Thickness Of Sand Layer Research Articles

Recommended strategies for assessing and managing groundwater dewatering during subsurface construction in sediments adjacent to large river systems: examples from Wuhan in China

Using the principles of Quaternary geology and geomorphology, this study analyzed the genetic types, composition, lithofacies and spatial distribution of Quaternary deposits in the first terrace sediments adjacent to the Yangtze River in Wuhan. These sediments exhibit a typical binary structural sedimentation rhythm, where sedimentary particles in the same sediment are sequenced progressively fine downstream with river flow which also has obvious grading regularity that affects the engineering properties of these materials. A transverse cross-section outwards from the river channel indicates that the lower sand layer thickness decreases, while the thickness of the upper soft and interlayered sediments progressively increases with distance from the channel. The permeability of the aquifers increases monotonically with depth and the permeability coefficient is anisotropic. From upstream to downstream, the anisotropy coefficient increases significantly and this factor needs to be considered when designing a dewatering system. The main geotechnical engineering problems caused by underground water during the excavation of underground space in sediments adjacent to large river systems are put forward, and the corresponding countermeasures are also recommended.

PREDICTION OF CONSOLIDATED COHESIVE BOTTOM EROSION BY WAVE ACTION

A consolidated cohesive sediment layer exists below a layer of sand on some beaches along the Great Lakes (glacial till) and the Gulf of Mexico. The erosion process of consolidated cohesive sediment may be gradual but irreversible (no recovery) apart from sand and gravel released from the eroded consolidated cohesive sediment. The cohesive sediment erosion rate is increased by a thin mobile layer of sand and decreased by a thick sand layer. The complicated interactions of waves, sand and cohesive bottom are simplified and incorporated into an existing cross-shore numerical model.

A Study on the Hydrothermal Regime of Aeolian Sand and the Underlying Soil in the Frozen Soil Zone on the Qinghai-Tibetan Plateau

The hydrothermal process within the aeolian sand layer on the Qinghai-Tibetan Plateau (QTP) plays a key role in understanding the interaction between desertification and underlying frozen soil. However, little is known about the hydrothermal dynamics of aeolian sand and underling soil layer in the frozen soil zone on the QTP. In this study, a sparse vegetation cover site and three aeolian sand cover sites with different sand thicknesses were established to study the hydrothermal dynamics within aeolian sand layer. The results show that the thickness of aeolian sand is critical in the soil hydrothermal process under sand cover. The increase in thickness of the aeolian sand layer resulted in an advance in the onset of the freezing and thawing of soil, and accelerated movement of the freezing and thawing front. In addition, the increase in sand thickness caused an increase in soil temperature during the thawing stage and the warming period of the thawed stage, whereas a decrease occurred during the cooling period of the thawed stage, the freezing stage and the frozen stage, which ultimately caused the enlargement of the annual range of ground temperature. Furthermore, in the study area, the actual evapotranspiration of sand-covered surface was larger than that of the naked surface. The water content also decreased with increasing sand thickness in different stages, which separately decreased the heat budget in both the warm and cold season because of the smaller thermal conductivity of aeolian sand with a lower water content. This study states that through the special hydrothermal process, have an adverse impact on the occurrence and formation of the frozen soil in the QTP.

A Gravity Search for Oil and Gas and Groundwater in Egypt Using the Strike Angles Derived from EIGEN 6C4

We correlate the gravity aspects (descriptors), namely the strike angles, derived from a recent gravity field model, with the known oil, gas and groundwater deposits/reservoirs and hypothetical paleolakes with the locations of archaeological sites. This allows us to extrapolate the investigation, by analogy, to unknown regions. The gravity aspects, derived from the EIGEN 6C4 gravity field model, are used, together with EMAG 2 magnetic anomalies and ETOPO 1 topography model, for the investigation of oil, gas and water deposits in Egypt. One of the gravity aspects, s/c strike angle, is significantly combed (oriented in one direction locally) in places where the known deposits exist. However, they are combed also in some other places. This may be used as a guide as to where to seek new and promising deposits. Accounting for the combed strike angles and the relationship between gravity anomalies and height differences, we reconstructed potential paleolakes under thick sand layers in the Great Sand Sea, Western Egypt (our previous work), and between Kharga and Toshka, Southern Egypt (this work), consistent with the known archaeological sites.

