Sediment Physical Properties Research Articles

Methods to identify and distinguish the effects of weathering and landslides on sediment granulometry

Urbanization has resulted in the widespread development of built-up areas, often without considering the local geology and geomorphology. To improve risk assessments related to landslides, it is essential to determine the physical and chemical properties of sediments. The aim of this study is to exemplify an already mobilized and reworked layer based on granulometric properties of the sediments and characterize the chemical and physical properties which have changed during or after the mass movement. Ten red clay layers were sampled near Kulcs (Hungary) from a sliding surface and its environment. We measured grain size distribution, major element and modal composition, furthermore, conduct particle shape analysis, respectively. Grain size distribution suggest that samples from the sliding surface are weathered, with the exhibiting reworking characteristics. We calculate the weathering index from the major elements, which, in combination with the particle shape analyses of the silt fractions, indicate that the morphological parameters of the samples are in relation with weathering index. According to our results, while a fresh sliding event leaves marks on the granulometric properties, the main process which affects the grain morphology is the chemical abrasion (post the mass movement) and not the landslide event.

Mineral effects on methane hydrate formation and distribution in sand sediments

Methane hydrate is a promising energy resource widely occurring in the world, but the formation and distribution of methane hydrate in marine sediments with complex minerals remains unclear. Due to the small pore space and fine-grained size of clay minerals, the contact relationship between methane hydrate and clay mineral surface under excess water has not been characterized fully, which is required to investigate the mineral effect on methane hydrate formation. In this study, cryo-SEM was applied to observe the distribution of methane hydrate synthesized in pure quartz sands and the quartz sands mixed with montmorillonite or illite separately. According to the results of the research, methane hydrate dispersedly forms in the pore space away from and on the surface of quartz under a local excess water condition. In addition, methane hydrate occurs away from montmorillonite in pores with excess water and contacts the edge of montmorillonite under a local excess-gas condition. Moreover, methane hydrate was only observed to form away from illite aggregates in the pore with residual water. Montmorillonite and illite influence the preferable distribution of methane hydrate to occur away from mineral surface in excess water condition. In the sediments composed of different minerals, methane hydrate forms stochastically in the pore space and grows up individually. As a result, the findings of this study significantly expand the understanding of the formation and distribution of methane hydrate in marine sediments and the prediction of physical properties of hydrate-bearing sediments, and provide insights into natural gas hydrate exploration and production.

Identification and quantitative estimates of groundwater transfers to formerly charophyte dominated marl lakes with radon-222

Interaction with groundwater determines many processes in marl lakes. Net transfer of inorganic carbon helps define their chemical characteristics and determines their unique benthic flora. Nutrient enrichment weakens the biogeochemical buffering mechanisms which help maintain a clear-water state and many small, shallow marl lakes are prone to siltation. Despite hydrological processes being recognised as important for the complex interactions between plants, nutrient availability and physical sediment properties which shape marl lake ecology, groundwater discharge to many of these lakes has never been quantified. The aim of this study was to locate and quantify groundwater transfers to degraded marl lakes in a Special Area of Conservation on the island of Ireland. A RAD7 radon detector identified and measured elevated concentrations of 222Rn in three lakes for quantifying their groundwater influx with a 222Rn mass-balance equation. Conservative estimates of mean daily groundwater discharge to Kilroosky Lough, Drumacrittin Lough, and Dummy's Lough were 143 m3, 502 m3, and 269 m3 respectively. With extrapolation to the entire hydrological year, annual groundwater recharge contributed approximately 47 %, 155 %, and 50 % of the respective lake volumes. The areas within the lakes which were found to have the highest groundwater influence also closely matched the locations where substantial charophyte communities persist suggesting that the two are linked. These findings underline the importance of groundwater transfers for the water budget in small marl lakes and will inform management efforts to mitigate their eutrophication.

