Browsing by Subject "Sand"
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Item A Sedimentary Study of Dune Sands, Lamb and Bailey Counties, Texas, and White Sands National Monument, New Mexico(Texas Tech University, 1959-08) Jones, Billy RayStable and active dunes were studied in Lamb and Bailey counties, Texas and in White Sands National Monument, New Mexico. Composite surface samples were collected from these dunes and a mechanical analysis was made of the sand samples. Field relationships and mechanical analysis of the dune sand of Lamb and Bailey counties indicate that the sands were derived from local stream deposits and therefore all the characteristics of these sands are not the result of wind action. Some of the characteristics are attributed to the action of the streams. A comparison of the gypsum sands of White Sands, New Mexico and the quartz sands of Lamb and Bailey counties shows that the sands differ in grain size but are similar in other characteristics. It is concluded that the characteristics of dime sands are more strongly determined by source than by composition or method of transport.Item Clastic wedge development and sediment budget in a source-to-sink transect (Late Campanian western interior basin, SW Wyoming and N Colorado)(2009-12) Gomez, Carolina Andrea; Steel, R. J.The problem of how sand and mud was distributed downslope, within linked alluvial-brackish water-marine shoreline systems of an extensive clastic wedge is addressed here. The Iles Clastic wedge accumulated over a time period of a few million years (my), and its component high-frequency regressive-transgressive sequences have a duration of a few 100 thousand years (ky). The sediment partitioning study provides insight into where the thickest sandstones and mudstones were located, and generates a model that can be applied to improving the management of hydrocarbons or water resources. A 300 km 2-D study transect across the Iles Clastic Wedge in SW Wyoming and N Colorado included subsurface well log information and outcrop stratigraphic columns. This information was used to correlate high-frequency sequences across several hundred kilometers, characterize depositional processes from proximal to distal reaches, develop a sediment partitioning model, and understand the role of the likely drivers in the development of the wedge and its internal sequences. The main results of this study are: (1) The Iles Clastic Wedge spans 3 my (500 m thick) and is composed internally of 11 sequences of 200-400 ky, each of which have significant regressive-transgressive transits of up to 90 km. Sediment partitioning analysis shows that within the regressive limb of the large wedge, the component regressive compartments tend to thicken basinwards, whereas transgressive compartments thicken landwards. This geometry is driven by preferential erosion in proximal areas during regression, bypassing much sediment to the marine shorelines, and transgressive backfilling into proximal areas previously eroded more deeply. (2) The greatest concentration of sands tends to be located in the proximal fluvial and estuarine facies of the transgressive compartments and within the medial shoreline/deltaic facies of the regressive compartments. (3) As the high-frequency sequences developed, the effectiveness of basinward sand partitioning reaches a maximum value near the peak regression level of the wedge, reflecting stronger erosion and sediment bypass during this times. (4) The development of the Iles Clastic Wedge was influenced by both tectonic and eustatic drivers, with important tectonic control in the upstream reaches. On a 4th-order timescale, the Iles Wedge internal sequences were likely influenced mainly by eustasy.Item Development of a Method for Predictively Simulating Penetration of a Low Speed Impactor into a Weak Cohesionless Soil(2013-04-29) Arrington, Dusty RaySince the horrific attacks on September 11th 2001, the United States government and research community have been focused on how to better protect US assets across the Globe. This push for safety led the research community to develop ?F2656-07 Standard Test Method for Vehicle Crash Testing of Perimeter Barriers? in 2007 which standardized the method of validating a perimeter security barrier?s ability to withstand an impact from an attacking vehicle. Many of these security barriers rely on weak cohesionless soils to stop attacking vehicles. Designers currently rely heavily on hand calculations and engineering judgment when sizing these installations. This simplified analysis is generally used because of the complex nature of these soils under impact. These soils could be simulated in advanced finite element simulations; however, traditional modeling techniques will not allow for the simulation of these complex behaviors. Due to the complex nature of these simulations, new modeling techniques need to be evaluated and their use needed to be perfected. From this, a new method for creating a predictive simulation of a low speed impactor into a weak cohesionless soil was generated. This paper presents the development of a method by which a predictive simulation was created using only standard soil tests parameters. This paper also presents measured data from physical impact tests utilized to validate the method by which the simulation was generated. Next, the paper gives a detailed comparison of the results of the physical testing and the simulated impacts. The paper finally gives a summary of where the