Sand Layer Research Articles

Reliability analysis of pile-founded T-walls using the random variable method and random field method

The pile-founded walls (e.g., T-walls) are important civil infrastructure for flood protection. The stability analysis of floodwalls in the face of flooding hazards is a critical problem for the design and maintenance of floodwalls. However, most current studies for the stability assessment of floodwalls are based on deterministic analyses. The uncertainties of soil properties, which cannot be avoidable due to complex geological processes and depositional environment, are not sufficiently studied. To address the uncertainties of soil properties, a two-dimensional pile-founded T-wall system with several clay layers on the top and a sand layer on the bottom is taken as an example for the reliability analysis. Both the random variable method and random field method are adopted for the probabilistic analysis of floodwalls. The effect of the coefficient of variation (COV) and scales of fluctuation of soil properties are investigated by parametric studies. The results show that the probability of failure increases with the COV of soil properties for both methods. For the random field method, the effect of the vertical scale of fluctuation of soil properties is more profound than the horizontal scale of fluctuation. The probability of failure derived from the random variable method is generally larger than that from the random field method at high flood water elevations when the same COV of soil properties is applied. This study can provide useful references for risk-informed decision-making in the stability assessment of floodwalls in the face of flooding hazards.

Study on Prevention and Control Measures of Water–Sand Inrushes Based on Adaptive Adjustment of Mined Thickness

There have been frequent occurrences of water–sand inrushes in underground mines due to irregular mining activities under thick loose gravel layers. The morphological development characteristics of the caving zone and the changes in the geological conditionsin the working face under a thick loose sedimentlayerof the Pingan Coal Mine have been studied. The empirical formula and numerical simulations are carried out to explore the effect of different thicknesses of the bedrock on the height of the caving zoneand mining thickness. The method of solving the water-sand inrush of the fully mechanized caving face by adjusting the mining thickness was proposed. The results indicate that there is a linear relationshipbetween the height of the caving zone and the mined thickness. The caving height ratio decreases with an increase in the mined thickness and the correlation can be described by a power function. The maximum allowable height of the caving zone and mined thickness are determined based on the thickness of the bedrockand the changed tendency of the caving height ratio. This provides a mean to control the stability of the sand layer on the roof of the working face by adjusting the mined thickness of coal. The method has been applied in the Pingan mine to prevent water-sand inrushes successfully.

Study of Water Filtration Without Chemical Pre-Treatment

This research work focused on studying water purification without chemical pre-treatment. In the studies, alternative approaches were carried out to develop a filter bed suitable for filtering water without the use of chemical treatments that is also cost effective. Polyvinyl Chloride (PVC) pipes (100 × 1700) mm were used as filter boxes. The experiment carried out during the study was divided into two major parts; that is slow sand and rapid sand filter parameters. The slow sand filter consisted of two filter pipes, one consisting of a stratified layer of sand of size range of 0.20 – 0.60 mm with a depth of 700 mm as filter medium. The turbidity, filtration rate and head loss of the effluent across the filter were monitored for 15 days. It was found that slow sand filter plus granular activated carbon (GAC) and rapid sand filter plus GAC were more effective in the removal of turbidity. Turbidity reduced with the increase in time. Rapid sand filter was found to be the least effective in the removal of bacteria while slow sand filter plus GAC was the most effective. The slow sand filter unit gave a very high coliform count compared to other filter units. It was found that the filtration rate plays a vital role in the mechanism of filtration.

