Gravel Surface Research Articles

Thresholds and relations for soil‐hydraulic and soil‐physical properties as a function of burn severity 4 years after the 2011 Las Conchas Fire, New Mexico, USA

AbstractWildfire effects on soil‐physical and ‐hydraulic properties as a function of burn severity are poorly characterized, especially several years after wildfire. A stratified random sampling approach was used in 2015 to sample seven sites representing a spectrum of remotely sensed burn severity in the area impacted by the 2011 Las Conchas Fire in New Mexico, USA. Replicate samples from each site were analysed in the laboratory. Linear and linear indicator regression were used to assess thresholds in soil‐physical and ‐hydraulic properties and functional relations with remotely sensed burn severity. Significant thresholds were present for initial soil‐water content (θi) at 0–6 cm depth between the change in the Normalized Burn Ratio (dNBR) equal to 618–802, for bulk density (ρb) at 3–6 cm between dNBR equal to 416–533, for gravel fraction at 0–1 cm between dNBR equal to 416–533, for fines (the silt + clay fraction) at 0–1 cm for dNBR equal to 416–533, and for fines at 3–6 cm for dNBR equal to 293–416. Significant linear relations with dNBR were present between ρb at 0–1 cm, loss on ignition (LOI) at 0–1 cm, gravel fraction at 0–1 cm, and the large organic fraction at 1–3 cm. No thresholds or effects on soil‐hydraulic properties of field‐saturated hydraulic conductivity or sorptivity were observed. These results suggest that ρb and LOI at 0–1 cm have residual direct impacts from the wildfire heat impulse. The θi threshold is most likely from delayed groundcover/vegetation recovery that increases evaporation at the highest burn severity sites. Gravel and silt + clay thresholds at 0–1 cm at the transition to high burn severity suggest surface gravel lag development from hydraulic erosion. Thresholds in ρb from 3 to 6 cm and in silt + clay fraction from 3 to 6 cm appear to be the result of soil variability between sites rather than wildfire impacts. This work suggests that gravel‐rich soils may have increased resilience to sustained surface runoff generation and erosion following wildfire, with implications for assessments of postwildfire hydrologic and erosion recovery potential.

Statistical significance of spatial correlation patterns in armoured gravel beds

ABSTRACTStructure function analyses are increasingly used to investigate spatial correlation patterns of river bed roughness. However, traditional structure function analyses remain mostly qualitative as the statistical significance of correlation patterns has not been explicitly addressed. This paper proposes a methodology for the analysis of 2D second-order structure functions based on statistical significance testing. Using data from flume experiments with gravel beds, a method to create surrogate rough beds is proposed. The surrogate beds are subsequently used to carry out Monte-Carlo simulations which in turn are used to evaluate statistical significance of the structure functions values. The method is applied to two datasets of gravel surfaces and the results are used to investigate the physical meaning of the obtained significance patterns. The results confirm previous studies that the orientation of large grains can be described by 2D second-order structure functions through a central ellipse reflecting areas of high spatial correlation. The main axes of the ellipses can hence be interpreted to define characteristic roughness length scales. The novelty of the present paper is that the proposed significance testing allows for a more rigorous definition of the spatial extent of the central ellipse.

Spatial variation of topsoil features in soil wind erosion areas of northern China

