Since the 1960s, there has been an increasing interest in the understanding of the hydraulic flow inside a hard rock mass, since water inflow into deep tunnels constitute a hazard, in addition to ...being an important factor in controlling the advancement of excavation. The characterisation of fluid flow through hard rock masses is still one of the most challenging problems faced by geologists and engineers. A rock mass is characterised by networks of discrete and ubiquitous discontinuities that strongly affect its hydraulic properties, but detailed knowledge of the discontinuity properties allows for the evaluation of the hydraulic flow in the rock mass affected by the excavation of a tunnel. A geostructural field survey is fundamental in order to correctly define the discontinuity types, settings and networks. Numerous approaches have been proposed to estimate the water inflow based on empirical relations supported by field experience and case studies, as well as analytical solutions. Often, however, these approaches are not easily applicable in standard practice and in complex scenarios. The most appropriate approach to characterising the hydraulic flow of the rock mass and to predicting in the most effective way the expected water inflow during the excavation of a tunnel is based on a detailed geological model and geostructural analysis as described in this paper.
Cosserat theory of elasticity has been introduced for modelling micro-structured materials and structures. Micro-structured materials are able to re-distribute the stress resulting in lower stress ...peaks. Therefore, such effects are strongly underlined when composite structures have holes and discontinuities in which high stress gradients are generally observed in the classical theory of elasticity. However, general material configurations can be solved using numerical approaches, since exact solutions are only available for simple cases. The present paper deals with such problems using an advanced strong form pseudo-spectral method that uses domain decomposition to deal with geometric and material discontinuities.
Display omitted
•The paper presents stability analysis with stochastic representation of rock mass.•A robust block generation algorithm was developed to handle non-persistent joints.•Scenarios with ...varying mean joint size show necessity of modelling size accurately.•A case study application has also been carried out with validations of joints.•The key block statistics is assessed to provide better guidance for support design.
A stochastic key block method is developed for the analysis of complex blocky rock masses containing non-persistent joint sets. A robust block generation program is developed to model the non-persistent discontinuities. Various uncertainties of geological and geometrical parameters of the discontinuities are considered and Monte Carlo simulations of key blocks are performed. Based on the present analysis, progressive failure of a rock mass can be evaluated in a stochastic manner and the statistics of the key blocks including the total number and volume, the maximum and mean volume, shape and failure mechanism, etc. can be assessed. This approach is applied to a hypothetical horseshoe shaped tunnel in a highly fractured rock mass. Three scenarios with varying mean discontinuity size are analyzed to consider size effect on the predicted blocks and key blocks. It is shown quantitatively that a persistent discontinuity network assumption causes over-fragmentation of predicted blocks, overestimation of key blocks, and underestimation of the largest key block volume compared with non-persistent ones. More realistic representation of the discontinuities by considering the non-persistence is important to give out more reliable failure estimation of fractured rock mass. In addition, a case study application to a slope at the right bank of the Jinping I hydropower station has been conducted. Key block statistics is also helpful in support design.
Earnings distributions commonly exhibit statistically significant discontinuities at zero earnings, which are widely interpreted as evidence of earnings management to avoid a loss. In contrast, ...Durtschi and Easton (2005, 2009, hereafter DE) assert that discontinuities are instead explained by some combination of prior researchers׳ choice(s) of scaling and sample selection as well as a scaling-related effect due to a systematic relation between the sign of earnings and market prices. Resolution of the conflicting interpretations of discontinuities is important because (1) it affects how investors, regulators, and scholars view earnings management and (2) it demonstrates the importance of a close linkage between theory and research design choices. We point out that DE provide no evidence that scaling or selection create discontinuities, but only evidence showing that changes in scaling or selection eliminate discontinuities. We demonstrate why the research designs used by DE eliminate discontinuities and why alternative designs using the same data yield statistically significant discontinuities that cannot be attributed to either scaling or selection.
