Rock Ground Research Articles

Stochastic Modeling as a Method of Arriving at Higher Frequencies: An Application to κ Estimation

AbstractWe present a framework for stochastically modeling the Fourier spectrum of the noisy seismic recording based on the fundamental assumption that the latter constitutes a random rather than a deterministic quantity. First we demonstrate (mathematically and through simulations) that, under the stochastic‐signal assumption, the periodogram ordinates of the noisy recording can be considered independent exponential random variables with a frequency‐dependent mean. Using this finding, the estimation of seismological parameters is translated into a well‐defined maximum likelihood (ML) problem, allowing a fast, accurate, and robust solution. Although the proposed ML methodology constitutes a general estimation framework that we believe can improve any spectral analysis, here we specifically apply it to the high‐frequency attenuation parameter (κ), crucial for understanding rock ground motion. Other seismological parameters could be estimated by appropriately adapting the theoretical model and frequency band used. The greatest advantage of the proposed method is its ability to account for the presence of noise rather than simply try to avoid it, as is the case with all conventional κ approaches and many other spectral analysis approaches. This means that the proposed technique achieves acceptable results even for very low signal‐to‐noise ratios (SNR), thus pushing the boundary of what can be considered usable recording quality. The technique's superior performance in estimation is demonstrated through a series of experiments involving both synthetic and real seismic recordings. Our results also indicate that, compared to this new “noise‐modeling” approach, conventional “noise‐avoiding” approaches are likely to systematically underestimate the “true” kappa value in recordings of moderate‐to‐low SNR.

Current problems and objectives in geomechanics

The authors discuss one of the key objectives of geomechanics as a mining science. It consists on the investigation of deformation processes phenomena in rock mass and ground surface toward safe and efficient subsoil management as a type of economic activity, as well as for safe and sustainable operation of permanent underground and surface facilities of subsoil use. The emphasis is laid on the fact that subsoil facilities are not only the permanent structures meant for mineral mining and haulage but also the city and industry infrastructure, transportation lines, power generation and water bodies, high-rise structures, etc. for which underground rock mass and ground surface are the integral geotechnical component. All these subsoil use facilities are subject to risk of instability in case of natural and man-made disasters caused by deformation processes in rock masse and on ground surface. The current advances of geomechanics in the stress-strain analysis of rock mass, revealing its discreteness, mosaic structure and variability of stress and strain patterns in time, have offered a new insight into the sources and causes of natural and man-made catastrophes at the subsoil use objects and make it possible to push the limits of modern problems and objectives of geomechanics.

Microzonation map of the Abbottabad basin and immediate surroundings

This study presents seismic hazard and seismic microzonation maps for the Abbottabad basin and surroundings, which are used in assessment and seismic design of buildings and bridges and other infrastructures. This research work determines microzonation parameters (shear wave velocity, fundamental frequency, and acceleration on ground surface) using geotechnical and geophysical testing procedures. Standard penetration test (SPT) and H/V methods are used to characterize the soils by estimating shear wave velocity at different locations. Microzonation maps for Abbottabad are developed in terms of acceleration parameter for 10% and 2% probability of exceedances in 50 years return period. These maps have been obtained based on the mean of average spectral acceleration values between 0.10 and 1.00 s following the Borcherdt (1994) recommendations. Based on H/V data (using Tromino Engy Plus instrument), it has been observed that the study area has average fundamental frequency range from 1 to 5 Hz, which represents the deposition of alluvial sediments (i.e., stiff and dense soil). Site characterization based on shear wave velocity indicated that soil in the study area consists of categories C and D. For the return period (Tr) of 475 years, the surface acceleration values ranges from 0.623 to 0.673 g, and for Tr = 2475 years, the area ranges from 1.007 to 1.107 g. These results show that soils in the Abbottabad basin will amplify 0.540 and 0.548 time respectively for Tr = 475 and 2475 against bed rock ground motions. Microzonation maps for Abbottabad basin do not exist; the maps produced in this study will be the basic input for carrying out the earthquake resistant design of the structures in Abbottabad.

