loading is applied obliquely to the schistosity planes, while crack propagation is independent of weak edges when perpendicular to the planes. Three failure modes occur in the specimens with the change of the schistosity angle: tension-splitting failure, shear-slip failure, and shear failure. It is found that the mechanical anisotropy properties of the schist samples are closely associated with the content, morphology, and distribution characteristics of minerals and defects based on the analyses of the macro- and microquantitative data.

Fracture Analysis of Uranium-Bearing Rock in Eko-Remaja Exploration Tunnel at Depth 50-200 Meters, Kalan, West Kalimantan

Remaja Sector is one of the potential sectors of U mineralization at Kalan Area, West Kalimantan. Host rock of the mineralization is metasiltstone and schistosed metapelite. The 618 meters long Eko-Remaja Exploration Tunnel was built in 1980 to understand the character of uranium ore in this sector. The U mineralization in Kalan, West Kalimantan is influenced by the host rock type and fractures formed by regional tectonic. Regionally, ductile and brittle deformation occurs at Kalan. The ductile deformation observed from N 70o E fold plunging 30o NE that generate schistocity plane dipping 70-80o relatively to the north. First brittle deformation resulting open-mode fractures and schistocity planes that later filled by U-rich solution forming U veins, veinlets and breccia mineralization. Later, brittle deformation forming fractures that filled with calcite-gypsum solution afterwards, forming centimetric-desimetric vein and veinlet cutting the U vein. The purpose of this study is to determine the characteristics and main structure that control the U mineralization in the tunnel. The method is by collecting data of fracture such as joints and fault planes, schistosity planes (S1), and bedding plane (S0) together with its cross-cutting relationship at depth 50 - 200 meter from the tunnel mouth which at this interval representing the presence of mineralization in the Remaja Sector. The data then plotted and analyzed on upper hemisphere stereographic projection. Fracture analysis conducted to understand the families of fractures developed and the force direction resulting fractures the tunnel. From the analysis, the mineralization of U in the tunnel controlled by N 280o E fractures that relatively parallel to the schistocity plane as vein and breccia mineralization and analytical fold axis on Eko-Remaja Tunnel is N 73 E° / 30 tilted to E-NE. Joints in the tunnel mainly affected by faults that formed by couple force.

Structural failure process of schistosity rock under microwave radiation at high temperatures

The effects of high temperature induced by microwave radiation on the schistosity structural rock were investigated. A 1.45 kW commercial microwave system was employed to irradiate specimens to a designed temperature (300–800 °C) for 15 minutes. Cracking and local melting initially appeared in the biotite enrichment area at 500 °C. Macro-cracks in the dark area were parallel to the schistosity trend, owing to the weak connection in a direction perpendicular to the schistosity plane. The composition of the rock did not significantly change before and after microwave radiation. The diffraction peak intensity of the biotite decreased with temperature increase, owing to melting. The average peak stress decreased significantly with increasing temperature. It is concluded that the high temperature induced by microwave radiation promotes hard rock breakage and the schistosity structure of rock significantly affects the cracking pattern.

Investigation of Creep Behaviors of Wudang Mica Schist by Triaxial Compression Tests

Triaxial compression creep tests were conducted on Wudang mica schist samples to clarify the creep anisotropy characteristics. The mica schist samples were divided into parallel group and vertical group according to the angle of axial loading and schistosity plane. The creep tests were set up with step function loading under varied confining pressure conditions. The test results show that mica schist creep have 4 stages: instantaneous deformation stage, decay creep stage, steady creep stage and accelerating creep stage. The deformation is dominated by instantaneous deformation at low levels of stress. Then the creep value continued to increase as the stress grew. In comparison with the vertical group under same confining pressure and similar axial loads, the parallel group presented large instantaneous strain increments and axial creep value, high creep speed and short decay creep time. Experimental results showed that the vertical group was finally destructed in the form of shear fracture and the parallel group was finally destructed in the form of cleavage fracture, which indicated distinct creep anisotropy. A modified burgers creep model was introduced to describe mica schist’s creep characteristics and identify the creep parameters, and the result was proved to be efficient in description of mica schist’s creep features by the fitting results.

