Loose Deposits Research Articles

ПРИМЕНЕНИЕ МЕТОДОВ ЭЛЕКТРОМЕТРИИ ПРИ ИЗУЧЕНИИ РОССЫПНЫХ МЕСТОРОЖДЕНИЙ ЗОЛОТА ХАБАРОВСКОГО КРАЯ

The article presents the results of applying geophysical methods in the study of placers of various genetic types in the Khabarovsk Territory. The main research methods are vertical electrical and remote induction sounding. Geophysical studies of alluvial placers were carried out along river valleys, at the watersheds and small streams of the Turchikansky lode-and-placer gold cluster. The main tasks to be solved are the search for potential structural traps of gold (paleoriverbeds, ravines), determination of the nature of the bedrock surface and the thickness of the overlying loose deposits. The work performed allows us to identify a prospecting indicator for placer gold in a given territory, that is, lower electrical resistivity values in the presence of a local positive magnetic anomaly. The study on the coastal marine placer on the coast of the Gulf of Nicholas (Sea of Okhotsk) focused on the lithological breakdown of the geologic section by physical properties. The results of the work showed strong differences in the electrical conductivity of the bedrock at the base of the section, marine sediments, and continental deposits. The application of electrometry methods is supported by the fact that rocks differ very distinctly by electrical properties. This is confirmed by placer mining activities at the technogenic deposits of the Verkhnyaya Uda and the Sofia mine. Mining and geological factors complicating dredging operations, such as permafrost and bouldery debris, were studied at technogenic placers by induction methods. Research results revealed that the presence of boulders or frozen rocks is manifested in the same way in electrical readings, that is, in a sharp increase of electrical resistivity. Thus, areas of abnormally high resistivity are hazardous areas for the passage of the dredger. These findings indicate the high efficiency of the application of electrical exploration technologies in the study of different types of placer gold deposits.

ZEMİN SIVILAŞMASINA KARŞI GELİŞTİRİLEN KISMİ DOYGUNLUĞA İNDİRGEME METOTLARI ÜZERİNE DENEYSEL ÇALIŞMA: GAZ KABARCIKLARININ DAĞILIMI

Saturated deposits of sandy soils may liquefy during an earthquake event, causing detrimental effects on the site and structures. Mitigation of liquefaction-induced damage is of the essence when the structures are expected to exceed the acceptable limits of safety and serviceability. Induced Partial Saturation (IPS) has been recently proposed as a novel liquefaction countermeasure. In the present study, several laboratory tests were conducted on partially saturated sand models to offer insights into two IPS methods, paying more attention to the distribution of air/gas bubbles entrapped in pore spaces. For this purpose, loose deposits of partially saturated sand were prepared in transparent plexiglass boxes either injecting air or using a chemical substance. Digital images were recorded at different stages of the tests, which provided an opportunity to visualize the distribution of gas/air bubbles. Furthermore, moisture sensors were placed at different locations of sand models, allowing to capture the variation of the degree of saturation with time. Comprehensive analyses of the test data suggested that oxygen bubbles were generated through a reaction between water and chemical substance, and the distribution of oxygen bubbles was sufficiently uniform across the sand models. This method also allowed the preparation of sand models at the desired degrees of saturation. On the contrary, at 1-g injected air was observed to flow through a path of less resistance, and this technique was comparatively less successful in preparing sand models with uniformly distributed air bubbles and at lower degrees of saturation (i.e., below 90%).

Effects of boiling on iron particles in drinking water

Abstract Discoloration events in drinking water distribution systems (DWDSs) caused by iron particles have occurred worldwide, and boiling has been applied in drinking water treatment households globally, but the effects of boiling on iron particles are not clear. Here, the effect of boiling on different kinds of iron particles (including loose deposits from the DWDS and their main components FeOOH, Fe2O3, and Fe3O4) was studied. At 10 mg/L, the turbidity values before/after boiling of Fe2O3, Fe3O4, and FeOOH were 134.00/121.00, 25.07/21.22, and 120.40/114.20 NTU, respectively. All the particles had a lower degree of crystallinity after boiling. After boiling, the number of particles in loose deposits increased and the particle size decreased, while iron oxides were on the contrary. Among the three iron oxides, the existence of Fe3O4 and Fe2O3 had different effects on disinfection by-products (DBPs) formation. The activity of microorganisms was the highest under particle concentration of 0.1 mg/L than other concentrations for all the particles, but the total microbiological risks were still very low after boiling. Thus, the boiling treatment would increase the turbidity and risks of the particles. As the particle concentration under low concentration is hard to find, this risk is also hard to find.