•We show that scaling and selection do not cause discontinuities.•Distributions of unscaled earnings and unscaled EPS contain discontinuities.•Different population segments have different discontinuities.•Discontinuities are not explained by the absence of discontinuities in other segments.•Results demonstrate the importance of research design tailored to theory.
Time and frequency transfer through global navigation satellite system (GNSS) precise point positioning (PPP) based on carrier-phase measurements has been widely used for clock comparisons in ...national timing laboratories. However, the time jumps up to one nanosecond at the day boundary epochs of adjacent daily batches lead to discontinuities in the time transfer results. Therefore, it is a major obstacle to achieve continuous carrier phase time transfer. The day-boundary discontinuities have been studied for many years, and they are believed to be caused by the long-term pseudorange noise during estimation of the clock offset in the daily batches and are nearly in accordance with a Gaussian curve. Several methods of eliminating the day-boundary discontinuity were proposed during the past fifteen years, such as shift and overlapping, longer batch processing, clock handover, and ambiguity stacking. Some errors and new noise limit the use of such methods in the long-term clock stability comparison. One of the effective methods is phase ambiguity fixing resolution in zero-differenced PPP, which is based on the precise products of wide-lane satellite bias (WSB) provided by the new international GNSS Service (IGS) Analysis Center of Centre National d'Etudes Spatiales (CNES) and Collecte Localisation Satellites (CLS). However, it is not suitable for new GNSS, such as the Beidou Satellite System (BDS), GALILEO, and QZSS. For overcoming the drawbacks above, Multi-GNSS Experiment (MGEX) observation data of 10 whole days from MJD 58624 to 58633have been network processed by batch least square resolution. These observations come from several ground receivers located in different national timing laboratories. Code and carrier phase ionosphere-free measurements of GPS and BDS satellites are used, and the time transfer results from network processing are compared with PPP results provided by Bureau International des Poids et Mesures (BIPM) and used for international atomic time (TAI) computation (TAIPPP) and universal time coordination (UTC). It is shown that the time offsets of three different time links are almost continuous and the day-boundary discontinuities are sharply eliminated by network processing, although a little extent of day-boundary discontinuities still exist in the results of UTC(USNO)-UTC(PTB). The accuracy of time transfer has been significantly improved, and the frequency stability of UTC(NTSC)-UTC(PTB) can be up to 6.8 × 10
on average time of more than one day. Thus, it is suitable for continuous multi-GNSS time transfer, especially for long-term clock stability comparison.
Strong anisotropy of tensile behaviros and spatial anisotropic deformation have been found in transversely isotropic rock discs. There is seldom attention paid for the insightful analysis of ...anisotropy and spatial variability of tensile behaviours for jointed rock masses. In the paper, an index termed as the “directionality” was proposed to quantitatively assess both the directionality and spatial variability of tensile strength of jointed rock masses. Experimental Brazilian tensile tests were carried out on stratified biotite granulite rocks. Corresponding to the configurations of laboratory tests, numerical simulations of rock specimens with different joint distributions and discrete fractures network (DFN) models were then performed using PFC2D code. The results indicated that the stratified rock discs displayed distinct anisotropy and directionality in tensile strength, manifested by the decreasing strength with inclination angle. The maximum directionality of the stratified rocks measured in laboratory was 2.40/0°, which was perpendicular to the layered discontinuities, while the tensile strength determined by DFN models showed a lower anisotropy and directionality (1.38/30°). Obvious anisotropic characteristics were observed in the fracture patterns of failure in DFN models. This paper implies the necessity of consideirng the anisotropy and directionality for the study of failure mechanisms of surrounding rocks in underground tunnels.
A simple, drawable, and efficient equivalent circuit is proposed to represent a discontinuity/junction with N ports. The circuit is based on N transmission lines connected to the sides of a polygon ...with N side. N( N-1)/2 susceptances are placed on the sides and on the inner diagonals of the polygon. The circuit modularity permits to identify the N( N+1)/2 electrical parameters in a simple way. In fact, the lengths of the N transmission lines are obtained solving a system of N polynomial equations and the N( N-1)/2 susceptances are obtained solving a simple linear equation system. The proposed circuit is used to evaluate the equivalent circuit of some directional couplers in the horizontal plane and of a 3-D six-port coupler acting on the horizontal and vertical planes.