The particle size distribution (PSD), contents of soil organic matter (SOM) and calcium carbonate (CaCO3), and surface gravel coverage (GC) are the crucial factors affecting topsoil features, and consequently, these factors influence soil wind erosion and land use. The aim of this study is to understand the topsoil features in northern China, which is one of the regions of the world that experiences the most severe soil wind erosion. We used the topsoil data of the PSD, SOM content, CaCO3 content and GC derived from 610, 608, 503 and 2372 topsoil sampling sites, respectively. The results of the calculations and statistics showed that the particles in the topsoil were generally coarse; the areas of sandy loam, loam, loamy sand and silty loam accounted for 39.53%, 21.05%, 16.31% and 12.15% of the total area, respectively, and the other eight types of soils combined accounted for 10.96% of the total area. The areas with SOM contents of ≥5%, 1–5% and <1% accounted for 5.58%, 52.62% and 41.79% of the total area, respectively. The areas with CaCO3 contents of ≥10%, 5–10%, 1–5% and <1% accounted for 19.46%, 32.98%, 39.30% and 8.26% of the total area, respectively, in which sandy loam and silty loam soils with a CaCO3 content of 1–5% were the most susceptible to wind erosion. The areas with GC of 50–100%, 20–50%, 5–20% and <5% accounted for 10.77%, 12.80%, 18.90% and 57.53% of the total area, respectively; the areas with GC of >20% were mainly distributed in the northwest regions, which were occupied by Gobis and gravel deserts with rare vegetation. The areas with higher intensity levels of soil wind erosion were mainly distributed in the areas with higher values of gravel coverage; this seemingly abnormal phenomenon is caused by an abundance of erodible particles (0.02–0.84 mm in diameter) hiding amongst the gravels, rare vegetation and long duration of effective wind speeds that cause erosion.

Evidence for relationship between carbon storage and surface cover characteristics of soil in rangelands

Carbon storage (CS) and consequently carbon sequestration by plants is the most natural and least expensive method for atmospheric CO2 mitigation. Areas with high CS potential should be identified, maintained and subject to investment. CS depends strongly on status of vegetation and soil surface cover characteristics. Therefore, the objectives of the present study was an assessment of the relationship between aridisols CS and characteristics of soil cover in some plant types in western rangelands of Isfahan in Iran. Three different plant types including Scariola orientalis-Astragalus gossypinus, Hordeum fragile-Astragalus gossypinus and Cousinia bachtiarica-Astragalus gossypinus were identified. Then, some sampling plots were placed along the four transects in each plant type, which were placed obliquely to the general and the lateral slope of the region. Plants' characteristics and soil surface characteristics were recorded. The soil samples were taken along transects at depths of 0–20 and 20–75 cm. Soil samples were transferred to the soil laboratory and analysed. The results demonstrated that the soil carbon storge (SCS) is different between three plant types. SCS in Sc. or-As. go, Ho.fr-As. go and Co. ba-As.go plant types were 340, 182 and 173 kg/ha, respectivly. Moreover, there was a positive and significant relationship (R2 = 0.88|0.42, p < 0.01) between coverage and density of shrubby species and soil surface gravel with amount of CS.

Systematics, distribution and ecological analysis of rodents in Jordan.

Distributional and ecological data were given to all rodents of Jordan. The rodent fauna of Jordan consists of 28 species with 20 genera in eight families (Cricetidae, Dipodidae, Gliridae, Hystricidae, Muridae, Myocastoridae, Sciuridae,and Spalacidae), including four introduced species.Keys for families and species were provided, along with diagnosis for each species and cranial illustrations for most species. Habitat preference and zoogeographic affinities of rodents in Jordan wereanalyzed, as well as their status and conservation.Threat categories and causes of threats on the rodents of Jordan were also analyzed. The distribution of rodents in Jordan represents a reflection of their global distribution ranges and habitat preferences. Species associated with the temperate forest of northern Jordan includes Sciurus anomalus and two wood mice, Apodemus mystacinus and A. flavicollis, while non-forested areas are represented by Nannospalax ehrenbergi and Microtus guentheri. Strict sand dwellers include Gerbillus cheesmani and G. gerbillus. Petrophiles associated with sandstone or black lava deserts are exemplified by Acomys russatus, A. r. lewsi, H. indica and S. calurus. Others including: Jaculus jaculus, G. nanus, G. henleyi, Meriones crassus, and M. libycus are all desert-adapted species with wider ranges of distribution where scarce vegetation, wadibeds, and marabs with clay, loess, or gravel surfaces provide foraging grounds and shelter. A single species, Gerbillus dasyurus, exhibits a wide range of distribution over diverse habitat types. The rodent fauna of Jordan consists of assemblages of different zoogeographical affinities. Nine, three, and seven were restricted or had most of its range within the Mediterranean, Irano-Turanian, and Saharo Arabian, respectively. Sciurus anomalus, Apodemus sp., Nannospalax ehrenbergi, and Microtus guentheri reached their most southern range of distribution in the Mediterranean regions of Jordan. The distribution of Gerbillus cheesmani extends from Asian deserts in India westwards into the Arabian Peninsula crossing Jordan as its most western range of distribution. Typical rodents of Saharo-Arabian affinities are represented by desert jerboas, gerbils, and jirds. North African species such as G. andersoni, G. gerbillus reached their most eastern distribution in southern Jordan. Both G. henleyi and G. nanus are widely-distributed species across North Africa reaching as far as India to the east, representing most northern outpost for these two species. Sekeetamys calurus is a nearly endemic to the Eastern Mediterranean region within southern Jordan and Sinai. Relicts are represented by Eliomys melanurus and Acomys russatus lewisi. Several threats affecting the rodent biodiversity in Jordan were identified including habitat loss and degradation, human disturbance and related activity, legislative and public awareness. The global conservation status of the rodents of Jordan according to the IUCN Red List include 22 species as least concern, one as near threatened (Allactaga euphratica), and one as data deficient (Nannospalax ehrenbergi). According to the regional assessment, one species is critically endangered, three species are considered endangered, one vulnerable.

