Palaeomagnetic results from the Chiapanecan Volcanic Arc,Chiapas, Southern Mexico: geomagnetic and geodynamic significance

This article presents the first palaeomagnetic results from 13 independent cooling units in the Chiapanecan Volcanic Arc (ChVA). Six sites were directly dated by Ar–Ar or K–Ar methods: their dates range from 2.14 to 0.23 Ma. We isolated the characteristic palaeodirections for all 13 lavas. Eleven non-transitional directions yield a mean direction with inclination, I?=?30.7°, declination, D?=?4.1°, and precision parameters k?=?63 and α₉₅ = 5.8°. The corresponding mean palaeopole position is Plat = 83.3°, Plong = 203.8°, K?=?227, A ₉₅ = 5.1°. The mean inclination is in good agreement with the expected value for the last 5 million years, as derived from the synthetic North American polar wander path [Besse and Courtillot 2002 Besse, J. and Courtillot, V. 2002. Apparent and true polar wander and the geometry of the magnetic field in the last 200 million years. Journal of Geophysical Research, 107(B11) doi:10.1029/2000JB000050[Crossref], [Web of Science ®] , [Google Scholar], Apparent and true polar wander and the geometry of the magnetic field in the last 200 million years: Journal of Geophysical Research, v. 107, no. B11, p. 2300], but a measured rotation of the palaeodeclination of about 8° with respect to the expected direction suggests the possibility of a clockwise rotation of the studied ChVA units. We have estimated the characteristics of palaeosecular variation through study of the scatter of virtual geomagnetic poles, obtaining a palaeosecular variation parameter S _b = 14.5° with upper limit S _U = 19.6° and lower limit S _L = 11.7°, in reasonable agreement with the fit of model G [McFadden et al., 1988 Quidelleur, X., Carlut, J., Gillot, P.Y. and Soler, V. 2002. Evolution of the geomagnetic field prior to the Matuyama-Brunhes transition: Radiometric dating of a 820 ka excursion at La Palma. Geophysical Journal International, 151: F6–F10. [Crossref], [Web of Science ®] , [Google Scholar], Dipole/quadrupole family modeling of paleosecular variation: Journal of Geophysical Research, v. 93, no. B10, p. 11583–11588; 1991, Reversals of the Earth's magnetic field and temporal variations of the dynamo families: Journal of Geophysical Research, v. 96, no. B3, p. 3923–3933] to the Johnson et al. [2008 Johnson, C.L., Constable, C.G., Tauxe, L., Barendregt, R., Brown, L.L., Coe, R.S., Layer, P., Mejia, V., Opdyke, N.D., Singer, B.S., Staudigel, H. and Stone, D.B. 2008. Recent investigations of the 0–5 Ma geomagnetic field recorded by lava flows. Geochemistry, Geophysics, Geosystems, 9(4) ID Q04032, doi:10.1029/2007GC001696[Crossref], [Web of Science ®] , [Google Scholar], Recent investigations of the 0–5 Ma geomagnetic field recorded by lava flows: Geochemistry, Geophysics, Geosystems, v. 9, no. 4, ID Q04032, doi:10.1029/2007GC001696] databases for the last 5 million years. In those cases in which age determinations are available, the polarity obtained for the studied flows is consistent with their stratigraphic positions, except for the Huitepec site, which probably reflects the transitional geomagnetic regime prior to the Matuyama–Brunhes geomagnetic reversal.     

Analysis of strength and moduli of jointed rocks

This paper deals with two aspects of jointed rock mass behavior, first the finite element modeling of a jointed rock mass as an equivalent continuum, second the comparison of empirical strength criteria of a jointed rock mass. In finite element modeling the jointed rock properties are represented by a set of empirical relationships, which express the properties of the jointed medium as a function of joint factor and the properties of the intact rock. These relationships have been derived from a large set of experimental data of tangent elastic modulus. It is concluded that equivalent continuum analysis gives the best results for both single and multiple jointed rock. The reliability of the analysis depends on the estimation of joint factor, which is a function of the joint orientation, joint frequency and joint strength.Empirical strength criteria for jointed rocks, namely Hoek and Brown, Yudhbir et al., Ramamurthy and Arora, Mohr–Coulomb have been incorporated in a nonlinear finite element analysis of jointed rock using the equivalent continuum approach, to determine the failure stress. The major principal stress at failure, obtained using Ramamurthy's criteria, compares very well with experimental results.     