Acoustic properties of hydrate-bearing sediments in permafrost from hydrate formation to shear processes

Under depressurization, the hydrate reservoirs undergo complex mechanical behaviors such as consolidation or shear. To deeply understand the evolution in the mechanical properties of soil, triaxial equipment with an ultrasonic system was used to detect the shear wave velocity in hydrate-bearing sediments. The effects of hydrate saturation, water, and stress state on shear-wave velocity are studied. The experimental results show that: The hydrate saturation significantly affects the wave velocity in the hydrate formation stage, while the water content has little influence on it. During the consolidation period, the notable increase in shear wave velocity indicates a decrease in soil void ratio, which means the soil has significant settlement deformation. With continuous shearing, the soil elastic modulus is damaged, and finally, the maximum damage can reach 35%. The conclusions can deepen understanding of the physical and mechanical properties of hydrate-bearing sediments in permafrost, and provide a reference for predicting the stratum stability during hydrate exploitation.

Spatiotemporal patterns and co-occurrence patterns of dissimilatory nitrate reduction to ammonium community in sediments of the Lancang River cascade reservoirs.

Dissimilatory nitrate reduction to ammonium (DNRA) is an important nitrate reduction pathway in freshwater sediments. Many studies have focused on the DNRA process in various natural habitats. However, the joint operation of cascade reservoirs will affect the physical and chemical properties of sediments, which may change the DNRA process and bacterial community pattern in the surface sediments of cascade reservoirs. Our study was the first to investigate the spatiotemporal distribution patterns of potential DNRA rate, nrfA gene abundances, and DNRA bacterial community diversity in surface sediments of the Lancang River cascade reservoirs. The results of slurry incubation experiments combined with the 15N isotope tracer experiment ascertained that the potential rates of DNRA were 0.01-0.15 nmol-N cm-3 h-1, and qPCR results indicated that the abundance range of nrfA was 1.08 × 105-2.51 × 106 copies g-1 dry weight. High throughput sequencing of the nrfA gene revealed that the relative abundance of Anaeromyxobacter (4.52% on average), Polyangium (4.09%), Archangium (1.86%), Geobacter (1.34%), and Lacunisphaera (1.32%) were high. Pearson and RDA correlation analysis exhibited that nrfA gene abundance was positively correlated with altitude, pH, OC, and sand concentration. Anaeromyxobacter was positively correlated with reservoir age and DNRA potential rate. The deterministic environmental selection process plays a crucial role in the formation of the DNRA bacterial community. Network analysis displayed that the dominant DNRA genus was the key population of the DNRA microbial community in the sediments of Lancang River cascade reservoirs. This study reveals that the variation of DNRA bacterial activity and community structure is largely driven by the construction of cascade reservoirs, and provides a new idea for further understanding the characteristics of the DNRA community in the cascade reservoir ecosystem.

The influence of hydrocarbons on the physical properties of sea bottom sediments of the Black Sea of different stages of diagenesis under conditions of high pressures and temperatures and the degree of saturation

The influence of hydrocarbons on the physical properties of sea bottom sediments of the Black Sea of different stages of diagenesis under conditions of high pressures and temperatures and the degree of saturation

Correlation between the sound speed ratio and physical properties of seafloor sediments in the northwestern shelf of the south China sea