Roughness Spectra Derived from Multi-Scale LiDAR Point Clouds of a Gravel Surface: A Comparison and Sensitivity Analysis

The roughness spectrum (i.e., the power spectral density) is a derivative of digital terrain models (DTMs) that is used as a surface roughness descriptor in many geomorphological and physical models. Although light detection and ranging (LiDAR) has become one of the main data sources for DTM calculation, it is still unknown how roughness spectra are affected when calculated from different LiDAR point clouds, or when they are processed differently. In this paper, we used three different LiDAR point clouds of a 1 m × 10 m gravel plot to derive and analyze the roughness spectra from the interpolated DTMs. The LiDAR point clouds were acquired using terrestrial laser scanning (TLS), and laser scanning from both an unmanned aerial vehicle (ULS) and an airplane (ALS). The corresponding roughness spectra are derived first as ensemble averaged periodograms and then the spectral differences are analyzed with a dB threshold that is based on the 95% confidence intervals of the periodograms. The aim is to determine scales (spatial wavelengths) over which the analyzed spectra can be used interchangeably. The results show that one TLS scan can measure the roughness spectra for wavelengths larger than 1 cm (i.e., two times its footprint size) and up to 10 m, with spectral differences less than 0.65 dB. For the same dB threshold, the ULS and TLS spectra can be used interchangeably for wavelengths larger than about 1.2 dm (i.e., five times the ULS footprint size). However, the interpolation parameters should be optimized to make the ULS spectrum more accurate at wavelengths smaller than 1 m. The plot size was, however, too small to draw particular conclusions about ALS spectra. These results show that novel ULS data has a high potential to replace TLS for roughness spectrum calculation in many applications.

Study of the spatial and temporal distribution of accumulated solids in an experimental vertical-flow constructed wetland system

Clogging is the most serious problem in the operation of subsurface flow constructed wetlands (SSF CWs) and is caused by the accumulation of solids in substrates. Study of the solids accumulation process can provide a more accurate reference for the management and maintenance of SSF CWs. In this study, an experimental vertical-flow constructed wetland system was recreated in the lab, and substrates with different depth were sampled through different operation time to reveal the spatial and temporal distribution of accumulated solids. During the study, particulates mainly accumulated through adsorption along the gravel surface. Therefore, the matrix could still provide sufficient space for the particles to pass through and be intercepted or adsorbed into the system at a constant rate. At the end of the study, an increasing number of large particles had been intercepted and were accumulated in the 0–2cm layer of the matrix, indicating a significant decrease in the pore diameter at the top substrate layer. The spatial and temporal accumulation of substrate particulates during the study period was accurately simulated by first-order kinetics models, and the simulated results were in good agreement with measured values.