Earth Pressure Envelope for Retaining Wall in Jointed Rock Ground

Earth pressure against a retaining wall in a jointed rock ground are an important factor for design and construction. A physical model test, extensive numerical studies, and field observations were conducted and comprehensively analyzed. All of the results were integrated and analyzed to develop an earth pressure envelope for the design of retaining walls in a jointed rock ground. For this purpose, the rock mass conditions and induced earth pressures were systematically investigated for different analysis cases. The rock mass conditions were classified using the slope mass rating (SMR) method and divided into six rock mass classes. The induced earth pressures of cases in the same rock mass class were plotted together, and an earth pressure envelope that covers the induced earth pressures in each rock mass class was developed. The developed envelope was compared with field observations, which show that the field results are generally consistent with the developed envelope in the same rock mass class. The study results and developed earth pressure envelope could help to provide a better understanding and design of retaining walls in a jointed rock ground.

Mapping of ground motion amplifications for the Fraser River delta in Greater Vancouver, Canada

The Fraser River delta in Greater Vancouver, Canada consists of deep soft deposits of silts and clays, and it is well known that the deep soil deposits can amplify the low frequency contents of ground motions. This study aims to investigate the effects of deep soil deposits in the delta on ground motion amplifications by using thorough site response simulations that account for the full soil profiles and a suite of recorded ground motions that covers a wide range of intensity levels. Based on both equivalent-linear and nonlinear site response simulations, the effects of soil depth (represented by natural period of the soil, TS) on ground motion amplifications for various spectral periods are clearly demonstrated. The ground motion amplification maps for various spectral periods and rock ground motion intensity levels are also generated to be used in the regional seismic hazard assessment for infrastructure. It is found that ground motions for long periods are substantially amplified in the center of the delta, while those for short periods are de-amplified when input rock motions are large.

Empirical Linear Seismic Site Amplification in Central and Eastern North America

We present empirical linear site amplification models conditioned on time-averaged shear wave velocity in the upper 30 m ( VS30) for central and eastern North America. The models are derived from ground motion data and site condition information from the NGA-East project and are intended for use with reference rock ground motion models. Site amplification is found to scale with VS30for intermediate to stiff site conditions ( VS30> 300 m/s) in a weaker manner than for active tectonic regions such as the western United States. For stiff sites ( >800 m/s), we find differences in site amplification for previously glaciated and nonglaciated regions, with nonglaciated sites having lower amplification. The models were developed using a combination of least-squares, mixed effects, and Bayesian techniques; the latter show that accounting for predictor uncertainty does not appreciably affect the median model but decreases model dispersion. Our VS30-scaling models are modular and additive to simulation-based models for the nonlinear components of site response. A limitation of the present models is that they do not account for site-specific resonance effects.

A Generalized Strength Reduction Concept and Its Applications to Geotechnical Stability Analysis

Conventional strength reduction technique can’t be directly applied to geotechnical stability analyses involving nonlinear failure criteria, and hence a generalized strength reduction concept is proposed to solve the geotechnical problems involving nonlinear failure models. Although the concept has been used in some previous work, it hasn’t been recognized very well by geotechnical society. Based on the concept, the conventional strength reduction method may be viewed as the material zone/element-based strength reduction method, while the generalized strength reduction method can be regarded as the stress point-based method. One slope problem of unsaturated soil, two rock slope problems and one rigid foundation problem located on rock ground are adopted to validate the effectiveness of the generalized strength reduction concept. Numerical investigations disclose that the heuristic concept of stress point-based strength reduction can be freely applied to various geotechnical problems involving nonlinear failure models.

Typology of hard rock ground waters within the Lower Sassandra, a main catchment in humid tropical West Africa

Abstract Randomness of fracture networks still makes channelized flow a challenge to track in hard-rock aquifers. While not underestimating geological and hydrological criteria that are also handled here through mapping exercises, this study raises an issue of water quality encountered in lifelong boreholes. Chemical classification checked against a recent conceptual model of bedrock aquifers gives birth to a new typology of groundwater in a complex granitic aquifer system located in the SW of Ivory Coast (West Africa). Major ion chemistry, borehole completion data, digital elevation model and satellite images are used to interpret the geochemical water facies as an expression of connexions between the saprolite and the saprock, or transient insulation. From major ions ratios, cumulate mineralization, carbonate equilibrium, stable isotopes, the maturation of ground waters and mixing between bedrock layers are described at seasonal and local scales. The results highlight some vertical feeding of the water table into the main saprock aquifer owing to shortcuts through the saprolite, along with the existence of dead-ends in the hydraulically active fracture network. Also, some influence of fault zones, either drain or barrier, is confirmed on the (Ca, Mg) bicarbonate water facies within the saprock.

