Modeling of wave propagation induced by underground explosion

A piecewise linear Drucker–Prager strength criterion and an isotropic continuum damage model with the damage scalar depending on an equivalent tensile strain are suggested to model rock mass behavior under blast loading. A rate-dependent constitutive relation is employed to model the energy dissipation caused by two sources, namely irreversible degradation of damage and permanent deformation caused by plasticity. The suggested model is incorporated with a commercially available software AUTODYN through its user’s subroutine function. Coupling of Euler and Lagrange processors are used to include all the materials under consideration such as explosive, air and rock mass, in the calculation. Using AUTODYN and the suggested model, shock wave propagation in rock mass induced by an underground explosion is simulated. Numerical results obtained agree favorably well with those obtained from an independently conducted field test. It demonstrates that the suggested model can be used to predict the damage area, plastic zone and ground motions generated by underground explosions.     

The great 1815 eruption of Tambora and future risks from large‐scale volcanism

The year 2015 marks the bicentenary of the largest eruption in recent historic times: the 10–11 April 1815 eruption of Mount Tambora, Indonesia. Two hundred years after the eruption, an incomplete or inaccurate record of large eruptions over the past millennia, and uncertainties in determining the true sizes of eruptions, hamper our ability to predict when the next eruption of this scale may occur. Such events would have catastrophic effects locally and, possibly, world‐wide. The problem is compounded by a lack of detailed knowledge of how and over what timescales large magma reservoirs that feed such eruptions grow and assemble, and of the surface manifestations of these processes recorded through geophysical or geochemical monitoring techniques.     

Permeability determination of porous media using large‐scale finite elements and iterative solver

The problem of finite element simulation of incompressible fluid flow in porous medium is considered. The porous medium is characterized by the X‐ray microtomography technique in three dimensions. The finite calculus‐based stabilization technique is reviewed to implement the equal order finite element interpolation functions for both velocity and pressure. A noble preconditioner, the nodal block diagonal preconditioner, is considered whose performance is thoroughly investigated. Combining this preconditioner with a standard iterative solver during the computational homogenization procedure, it is possible to carry out the large‐scale fluid flow simulation for estimating permeability of the porous medium with reasonable accuracy and reliability. Copyright © 2013 John Wiley & Sons, Ltd.     

Accelerating strategies to the numerical simulation of large‐scale models for sequential excavation

In this paper, a novel combination of well‐established numerical procedures is explored in order to accelerate the simulation of sequential excavation. Usually, large‐scale models are used to represent these problems. Due to the high number of equations involved, the solver algorithm represents the critical aspect which makes the simulation very time consuming. The mutable nature of the excavation models makes this problem even more pronounced. To accomplish the representation of geometrical and mechanical aspects in an efficient and simple manner, the proposed solution employs the boundary element method with a multiple‐region strategy. Together with this representational system, a segmented storage scheme and a time‐ordered tracking of the changes form an adequate basis for the usage of fast updating methods instead of frontal solvers. The present development employs the Sherman–Morrison–Woodbury method to speed up the calculation due to sequential changes. The efficiency of the proposed framework is illustrated through the simulation of test examples of 2D and 3D models. Copyright © 2006 John Wiley & Sons, Ltd.     

A stepwise damping‐solvent extraction method for large‐scale dynamic soil–structure interaction analysis in time domain

Time‐domain analysis of dynamic soil–structure interaction based on the substructure method plays an increasing role in practical applications as compared with the frequency‐domain analysis. Efficient and accurate modelling of the unbounded soil or rock medium has been a key issue in such an analysis. This paper presents a subregional stepwise damping‐solvent extraction formulation for solving large‐scale dynamic soil–structure problems in the time domain. Accuracy and efficiency of the formulation are evaluated in detail for a classical problem involving a rigid strip foundation embedded in a half‐space. A practical large‐scale soil–structure interaction problem, which represents a high concrete gravity dam subjected to seismic load, is then analysed using the proposed method. Various responses of the dam, including time histories of the crest displacement and acceleration and contours of the peak principal stresses within the dam body, are presented. Comparisons are also made between these results with those obtained using other models for the unbounded medium. Copyright © 2007 John Wiley & Sons, Ltd.     