method is successful and where it needs improvement. The resulting methodology developed in this paper defines a reasonable process for creating a predictive simulation of a rigid impactor penetrating weak cohesionless sands. This finding is validated by a reasonable correlation between the measured and simulated impact penetrations. This paper also highlights the high variability of measured penetrations when testing with these soil materials.Item Dynamics of dilative slope failure(2013-12) You, Yao; Flemings, Peter Barry, 1960-; Mohrig, DavidSubmarine slope failure releases sediments; it is an important mechanism that changes the Earth surface morphology and builds sedimentary records. I study the mechanics of submarine slope failure in sediment that dilates under shear (dilative slope failure). Dilation drops pore pressure and increases the strength of the deposit during slope failure. Dilation should be common in the clean sand and silty sand deposits on the continental shelf, making it an important mechanism in transferring sand and silt into deep sea. Flume experiments show there are two types of dilative slope failure: pure breaching and dual-mode slope failure. Pure breaching is a style of retrogressive subaqueous slope failure characterized by a relatively slow (mm/s) and steady retreat of a near vertical failure front. The retreating rate, or the erosion rate, of breaching is proportional to the coefficient of consolidation of the deposit due to an equilibrium between pore pressure drop from erosion and pore pressure dissipation. The equilibrium creates a steady state pore pressure that is less than hydrostatic and is able to keep the deposit stable during pure breaching. Dual-mode slope failure is a combination of breaching and episodic sliding; during sliding a triangular wedge of sediment falls and causes the failure front to step back at a speed much faster than that from the breaching period. The pore pressure fluctuates periodically in dual-mode slope failure. Pore pressure rises during breaching period, weakens the deposit and leads to sliding when the deposit is unstable. Sliding drops the pore pressure, stabilizes the deposit and resumes breaching. The frequency of sliding is proportional to the coefficient of consolidation of the deposit because dissipation of pore pressure causes sliding. Numerical model results show that more dilation or higher friction angle in the deposit leads to pure breaching while less dilation or lower friction angle leads to dual-mode slope failure. As a consequence, pure breaching is limited to thinner deposits and deposits have higher relative density.Item Effects of oversized particles on the dynamic properties of sand specimens evaluated by resonant column testing(2014-08) Shin, Boonam; Stokoe, Kenneth H.This study was motivated by the fact that many times intact specimens with a number of oversized particles are dynamically tested in the laboratory and the impact of the particles on the dynamic properties is unknown. The effects of oversized particles represented by gravel particles on the shear modulus (G) and material damping ratio (D) of a uniform sand were evaluated in the linear (γ ≤ 0.001%) and nonlinear (γ > 0.001%) ranges of shear strain with combined resonant column and torsional shear (RCTS) equipment. The sand used in this investigation is a uniform sand as a reference, well-characterized material on the dynamic properties. Sand-gravel specimens were constructed using the undercompaction method. A variety of rounded gravel particles was used in building the specimens. Dynamic tests on the sand-gravel specimens were performed, and the tests results are presented. Among the findings of this investigation are that, compared to uniform sand: (1) oversized gravel particles symmetrically located along the longitudinal axis in uniform sand generally decreased slightly the small-strain shear modulus (Gmax), (2) oversized gravel particles asymmetrically located away from the longitudinal axis of rotation resulted in slight increases in Gmax and the small-strain material damping ratio (Dmin), (3) the G – log γ relationships of sand-gravel specimens with asymmetrically located gravel particles are generally above those with gravel particles symmetrically located along the longitudinal axis, and (4) the G/Gmax – log γ relationships of all specimens were reasonably close for the nonlinear ranges covered in these tests (γ < 0.05 % and G/Gmax > 0.6). As long as the oversized particles were near the axis of rotation, the particles had little effect on the dynamic properties (Gmax, Dmin and G – log γ relationships) regardless of sizes and numbers of particles. However, once the oversized particles were located away from the axis of rotation and closer to the perimeter of the specimen, the oversized particles influenced the dynamic properties. Finally, the additions of oversized particles located both symmetrically and asymmetrically in the uniform sand specimens have little impact on the nonlinear dynamic properties (G/Gmax – log γ and D – log γ relationships) which compared well with uniform sand.Item Exploratory study of infant/toddler involvement with selected outdoor equipment(Texas Tech University, 1981-08) Nauman, MarjorieNot availableItem Laterally loaded rigid piers in sand and sandy soils(Texas Tech University, 1984-08) Tseng, Tong-jongIn this research a model has been described to analyze and design rigid piers in sand and sandy soils. This model utilizes several