Geodetic study on earth surface loading with GNSS and GRACE

Ice,snow,and liquid water on the surface of the Earth exert downward force onto the solid earth and deform the lithosphere typically in seasonal timescale.Space techniques,such as Global Navigation Satellite System(GNSS),made it possible to directly measure subtle displacements caused by loading.We can also observe such loads with time-variable gravity using gravity recovery and climate experiment satellites.These techniques made surface loads an attracting scientific target of modern geodesy.In this paper we briefly review the history of geophysical studies of surface loads through geodetic observations of crustal deformation and time-variable gravity.We also review advanced topics such as short-term crustal deformation due to severe meteorological episodes and monitoring of terrestrial water storages.We also present a few related topics such as the change of the obliquity of the Earth due to loads and artificial crustal subsidence signals caused by snow accretion onto GNSS antenna radomes.

Effect of surface loading on the hydro-mechanical response of a tunnel in saturated ground

The design of underground spaces in urban areas must account not only for the current overburden load but also for future surface loads,such as from construction of high-rise buildings above underground structures.In saturated ground,the surface load will generate an additional mechanical response through stress changes and ground displacement,as well as a hydraulic response through pore pressure changes.These hydro-mechanical(H-M)changes can severely influence tunnel stability.This paper examines the effect of surface loading on the H-M response of a typical horseshoe-shaped tunnel in saturated ground.Two tunnel models were created in the computer code Fast Lagrangian Analysis of Continua(FLAC).One model represented weak and low permeability ground(stiff clay),and the other represented strong and high permeability ground(weathered granite).Each of the models was run under two liner permeabilities:permeable and impermeable.Two main cases were compared.In Case 1,the surface load was applied 10 years after tunnel construction.In Case 2,the surface load was applied after the steady state pore pressure condition was achieved.The simulation results show that tunnels with impermeable liners experienced the most severe influence from the surface loading,with high pore pressures,large inward displacement around the tunnels,and high bending moments in the liner.In addition,the severity of the response increased toward steady state.This induced H-M response was worse for tunnels in clay than for those in granite.Furthermore,the long-term liner stabilities in Case 1 and Case 2 were similar,indicating that the influence of the length of time between when the tunnel was completed and when the surface load was applied was negligible.These findings suggest that under surface loading,in addition to the ground strength,tunnel stability in saturated ground is largely influenced by liner permeability and the long-term H-M response of the ground.

Static response of a layered magneto-electro-elastic half-space structure under circular surface loading

A cylindrical system of vector functions, the stiffness matrix method and the corresponding recursive algorithm are proposed to investigate the static response of transversely isotropic,layered magneto-electro-elastic（MEE） structures over a homogeneous half-space substrate subjected to circular surface loading. In terms of the system of vector functions, we expand the extended displacements and stresses, and deduce two sets of ordinary differential equations, which are related to the expansion coeficients. The solution to one of the two sets of these ordinary differential equations can be evaluated by using the stiffness matrix method and the corresponding recursive algorithm. These expansion coeficients are then integrated by adaptive Gaussian quadrature to obtain the displacements and stresses in the physical domain. Two types of surface loads, mechanical pressure and electric loading,are considered in the numerical examples. The calculated results show that the proposed technique is stable and effective in analyzing the layered half-space MEE structures under surface loading.

Statistical approach to determination of overhaul and maintenance cost of loading equipment in surface mining

The purpose of this research was to develop a new approach in determination of overhaul and maintenance cost of loading equipment in surface mining. Two statistical models including univariate exponential regression (UER) and multivariate linear regression (MLR) were used in this study. Loading equipment parameters such as bucket capacity, machine weight, engine power, boom length, digging depth, and dumping height were considered as variables. The results obtained by models and mean absolute error rate indicate that these models can be applied as the useful tool in determination of overhaul and maintenance cost of loading equipment. The results of this study can be used by the decision-makers for the specific surface mining operations.