Based on a substantial number of seabed sediment samples and corresponding acoustic characteristic and physical property test data collected in the continental shelf area of the northwestern South China Sea, this study employed a sound speed ratio correction model to analyze the correlation between the sound speed ratio of seabed sediments and parameters such as porosity, density, mean grain size, and water content. This study resulted in the development of both single-parameter and double-parameter empirical formulas for the sound speed ratio of seabed sediments in this marine region. The determination coefficients (r2) for the single-parameter empirical formulas based on physical properties, excluding the mean grain size (r2 ≤ 0.75), were all above 0.78, indicating a strong correlation. Additionally, the fitting curve at 100 kHz was slightly greater than that at 50 kHz, consistent with the acoustic dispersion characteristics of sediments. To assess the applicability of the empirical formulas to different maritime areas, the formulas derived from the South Yellow Sea, East China Sea, and South China Sea were compared with those of the study area. The results indicated that the empirical formulas for the sound speed ratio established in this study have general applicability, especially for sediments with low porosity, high density, and low mean grain size. In addition, the determination coefficient of the dual-parameter empirical formula for the sound speed ratio–porosity–mean grain size is superior to that of the single-parameter empirical formula for the sound speed ratio–mean grain size. Through comparative studies with other marine areas, it was found that there are certain differences in the relationships between porosity and mean grain size established in different marine areas. Therefore, based on the rough sphere model, this study transforms the GS model into a single-parameter model built on either porosity or mean grain size. The error analysis results indicate that the single-parameter GS model has a smaller error than the measured data. However, the GS model controlled by a single parameter performs poorly compared to the predicted curves of the sound speed ratio–porosity and the sound speed ratio–mean grain size fitted in this study. This discrepancy may be attributed to the fact that the input parameters of the GS model are reference values, emphasizing the need for further research to determine suitable input parameters for the GS model in this marine area.

Biogeoacoustic variability in muddy ocean bottom sediment

Both physical and biological benthic processes can influence seabed heterogeneity and contribute to spatiotemporal variability in geoacoustic properties. In particular, how biological processes affect both sediment acoustic properties and their variability is poorly understood. To address this deficiency, recent measurements investigated spatial variability in the upper few decimeters of sediment near the water-seabed interface within a fine-grained sediment deposit on the New England shelf. At each measurement location, acoustic probes were inserted into the sediment to collect direct in situ measurements of sediment sound speed and attenuation at near-ambient conditions, after which cores were collected from the inter-probe propagation paths for ex situ analysis of sediment physical, biological, and acoustic properties. Relationships among sediment properties, such as bulk density, porosity, grain size distribution, organic matter composition, infaunal community composition, and acoustic measurements spanning several frequency decades (10–1000 kHz) will be explored in this paper. Frequency dependence of sediment acoustic properties will also be discussed in the context of sediment acoustics models for mud based on the viscous grain shearing and extended Biot theories. [Sponsored by ONR.]

A Study of the Physical and Mechanical Properties of Yellow River Sediments and Their Impact on the Reclamation of Coal-Mined Subsided Land

Coal mining in China has resulted in numerous subsided areas, exacerbating land scarcity issues. The Yellow River carries a high sediment load of nearly 1.6 billion tons annually. Cleaning up the accumulated silt is costly and takes up land. Reusing the sediment from the Yellow River to fill and reclaim the subsided areas caused by coal mining addresses both sedimentation and land reclamation issues, killing two birds with one stone. Nonetheless, technical challenges have emerged, such as machinery sinking into the soil, difficulty draining water, and poor soil quality improvement. To tackle these issues, understanding the physical and mechanical properties of Yellow River sediment is essential. Results show that the average particle size (D50) is 0.08 mm, categorized as fine-grained sandy soil with a relatively uniform particle size distribution. The permeability coefficient is 2.91 × 10−3 cm·s−1, similar to that of silty soil, indicating the feasibility for filling reclamation. However, the low permeability requires drainage improvement to accelerate construction timelines. The internal friction angle of the sediment ranges from 34.67° to 31.76°, with a cohesion from 20.79 to 23.92 kPa. To ensure safe and stable construction, machinery must not sink into the fill material. It is recommended to enhance drainage to about 13% for quicker drainage and stable construction. The sediment has a compression coefficient of 0.05 MPa−1, indicating low compressibility. Mechanical compression is not economically viable during the reclamation process. Design elevation (H) and fill elevation (h) should account for cumulative deformation settlement.