A probabilistic procedure to describe site amplification factors for seismic design codes

We introduce a site factor computation method for a region by extending the site-specific and probabilistic site amplification approach in Bazzuro and Cornell (2004). The site-factor exceedance probability is estimated from the exceedance probabilities of the reference rock ground motion and the soil amplification conditioned on the reference rock ground motion. The former probability is represented by regional hazard curves. The latter probability is computed from soil amplification models. The proposed method is capable of yielding site factors for a target exceedance probability. This property does not exist in the current code-based site factors. Given a site class, if the site factors and the reference rock spectrum possess the same exceedance probability the resulting spectrum would have the same probability of exceedance. The use of such probabilistically consistent earthquake demands would be more relevant for probability-based seismic design and assessment. Owing to the use of hazard curves, the proposed method can account for regional seismicity in the computation of site factors.

A Study on the Damping Correction Factors for the Korean Standard Design Spectrum

In this study, we develop and propose damping correction factors for the Korean standard design spectra. The newly proposed Korean standard design spectra has been given only for 5% damping ratio. But in practice, engineers need design spectra for damping values other than 5%. To obtain design spectra for various damping values from the standard spectra, damping correction factors are derived. These factors modify the shape of design spectra in accordance with the damping ratio. Response spectra for various damping values are calculated from the earthquake records that had been used to calculate standard design spectra. They consist of 55 records from 18 earthquakes occurred in overseas intraplate regions and Korea. The regressed spectra for the damping values ranging from 0.5% to 50 % are compared with standard spectra at three regions acceleration, velocity and displacement sensitive regions. The regression analysis of these data rendered formula for damping correction factors. Finally, a single formula for damping correction factors is recommended that is valid for both horizontal and vertical design spectra and that is applicable to the entire range of periods. One thing to note that recommended damping correction factors is valid for the design spectrum of the rock grounds because the design spectra was developed based on the earthquake records of the rock ground.

A Study on the Grouting Effect of Ultrafine Cement in Rock Ground

A Study on the Grouting Effect of Ultrafine Cement in Rock Ground

Numerical modeling of seismic wave propagation and ground motion in underground mines

Dynamic rock support plays a critical role in ensuring mine safety and its design depends on several key design inputs. For rock support design and forensic analysis of rockburst damage, it is important to understand seismic wave propagation and ground motion distribution near excavation boundaries for seismic waves generated from a remote fault slip seismic event. This study aims at achieving a better understanding of wave propagation patterns around mine tunnels and capturing ground motion (Peak Particle Velocity - PPV) accurately for dynamic support design and forensic analysis. An advanced seismic wave propagation modeling tool, SPECFEM2D, is used to study complex wave propagation in underground mines. Attentions are paid to studying the influence of different mine excavations and geological structures on wavefields and ground motions near excavation boundaries. The simulation results show that the wavefields and the ground motion distributions become more complicated as more mine excavations and geological structures are involved. Moreover, the PPV distribution around a tunnel can be altered, leading to high and low PPV zones around the tunnel. In addition, modulation of travel time and long S-coda waves can be observed in the complex seismograms. Using the modeling approach, areas in an underground mine that may experience high potentials of rockburst damage could be identified and mine safety could be improved by implementing dynamic rock ground support in these areas.

Simulating Aqueous-Phase Isoprene-Epoxydiol (IEPOX) Secondary Organic Aerosol Production During the 2013 Southern Oxidant and Aerosol Study (SOAS).

The lack of statistically robust relationships between IEPOX (isoprene epoxydiol)-derived SOA (IEPOX SOA) and aerosol liquid water and pH observed during the 2013 Southern Oxidant and Aerosol Study (SOAS) emphasizes the importance of modeling the whole system to understand the controlling factors governing IEPOX SOA formation. We present a mechanistic modeling investigation predicting IEPOX SOA based on Community Multiscale Air Quality (CMAQ) model algorithms and a recently introduced photochemical box model, simpleGAMMA. We aim to (1) simulate IEPOX SOA tracers from the SOAS Look Rock ground site, (2) compare the two model formulations, (3) determine the limiting factors in IEPOX SOA formation, and (4) test the impact of a hypothetical sulfate reduction scenario on IEPOX SOA. The estimated IEPOX SOA mass variability is in similar agreement (r2 ∼ 0.6) with measurements. Correlations of the estimated and measured IEPOX SOA tracers with observed aerosol surface area (r2 ∼ 0.5-0.7), rate of particle-phase reaction (r2 ∼ 0.4-0.7), and sulfate (r2 ∼ 0.4-0.5) suggest an important role of sulfate in tracer formation via both physical and chemical mechanisms. A hypothetical 25% reduction of sulfate results in ∼70% reduction of IEPOX SOA formation, reaffirming the importance of aqueous phase chemistry in IEPOX SOA production.

