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).

Experimental Investigation on the Behavior of Gravelly Sand Reinforced with Geogrid under Cyclic Loading

In view of the dynamic response of geogrid-reinforced gravel under high-speed train load, this paper explores the dynamic characteristics of geogrid-reinforced gravel under semi-sine wave cyclic loading. A number of large scale cyclic triaxial tests were performed on saturated gravelly soil reinforced with geogrid to study the influence of the number of reinforcement layers and loading frequencies on the dynamic responses of reinforced gravelly sand subgrade for high speed rail track. The variation of cumulative axial and volumetric strains, excess pore pressure and resilient modulus with number of loading cycles, loading frequency, and reinforcement arrangement are analyzed. The test results reveal that the cumulative axial strain decreases as the number of reinforcement layers increases, but increases with loading frequency. The resilience modulus increases with the number of reinforcement layers, but decreases as the loading frequency increases. The addition of geogrid can reduce the excess pore water pressure of the sample, but it can slightly enhance the rubber mold embedding effect of the sand sample. As the loading frequency increases, the rubber mold embedding effect gradually weakens.

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.

Effect of Particle Shape on the Deformation and Stress Reduction of a Gravel Soil Due to Wetting

In this paper, the effect of particle shape is investigated on the stress reduction and collapse deformation of gravelly soil using medium-scale direct shear test apparatus under different relative densities, normal stress, and shear stress levels. The Micro-Deval test was used to produce sub-angular particles from angular particles with continuous smoothening of the corners of the particles. Two series of soil specimens were obtained with the same rock type, particle size distribution, and relative density but different particle shapes. In addition to traditional direct shear tests on dry and wet specimens, a specific test procedure was applied to explore the stress reduction and collapse of soil specimens due to wetting. For instance, dry soil specimens under several normal pressure were subjected to shear loading while inundated at several levels of shear stresses. The results showed that the stress reduction and settlement due to wetting increased with vertical and shear stress level in both types of particle shapes, with higher values in angular particle shapes. The wetting of the samples had more impact on the particle breakage in angular gravel than sub-angular gravel, which increased linearly with the normal stress.

Grassland Restoration at a Graded Ski Slope: Effects of Propagation Material and Fertilisation on Plant Cover and Vegetation

The increasing anthropisation of mountain regions is a cause of soil degradation, which needs to be addressed. Conventional methods of ski slope revegetation often fail to stabilise the soil and recover natural vegetation. To test alternative methods to create a persistent, biodiversity-friendly plant cover, different sowing (site-adapted native propagation materials vs. forage cultivars vs. no sowing) and fertilisation treatments were compared over nine years at a graded ski slope. Because of the gravelly soil, the ninth-year plant cover was only 65%, which was sufficient to prevent erosion. All native propagation materials were equally efficient at recreating a semi-natural grassland. Except for Festuca rubra, the forage cultivars did not persist. However, native volunteer species from close natural ecosystems efficiently colonised plots sown with forage cultivars and plots that were not sown. This resulted in a lower plant cover but a high similarity to the surrounding vegetation. Fertilisation had a positive but transient effect on plant cover and a little negative effect on species richness. High-altitude sites with gravelly soils should be revegetated with native propagation materials. Using forage cultivars can attain a persistent plant cover only if the sown non-persistent cultivars are replaced by the species arriving from nearby surrounding vegetation.