Prediction Model of the Sound Speed of Seafloor Sediments on the Continental Shelf of the East China Sea Based on Empirical Equations

Based on the data of the acoustic and physical properties of seafloor sediments obtained on the continental shelf area of the East China Sea (ECS), prediction equations of the sediment sound speed based on single and dual parameters were established, and the correlation of the sound speed with physical parameters was discussed. The results show that the sediment sound speed (c) is strongly correlated with water content (w), density (ρ), void ratio (e), mean grain size (Mz) and median grain size (Md), and the coefficient of determination R2 of the empirical regression equation is generally greater than 0.80, while the empirical regression equation coefficient of determination R2 of the compression coefficient (a) and compression modulus (E) are slightly lower, with 0.79 and 0.73, respectively. The coefficients of determination of the dual parameter regression equations between sediment sound speed with physical property parameters are generally higher than those of the single parameter equations, which are all higher than 0.90 indicating better prediction performance. The sensitivity of the physical parameters to the sound speed was analyzed, and the result shows that the sequence of sensitivity from high to low influence on sediment sound speed is void ratio, density, compressibility coefficient, median grain size and mean grain size. The prediction equations established in this study are a good extension and supplement to marine geoacoustic models and is of great significance for obtaining the acoustic properties of the seafloor sediments on the shelf of the East China Sea.

Particle-size control on the structure and collapsibility of sediments formed by air-fall deposition

Aeolian deposition is significant to the landscape formation on Earth and even other planetary bodies. Particle size controls the transport distance of particles. However, the understanding of particle-size effects on the structure and mechanical behavior of aeolian accumulations remains limited. We investigate the effect of particle size on the structure and collapse of aeolian sediments by one-dimensional compression and collapse tests following the initial air-fall deposition of particles of various sizes from sand to fine silt. Results reveal that the relevance between interparticle forces and gravity controls the formation of two distinct sediment structures as the particle size varies. A loose structure with a packing density close to the simple cubic packing forms for sands and is not collapsible. An open structure with higher porosity forms as particle size becomes smaller. The structure can stack vertically. The stacking height, porosity, and collapsibility increase as particle size decreases. A dimensionless granular bond number Bo captures the relevance between van der Waals forces and gravity. A threshold particle size corresponding to Bo = 10 is identified, below which open and collapsible structures form. The structure forms due to distinctive accumulation behavior. Particle interaction forces create porous aggregates, stabilize the aggregate as it contacts the deposit, and retain open pores. The effect of fine particles on properties of deposited mixtures is also analyzed. Results are relevant to understanding the formation of collapsible aeolian deposits on Earth and may contribute to the estimation of the physical properties of aeolian sediments on other planetary bodies.

Investigating the influence of particle size ranges on the physical, mineralogical, and environmental properties of raw marine sediment

Annually, over one billion cubic meters of sediments are dredged worldwide. The field of construction suffer shortage of natural resources, these sediments present a potential local resource in various regions. Amongst the sectors, road construction stands as the largest consumer of aggregates, making the recovery of sediments an appealing solution. The dredged sediments made of three phases: solid, liquid, and air. The solid phase contains both mineral and organic components, each with particle size ranges. Particle size is a well-known factor significantly impacting material characteristics.This study's primary objective is to compare sediment particle size ranges as sub materials, particularly focusing on their classification for sediment recovery in road construction. The preparation of sediments for characterization tests in this context necessitates specific drying procedures, prompting an investigation into the effects of drying methods. Three distinct drying techniques-air drying, freeze drying, and oven drying were employed.Particle size ranges were extracted from raw marine sediment and categorized based on the following diameter ranges: 2–0.4 mm; 0.4–0.180 mm; 0.180–0.063 mm; and < 0.063 mm. Comprehensive physical, environmental, and chemical characterizations were conducted. The pivotal findings of this study unequivocally reveal variations in the distribution of organic matter across these different fractions. Notably, the fine fraction exerts a substantial influence on material-level attributes, especially concerning environmental characterization. Moreover, the choice of sample drying method before testing introduces variable effects on the investigated attributes. environmental impact analyses using leaching tests indicated higher values of elements like Barium (Ba), Molybdenum (Mo), Fluoride (F), and Chloride (Cl) in sediment fractions below 0.063 mm. The DRX analyses appear that the fine fraction had few clay particles, and higher values measured on different test were associated with organic matter.