Laboratory Evaluation of Bearing Capacity of Footing onClayeyBed Overlaid with Geocell Sand Mattress

The non–availability and scarcity of suitable construction soils at several worksites has led to the increased usage of soils with inadequate engineering properties. With regard this reason there is a dire necessity for in–situ modification of foundation soils to improve their engineering properties and to obtain adequate bearing capacity. Despite several existing methods of soil improvement techniques, the soil reinforcement is considered to be prominent methods of ground improvement techniques. These days three dimensional method and technique of soil confinement using geocells is gaining reputation for enhancement of bearing capacity of such soils. In the present investigation, the laboratory experimentation was planned and performed various tests to explore the prospective advantages of embedding geocell reinforced sand mattress laid on soil subgrade (clayey soil). Test parameters that varied during the testing included are thickness of plain sand layer and height (clear distance) of geocell sand mattress laid above the clay bed. The experimental results have shown that a considerable enhancement in load carrying capacity. It could be achieved by the spreading of geocell reinforced sand mattress above the clayey bed. Further, it is noted from the test results that, almost 5–fold improvement in bearing capacity is attained by providing geocell reinforced sand mattress embedded in sand layer of thickness equal to twice the dimensions of the footing i.e., 2B (B is the width of footing).

Behavior of a Deep Excavation and Damages on Adjacent Buildings: a Case Study in Vietnam

This paper investigates the behavior of deep excavations and damages on adjacent buildings based on an excavation in a thick sand layer in Vietnam. Firstly, measured horizontal displacements of diaphragm walls were used to calibrate soil stiffness parameters for finite element analysis (FEA). Then, the behavior of diaphragm walls, groundwater, ground surface deformation, and an adjacent building was analyzed. The analysis results and damages observed in the field were used to review the validity of the criteria for evaluating the damage potential of excavation to adjacent buildings. It can be concluded from the study that the damage potential of adjacent buildings as evaluated from FEA through the strain state chart proposed by Boscardin and Cording (1989) or the damage potential index (DPI) proposed by Schuster et al. (2009) is fairly accurate with field observations.

Performance and evaluation of an EPS plate to mitigate blast on underground protective structures

Explosions due to terrorist attacks or accidents can cause severe damage to critical infrastructure. To protect important facilities from explosion damage, they can be constructed belowground. Further, an explosion mitigation layer can be used to provide additional protection. In this study, an expanded polystyrene (EPS) plate has been incorporated into the soil layer for blast mitigation, and the performance of the system has been investigated experimentally. The results indicate that there is an optimum ratio of sand layer thickness and EPS plate thickness for decreasing and dispersing blast pressures. Formulas describing the peak pressure and scaled impulse on the bottom of the mitigation system as functions of a scaled distance from directly under the explosion source and scaled layer thickness have been derived.

Behaviour of circular footings confined by rigid base and geocell reinforcement

Soil in nature may exist in a stratified state. A possible condition is the case of a rigid layer underlying a weak sand stratum. In this instance, the bearing capacity of a shallow footing is affected by the lower rigid boundary. The treatment of thin soil layer by geocell reinforcement to raise the load carrying capacity of single shallow footing has been limited in the literature. Accordingly, rigid base and geocell reinforcement are investigated separately and in combination to study their influence on the behaviour and BC of shallow circular footings in dry sand bed. To capture that effect, different size rigid circular footings were tested on a bed in fully instrumented small- and large-scale laboratory installations. The ratio of sand layer thickness to footing diameter was changed considering optimum dimension and embedment depth for geocell mattress. The extensive laboratory part involved monitoring subgrade deformations, soil-geocell stresses and strains revealing the appropriate models for failure mechanisms in the presence of such confinements. Large increase in bearing capacity up to 225% and significant settlement reduction up to 66% are measured for the combined case. Base confinement less than three times the footing diameter in combination with the geocell mattress resulted in favourable higher design performance factors. New equations are proposed to estimate these factors for design and to extend classical formulations for footings strengthened by combined geocell-base confinement. A design performance factor is dependent on footing diameter, sand relative density and the ratio of layer thickness to footing diameter. As this ratio increases, this design factor decreases reaching a constant value at the critical depth.