Probabilistic seismic hazard assessment for the two layer fault system of Antalya (SW Turkey) area

Southwest Turkey, along Mediterranean coast, is prone to large earthquakes resulting from subduction of the African plate under the Eurasian plate and shallow crustal faults. Maximum observed magnitude of subduction earthquakes is Mw = 6.5 whereas that of crustal earthquakes is Mw = 6.6. Crustal earthquakes are sourced from faults which are related with Isparta Angle and Cyprus Arc tectonic structures. The primary goal of this study is to assess seismic hazard for Antalya area (SW Turkey) using a probabilistic approach. A new earthquake catalog for Antalya area, with unified moment magnitude scale, was prepared in the scope of the study. Seismicity of the area has been evaluated by the Gutenberg-Richter recurrence relationship. For hazard computation, CRISIS2007 software was used following the standard Cornell-McGuire methodology. Attenuation model developed by Youngs et al. Seismol Res Lett 68(1):58–73, (1997) was used for deep subduction earthquakes and Chiou and Youngs Earthq Spectra 24(1):173–215, (2008) model was used for shallow crustal earthquakes. A seismic hazard map was developed for peak ground acceleration and for rock ground with a hazard level of a 10% probability of exceedance in 50 years. Results of the study show that peak ground acceleration values on bedrock change between 0.215 and 0.23 g in the center of Antalya.

Failure mechanism and control technology of water-immersed roadway in high-stress and soft rock in a deep mine

Aiming at soft rock ground support issues under conditions of high stress and long-term water immersion, the ground failure mechanism is revealed by taking the deep-water sumps of Jiulong Mine as the engineering background and employing field investigation, tests of rock structure, mechanical properties and mineral composition. The main factors leading to the surrounding rock failure include the high and complex stress state of the water sumps, high-clay content and water-weakened rock, and the unreasonable support design. In this paper, the broken and fractured rock mass near roadway opening is considered as ground small-structure, and deep stable rock mass as ground large-structure. A support technology focusing on cutting off the water, strengthening the small structure of the rock and transferring the large structure of the rock is proposed. The proposed support technology of interconnecting the large and small structures, based on high-strength bolts, high-stiffness shotcrete layer plugging water, strengthening the small structure with deep-hole grouting and shallow-hole grouting, high-pretensioned cables tensioned twice to make the large and small structures bearing the pressure evenly, channel-steel and high-pretensioned cables are used to control floor heave. The numerical simulation and field test show that this support system can control the rock deformation of the water sumps and provide technical support to similar roadway support designs.

Ground motion prediction in Beirut: a multi-step procedure coupling empirical Green’s functions, ground motion prediction equations and instrumental transfer functions

The strike slip Yammouneh fault is the longest fault in Lebanon, crossing the territory from South to North. It was responsible for major historical earthquakes like the 1202 A.D. earthquake, estimated to Ms7.6. This paper presents a site-specific estimation of the ground motion caused by a potential Mw7.5 earthquake on the Yammouneh fault, similar to the 1202 event, for various sites within the Beirut area. The empirical Green’s function technique EGF is used to estimate the median and the standard deviations of the seismic ground motion at the reference station BHL, taking into account epistemic and aleatory uncertainties related to source parameters. These uncertainties were quantified through a sensitivity analysis of the position of the rupture nucleation Xnuc, the slip roughness parameter K, the corner frequency fc and the magnitude Mc of the EGF. The rock ground motion is then transferred to various other sites within the Beirut area, using instrumental Fourier transfer functions. Site amplification factors are next deduced by computing the ratio between response spectra at sediment sites and at a reference rock station. Considering the limits of the EGF method in the near field of extended sources, the EGF approach is considered only up to a magnitude Mw of 6.5. Selected Ground Motion Predictive Equations are then used to simulate a Mw7.5 event at a reference station. By applying the amplification factors, the response spectra at the different sites of Beirut are also calculated and compared with the actual response spectra used in the Lebanese regulations.