Interface Shear Strength Properties of Gravel Bases and Subgrades with Various Reinforcements

Reinforcing pavement layers with geosynthetics improve the pavement performance significantly. In addition to the use of geosynthetics, the hexagonal–steel–wire mesh has gained popularity as a reinforcing material in pavements. The interface shear property of pavement material and reinforcement is an important input parameter in numerical modeling of the reinforced pavement system. In this study, the interface shear parameters of various pavement materials, namely poor subgrade, fair subgrade, gravel base (GB), and gravel surface (GS) with geogrid and hexagonal–wire–mesh reinforcements is obtained using large-size direct shear test apparatus. GS and GB mixes are selected from Indian rural roads specification of unpaved surface and base layers of the pavement. In addition, the effect of the size of the aperture of geogrid reinforcement on interface properties is studied by considering two types of biaxial geogrids of different aperture sizes. The interface shear strength and interaction coefficients of different reinforcement types with pavement materials are also proposed. The interaction coefficients of three reinforcement types with the pavement materials considered in the study are found to range from 0.82 to 1.45. The interface shear modulus of different interfaces considered in this study ranges from about 12165–57337 kPa/m corresponding to normal streeses in the range of 30–90 kPa.

Experimental studies of ride quality of selfpropelled combine harvester

The given work is devoted to the study of dynamic loads acting upon a combine harvester, which is one of the most vibration-loaded types of modern transport and technological machines. The results on the evaluation of dynamic loads and ride quality parameters of a self-propelled combine harvester when driving along gravel and bituminous surfaces under various operating conditions are presented based on complex experimental studies carried out with the help of tensor and vibrometry methods. The method and conditions of measurements are given. On the basis of the experimental studies, the acceleration spectrum on the main parts of the combine harvester are presented and their description is given. Using the methods of spectral analysis and statistical processing, a vibration modal analysis has been carried out during a combine harvester movement. According to the results of the analysis, the basic vibrational modes have been determined, and it has been shown that the self-propelled combine harvester movement dynamics is determined by vertical and longitudinal-angular vibrations of its core on pneumatic tires. Further scientific research directions to improve the ride quality and to decrease the dynamic loads on a considered class of self-propelled agricultural machines have been determined.

Grain and bedform roughness properties isolated from gravel-patch DEMs

Remote sensing of gravel-bed patches and resulting high-resolution digital elevation models (DEMs) allow for the identification of various spatial scales of surface roughness. Thus far, dimensions relating to grain and bedform roughness scales have been determined using semivariograms or equivalent structure/autocorrelation functions. However, it is difficult to clearly differentiate roughness scales and separate analysis of roughness properties is not possible. This study examines the use of moving-window detrending on gravel-patch DEMs for isolating grain and bedform roughness and their respective topographic signatures. An extensive dataset of water-worked gravel surfaces collected in both laboratory and field environments is used. The measured bed topography is separated into two distinct DEMs: one representing grains, the other representing bedforms, and roughness properties are determined separately for grain and bedform DEMs. The results show that both roughness scales are controlled by the size of the coarse sediment forming the bed surface, with positive linear relationships connecting bed composition and vertical roughness. Coarse sediment is controlling bedform development by forming humps on the surface, in the lee of which finer sediment is sheltered. We present synthesis relationships connecting vertical roughness of gravel patches to the vertical roughness of grains and bedforms.

Surface Morphology of Meteorites in Lut Desert (Iran) Environment

It is believed that low chemical weathering in the desert has made it suitable for preservation and concentration of meteorites. The dry and warm climate causes low chemical weathering in the Lut Desert. But the effects of salt and temperature fluctuations, however, are the main culprits for physical fragmentation and reshaping the meteorites. The present study aims to illustrate surface morphology of meteorites in various erosion conditions in Lut Desert. To reach the purpose authors have studied surface morphology of the meteorite typed H5 which was fragmented by physical weathering in southwestern Lut Desert (yardangs region). Each piece of this meteor placed in different environment; Sandy land, salty land and lag gravel surface. The results show that meteorites are best preserved in sandy land and its outer crust remnant and that sandy land keeps more stable condition of humidity and temperature for protection meteorite from weathering so outer crust may keep thousands of years. But the most weathered part was exposed to salt and groundwater in salty land Meteorite on lag gavel surface are well developed under wind sculpture and show polished surface with bombardment porosity.