Interpolatory splines are usually useful to reconstruct data that present certain regularity. This paper is devoted to the construction and analysis of a new technique that allows to improve the ...accuracy of splines near corner singularities in the point values and jump discontinuities in the cell averages. The detection of discontinuities is easily done through the processing of the right hand side of the system of equations of the spline, that contains divided differences. The process of adaption will require some knowledge about the position of the discontinuity and the values of the function and its derivatives at the discontinuity. Using Harten’s multiresolution we can adapt splines to the presence of corner singularities and jump discontinuities. Thanks to the adaption, the smearing of corner singularities does not appear in the reconstruction obtained in the point values and Gibbs phenomenon and diffusion of jump discontinuities is also eliminated. These numerical effects are a consequence of assuming that the data used in the reconstruction comes from the discretization of a continuous function with certain regularity and this might not be true.
An unprecedented number of broadband seismic data from 165 stations were utilized to constrain the topographic variations in seismic discontinuities at the top and bottom of the mantle transition ...zone (MTZ) in the Java subduction zone. After moveout corrections under a nonplane wavefront assumption and time-to-depth conversions based on the IASP91 Earth model, the depth undulations of two discontinuities that border the MTZ (d410 and d660) were obtained by stacking P receiver functions that were grouped into circular bins with a radius of 1°. The apparent depths exhibit systematically spatial variations that range from 385 to 427 km for the d410 and 608 to 700 km for the d660, which result in a MTZ thickness of 217–309 km. The mean values are 406 ± 12, 665 ± 19, and 258 ± 18 km, suggesting thicker than normal MTZ by an average of 8 km. The major factor that accounts for the systematic depth variations across the study area originates from the subducted slab that perturbs the entirety of the MTZ, which induces a negative thermal anomaly, high velocity zone, and abnormal water presence concentrated in the lower MTZ of western Java. In Lombok and Sumbawa Islands, after the thermal and velocity heterogeneities from the subducted slab were considered, the remnant d660 uplift is found due to a significant thermal anomaly with a magnitude of up to +200 K near the d660. In eastern Java and adjacent regions, advective thermal upwelling associated with toroidal mantle flow that traversed a slab window in central Java induces a low velocity anomaly with a magnitude that is greater than the high velocity anomaly caused by the subducted slab, which apparently depressed the d410 and d660 by the same amount.
•MTZ discontinuities beneath Java and adjacent areas are imaged using receiver functions with an unprecedented resolution.•The abnormally thin MTZ underneath Lombok and Sumbawa Islandssuggests the presence of significant positive thermal anomaly.•The discontinuity depth undulations in eastern Java are associated with toroidal mantle flow traversing a slab window.
For monolithic microwave integrated circuit integration and antenna application, a novel W-band millimeter-wave transition from microstrip line to groove gap waveguide (GWG) is proposed in this ...communication. The transition is achieved by a modified planar triangular-microstrip patch resonator with an inner shorting via. To give a physical insight, E-field analysis is presented, and its working mechanism is similar to that of the passband filter based on coupled resonators. The proposed transition may contribute to a potential groove GWG application in the W-band radar and communication system. Finally, a back-to-back transition prototype is fabricated and assembled for measurement. To improve <inline-formula> <tex-math notation="LaTeX">S_{11} </tex-math></inline-formula> of the prototype, a modified CPW probe pad is applied. Moreover, the influences on <inline-formula> <tex-math notation="LaTeX">S_{11} </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">S_{21} </tex-math></inline-formula> of the conductor losses are given. The measured results show that there is an excellent transition passband from 90 to 99.5 GHz, in which frequency band, <inline-formula> <tex-math notation="LaTeX">S_{11} </tex-math></inline-formula> is almost below −12 dB.
PDF