The genetic relationship between hydrocarbon systems and Mississippi Valley-type Zn–Pb deposits along the SW margin of Sichuan Basin,China

The Chipu Mississippi Valley-type (MVT) deposit is located on the southwest (SW) margin of the Sichuan Basin. Occurrence of plentiful organic matter (bitumen) at this deposit and abundant hydrocarbon reservoirs in the SW Sichuan Basin implies a link between lead–zinc mineralization and hydrocarbon systems in this area. The high δ³⁴S values of most metal sulphides from the different ore stages suggest that H₂S-bearing gases and/or thermochemical sulphate reduction (TSR) by organic matter could have been the source of reduced sulphur involved in ore formation. Sulphides with small positive to negative δ³⁴S values can be attributed to organically bound sulphur at the Chipu deposit. Carbon and oxygen isotopic compositions from sparry carbonates suggest mixing of organic carbon with seawater-derived carbon in the mineralization process. From the early to the later ore stages, δ¹³C_PDB values of ore-hosting carbonates are increasingly more negative, which indicates strengthening of the TSR role during mineralization. Hydrogen and oxygen isotopes in fluid inclusions in the quartz gangue indicate the provenance of the ore-forming fluids in the hydrocarbons. Moreover, some extremely low hydrogen isotope values suggest the addition of hydrogen from the same source. The low H/C ratios and high non-hydrocarbon component of the bitumen (Zhang et al. 2010 Zhang, C.Q., Yu, J.J., Mao, J.W., Yu, H. and Li, H.M. 2010. Research on the biomarker from Chipu Pb-Zn Deposit, Sichuan. Acta Sedimentologica Sinica, 28: 832–844. v.p.in Chinese with English abstract [Google Scholar]) also suggest that the organic matter may have been involved in TSR and subjected to a strong oxidation by ore-bearing fluids. This study attempts to explain the lead–zinc mineralization process and the role of organic matter in it. As there is a demonstrable relationship between the evolution of the hydrocarbons and regional lead–zinc mineralization along the SW edge of the Sichuan Basin, we propose a possible model in which the MVT mineralization coincided with the degradation of hydrocarbon reservoirs due to the large-scale migration of basinal fluids, most likely driven by the late Indosinian orogeny in response to the closure of the Palaeo-Tethys Ocean.     

The Use of Rock Mass Classification Systems to Estimate the Modulus and Strength of Jointed Rock

Three-dimensional, elastic and elasto-plastic finite element (FE) programs have permitted calculation of the displacements and the factor of safety (FOS) for the excavation for a tower, 132.70 m high (above foundation) on the island of Tenerife. The tower is supported by a 2 m thick reinforced concrete slab on jointed, vesicular and weathered basalt and scoria. The installation of rod extensometers at different depths below the slab has permitted comparison between measured and calculated displacements and the estimation of in situ deformation modulus. The moduli deduced from the simple empirical equations proposed by Hoek et al. (In: NARMS-TAC, 2002) and Gokceoglu et al. (Int J Rock Mech Min Sci 40:701–710, 2003) as a function of GSI, and Nicholson and Bieniawski (Int J Min Geol Eng 8:181–202, 1990) as a function of RMR, provide an acceptable fit with the measured settlements in this type of rock. Good correlation is also obtained with the empirical equation presented by Verman et al. (Rock Mech Rock Eng 30(3):121–127, 1997) that incorporates the influence of confining stress in the deformation modulus. The FOS obtained from different correlations with geomechanical classifications is within a relatively narrow range. These results increase our confidence in the use of classification schemes to estimate the deformation and stability in jointed rock.     