Removal of orgRemoval of Organic Material in Free Water Surface Gravel Bed Filtersanic material in free water surface gravel bed filters

The removal of organic material in free surface gravel bed filters was investigatedand modelled. Two pilot wetland units of 7.5m x 1.5m x 0.7m were constructedadjacent to the University of Dar es Salaam waste stabilization ponds to receivemaximum organic and hydraulic loading rates of less than 185 kg/ha/d and 110l/m 2 /d, respectively. These units received wastewater of domestic characteristicsfrom primary stabilization pond. The entire depth of 0.7 m of the wetland unitswere packed with gravel of size 8 ~ 25 mm and porosity of 35%. Samples werecollected from the influent and effluent of wetland units and were tested forchemical oxygen demand (COD), temperature, dissolved oxygen, pH and otherparameters useful for testing of the model. A semi-empirical model representingthe major processes taking place in the wetland units was developed byincorporating suspended biomass, biofilm biomass, and sedimentation andfiltration components. The model was optimized using computer program. Themodel was successfully developed and showed that biofilm of gravel mediacontributed significantly to COD removal in wetlands.

Adsorptive removal capacity of gravel for metal cations in the absence/presence of competitive adsorption.

Locally available and low cost granular gravel as an adsorbent material was employed to determine its capacity to remove metal cations Cu(II), Fe(II), Ni(II), and Zn(II) from single metal solution and landfill leachate samples. Adsorption kinetics and mechanism under different parameters including dosage, time, and pH were studied. It was found that the experimental results fitted to the Freundlich model suggesting an adsorption process on a multilayer heterogeneous surface for both single metal solution and landfill leachate samples. The adsorption of metal cations followed second-order kinetics occurring in a single step on the surface of gravel. The order of removal efficiency of metals was found to be Cu(II)(98%) > Fe(II)(87.5%) > Zn(II)(76.05%) > Ni(II)(36.38%) in single metal solution and Cu(II)(98.3%) > Fe(II)(83%) > Zn(II)(48%) > Ni(II)(27.32%) in landfill leachate sample at pH 7. The regeneration efficiency of the metals adsorbed on the gravel resulted in the order of Fe(II)(99.54%) > Cu(II)(99%) > Ni(II)(49.46%) > Zn (II)(2.25%).

Wind tunnel test on the effect of metal net fences on sand flux in a Gobi Desert, China

The Lanzhou-Xinjiang High-speed Railway runs through an expansive windy area in a Gobi Desert, and sand-blocking fences were built to protect the railway from destruction by wind-blown sand. However, the shielding effect of the sand-blocking fence is below the expectation. In this study, effects of metal net fences with porosities of 0.5 and 0.7 were tested in a wind tunnel to determine the effectiveness of the employed two kinds of fences in reducing wind velocity and restraining wind-blown sand. Specifically, the horizontal wind velocities and sediment flux densities above the gravel surface were measured under different free-stream wind velocities for the following conditions: no fence at all, single fence with a porosity of 0.5, single fence with a porosity of 0.7, double fences with a porosity of 0.5, and double fences with a porosity of 0.7. Experimental results showed that the horizontal wind velocity was more significantly decreased by the fence with a porosity of 0.5, especially for the double fences. The horizontal wind velocity decreased approximately 65% at a distance of 3.25 m (i.e., 13H, where H denotes the fence height) downwind the double fences, and no reverse flow or vortex was observed on the leeward side. The sediment flux density decreased exponentially with height above the gravel surface downwind in all tested fences. The reduction percentage of total sediment flux density was higher for the fence with a porosity of 0.5 than for the fence with a porosity of 0.7, especially for the double fences. Furthermore, the decreasing percentage of total sediment flux density decreased with increasing free-stream wind velocity. The results suggest that compared with metal net fence with a porosity of 0.7, the metal net fence with a porosity of 0.5 is more effective for controlling wind-blown sand in the expansive windy area where the Lanzhou-Xinjiang High-speed Railway runs through.

