Poor fragmentation is one of the most side effects induced by blasting operations. Therefore, risk assessment and prediction of rock fragmentation are essential to reduce the mentioned effects. In ...the present study, an attempt has been made to evaluate the risk associated with rock fragmentation as well as its prediction at Sarcheshmeh copper mine, Iran, proposing the rock engineering system (RES) technique. A total number of 52 blasting events were collected and considered and the values of 10 key effective parameters in rock fragmentation were carefully measured in the mine. These 10 key parameters were only related to blasting design and rock mass properties were not considered in the analysis of this study due to some limitations regarding their measurements in the mine. The RES result showed that the level of overall risk, based on the considered blast events, is in the range of medium–high. Furthermore, it was found that the burden is the most interaction factor in the rock fragmentation. In case of rock fragmentation prediction, all of datasets were divided randomly to training and testing datasets for proposing RES model. For comparison purpose, non-linear multiple regression (NLMR) was also employed for estimating rock fragmentation. The performances of the proposed predictive models were examined according to three performance indices, i.e. coefficient of determination (
R
2
), root mean square error (RMSE) and variance account for (VAF). The obtained results of this study indicated that the RES is a reliable method to predict rock fragmentation with a higher degree of accuracy in comparison to NLMR model. For instance, RMSE values of 1.95 and 4.002 for testing datasets of RES and NLMR models, respectively, suggest the superiority of the RES model in predicting rock fragmentation compared to other developed model.
A micro-mechanical based numerical manifold method (NMM) is proposed in this study to investigate the micro-mechanisms underlying rock macroscopic response and fracture processes. The Voronoi ...tessellation technique is adopted to create randomly-sized polygonal rock micro-grains. A rock micro-grain based broken criterion is proposed and a corresponding grain breaking technique is developed. To better represent the contact behavior of rock grain bonds, a cohesive fracture model that considers tensile, shear and compressive behaviors together, is adopted to interpret the failure of rock grain bonds. The developed program is first validated by reproducing biaxial tests of Transjurane sandstone. Finally, the influences of micro-parameters on the rock macroscopic response and failure modes are investigated. The results show that the developed micro-based model can mimic the deformation and failure characteristics of the test closely. A parameter study shows that the grain contact cohesion has significant effects on the model uniaxial compressive strength. The fracture process and failure mode of rock are dependent on the ratio of grain contact shear stiffness to normal stiffness. With the increase of the contact stiffness ratio, the failure mode of rock under uniaxial compression changes from a diffuse pattern to a concentrated shear band.
•A micro-mechanical based NMM is proposed.•Voronoi tessellation technique is used to create the polygonal rock grains.•A rock micro-grain based broken criterion is proposed.•A cohesive fracture model is adopted to model the failure of rock grain bonds.•Influences of micro-parameters on rock macroscopic response are studied.
Pillar burst is one type of rockburst that occurs in underground mines. Simulating the stress change and obtaining insight into the pillar burst phenomenon under laboratory conditions are essential ...for studying the rock behavior during pillar burst in situ. To study the failure mechanism, a novel experimental technique was proposed and a series of tests were conducted on some granite specimens using a true-triaxial strainburst test system. Acoustic emission (AE) sensors were used to monitor the rock fracturing process. The damage evolution process was investigated using techniques such as macro and micro fracture characteristics observation, AE energy evolution, and
b
value analysis and fractal dimension analysis of cracks on fragments. The obtained results indicate that stepped loading and unloading simulated the pillar burst phenomenon well. Four deformation stages are divided as initial stress state, unloading step I, unloading step II, and final burst. It is observed that AE energy has a sharp increase at the initial stress state, accumulates slowly at unloading steps I and II, and increases dramatically at peak stress. Meanwhile, the mean
b
values fluctuate around 3.50 for the first three deformation stages and then decrease to 2.86 at the final stage, indicating the generation of a large amount of macro fractures. Before the test, the fractal dimension values are discrete and mainly vary between 1.10 and 1.25, whereas after failure the values concentrate around 1.25–1.35.
A series of benched excavations were typically carried out on the bedrock slope surface to improve the stability of the soil–rock mixture (S–RM) fill slope. It is difficult to devise an in situ, ...large-scale direct shear test for the interphase between the S–RM fill and the benched bedrock slope surface. This study introduced a comprehensive approach to investigate the shear deformation and strength of the interphase. First the soil–rock distribution characteristics were analyzed by test pitting, image analysis, and sieve test. Then the PFC2D random structure models with different rock block size distributions were built, and large-scale numerical shear tests for the interphase were performed after calibrating model parameters through laboratory tests. The stress evolution, damage evolution and failure, deformation localization (based on a principle proposed in this paper), rotation of rock blocks, and shear strength were systematically investigated. It was found that as the rock block proportion and rock block size (rock block proportion of 50 %) increase, the fluctuations of the post-peak shear stress–displacement curves of the interphase become more obvious, and the shear band/localized failure path network becomes wider. Generally, smaller rock blocks are of greater rotation angles in the shear band. The peak shear stress and internal friction angle of the interphase increase, while the cohesion decreases with growth of the rock block proportion. However, all these three parameters increase as the rock block size (rock block proportion of 50 %) increases.