Correlation of in situ modulus of deformation with degree of weathering, RMR and Q-system

Geotechnical investigation projects in Korea produced data on the in situ modulus of deformation of rock masses (E _M) measured with the borehole test, rock mass rating (RMR), and Q-system. The modulus of deformation of rock masses was correlated with the degree of weathering, RMR, and Q values. Determination of E _M for each degree of weathering allows for the results to be used to classify the degree of weathering or to predict E _M. The relation between E _M and RMR is represented by $ E_{\text{M}} = 10^{{\frac{{{\text{RMR}} - 16}}{50}}} $ , which returns values 2–3 times lower than those reported in previous studies. Despite scatter in the values, due to larger dataset used in this study, the proposed equation may be used to predict the in situ modulus of deformation from RMR values. In addition, the relation between modulus of deformation and Q values is $ E_{\text{M}} = 10^{{0.32{ \log }Q + 0.585}} $ .     

REVIEW OF THALLIUM,ITS GEOCHEMISTRY,MINERALOGY, PRINCIPAL GENETIC TYPES OF DEPOSITS,AND GEOCHEMICAL PROVINCES BY V.V. IVANOV,V.YU. VOLGIN,A.A. KRASNOV AND N.V. LIZUNOV

This book review takes the authors to task for omitting numerous references when they wrote this first comprehensive work on thallium. Among the omissions noted are; 1) the extreme toxicity of thallium; 2) the occurrence of thallium in various minerals:

REVIEW OF THALLIUM, ITS GEOCHEMISTRY, MINERALOGY, PRINCIPAL GENETIC TYPES OF DEPOSITS, AND GEOCHEMICAL PROVINCES BY V.V. IVANOV, V.YU. VOLGIN, A.A. KRASNOV AND N.V. LIZUNOV

All authors

V. V. Mogarovskiy

https://doi.org/10.1080/00206816409473950

Published online:

20 September 2010

Table     

Effect of foliation orientation on the P- and S-wave velocity anisotropies and dynamic elastic constants of the quartz-micaschists metamorphic rocks,Angouran mine,Iran

Laboratory measurements are required to study geophysical properties of the subsurface because of lacking direct observation of Earth’s crust. In this research, compressional (P) and shear (S) wave velocity measurements have been conducted on cylindrical specimens of Quartz-micaschist cored using rock blocks taken from the zinc and lead Angouran mine, Zanjan, northwest of Iran. Cylindrical rock specimens were prepared from the blocks by coring in 0°, 30°, 45°, 60°, and 90° into the foliation direction. P- and S-wave velocities were measured along the cylindrical specimens with different foliation orientations. Percent variations of the P- and S-wave velocities (Thomsen’s anisotropic parameters ε and γ) and constant dynamic modulus of test results have been determined. Percent variations of the P-wave velocity (ε) increase with an increase of the foliation angle with respect to the propagating waves direction by a parabolic function as it shows P-wave velocity differences up to a maximum value of 50 %. Thomsen’s anisotropic parameter of γ has also the same function with the foliation angle. Meanwhile, foliation orientation has a much greater influence on ε than γ for foliation angle from 45° to 90° as \( \frac{\varepsilon }{\gamma } \) ratio increases with an increase of foliation angle. Values of dynamic elastic modulus (E), Poisson’s ratio (ν), shear modulus (μ), bulk modulus (K), and Lamé’s constant (λ) increase with the increase of foliation angle with the parabolic function. The results show that dynamic elastic modulus, Poisson’s ratio, shear modulus, bulk modulus, and Lamé’s constant have anisotropic behavior in relation with the foliation orientation.     