Effects of porous media thickness and its hydraulic gradient history on the formation of sand boils: Experimental investigation

Sand boils occur where groundwater discharges to the land surface under sufficient hydraulic gradient to cause internal erosion and the upward transport of particles. A proper understanding of sand boil processes is essential in evaluating a wide range of geomechanical and sediment transport situations under which groundwater seepage occurs, such as the effects of groundwater discharge on beach stability. Although various empirical methods have been developed to estimate the critical hydraulic gradient (icr) leading to sand liquefaction, a prerequisite for sand boil occurrence, the effect of sand layer thickness and the implications of driving head fluctuations on the formation and reformation of sand boils have not been explored previously. This paper uses laboratory experiments to study sand boil formation and reformation for various sand thicknesses and hydraulic gradients to fill this knowledge gap. Sand layer thicknesses of 90 mm, 180 mm and 360 mm were adopted in evaluating sand boil reactivation, which was created by imposing hydraulic head fluctuations. While the first experiment (i.e., 90 mm sand layer) yielded a value for icr smaller (by 5%) than Terzaghi's (1922) value, the same theory underestimated icr by 12% and 4% for 180 mm and 360 mm sand layers, respectively. Moreover, icr needed for the reformation of sand boils decreased by 22%, 22% and 26% (relative to icr applicable to the initial sand boil) for the 90 mm, 180 mm and 360 mm sand layer thicknesses, respectively. We conclude that the formation of sand boils requires consideration of sand depth and the history of sand boil formation, particularly in relation to sand boils that form (and potentially reform) under oscillating pressures (e.g., tidal beaches).

Geological controls on the distribution of gas hydrates in the shallow parts of the gas hydrate stability zone – constraints from seafloor drilling off Taiwan

The presence of gas hydrates is well known in the marine realm southwest of Taiwan due to the widespread distribution of bottom simulating reflectors in seismic records. To learn more about gas hydrate systems and their dynamics at passive and active margins, we drilled boreholes with MARUM-MeBo200 seafloor drill rig at areas where geophysical indications for gas hydrates have been detected in the past. Several gas hydrate proxies like negative chloride anomalies in the pore water, cold spots detected by infrared thermal scans on cores, increased resistivity, and lithological parameters clearly showed the presence of hydrates in the drilled sections. However, gas hydrate was not recovered by MeBo most likely because of small crystal sizes which dissociated during recovery from the seafloor. Three holes were drilled at southern summit of Formosa Ridge down to 126 m below seafloor (mbsf) and recovered sediments from which in situ hydrate saturation values were estimated between 1 and 10% at 15–42 mbsf and even higher values of up to 38% below 100 mbsf. The latter are probably related to the sealing effect of carbonate precipitation which occur at 85–95 mbsf directly above the hydrate-enriched layer. Four holes were drilled at Four-Way Closure Ridge where a maximum drilling depth of 143.90 mbsf was reached. Hydrate presence starts in 65 mbsf continuing down-core with a range of 1–29% gas hydrate saturation in fine-grained homogenous clay. An abrupt change to higher gas hydrate saturation values of up to 80% occurs below 109 mbsf where silty and sandy turbidite layers are often intercalated. Such high gas hydrate contents only occur in the sand layers and not in the fine-grained sediments intercalated to the sand deposits.

Physical modelling of the interaction between a tunnel and a building in a liquefying ground and its mitigation

The fast growth of the built environment in liquefaction-prone areas requires new design challenges to be overcome. A significant soil shear strength and stiffness loss associated to soil liquefaction, possibly occurring during severe earthquakes, may induce effects on buildings and on shallow and light structures such as urban tunnels. In densely urbanised areas, interaction between underground and aboveground structures may results in a detrimental combination of such effects.The paper discusses the results of a series of centrifuge tests carried out at the Schofield Centre (Cambridge, UK) modelling the dynamic interaction between an urban tunnel and a building in sand undergoing cyclic liquefaction. Four reduced-scale models were tested at increased gravity to model a prototype 60 times larger. A rectangular aluminium frame embedded in a layer of homogeneous Hostun sand represented a section of a metro tunnel. An aluminium sway frame represented a simple building founded in the same layer, at a side of the tunnel. The experimental results show that in typical urban spacing, sand liquefaction in the foundation ground affects the reciprocal interaction between the kinematic of the tunnel and the building.Centrifuge modelling investigated whether it is possible to mitigate or prevent such interference by improving ground through the addition of hydrated laponite beneath the tunnel floor or as lateral vertical barrier between the building foundation and the tunnel. The results also show the importance of temporary structures – often used to support soil excavation during cut-and-cover tunnel construction – in reducing the effects of interaction between the tunnel and the building in the liquefying soil.