Deep and ultra-deep resources extraction has resulted in the challenge of drilling into high-pressure, high-temperature (HPHT) environments. Drilling challenges at such extreme conditions prompted ...NETL to develop a specialized ultra-deep drilling simulator (UDS) for investigating drill behavior in such conditions. Using the UDS apparatus, complex laboratory tests were performed on Carthage marble (Warsaw limestone) and Crab Orchard sandstone, which represent the rocks in the basins of the Tuscaloosa trend in southern Louisiana and the Arbuckle play in Oklahoma and North Texas. Additionally, numerical models of the UDS were developed for performing parametric analyses that would be impossible with the UDS alone. Subsequently, it was found that the input properties for these two rock types at such extreme pressure and temperature conditions were unavailable. Therefore, a suite of unconfined compressive strength, indirect tensile strength, and triaxial compression tests (
σ
1
>
σ
2
=
σ
3
) were performed on Carthage marble and Crab Orchard sandstone for investigating their behavior in HPHT environments. The HPHT experiments were performed at confining pressures ranging from atmospheric to 200 MPa, and with temperatures ranging from 25 to 180 °C. The influences of confining pressure and temperature on the mechanical properties of two rocks were investigated.
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.
The static and dynamic failure processes of hard rocks were simulated by compression tests to investigate the precursors of hard rock instability. In the tests, acoustic emission (AE) signals were ...acquired, and their clustering features were automatically extracted by the clustering unsupervised learning method. The results showed that a class of AE signals featured ‘high rise time, high ring count, high energy and low peak frequency and low quantity’ precede hard rock instability and can be used as an indicative precursor feature of hard rock instability. In addition, this class of signals can be used to predict the instability mode of hard rocks after occurrence of the slabbing failure phenomenon: the hard rocks eventually will experience spalling instability if the AE signals occur intermittently and tensile failure signals dominate; or rockburst instability if the AE signals occur continuously and shear failure signals dominate.
•Unsupervised learning method was used to extract the features of AE signals.•The cluster analysis of AE signals reveals the precursor signal's characteristics.•The precursor signal can be used as precursory indication of rock instability.•Two rock instability modes of rockburst & spalling can be predicted by clustering.
The Permo-Triassic adakitic magmatism in the southern Korean Peninsula preserves important tectonomagmatic records along the East Asian continental margin. In this study, we present ...SHRIMP/LA–MC–ICPMS U-Pb zircon ages and Hf isotope signature with whole-rock geochemical compositions of the Middle Permian to Middle Triassic granitoid gneiss-granitoid suites and the Middle to Late Triassic plutonic rocks in the southeastern Korean Peninsula. The former yields three age groups of ca. 272–263 Ma, ca. 258–251 Ma and ca. 243–240 Ma, respectively. The latter group yields ca. 237–216 Ma ages, indicating a long term magmatism that lasted from the Middle Permian to late Triassic. The granitoid gneiss-granitoid suites have chemical compositions similar to high silica adakitic rocks, showing high SiO2 (59.55–73.97 wt.%), Na2O (3.55–5.30 wt.%), Sr/Y (30–401), and La/YbN (11–173), and low MgO (0.18–1.82 wt.%), Y (2–14 ppm) and YbN (2–7). These rocks are peraluminous with high Ba and Sr, and show relatively high K2O contents and K2O/Na2O ratios (> 0.7), with positive correlation between La/YbN vs. Sr/Y ratios and high initial Sr ratios. These features reflect different contribution of the slab-derived adakite melts that interacted with peridotitic mantle in the metasomatized mantle wedge and the Middle Paleoproterozoic lower crustal basement of the Yeongnam Massif. On the contrary, the Triassic alkaline magmatism in the Yeongnam Massif is alternatively interpreted either by a tectonic switch to the extension-dominated arc system or by a delamination of an overthickened arc. The results from this study offer important evidence for a common subduction-accretion system existed between the North and South China Cratons and microcontinents between them along margins of the East Asian continental blocks, with different plate interaction in different locations generating distinct magmatic suites.
Display omitted
•The Permo-Triassic magmatic m rocks in southern Korea are adakitic rocks, having similar geochemical characteristics to adakites.•Tectonomagmatic records preserved in them might be linked to the magmatic responses to the Permo-Triassic tectonic events in East Asia.•The controversial tectonic nature of Late Triassic magmatism remains for further research in the Korean Peninsula.