Excess of REE in plant foods as a cause of geophagy in animals in the Teletskoye Lake basin, Altai Republic, Russia

Geological and hydrobiogeochemical studies carried out in two areas in the Teletskoye Lake basin in the Altai Mountains suggest that geophagy among wild and domestic herbivores in the studied areas develops in mountain‑taiga with steppe landscapes on Proterozoic metamorphic rocks near the Paleozoic granitoids with high concentrations of magmatogenic minerals of rare earth elements (REE). This fact is the reason for high concentrations of REE in loose diluvial deposits and glacial deposits adjacent to granitoids, as well as in derivative soils and vegetation. REE concentrations in the vegetation of the studied territories were almost similar to the geophagy sites previously investigated in the Sikhote‑Alin. The geochemical specificity of landscapes revealed both in the Altai Mountains and in the Sikhote‑Alin may be the cause of REE imbalance in the hormonal system of the body. It forces animals to address the resulting problems with mineral sorbents of the quartz‑feldspar‑illite‑chlorite type which can remove the excess of REE from the body. When selecting these, the animals tend to find sodium‑enriched varieties if possible.

Effect of Spacing and Slenderness Ratio of Piles on the Seismic Behavior of Building Frames

The general assumption of a rigid base at the bottom of building structures during analysis and design underestimates the seismic response. Building structures resting on loose sand and soft clayey soil are vulnerable to earthquake forces. The amplification of ground motion occurs due to the presence of this loose and soft soil deposit. Moreover, the spacing and slenderness ratio of piles play a vital role in altering the behavior of the overall soil-foundation-superstructure system. This study aimed at investigating the effect of soil-pile-structure interaction using 1-g shake-table testing. Free and forced vibration tests were performed on scaled building frames with either a rigid base or a flexible base, supported on sandy soil with 50% relative density. A laminar shear box container is used for an experimental study of soil-pile-structure interaction. The design parameters, such as the spacing (S = 3D, 5D, 7D, and 9D) and slenderness ratio (L/D = 15, 30, 45, and 60) of the piles, where S, D and L are spacing, diameter and length of the piles respectively, are considered in the analysis. The results, in terms of natural frequency, damping, pile-bending moment, story lateral displacement, and inter-story drift are estimated. From the findings, it is clear that the effects due to pile spacing are more considerable than the effects due to the slenderness ratio of the piles. The bending moment in the piles spaced at 3D is increased by 102% compared to the large-spacing (S = 9D) piles. This subsequently amplifies the story lateral displacement by 180% and amplifies the inter-story drift by 167%.

Geotechnical Characterization of the Subsurface Using Seismic and Electrical Resistivity Techniques in Mikinduri Meru County, Kenya

Abstract Geotechnical study of the Mikinduri area was conducted with the aim to establish the causes of landslides and ground subsidence during the heavy rainfall. Sounding curves, travel time curves, 2D geoelectric sections, and 2D seismic models revealed 3-5 lithologic units to a depth of 30-250m. The study established thick loose alluvium deposits mixed with clay to a depth of 0.3-15m on an impermeable sub-basement as the possible major trigger of the landslides witnessed during rainy seasons. The thick alluvium deposits are due to erosion. They have been transferred by the location of the Mikinduri area, which lies in the lower regions of the Nyambene domes. Geologically, the domes were formed during Mount Kenya volcanic series and parasitic activities between the early Miocene and late Pleistocene eras. Resistivity modeling revealed deep geologic structures, including possible intrusions extending from 50m deep and faulted regions to a depth of 60-150m in the central and northeast area of study. The faulted area is highly saturated, as revealed by the low resistivity values. The delineated top black cotton soils and alluvium deposit are 40-50% clay and have poor foundation bearing capabilities. In contrast, compacted gravel, silt, and compact basaltic rock basement have good foundation capabilities. Keywords: Geotechnical, characterization, subsurface, seismic, electrical resistivity, foundation, geoelectric layer, Mikinduri Meru, Kenya.