Penggunaan Data SPT dalam Penentuan Potensi Likuifaksi di Kota Solok

The area of West Sumatra which is at the confluence of 2 tectonic plates and 2 faults makes the area prone to earthquakes. One of the cities that has experienced an earthquake is Solok. One of the impacts of earthquakes is liquefaction events, namely the loss of strength of the sand layer due to increased pore water pressure. So that in planning construction in Solok it is necessary to review the potential for liquefaction in order to reduce construction damage and prevent liquefaction. To find out the potential for liquefaction as expressed by the value of the safety factor, it can be analyzed using standard penetration test data, namely N-SPT. The safety factor used in this study is the probability of 500 years and 2500 years. The results of the analysis of the safety factor obtained show that at each depth of the soil layer under review it has a value of < 1 so that the potential for liquefaction is quite high. The lowest safety factor is obtained at a depth of 4 – 6 m for a 500 year probability and 6 -7 m for a 2500 year probability which ranges from 0,12 – 0,16.

GEYSERNAYA RIVER ALLUVIUM (KAMCHATKA): COMPOSITION AND FEATURES OF FORMATION<a href="#FN2"><sup>2</sup></a>

A comprehensive compositional analysis of the alluvium from the river with active gas-hydrothermal manifestations was carried out for the first time. Geysernaya river alluvium is characterized by: poor roundness of boulders and pebbles (grades 1–2), poorly sorted fine-clastic component, abundance of rock fragments and intergrown minerals even in the fine sand fraction. All these indicate the sediment weak disintegration with significant amount of slope material in it, including redeposited by mudflows. The high content of smectite-zeolite and other newly formed (secondary) minerals aggregates (up to 70% of the light fraction 0.1–0.25 mm in size) and altered rock fragments (up to 70–80% in the pebble fraction of alluvium) indicate that a gas-hydrothermal activity significantly impact the bedrock and alluvium weathering within the thermal fields. The material accumulates predominant in the areas of: (1) active delivery of slope material (temporary dams), (2) the longitudinal profile flattening in dammed reservoirs, and (3) mudflow material removal. Formation of two dammed reservoirs over the past 15 years, as well as layers of fine sand found in the low terrace’s sediments, indicate that such short-lived basins form periodically in the Geysernaya river valley. The conditions of the fine sand deposition in sections of a single-branch channel and within dammed reservoirs are differ, which affects the heavy fraction leading minerals ratio. The well-rounded gravel and abundance of coarse sand, and their decrepit appearance indicates that, along with the processing of incoming slope and mudflow material large volumes the Geyzernaya river continues to cut in and erodes the ancient fluvial sediments.

Dolomite and organic compost application for preventing acid mine drainage formation in a mesocosm system

Acid mine drainage (AMD) is one of most serious environmental problems facing mining industries. It results from oxidation of sulfide minerals contained in mining wastes, such as rock disposals in mine sites. This study was to investigate AMD formation from waste rocks containing potentially-acid forming (PAF) materials treated with dolomite and compost in a mesocosm system. The system comprised a plastic drum of 150-cm height and 50-cm diameter filled with 15-cm sand at the botom layer, over-laid by 50-cm mixture of PAF+10% of either dolomite or compost, and 35-cm top-soil layer on the top. The drum surface of the sand layer was equipped with a valve to drain leached water into a collecting container. The control was a similar constructed mesocosm without addition of either ameliorant. The drums were installed into the ground of the mined land so that their surfaces were as high as the surrounding soil surface and left under field condition. The leachate samples were taken two-weekly in the early two months and monthly until the day 487. The system demonstrated that both dolomite and compost significantly increased pH from around 3 to pH>6 and reduced dissolved Al and Fe concentrations. However, the dissolved Mn concentration was still high (>20 mg L−1) in all treatments even at the pH reached >6. .