Dynamic behavior of single-layer latticed cylindrical shells subjected to seismic loading

The single-layer latticed cylindrical shell is one of the most widely adopted space-fl'amed structures.In this paper,free vibration properties and dynamic response to horizontal and vertical seismic waves of single-layer latticed cylindrical shells are analyzed by the finite element method using ANSYS software.In the numerical study,where hundreds of cases were analyzed,the parameters considered included rise-span ratio,length-span ratio,surface load and member section size.Moreover,to better define the actual behavior of single-layer latticed shells,the study is focused on the dynamic stress response to both axial forces and bending moments.Based on the numerical results,the effects of the parameters considered on the stresses are discussed and a modified seismic force coefficient method is suggested.In addition,some advice based on these research results is presented to help in the future design of such structures.

Risk Analysis of Breakwater Caisson Under Wave Attack Using Load Surface Approximation

A new load surface based approach to the reliability analysis of caisson-type breakwater is proposed. Uncertainties of the horizontal and vertical wave loads acting on breakwater are considered by using the so-called load surfaces, which can be estimated as functions of wave height, water level, and so on. Then, the first-order reliability method（FORM） can be applied to determine the probability of failure under the wave action. In this way, the reliability analysis of breakwaters with uncertainties both in wave height and in water level is possible. Moreover, the uncertainty in wave breaking can be taken into account by considering a random variable for wave height ratio which relates the significant wave height to the maximum wave height. The proposed approach is applied numerically to the reliability analysis of caisson breakwater under wave attack that may undergo partial or full wave breaking.

Mechanical Modeling of Dike Pathways in the Crust: Effect of Layering and Surface Loads

Magma is generated mostly in the Earth’s mantle by decompression melting and transported through the crust to reach the Earth’s surface.The main mechanism for magma transport is diking,but the pathways taken by

Fuel characteristics, loads and consumption in Scots pine forests of central Siberia

Forest fuel investigations in central and southern Siberian taiga of Scots pine forest stands dominated by lichen and feather moss ground vegetation cover revealed that total aboveground biomass varied from 13.1 to 21.0 kg/m 2.Stand biomass was higher in plots in the southern taiga,while ground fuel loads were higher in the central taiga.We developed equations for fuel biomass(both aerial and ground)that could be applicable to similar pine forest sites of Central Siberia.Fuel loading variability found among plots is related to the impact and recovery time since the last wildfi re and the mosaic distribution of living vegetation.Fuel consumption due to surface fi res of low to high-intensities ranged from 0.95 to 3.08 kg/m 2,that is,18–74%from prefi re values.The total amount of fuels available to burn in case of fi re was up to 4.5–6.5 kg/m 2.Moisture content of fuels(litter,lichen,feather moss)was related to weather conditions characterized by the Russian Fire Danger Index(PV-1)and FWI code of the Canadian Forest Fire Weather Index System.The data obtained provide a strong foundation for understanding and modeling fi re behavior,emissions,and fi re eff ects on ecosystem processes and carbon stocks and could be used to improve existing global and regional models that incorporate biomass and fuel characteristics.

Topology optimization of 3D structures with design-dependent loads

Topology optimization of continuum structures with design-dependent loads has long been a challenge. In this paper, the topology optimization of 3D structures subjected to design-dependent loads is investigated. A boundary search scheme is proposed for 3D problems, by means of which the load surface can be identified effectively and efficiently, and the difficulties arising in other approaches can be overcome. The load surfaces are made up of the boundaries of finite elements and the loads can be directly applied to corresponding element nodes, which leads to great convenience in the application of this method. Finally, the effectiveness and efficiency of the proposed method is validated by several numerical examples.

Estimation and Spatio-temporal Patterns of Carbon Emissions from Grassland Fires in Inner Mongolia,China