Development of stratigraphically controlled, eolian-modified unconsolidated gravel surfaces and yardang fields in the wind-eroded Hami Basin, northwestern China

Development of stratigraphically controlled, eolian-modified unconsolidated gravel surfaces and yardang fields in the wind-eroded Hami Basin, northwestern China

건식세척기술을 이용한 철도 도상자갈 정화 연구

본 연구에서는 오염된 자갈을 정화하기 위해서 새로운 방식의 건식세척장치를 제작하여 석유계총탄화수소(TPH) 및 산화철의 저감 성능을 알아보았다. 기존 연구에서는 회분식 처리 방식이 적용되었으나, 본 연구에서는 정화 성능 및 처리 효율 향상을 위하여 연속식 처리 방식을 적용하였다. 또한 오염자갈의 전처리를 위하여 건조기 및 선별기를 적용하였다. 본 실험에서는 총 12개의 노즐을 통해 약 <TEX>$5-6kg/cm^2$</TEX>의 압력으로 20-30분 동안 연마재를 자갈에 분사하여 석유계총탄화수소(TPH)와 산화철의 저감 성능을 확인하였다. 실험결과 석유계총탄화수소(TPH)와 산화철 모두 약 80-90%의 높은 처리효율을 나타냈다. 본 연구에서는 향후 추가 연구를 통해 정화효율을 높일 수 있는 방법을 제시하고자 한다. This study proposes a newly developed dry washing method for removing pollutants such as total petroleum hydrocarbon (TPH) and oxidized iron from the surface of ballast gravel. A batch-type dry washing method showed a good performance in a previous study. In this study, a continuous-type dry washing system, instead of a batch-type system, was prepared to improve the efficiency of the system. A drier and a separator were also applied to this system as pre-treatment process, and the performance of this system was evaluated. In this experiment, blasting media was blasted on the polluted gravels through 12 nozzles by a pressure of <TEX>$5-6kg/cm^2$</TEX> for 20-30 mins to remove TPH and oxidized iron. It was found to be possible to remove 80-90% of TPH and oxidized iron by using this system. Several ways to improve the performance were suggested in this study.

Rheological and mechanical behavior of High Strength Steel Fiber-River Gravel Self Compacting Concrete

This study reports the results of a comprehensive experimental campaign aimed at demonstrating the feasibility of using river gravels in substitution of ordinary crushed aggregates for the production of high strength Steel Fiber-River Gravel-Self Compacting Concrete (SFRGSCC). Due to geomorphological reasons, the river gravels represent the most common type of aggregates used in Amazon region for ordinary structural concrete production but only few researches focused on the use of this kind of raw material for the production of high performance cement-based composites. In fact, the river gravels present different intrinsic characteristic in comparison with crushed rocks such as, higher density and elastic modulus, rounded shape with a smoother surface and a more brittle behavior. As a consequence, when embedded in a cement-based matrix they can significantly affect the rheology and mechanical performance of both self-compacting concrete matrices (RGSCC) and Fiber Reinforced Concrete (SFRGSCC).In this context, the present study firstly analyzes the physical and mechanical properties of the alternative aggregates and then, investigates how the complete replacement of crushed aggregate by river gravel can influence the flowability, segregation potential, yield stress and plastic viscosity of the RGSCC and SFRGSCC in the fresh state as well as the stress-strain behavior under compression, direct tension and bending in the hardened state. The results highlight as the river gravel aggregates shape and surface roughness have relevant effects on the concrete performance as they improve the concrete rheology increasing the concrete flowing and reducing the corresponding yield stress and entrapped air while, on the other hand, reduce the strain capacity of the matrix resulting in a more fragile mechanical response under compression, tension and bending. The addition of steel fiber to the RGSCC resulted being more beneficial than to the reference crushed aggregate SCC. The reinforcement significantly enhanced the RGSCC toughness being this improvement even more pronounced when the samples were submitted to direct tension and bending loads.