Bearing capacity of ring footings placed on dense sand underlain by a loose sand layer

The ultimate bearing capacity of a ring footing on loose sand deposit, with an inclusion of a dense sand layer on its top, has been determined numerically in a bound form by following the finite element limit analysis (FELA). The friction angles ϕ1 and ϕ2 were varied from 40° to 46° and 30° to 36° for the top dense sand and the bottom loose sand respectively. The Mohr-Coulomb’s yield criterion has been assumed to be applicable. The bearing capacity has been found to increase quite extensively with an increase in the thickness of the dense sand layer thickness up to a certain optimal thickness before attaining a constant value. The magnitude of has been found to lie generally between 1.5 and 4.7, and the corresponding maximum value of the bearing capacity with an inclusion of the dense sand layer varies in a wide range of 2.32–82.45 times the corresponding value for an unimproved loose sand deposit; the parameters and refer to the inner and outer radii of the ring, respectively. Similar to a ring footing on homogeneous sand deposit, the bearing capacity for different chosen combinations of internal friction angles of the two sand layers, tends to become maximum generally for a value of closer to 0.25. For the validation, the results for a ring footing on two-layered sand deposit were also determined by using the displacements based elastoplastic finite element (EP-FE) method. The results from the FELA were found to compare well with (i) the obtained solutions based on the EP-FE method, and (ii) the published results by using experiments and the method of stress characteristics.

One-step fabrication superhydrophobic sand filter for capillary-driven separation of water-in-oil emulsions

The efficient separation of water-in-oil emulsion is of significance in environment and energy filed, and it has become a world-wide challenge. Herein, we have presented a one-step, facile and low-cost approach to prepare superhydrophobic sands for efficient separation of water-in-oil emulsion. The as-prepared sand layers possessed a water contact angle higher than 151°, demonstrating their superior superhydrophobic property. Besides, the as-prepared sand layers could separate water-in-emulsions with separation efficiency up to 99.7%, which is superior to both traditional and superwettable filtration membranes. The effect of thickness of sand layer on separation performance was also investigated. The results showed that the filtration flux decreased with the increased of filtration thickness while the separation efficiency increased. The as-prepared sand layer proposed by this study is a processing candidate for separating water-in-oil emulsion in practical industry. Additionally, the as-prepared superhydrophobic sand fabrication method also provides an alternative for desert water storage.

Numerical study of ultimate bearing capacity of rectangular footing on layered sand

Purpose: The purpose of this study is to investigate the ultimate bearing capacity of the rectangular footing resting over layered sand using finite element method. Design/methodology/approach: Finite element analysis was used to investigate the dimensionless ultimate bearing capacity of the rectangular footing resting on a limited thickness of upper dense sand layer overlying limitless thickness of lower loose sand layer. The friction angle of the upper dense sand layer was varied from 41° to 46° whereas for the lower loose sand layer it was varied from 31° to 36°. Findings: The results reveal that the dimensionless ultimate bearing capacity was found to increase up to an H/W ratio of about 1.75 beyond which the increase was marginal. The results further reveal that the dimensionless ultimate bearing capacity was the maximum for the upper dense and lower loose sand friction angles of 46° and 36°, while it was the lowest for the upper dense and lower loose sands corresponding to the friction angle of 41° and 31°. For H/W = 0.5 and 2, the dimensionless bearing capacity decreases with the increase in the L/W ratio from 0.5 to 6 beyond which the dimensionless ultimate bearing capacity remains constant for all combinations of parameters. The results were presented in nondimensional manner and compared with the previous studies available in literature. Research limitations/implications: The analysis is performed using a ABAQUS 2017 software. The limitation of this study is that only finite element analysis is performed without conducting any experiments in the laboratory. Further the study is conducted only for the vertical loading. Practical implications: This proposed numerical study can be used to predict the ultimate bearing capacity of the rectangular footing resting on layered sand. Originality/value: The present study gives idea about the ultimate bearing capacity of rectangular footing when placed on layered sand (dense sand over loose sand) as well as the effect of thickness of top dense sand layer on the ultimate bearing capacity. The findings could be used to calculate the ultimate bearing capacity of the rectangular footing on layered sand.