Preparation, properties and grouting process simulation of cement-based grout for loose deposits

In the case where grout is used in loose strata, the leakage is crucial to the control of plugging efficiency in the seepage channel. However, the existing grouting materials generally have insufficient properties to meet the engineering requirements in such conditions. Therefore, the present study developed a new cement-based grouting material on the basis of theoretical analysis and experimental investigation. With high adhesion ratio and rapid setting characteristics, the proposed grouting material can stick to the seepage channel with high proportion, thus plugging these channels rapidly. To this aim, based on the compounding of Portland cement with sulphoaluminate cement and the introduction of cement-modified admixtures, such as hydroxyethyl cellulose and sodium polyacrylate, the preparation of grouting formula by the factorial experiment design was comprehensively investigated. This method, the harmonized relationship among adhesion ratio, workability time and mechanical characteristics of the proposed formula was established. Simultaneously, the engineering application feasibility of the proposed grout mixture was verified from both qualitative and quantitative aspects by a newly designed grouting simulation set-up. Finally, the plugging mechanism of this grouting formula in seepage channels was further concluded by monitoring the change of grouting parameters and calculating the plugging efficiency of the injected medium. This study provides a new method to enhance the plugging efficiency of seepage channels in loose deposits by improving the properties of potential cement-based grouting materials.

Lichens in the Polar Deserts of the Northern Tip of the Novaya Zemlya Archipelago.

For the polar deserts of the Novaya Zemlya archipelago, the analysis of the dependence of the distribution of lichens on altitude above sea level, exposure by cardinal direction, the granulometric composition of soils, morphometric parameters of structural soils, the cover values of bryophytes and the total cover of cushion forms of plants and lichens was carried out. Based on 157 sample plots, nine lichenocenotypes (lichen community formed in a specific type of habitat) were identified. It is shown that with increasing height (during the transition from zonal to orozonal positions), the cover and the number of lichen species decrease. The cover of lichens also decreases with an increase in the cover of mosses. With an increase in the content of a fraction in soils of more than 0.125 mm, the species diversity and the cover of lichens increases. A total of 84lichen species were identified, of which Thamnolia vermicularis s. l. is classified as the most active, nine are highly active, 11-medium-active, the rest are little active and inactive. The current pattern of lichen distribution in the landscape of the far North of Novaya Zemlya is largely due to historical reasons-the youth of the landscape, recently freed from the ice cover, an exceptionally high degree of mobility of the cover of loose Quaternary deposits.

Mechanical and microscopic properties of soil according to the rate of increase in pore water pressure

Increases in pore water pressure affect the effective stress state of loess soil, resulting in deformation and even soil erosion. However, it is still unclear how the mechanical behaviours and microstructures of soil are influenced by the rate of increase in pore water pressure (RIPWP). To better understand the mechanical failure process and properties of soil under different RIPWPs, a series of constant-shear drained (CSD) triaxial tests were carried out on Q2 loess (silt loam, a loose aeolian deposit) in the South Jingyang Platform of China. Further, scanning electron microscopy (SEM) tests were conducted on the samples before and after the triaxial tests to observe the microscopic characteristics of the soil, and reveal the microscopic mechanism of liquefaction failure in soil under CSD triaxial tests. The results showed that the failure process was divided into two stages of 1) stable creep and 2) sharply unstable deformation. In the second stage, rapid-slow strain development was observed at relatively low RIPWPs. With increases in RIPWP, the critical pore pressure ratio u/σc increased within the range of 0.48–0.66. Microscopic analysis of the samples after shearing found clay particles filling the pores and obvious aggregation structures. In addition, macropores and mesopores were transformed into micropores. With increases in RIPWP, the orientations of particles and pores increased and the abundance and fractal dimension of pores decreased. In conclusion, the microscopic mechanism of soil instability under CSD triaxial testing was as follows. Increases in pore water pressure led to the dispersion of fine particles, weakening of cementation, and the rotation and recombination of coarse particles within the soil. In addition, the clay particles rolled, slipped and filled into pore throats, resulting in the blockage of seepage channels and, correspondingly, rapid increases in local pore water pressure. Finally, the loess liquefied due to a sudden collapse of its structure under the effect of long-term high pore water pressure. These results can provide a theoretical guidance for soil management and slope instability prevention.