地应力场下岩体爆体的数值模拟

建立了地应力作用下岩体在爆炸荷载作用下的运动微分方程,并对岩体中的地应力采用隐式分析方法,对爆炸的高速动载作用采用显式分析方法,通过隐式－显式连续求解完成地应力作用下岩体爆炸的数值模拟。数值算例结果表明,近爆腔处,较低的静应力场与较高的动应力场作用时爆炸动态应力波占主导地位,初始应力对爆破应力波影响较小。在远离爆腔处,高地应力存在改变了爆破应力波的传播规律,对爆炸岩体有很大影响。     

Review and enhancement of 3D concrete models for large‐scale numerical simulations of concrete structures

The present paper focuses on selected plasticity and damage‐plasticity models for describing the 3D material behavior of concrete. In particular, a plasticity model and a damage‐plasticity model are reviewed and evaluated. Based on the results of the evaluation, enhancements are proposed, aiming at improving the correspondence between predicted and observed material behavior and aiming at implementing a robust and efficient stress update algorithm in a finite element program for performing large‐scale 3D numerical simulations of concrete structures. The capabilities of the concrete models are demonstrated by 3D numerical simulations of benchmark tests with combined bending and torsional loading and combined compression and shear loading and by a large‐scale 3D finite element analysis of a model test of a concrete arch dam. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of wave non‐linearity on the standing‐wave‐induced seabed response

A standing wave in front of a seawall may reach a height more than twice of its incident component. When excess pore pressure occurs, it may even induce seabed instability, hence endangering the structure. This issue was studied previously using only linear wave theory. In this paper, standing‐wave theory to a second‐order approximation is applied, in order to demonstrate the differences between these two solutions. The spatial and temporal variations in the instantaneous pore pressure are first calculated, in addition to their vertical distributions. The effects of wave height, water depth and the degree of soil saturation on pore pressure distributions are then discussed, followed by the net pore pressure averaged over one wave cycle. The results suggest the existence of a residual pore pressure in the seabed and its net pore pressure can be used to estimate the wave‐induced liquefaction potential in a soil column. It also indicates that, in deep water, the second‐order solution predicts that a negative pore pressure at an antinode which may be greater than a positive pressure. Overall, the second‐order solution is found to agree better with the experimental results of the pore pressures available, compared to the linear solution. Copyright © 2000 John Wiley & Sons, Ltd.     

Numerical modelling of multistage caving processes: insights from multi‐seam longwall mining‐induced subsidence

Evaluating the induced subsidence is a critical step in multi‐seam longwall mining. Numerical modelling can be a cost‐effective approach to this problem. Numerical evaluation of longwall mining‐induced subsidence is much more complicated when more than one seam is to be extracted. Only a few research works have dealt with this problem. This paper discusses the essential requirements of a robust numerical modelling approach to simulation of multi‐seam longwall mining‐induced subsidence. In light of these requirements, the previous works on this topic are critically reviewed. A simple yet robust FEM‐based modelling approach is also proposed that is capable of simulating caving process, rock mass deterioration and subsidence around multi‐seam excavations. The effectiveness of this approach in comparison with two other conventional FEM approaches is demonstrated through numerical examples of two different multi‐seam mining configurations. Results show that the proposed numerical modelling approach is the only robust method, which is capable of simulating multi‐seam subsidence in both demonstrated cases. Copyright © 2016 John Wiley & Sons, Ltd.     

条形药包在隧道爆破中产生的应力场的实测分析

基于条形药包的爆破特性,针对隧道爆破的装药形式,把隧道爆破简化成几个条形药包的微差爆破,在隧道爆破区域的径向应力波为柱形,隧道掘进的轴向应力波为几个并列半圆形。应力波强度分布很不均匀,爆破区域的径向应力强度最大,向爆区端部延伸径向应力强度逐渐减小。进入爆区端部后,应力强度减小更明显。随着与爆区轴线夹角的减小,端部应力强度再次减小,爆区端部轴线方向应力强度最小。     

Time‐scale analysis in unsaturated porous media under external wave loads

Extreme waves caused by tsunamis and storm surges can lead to soil failures in the near‐shore region, which may have severe impact on coastal environments and communities. Multiphase flows in deformable porous media involve several coupled processes and multiple time scales, which are challenging for numerical simulations. The objective of this study is to investigate the roles of the various processes and their interactions in multiphase flows in unsaturated soils under external wave loading, via theoretical time‐scale analysis and numerical simulations. A coupled geomechanics–multiphase flow model based on conservation laws is used. Theoretical analysis based on coupled and decoupled models demonstrates that transient and steady‐state responses are governed by pore pressure diffusion and saturation front propagation, respectively, and that the two processes are essentially decoupled. Numerical simulations suggest that the compressibility of the pore fluids and the deformation of the soil skeleton are important when the transient responses of the media are of concern, while the steady‐state responses are not sensitive to these factors. The responses obtained from the fully coupled numerical simulations are explained by a simplified time‐scale analysis based on coupled and decoupled models. Copyright © 2010 John Wiley & Sons, Ltd.     