Excavation-Damaged Zone around Tunnel Surface under Different Release Ratios of Displacement

AbstractA tunnel excavation-damaged zone (EDZ) will gradually form with increasing release ratios of displacement (RRD) in the rock mass surrounding a tunnel. This paper presents a study of the longest subway tunnel in China, constructed with tunnel-boring machines (TBM) and the new Austrian tunneling method (NATM) in soft and weak rock ground. On the basis of the damage constitutive model, some studies are conducted using the FEM. The spatial distribution rules of EDZ and RRD are studied with a three-dimensional (3D) numerical simulation. The results show that the spatial support effect of the tunnel face is concentered in the range of approximately two times that of the tunnel diameter. A two-dimensional numerical simulation is carried out to study the relationship between the EDZ and RRD. The results show that the EDZ initiates when the RRD is more than 0.5, and the EDZ suddenly increases when RRD is more than 0.9.

Analysis on the damage behavior of mixed ground during TBM cutting process

Accurate prediction of rock cutting forces of disc cutters is especially significant for the design and construction of tunnel boring machine (TBM). Through the analysis of motion trajectory of TBM disc cutters, a three-dimensional model of rock breaking process of disc cutters is established. In terms of the rock strain which is resulted from the interaction between disc cutters and rock during the process of rock breaking, a three-dimensional cutting forces model is proposed with disc cutters set at certain parameters and in certain sizes. Subsequently, the equation of contacting forces between rock and disc cutter is derived. Moreover, a new method has been presented for the study of the rock breaking theory of the disc cutter and it also provides guidance for the design and application of TBM in tunnel excavation. The three-dimensional model for the rock breaking mechanism is used for predicting the cutting force for the situation of mixed ground.The damage field and the rock failure zone induced by disc cutter for mixed ground are also discussed in this study. In detail, the rock damage zones are divided into two parts, one is the left damage field which located in the outside of disc cutter. The other is the right damage field which located in the outside of disc cutter. The influence of the rock ground dip on the rock failure zone was also studied by parameter analysis.

Mechanical performance of TBM cutterhead in mixed rock ground conditions

The mechanical performance of TBM cutterhead including thrust, torque, eccentric force and overturning moment was calculated and analysed in different mixed rock ground conditions. The calculation model was built by identifying the rock type under each cutter using a ray intersection algorithm and calculating the cutting forces of each cutter using the CSM model. The mixed rock ground conditions were simplified as rock type distribution and rock strength classification. In the present paper, the rock distributions of the Layer-Banded Rock (LBR) and Random-Distributed Rock (RDR) types were considered. The influences of rock strength (Uniaxial Compressive Strength: UCS, Brazilian Tensile Strength: BTS), rock locations and number of rock layers were studied. For verification, a boring experiment was designed and conducted using an experimental cutterhead with 14 disc cutters. The rock box was poured with concrete C20, C40 and C60 layer by layer to prepare the LBR condition. The average torque and thrust of the calculation model and experiment were in good agreement. Some conclusions were drawn from the study on the rock strength, rock locations, area percentages of different rock layers and number of rock layers. And hence, some suggestions were proposed to enhance the tunnelling efficiency and reduce damage to the cutterhead.

지표면 유출 특성을 고려한 지하수위 변화가 지하차도 구조물 안정성에 미치는 영향

ABSTRACT: Ground water is one of important parameters in the designs of underpass structures because urban areas are characterized by soil ground which is relatively permeable than rock ground and a high level of ground water due to low elevation. Therefore, it is important properly to predict variations of the ground water when they can affect underpass structures. In this study, a series of numerical analyses are performed to predict the variations of ground water levels considering the degree of surface imperviousness and LID(Low Impact Development) application. In turn the stability of underground structure is assessed using predicted ground water level. The results show that an increase in the impervious surface area decreases the ground water level. The application of permeable pavement as a LID facility increases the ground water level, improving the infiltration capacity of rainfall into the ground. Seasonal variations of the ground water level are also verified in numerical simulation. The results of this study suggest that reasonable designs of underpass structures can be obtained with the suitable prediction and application of the ground water level considering the surface characteristics.Keywords: Underpass structure, Ground water, Buoyant force, Low impact development, Impervious surface