Dry Sand Layer Research Articles

The use of magnetic and geo-electrical data to delineate the subsurface structures and groundwater potentiality in Southeastern Sinai, Egypt

The study area is located in the southern part of Sinai Peninsula. This study was done to delineate the subsurface structure of the basement rocks affecting the groundwater potentiality in the study area and to perform the lateral and vertical variations in the subsurface lithologic properties. To achieve these, a high-resolution total intensity magnetic map and geo-electrical survey were acquired. Two-dimensional power spectrum, analytical signal, and Euler deconvolution techniques are applied on magnetic data. The geo-electric data interpretations concluded that, the study area can be classified into five units of sediments arranged as: (1) the top surficial layer of dry sand and gravels; (2) the second layer of silty sand layer with thickness ranging from 5 to 35 m; (3) the third layer of dry sand with thickness ranging from 5 to 130 m; (4) the fourth layer composed of saturated sand which was considered as the water-bearing zone of the investigated interval, its thickness ranges between 50m and more than 200 m; (5) the fifth layer is interpreted as basement rocks. The depth to the basement surface has an average value of 156 m at the eastern side and 758 m at the western side of the study area. This area is characterized by a graben structure bounded by major faults striking in the NW–SE direction and is considered one of the most promising regions for water resources in Sinai.

Estimation of Stresses in a Dry Sand Layer Tested on Shaking Table

Abstract Theoretical analysis of shaking table experiments, simulating earthquake response of a dry sand layer, is presented. The aim of such experiments is to study seismic-induced compaction of soil and resulting settlements. In order to determine the soil compaction, the cyclic stresses and strains should be calculated first. These stresses are caused by the cyclic horizontal acceleration at the base of soil layer, so it is important to determine the stress field as function of the base acceleration. It is particularly important for a proper interpretation of shaking table tests, where the base acceleration is controlled but the stresses are hard to measure, and they can only be deduced. Preliminary experiments have shown that small accelerations do not lead to essential settlements, whilst large accelerations cause some phenomena typical for limit states, including a visible appearance of slip lines. All these problems should be well understood for rational planning of experiments. The analysis of these problems is presented in this paper. First, some heuristic considerations about the dynamics of experimental system are presented. Then, the analysis of boundary conditions, expressed as resultants of respective stresses is shown. A particular form of boundary conditions has been chosen, which satisfies the macroscopic boundary conditions and the equilibrium equations. Then, some considerations are presented in order to obtain statically admissible stress field, which does not exceed the Coulomb-Mohr yield conditions. Such an approach leads to determination of the limit base accelerations, which do not cause the plastic state in soil. It was shown that larger accelerations lead to increase of the lateral stresses, and the respective method, which may replace complex plasticity analyses, is proposed. It is shown that it is the lateral stress coefficient K0 that controls the statically admissible stress field during the shaking table experiments.

Clay Movement in Sand Columns and its Pedological Ramifications

Movement of clay particles and other colloids through soil profi les has been investigated extensively during the past few decades. The pathway of movement is generally accepted as being predominantly downward. This study investigated the hypothesis that clay and colloids can move upward by capillarity, and is concomitant with water movement. To test this hypothesis, two experiments were conducted. The fi rst experiment used an empty transparent plastic column standing in a 500-mL glass beaker and packed with dry sand. A reddish clay suspension was used with a concentration of 24.2 g L−1, a pH of 7.1, and an electrical conductivity (EC) of 0.05 S m−1. The clay suspension was added to the beaker so that it could move upward within the sand column by capillarity. The second transparent plastic column was placed empty in a 500-mL glass beaker and was packed with a 30-cm layer of dry sand overlain by a 5-cm layer of sandy loam, which was then overlain by a 20-cm layer of dry sand. A water table was established to test the likelihood of clay particles moving upward via capillarity. In each experiment, the movements of the clay-sized materials were visually tracked using a digital camera. The results of the fi rst experiment showed that clay particles moved 25 cm upward and even accumulated at the surface. Clay particles moved upward in the second experiment and formed some clay bands in the sand layer overlying the sandy loam layer. Peer Reviewed Papers

Interaction of caisson foundations with a seismically rupturing normal fault: centrifuge testing versus numerical simulation