soil spring constants to analyze the resistance-displacement relationship of the pier in sand and sandy soils. The soil spring constants used are lateral spring constants, bottom vertical spring constant, bottom friction spring constant, bottom moment spring constant, and friction spring constants on the periphery of the pier. The most important aspect of obtaining the resistance-displacement relationship between the pier and the soils is to calculate the ultimate resistance capacity of each layer of soil, and the slope of the initial part of the resistance-displacement curve. These have been done efficiently and the results are promising that are described and discussed here. The minimum potential energy theorem is used to develop the system equations.Item Measurements of Vp and Vs in dry, unsaturated and saturated sand specimens with piezoelectric transducers(2006) Valle-Molina, Celestino; Stokoe, Kenneth H.Evaluation of the compression and shear wave velocities (Vp and VS) of sand specimens using piezoelectric transducers was performed in this study. The selected piezoelectric transducers were piezoelectric discs (PDs) and bender elements (BEs). These transducers were used to measure Vp and VS, respectively. The seismic measurements with PDs and BEs involved the development of an instrumented triaxial chamber (ITC) in which the transducers were placed. The same types of PDs and BEs were also installed in the top caps and base pedestals of a combined resonant column and torsional shear (RCTS) device. The soil tested was washed mortar sand, and all the specimens were formed using the undercompaction method. The sand specimens were seismically tested in dry, unsaturated and saturated conditions in the ITC. The ITC was designed to permit the evaluation of wave velocities for soils at different stages during the saturation process. Incorporation of piezoelectric transducers in the RCTS device allowed three different measurement techniques to be performed in the same soil specimen: (1) torsional resonance measurements, (2) direct measurement (slow cyclic) of the stress-strain loops in shear, and (3) direct-arrival-time measurements of wave propagating in the specimen to determine VS and Vp. In addition, seismic measurements using BEs were performed simultaneously with torsional shear tests in the RCTS device in a synchronized manner. Synchronization of the BEs measurements with the slow-cyclic torsional shear test allowed the determination of VS at the different points on the hysteresis loops applied to the specimens with the RCTS device. Among the findings of this study: (1) small-strain VS values measured using BEs were found to be about 3 to 7% greater than those measured with RC tests, (2) Vp measurements using PDs are a good way of studying the saturation process in soils when the degree of saturation is above 97%, and (3) synchronized measurements with BEs during slow-cyclic loading in the RCTS device represents a new experimental effort in the development of improved nonlinear soil models to describe cyclic stress-strain relationships in soils.Item Modeling and Simulation of Solid Particle Erosion of Protective Films(2011-02-22) Banerjee, SouravAmong many useful properties of elastomers, one is their ability to absorb energy by deforming to large strains without fracturing. This property combined with their good adhesion to substrates makes them suited as adhesive films and coatings for protection against impact damage. An example of practical significance is the erosion of helicopter rotor blades where the protection of leading edge is often achieved by mounting a film or applying a coat of polyurethane. Although this is a workable solution, there is currently little knowledge as to the durability of this elastomeric film/coat under impact of hard and angular particles such as sand. A deformation and failure analysis that deals with the angularity of the erodents and captures the local mechanisms responsible for erosion damage in elastomers is the sine qua non. The present endeavor tries to address these issues by considering a polyurethane layer on a quasi-rigid substrate, impacted by hard particles at velocities and angles of attack given by pre-specified distributions. A novel method is devised to address the angularity issue. A series of finite-element calculations are performed on the coating layer-substrate systems subjected to different velocities, incidence and angularity of the impacting erodents. An elasto-plastic material constitution with isotropic hardening is employed in the simulations and material parameters representative of polyurethane are used for the coat. Initial parametric deformation analyses provided an adequate qualitative estimate of erosion parameters. Incorporation of a stress based fracture criterion enabled a quantitative measure of material removal due to erosion to be achieved. The simulation results show good match with experimental trends of target mass loss as obtained under normal and inclined loadings with angular erodents. The current simulation framework has sufficient capability and versatility to incorporate more enriched polymer-models and advanced fracture criteria in the future, thereby allowing parametric studies toward selection of materials and coat-layer thicknesses thus predicting the erosion mass loss as accurately as measured by experiments.Item Suspension of bed material over lateral sand bars in the Lower Mississippi River, Southeastern Louisiana(2011-12) Ramirez, Michael