Evaluating the effects of layered soils on water flow, solute transport, and crop growth with a coupled agro-eco-hydrological model

PurposeSoil salinization and degradation in the arid and semiarid areas are a worldwide phenomenon. Soil capping with capillary barriers is a potential practice to hydraulically isolate contaminated soils, which may improve the soil environment for plant growth. This study aims to investigate the influences of soil capping on crop growth and soil salinization control in the arid area with shallow groundwater tables.Materials and methodsA one-dimensional agro-eco-hydrological model, LAWSTAC, capable of simulating water and solute transport in layered soil coupled with crop growth, was applied for simulating sunflower growth under field condition in Arid Northwest China. The model was calibrated and validated with the experimental data of 2012 and 2013 crop seasons. The calibrated model was then used to explore how the soil capping consisting of combinations of fine soil (10, 15, 17, 19, and 20 cm thick) and coarse sand (10, 5, 3, 1, and 0 cm thick correspondingly) would influence the soil water and salt dynamics, and seed yield.Results and discussionSimulation results by LAWSTAC compared well with the observed soil water content, salt concentration, leaf area index, and seed yield. Further scenario simulations showed that a sand layer in the soil capping could greatly affect the water and salt distribution in the soil above and below the sand layer. Though soil capping could decrease the water storage (WS) in the root zone, it caused no obvious increase in water stress to root uptake for sand thickness of 1–3 cm and also considerably reduced the root zone salt content (SC) in crop season compared with that without soil capping. The average WS during the crop season showed a negative correlation with the thickness of sand layer in the soil capping. The average SC from planting to harvest was significantly lower for thicker sand in the soil capping. To soils with high background salinization, the increase of sand thickness would be helpful for enhancing seed yield, until it reached a critical value.ConclusionsCoarse soil layer in the soil capping could prevent salt moving into the root zone, while fine soil could supply water to plant once water in coarse soil was low. Thus, in a long run, the soil capping consisting of combinations of fine and coarse soils with certain thicknesses would be an alternative practice for saline soil reclamation and improving crop production in arid area with shallow groundwater tables and soil salinization.

Groundwater Chemical Characteristics and Mining Potential Evaluation of the Quaternary in the Boxing Section of Shandong Province in the Lower Yellow River

Boxing is located in the lower reaches of the Yellow River, all of which are covered by loose rock layers. Quaternary loose rock pore water mainly exists in aqueous media such as medium sand, medium coarse sand and fine sand, forming multiple layers of loose rock pore water. Water-containing structure is interlayer confined water development. From the southeast to the northwest, the aquifer formation gradually becomes thinner with the Quaternary overburden, the thickness of the single-layer sand layer gradually becomes thinner, and the water richness gradually weakened. The chemical types of groundwater are mainly HCO3 and HCO3·Cl. The pore water of loose rocks in the middle and deep layers is decreasing from south to north, and the content of Cl- is increasing. From west to east, the percentage of HCO3 -mg equivalent decreases gradually, and the percentage of Cl-mg equivalent increases gradually. The area enclosed by the groundwater level buried depth 40m is the controlled mining area.

Effectiveness of geosynthetic reinforcement for load transfer in column-supported embankments

Many column-supported embankment (CSE) design methods include geosynthetic reinforcement for vertical load transfer and/or settlement reduction regardless of project conditions. However, geosynthetic reinforcement may not be necessary for all applications, particularly if a sufficiently thick and strong soil layer overlies the compressible soil. A strong soil layer can transfer embankment loads to the columns without much differential settlement at the base of the embankment, limiting the development of tension in the reinforcement. If weak and compressible soil extends to the ground surface and the area replacement ratio is low, differential settlements may be so large that it may not be practically possible to provide enough reinforcement to avoid excessive strain or rupture. This paper describes parametric studies using the Load Displacement Compatibility method to investigate the influences of embankment height, geosynthetic stiffness, column diameter, and thickness of an upper sand layer on geosynthetic strain, differential settlement at the base of the embankment, and load distribution among the CSE components. Results of the parametric study show that site conditions, CSE system geometry, and performance requirements limit the range of circumstances for which geosynthetic reinforcement for settlement reduction is needed, effective, and practically possible.