Dramatic failures have occurred in recent earthquakes as a result of the interplay of surface structures with outcropping fault ruptures, highlighting the need to account for fault-induced loading in seismic design. Current research into the mechanisms of fault rupture–foundation–structure interaction has revealed a potentially favourable role of caissons in comparison with other foundation types. This paper explores the mechanisms of normal fault rupture interaction with rigid caisson foundations, with an integrated approach using both experiments and analysis. A series of centrifuge model tests were first conducted to study the response of a square (in plan) caisson foundation of dimensions 5 m × 5 m × 10 m, founded on a 15 m thick layer of dry dense sand. A non-linear three-dimensional numerical simulation of the problem was then developed, and adequately validated against centrifuge test results. Depending on its position relative to the fault, the caisson interacts with the fault rupture, sometimes modifying spectacularly the free field rupture path. Acting as a kinematic constraint, the caisson ‘forces' the rupture to divert on either one, or both, of its sides. The numerical study was subsequently extended to gain further insight into the effect of the exact position of the caisson relative to the fault outcrop. Different mechanisms taking place for different caisson positions are identified, and their effect on the response of the system is discussed.

Measurement of Small-Strain Shear Moduli of Partially Saturated Sand During Infiltration in a Geotechnical Centrifuge

Abstract This paper describes the use of bender elements to measure changes in small strain shear modulus, Gmax, of sand layers due to the change in degree of saturation during centrifuge tests. The goal of the measurements is to verify that steady-state infiltration is an appropriate technique to control the effective stress in centrifuge physical modeling of partially saturated sands. Specifically, the suitability of infiltration is assessed by checking if the measured values of Gmax of partially saturated sand layers follow a similar trend to dry and saturated sand layers when the effective stress is defined from the suction and degree of saturation profiles during steady-state infiltration. Three pairs of bender elements were installed at different depths in a container of Ottawa sand, and the shear wave velocities of the sand were measured during steady-state infiltration into the sand layer. The applied infiltration rate was varied to obtain different uniform distributions of degrees of saturation with depth. Consistent with results from suction-controlled resonant column tests performed on the same sand, the values of Gmax measured from the bender element tests varied nonlinearly with degree of saturation with a peak value at a degree of saturation between 0.3 and 0.4. When interpreted in terms of mean effective stress, the values of Gmax from the bender element tests on partially saturated sands followed a unique trend consistent with measurements for dry and saturated sands.

As propriedades friccionais de areias de quartzo (natural e colorida): medidas efetuadas em experimentos físico-analógicos e em um ring-shear tester

Com o intuito de se determinarem as propriedades friccionais da areia de quartzo empregada em modelagens físico-analógicas foram desenvolvidos dois ensaios de laboratório. No primeiro, estimou-se o coeficiente de atrito interno a partir do ângulo de mergulho de falhas de empurrão, em caixas de areia, e, no segundo, realizaram-se medições em um ring-shear tester. Nesse aparelho, determinaram-se as propriedades, separadamente, para areias de quartzo tingidas em diferentes cores, da tinta Acrilex. Os valores do coeficiente de atrito interno revelaram-se mais altos e mais preciso no ring-shear tester do que nos modelos analógicos. A comparação dos resultados com dados da literatura mostrou que as areias testadas se enquadram em uma faixa de valores bastante elevada. Além disto, o estudo no ring-shear tester demonstrou que as areias tingidas em diversas cores possuem propriedades friccionais distintos da areia incolor (ângulo de atrito interno = 42,7º) e entre si. O fato é atribuído a diferenças na composição química da tinta e deve ser avaliado com cuidado em futuros experimentos, em caixas de areia.

Impact of fluid saturation on the reflection coefficient of a poroelastic layer

The impact of changes in saturation on the frequency-dependent reflection coefficient of a partially saturated layer was studied. Seismic attenuation and velocity dispersion in partially saturated (i.e., patchy saturated) poroelastic media were accounted for by using the analytical solution of the 1D White’s model for wave-induced fluid flow. White’s solution was applied in combination with an analytical solution for the normal-incidence reflection coefficient of an attenuating layer embedded in an elastic or attenuating background medium to investigate the effects of attenuation, velocity dispersion, and tuning on the reflection coefficient. Approximations for the frequency-dependent quality factor, its minimum value, and the frequency at which the minimum value of the quality factor occurs were derived. The approximations are valid for any two alternating sets of petrophysical parameters. An approximation for the normal-incidence reflection coefficient of an attenuating thin (compared to the wavelength) layer was also derived. This approximation gives insight into the influence of contrasts in acoustic impedance and/or attenuation on the reflectivity of a thin layer. Laboratory data for reflections from a water-saturated sand layer and from a dry sand layer were further fit with petrophysical parameters for unconsolidated sand partially saturated with water and air. The results showed that wave-induced fluid flow can explain low-frequency reflection anomalies, which are related to fluid saturation and can be observed in seismic field data. The results further indicate that reflection coefficients of partially saturated layers (e.g., hydrocarbon reservoirs) can vary significantly with frequency, especially at low seismic frequencies where partial saturation may often cause high attenuation.

