Seismic Wave Propagation Characteristics and Their Effects on the Dynamic Response of Layered Rock Sites

To investigate the seismic response of layered rock sites, a multidomain analysis method was proposed. Three finite element models with infinite element boundaries for layered sites were analysed. The results of this multidomain analysis show that stratum properties and elevation have an impact on wave propagation characteristics and the dynamic response of layered sites. Compared with the rock mass, the overlying gravel soil has a greater dynamic amplification effect at the sites. A time domain analysis parameter PGA(IMF) was proposed to analyse the effects of different strata on the seismic magnification effect of layered sites, and its application was also discussed in comparison with PGA. According to the frequency domain analysis, the interface of the rock mass strata has a low impact on the Fourier spectrum characteristics of the sites, but gravel soil has a great magnification effect on the spectrum amplitude in the high-frequency band (≥30 Hz) of waves. Moreover, the stratum properties have a great influence on the shape and peak value of the Hilbert energy and marginal spectrum at layered sites. When waves propagate from hard rock to soft rock, the peak value of the Hilbert energy spectrum changes from single to multiple peaks; then, in gravelly soil, the Hilbert energy spectral peak, its nearby amplitude and the amplitude in the high-frequency band (28–36 Hz) are obviously amplified. The frequency components and amplitude of the marginal spectrum become more abundant and larger from rock to gravelly soil in the high-frequency band (28–35 Hz).

Penetration Grouting Mechanism of Time-Dependent Power-Law Fluid for Reinforcing Loose Gravel Soil

The time-dependent behavior of power-law fluid has a significant influence on the grouting effects of reinforcing loose gravel soil. In this paper, based on basic rheological equations and the time-dependent behavior of rheological parameters (consistency coefficient and rheological index), rheological equations and penetration equations of time-dependent power-law fluid are proposed. Its penetration grouting diffusion mechanism for reinforcing loose gravel soil was then theoretically induced. A set of indoor experimental devices for simulating penetration grouting was designed to simulate the penetration grouting of power-law fluid with different time-dependent behaviors for reinforcing loose gravel soil. Then, relying on the COMSOL Multiphysics platform and Darcy’s law, three-dimensional numerical calculation programs for this mechanism were obtained using secondary-development programming technology. Thus, the numerical simulations of the penetration grouting process of power-law fluid with different time-dependent behaviors for reinforcing loose gravel soil were carried out. This theoretical mechanism was validated by comparing results from theoretical analyses, indoor experiments, and numerical simulations. Research results show that the three-dimensional numerical calculation programs can successfully simulate the penetration diffusion patterns of a time-dependent power-law fluid in loose gravel soil. The theoretical calculation values and numerical simulation values of the diffusion radius obtained from this mechanism are closer to indoor experimental values than those obtained from the penetration grouting diffusion theory of power-law fluid without considering time-dependent behavior. This mechanism can better reflect the penetration grouting diffusion laws of a power-law fluid in loose gravel soil than the theory, which can provide theoretical support and guidance for practical grouting construction.

Spatial patterns of insect herbivory within a forest landscape: the role of soil type and forest stratum

Background Insect herbivory has profound impacts on ecosystem processes and services. Although many efforts have been made to recognize the main drivers of insect herbivory at different scales, the results are inconsistent. One likely reason is that studies have insufficiently captured the spatially heterogeneous factors such as soil type and forest stratum within the stand that may significantly affect insect herbivory. In particular, there is a lack of studies that address the detailed spatial patterns of insect herbivory which are influenced by these factors. Methods We measured the detailed spatial patterns of insect herbivory on cork oak (Quercus variabilis Bl.) in response to soil type (gravel soil and loam) and forest stratum (the upper, lower, and sapling stratum), and correlated these patterns with a set of influencing factors (litter coverage, coverage of shrubs and herbs, soil nutrients, soil moisture, and leaf traits) in a forest landscape. Results Generally, insect herbivory was spatially heterogeneous within stands. Herbivory was significantly lower in gravel soil areas than in loam soil areas and the highest herbivory occurred in the lower stratum. However, there were also 41 individual plots in which the highest herbivory occurred in the upper stratum and 29 plots in which the highest herbivory occurred in the sapling stratum. There were significant differences in soil nutrient and water status between soil types, but no significant differences in leaf traits. The effects of forest stratum on leaf traits were also inconsistent with those on insect herbivory. Conclusions Leaf traits may not be the main factors influencing insect herbivory in the field. Soil type may have major effects on herbivory patterns by influencing litter coverage while higher coverage of shrubs and herbs may reduce herbivory in the sapling stratum. These findings may advance our understanding of tree-herbivore interactions in real-world situations and have important implications for the sustainable management of forest ecosystems.