Shaking Table Tests of Seismic Response of Multi-Segment Utility Tunnels in a Layered Liquefiable Site

Damage to underground structures caused by liquefaction is one of the important types of hazards in the field of geotechnical engineering. Utility tunnels are the lifeline projects of cities. To ensure the sustainable and safe operation of utility tunnels over a design life of 100 years, this paper investigates the seismic response pattern of utility tunnels in the liquefied site. In this paper, shaking table tests were carried out on the utility tunnel in a layered liquefiable site. Based on the test data, the distribution law of acceleration field and pore pressure field in the model and the deformation of the soil were analyzed first. Then the soil-structure interaction, the strain and uplift of the structure were investigated. The results show that liquefaction of sand layers under strong earthquakes, resulting in seismic energy loss. The acceleration of the upper clay layer is attenuated by the seismic isolation of the liquefied soil. The utility tunnel affects the propagation of soil acceleration, which decays faster beneath the structure for the same height. The process of pore water pressure growth is a process of energy accumulation and the pore water pressure ratio curve and Arias intensity are significantly correlated. During the test, the phenomenon of sand boil appeared, and the cracks appeared on the ground surface and developed continuously. The utility tunnel in liquefied soil is lifted under the action of excess pore water pressure. There are vertical and horizontal displacement differences at the deformation joints. The strain in the utility tunnel at the stratigraphic junction is mainly influenced by the action of the bending moment, large shear deformation in the transverse section. The strain at the connection between the partition wall and the top slab is the largest and is the weak position of the structure, followed by the connection between the side walls and the top slab, and the bottom slab of the structure have a smaller strain. The results provide insights into the dynamic properties of soils and structures in liquefaction sites.

Integrated Geophysical Approach of Groundwater Potential in Wadi Ranyah, Saudi Arabia, Using Gravity, Electrical Resistivity, and Remote-Sensing Techniques

In order to cope with the rise in human-caused demands, Saudi Arabia is exploring new groundwater sources. The groundwater potential of Wadi Ranyah was studied using a multi-dataset-integrated approach that included time-variable gravity data from the Gravity Recovery and Climate Experiment (GRACE), vertical electrical sounding (VES), and time-domain-electromagnetic (TDEM) data with other related datasets to examine the variations and occurrence of groundwater storage and to define the controlling factors affecting the groundwater potential in Wadi Ranyah in southwestern Saudi Arabia. Between April 2002 and December 2021, the estimated variation in groundwater resources was −3.85 ± 0.15 mm/yr. From 2002 to 2019, the area observed an average yearly precipitation rate of 100 mm. The sedimentary succession and the underlying fractured basement rocks are influenced by the structural patterns that run mainly in three different trends (NW, NE, and NS). The sedimentary cover varies from 0 to 27 m in thickness. The outputs of the electrical sounding revealed four primary geoelectric units in the study area: on top, a highly resistant geoelectrical unit with a resistivity of 235–1020 Ω.m, composed of unsorted, loose, recent sediments; this is followed by a layer of gravel and coarse-grained sands with a resistivity of 225–980 Ω.m; then, a water-bearing unit of saturated sediments and weathered, fractured, basement crystalline rocks with a resistivity of 40–105 Ω.m, its depth varying from 4 to ~9 m; and then the lowest fourth unit composed of massive basement rocks with higher resistivity values varying from 4780 to 7850 Ω.m. The seven built dams store surface-water runoff in the southwestern part of the wadi, close to the upstream section, in addition to the Ranyah dam, as the eighth one is located in the middle of the wadi. The subsurface NW- and NS-trending fault lines impede the groundwater from flowing downstream of the wadi, forming isolated water-bearing grabens. Minimal surface runoff might occur in the northern part of the wadi. The combined findings are beneficial because they provide a complete picture of the groundwater potential of Wadi Ranyah and the controlling structural patterns. Using this integrated technique, the groundwater potential in arid and semiarid regions can now be accurately assessed.