Negative Pore Air Pressure Generation in Backfill of Retaining Walls During Earthquakes and its Effect on Seismic Earth Pressure

In order to investigate the seismic behavior of conventional type and geosynthetic-reinforced soil retaining walls, 1-g model shaking tests were conducted. Model walls having a height of about 50 cm were placed on a subsoil layer and backfilled with a layer of dense dry Toyoura sand. They were subjected to several steps of horizontal irregular excitations. As a result, generation of negative pore air pressure in the backfill was observed. The maximum amplitude of the negative pore air pressure during each shaking step increased with the base acceleration. Based on analyses of the measured data, it was inferred that such negative pore air pressure was caused by outward wall displacement relative to the backfill and not by dilative behavior of the backfill. It would cause a reduction in the seismic earth pressures exerted from the backfill. This feature suggests an advantage of a rigid full-height facing for reinforced soil walls over the segmental types of facing. A simplified numerical procedure to evaluate earth pressure was applied while considering the effects of the negative pore air pressure, and it could qualitatively simulate the measured behavior in terms of the seismic earth pressure and the angle of failure plane in the backfill.

Effects of contact angle on fingered flow during non-ponding infiltration into dry sand layers

Gravity-driven fingered flow may readily occur in dry sand layers with small capillary force at the same order of magnitude as gravitational force. Capillary force is related to the contact angle. The present study examined the effects of contact angle on fingered flow development, finger size and fingertip velocity during non-ponding infiltration into dry sand layers. For contact angles of 48–87°, an induction zone always formed in the sand layer, and only one finger developed from the induction zone. Fingertip width reached a minimum value when the contact angle was approximately 70°, and the width and velocity of fingertips were negatively correlated. This finding suggests that a contact angle of approximately 70° has a physical significance for fingered flow to determine fingertip velocity and width. In addition, when the contact angle was 91°, the supplied water did not spontaneously penetrate the sand surface; instead, water drops built up on the surface and two fingers directly formed from the surface. This indicates that 90° is indeed the critical contact angle for water repellency and affects fingered flow development during non-ponding infiltration.

Spatial patterns of desert annuals in relation to shrub effects on soil moisture

Questions: What are the effects of a shrub (Haloxylon ammodendron) on spatial patterns of soil moisture in different seasons? How does productivity of understorey annuals respond to these effects? Are such effects always positive for annuals under shrubs? Location: South Gurbantunggut Desert, northwest China. Methods: Using geostatistics, we explored seasonal patterns of topsoil moisture in a 12 × 9-m plot over the growing season. To determine spatial patterns of understorey annuals in response to H. ammodendron presence, biomass of annuals was recorded in four 0.2 × 5.0-m transects from the centre of a shrub to the space between shrubs (interspace). We also investigated vertical distribution of root biomass for annuals and soil moisture dynamics across soil profiles in shrub-canopied areas and interspaces. Results: Topsoil moisture changed from autocorrelation in the wet spring to random structure in the dry season, while soil moisture below 20 cm was higher in shrub-canopied areas. Across all microhabitats, soil moisture in upper soil layers was higher than in deeper soil layers during the spring wet season, but lower during summer drought. Topsoil was close to air-dry during the dry season and developed a ‘dry sand layer’ that reduced evaporative loss of soil water from deeper layers recharged by snowmelt in spring. Aboveground biomass of understorey annuals was lowest adjacent to shrub stems and peaked at the shrub margin, forming a ‘ring’ of high herbaceous productivity surrounding individual shrubs. To acclimate to drier conditions, annuals in interspaces invested more root biomass in deeper soil with a root/shoot ratio (R/S) twice that in canopied areas. Conclusions: Positive and negative effects of shrubs on understorey plants in arid ecosystems are commonly related to nature of the environmental stress and tested species. Our results suggest there is also microhabitat-dependence in the Gurbantunggut Desert. Soil water under H. ammodendron is seasonally enriched in topsoil and deeper layers. Understorey annuals respond to the effect of shrubs on soil water availability with lower R/S and less root biomass in deeper soil layers and develop a ‘ring’ of high productivity at the shrub patch margin where positive and negative effects of shrubs are balanced.