Experimental and numerical studies of laterally loaded piles located near oil-contaminated sand slope

Oil spillage occurrences are due to wars, accidents, drilling, storage, natural disasters, and rapid industrialization, which lead to huge amounts of waste discharge into adjacent areas. Soil contamination is also detrimental to associated structures and foundations. Therefore, in this research, experimental and numerical studies on laterally loaded piles near an oil-contaminated sand slope were conducted to estimate the ultimate lateral capacity, lateral displacement, and maximum bending moment of a single pile embedded in contaminated and uncontaminated sand slope. To simulate the contamination content as in field conditions, preparation of oil-contaminated layers of sandy soil was performed by blending clean sand samples with heavy motor oil at proportions of 0–6% of the dried weight of soil. These studies were performed by varying the contaminated sand layer thickness (LC), oil content (O.C), pile slenderness ratio (LP/DP) and distance from the slope crest (X) to the pile head. The results demonstrated a considerable reduction in the friction angle (Ø) with increasing oil content. Therefore, the ultimate horizontal load (Hu) of the pile also reduced. Moreover, the raise in the thickness of oil-contaminated sandy soil layer (LC) has resulted in an increment in the lateral movement of the pile (y) and a reduction in the ultimate horizontal load (Hu). When the proportion of the oil content increased to 2% over that in clean sand, the maximum bending moment raised by about 11%. In addition, a good consistency between the numerical analysis and experimental tests was observed.

Geophysical signature of the Tunnunik impact structure, Northwest Territories, Canada

AbstractIn 2011, the discovery of shatter cones confirmed the 28 km diameter Tunnunik complex impact structure, Northwest Territories, Canada. This study presents the first results of ground‐based electromagnetic, gravimetric, and magnetic surveys over this impact structure. Its central area is characterized by a ~10 km wide negative gravity anomaly of about 3 mGal amplitude, roughly corresponding to the area of shatter cones, and associated with a positive magnetic field anomaly of ~120 nT amplitude and 3 km wavelength. The latter correlates well with the location of the deepest uplifted strata, an impact‐tilted Proterozoic dolomite layer of the Shaler Supergroup exposed near the center of the structure and intruded by dolerite dykes. Locally, electromagnetic field data unveil a conductive superficial formation which corresponds to an 80–100 m thick sand layer covering the impact structure. Based on the measurements of magnetic properties of rock samples, we model the source of the magnetic anomaly as the magnetic sediments of the Shaler Supergroup combined with a core of uplifted crystalline basement with enhanced magnetization. More classically, the low gravity signature is attributed to a reduction in density measured on the brecciated target rocks and to the isolated sand formations. However, the present‐day fractured zone does not extend deeper than ~1 km in our model, indicating a possible 1.5 km of erosion since the time of impact, about 430 Ma ago.

Behavior of circular foundation on sand layer of limited thickness subjected to eccentrically inclined load

A numerical study on the behavior of an eccentrically inclined loaded circular foundation on a sand layer of limited thickness underlain by a rigid rough base is presented. Specific attention is given to simulating the effect of the rigid rough base, load eccentricity (e), load inclination (α) and failure mechanisms in the finite element (FE) analysis assuming axisymmetric conditions. Analyses are performed using two models, namely, (i) an elastic-perfectly plastic Mohr-Coulomb model (MCM) and (ii) an elasto-plastic hyperbolic model called the hardening soil model (HSM) using Plaxis 3D. The results of the numerical modeling indicate that the bearing capacity is modified when the rigid rough base is located at a shallow depth below the base of the foundation and the extent of the failure surface. The results of the FE analysis appear to be in good agreement with those obtained from the tests by Sethy et al. (2019) for all H/B ratios, except for H/B = 0.3. However, the results obtained by the hardening soil model are all close to the results obtained from the laboratory model tests by Sethy et al. (2019). Based on the results of the finite element (FE) analysis and the results of the laboratory model tests by Sethy et al. (2019), the modified ultimate inclined load per unit area is seen to be dependent on the H/B ratio and becomes constant beyond H/B′ ratios (where B′=B-2e) that equal about three.

