In case of earthquakes and crustal movement, the concentration of impounding load over a large region of crust can cause disturbances to the stratum. In order to quantitatively investigate crack ...initiation, propagation and coalescence processes of jointed stratum based on thermal variations caused by concentrated load, a series of indentation tests were performed on jointed granite specimens, failure process was respectively recorded by synchronized digital image correlation system and infrared camera. Then, strain and infrared radiation temperature of mixed shear-tensile and tensile conical crack were analyzed. In the initiation process, experimental results indicate that the abnormities in the temperature concentration factors are caused by the frictional-thermal effect for mixed mode crack and the thermoelastic effect for tensile mode crack. Subsequently, in the propagation process, these two cracking types followed newly proposed criteria, namely, the maximum temperature gradient criterion for mixed mode crack and the minimum temperature gradient criterion for tensile mode crack. In addition, the intensity of temperature concentrations in crack initiation stage and coalescence stage are more pronounced than that of crack propagation stage. The new findings from the infrared radiation temperature distributions provide some fundamental references for geophysical prospecting in jointed rock mass.
In rock engineering design, significant advances have occurred in recent years in numerical modelling capability with increasing trends to ever greater use of synthetic rock mass models and discrete ...fracture network (DFN) modelling, but all too often with little comparative improvement in geologic base data. As a consequence, there is even more need that reliable estimates be available of strength and deformation characteristics of the rock masses on which or within which engineering structures are to be created, be it a tunnel, a foundation or a slope. Geological Strength Index (GSI) characterization, linked with Hoek-Brown strength determination as a basis for modelling has been widely adopted by engineers and geologists involved in design and construction of engineering structures. The need for geological definition of rock mass properties required as inputs into numerical analysis, constitutes one of the greatest reasons for application of the GSI chart, allowing characterization of even difficult-to-describe rock masses, including tackling even the most problematic of weak and complex rock masses. Back-analyses of tunnels, slopes and foundation behaviour using GSI and its reliable application in rock engineering designs attest to its reliability. With continuing use worldwide, the GSI system has continued to evolve, but greater understanding is needed in the definition of input constants, for establishing both GSI and intact rock properties. This need for improved evaluation, particularly from a geological perspective, is addressed in this paper. Geological processes of tectonism, weathering and alteration all affect GSI. Evaluation of these factors, which are each critical to proper GSI definition, are analyzed based on real rock mass cases. Suggested ranges in variability of intact rock parameters uniaxial compressive strength σci and material constant mi for common rock masses are presented in the context of a composite new GSI chart. This chart allows selection of appropriate GSI ranges for any specific rock suite. Specific key engineering geological characteristics that differentiate igneous, metamorphic and sedimentary one from each other are highlighted through discussion of various example rock units (including gneisses, granites, ophiolites, limestones, schists, siltstones/mudstones/shales, and molassic and flysch formations). Illustrations are given of how geological differentiation dictates variability in geotechnical properties of most common rock masses.
•GSI permits a wide variety of rock masses to be quantified, enhancing geological logic and reducing geo-uncertainty.•The interaction between GSI and geological processes of tectonism, weathering and alteration are analysed.•GSI system allows the influence of various engineering geological characteristics to be better defined.•Specific key engineering geological characteristics that differentiate various rocks from each other are highlighted.•How geological diversity dictates variability in GSI values and intact rock properties of most common rock units is studied.
The North Tianshan Ocean represents a critical southwestern segment of the Paleo-Asian Ocean and is crucial for understanding accretionary and collisional processes of the southwestern Central Asian ...Orogenic Belt. The Dananhu arc belt, an important porphyry Cu deposit metallogenic belt in the eastern North Tianshan, records Paleozoic episodic magmatism. However, the tectonic affinity and evolution processes of the Dananhu arc belt are still open to debate. Here, geochronology, major and trace elements, and Sr-Nd-Hf isotope compositions for magmatic rocks are conducted to reveal the ages, petrogenesis, and tectonic settings of these magmatic rocks in the Dannanhu arc belt. The Carboniferous dacite (328 Ma) and gneissic granite (310 Ma) show high-K calc-alkaline, enriched in large ion lithophile elements (LILEs; e.g. Rb, Th, and U), depleted in high field strength elements (HFSEs; e.g. Nb, Ta, and Ti), depleted isotopic compositions (εNd(t) = 1.3-3.4; εHt(t) = 0.5-12.5) and juvenile Nd-Hf model ages. Combining these Carboniferous magmatic rocks with the features of high Sr-Ba granitoid and Sr-Nd isotopic decoupling, we suggest that these Carboniferous rocks were probably formed through fractional crystallization of partial melting of mantle wedge that had been metasomatized by melts from subducted sediments in a forearc setting. The early Permian granites (289-276 Ma) show high K
2
O+Na
2
O (6.9-8.9 wt.%), low MgO (0.06-0.15 wt.%) contents, high positive zircon εHt(t) (10.5 to 12.1) and whole-rock εNd(t) (4.4-5.5) values, suggesting that the early Permian granites were derived from juvenile lower crust in a post-collisional setting. Our geochronological and geochemical data, together with published data, reveal that high flux arc magmatism with age peaks at ca. 431 and 332 Ma is consistent with porphyry copper mineralization in the Dananhu arc belt, implying a close genetic relationship. The final closure of the North Tianshan Ocean was constrained to the late Carboniferous and early Permian.