Grassland fires results in carbon emissions,which directly affects the carbon cycle of ecosystems and the carbon balance.The grassland area of Inner Mongolia accounts for 22%of the total grassland area in China,and many fires occur in the area every year.However,there are few models for estimation of carbon emissions from grassland fires.Accurate estimation of direct carbon emissions from grassland fires is critical to quantifying the contribution of grassland fires to the regional balance of atmospheric carbon.In this study,the regression equations for aboveground biomass(AGB)of grassland in growing season and MODIS NDVI(Normalized Difference Vegetation Index)were established through field experiments,then AGB during Nov.–Apr.were retrieved based on that in Oct.and decline rate,finally surface fuel load was obtained for whole year.Based on controlled combustion experiments of different grassland types in Inner Mongolia,the carbon emission rate of grassland fires for each grassland type were determined,then carbon emission was estimated using proposed method and carbon emission rate.Results revealed that annual average surface fuel load of grasslands in Inner Mongolia during 2000–2016 was approximately 1.1978×1012 kg.The total area of grassland which was burned in the Inner Mongolia region over the 17-year period was 5298.75 km2,with the annual average area of 311.69 km2.The spatial distribution of grassland surface fuel loads is characterized by decreasing from northeast to southwest in Inner Mongolia.The total carbon emissions from grassland fires amounted to 2.24×107 kg with an annual average of 1.32×106 for the study area.The areas with most carbon emissions were mainly concentrated in Old Barag Banner and New Barag Right Banner and on the right side of the Oroqin Autonomous Banner.The spatial characteristics of carbon emission depend on the location of grassland fire,mainly in the northeast of Inner Mongolia include Hulunbuir City,Hinggan League,Xilin Gol League and Ulanqab City.The area and spatial location of grassland fires can directly affect the total amount and spatial distribution of carbon emissions.This study provides a reference for estimating carbon emissions from steppe fires.The model and framework for estimation of carbon emissions from grassland fires established can provide a reference value for estimation of carbon emissions from grassland fires in other regions.

Mechanical responses of multi-layered ground due to shallow tunneling with arbitrary ground surface load

An analytical model based on complex variable theory is proposed to investigate ground responses due to shallow tunneling in multi-layered ground with an arbitrary ground surface load.The ground layers are assumed to be linear-elastic with full-stick contact between them.To solve the proposed multi-boundary problem,a series of analytic functions is introduced to accurately express the stresses and displacements contributed by different boundaries.Based on the principle of linear-elastic superposition,the multi-boundary problem is converted into a superposition of multiple single-boundary problems.The conformal mappings of different boundaries are independent of each other,which allows the stress and displacement fields to be obtained by the sum of components from each boundary.The analytical results are validated based on numerical and in situ monitoring results.The present model is superior to the classical model for analyzing ground responses of shallow tunneling in multi-layered ground;thus,it can be used with assurance to estimate the ground movement and surface building safety of shallow tunnel constructions beneath surface buildings.Moreover,the solution for the ground stress distribution can be used to estimate the safety of a single-layer composite ground.

Use of the Cam-Clay Model in Finite Element Calculations after Identification of Soils from Simple Mechanical Tests

In order to make the use of complex elasto-plastic behavior models more accessible, we attempted to identify the Cam-Clay model in two samples of tropical and lateritic soils (from Senegal/West Africa) from casagrande box shear and oedometric tests. This methodology was used as a substitute for triaxial trials. In this article, we first verify the test results by the finite element method with the Optum software. We use a simulation of the tests with the modified Cam Clay model as the behavior model. Then, we simulate the oedometric test on tropical soils with the Castem software and also use the modified Cam Clay model. These calculations make it possible to write the criterion of plasticity of the material starting from the expression of the surface of load while passing by the calculation of the volumetric and deviatoric stresses.

Collaborative optimization of screening efficiency and screen surface load-PartⅠ:Modeling and evaluation

The screen surface load(SSL)caused by granular materials is an important factor affecting the structural performance of vibrating screen.Based on virtual experiment,a multi-objective collaborative optimiza-tion method is proposed to control the SSL under high screening efficiency(SE)in this work.Firstly,a DEM model was established to study the influence of process parameters on SE and SSL.Secondly,the NSGA-Ⅱ(Non-dominated Sorting Genetic Algorithm)was employed to optimize the screening parameters with both SE and SSL as targets.The optimization method proves to be effective implementing on a linear vibrating screening.With SE equals to 98.5%,the SSL optimizable range is 39.2%.While compromising the SE to 88.7%,the SSL optimizable range improves to 48.6%.The result shows that the collaborative optimization could effectively control the SSL while maintaining a high SE,which is of great significance to improve the service life of screen surface and screen body.

Loaded-frequency selective surface

A new frequency-selective surface(FSS)with loadings is introduced in this paper and analyzed by way of period moment methods(PMMs).The simulated results show that FSS may operate in different bands and especially generate a large reduction in the resonant frequency for a fixed unit cell size through different loadings.This provides a new orientation in the development for FSS.Practical circuits are fabricated,and the measured results agree well with the simulated results.