Numerical modeling of vadose zone electrical resistivity to evaluate its hydraulic parameters

Studying and determining the physical properties and hydraulic parameters of vadose zone sediments is an important key to evaluate the infiltration rate into them and assessing the extent to which aquifer sediments benefit from rainwater harvesting in arid and semi-arid areas. Due to the lack of sufficient data on the characteristics of this zone depths, a numerical modeling was used to simulate the electrical resistivity of these sediments by applying the electrical resistivity method, because it is the most affected by the physical properties of dry and wet sediments. This study was applied as a proposal for application in northwestern KSA to calculate the vertical hydraulic conductivity and transmissivity for the vadose zone. This was implemented by assuming a three-layer model using COMSOL Multiphysics model with different electrical resistivity values depending on some in situ electrical resistivity measurements for shallow depths. Hence, the infiltration rate of sediments in this area can be predicted with depth and its effect on aquifer recharge. The focus was on calculating the vertical hydraulic parameters of the most widespread surface sediments with depth and comparing the results of calculating these parameters for some sediments laboratory-wise to ensure their accuracy. Then, their infiltration rate was inferred separately with depth, predicting their ability to aquifer recharge and make the most of rainwater harvesting. Finally, this study can be considered as a preliminary study to determine the expected forward model of electrical resistivity and hydraulic parameters values for the vadose zone sediments with depth along the area and in any other areas, and then apply them accurately in situ to estimate the extent of its usefulness in rainwater harvesting, especially aquifer recharge.

Spatiotemporal Evolution of Riparian Redox Zonation in Response to River Stage Fluctuation and Dynamic Biofilm Growth

AbstractRiparian zones are one of the most complex redox‐dynamic systems, where sequential redox zones of dissolved oxygen, nitrate, manganese dioxide, ferric hydroxide and sulfate reduction commonly form. River stage dynamics and microbes are two key controls on nutrient transformation in the riparian zone. Microbial growth, on one hand, increases the biogeochemical reaction rate by altering the microbial population. On the other hand, decreases the permeability of the media due to clogging effects, thereby increasing the residence time of solutes. However, previous studies have often concentrated on steady‐state flow systems and overlooked the impacts of river stage fluctuations and dynamic microbial growth on redox zonation. In this study, we investigated the interactions among river fluctuations, nutrient supplies, microbial metabolisms, and sediment physical properties in a dynamic riparian system. A column experiment was conducted, and a one‐dimensional modeling framework that coupled flow, reactive solute transport, dynamic microbial growth and bioclogging processes was developed to study the spatiotemporal evolution of redox zonation in response to river stage fluctuations and microbial growth. Our results showed that two redox zonation patterns, including a typical sequence and an interlaced sequence, could form in the dynamic riparian zone. Increasing exogenous dissolved organic carbon concentration facilitates the occurrence of anomalous sequence redox zonation. Modeling results also indicated that ignoring microbial growth leads to a significant difference in the spatiotemporal characterization of the redox zonation, especially for a more permeable sediment. Our results implicate the occurrence of more complicated redox zonation in a dynamic riparian system than previously reported.