Estimation of the Rock Deformation Modulus and RMR Based on Data Mining Techniques

In this work Data Mining tools are used to develop new and innovative models for the estimation of the rock deformation modulus and the Rock Mass Rating (RMR). A database published by Chun et al. (Int J Rock Mech Min Sci 46:649–658, 2008) was used to develop these models. The parameters of the database were the depth, the weightings of the RMR system related to the uniaxial compressive strength, the rock quality designation, the joint spacing, the joint condition, the groundwater condition and the discontinuity orientation adjustment, the RMR and the deformation modulus. As a modelling tool the R program environment was used to apply these advanced techniques. Several algorithms were tested and analysed using different sets of input parameters. It was possible to develop new models to predict the rock deformation modulus and the RMR with improved accuracy and, additionally, allowed to have an insight of the importance of the different input parameters.     

Experimental Investigation of Seepage Properties of Fractured Rocks Under Different Confining Pressures

The effectiveness of transmitting underground water in rock fractures is strongly influenced by the widths of the fractures and their interconnections. However, the geometries needed for water flow in fractured rock are also heavily controlled by the confining pressure conditions. This paper is intended to study the seepage properties of fractured rocks under different confining pressures. In order to do this, we designed and manufactured a water flow apparatus that can be connected to the electro-hydraulic servo-controlled test system MTS815.02, which provides loading and exhibits external pressures in the test. Using this apparatus, we tested fractured mudstone, limestone and sandstone specimens and obtained the relationship between seepage properties and variations in confining pressure. The calculation of the seepage properties based on the collection of water flow and confining pressure differences is specifically influenced by non-Darcy flow. The results show that: (1) The seepage properties of fractured rocks are related to confining pressure, i.e. with the increase of confining pressure, the permeability $ k $ decreases and the absolute value of non-Darcy flow coefficient $ \beta $ increases. (2) The sandstone coefficients $ k $ and $ \beta $ range from $ 1.03 \times 10^{ - 18} $ to $ 1.53 \times 10^{ - 17} $  m² and $ - 1.13 \times 10^{17} $ to $ - 2.35 \times 10^{18} $  m^?1, respectively, and exhibit a greater change compared to coefficients of mudstone and limestone. (3) From the regression analysis of experimental data, it is concluded that the polynomial function is a better fit than the power and logarithmic functions. The results obtained can provide an important reference for understanding the stability of rock surrounding roadways toward prevention of underground water gushing-out, and for developing underground resources (e.g. coal).     

ORDOVICIAN GRAPTOLITES OF THE CHU-ILIYSKIYE MOUNTAINS

The available information on the graptolite faunas of the Chu-Illyskiye Mountains is synthesized and comparisons made with other faunas of Kazakhstan, Europe, North America, and China. Comparison with Bet-Pak-la, 400 km NW of the Chu-Iliyskiye, shows almost no species common to contemporaneous units, a discrepancy attributed to facies differences. Correlation with the English standard is good although many details of zonal equation are arbitrary. Fifty species, of which 17 are new, are described and illustrated. Twenty-two are typically European, five North American, two Russian, and one Chinese; three are not formally named. Correlation between the graptolite zones of the Chu-Iliyskiye Mountains and the English standard zones is as follows:

ORDOVICIAN GRAPTOLITES OF THE CHU-ILIYSKIYE MOUNTAINS

All authors

B.M. Keller

https://doi.org/10.1080/00206816209474672

Published online:

01 September 2009

Table     

Structural and luminescent characterisation of uraniferous fluorapatite and haematite associated with phosphatic rocks of the Bijawar group in Sagar District,Madhya Pradesh (India)

The structural and spectroscopic characteristics of phosphatic ferruginous shale samples from the Bijawar Group rocks from Sagar District of Madhya Pradesh (India) have been probed for identification of uranium species. Fluorapatite (\(\hbox {Ca}_{5}\hbox {(PO}_{4})_{3}\hbox {F}\), FAP) and haematite (\(\upalpha \)-\(\hbox {Fe}_{2}\hbox {O}_{3}\)) were identified as the main phases in the separated mineral concentrates. The photoluminescence (PL) and X-ray absorption near edge spectroscopy (XANES) studies pointed to a strong experimental evidence of both U(IV) and U(VI) oxidation states in the mineral concentrate portion obtained from the same parent host rock. The PL spectrum has confirmed the charge transfer (f–d) transition bands in UV and near-UV regions with emission peaks at ca. 290, 313, 336, 399 and 416 nm, which has been attributed to the substitution of \(\hbox {Ca}^{2+}\) ions by U(IV) in FAP and broad structureless emission due to stabilisation of U(VI) as \(\hbox {UO}_{6}^{6-}\) in haematite. Time-resolved spectroscopy studies have revealed biexponential decay components lasting 2–5 ns for U(IV) species and \(10\,\upmu \hbox {s}\) for U(VI) species. These characterisations revealed the fundamental information about the oxidation state and form of uranium in this region. Remediation measures for the Bijawar region are also suggested.     