Seismic Bearing Capacity of Strip Footing Placed on Sand Layer Over Hoek–Brown Media using Finite Element Limit Analysis and Machine Learning Approach

Seismic Bearing Capacity of Strip Footing Placed on Sand Layer Over Hoek–Brown Media using Finite Element Limit Analysis and Machine Learning Approach

Enzymatic-Induced Calcite Precipitation (EICP) Method for Improving Hydraulic Erosion Resistance of Surface Sand Layer: A Laboratory Investigation

As a bio-inspired calcite precipitation method, bio-grouting via enzymatic-induced calcite precipitation (EICP) uses free urease enzyme to catalyze the urea hydrolysis reaction. This soil stabilization approach is relatively new and insufficiently investigated, especially for applications involving surface layer stabilization of sandy soil deposits for increasing hydraulic erosion resistance. This paper presents a laboratory investigation on the surface erosion resistance improvements for compacted medium-gradation quartz sand specimens mediated using 10 different EICP treatment protocols. They involved single- and two-cycle injections of the urease enzyme (activity of 2400 U/L) and 0.5, 0.75, or 1.0-M urea–CaCl2 cementation solution reagents. The urease enzyme was extracted from watermelon seeds. Erosion rates were determined for various hydraulic shear stresses applied using the erosion function apparatus. The spatial distribution and morphology of precipitated calcite within the pore-void spaces of the crustal sand layer were investigated with a scanning electron microscope. Compared to untreated sand, all 10 investigated EICP treatment protocols produced substantially improved erosion resistance, especially for the higher cementation solution concentration (1.0 M). Of these 10 EICP protocols, a single cycle of enzyme–1.0-M-cementation solutions injections was identified as the more pragmatic option for achieving near-optimum erosion resistance improvements. Highest and lowest amounts (18.8 and 5.0 wt%) of precipitated calcite corresponded to the best and worst performing EICP-treated specimens, although the calcite’s spatial distribution in treated specimens is another important factor.

Study of a Method for Drivability of Monopile in Complex Stratified Soil

At present, there is no commonly used method for predicting soil resistance to the driving (SRD) of monopiles, because all available methods are developed based on an installed offshore pile with a diameter of 2–3 m. In addition, due to the complexity of soil profiles in situ, the accuracy of methods used is often not stable under different soil conditions. Based on two typical stratified soil conditions of offshore wind farms in the East China Sea, which are clay-interlayered sand and sand-interlayered clay where, according to the pile driving records of the monopiles in sites, the SRD is obtained by back analysis using the method of the wave equation. At the same time, SRD is also calculated using Steven and Alm methods and compared with that of the back analysis. The results show that the SRDs from the Steven and Alm methods are basically consistent with that of the back analysis, but the predicted SRD of the clay layer is higher than that of back analysis, while the predicted SRD of the sand layer is lower. Based on the characteristics of SRD in different soil layers, a modified method for calculating unit friction in clay and the unit end resistance in sand is proposed for stratified soil, and the error between SRD of the proposed method and of the back analysis was approximately 20%. It could be helpful to improve the accuracy of the monopile drivability analysis in stratified soil.

Influence of spatial distribution of fine sand layers on the mechanical behavior of coral reef sand