Sedimentary characteristics of large‐scale lacustrine beach‐bars and their formation in the Eocene Boxing Sag of Bohai Bay Basin,East China

The beach‐bar reservoir play has become an important exploration target within the Bohai Bay Basin, especially in the Boxing Sag within the Dongying Depression, where a large‐scale lacustrine beach‐bar oil pool has been discovered recently. The sedimentary characteristics, distribution patterns and formation mechanisms of beach‐bar sand bodies in the upper fourth member of the Eocene Shahejie Formation (Es4s) in the Boxing Sag were studied in detail based on seismic, well log data and core data. The Es4s in the Boxing Sag is composed of a third‐order sequence consisting of three systems tracts, i.e. a lowstand systems tract, a transgressive systems tract and a highstand systems tract. Beach‐bar sand bodies were deposited widely in the basin during the lowstand systems tract period. The sandy beach‐bars are characterized by siltstones, fine‐grained silty sandstones interbedded with thin mudstone units. The presence of well‐developed sedimentary structures, such as swash bedding, parting lineation, parallel bedding, ellipsoidal mud clasts, ripples, terrestrial plant debris and vertical burrows, suggests that beach‐bars were deposited in a relatively shallow water environment under the influence of strong hydrodynamics. Laterally, the sandy beach facies occurred as a more continuous sheet‐like body around the sandy bar in most parts of the sag. Stratigraphically, beach‐bars were distributed mainly in the lowstand systems tract and they were less well‐developed in the transgressive systems tract and highstand systems tract. Several factors were probably responsible for the occurrence of the large‐scale beach‐bars during the lowstand systems tract period, including: (i) a gentle palaeoslope and relatively weak structural activities; (ii) a shallow‐water condition with a strong hydrodynamic environment; (iii) high‐frequency oscillations of the lake level; and (iv) an abundant terrigenous clastic feeding system with multiple‐point and linear sediment sources.     

地下洞室开挖爆破围岩松动圈的数值分析计算

根据数值计算提出了在地下洞室开挖爆破中,确定围岩松动圈的方法。给出了地下洞室开挖爆破的三维弹塑性损伤有限元计算方法。该方法论述了爆破荷载、重力荷载和开挖荷载的计算、施加以及迭代的方法,可以合理反应爆破对围岩稳定的影响和锚固支护施加的效果;结合岩石松动圈的实测方法,推导了判定围岩开始松动的损伤系数阈值公式,可以结合数值计算得到的洞周围岩损伤系数分布,确定在开挖爆破作用下围岩松动圈的范围。对实际工程的分析计算表明,根据数值计算判定的围岩松动范围与实测松动范围的规律基本一致,量值吻合较好,其结果为地下洞室开挖爆破的围岩松动圈的确定提供了有效的方法。     

Middle Pleistocene large‐mammal faunas from North Iberia: palaeobiogeographical and palaeoecological implications

The rich Quaternary fossil record from the Cantabrian region (NW Iberia) is virtually restricted to the Late Pleistocene, with Middle Pleistocene findings very rare. This work presents the study of two Middle Pleistocene palaeontological sites in the Cantabrian region: Llantrales quarry and Mestas de Con mine, both discovered and first described in the 1950s but never studied in detail thereafter. The material was here re‐analysed and re‐evaluated. Taxonomic attributions have been changed in most cases and, consequently, chronological assignments of the fossils have also been changed. This first detailed study of the assemblage from Llantrales quarry revealed the occurrence of the large‐sized deer Praemegaceros solilhacus, which has never been reported previously in North Iberia. Cervus cf. elaphus and Stephanorhinus cf. hundsheimensis were also identified. The age of these fossils was originally regarded as Pontian (late Miocene), but new palaeontological results indicate a much younger age, most likely from around 0.8 to 0.5 Ma. A taxonomic re‐evaluation of the fossils from Mestas de Con provided different results with respect to the 1950s works. The faunal association is composed of a large‐sized deer (probably corresponding to Praemegaceros), Cervus elaphus, Capreolus cf. capreolus, Bison sp. (small sized), Equus sp. (large sized), Stephanorhinus hemitoechus, Ursus sp. and Homotherim latidens. This faunal association was evaluated within a western European context and proves to be highly analogous to other contemporary assemblages there. The chronology was initially regarded as late Villafranchian (in a broader sense). New results, documenting the co‐occurrence of Stephanorhinus hemitoechus and Homotherium latidens, indicate a more precise and younger age, most likely between 0.6 and 0.4 Ma. These two fossil assemblages provide new and relevant information on the Middle Pleistocene faunas from a geographical region where this information, compared with other western European areas, is rare and poorly known.     