Coring tools have an effect on lithification and physical properties of marine carbonate sediments

Abstract. The International Ocean Discovery Program (IODP) JOIDES Resolution Science Operator typically uses an advanced piston corer (APC) in soft ooze and sediments and an extended core barrel (XCB) in firm sediments. The coring tool exchange typically occurs around the same depth in adjacent holes of the same site. However, during IODP Expedition 356, the coring tool switch occurred at different depths: IODP Sites U1463 and U1464 are marked by a stratigraphic interval (&gt; 25 m thick) that was XCB cored in one hole and APC cored in other holes. Shipboard scientists remarked that APC-cored sediments were unlithified or partially lithified, while XCB-cored sediments were fully lithified. This difference in sedimentological description of the same formation seems to be an effect of coring technique. To provide further insight, we assessed the physical properties (bulk density, porosity, and P-wave velocity), downhole wireline logging data, scanning electron microscope (SEM) images, and micro-computed tomography (µCT) scans of those intervals. We find systematic differences between the different coring techniques. XCB cores are characterized by systematically lower bulk density, higher porosity, and higher P-wave velocity than APC cores. Downhole logging data suggest that the original P-wave velocity of the formation is better preserved in XCB cores, despite the typical “biscuit-and-gravy” core disturbance (i.e. well-preserved core fragments surrounded by squelched core material). In conjunction with SEM and µCT images, we conclude that the APC tool destroyed early lithification by breaking cements between individual grains. Moreover, µCT images reveal denser packing and smaller pore volumes in the APC cores. These sedimentary changes likely occur when the APC pressure wave passes through the sediment. The destruction of grain-to-grain cements provides an explanation for the significantly lower P-wave velocities in APC cores. Interestingly, the gravy sections in XCB drilled cores mimic the destruction of early lithification and reduction of pore volume. We conclude that APC remains the tool of choice for recovering soft sediments, especially for paleoclimate purposes. However, for the study of lithification, XCB biscuits provide a more representative image of the formation. For the study of early diagenesis, further studies are required to ascertain the preservation of key sedimentary features using existing and new drilling tools.

A ∼5000 year multiproxy record of summer climate in NE Greenland

The High Arctic plays a vital role in Earth's climate system, and its ecosystems are highly sensitive to global climate change. High Arctic lakes are valuable sentinels of climate change, as their sediments integrate long-term natural climatic fluctuations and anthropogenic influences. Here, we present a high-resolution ∼5000 year-reconstruction of NE Greenland climate variability from Aucella Lake (74°N, 20°E) based on physical, chemical, and biological properties of lake sediments. We use CT-scans, hyperspectral imaging, organic matter, XRD, and diatom analyses to show that changing air temperatures were controlled by a mix of regional climatic changes and local landscape feedbacks. The latest Mid-Holocene (∼5.0–3.8 cal. ka BP) was characterized by relatively warmer conditions, while the onset of the Late-Holocene was marked by abrupt temperature decreases that coincided with the beginning of glacial advances elsewhere (∼3.8–3.4 cal. ka BP). From ∼3.4–2.4 cal. ka BP, the sedimentary record indicated progressive warming, with temperature peaking during the Medieval Climate Anomaly, although temperature rises were punctuated by abrupt, short-lived cold periods. From ∼1.1–0.05 cal. ka BP, the influence of landscape factors over the system diminished. Sedimentary indicators suggested a transition towards a colder, more humid climate, coinciding with the beginning of the Little Ice Age, that was characterized by a marked decrease in air temperature that reached minimum values at the end of this period. The last 50 years at Aucella Lake were marked by abrupt temperature rises, consistent with recently observed anthropogenic global warming. Our results illustrate the importance of high-resolution multiproxy studies for accurately characterizing lake linkages to their environment and climate.

A new index for the rapid generation of chlorophyll time series from hyperspectral imaging of sediment cores