Experimental study of wet porous sand layer air-drying characteristics

An experimental study has been carried out to investigate the convective air-drying characteristics of a wet sand layer. The experimental setup allows dynamic measurements of both sand layer weight and temperature, with hot air flowing towards the sand layer surface to ensure a uniform drying of it. Experiments are conducted for a 4 mm thick sand layer for three air temperatures of 45, 60 and 75 °C. The lumped parameter method is used to analyze the sand layer heat transfer. The results show that the sand layer temperature continuously increases throughout the drying process, which can be divided into three stages, i.e. the initial rapid, intermediate slow, and final rapid increase stages. There is no constant temperature stage that is often observed in water film evaporation experiment. The drying process can also be divided into three stages according to the sand layer drying rate variation, they are the increasing, constant, and decreasing rate stages, which roughly correspond to the three temperature rise stages. The lumped parameter analysis result supports that the convective heat from the hot air is used mainly for the water evaporation.

Simulation of the shielding properties of environmental components against the external radioactive radiation from the Ordovician Dictyonema shale

This paper presents the results of simulating the conditions of absorption of natural radionuclides (uranium-238, thorium-232, potassium-40) in different environment media (water and quartz sand) to assess the effect of the shielding properties of environmental components on the intensity of external radiation exposure to the benthic biota. The source of radiation was the lower Tremadocian Dictyonema shale, which formed the bottom of the Baltic Paleobasin. Water and quartz sand, which was gradually deposited on the roof of the Dictyonema shale, were used in the simulation as media (materials) absorbing the primary radiation. The manuscript shows an experiment conducted in full-scale conditions considering a single exposure of a section of Ordovician rocks that includes highly radioactive Dictyonema shale. This is a small area, but the simulation results are also valid for larger areas as the Baltic Paleobasin. During the late Tremadocian — Floian, along with transgression, benthic biota began to emerge. The experiment shows quantitatively what dosage this biota could have experienced over tens and hundreds of thousands of years, until the Dictyonema shale was covered with a sufficiently thick layer of water-flooded sediments. Experimental data show that the presence of a 10 cm thick layer of water reaches absorption of 40 % of the integral flux of all gamma lines of natural radionuclides (NRN), and in a moist quartz sand layer of the same thickness the absorption value does not exceed 50 %. Thus, despite the screening effect of the environment, the benthic biota of Baltoscandia in the Early Ordovician could have been under significant radiation exposure for millennia. The main value of the experiment is that it was performed in situ, and exclusively natural media were used as modelling elements.

Erosion by Wave Action of Consolidated Cohesive Bottom Containing Cohesionless Sediment

The erosion processes of consolidated cohesive sediment under irregular breaking waves were formulated to predict the profile evolution of a cohesive sediment beach with a layer of sand. The cohesive sediment is eroded by turbulence generated by wave energy dissipation caused by wave breaking and bottom friction. Sand released from the eroded sediment is transported onshore or offshore by wave action. The cohesive sediment erosion rate is increased by a thin mobile layer of sand and decreased by a thick sand layer. The complicated interactions of waves, sand and cohesive bottom were simplified and incorporated into an existing cross-shore numerical model. The model was compared with flume experiment data with measured till erosion rates on the order of 0.05 cm/h. The calibrated model was used to simulate the temporal change of the till erosion rate for a duration of 100 h. The scale effect was examined in hypothetical prototype tests of the same till with a length ratio of 1/4. The prototype 200-h simulations predicted much larger till erosion near the shoreline and sand deposition in the surf zone. The model will need to be compared with actual field data.