Evolution of gravel surfaces in a sediment‐recirculating flume

AbstractThe assumption of the equilibrium state of gravel surfaces in flume experiments under feeding or recirculating conditions is generally justified by three equilibrium criteria based on sediment transport, slopes, and bed features. When these parameters become stable, an experiment is expected to reach equilibrium. This equilibrium state, however, is based on a one‐dimensional model, the Exner equation, which may not truly reflect the equilibrium state of the system considering the complex flow and sediment processes. In this paper, the evolutionary process of a gravel surface is investigated based on a large‐scale recirculating flume experiment. The performances of the three equilibrium criteria are evaluated first, and then the evolution of the bed morphology is studied. The key findings include the following: (1) the sediment transport rate, slopes of water and bed surfaces, and one‐dimensional morphological features reach equilibrium roughly simultaneously; (2) two‐dimensional morphology continually evolves after these characteristics reach equilibrium, which is confirmed by the characteristics of the sediment transport process; and (3) the results from a numerical simulation suggest that a much longer time is required to reach an equilibrium state. Our results suggest that sufficient experimental time is required to investigate the equilibrium morphological characteristics of gravel surfaces, which is much longer than the equilibrium time reflected by the one‐dimensional equilibrium criteria. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Experimental and Numerical Study of the Effects of Coal on Pavement Performance in Mine Haul Road

Coal has many applications for fuel and energy production; therefore, coal mining has always been taken into consideration. When the coal is transported by trucks, it falls on the mine haul road and influence on the geotechnical properties of road pavement. Since, there have been scarce researches on the effects of coal on mine haul road pavement, the aim of this study is to investigate experimentally and numerically the effects of coal on the physical and geotechnical properties of the mine haul road pavement. Therefore, coal was sampled from “Hojedk” coal mine located in Kerman- Iran and was added to the sandy gravel surface layer with weight percentages of 2, 4, 6, and 8%, and its geotechnical properties were examined in compaction, California Bearing Ratio (CBR), unconfined compression strength, direct shear, permeability, sand equivalent, and liquid limit tests. The results indicate that with increase of coal from 0 to 8%, the maximum dry density, CBR, and coefficient of permeability increased to 362, 361, and 132%, respectively, and the sand equivalent decreased by 20%. Also, with increase the percentages of coal from 0 to 4%, unconfined compressive strength and cohesion increased up to 102 and 194%, respectively and with increase the percentages of coal from 4 to 8%, these values decreased by 31 and 43%, respectively. According to scanning electron micrograph test, the sample without coal had more pores than the sample with coal which led to increase the soil permeability and reduction in strength of soil. According to numerical analysis of mine haul road with finite element software OpenSees, it was found that by subjecting the standard wheel load (850 kPa), the least maximum settlement of pavement was observed in the pavement containing 4% coal at 4.4 cm.

The contribution of plateau pika disturbance and erosion on patchy alpine grassland soil on the Qinghai-Tibetan Plateau: Implications for grassland restoration

Patchy alpine grassland with soil excavated by plateau pika (Ochotona curzoniae) and with bald patches is common on the Qinghai-Tibetan Plateau (QTP) where desertification has developed rapidly over the last few decades. This may have significant effects on alpine grassland restoration, by changing soil properties. In this study, the contribution of plateau pika disturbance and erosion on patchy alpine grassland soil were examined by classifying the surface of the patchy grassland into 4 types—vegetation patch, new pika pile, old pika pile and bald patch—and comparing the gravel content of the top layer of soil, soil moisture, soil hardness, soil organic carbon (SOC), and soil total nitrogen (TN) among them in the four study areas with different climatic conditions, altitudes, and grassland types on the QTP. We also analyzed the relationship between the amount of soil surface gravel and the Green Fractional Vegetation Cover (GFVC) using aerial photos. The results showed that (1) gravel content was significantly greater in bald patches and pika piles than in vegetation patches (p<0.05); (2) soil moisture, hardness, SOC and TN were the highest in vegetation patches, and significantly lower in pika piles than in vegetation patches (p<0.05); (3) GFVC was negatively and linearly correlated with the amount of soil surface gravel, with the amount of soil surface gravel in non-vegetation patches significantly greater than in vegetation patches (p<0.001). Our results suggested that pika burrowing activity may increase the gravel content of the top layer of soil and decrease soil moisture, hardness, SOC and TN, which can increase soil erosion and hinder vegetation restoration.