Mapping of the loose sediments of glacial and periglacial formations in areas with boreal vegetation using remote sensing

The southeastern Fennoscandian Shield is a specific region dominated by glacial and periglacial originated Quaternary deposits. In dense boreal vegetation zones, direct remote decoding of Quaternary sediments is impossible. Our aim is to assess the efficiency of machine learning algorithms for identification of types of Quaternary deposits based on spectral data of vegetation cover and digital elevation model data. A comparative analysis of two classification methods, discriminant analysis (DA) and classification and regression trees (CARTs), was performed. Two models, DA and CART, were constructed based on a set of spectral variables. They included principal components and spectral indices, such as the normalized difference vegetation index, the normalized difference moisture index, and the clay minerals ratio. When the absolute height and the topographic position index (DA+ and CART+ models) are added to a set of independent variables, the classification of Quaternary sediments becomes more accurate. The nonparametric CART method was shown to be more accurate in differentiating loose deposits. The correctness of the CART+ model for the reference sample of observation points was as high as 90.5%. According to the trained data, mapping of Quaternary deposits was carried out. Kappa analysis showed that the agreement with the map of Quaternary deposits for the CART+ and DA+ models was 0.5 and 0.44, respectively. For the DA and CART models, the agreement was much lower. It is noted that the sets of spectral data for the vegetation cover more clearly show the grain-size composition of loose sediments. To make the classification of Quaternary deposits more correct, morphometric indicators were added. Furthermore, the CART+ method was used to estimate the maximum height of glaciolacustrine sediments (117.5 m), which corresponds to the maximum absolute mark of the periglacial reservoir.

In Situ FTIR Spectroscopic Imaging of Asphaltene Deposition from Crude Oil under n-Heptane and Acetone Flows

Asphaltene deposition from crude oil, induced by n-heptane and acetone flows in a microfluidic device, was studied by optical and FTIR spectroscopic imaging techniques in situ. It was found that n-heptane and acetone penetrate crude oil in completely different ways, which is responsible for the formation of deposits with different structures and chemical compositions. The contact of the n-heptane flow with crude oil leads to fast aggregation of asphaltenes at the interface, resulting in the formation of a compact deposit fixed to the surface. Subsequent slow diffusion of n-heptane into crude oil causes asphaltene aggregation and precipitation of loose deposits. In the case of acetone, the flocculant diffuses (faster than n-heptane) into crude oil, which results in removal of its soluble components and in the formation of deposits appearing as strips as well. The distribution of the functional groups (–OH(NH), CH2–CH3, C=O, C–O, S=O) in the deposits is spatially heterogeneous. The asphaltenes deposits formed at the flocculant-crude oil interface are richer in the functional groups than those formed during diffusion. No carbonyl groups were revealed in the deposits formed in the acetone flow, while oxygen-containing groups such as –OH(NH) and S=O were present, which was an unusual result.

The effect of surficial soil on the seismic response characteristics and failure pattern of step-like slopes

