Study on Strength Characteristics of Cement-Solidified Bauxite Tailings Slime

The wet slime tailing pond formed during the production of accumulated bauxite is a source of artificial debris flow hazard with high potential energy. In order to explore the effectiveness of solidification technology in processing bauxite slime, experimental study was conducted on the strength characteristics of cement-solidified slime with bauxite slime as the test object, so as to investigate the impact of cement contents and curing ages on the compressive strength of cement-solidified slime. According to the test results, the strength and deformation characteristics of solidified slime are related to the cement content, and the higher the cement admixed amount, the greater the compressive strength of solidified slime; the cement-solidified slime samples are subject to brittle failure, and with the increase of strain, the stress first rises to its peak and then decreases rapidly. The findings may serve as reference in processing bauxite slime.

Debris Flow Assessment in the Gaizi-Bulunkou Section of Karakoram Highway

Highways frequently run through the flow and accumulation areas of debris flow gullies and thus are susceptible to debris flow hazards. Assessing debris flows along highways can provide references for highway planners and debris flow control, emergency management. However, the existing assessment methods mostly neglect the essential information of the flow paths and spreading areas of debris flows at the regional scale. Taking the Gaizi Village-Bulunkou Township Section (hereinafter referred to as “the Gaizi-Bulunkou Section”) of the Karakoram highway as the study area, this research introduces a simple empirical model (the Flow-R model) and establishes a method for assessing the debris flow hazard level. The main processes include data collection, inventory of former events, calculating source areas and spreading probability, verification of the model, extraction of hazard assessment factors, and calculation of debris flow hazard levels. The results show that: 1) the accuracy, sensitivity, and positive predictive power of the Flow-R model in simulating the debris flow spreading probability of the study area were 81.87, 70.80 and 72.70%, respectively. The errors mainly occurred in the debris flow fans. 2) The calculation results make it possible to divide debris flow hazard levels into four levels. N5, N19, and N28 gullies had the highest hazard level during the study period. 3) In the Gaizi-Bulunkou Section of the Karakoram highway, during the study period, the highways with very high, high, medium, and low hazards were 4.33, 0.62, 1.41, and 1.68 km in length, respectively.

POSSIBILITIES OF THE SAGA GIS IN THE STUDY AND MAPPING OF THE DEBRIS FLOW HAZARD OF THE BAIKAL MOUNTAIN COUNTRY

The possibilities and limitations of SAGA GIS for processing DEM and remote sensing materials of free access in the interests of specialized mapping of debris flow hazard in the Baikal region are considered. The results of processing the SRTM and ASTER GRID DEMS, as well as the spectrosonal images obtained from the Landsat-8 and Sentinel-2 satellites in the SAGA environment are compared. The most effective tools of GIS-analysis of territories from the point of view of the potential hazard assessment of debris flows based on remote sensing data are determined.

Debris-Flow Hazard Assessments: A Practitioner's View

ABSTRACT Substantial advances have been achieved in various aspects of debris-flow hazard assessments over the past decade. These advances include sophisticated ways to date previous events, two- and three-dimensional runout models including multi-phase flows and debris entrainment options, and applications of extreme value statistics to assemble frequency–magnitude analyses. Pertinent questions have remained the same: How often, how big, how fast, how deep, how intense, and how far? Similarly, although major life loss attributable to debris flows can often, but not always, be avoided in developed nations, debris flows remain one of the principal geophysical killers in mountainous terrains. Substantial differences in debris-flow hazard persist between nations. Some rely on a design magnitude associated with a specific return period; others use relationships between intensity and frequency; and some allow for, but do not mandate, in-depth quantitative risk assessments. Differences exist in the management of debris-flow risks, from highly sophisticated and nation-wide applied protocols to retroaction in which catastrophic debris flows occur before they are considered for mitigation. Two factors conspire to challenge future generations of debris-flow researchers, practitioners, and decision makers: Population growth and climate change, which are increasingly manifested by augmenting hydroclimatic extremes. While researchers will undoubtedly finesse future remote sensing, dating, and runout techniques and models, practitioners will need to focus on translating those advances into practical cost-efficient tools and integrating those tools into long-term debris-flow risk management.