Towler; Allison, Mead A. (Mead Ashton); Kim, Wonsuck; Mohrig, DavidUnderstanding specific pathways for sand transport in the lower reaches of large rivers, particularly the Mississippi, is the key to addressing multiple significant geologic problems and for environmental restoration efforts. Field studies were performed in the Mississippi River 75-100 km upstream of the Gulf of Mexico outlet in April 2010 (water discharge: 23,000 m³ s⁻¹), May 2010 (18,500-20,500 m³ s⁻¹), and March 2011 (27,000 m³ s⁻¹) to examine sediment transport phenomena in the river channel. Methods comprised multibeam sonar bathymetric surveys, acoustic Doppler current profiler measurements of current velocity and acoustic backscatter, point-integrated isokinetic suspended sediment sampling, and channel-bed grab sampling. Channel morphology surveys revealed a 30-60 m deep thalweg, alternating between banks every 2-3 km, opposite bedform-covered lateral sand bars. Dune sizes nearest the thalweg ranged from 7 m wavelength and 0.3 m height to over 100 m wavelength and 2.3 m height as a function of water discharge, with decreasing dune sizes towards shallow water. Material comprising the dunes was well-sorted, 125-500 [mu]m sand. Bedload transport rates increased exponentially with water discharge in April 2010 and March 2011 comparable to previous studies in this reach, though rates in May 2011 were well below predicted values for a site (Myrtle Grove) immediately downriver of a sand-mining project. Average water velocities ranged from 1.3 m s⁻¹ in May 2010 to 2 m s⁻¹ in March 2011. Skin-friction shear stress increased with water discharge, but varied over an order of magnitude at all measured discharges. Suspended sand concentration and grain size increased with proximity to the bed during all study periods, and was most pronounced in March 2011. Suspended sand concentrations were greatest over the center of lateral bars, and lowest in the thalweg, indicating that sand transport downstream occurs primarily over lateral sand bars where there is a combination of high shear stress and available bed material. Total bed-material discharge increased exponentially with water discharge. Bedform-induced turbulence may be responsible for the bed material suspension. These results are relevant to coastal restoration efforts by river diversion which seek to distribute sand from the upper water column to deltaic interdistributary wetlands.Item Undrained, monotonic shear strength of loose, saturated sand treated with a thixotropic bentonite suspension for soil improvement(2010-08) Rugg, Dennis A.; El Mohtar, Chadi Said; Rathje, Ellen M.Liquefaction is a phenomenon that occurs in loose saturated sand deposits that are subjected to earthquake loading. This phenomenon can cause massive displacements and significant destruction. Many methods for mitigating liquefaction have been proposed and investigated including compaction, drainage, and grouting. One such liquefaction mitigation technique involves the addition of bentonite fines to the pore spaces of a loose, saturated sand via permeation of an engineered clay suspension. This method of soil improvement has provided the basis and motivation for this research. Also, the effect of plastic and non-plastic fines on the static and cyclic response of sands is somewhat contradictory throughout the literature. Thus, the primary objective of this study was to characterize the affect of an engineered bentonite pore fluid on the undrained monotonic response of loose, saturated Ottawa sand in order to determine its feasibility for use as an effective method for liquefaction mitigation. The permeation of engineered bentonite suspensions is proposed as a passive site remediation technique. Thus, the suspensions were delivered to loose Ottawa sand specimens in the laboratory by permeation in a newly designed three-way split mold. This split mold was used to create easily tested specimens that would have an initial soil fabric similar to that expected after permeation in the field. The bentonite suspensions were treated with sodium pyrophosphate to reduce the initial yield stress and viscosity in order to allow for permeation. Three different bentonite suspensions were utilized throughout this study each having different properties and delivering slightly different amounts of bentonite to the loose, saturated sand. The affect of this engineered pore fluid on the undrained shear response of loose, saturated Ottawa sand was compared to the undrained shear response of clean sand and dry-mixed sand and bentonite. The specimen preparation method (dry-mixed or permeated) was shown to have a significant effect on the response of the sand specimens. While the dry-mixed specimens produced larger and more sustained positive pore water pressures than the clean sand (resulting in an increased tendency to flow), the permeated specimens showed a marked decrease in the generation of excess pore water pressures, displayed a more dilative response, and thus resulted in a soil structure that was less likely to flow. Finally, the results of tests on specimens permeated with engineered bentonite suspensions show that there is little to no change in the effective friction angle at critical state. A method for effectively testing permeated soil specimens was developed in this study. This method has laid the framework for further investigations into the use of engineered bentonite suspensions for liquefaction mitigation by permeation grouting.