A LABORATORY MODEL FOR THE ADSORPTION AND LOSS OF THE SULFATE TRANSPORT IN MULTI POROUS MEDIA OF SOIL

Development of industries and agriculture, salts, especially sulfates, used in many industries, such as fertilizers and pesticides, have become one of the most common problems. In this paper, a laboratory model was established to study the sulfate-contaminated transport process. Four samples of porous media contain the same pollutant, sandy soil, sandy gravel soil, agricultural (organic) soil, and calcareous soil. Where a pollutant is pumped at a concentration of 280 mg/l through a system consisting of a tube of length 4 meters and 8 cm thickness and distributed in the soil Each type is one meter. The results showed that all types of soils, except organic, had leaching or loss of sulfates from the soil and dissolving them with a soil solution. The transfer of pollutants from soil to the solution may reach between 50 to 300 mg/l per meter, while organic soil showed the ability to Absorption up to 100 mg/L per meter. However, it was found that organic soil contains the largest amount of sulfate and was able to adsorption, and it was found that bacterial activity has a role in reducing sulfate in organic soil and thus returning the soil to adsorption after a certain time of saturation process.

Engineering Characteristics of Natural Wide Grading Gravelly Soil in Construction of Extra-High Earth-Rockfill Dam

Wide grading gravelly soil is an advantageous anti-seepage material in construction of high earth-rock dam. From the experience of earth-rockfill dam construction at home and abroad, it is more and more common to use wide grading gravelly soils such as moraine soil, weathered rock and gravel soil as anti-seepage material in construction of high earth-rockfill dams. Regarding the engineering characteristics of natural wide grading of soil material for 300m core-wall earth-rockfill dams in this paper, a series of physical and numerical tests were carried out to study its permeability and mechanical properties. By comparing the characteristics of impermeable soil materials of the projects already built and to be built at home and abroad, the preliminary indicators of impermeable soil materials are as follows: 1) Combined with the existing engineering experience and test results, the content of particles with particle size greater than 5mm should be neither over 50% nor lower than 30%. The content of particles with particle size less than 0.075mm should not be less than 15%; the content of clayey particles with particle size less than 0.005mm should not be less than 6%. 2) It is appropriate to control the permeability coefficient of impermeable soil material at less than 1×10-5cm/s.

Numerical Simulation Study on Compression Characteristics of Gravelly Soil Mixture Based on Soft Servo Method

Because of complex mechanical properties and deformation mechanism, gravel soil mixture is an important medium of concern in the field of geotechnical engineering. Based on the continuous-discontinuous coupling algorithm formed by the structure shell elements and the particle discrete element method (PFC3D), the soft servo loading of the sample is realized, and the typical triaxial compression test data are used to calibrate mesoscale parameters. Furthermore, the numerical tests under different rock contents and confining pressure are carried out. The change rule of shear strength of mixed medium is discussed. It shows that the continuous-discontinuous coupling algorithm achieves a good effect in reflecting the deformation process. Under the mechanism of the flexible servo, the failure mode of the sample takes on drum-failure mode, and the internal of the damaged sample forms an obvious asymmetric X-shaped shear band. With the increase of stone content, the internal friction angle and cohesive force distribution of the sample have certain discreteness, but on the whole, the internal friction angle and cohesive force increase with the increase of stone content. The results can provide a reference for the parameter determination of mixed mediums such as gravel soil.

A Constitutive Model of Sandy Gravel Soil under Large-Sized Loading/Unloading Triaxial Tests

Based on large-scale triaxial tests of sandy gravel materials, the strength and deformation characteristics under loading/unloading conditions are analyzed. At the same time, the applicability of the hyperbolic constitutive model to sandy gravel is studied using experimental data. The results indicate that sandy gravel under low confining pressures (0.2 and 0.4 MPa) shows a weak softening trend; the higher the confining pressure, the more obvious the hardening tendency (0.6 and 0.8 MPa) and the greater the peak strength. During unloading tests, strain softening occurs, and the peak strength increases with increasing confining pressure. During loading tests, dilatancy appears when the confining pressure is low (0.2 MPa). With increasing confining pressure (0.4, 0.6, and 0.8 MPa), the dilatancy trend gradually weakens, and the cumulative volume tric strain increases, which reflects the relevance of the stress paths. Through research, it is found that the hyperbolic constitutive model has good applicability to sandy gravel soils, and the corresponding model parameters are obtained.