Tailings composition effects on shear strength behavior of co-mixed mine waste rock and tailings

The objective of this study was to evaluate the effect of mine tailings composition on shear behavior and shear strength of co-mixed mine waste rock and tailings (WR&T). Crushed gravel was used as a synthetic waste rock and mixed with four types of tailings: (1) fine-grained garnet, (2) coarse-grained garnet, (3) copper, and (4) soda ash. Co-mixed WR&T specimens were prepared to target mixture ratios of mass of waste rock to mass of tailings (R) such that tailings “just filled” interparticle void space of the waste rock (i.e., optimum mixture ratio, R _opt). Triaxial compression tests were conducted on waste rock, tailings, and mixed waste at effective confining stresses (\(\sigma_{\text{c}}^{{\prime }}\)) ranging from 5 to 40 kPa to represent stresses anticipated in final earthen covers for waste containment facilities. Waste rock and co-mixed WR&T specimens were 150 mm in diameter by 300 mm tall, whereas tailings specimens were 38 mm in diameter by 76 mm tall. Shear strength was quantified using effective stress friction angles (?′) from undrained tests: ?′ for waste rock was 37°, ?′ for tailings ranged from 34° to 41°, and ?′ for WR&T mixtures ranged from 38° to 40°. Thus, shear strength of co-mixed WR&T was comparable to waste rock regardless of tailings composition. Shear behavior of WR&T mixtures was a function of R and tailings composition. Tailings influenced shear behavior for R < R _opt and when tailings predominantly were silt. Shear behavior was influenced by waste rock for R ≥ R _opt and when tailings predominantly were sand or included clay particles.     

Shear Behaviors of the Binary Structural Plane

Binary-medium contact interfaces widely exist in rock engineering. They have significant impacts on the safety of rock engineering due to their poor shear behavior. A material of different strength is produced by pouring mortar of a different sand-to-cement ratio on the top of a rock-like mortar material (with the ratio of 1:1), thereby forming a binary-medium structural plane. Then, direct shear test is performed on the structural plane by applying different normal stresses. The shear strength parameters of the structural plane (cohesion \(c\) and friction angle \(\varphi\)) are obtained from the Mohr–Coulomb criterion. Moreover, the mechanical behaviors of the structural plane are compared with the unitary-medium specimen in the shearing process. A similar shear stress–shear displacement rule is observed in the shearing process. However, the peak and residual shear strengths of the binary structural plane are far lower than those of the unitary ones. The difference between the unitary and binary planes at cohesion \(c\) decreases with the increasing sand–cement ratio, whereas a up-down trend is observed in the friction angle \(\varphi\) with the increasing sand-to-cement ratio. When the upper and lower parts of the structural plane are different in sand-to-cement ratio, the cohesion \(c\) of the structural plane slightly increases with the increasing ratio of the upper specimen. However, when the two parts are identical in ratio, the cohesion of the structural plane reaches the peak, and its friction angle \(\varphi\) substantially increases with the increasing ratio of the upper part.     