Earthquake-induced shallow landslides are widely distributed in earthquake-affected areas. These hazards mainly originate from fragmented surface rock masses or surficial loose deposits overlaid on bedrock structure slopes. The seismic response of the surficial soil-bedrock slope is the key to revealing the dynamic failure mechanism of earthquake-induced landslides. This study investigates the seismic response of a surficial soil-bedrock step-like slope to evaluate the acceleration ground motion amplification along the slope. Parametric analysis focusing on the geometry of the surficial soil, thickness of the surficial soil, surficial soil-bedrock impedance contrast and geometry of the slope is conducted using the finite difference modeling code FLAC3D. The results show that both the surficial soil characteristics and geometry of the slope have great influences on the acceleration amplification factor in the horizontal direction (AAF). A maximum AAF zone is always formed near the interface between the surficial soil and bedrock, and the AAF always abruptly amplifies near the slope surface, especially at the crest of the slope. The potential dynamic failure surfaces under earthquakes are formed near the interface between the surficial soil and bedrock, which is in accordance with the AAF amplification zone of the slope, and the depth of the dynamic failure of the surficial bedrock slope is deeper than the static failure surface. It can be concluded that the topographic effect on the seismic response of the slope is strongly dependent on the surficial soil material characteristics and geometry. The findings of this study can contribute to a better understanding of the mechanism of shallow earthquake-induced landslides and have a number of important implications for disaster prevention and mitigation.

FAUNA OF SMALL VERTEBRATES (AMPHIBIANS, REPTILES AND MAMMALS) FROM NEAR-SURFACE DEPOSITS OF CAVE LOCALITIES IN THE VALLEY OF THE MIDDLE REACHES OF THE YURYUZAN RIVER (SOUTHERN URALS)

When studying bone remains of small vertebrates from cave localities, the data obtained from the near-surface loose deposits of caves and grottoes are most often not considered due to a significant mixing of remains of different ages – recent, subrecent, Holocene and late Pleistocene. But according to a number of features – preservation, numerical quantity of remains, temporal and spatial distribution of the species defined in the layer, the material from the near-surface layers can be divided into groups of different ages and the time of accumulation of deposits can be established, which makes it possible to characterize in more detail the fauna of small vertebrates from cave localities. Bone remains of amphibians, reptiles, and small mammals from near-surface loose deposits of cave localities (Idrisovskaya Cave, Kazyrbak Cave, I1–20 Grotto, L1–20 Grotto, Grebnevaya Cave) of the middle reaches of the Yuryuzan River (Southern Urals) were studied. Using the species composition, ecological characteristics and abundance of species remains, it has been established that near-surface deposits of cave localities in the middle reaches of the Yuryuzan River contain bone remains of the Late Pleistocene–Early Holocene fauna of small mammals (Idrisovskaya Cave), Middle Holocene fauna of reptiles and small mammals (Kazyrbak Cave), Late Holocene forest–steppe fauna small mammals (I1–20 Grotto, L1–20 Grotto, Grebnevaya Сave). And in all localities, there is a subrecent forest fauna of amphibians, reptiles and small mammals.

The starting mechanism study on rainfall-induced sloop loose source in strong earthquake area

The 5.12 Wenchuan earthquake in 2008 led to a large number of loose deposits on the slope on both sides of the gully in the formation area. Under the triggering action of heavy rainfall, the previously unrecognized slope loose source in formation areas easily failed and started earlier than the overall start of the gully debris flow, which has practical significance for realizing the early warning of the gully debris flow starting. The special loose source conditions and postearthquake geological environment change the hydraulic mechanism of traditional debris flow start-up, which brings great difficulties to the monitoring and early warning of postearthquake debris flows. Therefore, based on hydraulics, on the premise of building a hydraulic model of groundwater level change of loose slope accumulation body, the characteristics and rules of groundwater level change are analyzed with the aid of hydraulic seepage theories, and the action characteristics of hydrodynamic pressure and hydrostatic pressure on the accumulation body are quantitatively studied. Based on field exploration data and average slope gradient, we divided the accumulation body in a reasonable manner; completed the sliding force, anti-sliding force and residual-sliding force mechanical expression and establishment; and performed a slope stability analysis. The research results show that the slope starting mode is divided into the thrust-type landslide and the retrogressive landslide mode of the subsection disintegration. The hydraulic deposit mechanism analytical results can also reverse the critical rainfall condition of slope failure. Finally, taking the Yindongzi gully in Dujiangyan as an example, the hydraulic mechanism of typical slope deposits in the formation area was analyzed and combined with the historical debris flow events in the study area to verify the physical simulation test, which was consistent with the field investigation results after the disaster.