AbstractTime series analyses of pigment concentrations are key to understanding past aquatic ecosystem dynamics. As lake sediments provide a window into longer‐term changes, innovative paleolimnological chlorophyll quantification could provide impactful insights into past environmental processes. Lab‐based hyperspectral imaging of sediment cores is an emerging technique to develop rapid, non‐destructive, high‐resolution chlorophyll inferences but it requires more extensive vetting. Despite recent advances in model development, there is still a knowledge gap about the reliability of chlorophyll models when applied in lakes with diverse properties, as well as the potential confounding effects of physical sediment properties on these models. We assessed the performance of 23 chlorophyll indices based on paired measurements collected via hyperspectral imaging and spectrophotometry for 202 samples spread across seven Canadian lake sediment cores. The best performance was by a new index based on the wavelength of the red‐edge minimum point (λREMP). We tested the applicability of λREMP to a broad range of sediment cores using a database of 116 cores, and found the index to provide reliable reconstructions of ƩChl (i.e., chlorophyll a and b and their degradation products) trends in 84% of sites. Further analyses indicated that sediment characteristics including particle size, organic matter content, water content, and density had no systematic impact on ƩChl, but greater sediment brightness did increase ƩChl inferences from hyperspectral images. Hyperspectral core scanning is poised to facilitate the generation of high‐resolution chlorophyll time series data, which could greatly improve our understanding of trajectories of change from the local to global scales.

Relationship between resistivity and physical properties of seafloor sediments in the hydrate production test area of the South China Sea

The vast distribution, abundant reserves, and high combustion utilization rate of natural gas hydrate make it an appealing alternative energy source. Nevertheless, the special physical and mechanical properties of the hydrate production test area in the South China Sea have led to frequent geological disasters, requiring monitoring and early warning of potential geohazards. To facilitate this process, a model was established to determine the relationship between sediment resistivity and physical properties in this area. However, there is currently no suitable sediment resistivity inversion model for this region. We obtained an 8 m-long core sediment sample from the hydrate production test area in the South China Sea using a core sediment sampler aboard the research vessel “Marine Geology 6”. Indoor geotechnical tests were conducted to determine the vertical variation characteristics of the sediment, and indoor resistivity tests were performed to obtain its resistivity vertical variation. Using empirical power function formulae, we established a relationship model between resistivity and physical properties, which we then compared with relevant data from nearby sea areas. This model lays the foundation for using in situ resistivity to invert the dynamic changes of sediment physical properties and promote the development of deep-sea engineering geology.

Model prediction controller for penetration mechanism of seabed cone penetration test system

The system of seabed Cone Penetration Test (CPT) is a kind of equipment for offshore investigations. Seabed CPT is used to assess multiple physical properties of marine sediments. Constant-rate penetration mechanism is the core part of seabed CPT, which adopts dual-cylinder drive to penetrate the probe rod into the seafloor sediments at a constant speed (2cm/s). At present, the domestic CPT and its penetration equipment almost all rely on imports. In the process of system design, we found that the traditional PID control of the hydraulic cylinder position control accuracy is low, so we need to study higher precision position tracking control method to achieve uniform penetration of the probe rod. In this paper, a Linear Time-Varying Model Predictive Controller (LTV-MPC) is introduced, which can control two hydraulic cylinders to penetrate probe rod into the seabed sediment with smaller penetration rate error under the condition of changing penetration resistance.

Effects of adding loose materials on improvement of the physical properties of sediment and growth of green plants

Effects of different loose materials on the growth of green plants in the sediment and the improvement of the physical properties of the sediment were studied in pot experiments. Two types of loose materials, vermiculite and shale, were chosen. The addition ratio of loose materials and sediment were set to 1:1, 1:2, 1:5. Results showed that, the sediment after adding vermiculite was more conducive to the growth of ryegrass, and when the addition ratio was 1:1 and 1:2, the growth conditions of ryegrass were the best. The fresh weight of ryegrass in the treatment with the ratio of vermiculite and sediment at 1:1 increased by 43.94% compared to that in pure sediment; In the treatment with the ratio of 1:2, the plant height increased the most, which was 6 cm higher than that in pure sediment; When large amount of loose materials were added, the moisture content of the sediment increased compared to the pure sediment treatment; after the addition of loose materials, the bulk density of the sediment decreased, and the addition of too large amount would easily lead to a low bulk density, which was not conducive to water and fertilizer retention; The addition of vermiculite can reduce the bottom sediment. Bangladesh J. Bot. 52(2): 487-493, 2023 (June) Special