Origin of fault domains and fault-domain boundaries (transfer zones and accommodation zones) in extensional provinces: Result of random nucleation and self-organized fault growth

In many extensional provinces, large normal faults dip in the same direction forming fault domains. Features variously named transfer faults, transfer zones, and accommodation zones (hereafter non-genetically referred to as fault-domain boundaries) separate adjacent fault domains. Experimental modeling of distributed extension provides insights on the origin, geometry, and evolution of these fault domains and fault-domain boundaries. In our scaled models, a homogeneous layer of wet clay or dry sand overlies a latex sheet that is stretched orthogonally or obliquely between two rigid sheets. Fault domains and fault-domain boundaries develop in all models in both map view and cross-section. The number, size, and arrangement of fault domains as well as the number and orientation of fault-domain boundaries are variable, even for models with identical boundary conditions. The fault-domain boundaries in our models differ profoundly from those in many published conceptual models of transfer/accommodation zones. In our models, fault-domain boundaries are broad zones of deformation (not discrete strike-slip or oblique-slip faults), their orientations are not systematically related to the extension direction, and they can form spontaneously without any prescribed pre-existing zones of weakness. We propose that fault domains develop because early-formed faults perturb the stress field, causing new nearby faults to dip in the same direction (self-organized growth). As extension continues, faults from adjacent fault domains propagate toward each another. Because opposite-dipping faults interfere with one another in the zone of overlap, the faults stop propagating. In this case, the geometry of the domain boundaries depends on the spatial arrangement of the earliest formed faults, a result of the random distribution of the largest flaws at which the faults nucleate.

Comment on “Solving the mystery of booming sand dunes” by Nathalie M. Vriend et al.

[1] We show here that the standard physical model used by Vriend et al. [2007] to analyse seismograph data, namely a non-dispersive bulk propagation, does not apply to the surface layer of sand dunes. According to several experimental, theoretical and field results, the only possible propagation of sound waves in a dry sand bed under gravity is through an infinite, yet discrete, number of dispersive surface modes. Besides, we present a series of evidences, most of which have already been published in the literature, that the frequency of booming avalanches is not controlled by any resonance as argued in this article. In particular, plotting the data provided by Vriend et al. [2007] as a table, it turns out that they do not present any correlation between the booming frequency and their estimate of the resonant frequency.

Solving the mystery of booming sand dunes

Desert booming can be heard after a natural slumping event or during a sand avalanche generated by humans sliding down the slip face of a large dune. The sound is remarkable because it is composed of one dominant audible frequency (70 to 105 Hz) plus several higher harmonics. This study challenges earlier reports that the dunes' frequency is a function of average grain size by demonstrating through extensive field measurements that the booming frequency results from a natural waveguide associated with the dune. The booming frequency is fixed by the depth of the surficial layer of dry loose sand that is sandwiched between two regions of higher compressional body wave velocity. This letter presents measurements of the booming frequencies, compressional wave velocities, depth of surficial layer, along with an analytical prediction of the frequency based on constructive interference of propagating waves generated by avalanching along the dune surface.

Geochemical Information Indicating the Water Recharge to Lakes and Immovable Megadunes in the Badain Jaran Desert

Calc-sinters distributed in the middle of lakes and rhizoconcretions scattered at the slopes of sand dunes were observed during three explorations to the Badain Jaran Desert in the past two years. Wet sands were also found underneath the dry surface sand layers of about 20–50 cm in thickness. The geochemical parameters were measured on minerals and water samples collected from the Badain Jaran Desert and neighboring areas. The results show that the water system in the desert may be recharged from the groundwater originating from the precipitation of the Qilian Mountains and/or the Tibetan Plateau rather than the local rainfalls.

Effect of cyclic shearing on shear localisation in granular bodies

Cyclic shearing of an infinite narrow layer of dry and cohesionless sand between two very rough boundaries under constant vertical pressure is numerically modelled with the finite element method using a polar hypoplastic constitutive relation. The constitutive relation was obtained through an extension of a non-polar model by polar quantities, viz. particle rotations, curvatures, couple stresses using the mean grain diameter as a characteristic length. The proposed model captures the essential mechanical features of granular bodies in a wide range of densities and pressures with a single set of constants. The material constants can be easily determined from granulometric properties and laboratory tests. The attention of numerical simulations is laid on the influence of number of cycles on the thickness of an induced shear zone for both an initially dense and loose granular specimen. In addition, the effect of a stochastic distribution of the initial void ratio on shear localisation is demonstrated.