An analytical model for shear behaviour of bolted rock joints Ma, Shuqi; Zhao, Zhiye; Shang, Junlong
International journal of rock mechanics and mining sciences (Oxford, England : 1997),
September 2019, 2019-09-00, 20190901, Volume:
121
Journal Article
Peer reviewed
Open access
Rock bolts have been widely used to reinforce the jointed rock mass. Modelling the mechanical shear behaviors of the bolted rock joints are difficult due to the complex interactions between bolts and ...rock joints. The applied pretension forces combined with the axial loads developed in the bolt act as the normal forces which are applied to the rock joints. However, these combined normal forces are not considered in the existing analytical models. An analytical model is proposed in this study to predict the shear behavior of the bolted rock joints, by taking into account the pretension forces, the axial forces developed in the bolt, the interfacial bond stress between the bolt and grout, and dowel shear loads acting transversely to the bolt axis. The proposed analytical model is able to provide complete curves of the dowel shear loads, axial loads, and the global shear loads as a function of the joint shear displacement. The analytically predicted axial load vs shear displacement curves and the global shear load vs shear displacement curves are verified by available experimental tests. The validation shows that the proposed model has the capacity to predict the global shear load evolution as well as the axial load evolution. The factors such as the pretension forces, the bolt inclination angles, the concrete strength and the rock joint friction are successfully accounted for in the analytical model.
The granite complex in the Maohuo area of Litang County is located in the central and western parts of the Yidun-Shaluri island arc in the Sanjiang area; the intrusion is located in the sand slate of ...the Tumugou Formation in Daocheng District. In this paper, the petrographic analysis of the granodiorite porphyry and biotite monzogranite in the granite complex in the Volcano area is carried out, a systematic study of rock geochemical characteristics and chronology, elucidating the genetic connection between the two in the nature and tectonic background of the source region. Zircon LA-ICP-MS U–Pb dating shows, granodiorite porphyry, medium-coarse-grained biotite monzogranite, the ages of diorite inclusions in biotite monzonitic granites are 220.7 ± 1.3 Ma, 220.4 ± 1.6 Ma, and 219.8 ± 1.4 Ma, three are roughly formed at the same time, and it is a product of late Triassic magmatic activity. Rock geochemical features show that granodiorite porphyry in the granite complex, biotite monzonite granite, scintillation inclusions it has high total alkali, Rb content and relatively low Al
2
O
3
, Sr and other content, has a moderately negative europium anomaly, obvious loss of Ta, Nb, Ti and other high field strength elements, and aluminum saturation index < 1.1 is characterized. Combined with geological data granodiorite porphyry, both biotite monzonitic granites are also I-type granites formed in a typical island-arc environment. Combined with rock geochemical characteristics and U–Pb chronology research results, three should be a set of rock assemblages formed by the evolution of a set of magma melting events. Among them, biotite monzogranite and granodiorite porphyry are the products of homologous magma crystallization and differentiation. The diorite enclaves in the biotite monzogranites are the result of their own evolution when the granitic magma undergoes fusion and immiscibility.
To determine the fracture mechanism of the hard and brittle surrounding rock containing natural cracks, a biaxial compression test was performed on a rhyolite, which was extracted from the deep ...buried Niba Mountain of the expressway in Sichuan Province, China. An inverted U-shaped opening was machined in the specimen to investigate the initiation, propagation and coalescence of cracks around the opening. The fracture modes, tangential strain and principal strain around the opening were monitored and discussed. According to the measured strains in different locations of surrounding rock, the floor was firstly tensile fractured and the roof followed. The “dumbbell-like” compressive strain concentration was found in the sidewall. However, the intense influence region of stress was limited in the shallow rock which was about 0.5r in this experiment, since the deep surrounding rock was in the state of slight compression and tension. Considering the fracture process, “V-shaped” shear wedge was formed to lead to shear slipping under the “dumbbell-like” compressive strain concentration in the sidewall. It indicated that the pre-existing natural cracks in the hard and brittle rock played an important role in consuming strain energy by initiating and propagating during biaxial compression. Slight fracture-induced damage, shear slipping in the sidewall, was occurred instead of common splitting and rockburst. On the basis of the experimental achievements, it was important to strengthen the shallow surrounding rock and prevent the hysteretic failure in the fractured sidewall of the inverted U-shaped opening.