Fine coral sand commonly distributes in coral sand artificial foundation due to the effect of gravity sorting during hydraulic process and the particle breakage of coarse particle. Considering that the significant impact of the distribution form of fine sand on the strength and deformation properties of coral sand foundation, the effect of spatial distribution of fine sand layers on the mechanical behavior of coral sand was studied. The mechanical behavior of coral sand in the consolidated undrained (CU) shear tests were simulated by discrete element models (DEM) analysis method, and the impact mechanism of fine sand interlayers on mechanical strength was analyzed. The effect of thickness and number of fine sand interlayer on the mechanical behavior and shear deformation of coral sand specimens were analyzed based on the proposed uniformity degree, a parameter that quantify the spatial distribution of fine particle interlayers. The results show that the mechanical behavior of coral sand was simulated well by DEM based on particle scanning results. Under the condition of constant fine particle content, the average coordination number of particles increased and the minimum contact force between particles decreased when fine particles were distributed in the form of interlayer. It indicates that the fine particle interlayer has a diffusion effect on stress transfer, which revealed the mechanism of the macro increasing strength of 10%–20% under the same confining pressure. A linear relationship was found between the proposed parameter uniformity and the peak deviator stress of specimens, and the impact of uniformity on the strength was particularly significant under high confining pressures.

APPLICATION OF GEOELECTRICAL METHOD TO STUDY GROUNDWATER POTENTIAL IN ISARA, REMO NORTH MUNICIPAL AREA OF OGUN STATE, NIGERIA.

Fifteen (15) Vertical Electrical Sounding (VES) and three (3) Constant Separation Traversing (CST) data were acquired within the study area using Pasi Terrameter (model 16GL). The Schlumberger electrode array was deployed for the VES while Wenner array was used for the 2-D CST. Both qualitative and quantitative approach were used for the VES measurements. The raw data were Curve-matched and inversion of the data using WinResist (1.0) to create a model of perfect fit indicating layer thickness and resistivity values for individual layers while the 2D resistivity data were processed using Res2Dinv software. The 2D resistivity structures revealed the lateral and the vertical variations of the subsurface information having resistivity values ranging from 81.8 to 5250 Ωm. The geoelectric sections revealed five to six geoelectric layers, which correspond to the topsoil, clayey sand, lateritic clayey sand and sand. The topsoil is characterized by resistivity values ranging from 29.8 to 358.5 Ωm and layer thickness of 0.6 to 0.8 m. The clayey sand had resistivity and layer thickness values ranging from 81.4 to 278.0 Ωm and 2.4 to 7.1 m respectively. The lateritic clayey sand had resistivity values ranging from 782.0 to 2414.1 Ωm. and layer thickness of 5.4 to 61.2 m. The sand in the third layer in VES 1 to 7, 9 and 10 has resistivity values ranging from 398.6 to 600.7 Ωm and layer thickness of 2.3 to 25 3 m is characterized as seasonal aquifer. The result of this study has further highlighted the capabilities of the electrical resistivity techniques in groundwater investigation

Study on self‐healing gel plugging agent based on non‐covalent bonding interaction for drilling fluid

AbstractDuring drilling in deep formations, it is challenging to form an effective plug to avoid borehole collapse under high temperatures and pressures. In order to simultaneously improve the high‐temperature resistance and interparticle interaction capability of traditional plugging agents, a new gel plugging agent (PCAA) with self‐healing capability was developed using chitosan, acrylamide, and acrylic acid. The rheological properties of the PCAA indicate that all monomers of PCAA are essential components to improve the performance of the plugging agent. Each monomer has a unique capability, such as acrylamide playing a dominant role in the construction of the gel network, acrylic acid enhancing the gel structure, and chitosan improving the gel adhesion. PCAA can be stretched to 8.8 times prolonged, and its tensile stresses and self‐healing rate in 16 h are 17.2 kPa and 78.5%, respectively. Under the extreme conditions of 180°C and 8% NaCl, PCAA still performs well in preventing drilling fluid from invading the sand layer due to its self‐healing and plugging effects. In addition, the interaction of PCAA and clay improves the stability, rheological properties, and filtration reduction of drilling fluids at high temperatures. The developed PCAA has been successfully applied to the field with extreme conditions, providing insights into plugging agent design.