Assessing the capacity of dredging excavations to place dredging tailings dumps in the course of deep and man-made placer mining

Introduction. The dredge stern is often backed up by dredging tailings in the course of deep and man-made placers dredging. One of the reasons for that is the decreased capacity of dredging excavations at the dumping point caused by collapsed pit walls, which is not taken into account by known design methods. Research objective is to evaluate the degree of the developed space capacity reduction at dredging pits for dredging tailings storage, depending on the dredging conditions. Methods of research. Capacity prediction for a dredging excavation for dredging tailings storage should consider natural slope formation of open pit walls during the period of dredge advance to a distance equal to the distance of the poop decks from the face. The degree of reduction in dredging excavation lower part receiving capacity should be set based on pit walls flattening, which depends on rock composition (cohesiveness degree), loose deposits thickness, face width, and dredge working parameters. Results. The results of graphic-analytical calculation revealed that dredging excavation lower part receiving capacity is reduced from 3 to 10% due to pit walls collapse as loose deposits thickness increases from 10 to 34 m for the most favorable face width of a 380-liter dredge, which may result in a significant increase in dredge stern backing up by dredging tailings. Conclusions. At deep and man-made placers, when calculating the parameters of a dredging tailings dump, it is recommended to introduce an amendment into the existing methods, that considers the developed space lower part capacity reduction due to pit walls collapse.

Experimental study on the mechanism of sand boils and associated settlements due to soil liquefaction in loose sand

Sand boils are a recognized phenomenon associated with soil liquefaction. However, the exact conditions required to produce sand boils remain unclear, and sand boil-induced settlement is difficult to quantify. The mechanism of sand boils and associated settlements due to soil liquefaction is investigated in this study using model testing. Loose saturated sand deposit is made in a transparent acrylic cylinder applied with torsional shaking to reproduce liquefaction and sand boils. An acrylic circular plate, whose diameter is slightly smaller than the cylinder's inner diameter, is placed on the model ground surface to mimic a non-liquefiable layer. The gap allows the liquefied sand to be ejected, leading to sand boils. The mechanism of sand boils and induced settlements is investigated by the transient variations of the measured water pressure at the sidewall, the recorded plate settlement, and the monitored video image. The influence of different thicknesses of the non-liquefiable layer, the gap sizes, and the overburden pressures on the sand boil-induced settlement is assessed quantitatively. It is found that the thicker the non-liquefied layer or the smaller ejecta gap size, the lower the amount of ejecta and associated subsidence is observed. The overburden pressure had relatively minor effect on the amount of ejecta, but it affected the amount of consolidation settlement significantly. Based on the observation of test results, a theoretical ejection head is proposed to determine the condition leading to sand boils.

Capturing and tracing the spatiotemporal variations of planktonic and particle-associated bacteria in an unchlorinated drinking water distribution system

The aperiodic changes in the quantity and community of planktonic and particle-associated bacteria have hampered the understanding and management of microbiological water quality in drinking water distribution systems. In this study, online sampling was combined with the microbial fingerprint-based SourceTracker2 to capture and trace the spatiotemporal variations in planktonic and particle-associated bacteria in an unchlorinated distribution system. The results showed that spatially, the particle load significantly increased, while in contrast, the quantity of particle-associated bacteria decreased sharply from the treatment plant to the distribution network. Similar to the trend of particle-associated bacterial diversity, the number of observed OTUs first slightly decreased from the treatment plant to the transportation network and then sharply increased from the transportation network to the distribution network. The SourceTracker2 results revealed that the contribution of particle-associated bacteria from the treatment plant decreased along the distribution distance. The spatial results indicate the dominant role of sedimentation of particles from the treatment plant, while the observed increases in particles and the associated bacteria mainly originated from the distribution network, which were confirmed directly by the increased contributions of loose deposits and biofilm. Temporally, the daily peaks of particle-associated bacterial quantity, observed OTU number, and contributions of loose deposits and biofilms were captured during water demand peaks (e.g., 18–21 h). The temporal results reveal clear linkages between the distribution system harboring bacteria (e.g., within loose deposits and biofilms) and the planktonic and particle-associated bacteria flowing through the distribution system, which are dynamically connected and interact. This study highlights that the spatiotemporal variations in planktonic and particle-associated bacteria are valuable and unneglectable for the widely on-going sampling campaigns required by water quality regulations and/or drinking water microbiological studies.