Solution of quasi‐static large‐strain problems by the material point method

A procedure for solving quasi‐static large‐strain problems by the material point method is presented. Owing to the Lagrangian–Eulerian features of the method, problems associated with excessive mesh distortions that develop in the Lagrangian formulations of the finite element method are avoided. Three‐dimensional problems are solved utilizing 15‐noded prismatic and 10‐noded tetrahedral elements with quadratic interpolation functions as well as an implicit integration scheme. An algorithm for exploiting the numerical integration procedure on the computational mesh is proposed. Several numerical examples are shown. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical analysis of 1‐D compression wave propagation in saturated poroelastic media

A numerical procedure is presented for the simulation of 1‐D compression wave propagation in saturated poroelastic media. The media are modelled as a two‐phase system consisting of compressible fluid and solids. Viscous coupling forces resulting from the relative motion between phases are characterized as Darcy type. The numerical procedure can account for effects of axial strain, nonlinear material behaviour, and various drained and undrained boundary conditions. Time integration is carried out explicitly and isothermal conditions are assumed. The method is capable of modelling shock wave fronts without introducing artificial viscosity. Numerical results are in close agreement with analytical solutions for several simplified cases and indicate that mass coupling may have important effects on fluid velocity and wave speed. Corresponding effects on solid velocity and wave speed are much smaller. Numerical results also indicate that damping occurs in a saturated poroelastic column and is dependent on the value of hydraulic conductivity. Copyright © 2007 John Wiley & Sons, Ltd.     

应力波作用下巷道层裂破坏的数值模拟研究

采用LS-DYNA软件,对扰动应力波作用下巷帮围岩层裂破坏结构的形成过程、扰动应力波强度pmax对层裂结构形成的影响进行了有效的数值模拟,得到了一定巷道围岩应力状态下巷帮围岩层裂结构的形状、厚度等特征。结果表明：扰动应力波是形成巷帮层裂结构,继而诱发冲击矿压的重要因素;扰动应力波的强度决定了是否形成巷帮层裂结构及其层裂结构的范围大小。研究结果对揭示煤矿冲击矿压的诱发机理,及采取有效地防治技术具有重要意义     

Numerical prediction of gas migration properties in Callovo‐Oxfordian (COx) argillite using morpho‐mathematical operations

The feasibility study of long‐term radioactive waste storage in low‐permeable rocks has been performed by considering various damage and failure scenarios. This study aims at the numerical investigation of gas (mainly produced by corrosion of metallic parts) migration properties through the low‐permeable formation of Callovo‐Oxfordian argillite. Traditional methods, based on macroscopic approaches or homogeneous transport properties, are inappropriate to analyze this issue at the mesoscopic/microscopic scale. In this study, realistic porous space morphologies are constructed through union of excursions of random fields considering different experimental pore size distributions. Afterwards, purely geometric analysis of pore space is conducted by morpho‐mathematical operations for the purpose of the extraction of preferential gas transport pathways and the prediction of the gas entry pressure, the gas breakthrough pressure, and the following imbibition process.     

A three‐phase soil model for simulating stress wave propagation due to blast loading

A three‐phase soil model is proposed to simulate stress wave propagation in soil mass to blast loading. The soil is modelled as a three‐phase mass that includes the solid particles, water and air. It is considered as a structure that the solid particles form a skeleton and their voids are filled with water and air. The equation of state (EOS) of the soil is derived. The elastic–plastic theory is adopted to model the constitutive relation of the soil skeleton. The damage of the soil skeleton is also modelled. The Drucker–Prager strength model including the strain rate effect is used to describe the strength of the soil skeleton. The model is implemented into a hydrocode Autodyn. The recorded results obtained by explosion tests in soil are used to validate the proposed model. Copyright © 2004 John Wiley & Sons, Ltd.