Mikaşistlerin deformabilite, modül oranı ve anizotropik davranışlarının belirlenmesi; Burgaz baraj sahasından (İzmir-Türkiye) örnek bir çalışma

Base rock of the Burgaz dam in the eastern part of the city of İzmir consists of micaschists having different physical and mechanical properties due to weathering and fracturing. The first aim is to compute the amount of settlement and ultimate bearing capacity value of micaschist both in and beneath the cutoff zone by using the results of pressuremeter tests. In addition, data from in-situ and some laboratory tests, which were used in the establishment of the relations between elastic modulus of the micaschist rock mass (EM) and uniaxial compressive strength (σc), EM/Eintact ratios and RQD values. Comparison of in-situ and estimated rock mass deformation moduli by considering the RQD values was also performed. Pressuremeter tests indicate that for a dam with 115 m height and a base width of 58 m, the settlement will vary between 2.13 and 2.26 mm. The second aim of this work is to measure compression and shear wave velocities in order to obtain both the ratio of dynamic elastic modulus to Poisson′s ratio (E/v) dynamic and to compare (E/v)dynamic to (E/v)static. Test results reveal a positive linear relation of (E/v) dynamic =(E/v) static0.968. The sonic wave velocity of the micaschist is highly related to the testing direction. This study not only discusses the relationships between Estatic and sonic wave velocity (Vp) and Edynamic, but also the anisotropy effect arisen due to the schistosity planes with different orientations.

ARMR, a new classification system for the rating of anisotropic rock masses

The engineering behavior of rock masses is strongly dependent on anisotropy, which is present at different scales, from the microscale in the intact rock due to the alignment of rock crystals (inherent anisotropy) to the macroscale in rock masses with anisotropic rock structure, characterized by distinct bedding or schistosity planes. This paper presents a new rock mass classification system, Anisotropic Rock Mass Rating (ARMR), specifically developed for the classification of anisotropic rock masses. ARMR considers the following rating parameters: (a) anisotropy strength index, RC; (b) uniaxial compressive strength of intact rock; (c) degree of structure anisotropy; (d) corrected rock quality designation (RQD); (e) condition of anisotropy surfaces; and (f) groundwater conditions. Its use is illustrated and explained by application to specific case studies in anisotropic rock masses, and the advantages and limitations of the classification system are outlined. The strength of anisotropic rock masses is determined using the modified Hoek–Brown criterion (Saroglou and Tsiambaos, Int J Rock Mech Mining Sci 45:223–234, 2008), which is extended to rock masses with the use of ARMR.

Uranium distribution and mobility in the weathering zone of the Nisa deposit, Portugal

The Nisa deposit is the largest known uranium reserve in the country, and is hosted by metasediments of the Beiras Group, in the Alto Alentejo region, central Portugal. After almost two decades without significant studies, the current trend to seek improved knowledge of raw materials motivated the application of different surface geophysical and geochemical characterization methods, which proved to be a valuable exploration approach for this type of deposit. Detailed mapping in the experimental open pit showed the structural aspects controlling the mineralization. A radiometric survey of the deposit was carried out, providing a map of the main sites of mineralization. The U mineralization is of secondary origin, formed exclusively by uranyl phosphates that were formed during the development of a weathering profile. The mineralization occurs along schistosity planes, quartz veinlets and alteration zones, along a general trend N60°–80°W (approximately the same as S0) in association with iron oxyhydroxides, as demonstrated by both petrographic and geochemical data. These hydroxides, in addition to the geochemical characteristics of the host rocks, were key factors in the precipitation and trapping of dissolved uranyl ions.