Assessment of Liquefaction-Induced Differential Ground Settlement and Lateral Displacement Using Standard Penetration Tests with Consideration of Soil Spatial Variability

One of the major risks to civil structures during an earthquake is the occurrence of liquefaction in loose saturated sand deposits. The main consequences of liquefaction include lateral spreading deformations and postliqufaction reconsolidation settlement. In situ tests, such as standard penetration tests (SPTs), commonly are used in one-dimensional models for estimating liquefaction-induced deformation, which provide ground deformation only at limited locations at which SPTs are performed. However, magnitudes of liquefaction-induced ground deformation within a specific site may exhibit significant spatial variation when subsurface soils are not homogeneous or when they vary spatially within a site. Therefore, using the ground deformations estimated from limited SPT locations to represent a whole site might provide misleading results and cannot properly predict the differential ground settlement or displacement, posing a significant risk to civil structures. To deal with this challenge, a novel approach was developed in this study for characterizing spatial variation of the soil lateral spreading displacement and reconsolidation settlement in a cross section of a specific site from limited SPTs with consideration of soil spatial variability along both depth and the horizontal direction. The proposed method was illustrated using both simulated data and real data.

Quantitative risk assessment of two successive landslide dams in 2018 in the Jinsha River, China

Two large successive co-site landslide dams blocked the Jinsha River in the Sichuan Province of China in 2018. A quantitative risk analysis was carried out to quantify potential human and economic losses resulting from the failure of these dams, especially the interaction between the co-site landslide dams, and to further investigate the influence of digging a diversion channel on risk mitigation. Flood routing for three scenarios (i.e. after the first dam formation, when the second landslide mass was added, and with a diversion channel after failures) were simulated using HEC-RAS. The human and economic losses were evaluated using a human risk assessment model together with empirical formulations. The results show that the risk of breaching floods had increased significantly after the second co-site landslide dam formation on the pre-existing loose deposits of the first dam. This amplification effect of outburst floods was so great that the peak outflow resulting from the breaching of the second landslide dams was more important, leading to greater economic losses than those resulting from the breaching of the first dam. However, the expected loss of life caused by the breach of the two landslide dams appeared small because of the sufficient time lag provided by the long distance between the residential area and the dam site. The simulations also outline the importance of the diversion channel in decreasing the peak outflow rate and hence downstream risks. A parametric analysis shows that a deep channel with a moderate longitudinal gradient can significantly decrease the peak outflow discharge at the dam site. Flood intensity and risks to downstream towns did not change because of the relatively small attenuation rate of the peak outflow rate. However, a shorter height of the residual dam can be obtained by optimizing the diversion channel, and the amplification effects of such co-site dam can be significantly reduced in the future.

A model for the formation and evolution of structure of initial loess deposits

The wetting and drying process is one of the commonest natural conditions the loess deposit encounter in its life span, and drives the formation and evolution of loess structure. Understanding the genesis of loess structure is essential for reconstructing paleoclimate and predicting the future structure. The common belief is that drying-induced shrinkage is responsible for formation and propagation of cracks in soil, while wetting-induced swelling minimizes pre-existing cracks. Contrary to this, it was lately found that the wetting rather than drying dominates the initiation of vertical cracks in loose and uncemented initial loess deposits. In present study, we investigated the structural evolution mechanism of initial loess deposits subjected to wetting and drying using physical monitoring test, numerical simulation and theoretical analysis. Results show that the structural evolution was controlled by capillarity. This can be interpreted by a mechanical model which indicates that due to the loose particle packing, the interparticle force caused by the capillarity, especially in the wetting process, is enough to overcome the resistance (mainly friction) and pull adjacent particles close to each other, modifying the overhead pores into vertical cracks. Our findings confirm the main contribution of wetting-induced shrinkage to the formation and evolution of early loess structure, which challenges the current understanding of loessification process.