Experimental Study of Ultrasonic Waves Propagating Through a Rock Mass with a Single Joint and Multiple Parallel Joints

Experiments were conducted to study the relationship between the transmission ratio (TR) and normal stress, joint roughness, joint number and frequency of incident waves, respectively, when ultrasonic waves pass across a rock mass with one joint and multiple parallel joints oriented normally. The ultrasonic waves were generated and received by pairs of piezoelectric transducers and recorded by an ultrasonic detector. The specimens were subjected to normal stress by a hydraulic jack and loading frame. The jointed rock mass was produced by superposing rock blocks in the study. Rough joints were produced by grooving notches on the planar joints formed by sawing directly. In the case of multiple parallel joints, the overall thickness of specimens was maintained while the joint number changed. Three pairs of P-wave transducers and one pair of S-wave transducers with different frequencies were, respectively, applied and all transducers emitted signals perpendicular to the joints in the experiment. The results indicate that TR increases with increasing normal stress while the increment rate decreases gradually. This is particularly so when the normal stress is high enough that TR will approximate 1 even if the rock mass has many joints. In addition, the experiments indicate that the higher the wave’s frequency, the lower its TR, and this phenomenon is gradually reduced as the normal stress increases. In response to S-waves, TR increases with increase in joint roughness; however, in response to P-waves, TR decreases gradually with increase in joint roughness. For multiple parallel joints in a fixed thickness rock mass with normally incident P-waves, TR does not always decrease with increase in the number of joints, and there is a threshold joint spacing for a certain incident wave: when the joint spacing is smaller than the threshold value, TR will increase with a decrease in joint spacing. The experimental results support similar conclusions based on analytical results drawn by Cai and Zhao (Int J Rock Mech Min Sci 37(4):661–682, 2000), Zhao et al. (Int J Rock Mech Min Sci 43(5):776–788, 2006b) and Zhu et al. (J Appl Geophys 73:283–288, 2011a).     

Correlation analyses of effects of temperature on physical and mechanical properties of clay

In determining the physical and mechanical parameters of clay, it is sometimes necessary to determine them indirectly from other parameters since they cannot be measured directly from laboratory or field tests. In order to determine the effect of temperature on the behavior of clay, an indirect approach is used here by analyzing the changes of mass (\(\Delta m\)), density (\(\rho\)), porosity (\(\phi\)), P-wave velocity (\({v_p}\)), thermal conductivity (\(\lambda\)), specific heat capacity (c), resistivity (R) and uniaxial compressive strength (f) of clay from eastern China for a temperature range between 20 and 800 °C. The results indicate that temperature has a significant effect on these parameters. Comparisons between \(\Delta m\) and \(\rho\), \(\Delta m\) and \({v_p}\), \(\rho\) and \({v_p}\), \(\phi\) and \(\lambda\), \({v_p}\) and f, R and f show a linear change among these parameters,whereas the relationships among \(\Delta m\) and \(\phi\), \(\phi\) and \({v_p}\), \(\phi\) and R, \({v_p}\) and \(\lambda\), \(\phi\) and f are exponential. It is difficult to obtain these relationships by using regression analysis with high levels of accuracy. Further refinement is therefore required.     

Correlation of large displacement drained shear strength of landslide soils measured by direct shear and ring shear devices

Based on a laboratory study of drained direct shear tests of remoulded, pre-cut and polished specimens and drained ring shear tests of uncut and remoulded specimens of slip surface materials of five landslide soils, significant correlations of the mobilized shear strength parameters, cohesion (c, c _r) and internal friction angle (Φ, Φ_r), are proposed. The investigated soils consisted of the slip surface material belonging to tuffaceous clay, mudstone, loess and siltstone. Most of the previous studies on residual shear strength measured by reversal direct shear and ring shear devices have obtained significantly different results using the two devices, even when pre-cut and polished specimens were used in the direct shear device. In this study, the residual shear strength values of remoulded specimens measured by a ring shear device are shown to significantly correlate with the drained large displacement shear strength values of remoulded specimens, which were measured using pre-cut and polished specimens in a direct shear device. The correlation between the cohesion measured in the two shear devices is expressed by the linear relationship, $ {c_{\text{r}}} = 0.{7394}c - {6}.{6857} $ , while the correlation between the friction angle measured in the two devices is expressed by the linear relationship, $ {\Phi_{\text{r}}} = {1}.0{852}\Phi - {6}.0{247} $ . The proposed linear correlations for effective cohesion (c′) and effective friction angle (Φ′) have yielded significant coefficients of determination within an effective normal stress range of 30–150?kN/m².     