New methodology for estimating the shear strength of layering in slate by using the Brazilian test

A new method is proposed in order to estimate the shear strength of schistosity planes in slate in terms of Mohr–Coulomb cohesion and internal friction angle. The procedure consists in carrying out the Brazilian method under different loading-foliation angles, for which experimental tests were achieved in slates from the northwest of the Iberian Peninsula (Spain). The experimental fracture patterns were analytically studied and justified by simulating the stress field in the discontinuity planes contained in the whole sample, taking into account the first failure registered in the tests. By combining experimental and analytical studies and a procedure based on the representation of the threshold state of stresses—in the elastic regime—in the failure plane, it is possible to estimate the foliation’s strength envelope through a lineal adjustment according to the Mohr–Coulomb criterion and, thus, to characterize the layering. Finally, the proposed procedure was validated by the direct shear test. The cohesion and the internal friction angle obtained with this convenctional test were very close to that calculated by the proposed method, verifying the methodology developed by the authors. This procedure may be interesting in various engineering applications, either in the study of the properties of cleavage in slate, which is commonly used as an industrial rock, or in dam foundations, underground excavations and slope engineering, since one of the main failures in civil engineering is due to sliding along weak planes.

Mechanical Properties and Deformation and Failure Characteristics of Surrounding Rocks of Tunnels Excavated in Soft Rocks

As soft rocks are likely to soften, slime and swell while contacting water, the existence of soft rocks is harmful for stability of surrounding rocks and supporting structures of tunnels. Through uniaxial and triaxial tests under dry condition and triaxial test with different moisture contents, the mechanical properties and failure modes of soft rocks were studied under conditions that the schistosity plane of the rock samples was vertical to, presented an oblique angle with, and paralleled to the loading direction. The results showed that peak strengths in natural and water-bearing states increased with increasing confining pressures, while those in water-bearing state were 40% lower than those in natural state. The samples were mainly subjected to ductile failure in both natural and water-bearing states while the samples in natural state exhibited a certain brittle failure characteristic in post-peak phase. With the increase of confining pressures, the post-peak curve gradually became gentle after certain brittle failure while the post-peak stresses had an insignificant change. In comparison, the samples in water-bearing state showed significant post-peak disparity, that is, exhibited strong ductile failure characteristic. Moreover, the fitting relationship between triaxial compressive strength and moisture of soft rocks can be expresses as σ 1 = Aω + B (A 0) while that between elasticity modulus and moisture can be expresses as E = Aω + B (A 0).

Geo-stress Characteristics of Schist of Erdaoya Tunnel and Physical Properties of Rock Masses

Erdaoya tunnel in the highway connecting Shiyan (Hubei province) and Manchuan, (Shanxi province) was studied in the study. Various problems occurred in the construction of the tunnel, including large deformation of surrounding rocks, cracks of preliminary supports and secondary linings as well as creeping down and collapse of surrounding rock masses along schistosity planes. In which, the most serious problem was large deformation of surrounding rocks, which not only dramatically delayed the normal construction progress of the tunnel, but also brought a huge challenge for the safety of builders. In order to solve this problem, detailed investigations were made on site in the study to reveal the regional geological, engineering geological and hydrogeological conditions of the tunnel. By conducting geo-stress measurement on site, the characteristics of geo-stress field of Erdaoya tunnel were analyzed from four aspects, including magnitudes of stress, coefficient of lateral pressure, orientation of stress and the relationship between magnitudes of geo-stresses and depths. By applying the DIPS software for interactively analyzing geological locator data, structure characteristics of rock masses were analyzed for preferred structural planes and schistosity planes in the tunnel site. Furthermore, the authors tested the physical and hydrological properties of the rock specimens collected on-site. So various physical properties (density, void fraction, and wave velocity) and water absorption hydrological property of schist were obtained, which provide underlying parameters support for the deformation and support of surrounding rocks of the tunnel.