Quantifying the impact of earthquakes and geological factors on spatial heterogeneity of debris-flow prone areas:A case study in the Hengduan Mountains

Understanding the spatial heterogeneity of debris-flow-prone areas holds significant implications for regional risk management, particularly in seismically active regions with geological faults. Despite the significance of this knowledge, a comprehensive quantification of the influence of regional topographical and geological factors on the spatial heterogeneity of debris-flow-prone areas has been lacking. This study selected the Hengduan Mountains, an earthquake-prone region characterized by diverse surface conditions and complex landforms, as a representative study area. An improved units zoning and objective factors identification methodology was employed in earthquake and fault analysis to assess the impact of seismic activity and geological factors on spatial heterogeneity of debrisflow prone areas. Results showed that the application of GIS technology with hydrodynamic intensity and geographical units analysis can effectively analyze debris-flow prone areas. Meanwhile, earthquake and fault zones obviously increase the density of debrisflow prone catchments and make them unevenly distributed. The number of debris-flow prone areas shows a nonlinear variation with the gradual increase of geomorphic factor value. Specifically, the area with 1000 m-2500 m elevation difference, 25°-30° average slope, and 0.13-0.15 land use index is the most favorable conditions for debris-flow occurrence;The average annual rainfall from 600 to 1150 mm and landslides gradient from 16° to 35° are the main causal factors to trigger debris flow. Our study sheds light on the quantification of spatial heterogeneity in debris flow-prone areas in earthquake-prone regions, which can offer crucial support for post-debris flow risk management strategies.

Pressure characteristics of landslide-generated impulse waves

The destructiveness of impulse waves generated by landslides(IWL) originates from the wave’s movement and load, wherein the impulse wave’s load is the major cause of sub-aerial building damage and casualties. In this study, an experiment involving 16 groups of physical tests for the wave pressure generated by a landslide was designed, consisting of 4 sets of IWL and 4 opposite bank slope angles. A high-frequency strain system was used to measure the total pressure of the impulse wave in a water tank. The tests showed that the dynamic pressure caused by the IWL can be divided into two types: impact pressure generated by the jetflow and the pulsating pressure caused by the wave. Under the same impulse wave conditions, the maximum run-up becomes smaller as the opposite bank’s slope angle increases, and the jetflow maximum impact pressure experienced by the opposite bank increases, while the maximum pulsating pressure caused by the impulse wave is slightly decreased. Different from previous studies, the spatial maximum pressure distributions of the wave generated by landslide were concluded that the position of the maximum pulsating pressure appears adjacent to the still water surface, and the overall spatial distribution pattern of maximum wave pressure is presented as an inclined 'M' shape.Meanwhile, this study is the first to quantitatively analyzed that impact pressure has a very short action time, is even 7 times of the pulse pressure value, and there is a simple mathematical linear relationship between the two. Currently, some wave-load formulas for wind waves and tides are not applicable to calculating the loads of IWL. Research on the load of IWL will explain the hazard of impulse wave very clearly, and will greatly contribute to hazard prevention, mitigation and risk assessment work associated with IWL.

Energy conversion and deposition behaviour in gravitational collapse of granular columns

The high-density gravitational collapse of granular columns is very similar to the movements of large collapsing columns in nature. Based on the development of dangerous columnar rock mass in fields, granular column collapse boundary condition in the physical experiments of this study is a new type of boundary conditions with a single free face and a three-dimensional deposit. Physical experiments have shown that the mobility of small particles during the collapse of granular columns was greater than that of large particles. For example, when particle size was increased from 5 to 15 mm, deposit runout was decreased by about 16.4%. When a column consisted of two particle types with different sizes, these particles could mix in the vicinity of layer interfaces and small particles might increase the mobility of large particles. In the process of collapse, potential and kinetic energy conversion rate is fluctuated. By increasing initial aspect ratio a, the ratio of the initial height of column to its length along flow direction,potential and kinetic energy conversion rate is decreased. For example, as a was increased from 0.5 to 4, the ratio of maximum kinetic energy obtained and total potential energy loss was decreased from47.6% to 7.4%. After movement stopped, an almost trapezoidal body remained in the column and a fanlike or fan-shaped accumulation was formed on the periphery of column. Using multiple exponential functions of the aspect ratio a, the planar morphology of the collapse deposit of granular columns could be quantitatively characterized. The movement of pillar dangerous rock masses with collapse failure mode could be evaluated using this granular column experimental results.

Channelized and unchannelized collapses of granular columns on a horizontal surface

Columnar dangerous rock mass is widely developed in many high and steep mountain areas around the world.It often collapses,disintegrates and produces debris flow,which is disastrous.The collapse process of the columnar dangerous rock mass is very similar to the collapse of granular column.In this paper,we report the results of an experimental investigation of the flow induced by the collapse of a column of granular material over a horizontal surface.Two different setups are used,namely,a channelized granular column collapse(i.e.,two-dimensional) and an unchannelized granular column collapse(i.e.,three-dimensional),allowing us to compare channelized and unchannelized collapses flows.The experimental data suggest that our experimental findings were markedly different from those reported by previous authors(i.e.,include the channelized and unchannelized collapse flows showed differences in energy conversion and dissipation).In channelized collapse flows,the maximum vertical speed appears in the free fall regime,while,the maximum speed in the vertical direction of unchannelized collapse flows appears in the spreading regime.During the whole collapse process,i.e.,in channelized and unchannelized collapse flows,the conversion of potential energy and kinetic energy does not occur uniformly,and the maximum kinetic energy of the channelized collapse flows is higher than that of the unchannelized collapse flows,and compared with the unchannelized collapse flows,the dissipation energy in the channelized collapse flows is lower.A series of experiments was performed to predict the behaviour of different granular columns(characterized by different initial aspect ratio(a),varying from 1 to 4).The data obtained from 2 D experimental model and3 D experimental model have certain amount of difference,such as the particle runout distance(d1),the maximum central height(h2),and the deposition angle(i.e.,β1,β2).These differences show that the 2 D experimental model does not fully represent the 3 D conditions(i.e.,the role of side-walls on the channelized collapse flows characteristic is nonnegligible).Accordingly,care must be taken when validating 3 D models with 2 D experimental data.The movement of the tower dangerous rock masses with collapse failure mode could be evaluated using this channelized and unchannelized granular column experimental results.