This paper investigates a series of experimental results and numerical simulations employed to estimate the deformation modulus of a stratified rock mass. The deformation modulus of rock mass has a ...significant importance for some applications in engineering geology and geotechnical projects including foundation, slope, and tunnel designs. Deformation modulus of a rock mass can be determined using large scale in-situ tests. This large scale sophisticated in-situ testing equipments are sometimes difficult to install, plus time consuming to be employed in the field. Therefore, this study aims to estimate indirectly the deformation modulus values via empirical methods such as the neural network, neuro fuzzy and genetic programming approaches. A series of analyses have been developed for correlating various relationships between the deformation modulus of rock mass, rock mass rating, rock quality designation, uniaxial compressive strength, and elasticity modulus of intact rock parameters. The performance capacities of proposed models are assessed and found as quite satisfactory. At the completion of a comparative study on the accuracy of models, in the results, it is seen that overall genetic programming models yielded more precise results than neural network and neuro fuzzy models.
•Engineers prefer to determine deformation modulus of rock mass (Em) indirectly.•Estimating the Em using new techniques will help us obtain more realistic Em values.•It is aimed to obtain indirectly more realistic and reliable Em values in this paper.•Artificial neural network, neuro fuzzy and genetic programming methods were used.•The performance of expressions obtained from methods used are quite satisfactory.
The Eslamieh Peninsula in NW Iran exposes Miocene potassic to ultrapotassic volcanic rocks that are often associated with a variety of ultramafic xenoliths. Based on geochemical features, the rocks ...investigated in this study can be subdivided into two main groups: 1) MgO-rich (8.0–13.9 wt%) basic (SiO2 = 46.1–50.9 wt%) rocks, which comprise mafic lamprophyres and pyroxenite xenoliths, and 2) MgO-poor (1.5–6.4 wt%) basic to intermediate (SiO2 = 48.2–61.2 wt%) rocks, mainly consisting of trachytes, felsic lamprophyres, and analcime-bearing tephriphonolites and phonotephrites. Rocks in both groups have variable but generally low Ni (10–115 ppm; mostly <60 ppm) and Cr (6–628 ppm; mostly <200 ppm), and display enrichment in LREE over HREE (e.g., La/Yb = 17–55), with a large overlap between the MgO-rich and MgO-poor types. These features are coupled with enriched LILE/HFSE ratios (e.g., Ba/Nb mostly 16–116), negative Nb-Ta-Ti anomalies and positive Pb peaks in primitive mantle-normalised diagrams (e.g., Nb/Nb* mostly <0.7). Both high-and poor-MgO samples have strongly radiogenic (87Sr/86Sr)i ratios (0.7078–0.7086), (143Nd/144Nd)i below the Chondritic Uniform Reservoir (CHUR) = 0.51235–0.51244, and ɛHfi ranging from −3.1 to −11.1‰, suggesting involvement of a lower continental crust component in their genesis. The major oxide and trace element contents the high-MgO and high-CaO rocks indicate derivation from a subcontinental lithospheric mantle source, variably metasomatised by fluids and melts released by a subducted slab in a mantle wedge. Primitive melts evolved via mafic mineral fractionation and possible assimilation of lower crust, generating the SiO2 higher and CaO-MgO-poorer group. We suggest that small degree partial melting of the enriched mantle sources could have been triggered by Neo-Tethys slab roll-back during the Arabian-Iranian collision.
•Mantle peridotite played a role in the genesis of potassic to ultrapotassic magmas•High-MgO and low-MgO magmas are derived from peridotite and peridotite-melt reactions•Pyroxenite and glimmerite xenoliths were genetically related with mantle sources
•The methods of geological investigation, 3D scanning and CT scanning were adopted.•Natural structures of columnar jointed rock mass were investigated.•P-wave velocities of large scale columnar ...jointed basalt cores were tested.•Relationship between P-wave anisotropy and columnar joint was determined.•Distribution of internal implicit joint and its affect to anisotropy were analyzed.
Researches about the structural characteristics of rock mass are the basis for understanding their failure modes, mechanism properties as well as evaluation of structural stability during the process of excavation. Natural columnar jointed basalt has complex structures and exhibits remarkable anisotropy and size effect. In this study, the observation window method was firstly applied to describe the natural columnar joints and pillar shapes at engineering scale and then the structural characteristics of columnar joints were analyzed. The roughness of columnar joints scanned from large-size rock core obtained at drainage tunnel #1-1 was secondly investigated based on the 3D scanning method. Some techniques, such as field statistical analysis and CT scanning were used to analyse the characteristics of internal implicit joints in columnar jointed basalt. Thirdly, the large scale columnar jointed basalt cores were tested by P-wave, which assisted to investigating the anisotropy of columnar jointed basalt. The experimental and analytical results indicate that, at the engineering scale, natural columnar jointed basalt is heterogeneous, exhibiting the features of mosaic structure and mainly quadrilateral in shape. At the large-size rock core scale, the roughness of columnar joints is low with the value of 5.558. At the basalt column scale, the internal implicit joints are not randomly distributed, instead, showing obvious tendency. The internal implicit joints and columnar joints are important factors contributing to the special failure mode of columnar jointed basalt. At the rock core scale, with increasing angle between the P-wave propagation direction and column, the anisotropy of columnar jointed basalt core gradually increases and the degree of anisotropy is proportional to the number of columnar joints. The internal implicit joints could also affect the P-wave anisotropy of basalt column and the results in this study can provide some references for projects related to columnar jointed rock mass.
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