Clogging mechanisms of filter barriers against debris-flow hazard

<p>Debris flows are amongst the most hazardous landslide phenomena (Jakob & Hungr, 2005). They are mixtures of flowing water and granular materials, which range in size from microscopic soil particles to massive rock boulders. Due to their unpredictability and rapidity, they pose severe hazard on infrastructure, structures, and human lives. To dissipate the destructive kinetic energy of debris flows and induce deposition of the coarsest fraction of the flow, mitigation systems often include the use of filter barriers. Filter barriers are built both in steel and reinforced concrete, and their openings should be designed according to a reference grain diameter. This key parameter is often chosen arbitrarily due to the difficulties in considering the full grain size distribution of the deposit. Sufficiently small outlets, however, leads to premature clogging of the barriers, blocking further outflow (Ashour et al., 2017). This can result in excessive maintenance costs.</p><p>This work focuses on the clogging mechanism of three different kinds of filter barriers: nets, slit dams, and slot dams. The aim is to evaluate the influence of grainsize dispersity into the clogging/non-clogging transition. Starting from simpler monodisperse granular material, we determine via DEM simulations the particle diameter D that induces clogging in the openings, as a function of the opening size S. Thus, for monodisperse grains, a set of threshold values for S/D can be detected: on one side of the threshold the particles are too small to clog the opening, on the other side they are too large to allow free passage of the material.</p><p>However, natural debris deposits are far from uniform. To analyse the role of grainsize dispersity, bidisperse specimens are created mixing grains with two different diameters: a small diameter and a large diameter. By varying the composition of large and small particles, a transition is observed between clogging and free-flow, in analogy with what obtained in the simulation with monodisperse grains. The comparison of results obtained with bidisperse and monodisperse samples indicates that an analogy in terms of trends and thresholds exists, as long as an equivalent diameter D* is introduced for bidisperse mixtures (Marchelli, 2018). This parameter is therefore suggested as the reference diameter to be adopted in the barrier design.</p>

Sediment-trapping effectiveness of check dams with multiple debris-flow surges: Experimental study

<p>A series of check dams were constructed for debris-flow hazard mitigation in China. Based on the results of field investigation, check dam has a significant impact on the geomorphology of debris flow gully, especially the upstream and downstream of a check dam. According to the relationship between the sediment deposition thickness and the check dam height, the running status of a check dam can be divided into three states: without sediment deposition, half of the storage capacity with sediment deposition, and full of sediment deposition. With the accumulation of sediment transport, the running state of a check dam gradually changed and the sediment-trapping effect of check dams has gradually weakened, leading to the loss of part of the disaster mitigation effect, increasing the risk of downstream infrastructure and human security. Therefore, experiments with multi-surges of debris flows were carried out to study the geomorphic and sediment-trapping effectiveness of check dams. The results showed that with the increase of the sediment amount with multi-surges, the deposition slope in the downstream dam approached or even exceeded that of upstream dam. For one surge, deposition morphology has slightly difference in the cascade dams. At last, a method for calculating the reduction coefficient of deposition slope considering the check dam height and sediment amount with multi-surges is proposed.</p>

Dynamic process and failure mechanism of rammed building structure subject to debris flow

<p>The failure mechanism of building structure is important for quantitatively assessing vulnerability of elements at risk, which is a critical step in risk assessment of debris flow. Scholars have recently made great processes in the researches on debris flow hazard effects and vulnerability of elements at risk. Statistical analysis methods have widely used to analyze field survey data and build vulnerability functions. Based on numerical simulation and model experiment, structural dynamic response process was analyzed to evaluate structure vulnerability. However, due to the lack of quantitative relationship between the debris flow hazard-forming mechanism and the dynamic response of building structure, it is essential to analyze the dynamic response characteristics and process of building structure subject to debris flow, which would play an important guiding role in disaster prevention and disaster mitigation.</p><p>Through hazard field investigation, the failure modes of rammed earth building caused by debris flow were summarized as burying, scouring and impact. Figure 1 shows the debris flow hazard in Jiende Gully, Liangshan. In addition, by using the finite element analysis method, the structure model of rammed earth building was established to simulate to the impact process of debris flow on the structure. During the dynamic failure process of rammed earth building shown in Figure 2, the failure types of building wall impacted by the debris flow mainly presented at crushed failure of the impact point, tensile failure of the inside wall and shear failure of the corner. Then debris flow destroyed the gable wall, rushed into the room, and broke the doorway, which resulted in damage of the longitudinal wall. Moreover, the response characteristics and failure mechanism of rammed earth buildings under the impact of debris flow further show that the integrity of rammed earth building is poor and the development of cracks cuts off the propagation path of stress, which effectively protects other walls. The transform-shape locations of the rammed earth building including were initially destroyed at the points of the wall foundation, corners of wall and the points impacted by big rocks of debris flow. Therefore, the reinforced measures on the locations where stress suddenly changes, such as wall foundations and wall corners should be paid more attention to protect rammed structure of buildings.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.451b729a870062696011161/sdaolpUECMynit/12UGE&app=m&a=0&c=2ed88a397ba9c221f12dfdaaa040b3d2&ct=x&pn=gepj.elif&d=1" alt=""><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.84a0a2aa870068796011161/sdaolpUECMynit/12UGE&app=m&a=0&c=b7eec20b0a3f0afb5c82791d9e72d449&ct=x&pn=gepj.elif&d=1" alt=""></p>