Analysis of the Effect of Pore Water Pressure on a Small Radius Curve Section of a Fine Sand Layer under Cyclic Metro

Small curved metro shield tunnels located in fine sand layers are sensitive to the response of horizontal and vertical cyclic loads from train operations, especially for centrifugal horizontal loads. The majority of Zhengzhou’s strata are dominated by this geological composition. Therefore, the dynamic response of the fine sand layer under the train vibration load will lead to the settlement of the sand layer, which brings great hidden danger to the train operation. Long-term pore water monitoring was carried out in this paper, and the use of MIDAS-GTS (Multi-candidate Iterative Design with Adaptive Selection) finite element calculation platform to establish the metro ballast-lining-soil coupling dynamic model for mutual verification. The variation patterns of pore water pressure and super pore water pressure during train operation and the vibration response pattern of the soil layer around the tunnel were investigated. The results suggest that: (1) The pore and excess pore water pressures generated at the start of vibration are not easily dissipated and transferred, making them larger in the early stages of train operation. In contrast, the fine-grained powdered sandy soil has a small amount of clay particles, giving strength and cohesion to the soil layer. Vibrating hole pressure and excess pore water pressure stabilize with the train at a later stage; (2) The low probability of liquefaction in the silt layer surrounding the tunnel; (3) Under vibrating loads, areas of significant soil settlement are concentrated on the soil surface, on the upper side of the tunnel in the silty sand layer and at the bottom 3 m of the tunnel, however, its low variation in settlement has a low impact on the tunnel.

Contrastive mechanisms of groundwater ammonium enrichment in different hydrogeologic settings

Although high levels of geogenic ammonium in groundwater have been widely reported, the mechanisms controlling its heterogeneous distribution are not yet well understood. In this study, a comprehensive investigation of hydrogeology, sediments, and groundwater chemistry was coupled with a set of incubation experiments to reveal the contrasting mechanisms of groundwater ammonium enrichment at two adjacent monitoring sites with different hydrogeologic settings in the central Yangtze River basin. Significant differences were found in the ammonium concentrations of groundwater at two monitoring sites, with the ammonium concentrations in the Maozui (MZ) section (0.30–5.88 mg/L; average of 2.93 mg/L) being much higher than those in the Shenjiang (SJ) section (0.12–2.43 mg/L; average of 0.90 mg/L). For the SJ section, the aquifer medium had a low organic matter (OM) content and a weak mineralization capability, leading to a limited potential for geogenic ammonium release. Moreover, due to the presence of alternating silt and continuous fine sand layers (with coarse grains) above the underlying confined aquifer, the groundwater was in a relatively open environment with oxidizing conditions, which may have promoted the removal of ammonium. For the MZ section, the aquifer medium had a high OM content and a strong mineralization capability, leading to a much higher potential for geogenic ammonium release. Furthermore, due to the presence of a thick and continuous muddy clay layer (aquitard) above the underlying confined aquifer, the groundwater was in a closed environment with strong reducing conditions, which was conductive to the storage of ammonium. Larger sources of ammonium in the MZ section and greater consumption of ammonium in the SJ section contributed collectively to the significant differences in groundwater ammonium concentrations. This study identified contrasting mechanism of groundwater ammonium enrichment in different hydrogeologic settings, which can help explain the heterogeneous distribution of ammonium levels in groundwater.

Non-Visual Sensing of Metallic Pavement Markers From a Moving Vehicle

Snow and ice covering paved surfaces cause problems for roads and other vehicles operating in cold regions. There are notable risks for road accidents and reduced performance of vehicle movements, e.g., in industrial facilities such as ports, when road markings and marked pathways are not visually observable. In this study, metallic paved surface markers identified by metal sensors are tested. The sound signals captured by a metal detector attached to the vehicle are used to detect the markings. Results indicate that the tested method for reading markings through snow is effective at lower speeds. The main advantages of the tested technology are effectiveness in snowy and icy surface conditions, low upfront cost detection technology in some environments, robust system without moving parts, high sampling rate, and low operating costs. The procedure is not restricted to specific environmental conditions, such as snow and ice; it also has the potential to detect markings through layers of mud, tree leaves or sand. The detectors have application prospects in intelligent transportation system applications at airports, logistics terminals and industrial facilities.