预制节理岩体试件强度及破坏模式的试验研究

采用相似材料模型试验对不同节理倾角、节理贯通度、节理组数、载荷应变率、试件长径比、节理充填物厚度及类型等7种工况下的预制节理岩体在单轴压缩下的峰值强度及破坏模式进行了研究。结果表明：节理岩体的破坏模式及峰值强度与节理构造形态密切相关。贯通节理岩体将产生沿节理面的剪切破坏或穿切节理面破坏,且与第1种破坏模式对应的岩体峰值强度更低。非贯通节理岩体的强度介于完整岩体和贯通节理岩体之间。随着平行节理组数的增加,岩体峰值强度逐渐下降。随着载荷应变率的增加,岩体峰值强度逐渐增大,相应地试件的破坏模式也变得更加复杂。试件长径比基本没有改变其破坏模式,完整试件仍主要是以张拉破坏为主,而节理试件仍以剪切破坏为主。随着长径比增加,试件峰值强度逐渐增大。随着节理充填物厚度增加,试件峰值强度降低。不同节理填充物对试件峰值强度也有一定影响。     

Prediction of rock burst classification using the technique of cloud models with attribution weight

Rock burst is one of the common failures in hard rock mining and civil construction. This study focuses on the prediction of rock burst classification with case instances using cloud models and attribution weight. First, cloud models are introduced briefly related to the rock burst classification problem. Then, the attribution weight method is presented to quantify the contribution of each rock burst indicator for classification. The approach is implemented to predict the classes of rock burst intensity for the 164 rock burst instances collected. The clustering figures are generated by cloud models for each rock burst class. The computed weight values of the indicators show that the stress ratio $ Ts = \sigma_{\theta } /\sigma_{c} $ Ts = σ θ / σ c is the most vulnerable parameter and the elastic strain energy storage index W _et and the brittleness factor $ B = \sigma_{c} /\sigma_{t} $ B = σ c / σ t take the second and third place, respectively, contributing to the rock burst classification. Besides, the predictive performance of the strategy introduced in this study is compared with that of some empirical methods, the regression analysis, the neural networks and support vector machines. The results turn out that cloud models perform better than the empirical methods and regression analysis and have superior generalization ability than the neural networks in modelling the rock burst cases. Hence, cloud models are feasible and applicable for prediction of rock burst classification. Finally, different models with varying indicators are investigated to validate the parameter sensitivity results obtained by cloud clustering analysis and regression analysis in context to rock burst classification.     

Pressuremeter Modulus and Limit Pressure of Clayey Soils Using <Emphasis Type="Italic">GMDH</Emphasis>-Type Neural Network and Genetic Algorithms

Pressuremeter modulus (\(E_{M}\)) and limit pressure (\(P_{L}\)) are used for the calculation of the settlement and bearing capacity of foundation respectively. As the determination of these parameters from pressuremeter test (PMT) is relatively time-consuming and expensive, various empirical correlations have been proposed to correlate the \(E_{M}\) and \(P_{L}\) to other soil parameters. For the existing equations are incapable of estimating these PMT parameters well, in present research group method of data handling type neural network is used to estimate the \(E_{M}\) and \(P_{L}\) of clayey soils. The \(E_{M}\) and \(P_{L}\) were modeled as a function of three variables including the moisture content (\(\omega\)), plasticity index and corrected SPT blow counts (\(N_{60}\)). A database containing 51 data sets have been used for training and testing of the models. The performances of proposed models are compared with those of existing empirical equations. The results demonstrate that appreciable improvement with respect to the other correlations has been achieved. At the end, sensitivity analysis of the obtained models has been performed to study the influence of input parameters on model outputs and shows that the \(N_{60}\) is the most influential parameter on the PMT parameters.