Subsurface old drainage detection and paleoenvironment analysis using spaceborne radar images in Alxa Plateau

For geological and environmental research in an arid area, a unique advantage of radar remote sensing is that radar wave can penetrate a certain layer of dry sand (a few centimeters to meters thick) to reach the buried bedrock. The penetration capability is able to reveal the subsurface geological structure and old drainage paths. Based on the analysis of SIR-A, SIR-B, SIR-C, Radarsat ScanSAR, Landsat MSS and Landsat TM images acquired on different dates and the investigations made in several field trips in Alxa Plateau of Inner Mongolia, a number of old river valley and lake basins buried by wind-blown sand were recognized. Two parallel old drainage systems in the north and middle of the study area are delineated. The study suggests that the moving sand belts mainly follow the old drainage courses. This study also establishes a preliminary drainage evolution model for an area of about 300 000 km2 since the Tertiary, and finds that the Alxa Plateau was once an area with many rivers and lakes with a warm and humid climate. The relief reversion caused by neotectonic movement since “Qinghai-Tibet movement” is also analyzed.

Effects of weak layers on particle velocity measurements

Results are presented from a testing program to study the effect weak layers embedded in a strong rock strata have on particle velocity when subjected to explosive loading. A similar computational study had been conducted earlier with WONDY — a finite difference Langrangian code developed at Sandia National Laboratory. The experiments were conducted using models fabricated from Hydrocal containing a single dry sand layer or clay layer through which the stress wave traveled. Particle velocity was measured in front of and past the weak layer to determine attenuation, pulse shape changes, and displacement loss. The results from the model testing indicated that particle velocity amplitude decreased significantly when the stress wave passed through the weak layer. The velocity pulse width on the other hand was found to remain relatively constant when passing through the weak layer. The computational results from WONDY predicted similar behavior and hence were in good agreement with the tests. In the experiments, the velocity loss across a sand layer was found to be much larger than the loss across a clay layer. The stress wave velocity in the sand layer was found to be significantly smaller than in the Hydrocal while the experimentally determined wave velocity in the clay was nearly equal to the wave velocity in the Hydrocal.

Deformation Produced by Subsait Normal Fauitlng: An Experimental Study with Implications for Seismic Interpretation: ABSTRACT

We have conducted a series of scaled physical models to study the deformation produced by subsalt normal faulting. In the models, a constant-thickness layer of silicone putty represents a salt sheet, and a layer of homogenous dry sand or wet clay represents the sedimentary cover. Movement on a precut, 45[degrees]-dipping surface below the silicone putty simulates subsalt normal faulting. We have tested the sensitivity of the modeling results, by varying the thickness of the putty layer, the thickness of the sand/clay cover, the magnitude of the fault displacement, the rate of fault displacement, and deposition during deformation. Our modeling results imply that a broad forced fold forms above an active subsalt normal fault. The width of the monoclinal limb increases as the salt thickness increases and if nominal deposition occurs during deformation. The dip of the limb increases as the magnitude of the fault displacement increases, as the salt thickness decreases, and if deposition occurs during deformation. Our modeling results also imply that normal faults can form in the sedimentary cover above the salt sheet during subsalt normal faulting. These normal faults commonly form near the footwall hinge of the monocline and are offset and detached from the underlying subsaltmore » normal fault. They are more likely to develop if the salt sheet is thin, if the sedimentary cover is thick, if the fault displacement is large, and if deposition occurs during deformation. The experimental results suggest that the structural geometries of suprasalt folds and faults provide information about subsalt faulting. Seismic examples from Norway, Alaska, and the Gulf of Mexico support these conclusions.« less

Evaporation rates of liquid hydrogen and liquid oxygen spilled onto the ground

Abstract The evaporation rates of liquid hydrogen and oxygen spilled onto the ground surface were measured in laboratory tests. To simulate the ground, concrete, dry sand and wet sand layers were used in a vacuum-insulated cylindrical glass vessel. Based on the temperature variations within the layer and detailed observation through the side of the vessel, the heat transfer modes controlling the evaporation phenomenon were elucidated. When a wet sand layer was used, the liquid oxygen or hydrogen did not soak into the layer, because the frozen layer of water between the liquid and the sand layer acted as a barrier. When a concrete layer was used, the liquid vaporized above the layer. In these cases, the evaporation rates were inversely proportional to the square root of the time, except in the early stage just after the start of vaporization. This relationship could be predicted by a simple calculation of heat conduction within the layer. On the other hand, when a dry sand layer was used, liquid oxygen was observed to vaporize while constantly soaking into and rolling up the upper section of the layer. In this case, the evaporation rate was determined simply by the velocity of liquid penetration downward through the sand layer. When liquid hydrogen was used, the liquid did not soak into the dry sand layer, and the evaporation mechanism seemed to be the same as that for the wet sand layer, because the air contained within interparticle cavities in the dry sand layer solidifies at the boiling point of liquid hydrogen.

砂丘地における乾砂層の蒸発抑制効果

砂丘地における乾砂層の蒸発抑制効果