Dynamic analysis of impulse waves generated by the collapse of granular pillars

Impulse waves generated by the collapse of pillar-shaped rock masses in Three Gorges, China,have attracted the attention of both researchers and local authorities owing to their catastrophic consequences. In this work, particle imaging velocimetry(PIV) was used to study impulse waves generated by the collapse of granular pillars during a series of physical experiments. Subsequently, the scenes of particles collapsing into water and the resulting impulse waves were analysed in terms of the solid/fluid fields. The energy obtained by the water during this process is mainly derived from the volume encroachment and continuous thrusting of particles.As indicated by the experimental results, as the aspect ratio(a) of the pillar and water depth increased, the potential energy of the granular pillar became more prone to reduction, whereas the efficiency of energy conversion to the liquid phase reduced. At constant water depth and granular pillar width, the maximum amplitude generated by the collapse of the granular pillar remained essentially the same(i.e., "saturation"was achieved) once the aspect ratio exceeded a certain threshold. The maximum impulse wave(the primary wave) formed before the main body of particles collapsed, resulting in the "saturation" of the maximum amplitude. When the kinetic energy of the particles reaches the maximum, the ratio of energy dissipation of the particles is the lowest;as the energy of water reaches the maximum, the particle collapse process does not end. The dynamic analysis of the impulse waves generated by the collapse of granular pillars provides a new approach to obtain an in-depth understanding of landslides and impulse waves. This can provide technical guidelines for disaster prevention and mitigation of impulse waves generated by bank collapse or coastline collapse.

Quantifying soil nitrous oxide emissions in spring freezing-thawing period over different vegetation types in Northeast China

Environmental changes significantly alter the structure,diversity and activity of soil microbial communities during spring freezing-thawing period,leading to changes in the soil microbial nitrogen cycle.Changes in N_(2)O fluxes after land use conversion from primary forest to secondary forest,Korean pine plantation and cropland in northeast China have not been quantified.Field experiments were conducted to measure soil N_(2)O fluxes in a primary forest,two secondary forests,a Korean pine plantation,and one maize field in a temperate region in northeast China from 2017-03-06 to 2017-05-28.During the experimental period,the soil was exclusively a nitrogen source for all land uses.We found that N_(2)O emissions ranged from 15.63 to 68.74μg m^(-2) h^(-1),and cumulative N_(2)O emissions ranged from 0.33 to 2.10 kg ha^(-1) during the period.Cumulative N_(2)O emissions from the maize field were significantly higher than that from primary forest,Korean pine plantation,hardwood forest,and Betula platyphylla forest by 262.1% to 536.4%.Compared with other ecosystems in similar studies,the N_(2)O emission rates of all ecosystem types in this study were low during the spring thaw period.Stepwise multiple linear regression indicated that there were significant correlations between N_(2)O emissions and environmental factors(air temperature and soil temperature,soil water content,soil p H,NH_(4)^(+)-N,NO_(3)^(-)-N,and soil organic carbon).The results showed that conversion of land use from primary forest to hardwood forest,Korean pine plantation or maize field greatly increased soil N_(2)O emissions during spring freezing-thawing period,and N_(2)O emissions from primary forest were almost the same as those from Betula platyphylla forest.

Effects of fibers on the mechanical properties of UHPC:A review

Ultra-high performance concrete(UHPC) developed rapidly in research and commercial use during the recent decade. Significant progress has been achieved in its material science and technology, including why and how to add discontinuous fiber reinforcement in it.This paper reviews the researches on understanding the effects of various fibers on the mechanical properties of UHPC, focus on the straight steel fibers but involving also deformed steel fibers, non-steel fibers as well as hybrid fibers. It also discusses the research methodology, prediction of mechanical properties by fiber factors, and the classification of UHPC mechanical properties related to this topic. It shows that(1) the experimental research is the main methodology for investigating the effect of the fibers on the mechanical properties of UHPC;the tensile performance of UHPC should be studied by uniaxial tensile tests and its representative indicators should include tensile strength, initial cracking strength, and peak tensile strain;(2) fiber plays an essential role in the reinforcement of the tensile strength, compressive strength, modulus of elasticity, and other material properties of UHPC, but in weakening the flowability of fresh UHPC. The positive and negative effects of fibers on the mechanical properties of UHPC should be considered,and the technology should be developed to maintain the flowability when high volume fraction of fibers is added in the UHPC;(3) the parameters of steel fibers affecting the mechanical properties of UHPC include volume fraction, size, shape, orientation and distribution, average bonding strength and minimum tensile strength, etc., which are mainly studied independently in the existing research. The studies on the combined effect of these parameters are limited but worthy of further investigation;(4) hybrid fibers could efficiently produce reinforcement effects for UHPC. It has great practical and research significance to conduct in-depth studies though the theoretical analysis and quantitative prediction are complex.